OS Therapies Aligns With FDA, MHRA and EMA on Adaptive Phase 3 Design for OST-HER2 in Metastatic Osteosarcoma
核心洞察
OS Therapies reached incremental alignment with the FDA on an adaptive Phase 3 trial design for OST-HER2 previously agreed with the MHRA and EMA.
The company accepted an MHRA request to serve as its representative to Project Orbis, harmonizing oncology regulatory review across the US, UK and Europe.
The Phase 3 trial in fully-resected, pulmonary metastatic osteosarcoma (搜索) is expected to begin in the fourth quarter of 2026.
OS Therapies, Inc. (NYSE American: OSTX) has achieved incremental alignment with the U.S. Food & Drug Administration on the adaptive design for its pending Phase 3 trial of OST-HER2 in the prevention or delay of recurrence in fully-resected, pulmonary metastatic osteosarcoma (搜索), the company announced on September 17, 2026. The design had previously been agreed upon with the U.K.'s Medicines and Healthcare products Regulatory Agency (搜索) and the European Medicines Agency (搜索), and the FDA's alignment brings the three regulators onto a common trial framework.
The company said the Phase 3 trial is expected to commence in the fourth quarter of 2026. OS Therapies also expects to hold its previously disclosed invited Type B Pre-BLA meeting with the FDA in the fourth quarter of 2026, following submission of the clinical section of its Biologics License Application, inclusive of 3-year overall survival data. That submission would complete the ongoing BLA filing initiated in January 2026.
MHRA Steps Into Project Orbis Role
Concurrent with the FDA alignment, OS Therapies announced it accepted a request from the MHRA to become the company's representative to Project Orbis, following a successful Statistical Methods Scientific Advice Meeting. Project Orbis is a reciprocal global initiative launched by the FDA to facilitate international regulatory collaboration in oncology, aiming to streamline cancer drug approvals through simultaneous submission and review of oncology products across multiple countries. The FDA's Center for Biologics Evaluation and Research recently re-opened Project Orbis to foreign-sponsored U.S. companies.
"With alignment in hand with FDA on the most recent updates to the proposed adaptive design for the Phase 3 trial design reviewed with MHRA and EMA, we have overcome the key hurdle to initiating the Phase 3 in the U.K. and beyond," said Paul Romness, MPH, Chairman & CEO of OS Therapies. "More importantly, now that MHRA has stepped up and volunteered to take the international lead with Project Orbis, we expect to be able to move expeditiously through the regulatory process in the U.K., U.S. and Europe."
Designations and Regulatory Pathways
OST-HER2 has received Orphan Drug Designation, Fast Track Designation and Rare Pediatric Disease Designation from the FDA, and Orphan Drug Designation, Fast Track Designation and Advanced Therapy Medicinal Products status from the EMA. Under the Rare Pediatric Disease Designation program, if the company is granted a BLA in the United States, it would become eligible to receive a Priority Review Voucher that it intends to sell. The most recent PRV sale occurred in August 2026 for $220 million, though the company cautioned there can be no assurance it would realize comparable value in any future sale.
OS Therapies has completed resubmission of a Regenerative Medicine Advanced Therapy request, and its Commissioner's National Priority Review Voucher letter of intent has been accepted by the FDA. The company is seeking a BLA under the Accelerated Approval Program in the U.S. and Conditional Marketing Authorization Applications in Europe, the U.K. and Australia for OST-HER2 in metastatic osteosarcoma (搜索) in the fourth quarter of 2026.
Mechanism and Prior Clinical Data
OST-HER2 is an immunotherapy that leverages the immune-stimulatory effects of Listeria bacteria to initiate an immune response targeting the HER2 (搜索) protein. The agent is designed to target two mutated extracellular epitopes and one mutated intracellular epitope of the HER2 oncogene, requiring only one of the three epitopes to be present in a tumor or micro-metastasis to trigger the desired immune response.
The company reported positive data from its Phase 2b clinical trial of OST-HER2 in the prevention or delay of recurrence in fully resected, pulmonary metastatic osteosarcoma (搜索), demonstrating clinically significant benefit on the study's 12-month event-free survival primary endpoint and on the overall survival secondary endpoint. OST-HER2 has also completed a Phase 1 clinical study primarily in breast cancer (搜索) patients and has shown preclinical efficacy data in various models of breast cancer. The agent was previously conditionally approved by the U.S. Department of Agriculture for the treatment of canines with osteosarcoma.
Beyond OST-HER2, OS Therapies has completed dosing in a Phase 1 study of OST-504 (搜索) for castration-resistant prostate cancer (搜索). The company is also advancing a next-generation antibody-drug conjugate and drug conjugate platform known as tunable ADC, which features tunable antibody-linker-payload candidates and leverages its proprietary silicon Si-Linker and Conditionally Active Payload technology, enabling delivery of multiple payloads per linker.