A novel approach to treating prostate cancer, developed by US company Cougar Biotechnology, has shown early activity in a Phase I trial reported at the National cancer Research Institute conference in Birmingham, UK.

CB7630 (abiraterone acetate), which works by inhibiting the 17-alpha hydroxylase/c17,20 lyase enzyme, was well tolerated in all 14 castration-refractory prostate cancer patients enrolled into the study at doses up to 2,000mg/day, and two-thirds of patients exhibited a drop in prostate-specific antigen levels, a marker for disease activity, of more than 50%.

In addition, out of five evaluable patients with measurable tumour lesions, treatment with CB7630 resulted in partial radiological responses in three patients.

The drug works by inhibiting the synthesis of androgen hormones, which drive the growth of prostate cancers. All the 14 patients in the study had progressive disease despite treatment with LHRH analogues and multiple other hormonal therapies including antiandrogens, diethylstilboestrol and dexamethasone.

A spokesman for the company said that the data were the first to support the use of CB7630 as a second-line hormonal therapy for prostate cancer, and supported the continue development of the drug in this setting.

Cougar is also developing an inhibitor of microtubule dynamics which is currently in a Phase I trial in haematological malignancies and CB1089, an analogue of vitamin D which has been clinically tested in a number of solid tumour types.