Profiling the anti-protozoal activity of anti-cancer HDAC inhibitors against Plasmodium and Trypanosoma parasites.

Histone deacetylase (HDAC) enzymes work together with histone acetyltransferases (HATs) to reversibly acetylate both histone and non-histone proteins. As a result, these enzymes are involved in regulating chromatin structure and gene expression as well as other important cellular processes. HDACs are validated drug targets for some types of cancer, with four HDAC inhibitors clinically approved. However, they are also showing promise as novel drug targets for other indications, including malaria and other parasitic diseases. In this study the in vitro activity of four anti-cancer HDAC inhibitors was examined against parasites that cause malaria and trypanosomiasis. Three of these inhibitors, suberoylanilide hydroxamic acid (SAHA; vorinostat(®)), romidepsin (Istodax(®)) and belinostat (Beleodaq(®)), are clinically approved for the treatment of T-cell lymphoma, while the fourth, panobinostat, has recently been approved for combination therapy use in certain patients with multiple myeloma. All HDAC inhibitors were found to inhibit the growth of asexual-stage Plasmodium falciparum malaria parasites in the nanomolar range (IC50 10-200 nM), while only romidepsin was active at sub-µM concentrations against bloodstream form Trypanosoma brucei brucei parasites (IC50 35 nM). The compounds were found to have some selectivity for malaria parasites compared with mammalian cells, but were not selective for trypanosome parasites versus mammalian cells. All compounds caused hyperacetylation of histone and non-histone proteins in P. falciparum asexual stage parasites and inhibited deacetylase activity in P. falciparum nuclear extracts in addition to recombinant PfHDAC1 activity. P. falciparum histone hyperacetylation data indicate that HDAC inhibitors may differentially affect the acetylation profiles of histone H3 and H4.

Lysine acetylation in sexual stage malaria parasites is a target for antimalarial small molecules.

Therapies to prevent transmission of malaria parasites to the mosquito vector are a vital part of the global malaria elimination agenda. Primaquine is currently the only drug with such activity; however, its use is limited by side effects. The development of transmission-blocking strategies requires an understanding of sexual stage malaria parasite (gametocyte) biology and the identification of new drug leads. Lysine acetylation is an important posttranslational modification involved in regulating eukaryotic gene expression and other essential processes. Interfering with this process with histone deacetylase (HDAC) inhibitors is a validated strategy for cancer and other diseases, including asexual stage malaria parasites. Here we confirm the expression of at least one HDAC protein in Plasmodium falciparum gametocytes and show that histone and nonhistone protein acetylation occurs in this life cycle stage. The activity of the canonical HDAC inhibitors trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA; Vorinostat) and a panel of novel HDAC inhibitors on early/late-stage gametocytes and on gamete formation was examined. Several compounds displayed early/late-stage gametocytocidal activity, with TSA being the most potent (50% inhibitory concentration, 70 to 90 nM). In contrast, no inhibitory activity was observed in P. falciparum gametocyte exflagellation experiments. Gametocytocidal HDAC inhibitors caused hyperacetylation of gametocyte histones, consistent with a mode of action targeting HDAC activity. Our data identify HDAC inhibitors as being among a limited number of compounds that target both asexual and sexual stage malaria parasites, making them a potential new starting point for gametocytocidal drug leads and valuable tools for dissecting gametocyte biology.

Antimalarial activity of compounds comprising a primary benzene sulfonamide fragment.

Despite the urgent need for effective antimalarial drugs with novel modes of action no new chemical class of antimalarial drug has been approved for use since 1996. To address this, we have used a rational approach to investigate compounds comprising the primary benzene sulfonamide fragment as a potential new antimalarial chemotype. We report the in vitro activity against Plasmodium falciparum drug sensitive (3D7) and resistant (Dd2) parasites for a panel of fourteen primary benzene sulfonamide compounds. Our findings provide a platform to support the further evaluation of primary benzene sulfonamides as a new antimalarial chemotype, including the identification of the target of these compounds in the parasite.

Antimalarial activity of the anticancer histone deacetylase inhibitor SB939.

Histone deacetylase (HDAC) enzymes posttranslationally modify lysines on histone and nonhistone proteins and play crucial roles in epigenetic regulation and other important cellular processes. HDAC inhibitors (e.g., suberoylanilide hydroxamic acid [SAHA; also known as vorinostat]) are used clinically to treat some cancers and are under investigation for use against many other diseases. Development of new HDAC inhibitors for noncancer indications has the potential to be accelerated by piggybacking onto cancer studies, as several HDAC inhibitors have undergone or are undergoing clinical trials. One such compound, SB939, is a new orally active hydroxamate-based HDAC inhibitor with an improved pharmacokinetic profile compared to that of SAHA. In this study, the in vitro and in vivo antiplasmodial activities of SB939 were investigated. SB939 was found to be a potent inhibitor of the growth of Plasmodium falciparum asexual-stage parasites in vitro (50% inhibitory concentration [IC(50)], 100 to 200 nM), causing hyperacetylation of parasite histone and nonhistone proteins. In combination with the aspartic protease inhibitor lopinavir, SB939 displayed additive activity. SB939 also potently inhibited the in vitro growth of exoerythrocytic-stage Plasmodium parasites in liver cells (IC(50), ~150 nM), suggesting that inhibitor targeting to multiple malaria parasite life cycle stages may be possible. In an experimental in vivo murine model of cerebral malaria, orally administered SB939 significantly inhibited P. berghei ANKA parasite growth, preventing development of cerebral malaria-like symptoms. These results identify SB939 as a potent new antimalarial HDAC inhibitor and underscore the potential of investigating next-generation anticancer HDAC inhibitors as prospective new drug leads for treatment of malaria.