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Dynamics of epigenetic modifications such as acetylation and deacetylation of histone proteins have been shown to be crucial for the life cycle development and survival of Plasmodium falciparum, the deadliest malaria parasite. In this study, we present a novel series of peptoid-based histone deacetylase (HDAC) inhibitors incorporating nitrogen-containing bicyclic heteroaryl residues as a new generation of antiplasmodial peptoid-based HDAC inhibitors. We synthesized the HDAC inhibitors by an efficient multicomponent protocol based on the Ugi four-component reaction. The subsequent screening of 16 compounds from our mini-library identified 6i as the most promising candidate, demonstrating potent activity against asexual blood-stage parasites (IC 50 Pf3D7 = 30 nM; IC 50 PfDd2 = 98 nM), low submicromolar activity against liver-stage parasites (IC 50 PbEEF = 0.25 μM), excellent microsomal stability (t 1/2  > 60 min), and low cytotoxicity to HEK293 cells (IC 50  = 136 μM)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Masson SAS.. All rights reserved.)

Histone deacetylases (HDACs) have been identified as emerging antiplasmodial drug targets. In this work, we report on the synthesis, structure-activity relationships, metabolic stability and in vivo efficacy of new peptoid-based HDAC inhibitors with dual-stage antiplasmodial activity. A mini library of HDAC inhibitors was synthesized using a one-pot, multi-component protocol or submonomer pathways. The screening of the target compounds for their activity against asexual blood stage parasites, human cell cytotoxicity, liver stage parasites, and selected human HDAC isoforms provided important structure-activity relationship data. The most promising HDAC inhibitor from this series, compound 3n, demonstrated potent activity against drug-sensitive and drug-resistant asexual stage P. falciparum parasites and was selective for the parasite versus human cells (Pf3D7 IC 50 0.016 μM; SI HepG2/Pf3D7 573; PfDd2 IC 50 0.002 μM; SI HepG2/PfDd2 4580) combined with activity against P. berghei exoerythrocytic liver stages (PbEEF IC 50 0.48 μM). While compound 3n displayed high stability in human (Cl int 5 μL/min/mg) and mouse (Cl int 6 μL/min/mg) liver microsomes, only modest oral in vivo efficacy was observed in P. berghei infected mice. Together these data provide a foundation for future work to improve the properties of these dual-stage inhibitors as drug leads for malaria., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Histone deacetylase (HDAC) enzymes are targets for the development of antimalarial drugs with a different mode of action to established antimalarials. Broad-spectrum HDAC-inhibitors show high potency against Plasmodium falciparum, but displayed some toxicity towards human cells. Inhibitors of human HDAC6 are new drug candidates with supposed reduced toxicity to human cells and favorable activities against laboratory P. falciparum strains. We investigated the potency of 12 peptoid-based HDAC-inhibitors against asexual stages of P. falciparum clinical isolates. Parasites representing different genetic backgrounds were isolated from adults and children with uncomplicated malaria in Gabon. Clinical studies on (non-HDAC-inhibitors) antimalarials, moreover, found lower drug efficacy in children, mainly attributed to acquired immunity with age in endemic areas. Therefore, we compared the in vitro sensitivity profiles of adult- and child-derived isolates to antimalarials (HDAC and standard drugs). All HDAC-inhibitors showed 50% inhibitory concentrations at nanomolar ranges with higher activities than the FDA approved reference HDAC-inhibitor SAHA. We propose peptoid-based HDAC6-inhibitors to be lead structures for further development as antimalarial chemotherapeutics. Our results further suggest no differences in activity of the tested antimalarials between P. falciparum parasites isolated from children and adults.

Novel malaria intervention strategies are of great importance, given the development of drug resistance in malaria-endemic countries. In this regard, histone deacetylases (HDACs) have emerged as new and promising malaria drug targets. In this work, we present the design, synthesis, and biological evaluation of 20 novel HDAC inhibitors with antiplasmodial activity. Based on a previously discovered peptoid-based hit compound, we modified all regions of the peptoid scaffold by using a one-pot multicomponent pathway and submonomer routes to gain a deeper understanding of the structure-activity and structure-toxicity relationships. Most compounds displayed potent activity against asexual blood-stage P. falciparum parasites, with IC 50 values in the range of 0.0052-0.25 μm and promising selectivity over mammalian cells (SI Pf3D7/HepG2 : 170-1483). In addition, several compounds showed encouraging sub-micromolar activity against P. berghei exo-erythrocytic forms (PbEEF). Our study led to the discovery of the hit compound N-(2-(benzylamino)-2-oxoethyl)-N-(4-(hydroxycarbamoyl)benzyl)-4-isopropylbenzamide (2 h) as a potent and parasite-specific dual-stage antiplasmodial HDAC inhibitor (IC 50  Pf3D7=0.0052 μm, IC 50  PbEEF=0.016 μm)., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Malaria drug discovery has shifted from a focus on targeting asexual blood stage parasites, to the development of drugs that can also target exo-erythrocytic forms and/or gametocytes in order to prevent malaria and/or parasite transmission. In this work, we aimed to develop parasite-selective histone deacetylase inhibitors (HDACi) with activity against the disease-causing asexual blood stages of Plasmodium malaria parasites as well as with causal prophylactic and/or transmission blocking properties. An optimized one-pot, multi-component protocol via a sequential Ugi four-component reaction and hydroxylaminolysis was used for the preparation of a panel of peptoid-based HDACi. Several compounds displayed potent activity against drug-sensitive and drug-resistant P. falciparum asexual blood stages, high parasite-selectivity and submicromolar activity against exo-erythrocytic forms of P. berghei. Our optimization study resulted in the discovery of the hit compound 1u which combines high activity against asexual blood stage parasites (Pf 3D7 IC 50 : 4 nM; Pf Dd2 IC 50 : 1 nM) and P. berghei exo-erythrocytic forms (Pb EEF IC 50 : 25 nM) with promising parasite-specific activity (SI Pf 3D7/HepG2 : 2496, SI Pf Dd2/HepG2 : 9990, and SI Pb EEF/HepG2 : 400)., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Despite recent declines in mortality, malaria remains an important global health problem. New therapies are needed, including new drugs with novel modes of action compared to existing agents. Among new potential therapeutic targets for malaria, inhibition of parasitic histone deacetylases (HDACs) is a promising approach. Homology modeling of PfHDAC1, a known target of some anti-plasmodial HDAC inhibitors, revealed a unique threonine residue at the rim of the active site in close proximity to the location of the cap group of vorinostat-type HDAC inhibitors. Aiming to obtain HDAC inhibitors with potent and preferential anti-plasmodial activity, we synthesized a mini-library of alkoxyamide-based HDAC inhibitors containing hydrogen bond acceptors in the cap group. Using a 5-step synthetic route, 12 new inhibitors were synthesized and assayed against Plasmodium falciparum asexual blood stage parasites (clones 3D7 and Dd2) and human cells (HepG2). The most active compound 6h (Pf3D7 IC 50 : 0.07 µM; PfDd2 IC 50 : 0.07 µM) was 25-fold more toxic against the parasite versus human HepG2 cells. Selected compounds were shown to cause hyperacetylation of P. falciparum histone H4, indicating inhibition of one or more PfHDACs., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Histone deacetylase (HDAC) inhibitors are an emerging class of potential antimalarial drugs. We investigated the antiplasmodial properties of 16 alkoxyurea-based HDAC inhibitors containing various cap and zinc binding groups (ZBGs). Ten compounds displayed sub-micromolar activity against the 3D7 line of Plasmodium falciparum. Structure-activity relationship studies revealed that a hydroxamic acid ZBG is crucial for antiplasmodial activity, and that the introduction of bulky alkyl substituents to cap groups increases potency against asexual blood-stage parasites. We also demonstrate that selected compounds cause hyperacetylation of P. falciparum histone H4, indicating inhibition of one or more PfHDACs. To assess the selectivity of alkoxyurea-based HDAC inhibitors for parasite over normal mammalian cells, the cytotoxicity of representative compounds was evaluated against neonatal foreskin fibroblast (NFF) cells. The most active compound, 6-((3-(4-(tert-butyl)phenyl)ureido)oxy)-N-hydroxyhexanamide (1 e, Pf3D7 IC50 : 0.16 μM) was 31-fold more toxic against the asexual blood stages than towards normal mammalian cells. Moreover, a subset of four structurally diverse HDAC inhibitors revealed moderate activity against late-stage (IV-V) gametocytes., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Artemisinin-based combination therapies (ACTs) are the gold standard for the treatment of malaria, but the efficacy is threatened by the development of parasite resistance. Histone deacetylase inhibitors (HDACis) are an emerging new class of potential antiplasmodial drugs. In this work, we present the design, synthesis, and biological evaluation of a mini library of dihydroartemisinin–HDACi hybrid molecules. The screening of the hybrid molecules for their activity against selected human HDAC isoforms, asexual blood stage P. falciparum parasites, and a panel of leukemia cell lines delivered important structure–activity relationships. All synthesized compounds demonstrated potent activity against the 3D7 and Dd2 line of P. falciparum with IC50 values in the single-digit nanomolar range. Furthermore, the hybrid (α)-7c displayed improved activity against artemisinin-resistant parasites compared to dihydroartemisinin. The screening of the compounds against five cell lines from different leukemia entities revealed that all hydroxamate-based hybrids (7a–e) and the ortho-aminoanilide 8 exceeded the antiproliferative activity of dihydroartemisinin in four out of five cell lines. Taken together, this series of hybrid molecules represents an excellent starting point toward the development of antimalarial and antileukemia drug leads. [ABSTRACT FROM AUTHOR]

A small series of histone deacetylase (HDAC) inhibitors (VI) are synthesized and evaluated together with previously described HDAC inhibitors for their antiplasmodial properties. [ABSTRACT FROM AUTHOR]