Use of camptothecin-resistant mammalian cell lines to evaluate the role of topoisomerase I in the antiproliferative activity of the indolocarbazole, NB-506, and its topoisomerase I binding site.
NB-506 is a topoisomerase I (top1) inhibitor in clinical trials. In this study, we used a series of camptothecin (CPT)-resistant cell lines with known top1 alterations. We show that three mutations in different domains of the top1 enzyme that confer CPT resistance also confer cross-resistance to NB-506. The CPT-resistant cell lines and corresponding mutations were: human prostate carcinoma cells DU-145/RC1 (mutation R364H), Chinese hamster fibroblasts DC3F/C10 (mutation G503S), and human leukemia CEM/C2 cells (N722S). This result suggests that NB-506 and CPT share a common binding site in the top1-DNA complex. We next used these three cell lines and their parental cells to study the relationship between top1 poisoning by NB-506 and antiproliferative activity. We found that the CPT-resistant cells were only 2-10-fold resistant to NB-506, which suggests that NB-506 targets other cellular processes/pathways besides top1. This conclusion was further supported by the limited cross-resistance of top1-deficient murine leukemia P388/CPT45 cells (2-fold). Cross-resistance was also limited for J-109,382, an isomer of NB-506 that does not intercalate into DNA, indicating that the non-top1-mediated antiproliferative activity of NB-506 is not attributable to DNA intercalation. Together, these data indicate that NB-506 and indolocarbazoles are promising agents to overcome CPT resistance.
Urasaki
Y
Y
Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Laco
G
G
Takebayashi
Y
Y
Bailly
C
C
Kohlhagen
G
G
Pommier
Y
Y
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001665:Binding Sites; D002166:Camptothecin / Q000494:pharmacology*; D002227:Carbazoles / Q000737:chemistry / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D005960:Glucosides / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007364:Intercalating Agents / Q000494:pharmacology; D009154:Mutation; D013237:Stereoisomerism; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D002227:Carbazoles; D004273:DNA, Neoplasm; D005960:Glucosides; D007364:Intercalating Agents; C092476:NB 506; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin