Disruption of oncogenic K-Ras4B processing and signaling by a potent geranylgeranyltransferase I inhibitor

Prenylation of the carboxyl-terminal CAAX (C, cysteine; A, aliphatic acid; and X, any amino acid) of Ras is required for its biological activity. We have designed a CAAX peptidomimetic, GGTI-287, which is 10 times more potent toward inhibiting geranylgeranyltransferase I (GGTase I) in vitro (IC₅₀ = 5 nM) than our previously reported farnesyltransferase inhibitor, FTI-276. In whole cells, the methyl ester derivative of GGTI-287, GGTI-286, was 25-fold more potent (IC₅₀ = 2 μM) than the corresponding methyl ester of FTI-276, FTI-277, toward inhibiting the processing of the geranylgeranylated protein Rap1A. Furthermore, GGTI-286 is highly selective for geranylgeranylation over farnesylation since it inhibited the processing of farnesylated H-Ras only at much higher concentrations (IC₅₀ > 30 μM). While the processing of H-Ras was very sensitive to inhibition by FTI-277 (IC₅₀ = 100 nM), that of K- Ras4B was highly resistant (IC₅₀ = 10 μM). In contrast, we found the processing of K-Ras4B to be much more sensitive to GGT1-286 (IC₅₀ = 2 μM). Furthermore, oncogenic K-Ras4B stimulation of mitogen-activated protein (MAP) kinase was inhibited potently by GGTI-286 (IC₅₀ = 1 μM) but weakly by FTI- 277 (IC₅₀ = 30 μM). Significant inhibition of oncogenic K-Ras4B stimulation of MAP kinase by GGTI-286 occurred at concentrations (1-3 μM) that did not inhibit oncogenic H-Ras stimulation of MAP kinase. The data presented in this study provide the first demonstration of selective disruption of oncogenic K-Ras4B processing and signaling by a CAAX peptidomimetic. The higher sensitivity of K-Ras4B toward a GGTase I inhibitor has a tremendous impact on future research directions targeting Ras in anticancer therapy.