OS Therapies Reports Positive Phase 1 Safety Data and Preclinical Efficacy for OST-HER2 in HER2-Positive Breast Cancer

ROCKVILLE, MD, USA, July 24, 2024 - OS Therapies, Inc. (NYSE-A: OSTX), a company engaged in oncology-focused immunotherapy, announced encouraging outcomes from its Phase 1 clinical trial for OST-HER2. This trial involved patients with HER2-expressing solid tumors, including those suffering from breast cancer. Alongside this, the company also shared positive preclinical efficacy data for OST-HER2 in multiple breast cancer models.

The FDA has recognized OST-HER2 with Rare Pediatric Disease Designation (RPDD), Orphan Drug Designation (ODD), and Fast Track Designation (FTD) for treating Osteosarcoma. OST-HER2 is a biologic therapeutic developed as a Listeria monocytogenes (Lm) vector-based immunotherapeutic vaccine. This off-the-shelf vaccine aims to prevent metastasis, delay recurrence, and enhance overall survival rates in patients with osteosarcoma and other solid tumors. Its mechanism is predicated on stimulating innate and adaptive immune responses via the Lm vector. The treatment generates T cells that target micrometastases, potentially preventing them from developing into recurrent osteosarcoma and other solid tumors, such as breast cancer. T cell responses focus on HER2 expressed by the tumor, leading to cell death and the release of additional tumor targets. Currently, no approved adjuvant treatments are available for recurrent osteosarcoma in the U.S.

In the Phase 1b clinical study, twelve patients with a history of HER2 positive cancer were enrolled, including ten with breast cancer, one with esophageal cancer, and one with GE junction cancer. OST-HER2 was found to be safe and well-tolerated in patients with HER2-expressing solid tumors, even at doses being used in the ongoing Phase 2b clinical trial for recurrent, resected osteosarcoma (AOST-2121, NCT04974008). The company had previously reported positive interim data for this trial and is currently in discussions with the US FDA regarding a Breakthrough Therapy Designation (BTD) application for OST-HER2 based on these interim results. OS Therapies aims for approval of OST-HER2 in osteosarcoma before expanding its development to breast cancer and other HER2-expressing cancers, such as esophageal and colorectal cancer.

Additionally, the company reported positive preclinical data for OST-HER2 in various breast cancer models. The treatment has already demonstrated significant efficacy in these preclinical studies, showing promise for future clinical applications in breast cancer.

OS Therapies, Inc. (NYSE-A: OSTX), is dedicated to identifying, developing, and commercializing treatments for osteosarcoma and other solid tumors. OST-HER2, an immunotherapy, utilizes the immune-stimulatory properties of Listeria bacteria to generate a robust immune response against the HER2 protein. The company has fully enrolled a 41-patient Phase 2b clinical trial of OST-HER2 in resected, recurrent osteosarcoma, with results anticipated in the fourth quarter of 2024. OST-HER2 has also completed a Phase 1b trial in other solid tumors and has shown efficacy in preclinical breast cancer models. OS Therapies is working on next-generation Antibody Drug Conjugate (ADC) platforms, particularly focusing on tunable ADC (tADC) technology. This involves customized antibody-linker-payload candidates using the company’s unique silicone linker technology, designed to deliver multiple payloads per linker.

The OST-HER2 Lm vector technology has been administered to over 450 cancer patients across various clinical trials. The AOST-2121 Phase IIB trial aims to prevent or delay metastasis and improve overall survival in osteosarcoma. OST-HER2 has already received Fast-Track, Orphan, and Rare Disease Designation (RDD). OS Therapies intends to pursue a Breakthrough Therapy Designation (BTD) based on the data from this Phase IIb trial. Furthermore, OST31-164 has received USDA provisional approval for treating osteosarcoma in canines, with a completed Phase III canine study demonstrating a significant survival benefit.