Hypersensitivity of NIH3T3 cells transformed by H-ras gene to DNA-topoisomerase-I inhibitors.
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.
Ohira
T
T
Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
Nishio
K
K
Kanzawa
F
F
Ishida
T
T
Ohe
Y
Y
Arioka
H
H
Funayama
Y
Y
Ogasawara
H
H
Kato
H
H
Saijo
N
N
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
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