Ambrx Announces ARX517, a PSMA-Targeted ADC, Demonstrates a Promising 52% PSA50 (≥50% Reduction) and a Highly Differentiated Safety and PK Profile in Patients with mCRPC, who Progressed on Multiple FDA-Approved Treatments - Seite 2

APEX-01 opened for enrollment in July 2021 and is the only on-going clinical trial in the United States targeting PSMA with an ADC. The two primary objectives of APEX-01 are to analyze the safety and tolerability of ARX517 and establish a recommended Phase 2 dose.

Dr. John Shen, a medical oncologist at UCLA and an investigator on APEX-01, stated that, “The PSA results are very encouraging especially in this heavily pre-treated patient population where eligible patients would have exhausted all available and appropriate treatment options prior to enrolling in this study.”

Data Highlights

As of the data cutoff date (September 5, 2023), highlights from the safety and efficacy data are summarized below:

• Deep PSA reductions have been seen with increasing ARX517 dose. PSA reductions deepened as dose levels increased, demonstrating a dose dependent PSA reduction:
  • ≥50% PSA reduction observed in 25% (4/16) and 50% (7/14) of patients at 1.4 mg/kg (Cohort 4) and 2.0 mg/kg (Cohort 6), respectively
  • ≥90% PSA reduction observed in 6% (1/16) and 36% (5/14) of patients at 1.4 mg/kg (Cohort 4) and 2.0 mg/kg (Cohort 6), respectively
• Multiple coinciding efficacy endpoints demonstrate a consistent and promising anti-cancer activity at therapeutic doses of 2.0 – 2.88 mg/kg (Cohorts 6-8):
  • 52% (12/23) patients experienced a ≥50% PSA reduction
    • 7 of 14 patients at 2.0 mg/kg (Cohort 6)
    • 3 of 6 patients at 2.4 mg/kg (Cohort 7)
    • 2 of 3 patients at 2.88 mg/kg (Cohort 8)
  • 81% (17/21) patients experienced a ≥50% ctDNA reduction
  • 50% (2/4) experienced a >30% reduction in target lesion(s), one of which had a reduction in liver and lung lesions

Regarding the recent data, Dr. Oliver Sartor, a medical oncologist and translational researcher with 33 years of professional experience and a special focus on prostate cancer, commented, "Patients with late stage mCRPC have few effective systemic therapy options. The data from the APEX-01 study show very promising PSA declines as well as ctDNA reductions, all pointing in the right direction, based on the safety and preliminary efficacy data presented in the poster. I believe this drug is worthy of further development.”