Bleomycin hydrolase activity and cytotoxicity in human tumors

A sensitive new method to assay bleomycin (BLM) metabolism was developed using an ion-paired, reverse-phase high-pressure liquid chromatography technique in conjunction with fluorescence detection that allowed levels of BLM less than 20 ng/ml to be detected. The metabolism of bleomycin B2 in homogenates from benign and malignant human tumors was studied, and all 14 tumors were capable of metabolizing bleomycin to desamidobleomycin B2. Metabolites other than desamidobleomycin B2 were not detected. BLM hydrolase activities in individual tumors varied more than 7-fold. The importance of BLM hydrolase in limiting the therapeutic effectiveness of BLM was examined by measuring BLM hydrolase activity and response of human tumors to BLM in culture. Response to BLM in culture was measured by dissociating human tumors to form single-cell suspensions and exposing the cells to 0.05 or 1 microgram/ml of BLM for 1 hr. Colony formation after BLM treatment was determined in soft agar and when compared to that of untreated cells, varied by more than 100-fold. No correlation was observed, however, between BLM hydrolase activity and response to BLM in soft agar. Thus, human tumors can metabolize BLM, and while BLM hydrolase activity may be important in tumor resistance to the drug, these data suggest that either (a) the enzyme activity in the tumor homogenate does not reflect that in the clonogenic cells or (b) other mechanisms of resistance may be operative.