To acquire transforming potential, the precursor of the Ras oncoprotein must undergo farnesylation of the cysteine residue located in a carboxyl-terminal tetrapeptide. Inhibitors of the enzyme that catalyzes this modification, farnesyl protein transferase (FPTase), have therefore been suggested as anticancer agents for tumors in which Ras contributes to transformation. The tetrapeptide analog L-731,735 is a potent and selective inhibitor of FPTase in vitro. A prodrug of this compound, L-731,734, inhibited Ras processing in cells transformed with v-ras. L-731,734 decreased the ability of v-ras-transformed cells to form colonies in soft agar but had no effect on the efficiency of colony formation of cells transformed by either the v-raf or v-mos oncogenes. The results demonstrate selective inhibition of ras-dependent cell transformation with a synthetic organic inhibitor of FPTase.

For Ras oncoproteins to transform mammalian cells, they must be post-translationally modified with a farnesyl group in a reaction catalysed by the enzyme farnesyl-protein transferase (FPTase). Inhibitors of FPTase have therefore been proposed as anti-cancer agents. We show that L-744,832, which mimics the CaaX motif to which the farnesyl group is added, is a potent and selective inhibitor of FPTase. In MMTV-v-Ha-ras mice bearing palpable tumours, daily administration of L-744,832 caused tumour regression. Following cessation of treatment, tumours reappeared, the majority of which regressed upon retreatment. No systemic toxicity was found upon necropsy of L-744,832-treated mice. This first demonstration of anti-FPTase-mediated tumour regression suggests that FPTase inhibitors may be safe and effective anti-tumour agents in some cancers.

A potent and specific small molecule inhibitor of farnesyl-protein transferase, L-739,749, caused rapid morphological reversion and growth inhibition of ras-transformed fibroblasts (Ratl/ras cells). Morphological reversion occurred within 18 h of L-739,749 addition. The reverted phenotype was stable for several days in the absence of inhibitor before the transformed phenotype reappeared. Cell enlargement and actin stress fiber formation accompanied treatment of both Ratl/ras and normal Ratl cells. Significantly, inhibition of Ras processing did not correlate with the initiation or maintenance of the reverted phenotype. While a single treatment with L-739,749 was sufficient to morphologically revert Ratl/ras cells, repetitive inhibitor treatment was required to significantly reduce cell growth rate. Thus, the effects of L-739,749 on transformed cell morphology and cytoskeletal actin organization could be separated from effects on cell growth, depending on whether exposure to a farnesyl-protein transferase inhibitor was transient or repetitive. In contrast, L-739,749 had no effect on the growth, morphology, or actin organization of v-raf-transformed cells. Taken together, the results suggest that the mechanism of morphological reversion is complex and may involve farnesylated proteins that control the organization of cytoskeletal actin.

The posttranslational addition of a farnesyl moiety to the Ras oncoprotein is essential for its transforming activity. Cell-active inhibitors of the enzyme that catalyzes this reaction, protein farnesyltransferase, have been shown to selectively block ras-dependent transformation of cells in culture. Here we describe the protein farnesyltransferase inhibitor

The roles of 11 conserved amino acids of the ␤-subunit of human farnesyl:protein transferase (FTase) were examined by performing kinetic and biochemical analyses of site-directed mutants. This biochemical information along with the x-ray crystal structure of rat FTase indicates that residues His-248, Arg-291, Lys-294, and Trp-303 are involved with binding and utilization of the substrate farnesyl diphosphate. Our data confirm structural evidence that amino acids Cys-299, Asp-297, and His-362 are ligands for the essential Zn 2؉ ion and suggest that Asp-359 may also play a role in Zn 2؉ binding. Additionally, we demonstrate that Arg-202 is important for binding the essential C-terminal carboxylate of the protein substrate.Farnesyl:protein transferase (FTase) 1 catalyzes thioether bond formation between farnesyl, from farnesyl diphosphate (FPP), and the sulfur atom of a cysteine residue near the C terminus of its protein substrate (1, 2). The protein substrate cysteine residue is located within a C-terminal motif called a CAAX box in which C is the cysteine that is S-farnesylated, A is often an aliphatic amino acid, and X is methionine, serine, glutamine, cysteine, or alanine (1, 3, 4). S-Farnesylation is the first step by which a number of proteins, including all forms of the Ras proto-oncoprotein, are post-translationally lipid-modified, facilitating membrane association and in some cases protein-protein interaction (2). Membrane association is required for Ras function, thus inhibitors of FTase have been proposed as antitumor agents (5). FTase inhibitors (FTIs) have been shown to inhibit anchorage-independent growth of ras-transformed rodent fibroblasts and human tumor cell lines (6 -8). In addition, FTIs have shown antitumor effects in rodents (6, 9).FTase kinetically proceeds through an ordered, sequential mechanism in which FPP is the first substrate bound (10, 11). Subsequent protein substrate binding to FTase depends on an enzyme-bound Zn 2ϩ ion (12, 13). Recent spectral data indicate that upon formation of the FTase⅐FPP⅐CAAX ternary complex, the cysteine thiol of the CAAX sequence interacts directly with Zn 2ϩ