DISEASE CHARACTERISTICS: Histologically or cytologically confirmed metastatic or locally recurrent adenocarcinoma of the colon or rectum No curable stage of disease At least 1 unidimensionally measurable lesion At 20 mm by conventional techniques OR At least 10 mm by spiral CT scan No tumor lesions in previously irradiated area except clearly measurable lesion documented histologically to be consistent with recurrent tumor in previously irradiated bed within pelvis The following are considered nonmeasurable disease: Bone lesions Leptomeningeal disease Ascites Pleural/pericardial effusion Inflammatory breast disease Lymphangitis cutis/pulmonis Abdominal masses not confirmed and followed by imaging techniques Cystic lesions No known brain metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 OR Karnofsky 60-100% Life expectancy: More than 12 weeks Hematopoietic: WBC at least 3,000/mm3 Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin normal AST/ALT no greater than 2.5 times upper limit of normal Renal: Creatinine normal OR Creatinine clearance at least 60 mL/min Cardiovascular: No symptomatic congestive heart failure No unstable angina pectoris No cardiac arrhythmia Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception during and for 6 months after study Eligible for placement of a central venous catheter No prior allergic reactions attributed to compounds of similar chemical or biologic composition to rebeccamycin analogue No other uncontrolled concurrent illness No ongoing or active infection No psychiatric illness or social situation that would preclude study compliance

PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent prophylactic growth factors (e.g., epoetin alfa) except for clinically defined indication (e.g., filgrastim (G-CSF) for febrile neutropenia) Chemotherapy: At least 4 weeks since prior chemotherapy (e.g., fluorouracil, oral fluoropyrimidines, irinotecan, or oxaliplatin) (6 weeks for nitrosoureas or mitomycin) No other concurrent chemotherapy Endocrine therapy: No concurrent hormones except for clinically defined indication Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy (including to bony sites, whole pelvis, lung, liver, or spinal cord/brain) and recovered No prior total dose of radiotherapy more than 7,000 cGy No prior radiotherapy to 40% or more of total bone marrow No prior radiotherapy to only site of measurable disease No concurrent radiotherapy Surgery: Not specified Other: Recovered from prior therapy 1 prior adjuvant treatment allowed 1 prior treatment for advanced disease allowed At least 4 weeks since prior investigational agents No other concurrent investigational antineoplastic drugs No other concurrent investigational agents No concurrent commercial agents for colorectal cancer No concurrent combination antiretroviral therapy for HIV-positive patients