KRRO

KRRO-121, a potential first-in-class transformational treatment for hyperammonemia, remains on track to commence first-in-human clinical trial in second half of 2026 Received Orphan Drug Designation from the European Medicines Agency (EMA) for KRRO-121 for patients with urea cycle disorders (UCDs) Nominated KRRO-111 as development candidate for the treatment of Alpha-1 Antitrypsin Deficiency (AATD); potential best-in-class therapeutic delivered subcutaneously (GalNAc-conjugated oligonucleotide) for a debilitating genetic condition impacting both the liver and lungs Ended second quarter 2026 with $137.9 million in cash, cash equivalents and marketable securities; provides sufficient resources to achieve value inflection points for multiple RNA editing programs including clinical data for KRRO-121 and KRRO-111; cash runway into the second half of 2028 CAMBRIDGE, Mass., Aug. 06, 2026 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA (OPERA®) platform to develop a new class of genetic medicines for rare and highly prevalent diseases, today reported results for the second quarter ended June 30, 2026, and provided a corporate update. “The second quarter reflected the compounding payoff of a strategy we've been executing over several years,” commented Ram Aiyar, Ph.D., Chief Executive Officer and President of Korro Bio. “Adding KRRO-111 for AATD and being on track to add a third GalNAc-conjugated program this year is testament to the evolution of OPERA, our proprietary RNA editing platform to more efficiently nominate therapeutic candidates. Moving forward our focus remains steadfast on executing our clinical and corporate growth strategy to bring transformational therapeutics to patients suffering from debilitating diseases.” Second Quarter 2026 Highlights and Recent Developments Received Orphan Drug Designation from the EMA for KRRO-121 for patients with UCDs Continued preparations to obtain regulatory approvals for KRRO-121 in the second half of 2026 to commence its clinical development program Enhanced pipeline with addition of KRRO-111, a potential best-in-class treatment for AATD Continued to refine the potency of Korro’s REOs by making improvements to its oligonucleotide chemistry that boost the efficiency of its proprietary OPERA platform Multiple oral and poster presentations at the American Society of Gene and Cell Therapy 29th Annual Meeting (ASGCT) featuring Korro’s OPERA platform, KRRO-121 and KRRO-111 Participated in leading healthcare dedicated investor conferences and scientific forums Upcoming 2026 Milestones Regulatory approval for KRRO-121 to initiate clinical trials in the second half of 2026 Nominate development candidate for a third GalNAc-conjugated program in the second half of 2026 Upcoming Scientific and Investor Conferences Society for the Study of Inborn Errors of Metabolism (SSIEM) Annual Symposium, August 25-28 The XXVI International Round Table (IRT) on Nucleosides, Nucleotides and Nucleic Acids, August 25-28 Cantor Global Healthcare Conference 2026, September 9-11 Citi’s 2026 Biopharma Back to School Conference, September 9-10 Second Quarter 2026 Financial Results Cash Position: Cash, cash equivalents and marketable securities were $137.9 million as of June 30, 2026, compared to $85.2 million as of December 31, 2025. Korro expects its cash, cash equivalents and marketable securities as of June 30, 2026 will fund operating expenses and capital expenditure requirements into the second half of 2028. Collaboration Revenue: There was no collaboration revenue for the three months ended June 30, 2026, as compared to $1.5 million of collaboration revenue for the three months ended June 30, 2025. The decrease was due to the agreed 12-month pause of the collaboration agreement with Novo Nordisk in November 2025. Research and Development (R&D) Expenses: R&D expenses were $13.6 million for the three months ended June 30, 2026, as compared to $20.1 million for the three months ended June 30, 2025. The decrease was driven primarily by decreases in KRRO-110 external expenses, personnel expenses and other research and pre-development candidate expenses, partially offset by an increase in KRRO-121 and KRRO-111 external expenses. General and Administrative (G&A) Expenses: G&A expenses were $6.5 million for the three months ended June 30, 2026, as compared to $7.3 million for the three months ended June 30, 2025. The decrease was primarily due to a decrease in information technology expenses, facilities expenses and professional service fees, partially offset by an increase in personnel expenses mainly due to increased stock-based compensation costs. Net Loss: Korro’s net loss was $18.9 million for the three months ended June 30, 2026, as compared to $25.8 million for the three months ended June 30, 2025. About Korro Korro is a biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA (OPERA®) platform to develop a new class of genetic medicines for rare and highly prevalent diseases. OPERA provides precise, tissue-directed delivery of RNA-editing oligonucleotides (REOs) that modify the targeted native mRNA transcript to repair or form a de-novo protein with enhanced functionality. The platform combines a suite of capabilities consisting of sophisticated knowledge of transcription biology through ADAR proteins (Adenosine Deaminases Acting on RNA), machine learning optimization of REOs, linker chemistry expertise, along with use of a highly targeted tissue-specific delivery methodology. As such, the OPERA platform has enabled Korro to generate and advance a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, providing precise yet transient single base edits to produce therapeutic proteins with augmented activity versus its endogenous counterpart. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an REO-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary OPERA platform with precedented delivery modalities, including N-acetylgalactosamine (GalNAc) conjugated for delivery for subcutaneous administration, manufacturing know-how, and established regulatory pathways of approved oligonucleotide medicines. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. About Hyperammonemia Hyperammonemia, the dangerous accumulation of ammonia in the blood, manifests across multiple indications, including urea cycle disorders (UCDs) and hepatic encephalopathy (HE). UCDs are rare inborn errors of metabolism involving deficiencies of enzymes required for ureagenesis, the process of converting ammonia to urea for excretion. The absence or deficiency of any of the seven urea cycle enzymes can result in hyperammonemia and an increased risk of hyperammonemic crises (HACs), which can result in severe and permanent neurological symptoms, coma, and death. HE is a neuropsychiatric complication of liver disease characterized by cognitive dysfunction and altered consciousness. HE is primarily caused by the liver’s inability to adequately detoxify ammonia, typically occurring in patients with liver cirrhosis compromising their urea cycle. This leads to ammonia accumulating in the bloodstream and crossing the blood-brain barrier, causing brain dysfunction that ranges from subtle cognitive impairment to severe confusion and coma. About KRRO-121 KRRO-121 is a GalNAc-conjugated RNA editing oligonucleotide (REO) for the potential treatment of hyperammonemia in patients with UCDs of any mutational background as well as patients with HE. Utilizing Korro’s proprietary OPERA® platform, KRRO-121 is designed to obviate the need for a functional urea cycle and instead generate a stabilized, de novo glutamine synthetase (GS) protein, a critical enzyme in an alternate pathway involved in ammonia clearance. This synthetic rescue approach is designed to augment ammonia clearance in hyperammonemia-driven diseases such as UCDs and HE. Korro’s preclinical data support the potential for KRRO-121 to be a pan-UCD treatment that may control ammonia levels, along with the potential to enable diet liberalization, reduce dependence on nitrogen scavengers, and lower the risk of HACs. KRRO-121 also has the potential to enhance ammonia control in HE patients, which may reduce the risk of recurrent HE episodes. KRRO-121 may offer infrequent subcutaneous dosing, which, if confirmed in clinical studies, could offer significant improvement over current treatments that require multiple daily doses. KRRO-121 has the potential to be a differentiated, first-in-class, disease-modifying therapy for both UCD and HE. About Alpha-1 Antitrypsin Deficiency (AATD) AATD is a genetic disorder most commonly caused by a single missense mutation (G-to-A) in the SERPINA1 gene coding for protein alpha-1 antitrypsin. Affected adults experience pulmonary emphysema and/or hepatic cirrhosis, as well as end organ manifestations. Greater than 95% of severe clinical cases of AATD are homozygous for the PiZ mutation (known as the PiZZ genotype). Additionally, there are an estimated 3.4 million individuals globally with AATD-deficient heterozygous allele combinations. The only current FDA-approved treatment for AATD is augmentation therapy, a once-weekly infusion of pooled human plasma-derived AAT protein, which does not adequately address the manifestations of AATD. About KRRO-111 KRRO-111 is a proprietary GalNAc-conjugated RNA-editing oligonucleotide (REO) that is delivered subcutaneously to the liver cells, where it is engineered to co-opt the hepatocytes’ endogenous Adenosine Deaminase Acting on RNA (ADAR) enzyme and repair a pathogenic single nucleotide variant (SNV) on AAT mRNA to restore production of normal alpha-1 antitrypsin (AAT) protein. This therapeutic profile and titratable dosing position the compound as a potential best-in-class candidate. In preclinical studies, KRRO-111 demonstrated best-in-class RNA editing where over 90% of the AAT transcripts in the liver cells have been corrected, translating into approximately 90% M-AAT protein. In a repeat-dose study, KRRO-111 was administered to PiZZ mice with a loading phase followed by dosing once every two weeks. KRRO-111 nearly eliminated active Z protein production, reducing non-inclusion Z-AAT by approximately 95% versus vehicle at both days 28 and 56, reflecting near-complete cessation of Z protein synthesis across the hepatocyte population. Pre-existing aggregates were progressively cleared, with inclusion-associated Z-AAT significantly reduced by approximately 62% at day 28, consistent with autophagic clearance of accumulated protein following successful editing. By simultaneously increasing circulating M-AAT protein and decreasing pathogenic Z-AAT aggregates in the lung, KRRO-111 has the potential to be the best-in-disease agent, improving both lung and liver manifestations of the disease. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of regulatory approval for KRRO-121 to commence a clinical trial; the potential and market opportunity for, KRRO-121 and KRRO-111; timing of announcing a development candidate for a third GalNAc-conjugated program; Korro’s cash runway and financial resources; the therapeutic potential of the OPERA platform; reaching clinical milestones across multiple programs; and the possibility of achieving functional equivalent of DNA modification; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks associated with pre-clinical studies and conducting clinical trials; risks associated with validating in clinical trials observations from pre-clinical studies; risks associated with collaborating with third parties; other risks associated with protecting intellectual property; as well as risks associated with general economic conditions; and other risks and uncertainties indicated from time to time in Korro’s filings with the Securities and Exchange Commission (SEC), including Part II Item 1A. “Risk Factors” in Korro’s Quarterly Report on Form 10-Q filed with the SEC on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact  Malini Chatterjee, Ph.DBlueprint Life Science [email protected] or [email protected]

Hosted virtual Analyst Day showcasing lead program KRRO-121’s potential to be a first-in-class transformational treatment for hyperammonemia in patients with urea cycle disorders (UCDs) and hepatic encephalopathy (HE); regulatory filing for KRRO-121 expected in the second half of 2026 Advanced early-stage research and development programs highlighted by a GalNac-conjugated oligonucleotide for alpha-1 antitrypsin deficiency (AATD); on track to announce development candidate in second quarter of 2026 Executed oversubscribed $85 million private placement to support the achievement of value inflection points for multiple RNA editing clinical programs and extend cash runway into the second half of 2028 CAMBRIDGE, Mass., May 07, 2026 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA (OPERA®) platform to develop a new class of genetic medicines for rare and highly prevalent diseases, today reported results for the first quarter ended March 31, 2026, and provided a corporate update. “The first quarter marked significant scientific progress for Korro as we continued to advance our OPERA platform and build a pipeline of differentiated RNA editing medicines,” commented Ram Aiyar, Ph.D., Chief Executive Officer and President of Korro Bio. “Our lead program, KRRO-121, remains on track for its regulatory filing in the second half of 2026, bringing us closer to delivering a potential first-in-class treatment for patients suffering from hyperammonemia in urea cycle disorders and hepatic encephalopathy. At the same time, our GalNAc-conjugated program for alpha-1 antitrypsin deficiency achieved greater than 90% in vivo RNA editing, a result that reinforces the broad therapeutic potential of the OPERA platform and the first demonstration that close to 100% of RNA can be edited with an oligonucleotide. We are well capitalized following our oversubscribed private placement, which provides us with the resources to reach meaningful clinical milestones across multiple programs. On behalf of the entire Korro team, I wish to extend gratitude to all Korro stakeholders for their belief in the potential of our novel RNA editing platform to transform the treatment of debilitating diseases.” First Quarter 2026 Highlights and Recent Developments Hosted Analyst Day showcasing KRRO-121’s potential to treat hyperammonemia in patients with UCDs and HE Forum featured Bruce Scharschmidt, MD, hepatologist and former Chief Medical Officer of Hyperion Therapeutics, and Michelle Dinon, parent of a child impacted by a UCD and UCD patient advocate. Focused on profiling the unmet need in serving both patient populations afflicted with hyperammonemia, and KRRO-121’s potential to become a first-in-class transformational treatment. Advanced a GalNac-conjugated oligonucleotide for AATD Achieved >90% in vivo RNA editing, demonstrating the high therapeutic potential of RNA editing oligonucleotides and highlighting the possibility of repeat dose therapy to achieve the functional equivalent of a DNA modification without altering the genome. Preliminary preclinical data from Korro’s AATD GalNac program to be presented at the American Society of Gene and Cell Therapy 29th Annual Meeting (ASGCT) taking place on May 11-15, 2026. Executed oversubscribed $85 million private placement led by Venrock Healthcare Capital Partners with strong participation from new and existing investors Expected to extend cash runway into the second half of 2028 and provide sufficient capital to report clinical data for KRRO-121 and AATD programs. Continued to refine the potency of Korro’s RNA editors by making improvements to its oligonucleotide chemistry that boost the efficiency of its proprietary OPERA platform. Data to be presented at ASGCT 2026. Advanced pre-clinical R&D for AMPKγ1 as “longevity” medicine to circumvent age-related metabolic diseases and TDP-43 for amyotrophic lateral sclerosis (ALS). Participated in leading healthcare dedicated investor conferences and scientific forums 44th Annual JP Morgan Healthcare Conference, TD Cowen 46th Annual Healthcare Conference. 3rd International Conference on Ureagenesis Defects and Allied Conditions. Upcoming Milestones Announce development candidate for GalNAc AATD Program in the second quarter of 2026 Regulatory filing for KRRO-121 in the second half of 2026 Nominate development candidate for a third GalNAc-conjugated program in the second half of 2026 Upcoming Scientific and Investor Conferences American Society of Gene and Cell Therapy 29th Annual Meeting (ASGCT), May 11th– 15th Tides USA 2026: Oligonucleotide and Peptide Therapeutic Conference, May 11th-14th EASL Congress 2026, May 27th-30th HCW 4th Annual BioConnect Nasdaq Investor Conference, May 19th 2026 RBC Capital Markets Global Healthcare Conference, May 20th First Quarter 2026 Financial Results Cash Position: Cash, cash equivalents and marketable securities were $157.1 million as of March 31, 2026, compared to $85.2 million as of December 31, 2025. Korro expects its cash, cash equivalents and marketable securities as of March 31, 2026 will fund operating expenses and capital expenditure requirements into the second half of 2028. Collaboration Revenue: There was no collaboration revenue for the three months ended March 31, 2026, as compared to $2.6 million of collaboration revenue for the three months ended March 31, 2025. The decrease was due to the agreed 12-month pause of the collaboration agreement with Novo Nordisk in November 2025. Research and Development (R&D) Expenses: R&D expenses were $12.9 million for the three months ended March 31, 2026, as compared to $19.7 million for the three months ended March 31, 2025. The decrease was driven primarily by decreases in KRRO-110 external expenses, personnel expenses and other research and pre-development candidate expenses, partially offset by an increase in KRRO-121 external expenses. General and Administration (G&A) Expenses: G&A expenses were $7.5 million for the three months ended March 31, 2026, as compared to $7.8 million for the three months ended March 31, 2025. The decrease was primarily due to a decrease in facilities expenses and information technology expenses, partially offset by an increase in personnel expenses mainly due to increased stock-based compensation costs. Net Loss: Korro’s net loss was $19.6 million for the three months ended March 31, 2026, as compared to $23.4 million for the three months ended March 31, 2025. About Korro Korro is a biopharmaceutical company leveraging a novel oligonucleotide promoted editing of RNA (OPERA®) platform to develop a new class of genetic medicines for rare and highly prevalent diseases. OPERA provides precise, tissue-directed delivery of oligonucleotides that modify the targeted native mRNA transcript to repair or form a de-novo protein with enhanced functionality. The platform combines a suite of capabilities consisting of sophisticated knowledge of transcription biology through ADAR proteins (Adenosine Deaminases Acting on RNA), machine learning optimization of oligonucleotides, linker chemistry expertise, along with use of a highly targeted tissue-specific delivery methodology. As such, the OPERA platform has enabled Korro to generate and advance a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, providing precise yet transient single base edits to produce therapeutic proteins with augmented activity versus its endogenous counterpart. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary OPERA platform with precedented delivery modalities, including N-acetylgalactosamine (GalNAc) conjugated for delivery for subcutaneous administration, manufacturing know-how, and established regulatory pathways of approved oligonucleotide medicines. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. About Hyperammonemia Hyperammonemia, the dangerous accumulation of ammonia in the blood, manifests across multiple indications, including urea cycle disorders (UCDs) and hepatic encephalopathy (HE). UCDs are rare inborn errors of metabolism involving deficiencies of enzymes required for ureagenesis, the process of converting ammonia to urea for excretion. The absence or deficiency of any of the urea cycle enzymes can result in hyperammonemia and an increased risk of hyperammonemic crises (HACs), which can result in severe and permanent neurological symptoms, coma, and death. HE is a neuropsychiatric complication of liver disease characterized by cognitive dysfunction and altered consciousness. HE is primarily caused by the liver’s inability to adequately detoxify ammonia, typically occurring in patients with liver cirrhosis. This leads to ammonia accumulating in the bloodstream and crossing the blood-brain barrier, causing brain dysfunction that ranges from subtle cognitive impairment to severe confusion and coma. About KRRO-121 KRRO-121 is a GalNAc-conjugated RNA editing oligonucleotide for the potential treatment of hyperammonemia in patients with UCDs of any mutational background as well as patients with HE. Utilizing Korro’s proprietary OPERA® platform, KRRO-121 is designed to generate a stabilized, de novo glutamine synthetase (GS) protein, a critical enzyme involved in ammonia clearance. This synthetic rescue approach is designed to augment ammonia clearance in hyperammonemia-driven diseases such as UCDs and HE. Korro’s preclinical data support the potential for KRRO-121 to be a pan-UCD treatment that may control ammonia levels, along with the potential to enable diet liberalization, reduce dependence on nitrogen scavengers, and lower the risk of HACs. KRRO-121 also has the potential to enhance ammonia control in HE patients, which may reduce the risk of recurrent HE episodes. KRRO-121 may offer infrequent subcutaneous dosing, which, if confirmed in clinical studies, could offer significant improvement over current treatments that require multiple daily doses. KRRO-121 has the potential to be a differentiated, first-in-class, disease-modifying therapy for both UCD and HE. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of the regulatory filing for KRRO-121; the first-in-class potential of, and market opportunity for, KRRO-121 as a treatment for hyperammonemia for patients with UCDs and HE; timing of announcing a development candidate for Korro’s GalNAc-conjugated program for AATD and third GalNAc-conjugated program; Korro’s cash runway and financial resources; the therapeutic potential of the OPERA platform; reaching clinical milestones across multiple programs; and the possibility of achieving functional equivalent of DNA modification; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks associated with pre-clinical studies and conducting clinical trials; risks associated with validating in clinical trials observations from pre-clinical studies; risks associated with collaborating with third parties; other risks associated with protecting intellectual property; as well as risks associated with general economic conditions; and other risks and uncertainties indicated from time to time in Korro’s filings with the Securities and Exchange Commission (SEC), including Part II Item 1A. “Risk Factors” in Korro’s Quarterly Report on Form 10-Q filed with the SEC on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact Malini Chatterjee, Ph.D Blueprint Life Science Group [email protected] or [email protected] 917.330.4269

Nominated KRRO-121 development candidate for the potential treatment of hyperammonemia in patients with urea cycle disorders and hepatic encephalopathy Advanced GalNAc-conjugated oligonucleotide for alpha-1 antitrypsin deficiency; on track to nominate development candidate second quarter of 2026 Recent oversubscribed $85 million private placement extends cash runway into the second half of 2028 CAMBRIDGE, Mass., March 12, 2026 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a biopharmaceutical company developing a new class of genetic medicines based on RNA editing for rare and highly prevalent diseases, today reported results for the fourth quarter and full year ended on December 31, 2025, and provided a corporate update. “This past year and in particular, the fourth quarter proved to be an important period for the company as we continued our mission to develop treatments for debilitating diseases using our novel RNA editing platform,” commented Ram Aiyar, Ph.D., Chief Executive Officer and President of Korro Bio. “We entered 2026 with a great deal of momentum, and with the recent closing of a private placement financing, are now well positioned to achieve our clinical and corporate growth objectives.” Fourth Quarter 2025 Highlights and Recent Developments: Nominated KRRO-121 for clinical development for the treatment of hyperammonemia in patients with urea cycle disorders (UCDs) and hepatic encephalopathy (HE) Potential first-in-class transformational therapy for two diseases with debilitating unmet medical needs each representing >$1 billion market opportunities. UCDs are inherited genetic conditions that impact the body’s ability to remove toxic ammonia from the blood. When one of the enzymes in the urea cycle is deficient or missing, ammonia accumulates to dangerous levels. Current treatments require severe diet restrictions, multiple doses of medications per day and can cause unpleasant side effects, including poor palatability, body odor, and gastrointestinal issues. Regardless, strict adherence to these regimens is necessary to reduce the risk of hyperammonemic crises, which can result in severe and permanent neurological symptoms, coma, or death. HE is a neuropsychiatric complication of liver disease characterized by cognitive dysfunction and altered consciousness. Primarily caused by the body’s inability to detoxify ammonia, HE leads to ammonia accumulating in the bloodstream and crossing the blood-brain barrier, causing brain dysfunction that ranges from subtle cognitive impairment to severe confusion and coma. Current treatments focus on reducing ammonia production and promoting its excretion via the gut. However, these regimens are often poorly tolerated and have little to no impact on blood ammonia levels, and many patients suffer from recurrent episodes. KRRO-121 is designed to edit glutamine synthase (GS) RNA to generate a stabilized, de novo variant of GS protein, with the ability to maintain ammonia clearance capacity in the liver for longer duration through a synthetic rescue approach. GalNAc-conjugation is used to bring KRRO-121 directly to the liver cells (hepatocytes) where KRRO-121 is engineered to edit GS RNA to create a de novo protein with a single amino acid change. The de novo protein prevents glutamine-induced proteasomal degradation of GS, creating a compensating protein through a synthetic rescue approach rather than repairing a specific mutation of an enzyme involved in the urea cycle. Intended to provide direct ammonia control through stabilization of GS protein in the liver and convenient subcutaneous delivery using precedented GalNAc-conjugated technology, a potential improvement for patient convenience and compliance versus the 2-4 times a day dosing schedule for current therapies. Pre-clinical data suggests potential to be a pan-UCD treatment addressing multiple UCD subtypes irrespective of their enzyme deficiencies in the urea cycle. Hosted Virtual Analyst Day, which provided an overview of the unmet medical need in hyperammonemia conditions, the associated burden on the healthcare system, and the scientific rationale behind KRRO-121 for UCD and HE. Significantly progressed new alpha-1 antitrypsin deficiency (AATD) program reflecting pivot to GalNAc delivery after announcing in November 2025 that KRRO-110 did not reach projected levels of functional protein following a single administration. Advanced a GalNAc-conjugated oligonucleotide, which achieved >90% in vivo RNA editing, demonstrating the high therapeutic potential of RNA editing oligonucleotides and highlighting the possibility of repeat dose therapy to achieve the functional equivalent of a DNA modification without altering the genome. Continued pre-clinical R&D programs targeting the activation of AMPKγ1 for longevity and liver health and the creation of a de novo variant of TDP-43 for amyotrophic lateral sclerosis (ALS). Continued to refine the potency of its oligonucleotides and efficiency of its proprietary Oligonucleotide Promoted Editing of RNA (OPERA®) platform to identify and develop potentially transformational therapies for previously undruggable targets. Closed an oversubscribed $85 million private placement financing led by Venrock Healthcare Capital Partners with strong participation from new and existing investors on March 10, 2026. Concluded fourth quarter 2025 with $85.2 million in cash, cash equivalents and marketable securities; and following the completion of the March 2026 private placement financing, expect cash runway to extend into second half of 2028. Upcoming Milestones: Nominate development candidate for GalNAc AATD program in the second quarter of 2026 Regulatory filing for KRRO-121 in the second half of 2026 Nominate development candidate for a third GalNAc-conjugated program in the second half of 2026 2025 Full Year and Fourth Quarter Financial Results Cash Position: Cash, cash equivalents and marketable securities were $85.2 million as of December 31, 2025, compared to $163.1 million as of December 31, 2024. Korro expects its cash, cash equivalents and marketable securities, along with funds from the recent March 2026 private placement financing, to fund operating expenses and capital expenditure requirements into the second half of 2028. Collaboration Revenue: There was $6.4 million of collaboration revenue for the year ended December 31, 2025, as compared to $2.3 million for the year ended December 31, 2024. The increase was due to collaboration revenue earned in the full year of 2025 compared to only the fourth quarter of 2024 under the research and collaboration agreement with Novo Nordisk (which was paused for 12 months beginning in November 2025). Research and Development (R&D) Expenses: R&D expenses were $65.6 million for the year ended December 31, 2025, as compared to $63.6 million for the year ended December 31, 2024. The increase was driven primarily by increases in KRRO-121 external research and development expenses and personnel expenses, partially offset by a decrease in KRRO-110 external expenses and other research and pre-development candidate expenses. General and Administration (G&A) Expenses: G&A expenses were $28.2 million for the year ended December 31, 2025, as compared to $30.5 million for the year ended December 31, 2024. The decrease was primarily due to decreased professional fees, offset by an increase in personnel expenses. Long-lived asset impairment charges: In connection with the November 2025 announcement regarding KRRO-110 and the workforce reductions, Korro determined that indicators of impairment existed and, as a result, incurred non-cash long-lived assets impairment charges, which consisted of $15.0 million and $15.9 million of non-cash impairment charges on Korro’s operating lease right-of-use asset and fixed assets, respectively, for the year ended December 31, 2025. Korro did not incur any impairment charges for the year ended December 31, 2024. Restructuring charges: Restructuring charges for the year ended December 31, 2025 consisted of $3.6 million of employee termination benefits related to Korro workforce reductions in May and November 2025. During the year ended December 31, 2025, all activities related to the May 2025 workforce reduction were completed. The remaining payments related to the November 2025 workforce reduction are expected to be paid by the third quarter of 2026. Korro did not incur any restructuring charges for the year ended December 31, 2024. Net Loss: Korro’s net loss was $117.3 million for the year ended December 31, 2025, as compared to $83.6 million for the year ended December 31, 2024. The increase is primarily due to the long-lived asset non-cash impairment charges of $30.9 million during fourth quarter of 2025. About Korro Korro is a biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases. Korro is generating a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, enabling a precise yet transient single base edit. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary platform with precedented delivery modalities, manufacturing know-how, and established regulatory pathways of approved oligonucleotide drugs. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. About Hyperammonemia and KRRO-121 Hyperammonemia is due to insufficient clearance of ammonia from the blood stream. It manifests in multiple indications such as urea cycle disorders (UCD) and hepatic encephalopathy (HE). UCD are rare inborn errors of metabolism involving deficiencies of enzymes required for ureagenesis. The absence or deficiency of any of the urea cycle enzymes results in increased ammonia in the blood to dangerous levels. HE is a neuropsychiatric complication of liver disease characterized by cognitive dysfunction and altered consciousness. HE is primarily caused by the liver’s inability to detoxify ammonia and occurs typically in patients with cirrhotic livers. This leads to ammonia accumulating in the bloodstream after crossing the blood-brain barrier, causing brain dysfunction that ranges from subtle cognitive impairment to severe confusion and coma. KRRO-121 is an RNA-editing oligonucleotide conjugated with GalNAc for the potential treatment of hyperammonemia in patients with UCD of any mutational background in adults and adolescents as well as patients with HE. Utilizing Korro’s proprietary OPERA® platform, KRRO-121 is designed to stabilize a critical enzyme involved in reducing ammonia levels. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of the regulatory filing for KRRO-121; the first-in-class potential of, and market opportunity for, KRRO-121 as a treatment for hyperammonemia for patients with UCDs and HE; timing of nominating a development candidate for Korro’s GalNAc-conjugated program for AATD and third GalNAc-conjugated program; and Korro’s cash runway and financial resources; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks associated with pre-clinical studies and conducting clinical trials; risks associated with validating in clinical trials observations from pre-clinical studies; risks associated with collaborating with third parties; other risks associated with protecting intellectual property; as well as risks associated with general economic conditions; and other risks and uncertainties indicated from time to time in Korro’s filings with the Securities and Exchange Commission (SEC), including Part I Item 1A. “Risk Factors” in Korro’s Annual Report on Form 10-K filed with the SEC on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact Malini Chatterjee, Ph.D Blueprint Life Science Group [email protected] or [email protected] 917.330.4269 (1) Working capital is defined as current assets less current liabilities.

Collegium Pharmaceutical (COLL) came out with quarterly earnings of $2.04 per share, missing the Zacks Consensus Estimate of $2.19 per share. This compares to earnings of $1.77 per share a year ago. These figures are adjusted for non-recurring items. This quarterly report represents an earnings surprise of -6.99%. A quarter ago, it was expected that this specialty pharmaceutical company would post earnings of $1.88 per share when it actually produced earnings of $2.25, delivering a surprise of +19.68%. Over the last four quarters, the company has surpassed consensus EPS estimates three times. Collegium Pharmaceutical, which belongs to the Zacks Medical - Drugs industry, posted revenues of $205.45 million for the quarter ended December 2025, missing the Zacks Consensus Estimate by 1.53%. This compares to year-ago revenues of $181.95 million. The company has topped consensus revenue estimates three times over the last four quarters. The sustainability of the stock's immediate price movement based on the recently-released numbers and future earnings expectations will mostly depend on management's commentary on the earnings call. Collegium Pharmaceutical shares have lost about 1.2% since the beginning of the year versus the S&P 500's gain of 1.5%. While Collegium Pharmaceutical has underperformed the market so far this year, the question that comes to investors' minds is: what's next for the stock? There are no easy answers to this key question, but one reliable measure that can help investors address this is the company's earnings outlook. Not only does this include current consensus earnings expectations for the coming quarter(s), but also how these expectations have changed lately. Empirical research shows a strong correlation between near-term stock movements and trends in earnings estimate revisions. Investors can track such revisions by themselves or rely on a tried-and-tested rating tool like the Zacks Rank, which has an impressive track record of harnessing the power of earnings estimate revisions. Ahead of this earnings release, the estimate revisions trend for Collegium Pharmaceutical was mixed. While the magnitude and direction of estimate revisions could change following the company's just-released earnings report, the current status translates into a Zacks Rank #3 (Hold) for the stock. So, the shares are expected to perform in line with the market in the near future. You can see the complete list of today's Zacks #1 Rank (Strong Buy) stocks here. It will be interesting to see how estimates for the coming quarters and the current fiscal year change in the days ahead. The current consensus EPS estimate is $1.59 on $195.35 million in revenues for the coming quarter and $7.35 on $806 million in revenues for the current fiscal year. Investors should be mindful of the fact that the outlook for the industry can have a material impact on the performance of the stock as well. In terms of the Zacks Industry Rank, Medical - Drugs is currently in the bottom 44% of the 250 plus Zacks industries. Our research shows that the top 50% of the Zacks-ranked industries outperform the bottom 50% by a factor of more than 2 to 1. One other stock from the same industry, Korro Bio, Inc. (KRRO), is yet to report results for the quarter ended December 2025. This company is expected to post quarterly loss of $1.93 per share in its upcoming report, which represents a year-over-year change of +14.6%. The consensus EPS estimate for the quarter has been revised 13.7% lower over the last 30 days to the current level. Korro Bio, Inc.'s revenues are expected to be $1.5 million, down 33.9% from the year-ago quarter. Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Collegium Pharmaceutical, Inc. (COLL) : Free Stock Analysis Report Korro Bio, Inc. (KRRO) : Free Stock Analysis Report This article originally published on Zacks Investment Research (zacks.com). Zacks Investment Research

— Interim readout from Phase 1/2a REWRITE clinical trial of KRRO-110 on track for the second half of 2025 — Completed dosing of over 80% of planned REWRITE healthy volunteers across multiple single ascending dose (SAD) cohorts with no treatment emergent serious adverse events (SAEs) or dose limiting toxicities observed — European Medicines Agency (EMA) granted Orphan Drug Designation to KRRO-110 for the treatment of Alpha-1 Antitrypsin Deficiency (AATD) — Development candidate for Korro’s rare metabolic disorder program will be announced by end of 2025 — Ended second quarter 2025 with $119.6 million in cash, cash equivalents and marketable securities CAMBRIDGE, Mass., Aug. 12, 2025 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases, today reported financial results for the second quarter of 2025 and provided a business update. Ram Aiyar, Ph.D., CEO and President of Korro, said, “Throughout the second quarter we made excellent progress dosing healthy volunteers in our Phase 1/2a REWRITE clinical trial. We expect to report interim data in the second half of 2025 that we believe may highlight KRRO-110’s best-in-class potential, which would be a key milestone for the company and the AATD community. Our 3-2-1 strategy continues to generate momentum, positioning us to announce our rare metabolic disorder development candidate by the end of 2025. We have high confidence in our ability to realize the value of our science and expand our wholly owned platform to bring patients potentially best-in-class genetic medicines for diseases with high prevalence and substantial unmet clinical need.” Pipeline and Business Updates: Continued to advance the Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD. To date more than 80% of planned healthy volunteers have received KRRO-110 across multiple SAD cohorts, including dose levels that are expected to be pharmacologically relevant in PiZZ patients. KRRO-110 continues to be safe and well-tolerated with no treatment emergent SAEs or dose limiting toxicities observed through August 12, 2025. The study is divided into two parts: Part 1 is the SAD portion and Part 2 is the multiple ascending dose (MAD) portion. An interim readout of Part 1 is expected in the second half of 2025, and trial completion, including the Part 2 MAD portion, is expected in 2026. KRRO-110 granted orphan drug designation by the EMA for the treatment of AATD. The EMA grants orphan designation status to medicines intended for the treatment, prevention or diagnosis of life-threatening or chronically debilitating diseases affecting fewer than five in 10,000 people in the European Union, and the medicine must be of significant benefit to patients. Orphan drug designation provides companies with various development incentives, including protocol assistance, reduced regulatory fees, and market exclusivity once the medicine is approved. In March 2025, KRRO-110 also received orphan drug designation from the U.S. Food and Drug Administration for the treatment of AATD. Executing 3-2-1 strategy through end of 2027. Korro continues to execute the 3-2-1 strategy with the goal of establishing three clinical-stage development programs, targeting two tissue types by leveraging the capabilities of its Oligonucleotide Promoted Editing of RNA (OPERA®) platform. Current pipeline and collaboration with Novo Nordisk continue to progress. In addition to advancing KRRO-110 for AATD and its second program in a rare metabolic disorder, Korro continues to execute on its central nervous system programs and its collaboration with Novo Nordisk. Under the Novo Nordisk collaboration, Korro is working to advance up to two programs through preclinical development using its proprietary OPERA platform, with the initial target intended to treat cardiometabolic diseases. Anticipated Upcoming Milestones: Interim readout from Part 1 SAD portion of the Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD expected in the second half of 2025, and completion of the REWRITE clinical trial, including the Part 2 MAD portion, expected in 2026. Announce a development candidate for its rare metabolic disorder program by the end of 2025. This candidate will be administered subcutaneously and targeted to the liver using GalNAc to create de novo protein variants designed to have therapeutic effect. Progress partnership with Novo Nordisk in cardiometabolic diseases with high prevalence and substantial unmet clinical need. Second Quarter 2025 Financial Results: Cash Position: Cash, cash equivalents and marketable securities were $119.6 million as of June 30, 2025, compared to $163.1 million as of December 31, 2024. Korro expects its cash, cash equivalents and marketable securities as of June 30, 2025 will fund operating expenses and capital expenditure requirements into 2027. Collaboration Revenue: Collaboration revenue was $1.5 million for the three months ended June 30, 2025, as compared to no collaboration revenue for the three months ended June 30, 2024. The increase was due to collaboration revenue earned in the second quarter of 2025 from Korro's collaboration with Novo Nordisk. Research and Development (R&D) Expenses: R&D expenses were $21.0 million for the three months ended June 30, 2025, as compared to $17.1 million for the three months ended June 30, 2024. The increase was driven primarily by increases in personnel expenses and other research and pre-development candidate expenses. General and Administration (G&A) Expenses: G&A expenses were $7.6 million for the three months ended June 30, 2025, as compared to $7.0 million for the three months ended June 30, 2024. The increase was primarily driven by a $1.0 million increase in personnel-related expenses offset by a $0.4 million decrease in professional services. Net Loss: Korro’s net loss was $25.8 million for the three months ended June 30, 2025, as compared to $21.8 million for the three months ended June 30, 2024. About REWRITE REWRITE is a two-part single and multiple dose-escalating study that will evaluate the safety and tolerability of KRRO-110, in up to 64 participants, including healthy adults and clinically stable AATD patients with the PiZZ genotype. Secondary and exploratory endpoints include pharmacokinetic and pharmacodynamic parameters that will guide optimal dose selection for later stage studies. Interim data from Part 1 (single ascending doses in healthy volunteers and individuals with AATD) is expected in second half of 2025 and completion of the study, including Part 2 (multiple ascending doses in individuals with AATD), is anticipated in 2026. For additional information about the REWRITE study, visit ClinicalTrials.gov (NCT06677307). About Alpha-1 Antitrypsin Deficiency (AATD) and KRRO-110 AATD is a genetic disorder most commonly caused by a single missense mutation (G-to-A) in the SERPINA1 gene. Affected adults experience pulmonary emphysema and/or hepatic cirrhosis, as well as end organ manifestations. KRRO-110 is the first RNA editing oligonucleotide product candidate from Korro’s proprietary RNA editing platform, Oligonucleotide Promoted Editing of RNA (OPERA®). KRRO-110, a potential best-in-class compound based on preclinical data, is designed to co-opt an endogenous enzyme, Adenosine Deaminase Acting on RNA (ADAR), to edit the “A” variant on SERPINA1 RNA, repair an amino acid codon, and restore secretion of normal AAT protein. This repair of the endogenous protein has the potential to clear protein aggregates from within liver cells to create a potentially clinically differentiated benefit for liver function and to preserve lung function by providing an adequate amount of normal AAT protein. About Korro Korro is a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases. Korro is generating a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, enabling a precise yet transient single base edit. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary platform with precedented delivery modalities, manufacturing know-how, and established regulatory pathways of approved oligonucleotide drugs. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of data readouts and completion of the Phase 1/2a REWRITE clinical trial; timing of announcement of a development candidate for Korro’s rare metabolic disorder program; KRRO-110’s best-in-class potential; bringing patients potentially best-in-class genetic medicines for diseases with high prevalence and substantial unmet clinical need; expectations for KRRO-110 dose levels to be pharmacologically relevant in PiZZ patients; execution of the 3-2-1 strategy; Korro’s collaboration with Novo Nordisk; Korro’s cash runway and uses thereof; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks of realizing the benefits of KRRO-110’s orphan drug designation for the treatment of AATD; risks of conducting a clinical trial; risks associated with regulatory oversight of clinical trials, enrollment risks and risks of expanding to other jurisdictions along with other risks inherent in biopharmaceutical development; risks associated with pre-clinical studies and clinical trials; and other risks associated with obtaining regulatory approvals and protecting intellectual property; risks of developing product candidates in collaboration with third parties; as well as risks associated with general economic conditions (including recent geopolitical uncertainty and potential supply chain disruptions due to changes in economic policy); and other risks and uncertainties indicated from time to time in Korro’s filings with the SEC, including Part I Item 1A. “Risk Factors” in Korro’s Quarterly Report on Form 10-Q filed with the SEC on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact [email protected] This press release was published by a CLEAR® Verified individual.

CAMBRIDGE, Mass., May 07, 2025 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases, today reported financial results for the first quarter of 2025 and provided a business update. Ram Aiyar, Ph.D., CEO and President of Korro, said, “We remain on track to achieve our clinical and pipeline milestones, most notably reporting interim data from our Phase 1/2a REWRITE clinical trial of KRRO-110 in the second half of 2025. We believe that KRRO-110 represents a groundbreaking therapy with best-in-class potential for patients with AATD. At the same time, we remain focused on executing our 3-2-1 strategy through 2027 with the goal of developing novel genetic medicines to improve lives of patients with rare and highly prevalent diseases.” Streamlining Operations and Workforce Reduction: Streamlining operations and workforce reduction enables potential value generating program milestones. Korro is streamlining its operations across the organization and reducing its workforce by approximately 20% to advance its programs to key value inflection points, including completing the Phase 1/2a REWRITE clinical trial in 2026, nominating a second development candidate, and advancing up to two programs under the collaboration with Novo Nordisk. Korro estimates that it will incur one-time restructuring charges of approximately $1.2 million including employee severance, benefits and related termination costs, the majority of which Korro expects to recognize during the second quarter of 2025. “Streamlining the organization is essential to enable Korro’s long-term success. We will continue to prioritize the development of KRRO-110 while making focused investments in our OPERA platform to efficiently advance innovation. The reduction in our workforce was not an easy decision, and we are committed to supporting our current and former employees during this transition,” said Todd Chappell, COO of Korro. Pipeline and Business Updates: Continue to advance the Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD. Korro received regulatory approval to expand the REWRITE clinical trial in New Zealand, and continues to progress enrollment, site activation and expansion into other geographies beyond Australia and New Zealand, including the United States. An interim readout is expected in the second half of 2025 and trial completion is expected in 2026. Executing 3-2-1 strategy through end of 2027. Korro continues to execute the 3-2-1 strategy with the goal of establishing three clinical-stage development programs, targeting two tissue types by leveraging the capabilities of its Oligonucleotide Promoted Editing of RNA (OPERA™) platform. Strengthened leadership team with appointments of Loïc Vincent, Ph.D., as Chief Scientific Officer and GaoZhong Zhu, Ph.D., as Senior Vice President of Chemistry, Manufacturing and Controls. Dr. Vincent joins Korro with more than 20 years in drug discovery and translational research across academia, biotech and the pharmaceutical industry. Throughout his career, Dr. Vincent led teams that advanced more than 20 drugs into clinical development based on various therapeutic modalities including small molecules, biologics, viral platforms and cell therapies. Dr. Zhu has more than 25 years of industrial experience in developing and implementing CMC strategies for various types of pharmaceuticals, with a proven track record of bringing new products from conception to commercialization, further reinforcing Korro’s commitment to advancing its innovative pipeline. Current pipeline and collaboration with Novo Nordisk continue to progress. In addition to advancing KRRO-110 for AATD and its second program, Korro continues to execute on its CNS programs and its collaboration with Novo Nordisk. Under the Novo Nordisk collaboration, Korro is working to advance up to two programs through preclinical development using its proprietary OPERA™ platform, with the initial target intended to treat cardiometabolic diseases. Anticipated Upcoming Milestones: Interim readout from Phase 1/2a REWRITE clinical trial of KRRO-110 for AATD expected in the second half of 2025, and completion of the REWRITE clinical trial expected in 2026. Korro expects to nominate a development candidate by the end of 2025 for its rare metabolic disorder program targeting the liver (GalNAc) with subcutaneous delivery to create de novo protein variants. Progress partnership with Novo Nordisk in cardiometabolic diseases with high prevalence. First Quarter 2025 Financial Results: Cash Position: Cash, cash equivalents and marketable securities were $139.0 million as of March 31, 2025, compared to $163.1 million as of December 31, 2024. Korro expects its cash, cash equivalents and marketable securities as of March 31, 2025 will fund operating expenses and capital expenditure requirements into 2027. Collaboration Revenue: There was $2.6 million of collaboration revenue for the three months ended March 31, 2025, as compared to no collaboration revenue for the three months ended March 31, 2024. The increase was due to collaboration revenue earned in the first quarter of 2025 from its agreement with Novo Nordisk. Research and Development (R&D) Expenses: R&D expenses were $19.7 million for the three months ended March 31, 2025, as compared to $13.6 million for the three months ended March 31, 2024. The increase was driven primarily by increases in KRRO-110 external research and development expenses, personnel expenses and other research and pre-development candidate expenses. General and Administration (G&A) Expenses: G&A expenses were $7.8 million for the three months ended March 31, 2025, as compared to $7.9 million for the three months ended March 31, 2024. The minor decrease was primarily driven by a $0.1 million decrease in professional service fees and facilities expenses, partially offset by an increase in personnel expenses. Net Loss: Korro’s net loss was $23.4 million for the three months ended March 31, 2025, as compared to $19.6 million for the three months ended March 31, 2024. About REWRITE REWRITE is a two-part single and multiple dose-escalating study that will evaluate the safety and tolerability of KRRO-110, in up to 64 participants, including healthy adults and clinically stable AATD patients with the PiZZ genotype. Secondary and exploratory endpoints include pharmacokinetic and pharmacodynamic parameters that will guide optimal dose selection for later stage studies. Interim data from Part 1 (single ascending doses in healthy volunteers and individuals with AATD) is expected in the second half of 2025, and completion of the study is anticipated in 2026. For additional information about the REWRITE study, visit ClinicalTrials.gov (NCT06677307). About Alpha-1 Antitrypsin Deficiency (AATD) and KRRO-110 AATD is a genetic disorder most commonly caused by a single missense mutation (G-to-A) in the SERPINA1 gene. Affected adults experience pulmonary emphysema and/or hepatic cirrhosis, as well as end organ manifestations. KRRO-110 is the first RNA editing oligonucleotide product candidate from Korro’s proprietary RNA editing platform, Oligonucleotide Promoted Editing of RNA (OPERA™). KRRO-110, a potential best-in-class compound based on preclinical data, is designed to co-opt an endogenous enzyme, Adenosine Deaminase Acting on RNA (ADAR), to edit the “A” variant on SERPINA1 RNA, repair an amino acid codon, and restore secretion of normal AAT protein. This repair of the endogenous protein has the potential to clear protein aggregates from within liver cells to create a potentially clinically differentiated benefit for liver function and to preserve lung function by providing an adequate amount of normal AAT protein. About Korro Korro is a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases. Korro is generating a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, enabling a precise yet transient single base edit. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary platform with precedented delivery modalities, manufacturing know-how, and established regulatory pathways of approved oligonucleotide drugs. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of data readouts and completion of the Phase 1/2a REWRITE clinical trial; enrollment and expansion of the Phase 1/2a REWRITE clinical trial; execution of the 3-2-1 strategy; timing of nomination and target of a second development candidate; Korro’s cash runway and uses thereof; KRRO-110’s best-in-class potential; the costs of Korro’s workforce reduction and organizational streamlining, and the benefits thereof; and Korro’s collaboration with Novo Nordisk; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks of realizing the benefits of its workforce reduction and organizational streamlining; estimating the costs of such workforce reduction and organizational streamlining; the impact of the workforce reduction and organizational streamlining on operations; risks of conducting a clinical trial; risks associated with regulatory oversight of clinical trials, enrollment risks and risks of expanding to other jurisdictions along with other risks inherent in biopharmaceutical development; risks associated with pre-clinical studies and clinical trials; and other risks associated with obtaining regulatory approvals and protecting intellectual property; as well as risks associated with general economic conditions (including recent geopolitical uncertainty and potential supply chain disruptions due to changes in economic policy); and other risks and uncertainties indicated from time to time in Korro’s filings with the SEC, including Part I Item 1A. “Risk Factors” in Korro’s Quarterly Report on Form 10-Q filed with the SEC on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact [email protected]

CAMBRIDGE, Mass., March 18, 2025 (GLOBE NEWSWIRE) -- Korro Bio, Inc. (Korro) (Nasdaq: KRRO), a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases, today reported full-year 2024 financial results, and provided an update on recent progress and anticipated milestones. “We executed on our key objectives in 2024 by initiating the Phase 1/2a REWRITE clinical study of KRRO-110 for AATD, announcing a collaboration with Novo Nordisk, and advancing multiple product candidates in our pipeline,” said Ram Aiyar, PhD, CEO and President of Korro. “KRRO-110 has best-in-class potential based on our preclinical data, and we are excited to potentially demonstrate this in PiZZ patients in the second half of 2025 with the interim data readout of REWRITE. We also anticipate announcing our second development candidate by the end of 2025. Our strategy of taking three development candidates in two tissue types with a single RNA-editing platform in the clinic by the end of 2027 will expand the possibilities of RNA editing, underscoring our commitment to progressing both our wholly owned and partnered programs.” Pipeline and Business Updates: Completed dosing of the first two single ascending dose cohorts in healthy adult volunteers in Phase 1/2a REWRITE clinical study of KRRO-110. Korro has not observed any serious adverse events through completion of dosing of the first two cohorts as of today and continues to progress enrollment in Australia, and potential expansion into multiple jurisdictions, including the United States. An interim readout is expected in the second half of 2025 and study completion expected in 2026. KRRO-110 Granted Orphan Drug Designation for the treatment of AATD. The FDA's Office of Orphan Products Development grants orphan designation status to drugs and biologics that are intended for the treatment of rare diseases affecting fewer than 200,000 people in the United States. Orphan Drug designation provides various development incentives, including tax credits for qualified clinical testing, prescription drug user fee exemptions, and the potential for market exclusivity following FDA approval. Executing 3-2-1 strategy through end of 2027. Korro expects to establish three clinical-stage development programs, in two tissue types with a single modular RNA-editing platform. Strengthened leadership with key appointments to board and management team. Korro formed a Clinical Advisory Board, consisting of esteemed lung and liver scientific experts, to guide the development strategy of KRRO-110. GaoZhong Zhu, Ph.D. also joined Korro as Senior Vice President of Chemistry, Manufacturing and Controls (CMC) & Technical Operations to further reinforce Korro’s commitment to advancing its innovative pipeline. In February 2025, the American College of Chest Physicians (CHEST) Journal published, “Editing Approaches to Treat Alpha-1 Antitrypsin Deficiency.” The publication highlights the merits of RNA editing in AATD and its potential for treatment for both liver and lung disease, while highlighting KRRO-110 as an RNA editing oligonucleotide delivered via lipid nanoparticle. Collaboration with Novo Nordisk continues to progress. Korro’s partnership with Novo Nordisk focuses on leveraging Korro’s OPERA platform for up to two disease targets, with the initial target intended to treat cardiometabolic diseases. Upcoming Milestones: Interim readout from Phase 1/2a REWRITE clinical study of KRRO-110 for AATD expected in the second half of 2025, and completion of the REWRITE clinical study expected in 2026. Korro expects to nominate a development candidate for its rare metabolic disorder program targeting the liver (GalNAc) with subcutaneous delivery to create de novo protein variants by the end of 2025. Progress partnership with Novo Nordisk in cardiometabolic diseases with high prevalence. Full Year 2024 Financial Results: Cash Position: Cash, cash equivalents and marketable securities were $163.1 million as of December 31, 2024, compared to $166.1 million as of December 31, 2023. Korro expects its cash, cash equivalents and marketable securities will fund operating expenses and capital expenditure requirements into the second half of 2026. Collaboration Revenue: There was $2.3 million of collaboration revenue for the year ended December 31, 2024, as compared to no collaboration revenue for the year ended December 31, 2023. The increase was due to collaboration revenue earned in the fourth quarter of 2024 from the company’s partnership with Novo Nordisk. Research and Development (R&D) Expenses: R&D expenses were $63.6 million for the year ended December 31, 2024, as compared to $57.2 million for the year ended December 31, 2023. The increase was driven primarily by increases in KRRO-110 external research and development expenses, personnel expenses and facilities expenses, offset by a decrease in other research and pre-development candidate expenses. General and Administration (G&A) Expenses: G&A expenses were $30.5 million for the year ended December 31, 2024, as compared to $27.3 million for the year ended December 31, 2023. The increase was primarily due to increased information technology, insurance and other costs, as well as increased professional fees and facility costs attributable to build-out of the G&A function. Net Loss: Korro’s net loss was $83.6 million for the year ended December 31, 2024, as compared to $81.2 million for the year ended December 31, 2023. About REWRITE REWRITE is a two-part single and multiple dose-escalating study that will evaluate the safety and tolerability of KRRO-110, in up to 64 participants, including healthy adults and clinically stable AATD patients with the PiZZ genotype. Secondary and exploratory endpoints include pharmacokinetic and pharmacodynamic parameters that will guide optimal dose selection for later stage studies. Interim data from Part 1 (single ascending doses in healthy volunteers and individuals with AATD) is expected in the second half of 2025, and completion of the study is anticipated in 2026. For additional information about the REWRITE study, visit ClinicalTrials.gov (NCT06677307). About Alpha-1 Antitrypsin Deficiency (AATD) and KRRO-110 AATD is a genetic disorder most commonly caused by a single missense mutation (G-to-A) in the SERPINA1 gene. Affected adults experience pulmonary emphysema and/or hepatic cirrhosis, as well as end organ manifestations. KRRO-110 is the first RNA editing oligonucleotide product candidate from Korro’s proprietary RNA editing platform, Oligonucleotide Promoted Editing of RNA (OPERA™). KRRO-110, a potential best-in-class compound based on preclinical data, is designed to co-opt an endogenous enzyme, Adenosine Deaminase Acting on RNA (ADAR), to edit the “A” variant on SERPINA1 RNA, repair an amino acid codon, and restore secretion of normal AAT protein. This repair of the endogenous protein has the potential to clear protein aggregates from within liver cells to create a potentially clinically differentiated benefit for liver function and to preserve lung function by providing an adequate amount of normal AAT protein. About Korro Korro is a clinical-stage biopharmaceutical company focused on developing a new class of genetic medicines based on editing RNA for both rare and highly prevalent diseases. Korro is generating a portfolio of differentiated programs that are designed to harness the body’s natural RNA editing process, enabling a precise yet transient single base edit. By editing RNA instead of DNA, Korro is expanding the reach of genetic medicines by delivering additional precision and tunability, which has the potential for increased specificity and improved long-term tolerability. Using an oligonucleotide-based approach, Korro expects to bring its medicines to patients by leveraging its proprietary platform with precedented delivery modalities, manufacturing know-how, and established regulatory pathways of approved oligonucleotide drugs. Korro is based in Cambridge, Massachusetts. For more information, visit korrobio.com. Korro intends to use its Investor Relations website, LinkedIn, and X (Twitter) as means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD. Accordingly, investors should monitor Korro’s Investor Relations website and follow @KorroBio on LinkedIn, and X (Twitter), in addition to following Korro’s press releases, SEC filings, public conference calls, presentations, and webcasts. Forward-Looking Statements Certain statements in this press release may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include, but are not limited to, express or implied statements regarding expectations, hopes, beliefs, intentions or strategies of Korro regarding the future including, without limitation, express or implied statements regarding: the timing of data readouts and completion of the Phase 1/2a REWRITE clinical trial; enrollment and expansion of the Phase 1/2a REWRITE clinical trial; execution of the 3-2-1 strategy; timing of nomination and target of a second development candidate; Korro’s cash runway and uses thereof; KRRO-110’s best-in-class potential; realizing the incentives offered from the orphan drug designation of KRRO-110; and Korro’s collaboration with Novo Nordisk; among others. In addition, any statements that refer to projections, forecasts, or other characterizations of future events or circumstances, including any underlying assumptions, are forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “might,” “plan,” “possible,” “potential,” “predict,” “project,” “should,” “strive,” “would,” “aim,” “target,” “commit,” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that statement is not forward looking. Forward-looking statements are based on current expectations and assumptions that, while considered reasonable are inherently uncertain. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Factors that may cause actual results to differ materially from current expectations include, but are not limited to, various factors beyond management’s control including risks of conducting a clinical study; risks associated with regulatory oversight of clinical studies, enrollment risks and risks of expanding to other jurisdictions along with other risks inherent in biopharmaceutical development; risks associated with pre-clinical studies and clinical studies; and other risks associated with obtaining regulatory approvals and protecting intellectual property; as well as risks associated with general economic conditions (including recent geopolitical uncertainty and potential supply chain disruptions due to changes in economic policy); and other risks and uncertainties indicated from time to time in Korro’s filings with the SEC, including Part I Item 1A. “Risk Factors” in Korro’s Annual Report on Form 10-K filed with the Securities and Exchange Commission, or SEC, on the date hereof, as such may be amended or supplemented by its other filings with the SEC. Nothing in this press release should be regarded as a representation by any person that the forward-looking statements set forth herein will be achieved or that any of the contemplated results of such forward-looking statements will be achieved. You should not place undue reliance on forward-looking statements in this press release, which speak only as of the date they are made and are qualified in their entirety by reference to the cautionary statements herein. Except as required by law, Korro does not undertake or accept any duty to release publicly any updates or revisions to any forward-looking statements to reflect any change in its expectations or in the events, conditions or circumstances on which any such statement is based. This press release does not purport to summarize all of the conditions, risks and other attributes of an investment in Korro. Korro Bio Contact Information Investor & Media Contact Tim Palmer [email protected] This press release was published by a CLEAR® Verified individual.