London - Mereo BioPharma Group plc (NASDAQ: MREO), ('Mereo' or 'the Company'), a clinical-stage biopharmaceutical company focused on rare diseases today announced that data from the Phase 2 'ASTRAEUS' trial of alvelestat for the treatment of Alpha-1 Antitrypsin Deficiency-associated Lung Disease (AATD-LD), as well as post-hoc analyses demonstrating the association between biomarker reductions with alvelestat and improvements in SGRQ, a key Patient-Reported Outcome (PRO) measure, were presented for the first time to the scientific community at the 2023 American Thoracic Society International Conference.

The ASTRAEUS data were presented during an oral abstract session on novel treatments and targets by Prof. Robert Stockley, Lung Investigation Unit, University of Birmingham (United Kingdom) and Chief Investigator of the ASTRAEUS trial, while the post-hoc analyses were presented in a poster session by Dr. Jackie Parkin, Senior Vice President and Therapeutic Head at Mereo.

Consistent with previously reported biomarker analyses, alvelestat demonstrated significant and consistent reductions in all three biomarkers related to AATD-LD disease activity: blood neutrophil elastase (NE), A-val360 and the elastin breakdown product, desmosine. Low - and high-dose alvelestat significantly suppressed NE activity compared to baseline (-83.5% and -93.3%, p=0.023 and p5% biomarker decrease (P=0.05 and p=0.02 respectively), compared to those on alvelestat without biomarker decrease. This association was not observed in the patients who received placebo. These data support a potential association between the effect of alvelestat on the NE pathway and improvement in how a patient feels and functions based on SGRQ score. Data from ASTRAEUS and other research support the hypothesis that longer term treatment is expected to lead to a deepening of the biomarker and associated clinical response.

Alvelestat has been generally safe, with no safety signals of concern observed to date. Adverse events leading to study drug discontinuation (one liver function and one prolonged QTc) resolved on study drug cessation. Three treatment-related SAEs of headache were reported in the alvelestat arms. Headache is a known adverse event associated with alvelestat and is being addressed through dose-escalation during initiation of alvelestat treatment.

'We are very pleased to have these data presented to the scientific community for the first time at ATS2023, These findings have informed our recent and ongoing discussions with both the FDA and EMA, and validate the proposed design for our planned Phase 3 trial, which we believe will be the first registrational study in AATD-LD to use both a PRO approach and an objective clinical outcome measure as independent primary endpoints,' said Dr. Denise Scots-Knight, CEO of Mereo BioPharma. 'We are excited by the potential of alvelestat to become the first-in-class oral neutrophil elastase inhibitor for the treatment of AATD-LD and look forward to continued collaboration with the regulatory authorities, scientific and patient communities as we further refine our development plans ahead of the pivotal study. We look forward to sharing further updates on the progress of the alvelestat program, including the results of the investigator-led Phase 2 ATALANTA study evaluating alvelestat in combination with augmentation therapy, which is expected to read out in Q3 2023.'

About Mereo BioPharma

Mereo BioPharma is a biopharmaceutical company focused on the development of innovative therapeutics for rare diseases. The Company has two rare disease product candidates, setrusumab for the treatment of Osteogenesis Imperfecta (OI) and alvelestat for the treatment of severe alpha-1-antitrypsin deficiency-associated lung disease (AATD-LD) and Bronchiolitis Obliterans Syndrome (BOS). The Company's partner, Ultragenyx Pharmaceutical, Inc., has initiated a pivotal Phase 2/3 pediatric study in young adults (5-25 years old) for setrusumab in OI and expects to initiate a study in pediatric patients (

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