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USC Opens Phase II Trial of Ambrx's ARX788 for HER2-Positive Breast Cancer

NEW YORK – The University of Southern California's Norris Comprehensive Cancer Center on Monday said it has opened a Phase II trial of Ambrx's antibody-drug conjugate ARX788 for advanced HER2-positive breast cancer patients.

The trial, which is sponsored by La Jolla, California-based Ambrx, will involve roughly 200 HER2-positive metastatic breast cancer patients who have previously received trastuzumab emtansine (Genentech's Kadcyla; T-DM1), trastuzumab deruxtecan (Daiichi Sankyo/AstraZeneca's Enhertu; T-DXd) or a treatment regimen containing tucatinib (Seagen's Tukysa).

The trial's primary endpoint is overall response rate on ARX788, and secondary endpoints are duration of response, overall survival, and progression-free survival, among other measures.

Ambrx's agent is an antibody-drug conjugate that consists of an anti-HER2 monoclonal antibody attached to a cytotoxic tubulin inhibitor, called Amberstatin269. Results from two previous Phase I trials demonstrated an overall response rate of 74 percent and disease control rate of up to 100 percent among patients treated with certain doses of ARX788.

In addition to its breast cancer agent, Ambrx is also evaluating its antibody drug conjugate ARX517 for PSMA-expressing solid tumors.

As of now, the HER2-positive breast cancer trial is open at 23 sites in the US and Australia and is anticipated to open at 150 sites total worldwide. The global principal investigator is Janice Lu, an oncologist and medical director of the comprehensive breast oncology program at USC's Keck Medicine.