Abstract

Farnesyltransferase inhibitors (FTIs) block the growth of tumor cells in vitro and in vivo with minimal toxicity toward normal cells. In general, inhibition of protein farnesylation results in G₀/G₁ cell cycle block, G₂/M cell cycle arrest, or has no effect on cell cycle progression. One aspect of FTI biology that is poorly understood is the ability of these drugs to induce cancer cell growth arrest at the G₂/M phase of cell cycle. In the present study, we investigated the effects of the farnesyltransferase inhibitor FTI-277 on two human liver cancer cell lines, HepG2 and Huh7. Treatment of these cells with FTI-277 inhibited Ras farnesylation in a dose-dependent manner. Both HepG2 and Huh7 cell growth was inhibited by FTI-277 and cells accumulated at the G₂/M phase of the cell cycle. In HepG2 and Huh7 cells, FTI-277 induced an up-regulation of the cyclin-dependent kinase inhibitor p27^Kip1 without affecting the cellular levels of p53 and p21^Waf1. This event correlated with reduced activity of the cyclin-dependent kinase 2 and cyclin-dependent kinase 1. Moreover, increased expression of Bcl-2 protein was observed in HepG2 and Huh7 cells treated with FTI-277, and this was coincidental with reduced association between Raf-1 and Bcl-2. Finally, transient transfection of a dominant-negative Ras allele induced Bcl-2 expression and reduced Bcl-2/Raf-1 association demonstrating a requirement for Ras. Taken together, these findings show that increased expression of p27^Kip1 and Bcl-2 is concomitant with altered association between Ras, Raf-1 and Bcl-2 and suggest that this is responsible for the growth-inhibitory properties of FTI-277.