Ambrx Biopharma Inc. announced that the U.S. Food and Drug Administration (FDA) has granted Fast Track designation to Ambrx's proprietary anti-PSMA antibody-drug conjugate (ADC) investigational therapy, ARX517, for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) upon progression on an androgen receptor pathway inhibitor. Fast Track designation is a process designed to facilitate the development and expedite the review of drugs which may demonstrate substantial improvement over available therapy for serious conditions with unmet medical need. ARX517 is currently being studied in APEX-01, a Phase 1/2, first-in-human, open label dose escalation and dose expansion trial enrolling patients with mCRPC whose tumors have progressed on at least two prior FDA approved treatments for prostate cancer, and patients must have one of the following three criteria met: PSA progression defined by a minimum of 2 rising PSA values; or radiographic progression by RECIST v 1.1 oriii) disease progression by the presence of new bone lesions.

APEX-01 is the only ongoing clinical trial in the United States targeting PSMA with an ADC. ARX517 is an antibody-drug conjugate composed of a fully humanized anti-PSMA mAb linked to AS269, a proprietary and potent microtubule inhibitor. Prostate-specific membrane antigen (PSMA) is highly expressed (>89%) in mCRPC and has been shown to be a validated therapeutic target.

Upon binding to PSMA on the surface of cancer cells, ARX517 is internalized and pAF-AS269, its cancer cell killing payload, is released following lysosomal metabolism.