Drug sensitivity and some characteristics of a bleomycin-resistant subline of mouse lymphoblastoma L5178Y cells.

Cellular resistance to bleomycin is important in the treatment of neoplasms. However, the mechanism of bleomycin resistance has been not well investigated. The resistance may be attributed to alterations of membrane transport, binding to DNA or other cell components, an inactivating enzyme, and/or a DNA repair system. MIYAKI et al. have examined the binding of [11C]bleomycin to DNA in bleomycin-sensitive and -resistant rat ascites hepatoma cells, and found that the resistance is due to increased activity of a bleomycin-inactivating enzyme but not to the transport barrier. BRABBS and WARR21 have reported a bleomycin-resistant clone of Chinese hamster ovary cells, in which a membrane change has been suggested. We have recently isolated a bleomycin-resistant subline of mouse lymphoblastoma L5178Y cells, and found that the resistance cannot be attributed to alteration of bleomycin-inactivating activity. The drug sensitivity and some characteristics of the resistant cell subline is presented in this publication. Bleomycin A2 (copper-free), peplomycin (pepleomycin), macromomycin and aclacinomycin A were generously given by Dr. HAMAO UMEZAWA, Institute of Microbial Chemistry. Mitomycin C and adriamycin were kindly supplied by Kyowa Hakko Kogyo Co., Ltd. Neocarzinostatin was a product of Kayaku Antibiotics Research Co., Ltd., blasticidin S of Kaken Chemical Co., Ltd., and fusidic acid of Leo Pharmaceutical Products, Ballerup, Denmark. The cells were grown in FISCHER'S medium supplemented with 10 % horse serum. A bleomycin-resistant subline of L5178Y cells was isolated by repeated injection of 10 mg/kg of bleomycin A_ to CDFI (BALB/cAnNCrj X DBA/2NCrj) female mice, 7-8 weeks of age, bearing L5178Y tumors. After 9 successive transplants, colonies of resistant cell sublines were selected in FISCHER'S medium supplemented with 15% horse serum, 0.15% agar, and 10 !eg/ml bleomycin A2. As illustrated in Fig. 1, the resistant cells grew a little more slowly than the parental cells. The