Prenylation of cysteine sulfhydryls is a critical post- translational modification that occurs in all eucaryotic cells. It is crucial to the biological activity of a series of signal transduction proteins including Ras proteins. Mutant Ras proteins are involved in about 30 percent of human cancers, and this fact has led to intense interest in protein-farnesyltransferase (FTase) inhibitors as potential cancer chemotherapeutic agents. A second active area of interest concerning protein prenylation has been the specific biological function of this modification. The central hypothesis of this proposal is that the prenyl group plays an active role in the targeting of the prenylated protein to the proper position inside the cell. An important corollary to this hypothesis is that modifications to the prenyl structure may lead to significant, biologically relevant effects on the activity of the unnaturally prenylated protein. The principal investigator's laboratory, in collaboration with other groups, has obtained two preliminary pieces of evidence in support of this corollary. The first specific aim of this proposal provides a test of the corollary and targets medically relevant processes. The second and third aims provide more basic tests of the hypothesis, and will generate knowledge that will inform the inhibitor design under aim 1. 1)Specifically substituted analogs of farnesyl diphosphate and the homologous isoprenoid geranylgeranyl diphosphate will be synthesized. These compounds will then be assayed as substrates or inhibitors of FTase and the closely related enzyme protein geranylgeranyltransferase I. Building on promising preliminary results in this area, select compounds from these assays will be tested as inhibitors of the growth of ras- transformed cells and various human cancer cell lines. 2) Certain farnesyl analogs available from the studies described in specific aim 1 will be elaborated to the corresponding a-factor yeast pheromone analogs. These compounds will then be tested for biological activity in a variety of well-established assay systems to provide information on the farnesyl group SAR in a tractable model system. 3) Various 13-C- labeled farnesyl derivatives will be synthesized. Labeled farnesyl diphosphates and solid state NMR will be utilized to determine the conformation of the farnesyl group in the FTase active site. Several labeled farnesylated peptides and proteins will also be prepared to investigate the conformation of the farnesyl moiety in various membrane environments.
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