Abstract A2: A Study of the effects of MDV3100 in the tumor microenvironment of bone metastatic castrate resistant prostate cancer (bmCRPC)

Abstract

Abstract Background: Androgen signaling remains a central driver in castrate-resistant prostate cancer. We performed a study to determine the effect of the antiandrogen MDV 3100 on bone marrow infiltrating CRPC. Methods: From February 2010 to June 2011, we performed an open-label, observational study of 60 bmCRPC patients (pts), who underwent transilial bone marrow biopsy (BMB) at baseline, 8 weeks and end of study. Pts received MDV3100 160mg orally once daily. The primary objective was to evaluate androgen signaling in bone marrow infiltrating cancer and testosterone in blood (BT) and bone marrow (BMT) and correlate findings with clinical observations. Androgen receptor (AR) c-terminus n-terminus, AR Variant 7 (ARV7), ERG, CYP17, phospho Src (pSrc), expression and mitotic index (Ki67 ) were assessed by immunohistochemistry, AR copy number by qPCR and BT and BMT by liquid chromatography mass spectrometry. Initial Findings: Maximal PSA decline of ≥50% occurred in 29 (48%) of 60 pts, and ≥90% in 13 (22%). Tumor involvement in BMB was detected in 28 (47%) pretreatment BMBs. Paired tumor infiltrated BMBs were found in 23 (38%) pts. Increased androgen receptor expression (n-terminal antibody used for IHC) was observed at pretreatment with heterogeneous CYP17 and pSrc extent of expression. Pretreatment intense nuclear AR expression combined with ≥10% CYP17 tumor expression or increased BMT correlate with ≥50% PSA decline (p value 0.02). AR subcellular localization shift from dominant nuclear to cytoplasmic and regression of bone marrow tumor infiltration correlate with ≥50% PSA decline (p value 0.05). Increased pretreatment p-Src expression is associated with lack of PSA decline (p value 0.002). Increase in BMT and BT is observed after 8 weeks of MDV3100 (mean pretreatment BMT 0.026 ng/ml, Wk8 BMT 0.04 in 33pts, p value 0.0001) (pretreatment BT 0.041, wk8 BT 0.066 in 37 pts, p value <0.0001). Interpretation: Pretreatment expression profile is consistent with persistent androgen signaling in bmCRPC. MDV3100 induces pharmacodynamic changes in androgen signaling. AR changes likely account for the reported therapeutic effect of MDV3100. These data prompt exploratory combinations of MDV3100 with androgen biosynthesis inhibitors and src inhibitors. Citation Format: Eleni Efstathiou, Patricia Troncoso, James Mohler, Christopher J. Logothetis, Mark Titus, Dimitra Tsavachidou, Sijin Wen, Anh Hoang, Robynne Ashe, Maria Karlou, Craig Berman. A study of the effects of MDV3100 in the tumor microenvironment of bone metastatic castrate-resistant prostate cancer (bmCRPC) [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A2.