Two analogues of fenarimol show curative activity in an experimental model of Chagas disease

Drugs in preclinical and early clinical development for the treatment of Chagas´s disease: the current status

INTRODUCTION

Chagas disease is spreading faster than expected in different countries, and little progress has been reported in the discovery of new drugs to combat Trypanosoma cruzi infection in humans. Recent clinical trials have ended with small hope. The pathophysiology of this neglected disease and the genetic diversity of parasites are exceptionally complex. The only two drugs available to treat patients are far from being safe, and their efficacy in the chronic phase is still unsatisfactory.

AREAS COVERED

This review offers a comprehensive examination and critical review of data reported in the last 10 years, and it is focused on findings of clinical trials and data acquired in vivo in preclinical studies.

EXPERT OPINION

The in vivo investigations classically in mice and dog models are also challenging and time-consuming to attest cure for infection. Poorly standardized protocols, availability of diagnosis methods and disease progression markers, the use of different T. cruzi strains with variable benznidazole sensitivities, and animals in different acute and chronic phases of infection contribute to it. More synchronized efforts between research groups in this field are required to put in evidence new promising substances, drug combinations, repurposing strategies, and new pharmaceutical formulations to impact the therapy.

Applications of palladium-catalyzed C-N cross-coupling reactions in pharmaceutical compounds

C-N cross-coupling bond formation reactions have become valuable approaches to synthesizing anilines and their derivatives, known as important chemical compounds. Recent developments in this field have focused on versatile catalysts, simple operation methods, and green reaction conditions. This review article presents an overview of C-N cross-coupling reactions in pharmaceutical compound synthesis reports. Selected examples of N-arylation reactions of various nitrogen-based compounds and aryl halides are defined for preparing pharmaceutical molecules.

Miltefosine and Benznidazole Combination Improve Anti-Trypanosoma cruzi In Vitro and In Vivo Efficacy

Drug repurposing and combination therapy have been proposed as cost-effective strategies to improve Chagas disease treatment. Miltefosine (MLT), a synthetic alkylphospholipid initially developed for breast cancer and repositioned for leishmaniasis, is a promising candidate against Trypanosoma cruzi infection. This study evaluates the efficacy of MLT as a monodrug and combined with benznidazole (BZ) in both in vitro and in vivo models of infection with T. cruzi (VD strain, DTU TcVI). MLT exhibited in vitro activity on amastigotes and trypomastigotes with values of IC_{50 =} 0.51 µM (0.48 µM; 0,55 µM) and LC_{50 =} 31.17 µM (29.56 µM; 32.87 µM), respectively. Drug interaction was studied with the fixed-ration method. The sum of the fractional inhibitory concentrations (ΣFICs) resulted in ∑FIC= 0.45 for trypomastigotes and ∑FIC= 0.71 for amastigotes, suggesting in vitro synergistic and additive effects, respectively. No cytotoxic effects on host cells were observed. MLT efficacy was also evaluated in a murine model of acute infection alone or combined with BZ. Treatment was well tolerated with few adverse effects, and all treated animals displayed significantly lower mean peak parasitemia and mortality than infected non-treated controls (p<0.05). The in vivo studies showed that MLT led to a dose-dependent parasitostatic effect as monotherapy which could be improved by combining with BZ, preventing parasitemia rebound after a stringent immunosuppression protocol. These results support MLT activity in clinically relevant stages from T. cruzi, and it is the first report of positive interaction with BZ, providing further support for evaluating combined schemes using MLT and exploring synthetic alkylphospholipids as drug candidates.

Identifying novel drugs with new modes of action for neglected tropical fungal skin diseases (fungal skinNTDs) using an Open Source Drug discovery approach

INTRODUCTION

The three fungal skin neglected tropical diseases (NTD) mycetoma, chromoblastomycosis and sporotrichosis currently lack prioritization and support to establish drug discovery programs in search for novel treatment options. This has made the efforts to identify novel drugs for these skinNTDs fragmented.

AREAS COVERED

To help escalate the discovery of novel drugs to treat these fungal skinNTDs, the authors have prepared an overview of the compounds with activity against fungal skinNTDs by analyzing data from individual drug discovery studies including those performed on the Medicines for Malaria Venture (MMV) open access boxes.

EXPERT OPINION

The authors were unable to identify studies in which causative agents of all three skinNTDs were included, indicating that an integrated approach is currently lacking. From the currently available data, the azoles and iodoquinol were the only compounds with activity against causative agents from the three different fungal skinNTDs. Fungal melanin inhibition enhanced the activity of antifungal agents. For mycetoma, the fenarimols, aminothiazoles and benzimidazole carbamates are currently being investigated in the MycetOS initiative. To come to a more integrated approach to identify drugs active against all three fungal skinNTDs, compounds made in the MycetOS initiative could also be explored for chromoblastomycosis and sporotrichosis.

Benznidazole Treatment: Time- and Dose-Dependence Varies with the Trypanosoma cruzi Strain

As the development of new drugs for Chagas disease is not a priority due to its neglected disease status, an option for increasing treatment adherence is to explore alternative treatment regimens, which may decrease the incidence of side effects. Therefore, we evaluated the efficacy of different therapeutic schemes with benznidazole (BNZ) on the acute and chronic phases of the disease, using mice infected with strains that have different BNZ susceptibilities. Our results show that the groups of animals infected by VL-10 strain, when treated in the chronic phase with a lower dose of BNZ for a longer period of time (40 mg/kg/day for 40 days) presented better treatment efficacy than with the standard protocol (100 mg/kg/day for 20 days) although the best result in the treatment of the animals infected by the VL-10 strain was with100 mg/kg/day for 40 days. In the acute infection by the Y and VL-10 strains of T. cruzi, the treatment with a standard dose, but with a longer time of treatment (100 mg/kg/day for 40 days) presented the best results. Given these data, our results indicate that for BNZ, the theory of dose and time proportionality does not apply to the phases of infection.

An Overview on the Therapeutics of Neglected Infectious Diseases-Leishmaniasis and Chagas Diseases

Neglected tropical diseases (NTDs) as termed by WHO include twenty different infectious diseases that are caused by bacteria, viruses, and parasites. Among these NTDs, Chagas disease and leishmaniasis are reported to cause high mortality in humans and are further associated with the limitations of existing drugs like severe toxicity and drug resistance. The above hitches have rendered researchers to focus on developing alternatives and novel therapeutics for the treatment of these diseases. In the past decade, several target-based drugs have emerged, which focus on specific biochemical pathways of the causative parasites. For leishmaniasis, the targets such as nucleoside analogs, inhibitors targeting nucleoside phosphate kinases of the parasite’s purine salvage pathway, 20S proteasome of Leishmania, mitochondria, and the associated proteins are reviewed along with the chemical structures of potential drug candidates. Similarly, in case of therapeutics for Chagas disease, several target-based drug candidates targeting sterol biosynthetic pathway (C14-ademethylase), L-cysteine protease, heme peroxidation, mitochondria, farnesyl pyrophosphate, etc., which are vital and unique to the causative parasite are discussed. Moreover, the use of nano-based formulations towards the therapeutics of the above diseases is also discussed.

Naturally Occurring Ecdysteroids in Triticum aestivum L. and Evaluation of Fenarimol as a Potential Inhibitor of Their Biosynthesis in Plants

Ecdysteroids (ECs) are steroid hormones originally found in the animal kingdom where they function as insect molting hormones. Interestingly, a relatively high number of these substances can also be formed in plant cells. Moreover, ECs have certain regulatory effects on plant physiology, but their role in plants still requires further study. One of the main aims of the present study was to verify a hypothesis that fenarimol, an inhibitor of the biosynthesis of ECs in the animal kingdom, also affects the content of endogenous ECs in plants using winter wheat Triticum aestivum L. as a model plant. The levels of endogenous ECs in winter wheat, including the estimation of their changes during a course of different temperature treatments, have been determined using a sensitive analytical method based on UHPLC-MS/MS. Under our experimental conditions, four substances of EC character were detected in the tissue of interest in amounts ranging from less than 1 to over 200 pg·g-1 FW: 20-hydroxyecdysone, polypodine B, turkesterone, and isovitexirone. Among them, turkesterone was observed to be the most abundant EC and accumulated mainly in the crowns and leaves of wheat. Importantly, the level of ECs was observed to be dependent on the age of the plants, as well as on growth conditions (especially temperature). Fenarimol, an inhibitor of a cytochrome P450 monooxygenase, was shown to significantly decrease the level of naturally occurring ECs in experimental plants, which may indicate its potential use in studies related to the biosynthesis and physiological function of these substances in plants.

Re-evaluating pretomanid analogues for Chagas disease: Hit-to-lead studies reveal both in vitro and in vivo trypanocidal efficacy

Phenotypic screening of a 900 compound library of antitubercular nitroimidazole derivatives related to pretomanid against the protozoan parasite Trypanosoma cruzi (the causative agent for Chagas disease) identified several structurally diverse hits with an unknown mode of action. Following initial profiling, a first proof-of-concept in vivo study was undertaken, in which once daily oral dosing of a 7-substituted 2-nitroimidazooxazine analogue suppressed blood parasitemia to low or undetectable levels, although sterile cure was not achieved. Limited hit expansion studies alongside counter-screening of new compounds targeted at visceral leishmaniasis laid the foundation for a more in-depth assessment of the best leads, focusing on both drug-like attributes (solubility, metabolic stability and safety) and maximal killing of the parasite in a shorter timeframe. Comparative appraisal of one preferred lead (58) in a chronic infection mouse model, monitored by highly sensitive bioluminescence imaging, provided the first definitive evidence of (partial) curative efficacy with this promising nitroimidazooxazine class.

A new chemotype with promise against Trypanosoma cruzi

Pyridyl benzamide 2 is a potent inhibitor of Trypanosoma cruzi, but not other protozoan parasites, and had a selectivity-index of ≥10. The initial structure-activity relationship (SAR) indicates that benzamide and sulfonamide functional groups, and N-methylpiperazine and sterically unhindered 3-pyridyl substructures are required for high activity against T. cruzi. Compound 2 and its active analogs had low to moderate metabolic stabilities in human and mouse liver microsomes.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.

Experimental models in Chagas disease: a review of the methodologies applied for screening compounds against Trypanosoma cruzi

One of the main problems of Chagas disease (CD), the parasitic infection caused by Trypanosoma cruzi, is the lack of a completely satisfactory treatment, which is currently based on two old nitroheterocyclic drugs (i.e., nifurtimox and benznidazole) that show important limitations for treating patients. In this context, many laboratories look for alternative therapies potentially applicable to the treatment, and therefore, research in CD chemotherapy works in the design of experimental protocols for detecting molecules with activity against T. cruzi. Phenotypic assays are considered the most valuable strategy for screening these antiparasitic compounds. Among them, in vitro experiments are the first step to test potential anti-T. cruzi drugs directly on the different parasite forms (i.e., epimastigotes, trypomastigotes, and amastigotes) and to detect cytotoxicity. Once the putative trypanocidal drug has been identified in vitro, it must be moved to in vivo models of T. cruzi infection, to explore (i) acute toxicity, (ii) efficacy during the acute infection, and (iii) efficacy in the chronic disease. Moreover, in silico approaches for predicting activity have emerged as a supporting tool for drug screening procedures. Accordingly, this work reviews those in vitro, in vivo, and in silico methods that have been routinely applied during the last decades, aiming to discover trypanocidal compounds that contribute to developing more effective CD treatments.

Addressing the most neglected diseases through an open research model: The discovery of fenarimols as novel drug candidates for eumycetoma

Eumycetoma is a chronic infectious disease characterized by a large subcutaneous mass, often caused by the fungus Madurella mycetomatis. A combination of surgery and prolonged medication is needed to treat this infection with a success rate of only 30%. There is, therefore, an urgent need to find more effective drugs for the treatment of this disease. In this study, we screened 800 diverse drug-like molecules and identified 215 molecules that were active in vitro. Minimal inhibitory concentrations were determined for the 13 most active compounds. One of the most potent compounds, a fenarimol analogue for which a large analogue library is available, led to the screening of an additional 35 compounds for their in vitro activity against M. mycetomatis hyphae, rendering four further hit compounds. To assess the in vivo potency of these hit compounds, a Galleria mellonella larvae model infected with M. mycetomatis was used. Several of the compounds identified in vitro demonstrated promising efficacy in vivo in terms of prolonged larval survival and/or reduced fungal burden. The results presented in this paper are the starting point of an Open Source Mycetoma (MycetOS) approach in which members of the global scientific community are invited to participate and contribute as equal partners. We hope that this initiative, coupled with the promising new hits we have reported, will lead to progress in drug discovery for this most neglected of neglected tropical diseases.

Searching for new drugs for Chagas diseases: triazole analogs display high in vitro activity against Trypanosoma cruzi and low toxicity toward mammalian cells

Chagas disease is one of the most relevant endemic diseases in Latin America caused by the flagellate protozoan Trypanosoma cruzi. Nifurtimox and benzonidazole are the drugs used in the treatment of this disease, but they commonly are toxic and present severe side effects. New effective molecules, without collateral effects, has promoted the investigation to develop new lead compounds with to advance for clinical trials. Previously, 3-nitro-1H-1,2,4-triazole-based amines and 1,2,3-triazoles demonstrated significant trypanocidal activity against T. cruzi. In this paper, we synthesized a new series of 92 examples of 1,2,3-triazoles. Six compounds exhibited antiparasitic activity, 14, 25, 27, 31 and 40, 43 and were effective against epimastigotes of two strains of T. cruzi (Y and Dm28-C) and 25, 27 and 31 exhibited trypanocidal activity similar to benzonidazole. Notably, the compound 25 compared to benzonidazole increase the toxicity against T. cruzi, with no apparent toxicity to the cell line of mice macrophages or primary mice peritoneal macrophages. As results, we calculated selectivity indexes up to 2000 to 25 and 31 in both T. cruzi strains. Derivative 14 caused a trypanostatic effect because it did not damage external epimastigote membrane. Triazoles 40 and 43 impaired parasites viability using a pathway not dependent on ROS production.

The effect of reinfection and mixed Trypanosoma cruzi infections on disease progression in mice

The progression of Chagas disease (CD) varies significantly from host to host and is affected by multiple factors. In particular, mixed strain infections and reinfections have the potential to exacerbate disease progression subsequently affecting clinical management of patients with CD. Consequently, an associated reduction in therapeutic intervention and poor prognosis may occur due to this exacerbated disease state. This study investigated the effects of mixed strain infections and reinfection with Trypanosoma cruzi in mice, using two isolates from different discrete typing units, TcI (C8 clone 1) and TcIV (10R26). There were no significant differences in mortality rate, body weight or body condition among mice infected with either C8 clone 1, 10R26, or a mixture of both isolates. However, the parasite was found in a significantly greater number of host organs in mice infected with a mixture of isolates, and the histopathological response to infection was significantly greater in mice infected with C8 clone 1 alone, and C8 clone 1+10R26 mixed infections than in mice infected with 10R26 alone. To investigate the effects of reinfection, mice received either a double exposure to C8 clone 1; a double exposure to 10R26; exposure to C8 clone 1 followed by 10R26; or exposure to 10R26 followed by C8 clone 1. Compared to single infection groups, mortality was significantly increased, while survival time, body weight and body condition were all significantly decreased across all reinfection groups, with no significant differences among these groups. The mortality rate over all reinfection groups was 63.6%, compared to 0% in single infection groups, however there was no evidence of a greater histopathological response to infection. These results suggest firstly, that the C8 clone 1 isolate is more virulent than the 10R26 isolate, and secondly, that a more disseminated infection may occur with a mixture of isolates than with single isolates, although there is no evidence that mixed infections have a greater pathological effect. By contrast, reinfections do have major effects on host survivability and thus disease outcome. This confirms previous research demonstrating spontaneous deaths following reinfection, a phenomenon that to our knowledge has only been reported once before.

Experimental and Clinical Treatment of Chagas Disease: A Review

Chagas disease (CD) is caused by the protozoan parasite Trypanosoma cruzi that infects a broad range of triatomines and mammalian species, including man. It afflicts 8 million people in Latin America, and its incidence is increasing in nonendemic countries owing to rising international immigration and nonvectorial transmission routes such as blood donation. Since the 1960s, the only drugs available for the clinical treatment of this infection have been benznidazole (BZ) and nifurtimox (NFX). Treatment with these trypanocidal drugs is recommended in both the acute and chronic phases of CD. These drugs have low cure rates mainly during the chronic phase, in addition both drugs present side effects that may result in the interruption of the treatment. Thus, more efficient and better-tolerated new drugs or pharmaceutical formulations containing BZ or NFX are urgently needed. Here, we review the drugs currently used for CD chemotherapy, ongoing clinical assays, and most-promising new experimental drugs. In addition, the mechanism of action of the commercially available drugs, NFX and BZ, the biodistribution of the latter, and the potential for novel formulations of BZ based on nanotechnology are discussed. Taken together, the literature emphasizes the urgent need for new therapies for acute and chronic CD.

Electrochemically Enabled, Nickel-Catalyzed Amination

Along with amide bond formation, Suzuki cross-coupling, and reductive amination, the Buchwald-Hartwig-Ullmann-type amination of aryl halides stands as one of the most employed reactions in modern medicinal chemistry. The work herein demonstrates the potential of utilizing electrochemistry to provide a complementary avenue to access such critical bonds using an inexpensive nickel catalyst under mild reaction conditions. Of note is the scalability, functional-group tolerance, rapid rate, and the ability to employ a variety of aryl donors (Ar-Cl, Ar-Br, Ar-I, Ar-OTf), amine types (primary and secondary), and even alternative X-H donors (alcohols and amides).

Discovery and Optimization of 5-Amino-1,2,3-triazole-4-carboxamide Series against Trypanosoma cruzi

Chagas’ disease, caused by the protozoan parasite Trypanosoma cruzi, is the most common cause of cardiac-related deaths in endemic regions of Latin America. There is an urgent need for new safer treatments because current standard therapeutic options, benznidazole and nifurtimox, have significant side effects and are only effective in the acute phase of the infection with limited efficacy in the chronic phase. Phenotypic high content screening against the intracellular parasite in infected VERO cells was used to identify a novel hit series of 5-amino-1,2,3-triazole-4-carboxamides (ATC). Optimization of the ATC series gave improvements in potency, aqueous solubility, and metabolic stability, which combined to give significant improvements in oral exposure. Mitigation of a potential Ames and hERG liability ultimately led to two promising compounds, one of which demonstrated significant suppression of parasite burden in a mouse model of Chagas’ disease.

2D and 3D QSAR Studies on a Series of Antichagasic Fenarimol Derivatives

Chagas disease is one of the most important neglected tropical diseases. Endemic in Latin America, the disease is a global public health problem, affecting several countries in North America, Europe, Asia and Oceania. The disease affects around 8-10 million people worldwide and the limited treatments available present low efficacy and severe side effects, highlighting the urgent need for new therapeutic options. In this work, the authors developed QSAR models for a series of fenarimol derivatives exhibiting anti-T. cruzi activity. The models were constructed using the Hologram QSAR (HQSAR), Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) methods. The QSAR models presented substantial predictive ability for a series of test set compounds (HQSAR, r2pred = 0.66; CoMFA, r2pred = 0.82; and CoMSIA, r2pred = 0.76), and were valuable to identify key structural features related to the observed trypanocidal activity. The results reported herein are useful for the design of novel derivatives having improved antichagasic properties.

In vitro drug susceptibility of two strains of the wildlife trypanosome, Trypanosoma copemani: A comparison with Trypanosoma cruzi

Trypanosomes are blood protozoan parasites that are capable of producing illness in the vertebrate host. Within Australia, several native Trypanosoma species have been described infecting wildlife. However, only Trypanosoma copemani has been associated with pathological lesions in wildlife hosts and more recently has been associated with the drastic decline of the critically endangered woylie (Bettongia penicillata). The impact that some trypanosomes have on the health of the vertebrate host has led to the development of numerous drug compounds that could inhibit the growth or kill the parasite. This study investigated and compared the in vitro susceptibility of two strains of T. copemani (G1 and G2) and one strain of Trypanosoma cruzi (10R26) against drugs that are known to show trypanocidal activity (benznidazole, posaconazole, miltefosine and melarsoprol) and against four lead compounds, two fenarimols and two pyridine derivatives (EPL-BS1937, EPL-BS2391, EPL-BS0967, and EPL-BS1246), that have been developed primarily against T.cruzi. The in vitro cytotoxicity of all drugs against L6 rat myoblast cells was also assessed. Results showed that both strains of T. copemani were more susceptible to all drugs and lead compounds than T. cruzi, with all IC50 values in the low and sub-μM range for both species. Melarsoprol and miltefosine exhibited the highest drug activity against both T. copemani and T. cruzi, but they also showed the highest toxicity in L6 cells. Interestingly, both fenarimol and pyridine derivative compounds were more active against T. copemani and T. cruzi than the reference drugs benznidazole and posaconazole. T. copemani strains exhibited differences in susceptibility to all drugs demonstrating once again considerable differences in their biological behaviour.

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions

Pd-catalyzed cross-coupling reactions that form C–N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C–N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Translational challenges of animal models in Chagas disease drug development: a review

Chagas disease, or American trypanosomiasis, caused by Trypanosoma cruzi parasite infection is endemic in Latin America and presents an increasing clinical challenge due to migrating populations. Despite being first identified over a century ago, only two drugs are available for its treatment, and recent outcomes from the first clinical trials in 40 years were lackluster. There is a critical need to develop new drugs to treat Chagas disease. This requires a better understanding of the progression of parasite infection, and standardization of animal models designed for Chagas disease drug discovery. Such measures would improve comparison of generated data and the predictability of test hypotheses and models designed for translation to human disease. Existing animal models address both disease pathology and treatment efficacy. Available models have limited predictive value for the preclinical evaluation of novel therapies and need to more confidently predict the efficacy of new drug candidates in clinical trials. This review highlights the overall lack of standardized methodology and assessment tools, which has hampered the development of efficacious compounds to treat Chagas disease. We provide an overview of animal models for Chagas disease, and propose steps that could be undertaken to reduce variability and improve predictability of drug candidate efficacy. New technological developments and tools may contribute to a much needed boost in the drug discovery process.

Enantiomers of nifurtimox do not exhibit stereoselective anti-Trypanosoma cruzi activity, toxicity, or pharmacokinetic properties

With the aim of improving the available drugs for the treatment of Chagas disease, individual enantiomers of nifurtimox were characterized. The results indicate that the enantiomers are equivalent in their in vitro activity against a panel of Trypanosoma cruzi strains; in vivo efficacy in a murine model of Chagas disease; in vitro toxicity and absorption, distribution, metabolism, and excretion characteristics; and in vivo pharmacokinetic properties. There is unlikely to be any therapeutic benefit of an individual nifurtimox enantiomer over the racemic mixture.

Binding mode and potency of N-indolyloxopyridinyl-4-aminopropanyl-based inhibitors targeting Trypanosoma cruzi CYP51

Chagas disease is a chronic infection in humans caused by Trypanosoma cruzi and manifested in progressive cardiomyopathy and/or gastrointestinal dysfunction. Limited therapeutic options to prevent and treat Chagas disease put 8 million people infected with T. cruzi worldwide at risk. CYP51, involved in the biosynthesis of the membrane sterol component in eukaryotes, is a promising drug target in T. cruzi. We report the structure–activity relationships (SAR) of an N-arylpiperazine series of N-indolyloxopyridinyl-4-aminopropanyl-based inhibitors designed to probe the impact of substituents in the terminal N-phenyl ring on binding mode, selectivity and potency. Depending on the substituents at C-4, two distinct ring binding modes, buried and solvent-exposed, have been observed by X-ray structure analysis (resolution of 1.95–2.48 Å). The 5-chloro-substituted analogs 9 and 10 with no substituent at C-4 demonstrated improved selectivity and potency, suppressing ≥99.8% parasitemia in mice when administered orally at 25 mg/kg, b.i.d., for 4 days.

A new experimental model for assessing drug efficacy against Trypanosoma cruzi infection based on highly sensitive in vivo imaging

The protozoan Trypanosoma cruzi is the causative agent of Chagas disease, one of the world’s major neglected infections. Although development of improved antiparasitic drugs is considered a priority, there have been no significant treatment advances in the past 40 years. Factors that have limited progress include an incomplete understanding of pathogenesis, tissue tropism, and disease progression. In addition, in vivo models, which allow parasite burdens to be tracked throughout the chronic stage of infection, have been lacking. To address these issues, we have developed a highly sensitive in vivo imaging system based on bioluminescent T. cruzi, which express a red-shifted luciferase that emits light in the tissue-penetrating orange-red region of the spectrum. The exquisite sensitivity of this noninvasive murine model has been exploited to monitor parasite burden in real time throughout the chronic stage, has allowed the identification of the gastrointestinal tract as the major niche of long-term infection, and has demonstrated that chagasic heart disease can develop in the absence of locally persistent parasites. Here, we review the parameters of the imaging system and describe how this experimental model can be incorporated into drug development programs as a valuable tool for assessing efficacy against both acute and chronic T. cruzi infections.

Lead Identification to Clinical Candidate Selection

Chagas disease affects 8 million people worldwide and remains a main cause of death due to heart failure in Latin America. The number of cases in the United States is now estimated to be 300,000, but there are currently no Food and Drug Administration (FDA)–approved drugs available for patients with Chagas disease. To fill this gap, we have established a public-private partnership between the University of California, San Francisco and the Genomics Institute of the Novartis Research Foundation (GNF) with the goal of delivering clinical candidates to treat Chagas disease. The discovery phase, based on the screening of more than 160,000 compounds from the GNF Academic Collaboration Library, led to the identification of new anti-Chagas scaffolds. Part of the screening campaign used and compared two screening methods, including a colorimetric-based assay using Trypanosoma cruzi expressing β-galactosidase and an image-based, high-content screening (HCS) assay using the CA-I/72 strain of T. cruzi. Comparing molecules tested in both assays, we found that ergosterol biosynthesis inhibitors had greater potency in the colorimetric assay than in the HCS assay. Both assays were used to inform structure-activity relationships for antiparasitic efficacy and pharmacokinetics. A new anti– T. cruzi scaffold derived from xanthine was identified, and we describe its development as lead series.

4-Aminopyridyl-based CYP51 inhibitors as anti-Trypanosoma cruzi drug leads with improved pharmacokinetic profile and in vivo potency

CYP51 is a P450 enzyme involved in the biosynthesis of the sterol components of eukaryotic cell membranes. CYP51 inhibitors have been developed to treat infections caused by fungi, and more recently the protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. To specifically optimize drug candidates for T. cruzi CYP51 (TcCYP51), we explored the structure-activity relationship (SAR) of a N-indolyl-oxopyridinyl-4-aminopropanyl-based scaffold originally identified in a target-based screen. This scaffold evolved via medicinal chemistry to yield orally bioavailable leads with potent anti-T. cruzi activity in vivo. Using an animal model of infection with a transgenic T. cruzi Y luc strain expressing firefly luciferase, we prioritized the biaryl and N-arylpiperazine analogues by oral bioavailability and potency. The drug-target complexes for both scaffold variants were characterized by X-ray structure analysis. Optimization of both binding mode and pharmacokinetic properties of these compounds led to potent inhibitors against experimental T. cruzi infection.