Sequential modifications of topoisomerase I activity in a camptothecin-resistant cell line established by progressive adaptation.
The DNA-topoisomerase I (Topo I) inhibitor, camptothecin (CPT), is a plant alkaloid with an important antitumor activity. In order to investigate the cellular mechanism leading to the development of the resistance to this agent, we have established by progressive adaptation a P388 subline resistant to CPT. After 5 months of continuous drug exposure, the resistance index reached a value of 20 and the resistant cell line, P388CPT0.3, was maintained in the presence of CPT. CPT-induced single strand breaks measured by alkaline elution were found drastically reduced in the resistant cell line. Topo I activity and CPT-induced DNA cleavage were measured on cells at different steps of resistance. We first observed that the Topo I activity was strongly decreased. In addition, the resistant cells recovered the ATP-independent relaxation activity after 3 months of exposure to CPT, but still kept a reduced CPT-induced DNA cleavage. Further evaluations at the final stage of the resistance induction have indicated that cells presented a CPT-resistant form of Topo I. Rearranged Topo I gene on one allele and a reduced Topo I transcription were also observed in resistant cells. The putative role of the rearrangement was discussed. These data show that the resistance mechanism has evolved from a decreased Topo I activity to an altered form of the enzyme, and suggest that multiple mechanisms of Topo I modifications could contribute to CPT resistance.
Rhône-Poulenc Rorer, Département Biologie, Centre de Recherche de Vitry-Alfortville, Vitry-sur-Seine, France.
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D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000187:drug effects; D004351:Drug Resistance; D015321:Gene Rearrangement; D051379:Mice; D012333:RNA, Messenger / Q000032:analysis; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000970:Antineoplastic Agents; D004277:DNA, Single-Stranded; D012333:RNA, Messenger; D059005:Topoisomerase II Inhibitors; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin