GGTI-286 TFA, a potent and cell-permeable GGTase I inhibitor, is 25-fold more potent (IC50=2 μM) than the corresponding methyl ester of FTI-276 (HY-15873A). GGTI-286 TFA selectively inhibits geranylgeranylation of Rap1A over farnesylation of H-Ras in NIH3T3 cells (IC50s=2 and >30 μM, respectively). GGTI-286 TFA also potently inhibits oncogenic K-Ras4B stimulation with an IC50 of 1 μM[1][2].