BackgroundChagas disease, caused by the protozoan parasite Trypanosoma cruzi, represents a very important public health problem in Latin America where it is endemic. Although mostly asymptomatic at its initial stage, after the disease becomes chronic, about a third of the infected patients progress to a potentially fatal outcome due to severe damage of heart and gut tissues. There is an urgent need for new drugs against Chagas disease since there are only two drugs available, benznidazole and nifurtimox, and both show toxic side effects and variable efficacy against the chronic stage of the disease.Methodology/Principal FindingsGenetically engineered parasitic strains are used for high throughput screening (HTS) of large chemical collections in the search for new anti-parasitic compounds. These assays, although successful, are limited to reporter transgenic parasites and do not cover the wide T. cruzi genetic background. With the aim to contribute to the early drug discovery process against Chagas disease we have developed an automated image-based 384-well plate HTS assay for T. cruzi amastigote replication in a rat myoblast host cell line. An image analysis script was designed to inform on three outputs: total number of host cells, ratio of T. cruzi amastigotes per cell and percentage of infected cells, which respectively provides one host cell toxicity and two T. cruzi toxicity readouts. The assay was statistically robust (Z´ values >0.6) and was validated against a series of known anti-trypanosomatid drugs.Conclusions/SignificanceWe have established a highly reproducible, high content HTS assay for screening of chemical compounds against T. cruzi infection of myoblasts that is amenable for use with any T. cruzi strain capable of in vitro infection. Our visual assay informs on both anti-parasitic and host cell toxicity readouts in a single experiment, allowing the direct identification of compounds selectively targeted to the parasite.

In response to a call for the global eradication of malaria, drug discovery has recently been extended to identify compounds that prevent the onward transmission of the parasite, which is mediated by Plasmodium falciparum stage V gametocytes. Lately, metabolic activity has been used in vitro as a surrogate for gametocyte viability; however, as gametocytes remain relatively quiescent at this stage, their ability to undergo onward development (gamete formation) may be a better measure of their functional viability. During gamete formation, female gametocytes undergo profound morphological changes and express translationally repressed mRNA. By assessing female gamete cell surface expression of one such repressed protein, Pfs25, as the readout for female gametocyte functional viability, we developed an imaging-based high-throughput screening (HTS) assay to identify transmission-blocking compounds. This assay, designated the P. falciparum female gametocyte activation assay (FGAA), was scaled up to a high-throughput format (Z= factor, 0.7 ؎ 0.1) and subsequently validated using a selection of 50 known antimalarials from diverse chemical families. Only a few of these agents showed submicromolar 50% inhibitory concentrations in the assay: thiostrepton, methylene blue, and some endoperoxides. To determine the best conditions for HTS, a robustness test was performed with a selection of the GlaxoSmithKline Tres Cantos Antimalarial Set (TCAMS) and the final screening conditions for this library were determined to be a 2 M concentration and 48 h of incubation with gametocytes. The P. falciparum FGAA has been proven to be a robust HTS assay faithful to Plasmodium transmission-stage cell biology, and it is an innovative useful tool for antimalarial drug discovery which aims to identify new molecules with transmission-blocking potential. D espite the efforts made over decades of scientific research, malaria still remains a major health problem in tropical and subtropical areas, with more than 220 million cases and 600,000 deaths being registered per year (1). This parasitic disease is caused by Plasmodium infection through the bite of infected Anopheles female mosquitoes, with Plasmodium falciparum being responsible for the highest mortality rates (2).Traditionally, pharmacological antimalarial treatments have targeted parasite asexual reproduction inside erythrocytes, which leads to the clinical symptoms of malaria. However, a small proportion of these asexual blood stages (0.2 to 1%) are committed to develop into sexual stages: male and female gametocytes (3, 4). Their differentiation process inside erythrocytes takes 8 to 12 days for P. falciparum, and inside erythrocytes they undergo a series of morphological and metabolic changes classically categorized into five stages of maturation (5, 6). While most schizonticides, such as chloroquine, affect young gametocytes (stages I, II, and III), gametocytes at late stages of maturation are not sensitive to them (7). These insensitive stage V gametocytes, which are responsible for ...

The protozoan parasite Leishmania donovani is the causative agent of visceral leishmaniasis, a disease potentially fatal if not treated. Current available treatments have major limitations, and new and safer drugs are urgently needed. In recent years, advances in high-throughput screening technologies have enabled the screening of millions of compounds to identify new antileishmanial agents. However, most of the compounds identified in vitro did not translate their activities when tested in in vivo models, highlighting the need to develop more predictive in vitro assays. In the present work, we describe the development of a robust replicative, high-content, in vitro intracellular L. donovani assay. Horse serum was included in the assay media to replace standard fetal bovine serum, to completely eliminate the extracellular parasites derived from the infection process. A novel phenotypic in vitro infection model has been developed, complemented with the identification of the proliferation of intracellular amastigotes measured by EdU incorporation. In vitro and in vivo results for miltefosine, amphotericin B, and the selected compound 1 have been included to validate the assay.T he leishmaniases are a complex of diseases, with visceral and cutaneous manifestations caused by protozoan parasites of the genus Leishmania. Visceral leishmaniasis (VL) has been the main focus for drug research and development over the past 2 decades, due to the large disease burden in East Africa and South Asia (1) and potential patient death if not treated. For VL, there has been progress in treatment over the past decade, with clinical evidence for efficacy of and registration for use of oral miltefosine, paromomycin, and the liposomal formulation of amphotericin B (AmBisome, Gilead, USA) in South Asia (2), as well as combinations of these standard drugs (3). The need for new drugs to treat VL remains, as (i) miltefosine is the only approved oral treatment but requires 28 days of treatment and potential teratogenicity limits its use (4), (ii) paromomycin requires 21 days of treatment and intramuscular administration (http://www.dndi.org/diseases-projects/diseases /vl/current-treatment/current-treatment-vl.html), and (iii) liposomal amphotericin B formulations, which have successful cure rates with a single dose (5), require intravenous (i.v.) infusion, have a high cost if not donated, and have a requirement for cold storage, limiting use in countries where the disease is endemic (6). As part of the drive to find new treatments, there has been a refocus on the assays and models used to identify and develop new molecules as antileishmanial drugs. For in vitro screens and assays, this has ranged from the need to develop methods that (i) are adaptable to and enable high-throughput screens against the replicative intracellular-macrophage amastigote stage of Leishmania donovani, one of the causative species of VL (7); and (ii) include high-throughput technologies that enable the collection of more information compared to the traditionally use...

The mechanical retention of rigid erythrocytes in the spleen is central in major hematological diseases such as hereditary spherocytosis, sickle-cell disease and malaria. Here, we describe the use of microsphiltration (microsphere filtration) to assess erythrocyte deformability in hundreds to thousands of samples in parallel, by filtering them through microsphere layers in 384-well plates adapted for the discovery of compounds that stiffen Plasmodium falciparum gametocytes, with the aim of interrupting malaria transmission. Compound-exposed gametocytes are loaded into microsphiltration plates, filtered and then transferred to imaging plates for analysis. High-content imaging detects viable gametocytes upstream and downstream from filters and quantifies spleen-like retention. This screening assay takes 3-4 d. Unlike currently available methods used to assess red blood cell (RBC) deformability, microsphiltration enables high-throughput pharmacological screening (tens of thousands of compounds tested in a matter of months) and involves a cell mechanical challenge that induces a physiologically relevant dumbbell-shape deformation. It therefore directly assesses the ability of RBCs to cross inter-endothelial splenic slits in vivo. This protocol has potential applications in quality control for transfusion and in determination of phenotypic markers of erythrocytes in hematological diseases.

No abstract