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