title: Hypersensitivity of NIH3T3 cells transformed by H-ras gene to DNA-topoisomerase-I inhibitors.
abstract: We examined the effects of the introduction of H-ras oncogene into murine cell line NIH3T3 on growth inhibition by topoisomerase-I (topo-I) inhibitors. The H-ras-transformed cells (pT22-3) showed approximately 12-fold increased sensitivity to a novel topo-I inhibitor, NB-506 [6-N-formylamino-12,13-dihydro-1,11-dihydroxy-13-(beta-D-glucopyranosyl) -5H-indolo(2,3-a)pyrrolo(3,4-c) carbazole-5,7(6H)-dione], compared with the parental NIH3T3 cells. pT22-3 also showed increased sensitivity to other topo-I inhibitors such as camptothecin (approx. 3.0-fold) and CPT-11 (irinotecan, approx. 3.0-fold). Transformation of NIH3T3 by another oncogene (erbB2) did not affect their sensitivity to these topo-I inhibitors. pT22-3 had approximately 32-fold higher topo-I activity than NIH3T3, but the same topo-I content. In a cell-free system, topo-I activity was increased 2-fold by addition of the H-ras protein precipitated from pT22-3 cells. Topo I in the nuclear extract of pT22-3 was eluted easily by low concentrations of NaCl compared with that of NIH3T3, suggesting a qualitative change in pT22-3 topo 1. Increased phosphorylation of topo I was observed in pT22-3. Furthermore, NB-506 decreased the amount of the GTP-bound form of the H-ras product in pT22-3 cells. These results suggest that the high growth-inhibitory effect of a topo-I inhibitor, NB-506, on H-ras-transformed NIH3T3 cells is due to the H-ras-mediated signal-transduction pathway.
authors.affiliation: Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ohira
authors.forename: K
authors.initials: K
authors.lastname: Nishio
authors.forename: F
authors.initials: F
authors.lastname: Kanzawa
authors.forename: T
authors.initials: T
authors.lastname: Ishida
authors.forename: Y
authors.initials: Y
authors.lastname: Ohe
authors.forename: H
authors.initials: H
authors.lastname: Arioka
authors.forename: Y
authors.initials: Y
authors.lastname: Funayama
authors.forename: H
authors.initials: H
authors.lastname: Ogasawara
authors.forename: H
authors.initials: H
authors.lastname: Kato
authors.forename: N
authors.initials: N
authors.lastname: Saijo
mesh_terms: D016475:3T3 Cells / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D002461:Cell Line, Transformed; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D011905:Genes, ras; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D015151:Immunoblotting; D000077146:Irinotecan; D051379:Mice; D010766:Phosphorylation; D059004:Topoisomerase I Inhibitors; D018631:ras Proteins / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D006153:Guanosine Diphosphate; D000077146:Irinotecan; D006160:Guanosine Triphosphate; D018631:ras Proteins; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin