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 Pas 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 mu M) 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-Pas only at much higher concentrations (IC50 > 30 mu M), While the processing of H-Pas was very sensitive to inhibition by FTI-277 (IC50 = 100 nM), that of K-Ras4B was highly resistant (IC50 = 10 mu M). In contrast, we found the processing of K-Ras4B to be much more sensitive to GGTI-286 (IC50 = 2 mu M). Furthermore, oncogenic K-Ras4B stim ulation of mitogen-activated protein (MAP) kinase was inhibited potently by GGTI-286 (IC50 = 1 mu M) but weakly by FTI-277 (IC50 = 30 mu M). Significant inhibition of oncogenic K-Ras4B stimulation of MAP kinase by GGTI-286 occurred at concentrations (1-3 mu M) that did not inhibit oncogenic H-Ras stimulation of MAP kinase, The data presented in this study provide the first demonstration of seledtive 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 Pas in anticancer therapy.