J-104,871, A NOVEL FARNESYLTRANSFERASE INHIBITOR, BLOCKS RAS FARNESYLATION IN-VIVO IN A FARNESYL PYROPHOSPHATE-COMPETITIVE MANNER

Farnesylation of the activated ras oncogene product by protein farnesy ltransferase (FTase) is a critical step for its oncogenic function. Be cause squalene synthase and FTase recruit farnesyl pyrophosphate as a common substrate, we modified squalene synthase (SS) inhibitors to dev elop FTase inhibitors. Among the compounds tested, a novel FTase inhib itor termed J-104,871 inhibited rat brain FTase with an lc,, of 3.9 nM in the presence of 0.6 mu M farnesyl pyrophosphate (FPP), whereas it scarcely inhibited rat brain protein geranylgeranyltransferase-I or SS . The in vitro inhibition of rat brain FTase by J-104,871 depends on t he FPP concentration but not on the concentration of Ras peptide. Thus , in vitro studies strongly suggest that J-series compounds have an FP P-competitive nature. J-104,871 also inhibited Ras processing in activ ated H-ras-transformed NIH3T3 cells with an IC50 value of 3.1 mu M. We tested the effects of lovastatin and zaragozic acid A, which modify c ellular FPP levels, on Ras processing of J-104,871. Lovastatin, a hepa tic hydroxymenthyl coenzyme A reductase inhibitor that reduced the cel lular FPP pool, increased the activity of J-104,871, whereas 3 mu M za ragozic acid A, an SS inhibitor that raised the FPP level, completely abrogated the activity of J-104,871 even at 100 mu M. These results su ggest that J-104,871 inhibits FTase in an FPP-competitive manner in wh ole cells as well as in the in vitro system. Furthermore, J-104,871 su ppressed tumor growth in nude mice transplanted with activated H-ras-t ransformed NIH3T3 cells.