Potent inhibition of human tumor p21ras farnesyltransferase by A1A2-lacking p21ras CA1A2X peptidomimetics.

The ras oncogene product p21ras requires farnesylation and subsequent plasma membrane association for its transforming activity. This key post-translational modification is catalyzed by p21ras farnesyltransferase, which transfers farnesyl from farnesylpyrophosphate to the cysteine of the CA1A2X carboxyl-terminal tetrapeptide of p21ras. In the present report, we describe potent inhibition of p21ras farnesyltransferase by CA1A2X peptidomimetics containing no peptidic amide bonds. We synthesized a series of CA1A2X analogues where the 2 aliphatic amino acids A1 and A2 were replaced by a hydrophobic spacer, 3-aminomethylbenzoic acid (AMBA). The peptidomimetic Cys-AMBA-Met, inhibits p21ras farnesyltransferase from human colon carcinoma (COLO-205) and Burkitt's lymphoma (Daudi) with IC50 values of 60 and 120 nM, respectively. Cys-AMBA-Met is 3-, 8-, and 9-fold (COLO-205) and 2-, 5-, and 7-fold (Daudi) more potent than the corresponding tetrapeptides of p21KB-ras (CVIM), p21N-ras (CVVM), and p21KA-ras (CIIM), respectively. Replacing methionine at the X position with negatively charged glutamate reduces its ability to inhibit the enzyme, whereas positively charged lysine at this position abolishes the inhibitory character of the peptidomimetic. A hydrophobic moiety at the X position, as in Cys-AMBA-Phe, retains potent inhibitory activity. Leucine in the X position of CA1A2X is a post-translational signal for protein geranylgeranylation rather than farnesylation, and, as expected, Cys-AMBA-Leu does not inhibit the enzyme. Furthermore, CVIM, CVVM, and CIIM are farnesylated by human p21ras farnesyltransferases and inhibit these enzymes by serving as alternative substrates. In contrast, the peptidomimetics described here are true p21ras farnesyltransferase inhibitors since none is farnesylated by this enzyme.