UAB and Mereo Announce Positive Top-line Results from COSTA a Phase 1b/2 Trial of Alvelestat (MPH966) in Hospitalized Patients with COVID-19 Respiratory Disease Alvelestat reported safe and well-tolerated in patients wit

UAB and Mereo Announce Positive Top-line Results from COSTA a Phase 1b/2 Trial of Alvelestat (MPH966) in Hospitalized Patients

with COVID-19 Respiratory Disease

Alvelestat reported safe and well-tolerated in patients with COVID-19

Alvelestat, on top of standard of care resulted in a more rapid time to improvement in WHO Disease Severity

score of >=2 in the first 5-7 days compared to placebo plus standard of care

London and Redwood City, Calif., December 22, 2021 The University of Alabama at Birmingham (UAB) and Mereo BioPharma

Group plc (NASDAQ: MREO), today announced top-line data from a Phase 1b/2 clinical trial evaluating alvelestat, a novel, orally active Neutrophil Elastase (NE) inhibitor in hospitalized COVID-19 Respiratory Disease patients.

The COSTA Phase 1b/2 trial (NCT04539795) is an investigator-led, single-centre study (Principal Investigator Dr. James M Wells, Associate Professor in

Pulmonary, Allergy and Critical Care Medicine, UAB). The trial is a double-blind, randomized, placebo-controlled study in adult patients (>18 years) with COVID-19 Respiratory Disease, evaluating the safety and tolerability of alvelestat on top of

Standard of Care in patients hospitalised with proven COVID-19 lung disease. Patients requiring mechanical ventilation were excluded. Enrolled subjects received alvelestat or matched placebo, twice daily, for 5 days, with optional extension to 10

days per investigator judgement. Initial subjects underwent dose escalation to evaluate safety and tolerability for the population. The Primary Endpoint was Safety and Tolerability to Day 60, with mortality assessment at Day 90. Secondary Endpoints

were clinical outcomes to Day 60. Biomarkers of inflammation, coagulopathy, were measured; biomarkers of neutrophil extracellular traps (NETs) were explored and desmosine was measured to the end of study drug treatment. The study was signal seeking

and not powered for the secondary measures.

Fifteen patients were randomized (10 male, 5 female), and all completed the Primary Endpoint Safety

assessment to Day 60 and the Day 90 final study assessment. The original design involved a 2:1 active to placebo ratio, however patients were enrolled 1:1 resulting in 8 patients on alvelestat and 7 patients on placebo. The mean age was 47.8 years;

the most common co-morbidities were hypertension, sleep apnea, hypercholesterolemia, and Type 2 diabetes. At entry to the study, all patients were requiring supplemental oxygen, all had initiated dexamethasone and 14 were on antiviral treatment with

remdesivir at baseline or initiated after randomization (7/7 on placebo and 7/8 on alvelestat). The majority of patients were WHO COVID-19 Ordinal Severity Scale Score 4 (hospitalized mild disease requiring supplemental oxygen) or 5 (hospitalized

severe disease, requiring non-invasive ventilation or high flow oxygen) at entry to the study.

TRIAL RESULTS HIGHLIGHTS

Primary Endpoint: Safety and Tolerability to Day 60

Secondary Efficacy Endpoints:

Clinical Outcome Measures

Inflammatory Biomarkers

There remains a significant unmet need to improve the outcomes of hospitalized patients with COVID-19. The early results with

alvelestat suggest a potential for clinical benefit over and above standard of care including dexamethasone and remdesivir. This is exciting given the ease of administration of a well-tolerated oral therapy in this acutely ill population, said

Dr. Mike Wells, Associate Professor in Pulmonary, Allergy and Critical Care Medicine, UAB. These findings provide strong data and set the stage for future studies with relevant clinical end-points.

These data whilst early and in a small study, are highly encouraging as the first evidence that alvelestat could offer clinical outcome benefit over and

above standard of care in patients hospitalized with COVID-19, said Dr. Denise Scots-Knight, Chief Executive Officer at Mereo. This clearly warrants further evaluation in a larger study. We are grateful to the patients who participated

in this study and to Dr. Mike Wells and his team at UAB for leading this important work.

Alvelestat is currently being investigated in two Phase 2 studies (ASTRAEUS and ATALANTa) for patients with alpha-1 antitrypsin deficiency (AATD) and a Phase

1b/2 for patients with bronchiolitis obliterans syndrome (BOS) following hematopoietic stem cell transplant. Mereo noted that both high and low doses of alvelestat in the ASTRAEUS Phase 2 study have shown good safety to-date and the study has now

recruited 99 patients and per protocol, enrollment has been biased towards the high dose. Top-line data for ASTRAEUS continue to be expected in early Q2 2022.

About Mereo BioPharma

Mereo BioPharma is a

biopharmaceutical company focused on the development and commercialization of innovative therapeutics that aim to improve outcomes for oncology and rare diseases. The Company has developed a portfolio of six clinical stage product candidates.

Mereo s lead oncology product candidate, etigilimab (anti-TIGIT), has advanced into an open label Phase 1b/2 basket study evaluating anti-TIGIT in combination with an anti-PD-1 in a range of tumor types including three rare tumors and three

gynecological carcinomas, cervical, ovarian, and endometrial carcinomas. The Company s second oncology product, navicixizumab, for the treatment of late line ovarian cancer, has completed a Phase 1 study and has been partnered with OncXerna

Therapeutics, Inc., formerly Oncologie, Inc. The Company has two rare disease product candidates, alvelestat for the treatment of severe Alpha-1 antitrypsin deficiency (AATD) and setrusumab for the treatment of osteogenesis imperfecta (OI).

Alvelestat has recently received U.S. Orphan Drug Designation for the treatment of AATD and is being investigated in an ongoing Phase 2 proof-of-concept study in the U.S. and Europe, with top-line data now expected in early Q2 2022. The

Company s partner, Ultragenyx Pharmaceutical, Inc., is expected to initiate a pivotal pediatric study for setrusumab in OI before the end of 2021.

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