Novel Tricyclic Inhibitors of Farnesyl Protein Transferase

Abstract

Oncogenic forms of Ras proteins are associated with a broad range of human cancers including an estimated 90% of all colon cancers (1). Ras proteins undergo a complex series of posttranslational processing events, which have been defined over the past several years (2, 3). The initial post-translational event is the transfer of the 15-carbon isoprene farnesyl from farnesyl pyrophosphate to a Cys residue (Cys 186 in Ha-Ras) in the conserved carboxyl-terminal "CAAX" motif (where "A" is an aliphatic residue) present in all Ras proteins (4, 5). Studies employing site-directed mutagenesis (6, 7) or inhibitors of hydroxymethylglutaryl-CoA reductase (8), the rate-limiting enzyme in isoprenoid biosynthesis, demonstrated that isoprenylation is required for Ras proteins to become membraneassociated and to induce cellular transformation. The farnesyl protein transferase (FPT) 1 that catalyzes this reaction has been purified (9) and cDNA clones for its ␣ and ␤ subunits isolated (10 -12).A number of other cellular proteins are also isoprenylated on a Cys residue near their COOH terminus (13,14). These include other substrates for FPT, such as the nuclear lamins (15). However, the majority of cellular isoprenylated proteins are modified with geranylgeranyl, a 20-carbon isoprene. Two distinct geranylgeranyl protein transferases (GGPT I and II) have been identified (16,17) and cDNA clones for their ␣ and ␤ subunits isolated (18,19). GGPT I and FPT share a common ␣ subunit (18,20).The primary determinant for recognition of protein substrates by the isoprenyl transferases is the substrate's carboxyl-terminal amino acid sequence. Proteins ending in Cys-X-XSer (or Met) are preferred substrates for FPT, while proteins terminating in Cys-X-X-Leu are preferred substrates for GGPT I (21, 22). Substitution of leucine for serine at the COOH terminus of the Ha-Ras CAAX box (Ser 189 3 Leu) makes this protein a substrate for geranylgeranylation (rather than farnesylation) both in vitro and in cells (23). The different substrate specificities of FPT and GGPT-1 are likely mediated by their distinct ␤ subunits. GGPT II utilizes protein substrates terminating in Cys-Cys or Cys-X-Cys (17,24).A number of inhibitors of FPT have been reported over the past several years (25). The design of CAAX peptidomimetics (26 -29) has resulted in potent and selective FPT inhibitors capable of blocking Ras processing in cells. These compounds have shown considerable promise as antitumor agents based on their ability to inhibit cellular transformation induced by oncogenic Ras proteins (26,27) and the growth of Ras-dependent

Protein Farnesyltransferase from Trypanosoma brucei

“…FTI-277 and GGTI-298 are the methyl ester prodrugs of the free acids FTI-276 and GGTI-297, respectively. FTI-277, L-745,631, SCH-44342, and GGTI-298 apparently penetrate into cells because they block Ras farnesylation or Rap 1A geranylgeranylation in mammalian cells (31,67,68). As reported previously, the Merck compound L-745,631 inhibits mammalian PFT in the low nanomolar range and is highly selective for PFT over PGGT-I (Table II).…”

Cdk inhibitors, roscovitine and olomoucine, synergize with farnesyltransferase inhibitor (FTI) to induce efficient apoptosis of human cancer cell lines

“…The observed e ects include morphological changes, inhibition of anchorage-independent growth and alteration of cell cycle progression (Garcia et al, 1993;James et al, 1993;Kohl et al, 1993;Prendergast et al, 1994;Bishop et al, 1995;Sepp-Lorenzino et al, 1995;Vogt et al, 1997;Suzuki et al, 1998a). We, as well as others, have recently shown that FTI is capable of inducing apoptosis of cancer cell lines (Lebowitz et al, 1997;Hung and Chuang, 1998;Suzuki et al, 1998b;Du et al, 1999).…”

Protein Prenyltransferases

“…The primary driving force for such efforts came from the finding that oncogenic forms of Ras proteins require farnesylation for their ability to transform cells. Inhibitors of FTase that have been synthesized or identified include analogs of both substrates (41)(42)(43)(44), fused forms of the two substrates (45), and a number of natural products and other compounds identified in screening programs (46,47). Many of these inhibitors block Ras processing and inhibit the growth of Ras-transformed cells (41).…”