Abstract
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 1. 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.
Original language | English |
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Pages (from-to) | 339-348 |
Number of pages | 10 |
Journal | Biochemical Pharmacology |
Volume | 45 |
Issue number | 2 |
Publication status | Published - 26 Jan 1993 |
Keywords / Materials (for Non-textual outputs)
- ACTINOMYCIN-D
- L1210 CELLS
- CANCER
- PHOSPHORYLATION
- INHIBITION
- EXPRESSION
- MUTANTS
- INVITRO
- BREAKS
- TUMORS