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Effect of novobiocin on cisplatin cytotoxicity and dna interstrand cross‐link formation in a cisplatin‐resistant, small‐cell lung carcinoma cell line
Author(s) -
De Jong Steven,
TimmerBosscha Hetty,
De Vries Elisabeth G. E.,
Mulder Nanno H.
Publication year - 1993
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910530121
Subject(s) - novobiocin , cytotoxicity , cisplatin , dna , cell culture , chemistry , biochemistry , biology , microbiology and biotechnology , chemotherapy , in vitro , genetics , antibiotics
Studies were performed to determine whether novobiocin can be used to enhance cisplatin (CDDP) cytotoxicity in a human small‐cell lung carcinoma cell line, GLC 4 /CDDP, resistant to CDDP. Continuous incubation with novobiocin enhanced the cytotoxicity of CDDP treatment 1.9‐fold in the parental cell line GLC 4 , but had no effect on its cytotoxicity in the resistant cell line GLC 4 /CDDP. Short incubation with novobiocin enhanced the cytotoxicity of CDDP treatment in GLC 4 and GLC 4 /CDDP by a factor of 4.1 and 2.8, respectively. Using the latter schedule, the amount of CDDP‐induced DNA interstrand cross‐links (DNA ISC) at 4 hr as well as at 24 hr after novobiocin and CDDP treatment was higher in GLC 4 than in GLC 4 /CDDP. In this case, the amount of DNA ISC had increased 1.6‐fold in GLC 4 and 1.3‐fold in GLC 4 /CDDP at 4hr, and 2.7‐fold and 1.4‐fold, respectively, in these cell lines at 24 hr after treatment compared to CDDP treatment alone. Our results suggest an effect of novobiocin on the formation of DNA ISC. The decreased efficacy of novobiocin, an inhibitor of DNA topoisomerase (Topo) II catalytic activity, in GLC 4 /CDDP may be due to the increased Topo II activity previously found in the resistant cells. In the present study, we showed that increased Topo II activity was not due to changes in amounts of Topo II in nuclei or nuclear extracts of GLC 4 /CDDP. Further analysis of the chromatin, that includes Topo II, showed that the chromatin in nuclei of GLC 4 /CDDP was more sensitive to micrococcal nuclease digestion than GLC 4 . In addition, the amount of a 56‐kDa protein was increased 2‐fold in nuclei and nuclear matrices from GLC 4 /CDDP. The reduced efficacy of novobiocin to increase the CDDP cytotoxicity as well as the formation of DNA ISC in GLC 4 /CDDP compared to GLC 4 may be due to changes in the chromatin structure of the resistant cells.