Famesyl-protein transferase

To function, Ras must be attached to the plasma membrane. Translocation from the cytoplasm to membrane requires a series of posttranslational modifications that begin with farnesylation of the cysteine residue, the fourth amino acid residue from the C terminus of the protein, by famesyl protein transferase (FPTase) (64). Attachment of the hydrophobic 15-carbon lipid farnesyl group allows Ras molecule insertion into the plasma membrane and is crucial for Ras signaling activity and transformation properties. As farnesylation is required for oncogenic Ras function, FPTase inhibitors (FTIs) are obvious candidate antineoplastic agents. Several drugs that inhibit Ras farnesylation are at various stages of clinical development (65). 

JMC5020>. Imidazole-containing diarylether and diarylsulfone inhibitors of famesyl-protein transferase has been described <99BML3301>. 

Four minor metabolites, psammaplins B-D (503-505) and presammaplin A (506) were isolated from Psammaplysilla purpurea, in addition to psammaplin A (500). Psammaplin B (503) is a thiocyanate bromotyrosine derivative, while psammaplin C (502) is a sulfanamide. Psammaplin D (505) displayed antimicrobial activity and mild tyrosine kinase inhibition [429]. The psammaplins Ai (507) and A2 (508) and aplysinellins A (509) and B (510) were isolated from Aplysinella rhax from both Pohnpei and Palau. These compounds inhibit famesyl protein transferase and leucine aminopeptidase [430]. Another sample of A. rhax from the Great Barrier Reef, Australia contained psammaplin A 11 -sulfate (511) and bisaprasin ll -sulfate (512), both of which inhibited [3H]-l,3-dipropyl-8-cyclopentylxanthine binding to rat brain adenosine Ai receptors [431]. 

The chlorinated cylindrol Bj (168) inhibits bovine famesyl-proteine transferase two-fold more potently (IC5o 2.8 pM) than the corresponding halogen-free analogue [129]. 

Singh SB, Ball RG, Bills GF, Cascales C, Gibbs JB, Goetz MA, Hoogsteen K, Jenkins RG, Liesch JM, Lingham RB, Silverman KC, Zink DL (1996) Chemistry and Biology of Cylindrols Novel Inhibitors of Ras Famesyl-Protein Transferase from Cylindrocarpon lucidum. J Org Chem 61 7727... 

Displacing the Essential Metal Ion in Biomolecules. It is estimated that approximately one third of all enzymes require metal as a cofactor or as a structural component. Those that involve metals as a structural component do so either for catalytic capability, for redox potential, or to confer steric arrangements necessary to protein function. Metals can cause toxicity via substitution reactions in which the native, essential metal is displaced/replaced by another metal. In some cases, the enzyme can still function after such a displacement reaction. More often, however, enzyme function is diminished or completely abolished. For example, Cd can substitute for Zn in the protein famesyl protein transferase, an important enzyme in adding famesyl groups to proteins such as Ras. In this case, Cd diminishes the activity of the protein by 50%. Pb can substitute for Zn in 8-aminolevulinic acid dehydratase (ALAD), and it causes inhibition in vivo and in vitro. ALAD contains eight subunits, each of which requires Zn. Another classic example of metal ions substituting for other metal ions is Pb substitution for Ca in bones. 

Gibbs, J.B., et al. (1993). Selective inhibition of famesyl-protein transferase blocks Ras processing in vivo. J Biol Chem 268 7617-7620. 

TABLE 18.1 Endpoints for Measuring Drug Effect at Different Levels for the New Class of Molecularly Targeted Anticancer Drugs That Inhibit Famesyl Protein Transferase... 

Holstein, S.A.. Cermak. D.M., Wiemer, D.E, Lewis. K.. and Hohl, R.J., Phosphonate and bisphosphonate analogues of fai nesyl pyrophosphate as potential inhibitors of famesyl protein transferase, Bioorg. Med. Chem.. 6. 687, 1998. 

Kaminski JJ, Rane DF, Snow ME, Weber L, Rothofsky ML, Anderson SD, Lin SL. Identification of novel famesyl protein transferase inhibitors using three-dimensional database searching methods. J Med Chem 1997 40 4103 4112. 

In a reaction catalyzed by famesyl protein transferase (FPTase) this SH can be alkylated... 

Scheme 1. Post-translational modification by famesylation. The cysteine as part of the consensus sequence CAAX (C, cysteine A, aliphatic amino acid residue X, serine or methionine) near the C-terminus in the Ras protein is famesylated by famesylpyrophosphate (FPP) catalyzed by famesyl protein transferase (FPTase). The famesylated protein can then attach itself to the plasma membrane. If mutated Ras proteins are famesylated and attached to the cell membrane this will lead to transformation.

Njoroge, F.G., Taveras, A.G., Kelly, J., Remiszewski, S., Mallams, A.K.,etaZ.(1998)( -t- )-4-[2-[4-(8-Chloro-3,10-dibromo-6,ll-dihydro-5H-benzo[5,6]cyclohepta[ 1,2-b]-pyridin-11 (R)-yl)-1 -piperidinyl]-2-oxo-ethyl]-l-piperidinecarboxamide (SCH-66336) a very potent famesyl protein transferase inhibitor as a novel antitumor agent. J. Med. Chem. 41 4890-4902. 

Liu, M., Bryant, M.S., Chen, J., Lee, S., Yaremko, B., et al. (1998) Antitumor activity of SCH 66336, an orally bioavailable tricyclic inhibitor of famesyl protein transferase, in human tumor xenograft models and wap-ras transgenic mice. Cancer Res. 58 4947-4956. 

Prenyl-protein transferases consist of three members that include famesyl-protein transferase (FPTase) and two isoforms of geranylgerany 1-protein (GGPTase I and II) transferase. Farnesyl and geranylgerany 1 protein transferases catalyze the transfer of 15-carbon or 20-carbon isoprene units, respectively, to specific intracellular signaling proteins. The prenyl-protein transferase proteins are heterodimers consisting of a and P-subunits with approximate molecular weights of 48,000 and 45,000 Da, respectively [29]. 

Several non-peptide small molecule compoimds from Merck, Schering-Plough, Bristol-Myers Squibb, and Janssen are in phase I clinical trials for the treatment of cancer. This has bolstered the significance of this approach of cancer chemotherapy. Other organizations that have ongoing active FPTase inhibitor programs include Abbott, Rhone Poulenc Rorer, Parke- Davis, Pfizer, Zeneca, Eisai and Biomeasure. While several review articles have recently been published that cover various aspects of FPTase inhibitors [25-28,31,60,61], the discussion of FPTase inhibitors derived from natural products is limited. Therefore, this article will not be an extensive review of the literature dealing with chemically derived inhibitors of farnesyl-protein transferase. Rather, it will focus on inhibitors of famesyl-protein transferase that have been identified from natural product sources discovered by Merck or other institutions. 

Both the mixed stems and stem bark, and the stems CHCls-soluble extracts of L. wallichii Kurz, were found to display significant inhibitory activity in a famesyl protein transferase (FPTase) assay system. It has been suggested that inhibitors of this enzyme may be considered as potential anticancer agents for tumors in which products of the ras oncogene contribute to transformation. The bioassay directed fractionation of the two active extracts [213] led to the isolation of the known lupane lactones, ochraceolide A (128), ochraceolide B (129), and the new compound dihydroochraceolide A (135), among other known triterpenes. The structure of 135 was confirmed by reduction of 128, Fig. (37) and the stereochemistry to the epoxide group of 129, not determined when this compound was first isolated from K. ochracea [211], was established by preparation of both epoxide isomers, 129 and the new semisynthetic derivative, 20-epi-ochraceolide B (136) from 128. 

Singh, J., Hamid, R., and Reddy, B.S., 1998, Dietary fish oil inhibits the expression of famesyl protein transferase and colon tumor development in rodents. Carcinogenesis, 19, 985. 

Data for Z. A IC50 (rat SQS) 15 nMol lowering of the cholesterol level in marmosets by 50% after 7 daily doses of 10 mg/kg. SQS catalyzes the reductive dimerization of famesyl pyrophosphate to squalene. All Z. thus show pronounced antifungal activities (IC50 in nMol range). As inhibitors of famesyl protein transferase the Z. are potential cytostatic agents. Several total syntheses of the Z. have been reported. Z. are structurally related to the CP compounds CP-225,9I7 and CP-263,1141... 

Figure 2 The use of a 3D hypothesis model to focus a virtual library on compounds possessing the activity pattern. Through the use of generalized chemical features, diverse compounds are chosen from which a library subset can be selected. The hypothesis shown is for famesyl protein transferase...

Wallace, A., Koblan, K.S., Hamilton, K., Marquis-Omer, D.J., Miller, P.J., Mosser, S.D., Omer, C.A., Schaber, M.D., Cortese, R., Oliff, A., Gibbs, J.B. and Pessi, A., Selection of potent inhibitors of famesyl-protein transferase from a synthetic tetrapeptide combinatorial library, J. Biol. Chem., 271... 

Ciccarone TM, MacTough SC, Williams TM et al (1999) Non-thiol 3-aminomethylbenzamide inhibitors of famesyl-protein transferase. Bioorg Med Chem Lett 9 1991-1996... 

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