 This is a multicenter, randomized, phase II study of the safety and efficacy of two dose levels of oral ATN-224 in patients with prostate cancer with a rising serum PSA in the absence of detectable disease. Patients will be randomized 1:1 after confirmation of eligibility requirements. The primary endpoint is to determine the proportion of patients who do not have PSA progression for 24 weeks. PSA progression is defined as at least a 50 increase in PSA and 5 ngmL from baseline or post-treatment nadir if lower than baseline, confirmed by another PSA at least 28 days later. 