OBJECTIVES: I. Compare symptomatic progression free survival among patients having metastatic, hormone refractory prostate cancer receiving one of two doses of matrix metalloprotease inhibitor AG3340 or placebo initially in combination with mitoxantrone and prednisone with provision for subsequent change in therapy. II. Compare the symptomatic response, quality of life, serologic (PSA) response, PSA progression free survival, radiographic response, radiographic progression free survival, one year survival, and overall survival of these patients. III. Evaluate the safety of AG3340 in regimen combination and in combination with therapies administered subsequent to first line in this patient population. IV. Evaluate the population pharmacokinetics of AG3340 when given in this treatment regimen.