Prostate Cancer Treatment ARX517 Granted FDA Fast Track Designation

The FDA granted ARX517 a Fast Track designation for the treatment of patients with prostate cancer.

The Food and Drug Administration (FDA) has granted Fast Track designation to the metastatic prostate cancer treatment ARX517, according to a press release from clinical stage biopharmaceutical company Ambrx Biopharma Inc., the company behind ARX517.

ARX517, Ambrx explained in the release, is an “anti-PSMA (prostate-specific membrane antigen) antibody-drug conjugate (ADC) investigational therapy … for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) upon progression on an androgen receptor pathway inhibitor.”

Fast Track designation is intended 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,” Ambrx noted.

“Receiving Fast Track designation from the FDA reinforces Ambrx’s belief in ARX517 as a potential novel treatment for mCRPC and underscores the urgent need for improved treatment options for patients at this advanced stage of prostate cancer,” said Sandra Aung, chief clinical officer of Ambrx, in the July 19 press release.

ARX517 is currently the subject of APEX-01, a phase 1/2, open-label dose escalation and dose expansion trial with an estimated 150 participants whose tumors have progressed following treatment with at least two prior FDA-approved prostate cancer treatments. The trial began in July 2021 and has an estimated completion date of March 2027, according to the APEX-01 listing on clinicaltrials.gov.

“Recently, (Pluvicto), which is a radiopharmaceutical from our point of view, has validated PSMA is a good and effective target in prostate cancer, and also established what we think is a meaningful commercial opportunity in the metastatic castration-resistant prostate cancer patient population, which is great. Those are two terrific things. However, when we look at (Pluvicto) and recognize that it's a radiopharmaceutical, we think that there may be some challenges or conversely, some advantages that ARX517, which is an infused ADC and not a radiopharmaceutical, may have (for patients with mCRPC),” Daniel O’Connor, chief executive officer of Ambrx, said in February as reported by Targeted Oncology®, a sister publication of CURE®.

At the time, O’Connor also said that of 22 patients evaluated for safety during APEX-01, there had been no drug-related serious side effects. “In essence, ARX517 has been well-tolerated with only grade 1 and grade 2 treatment-related adverse events being reported. The maximum tolerated dose has not yet been reached,” he said.

Initial data from APEX-01 released by Ambrx earlier this year shows that across seven dose-level cohorts of patients, there were reductions of prostate-specific antigen (PSA, a protein produced by the prostate gland used to diagnose and track prostate cancer) of greater than 30% in three patient cohorts, while in another cohort all patients had their PSA reduced by more than half.

“The preliminary data from patients with prostate cancer are highly encouraging,” said Dr. Michael Schweizer, an investigator on APEX-01 and associate professor in the division of medical oncology at the Fred Hutchinson Cancer Research Center, said in a news release at the time.

“ARX517 appears to be well-tolerated so far,” Schweizer said in the release. “I am very optimistic for its future development. We look forward to more data from APEX-01, as the dose escalation continues in this difficult-to-treat patient population.”

Castration-resistant prostate cancer, as the American Cancer Society explains on its website, “is cancer that is still growing despite the fact that hormone therapy (an orchiectomy or an LHRH agonist or antagonist) is keeping the testosterone level in the body as low as what would be expected if the testicles were removed (called castrate levels).”

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