Optimization of 2-(1H-imidazo-2-yl)piperazines series of Trypanosoma brucei growth inhibitors as potential treatment for the second stage of HAT

A previous publication from our laboratory reported the identification of a new class of 2-(1H-imidazo-2-yl)piperazines as potent T. brucei growth inhibitors as potential treatment for Human African Trypanosomiasis (HAT). This work describes the structure–activity relationship (SAR) around the hit compound 1, which led to the identification of the optimized compound 18, a single digit nanomolar inhibitor (EC₅₀ 7 nM), not cytotoxic and with optimal in vivo profile that made it a suitable candidate for efficacy studies in a mouse model mimicking the second stage of disease.     

Synthesis and biological evaluation of isoxazolyl-sulfonamides: A non-cytotoxic scaffold active against Trypanosoma cruzi, Leishmania amazonensis and Herpes Simplex Virus

In this study we report the synthesis, characterization, biological evaluation, and druglikeness assessment of a series of 20 novel isoxazolyl-sulfonamides, obtained by a four-step synthetic route. The compounds had their activity against Trypanosoma cruzi, Leishmania amazonensis, Herpes Simplex Virus type 1 and cytotoxicity evaluated in phenotypic assays. All compounds have drug-like properties, showed low cytotoxicity and were promising regarding all other biological activities reported herein, especially the inhibitory activity against T. cruzi. The compounds 8 and 16 showed significant potency and selectivity against T. cruzi (GI₅₀?=?14.3?µM, SI?>?34.8 and GI₅₀?=?11.6?µM, SI?=?29.1, respectively). These values, close to the values of the reference drug benznidazole (GI₅₀?=?10.2?µM), suggest that compounds 8 and 16 represent promising candidates for further pre-clinical development targeting Chagas disease.     

Dialkylimidazole inhibitors of Trypanosoma cruzi sterol 14α-demethylase as anti-Chagas disease agents

New dialkylimidazole based sterol 14α-demethylase inhibitors were prepared and tested as potential anti-Trypanosoma cruzi agents. Previous studies had identified compound 2 as the most potent and selective inhibitor against parasite cultures. In addition, animal studies had demonstrated that compound 2 is highly efficacious in the acute model of the disease. However, compound 2 has a high molecular weight and high hydrophobicity, issues addressed here. Systematic modifications were carried out at four positions on the scaffold and several inhibitors were identified which are highly potent (EC₅₀ <1 nM) against T. cruzi in culture. The halogenated derivatives 36j, 36k, and 36p, display excellent activity against T. cruzi amastigotes, with reduced molecular weight and lipophilicity, and exhibit suitable physicochemical properties for an oral drug candidate.     

Stearoyl-CoA desaturase is an essential enzyme for the parasitic protist Trypanosoma brucei

Trypanosoma brucei, the etiologic agent of sleeping sickness, is exposed to important changes in nutrients and temperature during its life cycle. To adapt to these changes, the fluidity of its membranes plays a crucial role. This fluidity, mediated by the fatty-acid composition, is regulated by enzymes named desaturases. We have previously shown that the oleoyl desaturase is essential for Trypanosoma cruzi and T. brucei. In this work, we present experimental support for the relevance of stearoyl-CoA desaturase (SCD) for T. brucei’s survival, in both its insect or procyclic-form (PCF) and bloodstream-form (BSF) stages. We evaluated this essentiality in two different ways: by generating a SCD knocked-down parasite line using RNA interference, and by chemical inhibition of the enzyme with two compounds, Isoxyl and a thiastearate with the sulfur atom at position 10 (10-TS). The effective concentration for 50% growth inhibition (EC₅₀) of PCF was 1.0 ± 0.2 μM for Isoxyl and 5 ± 2 μM for 10-TS, whereas BSF appeared more susceptible with EC₅₀ values 0.10 ± 0.03 μM (Isoxyl) and 1.0 ± 0.6 μM (10-TS). RNA interference showed to be deleterious for both stages of the parasite. In addition, T. brucei-infected mice were fed with Isoxyl, causing a reduction of the parasitemia and an increase of the rodents’ survival.     

Synthesis,in-vitro antiprotozoal activity and molecular docking study of isothiocyanate derivatives

Novel isothiocyanate derivatives were synthesized starting from noscapine, bile acids, amino acids, and some aromatic compounds. Antiparasitic activities of the synthesized derivatives were tested against four unicellular protozoa, i.e., Trypanosoma brucei rhodesiense, T. cruzi, Leishmania donovani, and Plasmodium falciparum. Interestingly, seven isothiocyanate analogues displayed promising antiparasitic activity against Leishmania donovani with IC₅₀ values between 0.4 and 1.0 µM and selectivity index (SI) ranged from 7.8 to 18.4, comparable to the standard drug miltefosine (IC₅₀ = 0.7 μM). Compound 7h demonstrated the best antileishmanial activity with an IC₅₀ value of 0.4 µM. Seven products exhibited inhibition activity against T. brucei rhodesiense with IC₅₀s below 2.0 μM and SI between 2.7 and 29.3. Four primary amine derivatives of noscapine and five isothiocyanate derivatives exhibited antiplasmodial activity with IC₅₀s in the range of 1.1–2.7 µM and SI values between 1.1 and 14.5. The isothiocyanate derivative 7c showed against T. cruzi with an IC₅₀ value of 1.9 µM and SI 4. Molecular docking and ADMET studies were performed to investigate the interaction between active ligands and T. brucei trypanothione reductase active site. The docking studies showed significant binding affinity of noscapine derivatives to enzyme active site and good compatibility with experimental data.     

Optimization of a binding fragment targeting the “enlarged methionine pocket” leads to potent Trypanosoma brucei methionyl-tRNA synthetase inhibitors

Potent inhibitors of Trypanosoma brucei methionyl-tRNA synthetase were previously designed using a structure-guided approach. Compounds 1 and 2 were the most active compounds in the cyclic and linear linker series, respectively. To further improve cellular potency, SAR investigation of a binding fragment targeting the “enlarged methionine pocket” (EMP) was performed. The optimization led to the identification of a 6,8-dichloro-tetrahydroquinoline ring as a favorable fragment to bind the EMP. Replacement of 3,5-dichloro-benzyl group (the EMP binding fragment) of inhibitor 2 using this tetrahydroquinoline fragment resulted in compound 13, that exhibited an EC₅₀ of 4 nM.     

Structure based drug design and in vitro metabolism study: Discovery of N-(4-methylthiophenyl)-N,2-dimethyl-cyclopenta[d]pyrimidine as a potent microtubule targeting agent

We report a series of tubulin targeting agents, some of which demonstrate potent antiproliferative activities. These analogs were designed to optimize the antiproliferative activity of 1 by varying the heteroatom substituent at the 4′-position, the basicity of the 4-position amino moiety, and conformational restriction. The potential metabolites of the active compounds were also synthesized. Some compounds demonstrated single digit nanomolar IC₅₀ values for antiproliferative effects in MDA-MB-435 melanoma cells. Particularly, the S-methyl analog 3 was more potent than 1 in MDA-MB-435 cells (IC₅₀?=?4.6?nM). Incubation of 3 with human liver microsomes showed that the primary metabolite of the S-methyl moiety of 3 was the methyl sulfinyl group, as in analog 5. This metabolite was equipotent with the lead compound 1 in MDA-MB-435 cells (IC₅₀?=?7.9?nM). Molecular modeling and electrostatic surface area were determined to explain the activities of the analogs. Most of the potent compounds overcome multiple mechanisms of drug resistance and compound 3 emerged as the lead compound for further SAR and preclinical development.     

Synergy Testing of FDA-Approved Drugs Identifies Potent Drug Combinations against Trypanosoma cruzi

An estimated 8 million persons, mainly in Latin America, are infected with Trypanosoma cruzi, the etiologic agent of Chagas disease. Existing antiparasitic drugs for Chagas disease have significant toxicities and suboptimal effectiveness, hence new therapeutic strategies need to be devised to address this neglected tropical disease. Due to the high research and development costs of bringing new chemical entities to the clinic, we and others have investigated the strategy of repurposing existing drugs for Chagas disease. Screens of FDA-approved drugs (described in this paper) have revealed a variety of chemical classes that have growth inhibitory activity against mammalian stage Trypanosoma cruzi parasites. Aside from azole antifungal drugs that have low or sub-nanomolar activity, most of the active compounds revealed in these screens have effective concentrations causing 50% inhibition (EC₅₀''s) in the low micromolar or high nanomolar range. For example, we have identified an antihistamine (clemastine, EC₅₀ of 0.4 µM), a selective serotonin reuptake inhibitor (fluoxetine, EC₅₀ of 4.4 µM), and an antifolate drug (pyrimethamine, EC₅₀ of 3.8 µM) and others. When tested alone in the murine model of Trypanosoma cruzi infection, most compounds had insufficient efficacy to lower parasitemia thus we investigated using combinations of compounds for additive or synergistic activity. Twenty-four active compounds were screened in vitro in all possible combinations. Follow up isobologram studies showed at least 8 drug pairs to have synergistic activity on T. cruzi growth. The combination of the calcium channel blocker, amlodipine, plus the antifungal drug, posaconazole, was found to be more effective at lowering parasitemia in mice than either drug alone, as was the combination of clemastine and posaconazole. Using combinations of FDA-approved drugs is a promising strategy for developing new treatments for Chagas disease.     

Optimization of the electrophile of chloronitrobenzamide leads active against Trypanosoma brucei

We previously reported the phenylchloronitrobenzamides (PCNBs), a novel class of compounds active against the species of trypanosomes that cause Human African Trypanosomiasis (HAT). Herein, we explored the potential to adjust the reactivity of the electrophilic chloronitrobenzamide core. These studies identified compound 7d that potently inhibited the growth of trypanosomes (EC₅₀ = 120 nM for Trypanosoma b. brucei, 18 nM for Trypanosoma b. rhodesiense, and 38 nM for Trypanosoma b. gambiense) without significant cytotoxicity against mammalian cell lines (EC₅₀ > 25 μM for HepG2, HEK293, Raji, and BJ cell lines) and also had good stability in microsomal models (t_1/2 > 4 h in both human and mouse). Overall these properties indicate the compound 7d and its analogs are worth further exploration as potential leads for HAT.     

Chemical evaluation of fatty acid desaturases as drug targets in Trypanosoma cruzi

Four positional isomers of Thiastearate (TS) and Isoxyl (Thiocarlide) were assayed as fatty acid desaturase inhibitors in Trypanosoma cruzi epimastigotes. 9-TS did not exert a significant effect on growth of T. cruzi, nor on the fatty acid profile of the parasite cells. One hundred micromolars of 10-TS totally inhibited growth, with an effective concentration for 50% growth inhibition (EC₅₀) of 3.0 ± 0.2 μM. Growth inhibition was reverted by supplementing the culture media with oleate. The fatty acid profile of treated cells revealed that conversion of stearate to oleate and palmitate to palmitoleate were drastically reduced and, as a consequence, the total level of unsaturated fatty acids decreased from 60% to 32%. Isoxyl, a known inhibitor of stearoyl-CoA Δ9 desaturase in mycobacteria, had similar effects on T. cruzi growth (EC₅₀ 2.0 ± 0.3 μM) and fatty acid content, indicating that Δ9 desaturase was the target of both drugs. 12- and 13-TS were inhibitors of growth with EC₅₀ values of 50 ± 2 and 10 ± 3 μM, respectively, but oleate or linoleate were unable to revert the effect. Both drugs increased the percentage of oleate and palmitate in the cell membrane and drastically reduced the content of linoleate from 38% to 16% and 12%, respectively, which is in agreement with a specific inhibition of oleate Δ12 desaturase. The absence of corresponding enzyme activity in mammalian cells and the significant structural differences between trypanosome and mammalian Δ9 desaturases, together with our results, highlight these enzymes as promising targets for selective chemotherapeutic intervention.     

Design,synthesis and biological evaluation of novel acetamide-substituted doravirine and its prodrugs as potent HIV-1 NNRTIs

A novel series of acetamide-substituted derivatives and two prodrugs of doravirine were designed and synthesized as potent HIV-1 NNRTIs by employing the structure-based drug design strategy. In MT-4 cell-based assays using the MTT method, it was found that most of the new compounds exhibited moderate to excellent inhibitory potency against the wild-type (WT) HIV-1 strain with a minimum EC₅₀ value of 54.8?nM. Among them, the two most potent compounds 8i (EC₅₀?=?59.5?nM) and 8k (EC₅₀?=?54.8?nM) displayed robust activity against WT HIV-1 with double-digit nanomolar EC₅₀ values, being superior to lamivudine (3TC, EC₅₀?=?12.8?μM) and comparable to doravirine (EC₅₀?=?13?nM). Besides, 8i and 8k shown moderate activity against the double RT mutant (K103N?+?Y181C) HIV-1 RES056 strain. The HIV-1 RT inhibition assay further validated the binding target. Molecular simulation of the representative compounds was employed to provide insight on their structure-activity relationships (SARs) and direct future design efforts. Finally, the aqueous solubility and chemical stability of the prodrugs 9 and 10 were investigated in detail.     

Chemical Validation of Trypanothione Synthetase: A POTENTIAL DRUG TARGET FOR HUMAN TRYPANOSOMIASIS*

In the search for new therapeutics for the treatment of human African trypanosomiasis, many potential drug targets in Trypanosoma brucei have been validated by genetic means, but very few have been chemically validated. Trypanothione synthetase (TryS; EC 6.3.1.9; spermidine/glutathionylspermidine:glutathione ligase (ADP-forming)) is one such target. To identify novel inhibitors of T. brucei TryS, we developed an in vitro enzyme assay, which was amenable to high throughput screening. The subsequent screen of a diverse compound library resulted in the identification of three novel series of TryS inhibitors. Further chemical exploration resulted in leads with nanomolar potency, which displayed mixed, uncompetitive, and allosteric-type inhibition with respect to spermidine, ATP, and glutathione, respectively. Representatives of all three series inhibited growth of bloodstream T. brucei in vitro. Exposure to one of our lead compounds (DDD86243; 2 × EC₅₀ for 72 h) decreased intracellular trypanothione levels to <10% of wild type. In addition, there was a corresponding 5-fold increase in the precursor metabolite, glutathione, providing strong evidence that DDD86243 was acting on target to inhibit TryS. This was confirmed with wild-type, TryS single knock-out, and TryS-overexpressing cell lines showing expected changes in potency to DDD86243. Taken together, these data provide initial chemical validation of TryS as a drug target in T. brucei.     

Synthesis and potent antiprotozoal activity of mono/di amidino 2-anilinobenzimidazoles versus Plasmodium falciparum and Trypanosoma brucei rhodesiense

A series of mono and dicationic new 2-anilinobenzimidazole carboxamidines were prepared in a four step process starting from 4-amino-3-nitrobenzonitrile and corresponding o-phenylenediamines. Their antiparasitic activity against Plasmodium falciparum (P. falciparum) and Trypanosoma brucei rhodesiense (T.b. rhodesiense) were evaluated in vitro. Some of the dicationic compounds (10,12,14) showed equal or very close activity against T.b. rhodesiense with melarsoprol and also showed promising activity against P. falciparum as compared to chloroquine. Among the monocationic derivatives compound 21 exhibited best inhibitory activity against P. falciparum.     

Antiplasmodial activity of hydroxyethylamine analogs: Synthesis,biological activity and structure activity relationship of plasmepsin inhibitors

Malaria, particularly in endemic countries remains a threat to the human health and is the leading the cause of mortality in the tropical and sub-tropical areas. Herein, we explored new C₂ symmetric hydroxyethylamine analogs as the potential inhibitors of Plasmodium falciparum (P. falciparum; 3D7) in in-vitro cultures. All the listed compounds were also evaluated against crucial drug targets, plasmepsin II (Plm II) and IV (Plm IV), enzymes found in the digestive vacuole of the P. falciparum. Analog 10f showed inhibitory activities against both the enzymes Plm II and Plm IV (K_i, 1.93?±?0.29?µM for Plm II; K_i, 1.99?±?0.05?µM for Plm IV). Among all these analogs, compounds 10g selectively inhibited the activity of Plm IV (K_i, 0.84?±?0.08?µM). In the in vitro screening assay, the growth inhibition of P. falciparum by both the analogs (IC₅₀, 2.27?±?0.95?µM for 10f; IC₅₀, 3.11?±?0.65?µM for 10g) displayed marked killing effect. A significant growth inhibition of the P. falciparum was displayed by analog 12c with IC₅₀ value of 1.35?±?0.85?µM, however, it did not show inhibitory activity against either Plms. The hemolytic assay suggested that the active compounds selectively inhibit the growth of the parasite. Further, potent analogs (10f and 12c) were evaluated for their cytotoxicity towards mammalian HepG2 and vero cells. The selectivity index (SI) values were noticed greater than 10 for both the analogs that suggested their poor toxicity. The present study indicates these analogs as putative lead structures and could serve as crucial for the development of new drug molecules.     

Synthesis, in vitro antimalarial activities and cytotoxicities of amino-artemisinin-ferrocene derivatives

Novel derivatives bearing a ferrocene attached via a piperazine linker to C-10 of the artemisinin nucleus were prepared from dihydroartemisinin and screened against chloroquine (CQ) sensitive NF54 and CQ resistant K1 and W2 strains of Plasmodium falciparum (Pf) parasites. The overall aim is to imprint oxidant (from the artemisinin) and redox (from the ferrocene) activities. In a preliminary assessment, these compounds were shown to possess activities in the low nM range with the most active being compound 6 with IC₅₀ values of 2.79?nM against Pf K1 and 3.2?nM against Pf W2. Overall the resistance indices indicate that the compounds have a low potential for cross resistance. Cytotoxicities were determined with Hek293 human embryonic kidney cells and activities against proliferating cells were assessed against A375 human malignant melanoma cells. The selectivity indices of the amino-artemisinin ferrocene derivatives indicate there is overall an appreciably higher selectivity towards the malaria parasite than mammalian cells.     

5-Substituted 3-chlorokenpaullone derivatives are potent inhibitors of Trypanosoma brucei bloodstream forms

Trypanothione synthetase is an essential enzyme for kinetoplastid parasites which cause highly disabling and fatal diseases in humans and animals. Inspired by the observation that N(5)-substituted paullones inhibit the trypanothione synthetase from the related parasite Leishmania infantum, we designed and synthesized a series of new derivatives. Although none of the new compounds displayed strong inhibition of Trypanosoma brucei trypanothione synthetase, several of them caused a remarkable growth inhibition of cultivated Trypanosoma brucei bloodstream forms. The most potent congener 3a showed antitrypanosomal activity in double digit nanomolar concentrations and a selectivity index of three orders of magnitude versus murine macrophage cells.     

2-Acylamino-5-nitro-1,3-thiazoles: Preparation and in vitro bioevaluation against four neglected protozoan parasites

The 2-acylamino-5-nitro-1,3-thiazole derivatives (1–14) were prepared using a one step reaction. All compounds were tested in vitro against four neglected protozoan parasites (Giardia intestinalis, Trichomonas vaginalis, Leishmania amazonensis and Trypanosoma cruzi). Acetamide (9), valeroylamide (10), benzamide (12), methylcarbamate (13) and ethyloxamate (14) derivatives were the most active compounds against G. intestinalis and T. vaginalis, showing nanomolar inhibition. Compound 13 (IC₅₀ = 10 nM), was 536-times more active than metronidazole, and 121-fold more effective than nitazoxanide against G. intestinalis. Compound 14 was 29-times more active than metronidazole and 6.5-fold more potent than nitazoxanide against T. vaginalis. Ureic derivatives 2, 3 and 5 showed moderate activity against L. amazonensis. None of them were active against T. cruzi. Ligand efficiency indexes analysis revealed higher intrinsic quality of the most active 2-acylamino derivatives than nitazoxanide and metronidazole. In silico toxicity profile was also computed for the most active compounds. A very low in vitro mammalian cytotoxicity was obtained for 13 and 14, showing selectivity indexes (SI) of 246,300 and 141,500, respectively. Nitazoxanide showed an excellent leishmanicidal and trypanocidal effect, repurposing this drug as potential new antikinetoplastid parasite compound     

New antiprotozoal agents: Their synthesis and biological evaluations

Here we report identification of new lead compounds based on quinoline and indenoquinolines with variable side chains as antiprotozoal agents. Quinolines 32, 36 and 37 (Table 1) and indenoquinoline derivatives 14 and 23 (Table 2) inhibit the in vitro growth of the Trypanosoma cruzi, Trypanosoma brucei, Trypanosoma brucei rhodesiense subspecies and Leishmania infantum with IC₅₀ = 0.25 μM. These five compounds have superior activity to that of the front-line drugs such as benznidazole, nifurtimox and comparable to amphotericin B. Thus these compounds constitute new ‘leads’ for further structure–activity studies as potential active antiprotozoal agents.     

Antiplasmodial flavanones and a stilbene from Carpha glomerata

Bioassay-guided fractionation of an extract of Carpha glomerata (Cyperaceae) led to the isolation of seven compounds. Compounds 1 (carphorin A), 3 (carphorin C), 4 (carphorin D), and 5 (carphabene) are new compounds, and compound 2 (8-(3″-hydroxyisoamyl)-naringenin) was isolated for the first time as a natural product. All structures were elucidated based on analyses of their HR-ESIMS and 1D and 2D NMR data. Compounds 1, 2, and 6, which have prenyl or hydroxyprenyl side chains, exhibited antiplasmodial activities with IC₅₀ values of 5.2?±?0.6, 3.4?±?0.4, and 6.7?±?0.8?µM against the drug-resistant Dd2 strain of Plasmodium falciparum. In addition the prenylated stilbene 5 also showed good activity, with IC₅₀ 5.8?±?0.7?µM.     

Synthesis and biological evaluation of 2-methyl-1H-benzimidazole-5-carbohydrazides derivatives as modifiers of redox homeostasis of Trypanosoma cruzi

Twelve novel benzimidazole derivatives were synthesized and their in vitro activities against epimastigotes of Trypanosoma cruzi were evaluated. Two derivatives (6 and 7), which have 4-hydroxy-3-methoxyphenyl moiety in their structures, proved to be the most active in inhibiting the parasite growth. Compound 6 showed a trypanocidal activity higher than benznidazole (IC₅₀ = 5 µM and 7.5 µM, respectively) and less than nifurtimox (IC₅₀ = 3.6 µM). In addition, the ability of 6 and 7 to modify the redox homeostasis in T cruzi epimastigote was studied; cysteine and glutathione increased in parasites exposed to both compounds, whereas trypanothione only increased with 7 treatment. These results suggest that the decrease in viability of T. cruzi may be attributed to the change in cellular redox balance caused by compound 6 or 7. Furthermore, compounds 6 and 7 showed CC₅₀ values of 160.64 and 160.66 µM when tested in mouse macrophage cell line J774 and selectivity indexes (macrophage/parasite) of 32 and 20.1, respectively.