Isoprenyl cysteine carboxymethyl transferase (ICMT) performs the final step in the post-translational modification of proteins bearing a C-terminal –Caax motif. Following isoprenylation of the cysteine residue and cleavage of the three terminal peptides, ICMT utilizes S-adenosyl-methionine as a substrate to methylate the C-terminal cysteine. This process is necessary for appropriate membrane localisation and protein stabilisation and there are >100 proteins that contain the C-term-Caax motif including the Ras, Rho and Rab families. As many of these proteins are involved in regulating various pathways critical in tumourigenesis ICMT presents itself as an possible anti-cancer target.
An in vitro Scintillation Promixity Assay (SPA)-based ICMT bioassay was used to perform high-throughput screening of chemical libraries to identify inhibitors with potential anti-cancer activity. A selection of actives was subjected to a lead identification programme that included the high content imaging of ICMT client proteins as a means of confirming small molecule inhibitors able to inhibit the protein methylation step. The outcomes from these studies will be presented.