[Studies on the mechanism of drug resistance in tumor cells and a new antitumor antibiotic].

Characteristics of Drug-Resistant Cell Sublines L5178Y: We isolated aclarubicin (ACR)-, adriamycin (ADM)-, bleomycin (BLM-, and macromomycin (MCR)-resistant (r) cell sublines. The BLMr cell line did not show cross-resistance to other drugs. The ACRr and ADMr cell lines displayed cross-resistance to other anthracyclines. The drug-resistance of these cell lines was due to changes in membrane transport. All four resistant cell lines showed higher activity of membrane alkaline phosphodiesterase (APD) than the parental cells. The APD of the BLMr scell line differed from that of the parental line in molecular size. 2-Crotonyloxymethyl-4, 5, 6-trihydroxycyclohex-2-enone: We isolated an inhibitor of APD from a Streptomyces species. This substance inhibited the drug-resistant cell lines of L5178Y more markedly than the parental line in culture and showed synergistic effects with ACR against the ACRr cell line. It was an SH-inhibitor, and prevented DNA polymerase alpha and some mitotic processes. Transplantability of Drug-Resistant L5178Y Cells: DBA/2 mice, the syngeneic host, exhibited more resistance to ip transplantation of drug-resistant cell lines than parental cells. The animals showed the strongest resistance to the ACRr cell line. Treatment with cyclophosphamide markedly reversed the host resistance, suggesting that the immune mechanism was involved in the resistance. The ACRr cells were sensitive to NK cells, but the parental cells were not. Injection with anti-asialo GM1 markedly decreased host resistance. The results suggested that NK cells were involved in the transplantation resistance of mice to the ACRr cells. 230-Kilodalton Membrane Protein of ACRr Cells Identified by Monoclonal Antibody: We prepared monoclonal antibodies to the ACRr cells, and found that a monoclonal antibody, designated SC438, specifically agglutinated the ACRr cells. A specific 230K membrane protein was found in the ACRr cells by immunoprecipitation. Natural BLM Resistance of Chinese Hamster V79 Cells: V79 cells were more resistant to BLM than CHO cells. This natural drug-resistance was is due to higher BLM hydrolase activity. We isolated BLM cell lines, and found that BLM supersensitivity was not due to BLM hydrolase, but to decreased repairing activity of DNA damage.