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Discrepancy between the initial DNA damage and cell survival after camptothecin treatment in two murine lymphoma L5178Y sublines
Author(s) -
Grądzka Iwona,
Szumiel Irena
Publication year - 1996
Publication title -
cell biochemistry and function
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 61
eISSN - 1099-0844
pISSN - 0263-6484
DOI - 10.1002/cbf.672
Subject(s) - camptothecin , microbiology and biotechnology , topoisomerase , dna , biology , incubation , cell culture , in vitro , growth inhibition , dna damage , dna synthesis , cell growth , biochemistry , genetics
Abstract Two L5178Y (LY) murine lymphoma cell sublines, LY‐R, resistant, and LY‐S, sensitive, to X‐irradiation display inverse cross‐sensitivity to camptothecin (CPT): LY‐R cells were more susceptible to this specific topoisomerase I inhibitor than LY‐S cells. After 1 h incubation with CPT, the doses that inhibited growth by 50 per cent (ID 50 ) after 48 h of incubation were 0·54μ M for LY‐R cells and 1·25 μ M for LY‐S cells. Initial numbers of DNA–protein crosslinks (DPCs) measured at this level of growth inhibition were two‐fold higher in LY‐R (5·6 Gray‐equivalents) than in LY‐S cells (3·1 Gray‐equivalents), which corresponds well with the greater in vitro sensitivity of Topo I from LY‐R cells to CPT. 1,2 Conversely, the initial levels of single‐strand DNA breaks (SSBs) and double‐strand DNA breaks (DSBs) were lower in LY‐R cells (4·2 Gray‐equivalent SSBs and 5·8 Gray equivalent DSBs) than in LY‐S cells (8·0 Gray‐equivalent SSBs and 12·0 Gray‐equivalent DSBs). Dissimilarity in the replication‐dependent DNA damage observed after 1 h of treatment with CPT was not due to a difference in the rate of DNA synthesis between the two cell lines, but may have arisen from a substantially slower repair of DNA breaks in LY‐S cells. 3 Release from G 2 block by caffeine co‐treatment significantly increased cell killing in the LY‐S subline, and only slightly inhibited growth of LY‐R cells. These results show that after CPT treatment cells arrest in G 2 , allowing them time to repair the long‐lived DSBs. As LY‐S cells are slower in repairing the DSBs, they were more susceptible to CPT in the presence of caffeine.