AstraZeneca announced that a study evaluating zibotentan for the treatment of men with metastatic castration resistant prostate cancer (CRPC) did not show a significant improvement in the primary endpoint of overall survival (OS).

Study 14 was a randomised, placebo controlled phase III study which evaluated zibotentan 10mg added to standard of care treatment in 594 patients with metastatic CRPC. The safety and tolerability profile of zibotentan in this trial was in line with previous studies.

Based on this study result, AstraZeneca plans no regulatory submissions for zibotentan at this time. The zibotentan ENTHUSE trial programme includes two other ongoing studies with zibotentan in different CRPC settings. The full results of study 14 will be published in 2011.

Zibotentan is a novel once daily tablet and works by blocking the endothelin pathway. As prostate cancer advances, this pathway becomes uncontrolled, which then drives the spread of cancer growth. By blocking the endothelin A receptor in this pathway, zibotentan can slow tumour growth and the spread of cancer cells.

Zibotentan is being studied in more than 3,000 men in the ENTHUSE (Endothelin A Use) clinical trials programme, to evaluate its efficacy and safety in extending survival in men with CRPC. There are two other studies in the ENTHUSE trial programme in addition to Study 14: Study 15 will evaluate zibotentan versus placebo, in men whose disease has not yet metastasised; Study 33 will evaluate zibotentan plus chemotherapy, versus chemotherapy alone, in men whose disease has metastasised and who have been prescribed treatment with chemotherapy

Prostate cancer primarily affects men over the age of 50. It is the most commonly diagnosed male cancer in many western countries and its incidence is increasing. Worldwide, more than 670,000 men are diagnosed with prostate cancer every year, accounting for one in nine of all new cancers in men. Prostate cancer is the second most common cancer in men after lung cancer and 1 in 5 men with prostate cancer will develop CRPC. CRPC is prostate cancer that is no longer responding to treatments that block the action of testosterone, the naturally occurring hormone that drives cancer growth. Whilst therapies that block testosterone (collectively known as hormonal treatments) provide great benefit for many men, the majority of patients eventually become resistant to hormonal treatments and develop CRPC. For these men chemotherapy is the only treatment that has demonstrated a survival benefit.

AstraZeneca is a global, innovation-driven biopharmaceutical business with a primary focus on the discovery, development and commercialisation of prescription medicines.