On June 3, 2024 OS Therapies, Inc. (NYSE-A: OSTX), a clinical-stage oncology-focused immunotherapy company developing cancer vaccines and antibody drug conjugate (ADC) therapeutic candidates, reported a positive clinical update for AOST-2121 (NCT04974008), its ongoing Phase 2b clinical trial of its immunotherapy OST-HER2 (OST31-154) in patients with resected, recurrent osteosarcoma (Press release, OS Therapies, JUN 3, 2024, View Source [SID1234644054]).

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OST-HER2, a biologic therapeutic candidate, is a Lm (Listeria monocytogenes) vector-based off-the-shelf immunotherapeutic vaccine designed to prevent metastasis, delay recurrence, and increase overall survival in patients with Osteosarcoma. The AOST-2121 study is designed to demonstrate efficacy in patients who have already had recurrent disease and are highly likely to recur again. A total of 18 OST-HER2 doses are administered once every three weeks, for a total 51 weeks. Radiographic evaluation of recurrence is evaluated throughout treatment.

The proposed OST-HER2 mechanism of action is based on innate and adaptive immune stimulating responses activated by the Lm vector. This treatment generates T cells that can eliminate or slow potential micrometastases that can grow into recurrent osteosarcoma. T cell responses home-in on HER2 expressed by the tumor and then kill the cell, releasing additional tumor targets. There are currently no approved adjuvant treatments for recurrent osteosarcoma in the United States.

AOST-2121 has achieved full enrollment of 41 patients treated with OST-HER2 at 21 clinical trial sites across the United States. A few patients remain in the active treatment stage with the remainder in follow-up for overall survival. The primary endpoints for the AOST-2121 study are Event Free Survival (‘EFS’, defined as absence of recurrence of primary tumor or metastasis) at 12 months and Overall Survival at 36 months, with interim Overall Survival endpoints at 12 months and 24 months. Topline EFS data, interim 1-year OS data, as well as additional secondary data analyses are expected to be reported in the fourth quarter of 2024. No novel therapeutic interventions have improved the clinical outcomes for patients with resected, recurrent osteosarcoma in over 40 years.

The clinical updates reported today include:

1-year EFS rate of 32.5% vs. 20% EFS rate for unsuccessful investigational therapeutic comparator1
1-year overall survival rate of 90.4%
18-month overall survival rate of 90.4%
Treatment has been well tolerated and there have been no grade 3, 4 or 5 treatment-related adverse events reported for the 41 patients.
"OST-HER2’s strong safety profile supports its potential to become a practical adjuvant therapy to delay or prevent subsequent recurrences and improve overall survival in the very difficult challenge of recurrent osteosarcoma. Promoting innate and adaptive immune surveillance against lurking micrometastases could become a potentially powerful tool for oncologists as they seek to improve the quality of life and prolong survival of patients who have suffered from Osteosarcoma," said Dr. Robert Petit, Chief Medical & Scientific Officer of OS Therapies. "OST-HER2 has the potential to significantly improve the standard of care in this difficult to treat patient population. In light of today’s encouraging clinical trial update, we are hopeful that final data coming in the fourth quarter of this year, combined with supplemental data that will follow in 2025, positions OST-HER2 to become available to help clinicians better protect people with difficult cancers like osteosarcoma."

"With historical 1-year EFS estimated in the low-to-mid teens with the current standard of care, and the most recent investigational therapeutic comparator yielding 1-year EFS of 20%, we believe that the 32.5% EFS data observed to date in this trial compares favorably and positions OS Therapies to deliver final Phase 2b co-primary endpoint data by the end of 2024," said Paul Romness, President & CEO of OS Therapies. "With OST-HER2’s strong safety profile and consistent overall survival at the 1-year and 18 month timepoints, and given the dearth of therapeutic options for the resected, recurrent osteosarcoma patient population, we are hopeful that OS Therapies will be gain approval for the first new osteosarcoma treatment, a novel immunotherapy, in over 40 years."

The FDA has granted Rare Pediatric Disease Designation (RPDD), Orphan Drug Designation (ODD), and Fast Track Designation (FTD) for OST-HER2 in Osteosarcoma.

References

Lagmay JP, Krailo MD, Dang H, et al: Outcome of patients with recurrent osteosarcoma enrolled in seven Phase II trials through Children’s Cancer Group, Pediatric Oncology Group, and Children’s Oncology Group: learning from the past to move forward. J Clin Oncol. 2016;34:3031-8.
About Osteosarcoma

Osteosarcoma is a solid tumor of the bone that predominantly occurs in adolescents and young adults (AYA). Standard treatment includes surgery and chemotherapy. For patients with metastatic osteosarcoma or have recurrence after chemotherapy, the prognosis is poor.