Histone Methyltransferase Inhibitors Are Orally Bioavailable, Fast-Acting Molecules with Activity against Different Species Causing Malaria in Humans

Abstract

l Current antimalarials are under continuous threat due to the relentless development of drug resistance by malaria parasites. We previously reported promising in vitro parasite-killing activity with the histone methyltransferase inhibitor BIX-01294 and its analogue TM2-115. Here, we further characterize these diaminoquinazolines for in vitro and in vivo efficacy and pharmacokinetic properties to prioritize and direct compound development. BIX-01294 and TM2-115 displayed potent in vitro activity, with 50% inhibitory concentrations (IC 50 s) of <50 nM against drug-sensitive laboratory strains and multidrug-resistant field isolates, including artemisinin-refractory Plasmodium falciparum isolates. Activities against ex vivo clinical isolates of both P. falciparum and Plasmodium vivax were similar, with potencies of 300 to 400 nM. Sexual-stage gametocyte inhibition occurs at micromolar levels; however, mature gametocyte progression to gamete formation is inhibited at submicromolar concentrations. Parasite reduction ratio analysis confirms a high asexual-stage rate of killing. Both compounds examined displayed oral efficacy in in vivo mouse models of Plasmodium berghei and P. falciparum infection. The discovery of a rapid and broadly acting antimalarial compound class targeting blood stage infection, including transmission stage parasites, and effective against multiple malaria-causing species reveals the diaminoquinazoline scaffold to be a very promising lead for development into greatly needed novel therapies to control malaria.T he continuous evolution of antimalarial drug resistance by Plasmodium parasites is a major impediment to the elimination of this devastating disease. Artemisinin combination therapies (ACTs) are the current mainstay of malaria chemotherapy, but the development of artemisinin resistance in parasites was reported in 2008 and 2009 along the Thai-Cambodian border (1). This underscores the need to validate new antimalarial targets within the parasite and to develop new antimalarial treatments based on novel scaffolds with desirable characteristics, such as fast killing activity against multiple parasite life stages; efficacy against multidrug-resistant strains and multiple species of human malaria parasites, including Plasmodium vivax; and favorable pharmacokinetics to allow oral administration.Epigenetic gene regulation mediated by histone-modifying enzymes has been shown to play an important role in malaria parasite transcriptional regulation, including the control of virulence genes involved in immune evasion (2, 3). Histone lysine methyltransferase (HKMT) enzymes present a novel potential target class for the development of antimalarials due to the association of histone methylation at distinct lysine positions with both overall transcriptional activation (H3K4me) and multicopy gene family transcriptional repression (H3K9me) (4, 5). Indeed, half of the identified Plasmodium falciparum HKMT enzymes were recently shown to be refractory to genetic disruption (6). The essential and important re...

Viability Screen of LOPAC 1280 Reveals Phosphorylation Inhibitor Auranofin as a Potent Inhibitor of Blastocystis Subtype 1, 4, and 7 Isolates

“…Because of this, BIX can induce autophagy-associated cell death via G9a dysfunction and intracellular reactive oxygen species production (30). Aside from studies involving human cell lines, BIX has also been studied against other parasites, such as Plasmodium falciparum (31,32). The compound could inhibit the parasite, including its sexual stage.…”

Adaptive immunity is essential in preventing recrudescence ofPlasmodium yoeliimalaria parasites after artesunate treatment

“…To determine the drug sensitivity of PyYM, a short-term ex vivo maturation culture of PyYM was performed (Chang, Malleret, Russell, Renia, & Claser, 2016), and various doses of ART (0.2-1500 ng/ml) were tested ( Figure 1). We also identified that the 50% inhibitory concentration (IC 50 ) of ART for PyYM is 62.14 nM ( Figure S1A), showing to be less susceptible to ART than Plasmodium berghei ANKA and P. falciparum, where in the same assay done independently, their IC 50 was 15.4 and 1.5 nM, respectively (Chang et al, 2016;Malmquist et al, 2015;Suwanarusk et al, 2015).…”

The Role of Chromatin Structure in Gene Regulation of the Human Malaria Parasite

“…Apicidin does so by causing hypermethylation of H3K9 and H4K8 residues, which leads to deregulation of the global transcriptional cascade. Disruption of histone acetylation and methylation levels, and in particular HKMTs, have also been shown to interfere with parasite growth and survival, although so far only a few small molecules potent enough to inhibit HKMT activity in P. falciparum have been identified [122,123]. Targeting HDAC and HKMT classes of enzymes as antimalarial therapies is a promising strategy.…”