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Background: This study investigated the safety, pharmacokinetics (PK) and clinical antitumor activity of ABT-751, a novel sulfonamide antimitotic and vascular disrupting agent, in combination with docetaxel (Taxotere) in patients with castration-resistant prostate cancer (CRPC)., Patients and Methods: Patients received docetaxel (60-75 mg/m(2)) i.v. on day 1 and ABT-751 (100-200 mg) orally daily for 14 days, repeated every 3 weeks for up to 10 times on four escalating dose levels (DLs)., Results: Thirty-two patients received a median of 8.5 treatment cycles (range 1-10). One of six patients on DL 3 (D 60 mg/m(2) + A 200 mg) and 4 (D 75 mg/m(2) + A 200 mg) experienced dose-limiting toxicity, and both DLs were expanded. Overall, severe adverse events occurred more commonly on DL 4 than 3 (47% versus 18% of patients). PK data for docetaxel and ABT-751 were similar to reported literature. Best post-treatment prostate-specific antigen decline of > or =50% occurred in 60% and objective responses occurred in 45% of patients. Median overall survival was 24 months (95% confidence interval 8.3-37.7 months)., Conclusions: The combination of ABT-751 and docetaxel is safe and active in CRPC. Based on the cumulative safety analysis, the recommended phase II dose of ABT-751 is 200 mg daily with docetaxel 60 mg/m(2) for this patient population.