PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 4 weeks since prior chemotherapy (6 weeks for mitomycin and nitrosoureas) and recovered No other concurrent cytotoxic therapy Endocrine therapy: Not specified Radiotherapy: At least 4 weeks since prior radiotherapy and recovered Surgery: At least 6 weeks since prior major surgery Other: At least 4 weeks since any other prior investigational agent No concurrent anticonvulsant therapy No concurrent aspirin greater than 100 mg per day, heparin, or nonsteroidal antiinflammatory medication No concurrent calcium channel blockers, antiarrhythmias, or anti-angina therapy Concurrent beta-blocking agents for hypertension or anxiety allowed