OS Therapies Inc, a clinical-stage cancer immunotherapy and antibody drug conjugate biotechnology company, has provided a regulatory update on its plans for filing marketing authorizations in the US and UK for OST-HER2 in the prevention or delay of recurrent, fully resected, pulmonary metastatic osteosarcoma based on a data generated from its completed phase 2b clinical trial currently in the long term follow-up phase.
The company has updated its regulatory filing sequence to prioritize the UK MHRA conditional marketing authorisation application (MAA) final module submission to immediately precede its US FDA biologics licensing application final module submission under the Accelerated Approval Programme. The company expects to complete the MHRA conditional MAA submission in December 2025, with the US FDA BLA Accelerated Approval submission expected in January 2025.
OS Therapies Inc has submitted a conditional MAA Pre-Submission Request following MHRA feedback arising from its August 2025 Scientific Advice Meeting (SAM). MHRA has aligned around the use of peer-reviewed historical control data as a suitable comparator arm to support the company's conditional MAA request. MHRA further agreed to support OS Therapies efforts to obtain case-matched external control arm data by providing access to the UK's Clinical Practice Research Datalink.
The information in the MHRA conditional MAA submission is closely aligned with the information in the planned US FDA BLA accelerated approval request, apart from alignment around an acceptable comparator arm against which to compare the efficacy data from the company's phase 2b trial of OST-HER2. After the End of phase 2 and follow-up conversations with FDA, general alignment was reached on all matters, except for suitable comparators. At the direction of FDA, the company has requested an additional Type C meeting to review updated overall survival and new biomarker data. The company intends to confirm whether immune activation biomarker data as the surrogate marker correlated with 2-year interim overall survival as a secondary endpoint would be a suitable surrogate marker of efficacy to support accelerated approval.
"We've gained a deeper understanding of what US FDA is now looking for to support an efficacy claim as a result of our interactions over the last 45 days," said Paul Romness, MHP, chairman & CEO of OS Therapies. "The FDA agreed with the Company that OST-HER2 had a strong safety profile and the canine overall survival data correlating with immune activation biomarker data recently published in Journal of Molecular Therapy, attributing clinical benefit to OST-HER2 treatment. We intend to present a similar data package generated from our phase 2b human clinical trial of OST-HER2 and believe the FDA will support this approach to accelerated approval."
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