title: In vivo circumvention of human colon carcinoma resistance to bleomycin.
abstract: Metabolic inactivation of bleomycin (BLM) by cysteine proteinase-like enzymes is thought to be a major mechanism of BLM tumor resistance. We now report that the human colon carcinoma COLO-205 is highly resistant to BLM and that E-64, a cysteine proteinase inhibitor, sensitizes COLO-205 to BLM. Treatment of COLO-205-bearing nude mice with either E-64 (40 mg/kg) or BLM (10 mg/kg) alone did not inhibit COLO-205 growth. However, pretreatment with E-64 prior to BLM prevented these xenografts from growing. Analysis by high performance liquid chromatography of in vivo BLM metabolism following [3H]BLM A2 treatment of COLO-205-bearing nude mice showed a different metabolic profile among the various organs and the tumor. Whereas [3H]BLM A2 was the only major radioactive peak detected in sera and tumors, several metabolites, including deamido-BLM A2, were found in kidney, liver, and lung as early as 15 min. Pretreatment of mice with E-64 inhibited tumor, kidney, and lung BLM A2 metabolism. Furthermore, pretreatment with E-64 increased BLM A2 accumulation in tumors (6.1-fold), kidney (4.0-fold), lung (2.8-fold), liver (1.8-fold), and serum (1.7-fold). E-64 pretreatment did not enhance the major toxicity of BLM, pulmonary fibrosis, as determined by both lung hydroxyproline levels and histopathology. Thus, the cysteine proteinase inhibitor E-64 affects the metabolic fate and the levels of accumulation of BLM in vivo. These results demonstrate that resistance of human COLO-205 tumors to BLM can be circumvented by E-64 without enhancement of the major side effect of BLM, suggesting a possible clinical use of this combination therapy.
authors.affiliation: Department of Pharmacology, University of Pittsburgh, School of Medicine, Pennsylvania 15261.
authors.forename: J P
authors.initials: JP
authors.lastname: Jani
authors.forename: J S
authors.initials: JS
authors.lastname: Mistry
authors.forename: G
authors.initials: G
authors.lastname: Morris
authors.forename: P
authors.initials: P
authors.lastname: Davies
authors.forename: J S
authors.initials: JS
authors.lastname: Lazo
authors.forename: S M
authors.initials: SM
authors.lastname: Sebti
mesh_terms: D000818:Animals; D001761:Bleomycin / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004347:Drug Interactions; D004351:Drug Resistance; D005260:Female; D006801:Humans; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008168:Lung / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011658:Pulmonary Fibrosis / Q000139:chemically induced; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014183:Transplantation, Heterologous
chemical_list: D015853:Cysteine Proteinase Inhibitors; D001761:Bleomycin; D007930:Leucine; C024974:E 64