title: Cross-resistance to camptothecin analogues in a mitoxantrone-resistant human breast carcinoma cell line is not due to DNA topoisomerase I alterations.
abstract: We have previously described a mitoxantrone-resistant human breast carcinoma cell line, MCF7/MX, in which resistance was associated with a defect in the energy-dependent accumulation of mitoxantrone in the absence of P-glycoprotein overexpression (M. Nakagawa et al., Cancer Res. 52: 6175-6181, 1992). We now report that this cell line is highly cross-resistant to the camptothecin analogues topotecan (180-fold), 9-aminocamptothecin (120-fold), CPT-11 (56-fold), and SN38 (101-fold), but is only mildly cross-resistant to the parent compound camptothecin (3.2-fold) and 10,11-methylenedioxy-camptothecin (2.9-fold). Topotecan accumulation was decreased in MCF7/MX cells compared to parental MCF7/WT cells, and there was a corresponding reduction in topotecan-mediated stimulation of the enzyme/DNA complex formation in MCF7/MX cells compared to MCF7/WT cells. No overexpression of the multidrug resistance-associated protein was detected compared to parental MCF7/WT cells. Furthermore, both sensitive MCF7/WT and mitoxantrone-resistant MCF7/MX cells contain equal amounts of DNA topoisomerase I protein, and DNA relaxation activities were equal in both cell lines and inhibited to the same extent by topotecan and camptothecin. Thus, these results suggest a novel mechanism of resistance to topoisomerase I inhibitors in cancer cells.
authors.affiliation: Medicine Branch, National Cancer Institute, Bethesda, Maryland 20892, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Yang
authors.forename: J K
authors.initials: JK
authors.lastname: Horton
authors.forename: K H
authors.initials: KH
authors.lastname: Cowan
authors.forename: E
authors.initials: E
authors.lastname: Schneider
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008942:Mitoxantrone / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors; D019772:Topotecan; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D059004:Topoisomerase I Inhibitors; D019772:Topotecan; D008942:Mitoxantrone; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin