Mutational activation of ras oncogene products (p21s) is involved in the loss of growth control in a high percentage of human tumors. Consequently, significant attention has focused on defining the biochemistry and pharmacology of p21s, with the ultimate goal of developing inhibitors of p21 to be used as antitumor drugs. P21s require extensive post-translational processing to express optimal transforming ability, including attachment of farnesyl and palmitoyl moieties to cysteine residues near the C-terminus. Several inhibitors of farnesyltransferase have been described; however, no selective inhibitors of the palmitoylation step have yet been reported. The applicant has identified the natural product cerulenin as the first compound with such anti-p21 activity. The compound potently inhibits the proliferation of H-ras-transformed cells in parallel with inhibition of palmitate incorporation into p21 and accumulation of p21 in the cell cytosol. In contrast, cerulenin does not inhibit lipid acylation or protein myristoylation. Preliminary structure-activity studies indicate that cerulenin analogs can be efficiently synthesized, which will allow optimization of potency and selectivity for p21:acyltransferase. Studies to be conducted will further define the biochemical and cellular mechanisms of action of cerulenin and analogs, with focus on its inhibition of p21 processing. The selectivity of the actions of these compounds toward palmitoylated species of p21 versus K-ras p21 will be determined. P21:acyl-transferase will be isolated and characterized at both the protein and DNA level. Cerulenin analogues will be synthesized and tested for activity in cell- and enzyme-based assays, and as antitumor agents for xenografts of ras-transformed cells. These studies should allow evaluation of p21:acyltransferase as a target for new anticancer drugs.
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