ALTERED TOPOISOMERASE-II-ALPHA IN A DRUG-RESISTANT SMALL-CELL LUNG-CANCER CELL-LINE SELECTED IN VP-16

作者：MIRSKI SEL; EVANS CD; ALMQUIST KC; SLOVAK ML; COLE SPC

来源：Cancer Research, 1993, 53(20): 4866-4873.

The H209/V6 cell line was derived from the H209 small cell lung cancer cell line by selection in etoposide (VP-16). Cytogenetic analysis indicates that the sensitive and resistant cell lines share 20 marker chromosomes and thus are clearly related. However, the H209/V6 cell line has four additional structurally altered chromosomes and a 2 N-modal chromosome number, while the H209 cell line is hypotetraploid (4 N-). H209/V6 cells are cross-resistant to some drugs that interact with topoisomerase II but not mitoxantrone. H209/V6 cells are also not cross-resistant to vincristine, trimetrexate, or cisplatin. The rates of VP-16 efflux are the same in the resistant and sensitive cell lines, which is consistent with the observation that P-glycoprotein mRNA is not detectable in either cell line. Fewer VP-16-induced DNA-protein complexes are observed in H209/V6 cells, and immunoblot analysis shows that levels of topoisomerase IIalpha are reduced in H209/V6 cells compared to the sensitive H209 cells. Furthermore, the topoisomerase IIalpha-related protein in H209/V6 cells has an increased electrophoretic mobility, with an apparent M(r) of 160,000. The levels of the topoisomerase IIalpha 6.1-kilobase mRNA in H209/V6 cells are reduced >10-fold. In addition, a second topoisomerase IIalpha-related mRNA of approximately 4.8 kilobases is observed in H209/V6 cells but not in H209 cells. The quantity and electrophoretic mobility of the M(r) 180,000 topoisomerase IIbeta protein and its 6.1-kilobase mRNA are the same in the sensitive and resistant cell lines. The topoisomerase II strand-passing activity in H209/V6 nuclear extracts is reduced about 2-fold, but this activity is not more resistant to inhibition by VP-16 than the activity in H209 cells. However, band depletion immunoblot experiments show that the topoisomerase IIalpha-related M(r) 160,000 protein in H209/V6 cells is not bound to DNA in the presence of concentrations of VP-16 that deplete the M(r) 170,000 topoisomerase IIalpha in H209 cells and the M(r) 180,000 topoisomerase IIbeta in both the resistant and sensitive cells. We conclude that quantitative and qualitative alterations in topoisomerase IIalpha have occurred in H209/V6 cells and are likely to contribute to its resistance phenotype.

• 出版日期1993-10-15