Inhibitors of prenylation of Ras and other G-proteins and their application as therapeutics

Anchoring of small G-proteins to cellular membranes via a covalently bound lipophylic prenyl group is essential fur the functioning of these proteins. For example, the farnesylation of Ras by the action of the enzyme protein: farnesyl transferase (PFT) is pivotal for its signalling function in cell g rowth and differentiation The development of inhibitors of PFT was triggere d by the role of mutated Ras in certain types of cancer and by the observat ion that non-farnesylated Ras is inactive. Besides the screening of existin g compounds for PFT inhibition, rational drug design has also led cu new in hibitors. Our research is in the field of atherosclerosis and concerns the development of inhibitors of the growth of vascular smooth muscle cells. Th e latter process gives rise to reocclusion of the coronary artery (restenos is) after balloon angioplasty. We and others have developed several analogu es of the two substrates of PFT, i.e. farnesyl pyrophosphate (FPP) and the so-called CAAX peptide consensus sequence, which were tested in vitro for t he inhibition of PFT and of other enzymes involved in protein prenylation, such as protein:geranylgeranyl transferase-1 (PGGT-1). The FPP analogue TR0 06, a strong inhibitor of PFT (IC50 of 67 nM), blocked the proliferation of cultured human smooth muscle cells and inhibited platelet-derived growth f actor- and basic fibroblast growth factor-induced DNA synthesis. Similar bu t more highly charged compounds failed in this respect, probably because of an impaired uptake in the cells. Less charged derivatives were designed to circumvent this problem. The effect on the GF-induced activation of interm ediates in signal transduction pathways was investigated in order to gain i nsight into the mechanism of action within the cells. TR006 decreased the b FGF activation of extracellular signal-regulated kinase 1 (ERK1), suggestin g its involvement in inhibiting Ras activity. Although other analogues inhi bited DNA synthesis, they affected neither ERK1 activation nor p38/stress-a ctivated protein kinase 2 or Jun N-terminal kinase 1 activation. Since some of these compounds were also shown to be inhibitors of in vitro PGGT-1 act ivity, the geranylgeranylation of other G-proteins may be decreased by thes e compounds. Rho seems to be a good candidate as a target for inhibitors of PGGT-1. This uncertainty as to the mechanism of action within non-transfor med as well as transformed cells applies to all prenylation inhibitors, but is not holding back their further development as drugs. Their current and possible future application as therapeutics in cancer, restenosis, angiogen esis, and osteoporosis is briefly discussed. BIOCHEM PHARMACOL 60;8:1061-10 68, 2000. (C) 2000 Elsevier Science Inc.