Synthesis, structure-activity relationship and trypanocidal activity of pyrazole-imidazoline and new pyrazole-tetrahydropyrimidine hybrids as promising chemotherapeutic agents for Chagas disease.

Drug therapy for Chagas disease remains a major challenge as potential candidate drugs have failed clinical trials. Currently available drugs have limited efficacy and induce serious side effects. Thus, the discovery of new drugs is urgently needed in the fight against Chagas' disease. Here, we synthesized and evaluated the biological effect of pyrazole-imidazoline (1a-i) and pyrazole-tetrahydropyrimidine (2a-i) derivatives against relevant clinical forms of Trypanosoma cruzi. The structure-activity relationship (SAR), drug-target search, physicochemical and ADMET properties of the major active compounds in vitro were also assessed in silico. Pyrazole derivatives showed no toxicity in Vero cells and also no cardiotoxicity. Phenotypic screening revealed two dichlorinated pyrazole-imidazoline derivatives (1c and 1d) with trypanocidal activity higher than that of benznidazole (Bz) against trypomastigotes; these were also the most potent compounds against intracellular amastigotes. Replacement of imidazoline with tetrahydropyrimidine in the pyrazole compounds completely abolished the trypanocidal activity of series 2(a-i) derivatives. The physicochemical and ADMET properties of the compounds predicted good permeability, good oral bioavailability, no toxicity and mutagenicity of 1c and 1d. Pyrazole nucleus had high frequency hits for cruzipain in drug-target search and structure activity relationship (SAR) analysis of pyrazole-imidazoline derivatives revealed enhanced activity when chlorine atom was inserted in meta-positions of the benzene ring. Additionally, we found evidence that both compounds (1c and 1d) have the potential to interact non-covalently with the active site of cruzipain and also inhibit the cysteine proteinase activity of T. cruzi. Collectively, the data presented here reveal pyrazole derivatives with promise for further optimization in the therapy of Chagas disease.

Trypanosoma cruzi heparin-binding proteins present a flagellar membrane localization and serine proteinase activity.

Heparin-binding proteins (HBPs) play a key role in Trypanosoma cruzi-host cell interactions. HBPs recognize heparan sulfate (HS) at the host cell surface and are able to induce the cytoadherence and invasion of this parasite. Herein, we analysed the biochemical properties of the HBPs and also evaluated the expression and subcellular localization of HBPs in T. cruzi trypomastigotes. A flow cytometry analysis revealed that HBPs are highly expressed at the surface of trypomastigotes, and their peculiar localization mainly at the flagellar membrane, which is known as an important signalling domain, may enhance their binding to HS and elicit the parasite invasion. The plasmon surface resonance results demonstrated the stability of HBPs and their affinity to HS and heparin. Additionally, gelatinolytic activities of 70 kDa, 65·8 kDa and 59 kDa HBPs over a broad pH range (5·5-8·0) were revealed using a zymography assay. These proteolytic activities were sensitive to serine proteinase inhibitors, such as aprotinin and phenylmethylsulfonyl fluoride, suggesting that HBPs have the properties of trypsin-like proteinases.

Trypanosoma cruzi heparin-binding proteins mediate the adherence of epimastigotes to the midgut epithelial cells of Rhodnius prolixus.

Heparin-binding proteins (HBPs) have been demonstrated in both infective forms of Trypanosoma cruzi and are involved in the recognition and invasion of mammalian cells. In this study, we evaluated the potential biological function of these proteins during the parasite-vector interaction. HBPs, with molecular masses of 65·8 kDa and 59 kDa, were isolated from epimastigotes by heparin affinity chromatography and identified by biotin-conjugated sulfated glycosaminoglycans (GAGs). Surface plasmon resonance biosensor analysis demonstrated stable receptor-ligand binding based on the association and dissociation values. Pre-incubation of epimastigotes with GAGs led to an inhibition of parasite binding to immobilized heparin. Competition assays were performed to evaluate the role of the HBP-GAG interaction in the recognition and adhesion of epimastigotes to midgut epithelial cells of Rhodnius prolixus. Epithelial cells pre-incubated with HBPs yielded a 3·8-fold inhibition in the adhesion of epimastigotes. The pre-treatment of epimastigotes with heparin, heparan sulfate and chondroitin sulfate significantly inhibited parasite adhesion to midgut epithelial cells, which was confirmed by scanning electron microscopy. We provide evidence that heparin-binding proteins are found on the surface of T. cruzi epimastigotes and demonstrate their key role in the recognition of sulfated GAGs on the surface of midgut epithelial cells of the insect vector.

Involvement of host cell heparan sulfate proteoglycan in Trypanosoma cruzi amastigote attachment and invasion.

Cell surface glycosaminoglycans (GAGs) play an important role in the attachment and invasion process of a variety of intracellular pathogens. We have previously demonstrated that heparan sulfate proteoglycans (HSPG) mediate the invasion of trypomastigote forms of Trypanosoma cruzi in cardiomyocytes. Herein, we analysed whether GAGs are also implicated in amastigote invasion. Competition assays with soluble GAGs revealed that treatment of T. cruzi amastigotes with heparin and heparan sulfate leads to a reduction in the infection ratio, achieving 82% and 65% inhibition of invasion, respectively. Other sulfated GAGs, such as chondroitin sulfate, dermatan sulfate and keratan sulfate, had no effect on the invasion process. In addition, a significant decrease in infection occurred after interaction of amastigotes with GAG-deficient Chinese Hamster Ovary (CHO) cells, decreasing from 20% and 28% in wild-type CHO cells to 5% and 9% in the mutant cells after 2 h and 4 h of infection, respectively. These findings suggest that amastigote invasion also involves host cell surface heparan sulfate proteoglycans. The knowledge of the mechanism triggered by heparan sulfate-binding T. cruzi proteins may provide new potential candidates for Chagas disease therapy.