The male hormone testosterone – a stimulant for cancer growth – is mostly made by the testes; however, small amounts are also produced in other body tissue, including the cancer itself. Currently available therapies only prevent testosterone production in the testes.
The enzyme cytochrome P17 (CYP17) is needed for its production. Abiraterone acetate blocks that enzyme thus preventing testosterone production in the entire body.
Although involving small numbers of patients with advanced prostate cancer, earlier studies showed significant tumour shrinkage as well as lower levels of a crucial protein produced by the cancer – prostate specific antigen – in most of the patients, who also reported substantial improvements in the quality of their lives (some even stopped using morphine to relieve pain caused by cancer spread to bones).
The drug is being tested at cancer centres in the USA and the United Kingdom. At the Institute of Cancer Research, a college of the University of London that works in partnership with The Royal Marsden NHS Foundation Trust, lead researcher Dr Johann de Bono said that, to date, the findings have been a major step forward in the treatment of the most aggressive form of prostate cancer, which is resistant to the available chemotherapy and almost always fatal within about 18 months. Current predictions are that it could treat up to 80% of these patients. However, he added that, as yet, it has not been possible to establish how abiraterone can affect life expectancy because no patient has received the new drug for longer than two-and-a-half years.
It is understood that 1,200 patients have been recruited for two Phase III trials, with the first Phase III trial testing abiraterone in patients with metastatic, castration-resistant prostate cancer who have progressed after docetaxel-based chemotherapy has failed, and the second Phase III trial studying the drug in patients with metastatic, castration-resistant prostate cancer who have yet to receive chemotherapy.
Trials will probably continue for about two years; it is hoped that the drug, in pill form, will become available in two to three years.
‘Abiraterone Acetate now becomes one of many new treatments we are developing, which we hope will change the course of cancer treatment by targeting cancer cells and the tumour micro-environment,’ added William N Hait MD PhD, Global Therapeutic Head for Oncology at Ortho Biotech Oncology R&D.