Abstract LB-203: Phase I/II study of the androgen receptor antagonist MDV3100 in castration-resistant prostate cancer

Abstract

Abstract Introduction: Overexpression of the androgen receptor (AR) is believed to contribute to the progression of CRPC. MDV3100 is a small molecule AR antagonist with a novel mechanism of action that blocks nuclear translocation of AR, DNA binding, and has no agonist activity when AR is overexpressed. MDV3100 has been shown to be effective in preclinical models of CRPC. In July 2007, a multi-center first-in-man Phase 1-2 trial was initiated to determine safety, pharmacokinetics (PK), and antitumor activity including effects on prostate-specific antigen (PSA), bone and soft tissue metastases, and in selected pts fluorodeoxyglucose (FDG) and fluorodihydrotestosterone (FDHT) uptake by positron emission tomography (PET). Methods: Pts were administered MDV3100 orally, once daily, starting at 30 mg with sequential escalations in cohorts of 3 pts. Enrollment was expanded at 60 mg and above to include up to 12 chemotherapy-naïve and 12 post-chemotherapy pts, once the safety of a dose was established. PK parameters for the dose-escalation cohorts were estimated using a 2-compartment model. Results: 85 pts have been enrolled to date on doses up to 240 mg. 21 pts at 60 mg, and 22 pts at 150 mg have been followed for 12+ and 8+ weeks respectively. MDV3100 has been well-tolerated without dose-limiting toxicity. PK were dose-linear with a half-life of approximately one week. At doses of 30, 60, 150, and 240 mg, geometric mean steady state Cmax values were 2.8, 6.1, 17.3, and 23.7 µg/mL and AUC24hr were 61, 120, 361, and 480 µg*hr/mL, respectively. Effective AR blockade by MDV3100 has been shown by PSA declines and by PET findings. Evaluation at the 12 week timepoint for 21 pts at 60 mg showed 9 pts (43%) had >50% decline in PSA from baseline. To date, 8 pts have had FDG and FDHT PET at baseline of whom 4 have had 1 or more follow-up scans. All 8 had abnormal FDHT accumulation at baseline while 4 of 4 with follow-up scans had no FDHT accumulation. Conclusions: MDV3100 is a novel AR antagonist in clinical investigation. The observed PSA declines are consistent with the inhibition of AR signaling. The inhibition of FDHT accumulation demonstrates receptor blockade in vivo. MDV3100 has been well-tolerated to date and appears to be a promising candidate for the treatment of CRPC. Pt follow-up and dose escalation are continuing. The analysis of the association between PSA declines and clinical outcomes is ongoing and will be reported at a future date.