Background: While satraplatin, a fourth generation oral platinum analogue, failed to improve overall survival (OS) in an unselected metastatic castrate-resistant prostate cancer (mCRPC) population (Sternberg, JCO 2009), anti-tumor activity was demonstrated, suggesting a “platinum-sensitive” subset of patients. Predictive biomarkers may not only select patients most likely to benefit from novel “targeted” therapies but also from standard (even discarded) cytotoxic agents. Development of predictive biomarkers in mCRPC is hampered by the fact that PC is associated with a long natural history and evolving genetic changes, highlighting the need for immediate pre-treatment metastatic tissue samples for biomarker development. In this trial, we sought to determine the feasibility of obtaining metastatic biopsies in patients with mCRPC treated with satraplatin. Methods: Docetaxel-refractory mCRPC patients underwent image-guided biopsy of metastatic lesions prior to treatment with satraplatin 80 mg/m² PO on days 1 to 5 of a 35-day cycle and prednisone 5 mg PO twice daily. Biopsy samples are analyzed by whole exome and RNA sequencing, and peripheral blood samples are undergoing transcriptional profiling, to facilitate biomarker development. Results: Thirteen patients were enrolled with a median age of 71 (range: 55 to 80), prostate-specific antigen (PSA) of 82 ng/ml (0.04-3057), and Gleason score 8 (7 to 9). All patients received prior docetaxel, four (31%) had more than or eqaul to two prior chemotherapies, and two (15%) received abiraterone. Drug-related grade 3/4 toxicities included leukopenia (23%), neutropenia (8%), thrombocytopenia (8%), fatigue (8%), renal failure (8%), dysphagia (17%), and diarrhea (8%). A median of four cycles of satraplatin were completed, with declines of serum PSA of greater than or equal to 30% achieved in 4 of 13 patients (31%; 95% CI, 57.3 to 85.4%). Median time to PSA progression was 12.4 weeks (95% CI, 7.2 to 29.7+ weeks). Metastatic pre-treatment biopsies were collected in all study patients; genomic analysis is ongoing. Conclusions: This study confirms that satraplatin has anti-cancer activity in a subset of patients with mCRPC. Trials that require pre-treatment metastatic tumor biopsies are feasible. Analysis of the correlation between molecular signatures and treatment response will be presented at the meeting. Clinical trial information: NCT01289067.