Zibotentan not effective when used alone in treatment of mCRPC


According to a media release this morning from AstraZeneca, the company’s investigational drug zibotentan (also known as ZD4054) was not effective in extending the overall survival of patients with metastatic castration-resistant prostate cancer (mCRPC) in a randomized, double-blind, placebo-controlled Phase III trial.

In this particular trial, patients had to have evident metastases on a bone of CT scan and a rising PSA after surgical or medical castration; they could not have received any form of chemotherapy; and they could not have levels of pain requiring the use of opiates. A total of 594 patients were randomized to be treated with either zibotentan or a placebo. All patients could also receive other forms of “standard prostate cancer therapy,” but we believe this would not have included chemotherapy. Exactly what was permissible as “standard prostate cancer therapy” is not clear from the summary of the trial protocol on the ClinicalTrials.gov web site.

This trial is one of three randomized, double-blind, placebo-controlled Phase III trials that had been developed to test the effectiveness and safety of zibotentan in patients with advanced forms of prostate cancer. The other two trials, which are ongoing, are designed to investigate:

The latter of these two trials is still enrolling patients.

This is the second large, Phase III clinical trial of an endothelin-1 receptor antagonist that has failed to demonstrate effectiveness in men with mCRPC. Several years ago Abbott Laboratories’ product atrasentan (Xinlay) was also unable to demonstrate effectiveness when used alone in this group of patients. Like zibotentan, atrasentan is also being tested in combination with docetaxel-based chemotherapy in men with mCRPC.

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