Development of new Rac1 inhibitors as potential pharmacological agents for the treatment of atherosclerosis

Experimental and clinical observations have documented the role of the small GTPase Rac1 protein and cardiovascular diseases opening to the development of new potential pharmacological intervention. In this study we characterized a new class of selective small molecule Rac inhibitors with the 3-aryl-1H-pyrazole-5-carboxamide nucleus. Starting from our previous identification of Rac inhibitors [1], through a computational approach, 57 chemical entities were identified and their Rac inhibitory efficacy evaluated by G-LISA assay. 23 compounds were found to reduce, Rac-GTP levels in cultured cells by more than 24.8%. A comparative analysis at 25 μM was then performed and compounds 1, 2, 3, 11 and 21 resulted the most potent. Compounds 1, 2, 3 and 21 did not affect the activation of RhoA protein, while compound 11 partially reduced RhoA-GTP levels. The IC50s for Rac inhibition of these compounds were between 2.9 and 29.1 μM and similar potencies were observed in a cell adhesion assay, a Rac1-dependent cellular event. From these analysis it was selected compound 2 as a most promising inhibitor to test in in-vitro and in-vivo models of atherosclerosis. Compound 2 profoundly affected cytoskeleton organization of cultured human SMCs and inhibited SMC migration in response to PDGF-BB in a concentration dependent manner with an IC50 value of 5.8 µM. More interestingly, incubation of human monocytic cell line THP-1 with Compound 2 (10 µM) completely abrogated their adhesion to cultured human umbilical endothelial cells (HUVEC) indicating a potent anti-inflammatory activity. Taken together, in the present study we identified a new selective small molecule Rac inhibitor capable to interfere with SMC migration and monocyte-endothelial cell adhesion, two pivotal features of atherogenesis. Further analysis will be carried out to test the effect of compound 2 on spontaneous atherosclerotic plaque development in apoE-/- mice. [1] Ferri N, Corsini A, Bottino P, Clerici F, Contini A, J Med Chem 2009, 52; 4087-4090.