The role of autophagy in cytotoxicity induced by new oncogenic B-Raf inhibitor UI-152 in v-Ha-ras transformed fibroblasts.
In human cancers, B-Raf is the most frequently mutated protein kinase in the MAPK signaling cascade, making it an important therapeutic target. We recently discovered a potent and selective B-Raf inhibitor, UI-152, by using a structure-based drug design strategy. In this study, we examined whether B-Raf inhibition by UI-152 may be an effective therapeutic strategy for eliminating cancer cells transformed with v-Ha-ras (Ras-NIH 3T3). UI-152 displayed selective cytotoxicity toward Ras-NIH 3T3 cells while having little to no effect on non-transformed NIH 3T3 cells. We found that treatment with UI-152 markedly increased autophagy and, to a lesser extent, apoptosis. However, inhibition of autophagy by addition of 3-MA failed to reverse the cytotoxic effects of UI-152 on Ras-NIH 3T3 cells, demonstrating that apoptosis and autophagy can act as cooperative partners to induce growth inhibition in Ras-NIH 3T3 cells treated with UI-152. Most interestingly, cell responses to UI-152 appear to be paradoxical. Here, we showed that although UI-152 inhibited ERK, it induced B-Raf binding to Raf-1 as well as Raf-1 activation. This paradoxical activation of Raf-1 by UI-152 is likely to be coupled with the inhibition of the mTOR pathway, an intracellular signaling pathway involved in autophagy. We also showed for the first time that, in multi-drug resistant cells, the combination of UI-152 with verapamil significantly decreased cell proliferation and increased autophagy. Thus, our findings suggest that the inhibition of autophagy, in combination with UI-152, offers a more effective therapeutic strategy for v-Ha-ras-transformed cells harboring wild-type B-Raf.
Division of Life Sciences, College of Natural Sciences, University of Incheon, Incheon 406-772, Republic of Korea.
Jun-Ho
JH
Ahn
Soon Kil
SK
Ahn
Michael
M
Lee
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D002461:Cell Line, Transformed; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects* / Q000473:pathology; D011905:Genes, ras; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors*; D011687:Purines / Q000494:pharmacology*; D013449:Sulfonamides / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology
D000970:Antineoplastic Agents; C570548:N-((3-(3-9H-purin-6-yl)pyridin-2-ylamino)-2,4-difluorophenyl)furan-3-sulfonamide; D047428:Protein Kinase Inhibitors; D011687:Purines; D013449:Sulfonamides; D014700:Verapamil; D048493:Proto-Oncogene Proteins B-raf