Evaluation of histone deacetylase inhibitors (HDACi) as therapeutic leads for human African trypanosomiasis (HAT).

Two of the histone deacetylases, TbDAC1 and TbDAC3, have been reported to be essential genes in trypanosomes. Therefore, we tested the activity of a panel of human histone deacetylase inhibitors (HDACi) for their ability to block proliferation of Trypanosoma brucei brucei. Among the HDACi's, the hydroxamic acid derivatives panobinostat and belinostat exhibited potency that appeared to make them viable candidates for development due to their reported pharmacokinetic characteristics. However, cellular pharmacodynamic analysis demonstrated that these drugs were unable to kill cultured parasites at exposures seen in patients at their tolerated doses and additionally failed to show any synergistic effects in combination with pentamidine, suramin, melarsoprol, or nifurtimox. Analysis of the potency of the entire HDACi panel revealed no correlations between potency against any human HDAC isoform and inhibition of T. brucei proliferation, suggesting that the trypanosome histone deacetylases possess a unique specificity. These studies confirmed that HDAC inhibitors have potential as leads against human African trypanosomiasis but that none of the current clinical candidates can be directly repurposed. Therefore, development of HDACi's with appropriate specificity and potency may be a viable route to a new class of anti-trypanosomal drugs.