Interim Phase II Results Support Efficacy Of CB7630 (Abiraterone Acetate) In Advanced Prostate Cancer Patients
Cougar Biotechnology, Inc. (NASDAQ:CGRB) today announced that results from an ongoing Phase II clinical trial of Cougar’s investigational drug CB7630 (abiraterone acetate) were presented today at the Prostate Cancer Foundation Scientific Retreat. The Prostate Cancer Foundation Scientific Retreat is currently taking place in Lake Tahoe, Nevada.
The clinical trial of CB7630 was conducted at the University of Texas M.D. Anderson Cancer Center in order to investigate associations between serum and microenvironment (bone marrow) androgen concentrations and response to CB7630. In the trial, CB7630 in combination with prednisone was administered orally, once daily, to patients with castration resistant prostate cancer (CRPC), who had progressive disease despite treatment with LHRH analogues and multiple other therapies. All of the 44 patients who were enrolled in the trial had radiological evidence of metastatic disease with bone metastases. Thirty-eight patients (86%) had at least 10 metastatic bone lesions, 7 patients (16%) had metastases in the liver and 14 patients (32%) had lymph node metastases. Twenty-five (57%) of the 44 patients had received prior treatment with ketoconazole and/or diethylstilbesterol and 38 patients (86%) had received prior treatment with chemotherapy, with 27 patients (61%) having received two or more prior chemotherapy regimens before entering the trial.
In her poster presentation entitled, “Identification of an androgen withdrawal responsive phenotype among patients with castrate resistant prostate cancer (CRPC) treated with abiraterone acetate, a selective CYP17 inhibitor (COU-AA-BMA),” Dr. Eleni Efstathiou from the University of Texas MD Anderson Cancer Center presented data on the 41 evaluable patients treated in the trial. Of the 41 evaluable patients, 21 patients (51%) experienced a confirmed decline in prostate specific antigen (PSA) levels of greater than 50% with a median duration of 6+ months. In addition, 5 patients (12%) experienced PSA declines of greater than 90%. Of the 41 evaluable patients, 24 (59%) experienced an improvement in performance status.
Of the 16 evaluable patients with bone metastases, after 6 months of treatment 4 patients (25%) showed an improvement in their bone scan and 11 patients (69%) showed a stable bone scan. Also, 5 of 5 patients with lymph node metastases showed stable disease after 6 months of treatment with CB7630 and 1 of 2 patients with liver metastases demonstrated a partial radiological response (as measured by the RECIST criteria).
Both serum and bone marrow testosterone levels were measured before and after treatment with CB7630. A decline in both serum and bone marrow testosterone levels to below detectable levels (<10ng/ml) was seen in all patients in the trial. Also, patients with depleted baseline bone marrow testosterone levels (<10ng/ml) appeared to progress earlier when treated with CB7630 (p=0.05) compared to patients with measurable baseline bone marrow testosterone levels. Further examination of the bone marrow biopsies of patients treated with CB7630 in this study revealed both overexpression of androgen receptor and CYP17 overexpression.
Alan H. Auerbach, Chief Executive Officer and President of Cougar Biotechnology, said, “The data from our COU-AA-BMA trial of CB7630 presented at the Prostate Cancer Foundation Scientific Retreat continues to support the potential role of the drug in the treatment of CRPC. We continue to be pleased with the strong evidence of antitumor activity in patients with chemotherapy refractory disease, which represents a significant unmet medical need in prostate cancer.”
Arturo Molina, M.D., M.S., FACP, Cougar’s Chief Medical Officer and Executive Vice President of Clinical Research and Development, added, “We are pleased to present the results of this Phase II study and we are intrigued by its findings. The identification of CYP17 expression in CRPC tumor metastases and observation that both serum and bone marrow testosterone levels decline after CB7630 therapy suggests that treatment with CB7630 results in the inhibition of adrenal and intra-tumoral androgen synthesis.”
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