Pseudopeptide Inhibitors of Ras Farnesyl-Protein Transferase

Abstract

Inhibitors of Ras farnesyl-protein transferase are described. These are reduced pseudopeptides related to the C-terminal tetrapeptide of the Ras protein that signals farnesylation. Deletion of the carbonyl groups between the first two residues of the tetrapeptides either preserves or improves activity, depending on the peptide sequence. The most potent in vitro enzyme inhibitor described (IC50 = 5 nM) is Cys [psi CH2NH]Ile[psi CH2NH]Phe-Met (3). To obtain compounds able to suppress Ras farnesylation in cell culture, further structural modification to include a homoserine lactone prodrug was required. Compound 18 (Cys[psi CH2NH]Ile[psi CH2NH]Ile-homoserine lactone) reduced the extent of Ras farnesylation by 50% in NIH3T3 fibroblasts in culture at a concentration of 50 microM. Structure-activity studies also led to 12 (Cys[psi CH2NH]Val-Ile-Leu), a potent and selective inhibitor of a related enzyme, the type-I geranylgeranyl protein transferase.

Ras CAAX Peptidomimetic FTI-277 Selectively Blocks Oncogenic Ras Signaling by Inducing Cytoplasmic Accumulation of Inactive Ras-Raf Complexes

“…Recently, we (20 -22, 27) and others (23)(24)(25)(26) have designed Ras CAAX peptidomimetics that inhibit FTase potently with concentrations in the nM range. However, these agents inhibited Ras processing in whole cells only at M levels (29,30).…”

“…Although CAAX peptides are potent competitive inhibitors of FTase, rapid degradation and low cellular uptake limit their use as therapeutic agents. Over the last 3 years, we (20 -22) and others (23)(24)(25)(26) have designed CAAX peptidomimetics that potently inhibit FTase in vitro and Ras processing in vivo but that retain several peptidic features. More recently, we have designed non-peptide CAAX mimetics that have several desirable features for further development as anti-cancer agents (27).…”

Farnesyltransferase inhibition causes morphological reversion of ras-transformed cells by a complex mechanism that involves regulation of the actin cytoskeleton.

“…To characterize the features of cell enlargement, we examined Ratl/ras cells since in this cell line the morphological change was more apparent. We found that the phenotypic conversion induced by L-739,749 was rapid, being detectable within 18 h and essentially complete by 24 h. However, cells continued to enlarge beyond this time to at least 38 h (Fig. 2B).…”

A Cell-Based Radioligand Binding Assay for Farnesyl: Protein Transferase Inhibitors

“…To investigate this possibility, we focused on L-778,123 (FTI-5), a compound evaluated in clinical trials by Merck & Co., 26 and a related compound, FTI-6. FTI-6 is a 10-fold more potent inhibitor of FPTase than FTI-5 in vitro (IC 50 0.2 nM and 2.0 nM for FTI-6 and FTI-5, respectively, as determined as described in Graham et al 16 [data not shown]). As seen in Figure 7A, the 2 compounds are equipotent inhibitors in H-ras-transformed Rat1 cells, as measured by CRAFTI (Mean IC 50 3.5 [n = 16] and 3.6 [n = 105] for FTI-6 and FTI-5, respectively).…”