MREO

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Exhibit 99.1

Mereo BioPharma Reports Second Quarter 2026 Financial Results and Provides Corporate Highlights

Entered into option and license agreement with Sentynl Therapeutics for alvelestat, Mereo’s investigational oral therapy for Alpha-1 Antitrypsin Deficiency-Associated Lung Disease (AATD-LD)

Mereo and partner Ultragenyx engaging with regulatory agencies on potential path forward for setrusumab in osteogenesis imperfecta (OI); further updates expected by year-end 2026

Cash and cash equivalents of $30.1 million at June 30, 2026, now expected to fund operations into late-2027

London, August 11, 2026 – Mereo BioPharma Group plc (NASDAQ: MREO) (“Mereo” or the “Company”), a clinical-stage biopharmaceutical company focused on rare diseases, today announced financial results for the second quarter ended June 30, 2026, and provided an update on recent corporate highlights.

The Company is also updating its previous cash runway guidance. As of June 30, 2026, cash and cash equivalents were approximately $30 million, which are expected to fund operations into late-2027.

“The partnership with Sentynl Therapeutics which we announced earlier today marks a significant milestone for our alvelestat program and for the Company as a whole. We are now working together to refine the design of the global Phase 3 study for our potential first-in-class oral therapy for AATD-LD and look forward to a continued close collaboration during the short option period. Assuming exercise of the license option by Sentynl, we plan to initiate the Phase 3 trial in early 2027,” said Denise Scots-Knight, Chief Executive Officer of Mereo BioPharma. “Additionally, alongside our partner Ultragenyx, we have had initial regulatory interactions on setrusumab with the FDA and the MHRA and we expect to be in a position to provide an update on the potential path forward by the end of this year. We finished the quarter with approximately $30 million in cash. Thanks to our careful expense management, we now expect that this cash will provide runway into late-2027, exclusive of the potential $40 million in upfront and R&D payments that we are eligible to receive on exercise of the alvelestat option by Sentynl.”

Second Quarter 2026 Highlights, Recent Developments, and Anticipated Milestones

Setrusumab (UX143)

• The Orbit and the Cosmic Phase 3 studies did not achieve statistical significance against the primary endpoints of reduction in annualized clinical fracture rate, however, both achieved high statistical significance against the key secondary endpoint of improvement in bone mineral density, as well as reductions in vertebral fractures and improvements in patient reported outcomes (PROs) associated with disease severity, pain / discomfort and daily activities, with these PRO improvements achieving statistical significance in the Orbit study. Setrusumab also achieved meaningful reductions in fractures in certain bones and in patients with higher fracture frequencies. Both studies demonstrated a safety profile consistent with that observed in previous trials.

• Mereo and its partner, Ultragenyx Pharmaceutical, Inc. (“Ultragenyx”), are engaged with regulatory agencies to determine a potential path forward for setrusumab in pediatric OI patients and, to-date, have held discussions with the regulators in the U.S. and the U.K. The FDA indicated openness to considering alternative approaches to fracture analysis, with additional conversations needed to further define what additional clinical data would be needed to support a potential BLA. In recent communications with the MHRA, they encouraged further dialogue on any future development proposal, and we plan to have further interactions following the FDA discussions.

Alvelestat (MPH-966)

• Mereo recently announced an option and license agreement with Sentynl Therapeutics, Inc. (Sentynl), a wholly owned subsidiary of Zydus Lifesciences Limited. Sentynl has the right to acquire a license for the U.S. commercial and global manufacturing rights to alvelestat for AATD-LD.

o Sentynl is a California-based, commercial-stage biopharmaceutical company with three currently approved products for rare diseases.

o Under the agreement, the companies will collaborate to refine the design of the planned global Phase 3 trial of alvelestat and to advance the manufacturing during the short option period.

• Mereo will receive a non-refundable option fee and, on option exercise, would also be eligible to receive $40 million in upfront and R&D payments, up to $435 million in regulatory and commercial milestone payments, as well as double-digit tiered royalties on U.S. net sales of alvelestat.

• Mereo will lead the global Phase 3 study and regulatory interactions until study completion and will retain rest-of-world commercial rights for alvelestat.

• On exercise of the option by Sentynl, the agreement provides funding for the global Phase 3 study, which could be initiat

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Exhibit 99.1

Mereo BioPharma Reports First Quarter 2026 Financial Results and Provides Corporate Highlights

London, May 12, 2026 – Mereo BioPharma Group plc (NASDAQ: MREO) (“Mereo” or the “Company”), a clinical-stage biopharmaceutical company focused on rare diseases, today announced financial results for the first quarter ended March 31, 2026, and provided an update on recent corporate developments.

“Based on extensive analysis of data across the two global Phase 3 studies of setrusumab in osteogenesis imperfecta in collaboration with our partner Ultragenyx, we believe there is basis to engage with the regulatory agencies to determine if there is a path forward in pediatric patients. These interactions have been initiated, and we plan to provide updates once we have some definitive feedback. We continue to believe that setrusumab has the potential to provide meaningful benefit for people living with OI, a condition with no FDA or EMA approved therapies,” said Denise Scots-Knight, Chief Executive Officer of Mereo. “We are actively engaged with potential partners for alvelestat in AATD-LD and believe alvelestat can quickly enter Phase 3 development following closing of a partnership transaction. Our other partnered program, vantictumab, is continuing to move forward with āshibio, who plan to initiate a Phase 2 trial in osteopetrosis in the second half of 2026. We continue to expect that our cash position, which totaled $36.2 million as of March 31, will provide runway into mid-2027, through several key inflection points expected during the remainder of this year.”

Recent Corporate Developments and Anticipated Milestones

Setrusumab (UX143)

• Further analyses of the data from the Orbit and Cosmic Phase 3 studies, including patient subgroups, have been completed.

• While neither study achieved statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo (Orbit) or bisphosphonates (Cosmic), both studies achieved high statistical significance against the key secondary endpoint of improvement in bone mineral density versus control as well as reductions in vertebral fractures and improvements in patient reported outcomes (PROs) associated with disease severity, pain / discomfort and daily activities, with these PRO improvements achieving statistical significance in the Orbit study.

• The safety profile of setrusumab was consistent with that observed in prior studies.

• Based on the Phase 3 data analysis from both global Phase 3 studies and the safety profile of setrusumab, Mereo and its partner Ultragenyx believe there is a basis to engage regulatory agencies to determine if there is a path forward for setrusumab in pediatric patients. These interactions have been initiated.

Alvelestat (MPH-966)

• Mereo is actively engaged in discussions with potential partners for the Phase 3 development and commercialization of alvelestat.

• Based on previous discussions with the FDA and EMA, Mereo anticipates a single Phase 3 trial enrolling approximately 220 early- and late-stage AATD-LD patients evaluating alvelestat over an 18-month treatment period will support regulatory submissions in both the U.S. and Europe.

o The primary efficacy endpoint for potential U.S. approval will be the St. George’s Respiratory Questionnaire (SGRQ) Total Score, with lung density measured by CT scan serving as the primary endpoint for potential European regulatory approval. These are independent primary endpoints.

o The Company believes initiation of the Phase 3 study could happen within 6 months of closing a potential partnership transaction.

Vantictumab (OMP18R5)

• The Company’s development partner for vantictumab, āshibio, Inc., is continuing to advance toward initiation of a Phase 2 clinical trial in autosomal dominant osteopetrosis Type 2 (ADO2), which is expected to commence in the second half of 2026.

• āshibio is responsible for funding the global clinical program and holds the right to commercialize vantictumab outside of Europe, where Mereo has retained commercial rights.

First Quarter 2026 Financial Results

Total research and development (“R&D”) expenses increased by $0.8 million, from $3.9 million in the first quarter of 2025 to $4.7 million in the first quarter of 2026. The increase was primarily due to increases of $1.8 million in R&D expenses for setrusumab, partially offset by reductions of $0.9 million in R&D expenses for alvelestat. The increase in program expenses for setrusumab was primarily driven by recognition of a payable for our share of certain costs related to the cancellation of manufacturing slots by our partner, Ultragenyx, partially offset by reductions of, and delays to, investment in manufacturing and ongoing activities, including medical affairs activities in Europe during the first quarter of 2026. The decrease in program expenses for alvelestat was primarily due to completion of activit

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EX-99.1

Exhibit 99.1

Mereo BioPharma Reports Full Year 2025 Financial Results and Provides Corporate Highlights

Additional data analyses from Orbit and Cosmic Phase 3 studies of setrusumab (UX143) in osteogenesis imperfecta ongoing

Cash of $41.0 million as of December 31, 2025, expected to provide runway into to mid-2027

London, March 19, 2026 – Mereo BioPharma Group plc (NASDAQ: MREO) (“Mereo” or the “Company”), a clinical-stage biopharmaceutical company focused on rare diseases, today announced financial results for the full year ended December 31, 2025, and provided an update on recent corporate developments.

“In collaboration with our partner Ultragenyx, we have analysed a significant part of the data from the Phase 3 Orbit and Cosmic studies of setrusumab in osteogenesis imperfecta and continue to develop our understanding of the fracture data and the patient reported outcomes (PROs), especially in patients aged 2–18 years old. We believe that these data, which include pre-specified sub-groups and ad hoc analyses, may provide the basis for engagement with the regulatory agencies,” said Denise Scots-Knight, Chief Executive Officer of Mereo. “There are no FDA or EMA therapies approved specifically for OI and although bisphosphonates are used to improved bone mineral density, it remains a high unmet need. Setrusumab has demonstrated statistically significant improvements in bone mineral density as well as compelling reductions in vertebral fractures and statistically significant improvements in PROs of disease pain and daily activity in pediatric and teenage patients. We look forward to providing updates on these efforts as we progress with next steps. Alongside this, our partnering discussions around alvelestat in AATD-LD are continuing to advance on multiple fronts and our partner āshibio has indicated that it plans to initiate a Phase 2 trial of vantictumab in osteopetrosis in the second half of this year. Following our cost reductions and delays to investment in manufacturing and pre-commercial activities for setrusumab, our revised financial runway into mid-2027 enables us to potentially deliver on several key milestones during 2026.”

Setrusumab (UX143)

• As announced on December 29, 2025, the Phase 3 Orbit and Cosmic studies of setrusumab in OI did not achieve statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively.

• Both studies achieved high statistical significance against the key secondary endpoint of improvement in bone mineral density versus a placebo or versus a bisphosphonate (standard of care) comparator.

o The improvement in bone mineral density in the Cosmic study was associated with a decreased rate of fracture in this younger, more highly fracturing patient population, although this was not statistically significant.

• Additionally, the studies demonstrated reductions in vertebral fractures, which are a key contributor to pain and disability in this patient population and are known to drive treatment decisions, as well as improvements in patient-reported outcomes of disease severity, pain / comfort and daily activities which were statistically significant in the Orbit study in pediatrics and teens.

• The safety profile of setrusumab was consistent with that observed in prior studies.

• Further analyses of the data from both studies, including patient subgroups, are ongoing ahead of any planned interactions with the regulatory agencies.

Alvelestat (MPH-966)

• The site feasibility work for initiation of the global Phase 3 pivotal study has been completed.

• Based on previous discussions with the FDA and EMA, Mereo anticipates a single Phase 3 trial enrolling approximately 220 early- and late-stage AATD-LD patients evaluating alvelestat over an 18-month treatment period will support regulatory submissions in both the U.S. and Europe.

o The primary efficacy endpoint for potential U.S. approval will be the St. George’s Respiratory Questionnaire (SGRQ) Total Score, with lung density measured by CT scan serving as the primary endpoint for potential European regulatory approval.

• Mereo continues to be in active discussions with potential partners for the Phase 3 development and commercialization of alvelestat.

• Additionally, the Company has designed a potential Phase 2b study of alvelestat in bronchiectasis to further support the ongoing partnering discussions.

o The proposed study would enroll approximately 250 patients, randomized 1:1:1 to receive one of two alvelestat doses with standard of care or placebo with standard of care, with a primary efficacy endpoint of change in exacerbation rate at six months.

o The proposed trial design is intended to substantially de-risk potential Phase 3 development, as exacerbations are a required confirmatory endpoint in registrational trials.

Vantictumab (OMP18R5)

• The Company outlicensed vanti