Janssen can't conjure up enough patients for phase 1 prostate cancer study with ESSA

After a fruitless search for patients with a specific type of prostate cancer, Janssen is suspending a phase 1 clinical trial that was being conducted with ESSA Pharma’s experimental small-molecule inhibitor.

The small Canadian pharma company announced Monday that Janssen has suspended enrollment in a study for EPI-7386 due to “operational recruitment challenges.” Janssen was testing ESSA’s therapy in combination with its approved hormone therapies Erleada or Zytiga plus prednisone in patients with metastatic castration-resistant prostate cancer (mCRPC).

Janssen did not come up completely empty-handed in the search for patients on which to test the combo therapies. The Johnson & Johnson pharmaceutical unit treated three patients before they received chemotherapy with EPI-7386 and Erleada or Zytiga plus prednisone for four months. ESSA said the therapy was well tolerated and sufficient exposure of the drugs was detected, suggesting pharmacological activity. The initial data also pointed to clinical activity in two out of three patients within 12 weeks.

ESSA CEO David Parkinson, M.D., expressed his disappointment in Janssen shutting down the trial but said the company is encouraged by the data collected to date, which supports a different study ESSA is working on testing EPI-7386 with Pfizer and Astellas Pharma’s Xtandi. Parkinson said discussions are ongoing with Janssen to provide Erleada and Zytiga for an ESSA-sponsored combo study. He promised additional details in the coming months.

A representative for ESSA said that the future study may be in earlier-line prostate cancer patients. 

According to the National Institutes of Health’s clinical trials database, the Janssen-sponsored trial began in March with an estimated primary completion date of January 2024. The aim was to collect 82 participants to help determine a phase 2 dose, evaluate safety and examine any dose-limiting toxicities.

ESSA also has strategic partnerships with Astellas and Bayer to test those companies’ androgen receptor inhibitors with EPI-7386. The Canadian company is developing the therapy as a way to delay drug resistance in prostate cancer treatment.

EPI-7386 has been granted a fast-track tag from the U.S. FDA for adult males with mCRPC resistant to standard-of-care treatment. ESSA has the rights to the therapy worldwide, meaning that the three Big Pharma partnerships only address clinical trial supply, according to the company. 

Janssen did not return a request for comment on the future of the ESSA partnership as of publication.

ESSA's shares dropped about 21% to around $3.48 as the market opened Monday.