SUMMARY: Parasitic protozoa comprise diverse aetiological agents responsible for important diseases in humans and animals including sleeping sickness, Chagas disease, leishmaniasis, malaria, toxoplasmosis and others. They are major causes of mortality and morbidity in tropical and subtropical countries, and are also responsible for important economic losses. However, up to now, for most of these parasitic diseases, effective vaccines are lacking and the approved chemotherapeutic compounds present high toxicity, increasing resistance, limited efficacy and require long periods of treatment. Many of these parasitic illnesses predominantly affect low-income populations of developing countries for which new pharmaceutical alternatives are urgently needed. Thus, very low research funding is available. Amidine-containing compounds such as pentamidine are DNA minor groove binders with a broad spectrum of activities against human and veterinary pathogens. Due to their promising microbicidal activity but their rather poor bioavailability and high toxicity, many analogues and derivatives, including pro-drugs, have been synthesized and screenedin vitroandin vivoin order to improve their selectivity and pharmacological properties. This review summarizes the knowledge on amidines and analogues with respect to their synthesis, pharmacological profile, mechanistic and biological effects upon a range of intracellular protozoan parasites. The bulk of these data may contribute to the future design and structure optimization of new aromatic dicationic compounds as novel antiparasitic drug candidates.

Background: Strategies for development of anti-parasite chemotherapy involve identification of active principles of plants, investigation of drugs already licensed for other pathologies, or validation of specific targets identified within key metabolic pathways. Objective: To review the state of the art of drug targets against Trypanosoma cruzi with emphasis on sterol metabolism, kinetoplast DNA (kDNA) sites, trypanothione reductase, cysteine proteinase, hypoxanthine–guanine phosphoribosyltransferase, dihydrofolate reductase and glyceraldehyde-3-phosphate dehydrogenase. Methods: Current knowledge, accumulated over the last three decades, on targets for design and development of new trypanocidal compounds is described. Results/conclusion: There is an urgent need for better drugs to treat chagasic patients. Since the introduction of benznidazole and nifurtimox only allopurinol and a few sterol inhibitors have moved to clinical trials, despite the long list of natural and synthetic compounds assayed against ...

Chagas disease affects more than 10 million people worldwide, and yet, as it has historically been known as a disease of the poor, it remains highly neglected. Two currently available drugs exhibit severe toxicity and low effectiveness, especially in the chronic phase, while new drug discovery has been halted for years as a result of a lack of interest from pharmaceutical companies. Although attempts to repurpose the antifungal drugs posaconazole and ravuconazole (inhibitors of fungal sterol 14α-demethylase [CYP51]) are finally in progress, development of cheaper and more efficient, preferably Trypanosoma cruzi -specific, chemotherapies would be highly advantageous. We have recently reported that the experimental T. cruzi CYP51 inhibitor VNI cures with 100% survival and 100% parasitological clearance both acute and chronic murine infections with the Tulahuen strain of T. cruzi . In this work, we further explored the potential of VNI by assaying nitro-derivative-resistant T. cruzi strains, Y and Colombiana, in highly stringent protocols of acute infection. The data show high antiparasitic efficacy of VNI and its derivative (VNI/VNF) against both forms of T. cruzi that are relevant for mammalian host infection (bloodstream and amastigotes), with the in vivo potency, at 25 mg/kg twice a day (b.i.d.), similar to that of benznidazole (100 mg/kg/day). Transmission electron microscopy and reverse mutation tests were performed to explore cellular ultrastructural and mutagenic aspects of VNI, respectively. No mutagenic potential could be seen by the Ames test at up to 3.5 μM, and the main ultrastructural damage induced by VNI in T. cruzi was related to Golgi apparatus and endoplasmic reticulum organization, with membrane blebs presenting an autophagic phenotype. Thus, these preliminary studies confirm VNI as a very promising trypanocidal drug candidate for Chagas disease therapy.

Chagas' disease, a neglected tropical illness for which current therapy is unsatisfactory, is caused by the intracellular parasite Trypanosoma cruzi . The goal of this work is to investigate the in vitro and in vivo effects of the arylimidamide (AIA) DB766 against T. cruzi . This arylimidamide exhibits strong trypanocidal activity and excellent selectivity for bloodstream trypomastigotes and intracellular amastigotes (Y strain), giving IC ₅₀ s (drug concentrations that reduce 50% of the number of the treated parasites) of 60 and 25 nM, respectively. DB766 also exerts striking effects upon different parasite stocks, including those naturally resistant to benznidazole, and displays higher activity in vitro than the reference drugs. By fluorescent and transmission electron microscopy analyses, we found that this AIA localizes in DNA-enriched compartments and induces considerable damage to the mitochondria. DB766 effectively reduces the parasite load in the blood and cardiac tissue and presents efficacy similar to that of benznidazole in mouse models of T. cruzi infection employing the Y and Colombian strains, using oral and intraperitoneal doses of up to 100 mg/kg/day that were given after the establishment of parasite infection. This AIA ameliorates electrocardiographic alterations, reduces hepatic and heart lesions induced by the infection, and provides 90 to 100% protection against mortality, which is similar to that provided by benznidazole. Our data clearly show the trypanocidal efficacy of DB766, suggesting that this AIA may represent a new lead compound candidate to Chagas' disease treatment.

Aromatic diamidines are DNA minor groove-binding ligands that display excellent antimicrobial activity against fungi, bacteria, and protozoa. Due to the currently unsatisfactory chemotherapy for Chagas’ disease and in view of our previous reports regarding the effect of diamidines and analogues against both in vitro and in vivo Trypanosoma cruzi infection, this study evaluated the effects of a diarylthiophene diamidine (DB1362) against both amastigotes and bloodstream trypomastigotes of T. cruzi , the etiological agent of Chagas’ disease. The data show the potent in vitro activity of DB1362 against both parasite forms that are relevant for mammalian infection at doses which do not exhibit cytotoxicity. Ultrastructural analysis and flow cytometry studies show striking alterations in the nuclei and mitochondria of the bloodstream parasites. In vivo studies were performed at two different drug concentrations (25 and 50 mg/kg/day) using a 2-day or a 10-day regimen. The best results were obtained when acutely infected mice were treated with two doses at the lower concentration, resulting in 100% survival, compared to the infected and untreated mice. Although it did not display higher efficacy than benznidazole, DB1362 reduced both cardiac parasitism and inflammation, and in addition, it protected against the cardiac alterations (determined by measurements) common in T. cruzi infection. These results support further investigation of diamidines and related compounds as potential agents against Chagas’ disease.