Calcitriol, Mitoxantrone, and Prednisone in Treating Patients With Metastatic Prostate Cancer

DISEASE CHARACTERISTICS: Histologically confirmed prostate cancer Androgen-independent disease, defined as disease progression while on standard hormonal management, including antiandrogen withdrawal Patients must continue primary hormonal therapy during study treatment Regional or distant metastases Prostate-specific antigen > 5 ng/mL No brain metastases PATIENT CHARACTERISTICS: Age 18 to 100 Performance status ECOG 0-3 Life expectancy Not specified Hematopoietic Adequate hematologic function Hepatic Adequate hepatic function Renal Adequate renal function No calcium-salt kidney stones within the past 5 years No hypercalcemia Cardiovascular Adequate cardiac function No significant cardiac disease No atrial fibrillation Other Fertile patients must use effective barrier contraception during and for 2 months after completion of study treatment No other serious medical illness No other active malignancy except nonmelanoma skin cancer PRIOR CONCURRENT THERAPY: Biologic therapy More than 28 days since prior biologic therapy Chemotherapy No prior chemotherapy Endocrine therapy See Disease Characteristics Radiotherapy No prior strontium chloride Sr 89 More than 28 days since prior radiotherapy More than 56 days since prior samarium Sm 153 lexidronam pentasodium Surgery Prior prostatectomy and/or orchiectomy allowed Other More than 28 days since prior investigational therapy