DISEASE CHARACTERISTICS:

• Histologically confirmed adenocarcinoma of the prostate with clinically progressive stage IVA or IVB disease after at least primary androgen ablation with either orchiectomy or LHRH agonist and only one cytotoxic chemotherapy regimen
• Measurable disease with a maximum of 10 measurable lesions OR nonmeasurable disease
• Serum testosterone no greater than 50 ng/mL if no prior bilateral orchiectomy

PATIENT CHARACTERISTICS:

Age:

• Not specified

Performance status:

• ECOG 0 or 1

Life expectancy:

• Not specified

Hematopoietic:

• Absolute neutrophil count at least 1,500/mm3
• Platelet count at least 100,000/mm3 (transfusion independent)
• No disseminated intravascular coagulation

Hepatic:

• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• AST and ALT no greater than 3 times ULN

Renal:

• Creatinine no greater than 1.5 times ULN

Other:

• Fertile patients must use effective contraception
• No currently active second malignancy other than nonmelanoma skin cancers
• No active infection

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• At least 4 weeks since prior immunotherapy and recovered

Chemotherapy:

• See Disease Characteristics
• At least 6 weeks since prior suramin
• At least 4 weeks since other prior chemotherapy
• No prior therapy with camptothecin or any of its analogues

Endocrine therapy:

• Prior second line hormonal therapy allowed
• At least 4 weeks since prior hormonal therapy
• Concurrent treatment with LHRH agonists allowed and required for
• patients without orchiectomy
• No concurrent hormonal therapy except for nondisease related conditions
• Concurrent corticosteroids allowed if on stable dose for at least 6 weeks
• before study
• No concurrent dexamethasone as an antiemetic

Radiotherapy:

• At least 4 weeks since prior radiotherapy and recovered
• No palliative radiotherapy
• At least 8 weeks since prior strontium 89 or samarium 153

Surgery:

• At least 3 weeks since major surgery and recovered