Significant effort is being made to understand the role of HDAC isotypes in human cancer and to develop antitumor agents with better therapeutic windows. A part of this endeavor was the exploration of the 14 A internal cavity adjacent to the enzyme catalytic site, which led to the design and synthesis of compound 4 with the unusual bis(aryl)-type pharmacophore. SAR studies around this lead resulted in optimization to potent, selective, nonhydroxamic acid HDAC inhibitors.

The design, synthesis, and biological evaluation of N-(2-aminophenyl)-4-[(4-pyridin-3-ylpyrimidin-2-ylamino)methyl]benzamide 8 (MGCD0103) is described. Compound 8 is an isotype-selective small molecule histone deacetylase (HDAC) inhibitor that selectively inhibits HDACs 1-3 and 11 at submicromolar concentrations in vitro. 8 blocks cancer cell proliferation and induces histone acetylation, p21 (cip/waf1) protein expression, cell-cycle arrest, and apoptosis. 8 is orally bioavailable, has significant antitumor activity in vivo, has entered clinical trials, and shows promise as an anticancer drug.

Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are enzymes that catalyze the deacetylation and acetylation of lysine residues located in the NH(2) terminal tails of histones and non-histone proteins. Perturbation of this balance is often observed in human cancers and inhibition of HDACs has emerged as a novel therapeutic strategy against cancer. To date, more that 30 groups, academic and industrial, are involved in research related to these target enzymes. Over the past year, dozens of research papers and patent applications describing new HDAC inhibitors belonging to different structural classes have been disclosed. The present review highlights the latest developments in design and synthesis of HDAC inhibitors -- potential anti-cancer drugs.

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