Synthesis and biological evaluation of largazole analogues with modified surface recognition cap groups

• The C7-epimer and several C2-modified analogues of largazole were synthesized.
• Their cell growth inhibition and HDAC inhibitory activities were determined.
• Inversion of configuration at C7 position of largazole leads to loss of activity.
• Bulky substituents at C7 position are tolerated if the stereochemistry is retained.
• MD simulations were used to characterize the reduced HDAC-binding of C7-epimer.

Several largazole analogues with modified surface recognition cap groups were synthesized and their HDAC inhibitory activities were determined. The C7-epimer 12 caused negligible inhibition of HDAC activity, failed to induce global histone 3 (H3) acetylation in the HCT116 colorectal cancer cell line and demonstrated minimal effect on growth. Although previous studies have shown some degree of tolerance of structural changes at C7 position of largazole, these data show the negative effect of conformational change accompanying change of configuration at this position. Similarly, analogue 16a with d-1-naphthylmethyl side chain at C2 too had negligible inhibition of HDAC activity, failed to induce global histone 3 (H3) acetylation in the HCT116 colorectal cancer cell line and demonstrated minimal effect on growth. In contrast, the l-allyl analogue 16b and the l-1-naphthylmethyl analogue 16c were potent HDAC inhibitors, showing robust induction of global H3 acetylation and significant effect on cell growth. The data suggest that even bulky substituents are tolerated at this position, provided the stereochemistry at C2 is retained. With bulky substituents, inversion of configuration at C2 results in loss of inhibitory activity. The activity profiles of 16b and 16c on Class I HDAC1 vs Class II HDAC6 are similar to those of largazole and, taken together with x-ray crystallography information of HDAC8-largazole complex, may suggest that the C2 position of largazole is not a suitable target for structural optimization to achieve isoform selectivity. The results of these studies may guide the synthesis of more potent and selective HDAC inhibitors.

Epigenetic regulation of gene expression by targeting histone deacetylase (HDAC) proteins is a novel approach to new therapeutic agents for cancer and other human disorders. The marine natural product largazole is a potent and selective HDAC inhibitor. Analogues of largazole with structural modifications at C2 and C7 positions of the depsipeptide ring were synthesized and their biological properties evaluated. The results will be useful in the design of more potent and selective HDAC inhibitors.Figure optionsDownload as PowerPoint slide