Inhibition of farnesyl protein transferase by monoterpene, curcumin derivatives and gallotannin.

Ras proteins must be isoprenylated at a conserved cysteine residue near the carboxyl terminus (Cys-186 in mammalian Ras p21 proteins) in order to extend their biological activity. Previous studies have indicate an intermediate in the mevalonate pathway, most likely farnesyl pyrophosphate, is the donor of this isoprenyl group, and that using inhibitors of the mevalonate pathway could block the transforming properties of ras oncogene. Unfortunately, mevalonate is a precursor of various end products essential to mammalian cells, such as dolichols, ubiquinones, heme A, and cholesterol. In this study, we partially purified farnesyl protein transferase (FPTase) capable of catalyzing the farnesylation of unprocessed Ras p21 proteins in vitro from porcine kidney epithelial-like LLC-PK 1 cells, human lung adenocarcinoma A549 cells and human pancreatic cancer MIA PaCa-2 cells. This FPTase activity requires a divalent cation, such as Mg2+ or Zn2+ ions, sulfhydryl protecting agent, DTT, as well as certain pH which is linear with time and with enzyme concentration, and is present in many mammalian normal cell and tumor cell lines. Sequentially, we observed the effects of the monoterpene compound, d-limonene; curcumin derivatives, CD-I and CD-II; polyphenol compound, gallotannin; Salvia miltiorrhiza derivative, SMD; and retinoid acid derivative, RAD on FPTase activity. We found that curcumin derivatives and gallotannin had a strong inhibition on FPTase besides d-limonene, while gallotannin was the strongest among synthetic and natural compounds tested. Salivia miltiorrhiza and retinoid acid derivatives had no influence on FPTase activity. Our results suggest that compounds containing polyphenol hydroxyl may be a new source of FPTase inhibitors. The experiment also showed that availability of an in vitro farnesyl protein transferase assay could be useful in screening for potential inhibitors of ras oncogene function that will not interfere with other aspects of the mevalonate pathway.