DISEASE CHARACTERISTICS:

• Histologically proven stage III or IV adenocarcinoma of the prostate not potentially curable by surgery or radiotherapy
• Measurable tumors or tumor markers
• No response to antiandrogen withdrawal

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Performance status:

• Karnofsky 60-100%

Life expectancy:

• At least 3 months

Hematopoietic:

• WBC at least 3000/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than 2.5 mg/dL
• SGOT no greater than 2 times normal
• No hepatic failure

Renal:

• BUN less than 60 mg/dL
• Creatinine no greater than 2.5 mg/dL OR
• Creatinine clearance greater than 60 mL/min
• Blood ammonia normal
• No chronic renal failure

Cardiovascular:

• No severe heart disease

Pulmonary:

• No severe lung disease

Other:

• Fertile patients must use effective contraception during and for 4 weeks after study participation
• No serious active infection or fever
• No other concurrent serious disease
• No other prior or concurrent malignancy within the past 2 years

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 4 weeks since prior immunotherapy and recovered

Chemotherapy:

• At least 4 weeks since prior chemotherapy and recovered

Endocrine therapy:

• At least 4 weeks since prior hormonal therapy and recovered
• Prior corticosteroids for at least 2 months allowed, but must be on stable or decreasing dose during study participation

Radiotherapy:

• See Disease Characteristics
• At least 4 weeks since prior radiotherapy and recovered

Surgery:

• See Disease Characteristics
• At least 4 weeks since prior surgery and recovered

Other:

• At least 4 weeks since prior experimental clinical trial
• No other concurrent therapy for metastatic disease