In vitro screening of 2-(1H-imidazol-1-yl)-1-phenylethanol derivatives as antiprotozoal agents and docking studies on Trypanosoma cruzi CYP51

Updates on Mechanisms of Cytochrome P450 Catalysis of Complex Steroid Oxidations

Cytochrome P450 (P450) enzymes dominate steroid metabolism. In general, the simple C-hydroxylation reactions are mechanistically straightforward and are generally agreed to involve a perferryl oxygen species (formally FeO3+). Several of the steroid transformations are more complex and involve C-C bond scission. We initiated mechanistic studies with several of these (i.e., 11A1, 17A1, 19A1, and 51A1) and have now established that the dominant modes of catalysis for P450s 19A1 and 51A1 involve a ferric peroxide anion (i.e., Fe3+O2¯) instead of a perferryl ion complex (FeO3+), as demonstrated with 18O incorporation studies. P450 17A1 is less clear. The indicated P450 reactions all involve sequential oxidations, and we have explored the processivity of these multi-step reactions. P450 19A1 is distributive, i.e., intermediate products dissociate and reassociate, but P450s 11A1 and 51A1 are highly processive. P450 17A1 shows intermediate processivity, as expected from the release of 17-hydroxysteroids for the biosynthesis of key molecules, and P450 19A1 is very distributive. P450 11B2 catalyzes a processive multi-step oxidation process with the complexity of a chemical closure of an intermediate to a locked lactol form.

Chemical Composition and In Vitro and In Silico Antileishmanial Evaluation of the Essential Oil from Croton linearis Jacq. Stems

Croton linearis Jacq. is an aromatic shrub that has been utilized in traditional medicine in the Bahamas, Jamaica, and Cuba. Recent studies have revealed the antiprotozoal potential of its leaves. The present work is aimed to identify the volatile constituents of essential oil from the stems of C. linearis (CLS-EO) and evaluate its in vitro antileishmanial activity. In addition, an in silico study of the molecular interactions was performed using molecular docking. A gas chromatographic-mass spectrometric analysis of CLS-EO identified 1,8-cineole (27.8%), α-pinene (11.1%), cis-sabinene (8.1%), p-cymene (5.7%), α-terpineol (4.4%), epi-γ-eudesmol (4.2%), linalool (3.9%), and terpinen-4-ol (2.6%) as major constituents. The evaluation of antileishmanial activity showed that CLS-EO has good activity on both parasite forms (IC_{50Promastigote} = 21.4 ± 0.1 μg/mL; IC_50Amastigote = 18.9 ± 0.3 μg/mL), with a CC₅₀ of 49.0 ± 5.0 μg/mL on peritoneal macrophages from BALB/c mice (selectivity index = 2 and 3 using the promastigote and amastigote results). Molecular docking showed good binding of epi-γ-eudesmol with different target enzymes of Leishmania. This study is the first report of the chemical composition and anti-Leishmania evaluation of CLS-EO. These findings provide support for further studies of the antileishmanial effect of this product.

2-(Nitroaryl)-5-Substituted-1,3,4-Thiadiazole Derivatives with Antiprotozoal Activities: In Vitro and In Vivo Study

Nitro-containing compounds are a well-known class of anti-infective agents, especially in the field of anti-parasitic drug discovery. HAT or sleeping sickness is a neglected tropical disease caused by a protozoan parasite, Trypanosoma brucei. Following the approval of fexinidazole as the first oral treatment for both stages of T. b. gambiense HAT, there is an increased interest in developing new nitro-containing compounds against parasitic diseases. In our previous projects, we synthesized several megazole derivatives that presented high activity against Leishmania major promastigotes. Here, we screened and evaluated their trypanocidal activity. Most of the compounds showed submicromolar IC50 against the BSF form of T. b. rhodesiense (STIB 900). To the best of our knowledge, compound 18c is one of the most potent nitro-containing agents reported against HAT in vitro. Compound 18g revealed an acceptable cure rate in the acute mouse model of HAT, accompanied with noteworthy in vitro activity against T. brucei, T. cruzi, and L. donovani. Taken together, these results suggest that these compounds are promising candidates to evaluate their pharmacokinetic and biological profiles in the future.

Planning new Trypanosoma cruzi CYP51 inhibitors using QSAR studies

Chagas disease kills over 10,000 people per year, and approximately 8 million people are infected by Trypanosoma cruzi. The reference drug for treatment of the disease, benznidazole, is the same since the 70s. In recent years, many CYP51 inhibitors were tested against this parasite's target. One of them, posaconazole, was even tested in clinical trials that unfortunately were not successful. Nevertheless, there are still many evidences that CYP51 is a great potential target to treat T. cruzi infection. The research for new effective molecules that can cure the chronic phase of the disease is essential. 2D and 3D-quantitative structure activity relationship (QSAR) studies were conducted in this work to create three QSAR models using the chemical structures of 197 published compounds that already went through either in vivo or in vitro tests. After the analysis of the models, new analogues not yet synthesized were suggested here and had their biological activity and synthetic availability assessed.

The role of imidazole and benzimidazole heterocycles in Chagas disease: A review

The haemoflagellate protozoan Trypanosoma cruzi (T. cruzi) is the causative agent of Chagas disease (CD), a potentially life-threatening disease. Little by little, remarkable progress has been achieved against CD, although it is still not enough. In the absence of effective chemotherapy, many research groups, organizations and pharmaceutical companies have focused their efforts on the search for compounds that could become viable drugs against CD. Within the wide variety of reported derivatives, this review summarizes and provides a global vision of the situation of those compounds that include broadly studied heterocycles in their structures due to their applications in medicinal chemistry: imidazole and benzimidazole rings. Therefore, the intention of this work is to present a compilation, as much as possible, of all the reported information, regarding these imidazole and benzimidazole derivatives against T. cruzi, as a starting point for future researchers in this field.

Synthesis and in vitro evaluation of new 5-substituted 6-nitroimidazooxazoles as antikinetoplastid agents

In continuation of our pharmacomodulation work on the nitroimidazooxazole series, we report the synthesis of new 5-substituted 6-nitroimidazooxazole derivatives. Our aim was to evaluate how functionalization of the 5-position of the 6-nitroimidazooxazole scaffold affects antileishmanial and antitrypanosomal in vitro activities. Twenty-one original compounds were synthesized and evaluated for their in vitro antileishmanial (L. donovani) and antitrypanosomal (T. cruzi) properties. Pallado-catalyzed cross-coupling reactions were used to introduce an aryl or ethynyl aryl substituent in 5-position from a 5-brominated-6-nitroimidazooxazole starting product. Unfortunately, the first series of compounds bearing an aryl group in 5-position presented limited in vitro activities against L. donovani and T. cruzi, with IC₅₀ > 10 μM (vs 0.18 μM and 2.31 μM for the reference drugs amphotericin B and benznidazole respectively). Interestingly, the second series of compounds bearing an ethynyl aryl substituent in 5-position showed more promising, particularly against T. cruzi. Compounds 6a, 6b, 6c, 6g and 6h had better activity than the reference drug benznidazole (0.92 μM ≤ IC₅₀ ≤ 2.18 μM vs IC₅₀ = 2.31 μM), whereas the non-functionalized 2-methyl-6-nitro-2,3-dihydroimidazo [2,1-b]oxazole 2 was not active against T. cruzi (IC₅₀ > 10 μM).

Recent Advances in the Discovery of Novel Antiprotozoal Agents

Parasitic diseases have serious health, social, and economic impacts, especially in the tropical regions of the world. Diseases caused by protozoan parasites are responsible for considerable mortality and morbidity, affecting more than 500 million people worldwide. Globally, the burden of protozoan diseases is increasing and is been exacerbated because of a lack of effective medication due to the drug resistance and toxicity of current antiprotozoal agents. These limitations have prompted many researchers to search for new drugs against protozoan parasites. In this review, we have compiled the latest information (2012-2017) on the structures and pharmacological activities of newly developed organic compounds against five major protozoan diseases, giardiasis, leishmaniasis, malaria, trichomoniasis, and trypanosomiasis, with the aim of showing recent advances in the discovery of new antiprotozoal drugs.

Construction of antifungal dual-target (SE, CYP51) pharmacophore models and the discovery of novel antifungal inhibitors

Fungal infections and drug-resistance are rapidly increasing with the deterioration of the external environment. Squalene cyclooxygenase (SE) and 14α-demethylase (CYP51) are considered to be important antifungal targets, and the corresponding pharmacophore models can be used to design and guide the discovery of novel inhibitors. Therefore, the common feature pharmacophore model (SE inhibitor) and structure-based pharmacophore model (CYP51 receptor) were constructed using different methods in this study. Then, appropriate organic fragments were selected and superimposed onto the pharmacophore features, and compounds 5, 6 and 8 were designed and produced by linking these organic fragments. It is noteworthy that compound 8 can simultaneously match the features of both the SE and CYP51 pharmacophores. Further analysis found that these compounds exhibit a potent antifungal activity. Preliminary mechanistic studies revealed that compound 8 could undergo dual-target inhibition (SE and CYP51) of Candida albicans. This study proved the rationale of pharmacophore models (SE and CYP51), which can guide the design and discovery of new antifungal inhibitors.

Quantitative Structure-Activity Relationships for Structurally Diverse Chemotypes Having Anti-Trypanosoma cruzi Activity

Small-molecule compounds that have promising activity against macromolecular targets from Trypanosoma cruzi occasionally fail when tested in whole-cell phenotypic assays. This outcome can be attributed to many factors, including inadequate physicochemical and pharmacokinetic properties. Unsuitable physicochemical profiles usually result in molecules with a poor ability to cross cell membranes. Quantitative structure-activity relationship (QSAR) analysis is a valuable approach to the investigation of how physicochemical characteristics affect biological activity. In this study, artificial neural networks (ANNs) and kernel-based partial least squares regression (KPLS) were developed using anti-T. cruzi activity data for broadly diverse chemotypes. The models exhibited a good predictive ability for the test set compounds, yielding q² values of 0.81 and 0.84 for the ANN and KPLS models, respectively. The results of this investigation highlighted privileged molecular scaffolds and the optimum physicochemical space associated with high anti-T. cruzi activity, which provided important guidelines for the design of novel trypanocidal agents having drug-like properties.

In vitro evaluation of arylsubstituted imidazoles derivatives as antiprotozoal agents and docking studies on sterol 14α-demethylase (CYP51) from Trypanosoma cruzi, Leishmania infantum, and Trypanosoma brucei

There is an urgent need to discover and develop new drugs to combat parasitic diseases as Chagas disease (Trypanosoma cruzi), sleeping sickness (Trypanosoma brucei), and leishmaniasis (Leishmania ssp.). These diseases are considered among the 13 most unattended diseases worldwide according to the WHO. In the present work, the synthesis of 14 arylsubstituted imidazoles and its molecular docking onto sterol 14α-demethylase (CYP51) was executed. In addition, the compounds, antiprotozoal activity against T. brucei, T. cruzi, Trypanosoma brucei rhodesiense, and Leishmania infantum was evaluated. In vitro antiparasitic results of the arylsubstituted imidazoles against T. brucei, T. cruzi, T.b. rhodesiense, and L. infantum indicated that all samples from arylsubstituted imidazole compounds presented interesting antiparasitic activity to various extent. The ligands 5a, 5c, 5e, 5f, 5g, 5i, and 5j exhibited strong activity against T. brucei, T. cruzi, T.b. rhodesiense, and L. infantum with IC₅₀ values ranging from 0.86 to 10.23 μM. Most samples were cytotoxic against MRC-5 cell lines (1.12 < CC₅₀ < 51.09 μM) and only ligand 5c showed a good selectivity against all tested parasites. According to the results of the molecular docking, the aromatic substituents in positions 1, 4, and 5 have mainly stabilizing hydrophobic interactions with the enzyme matrix, while the oxygen from NO₂, SO₃H, and OH groups interacts with the Fe²⁺ ion of the Heme group.

Synthesis and biological evaluation of N-alkyl naphthoimidazoles derived from β-lapachone against Trypanosoma cruzi bloodstream trypomastigotes

The QSAR study of 34 2-aryl-naphthoimidazoles screened so far revealed that σi is the most important factor for their lytic activity on the bloodstream trypomastigote forms of T. cruzi, the etiologic agent of Chagas disease. Based on this result, 16 new N-alkyl-naphthoimidazoles derived from 6,6-dimethyl-3,4,5,6-tetrahydrobenzo[7,8]chromene[5,6-d]imidazole (the product of the reaction of β-lapachone with paraformaldehyde) by its reaction with halo-alkanes were prepared and evaluated against the parasite and peritoneal macrophages. The N1-n-hexyl and N3-n-hexyl naphthoimidazoles were 2.2 and 3.2 times more active than the standard drug benznidazole with selectivity indices of 2.7 and 13.4, respectively.

Carbonic anhydrases from Trypanosoma and Leishmania as anti-protozoan drug targets

Trypanosoma cruzi and Leishmania spp. are protozoa of the Trypanosomatidae family, being the etiological agents of two widespread parasitic diseases, Chagas disease and leishmaniasis, respectively. Both parasites are the focus of worldwide research with the aim to find effective and less toxic drugs than the few ones available so far, and for controlling the spread of the diseases. Carbonic anhydrases (CAs, EC 4.2.1.1) belonging to the α- and β-class were recently identified in these protozoans and several studies suggested that they could be new targets for drug development. Sulfonamide, thiol and hydroxamate inhibitors effectively inhibited the α-CA from T. cruzi (TcCA) and the β-CA from L. donovani chagasi (LdccCA) in vitro, and some of them also showed in vivo efficacy in inhibiting the growth of the parasites in animal models of Chagas disease and leishmaniasis. As few therapeutic options are presently available for these orphan diseases, protozoan CA inhibition may represent a novel strategy to address this stringent health problem.

Trypanosoma brucei CYP51: Essentiality and Targeting Therapy in an Experimental Model

Trypanosoma brucei gambiense is the main causative agent of Human African Trypanosomiasis (HAT), also known as sleeping sickness. Because of limited alternatives and treatment toxicities, new therapeutic options are urgently needed for patients with HAT. Sterol 14alpha-demethylase (CYP51) is a potential drug target but its essentiality has not been determined in T. brucei. We used a tetracycline-inducible RNAi system to assess the essentiality of CYP51 in T. brucei bloodstream form (BSF) cells and we evaluated the effect of posaconazole, a well-tolerated triazole drug, within a panel of virulent strains in vitro and in a murine model. Expression of CYP51 in several T. brucei cell lines was demonstrated by western blot and its essentiality was demonstrated by RNA interference (CYP51RNAi) in vitro. Following reduction of TbCYP51 expression by RNAi, cell growth was reduced and eventually stopped compared to WT or non-induced cells, showing the requirement of CYP51 in T. brucei. These phenotypes were rescued by addition of ergosterol. Additionally, CYP51RNAi induction caused morphological defects with multiflagellated cells (p<0.05), suggesting cytokinesis dysfunction. The survival of CYP51RNAi Doxycycline-treated mice (p = 0.053) and of CYP51RNAi 5-day pre-induced Doxycycline-treated mice (p = 0.008) were improved compared to WT showing a CYP51 RNAi effect on trypanosomal virulence in mice. The posaconazole concentrations that inhibited parasite growth by 50% (IC50) were 8.5, 2.7, 1.6 and 0.12 μM for T. b. brucei 427 90-13, T. b. brucei Antat 1.1, T. b. gambiense Feo (Feo/ITMAP/1893) and T. b. gambiense Biyamina (MHOM/SD/82), respectively. During infection with these last three virulent strains, posaconazole-eflornithine and nifurtimox-eflornithine combinations showed similar improvement in mice survival (p≤0.001). Our results provide support for a CYP51 targeting based treatment in HAT. Thus posaconazole used in combination may represent a therapeutic alternative for trypanosomiasis.

Drug target identification in protozoan parasites

INTRODUCTION

Despite the fact that diseases caused by protozoan parasites represent serious challenges for public health, animal production and welfare, only a limited panel of drugs has been marketed for clinical applications.

AREAS COVERED

Herein, the authors investigate two strategies, namely whole organism screening and target-based drug design. The present pharmacopoeia has resulted from whole organism screening, and the mode of action and targets of selected drugs are discussed. However, the more recent extensive genome sequencing efforts and the development of dry and wet lab genomics and proteomics that allow high-throughput screening of interactions between micromolecules and recombinant proteins has resulted in target-based drug design as the predominant focus in anti-parasitic drug development. Selected examples of target-based drug design studies are presented, and calcium-dependent protein kinases, important drug targets in apicomplexan parasites, are discussed in more detail.

EXPERT OPINION

Despite the enormous efforts in target-based drug development, this approach has not yet generated market-ready antiprotozoal drugs. However, whole-organism screening approaches, comprising of both in vitro and in vivo investigations, should not be disregarded. The repurposing of already approved and marketed drugs could be a suitable strategy to avoid fastidious approval procedures, especially in the case of neglected or veterinary parasitoses.