OS Therapies Reports Positive Update from Phase 2b Trial in Recurrent Osteosarcoma

OS Therapies, Inc., a clinical-stage oncology-focused immunotherapy company, has provided an encouraging clinical update for its ongoing Phase 2b trial of OST-HER2 (OST31-154), an immunotherapy for patients with resected, recurrent osteosarcoma. The trial, identified as AOST-2121 (NCT04974008), is testing OST-HER2, a biologic therapy based on a Listeria monocytogenes vector, designed to prevent metastasis, delay recurrence, and enhance overall survival in osteosarcoma patients.

OST-HER2 is administered in 18 doses over 51 weeks, with radiographic evaluations conducted throughout treatment. The immunotherapy works by stimulating both innate and adaptive immune responses through the Lm vector, generating T cells that target and destroy micrometastases expressing HER2 proteins on the tumor cells. This approach aims to prevent the cells from recurring and metastasizing.

AOST-2121 has reached full enrollment with 41 patients across 21 clinical sites in the United States. The participants are in various stages of treatment and follow-up. The primary endpoints of the study are Event-Free Survival (EFS) at 12 months and Overall Survival (OS) at 36 months, with interim OS evaluations at 12 and 24 months. The 1-year EFS rate reported is 32.5%, a significant improvement over the 20% rate observed in a comparator group. Additionally, the 1-year and 18-month OS rates stand impressively at 90.4%.

The trial has been well tolerated, with no grade 3, 4, or 5 treatment-related adverse events reported among the 41 patients. The lack of severe adverse effects further supports OST-HER2’s potential as a viable treatment option.

Dr. Robert Petit, Chief Medical & Scientific Officer of OS Therapies, highlighted the promise shown by OST-HER2 in providing a new adjuvant therapy to prevent recurrences and improve survival rates in recurrent osteosarcoma patients. He emphasized the importance of enhancing immune surveillance against micrometastases to improve the quality of life and survival rates for osteosarcoma sufferers.

Paul Romness, President & CEO of OS Therapies, echoed the optimism, noting that the EFS data positions OS Therapies to deliver robust Phase 2b co-primary endpoint data by the end of 2024. Given the lack of novel treatments for resected, recurrent osteosarcoma in over four decades, OST-HER2 could represent a significant advancement in this area.

The FDA has recognized OST-HER2 with several designations, including Rare Pediatric Disease Designation (RPDD), Orphan Drug Designation (ODD), and Fast Track Designation (FTD) for osteosarcoma. This recognition underscores the urgent need for new therapeutic approaches to treat this rare and aggressive bone cancer, predominantly affecting adolescents and young adults.

In addition to its focus on osteosarcoma, OS Therapies is developing a next-generation Antibody Drug Conjugate (ADC) platform. The tunable ADC (tADC) technology aims to deliver multiple therapeutic payloads through a unique silicone linker mechanism.

Overall, OST-HER2 represents a promising development in the treatment of recurrent osteosarcoma, potentially offering a new standard of care for patients who have seen little advancement in therapeutic options for decades. The completion of the Phase 2b trial and the subsequent data could pave the way for essential new treatments in oncology.