Inhibition of human smooth muscle cell proliferation in culture by farnesyl pyrophosphate analogues, inhibitors of in vitro protein : farnesyl transferase

In this study, it was investigated whether and how inhibitors of protein:fa rnesyl transferase (PFT) can inhibit the proliferation of human smooth musc le cells (HSMC) in culture. Several farnesyl pyrophosphate (FPP) analogues were synthesized and tested in vitro for their specificity in inhibiting sq ualene synthase (SS), PFT, or protein:geranylgeranyl transferase-1 (PGGT-1) activities (the latter was determined using a newly designed assay). One o f these compounds appeared to be a strong PFT inhibitor (IC50, value: 340 n M) and a weak inhibitor in the other two enzyme assays. This compound (desi gnated as TR006) inhibited the farnesylation of Ras in a Ha-ras transfected cell line (Cohen et al., Biochem Pharmacol 49: 839-845, 1995) and concomit antly slowed down the growth of these cells. Twenty-five mu M of TR006 inhi bited the proliferation of HSMC isolated from left internal mammary artery, as measured by counting the cells over a period of three cell cycles (10 d ays). A structurally related compound (TR007), a specific SS inhibitor, did not influence HSMC proliferation under the same conditions. The inhibition by TR006 was concentration-dependent. In HSMC, synchronized by serum deple tion, platelet-derived growth factor (PDGF) or basic fibroblast growth fact or (bFGF)-induced DNA synthesis was decreased by a 29-hr pretreatment with 100 mu M of TR006, indicating that this inhibitor acted in an early phase o f the cell cycle, probably by preventing protein isoprenylation. Some other FPP analogues with comparable IC50 values in the in vitro PFT assay were a lso able to decrease bFGF-induced DNA synthesis without affecting cell viab ility. A more negatively charged member of this group, TR018, did not influ ence the growth factor-induced DNA synthesis, probably due to an impaired u ptake into the cells. However, the pivaloyloxomethyl derivative of this com pound, which is uncharged, and is thought to be converted into TR018 within the cells, showed a strong decrease in bFGF-induced DNA synthesis in HSMC. These data suggest that the compounds investigated may be developed furthe r for treatment of conditions in which undesirable proliferation of smooth muscle cells plays an important role. (C) 1999 Elsevier Science Inc.