Mini-review on CRISPR-Cas9 and its potential applications to help controlling neglected tropical diseases caused by Trypanosomatidae

Challenges and Tools for In Vitro Leishmania Exploratory Screening in the Drug Development Process: An Updated Review

Leishmaniases are a group of vector-borne diseases caused by infection with the protozoan parasites Leishmania spp. Some of them, such as Mediterranean visceral leishmaniasis, are zoonotic diseases transmitted from vertebrate to vertebrate by a hematophagous insect, the sand fly. As there is an endemic in more than 90 countries worldwide, this complex and major health problem has different clinical forms depending on the parasite species involved, with the visceral form being the most worrying since it is fatal when left untreated. Nevertheless, currently available antileishmanial therapies are significantly limited (low efficacy, toxicity, adverse side effects, drug-resistance, length of treatment, and cost), so there is an urgent need to discover new compounds with antileishmanial activity, which are ideally inexpensive and orally administrable with few side effects and a novel mechanism of action. Therefore, various powerful approaches were recently applied in many interesting antileishmanial drug development programs. The objective of this review is to focus on the very first step in developing a potential drug and to identify the exploratory methods currently used to screen in vitro hit compounds and the challenges involved, particularly in terms of harmonizing the results of work carried out by different research teams. This review also aims to identify innovative screening tools and methods for more extensive use in the drug development process.

In vitro evaluation of CRISPR PX-LmGP63 vector effect on pathogenicity of Leishmania major as a primary step to control leishmaniasis

Cutaneous leishmaniasis (CL) is caused by intracellular obligate parasites (Leishmania spp.) carried by the blood-sucking of female sandflies and transmitted between mammalian hosts. Despite the high incidence and prevalence of Leishmania cases in many countries, it has been a neglected tropical disease. The current treatment approaches are limited by the complications such as loss of fertility and drug resistance. It is, therefore, essential to find new medicines to treat leishmaniasis. CRISPR/Cas9 as a powerful genome-editing tool provides the opportunity to create precise genetic manipulation to investigate the molecular basis of different leishmaniasis cases. Therefore, our main goal was to evaluate the CRISPR PX-LmGP63 vector effect on pathogenicity of Leishmania majorin vitroto challenge for using CRISPR/Cas9 as a therapeutic CL through the reduction of L. major pathogenicity by manipulating the GP63 gene. In this study, L. major parasites were transfected with CRISPR/Cas9 vectors constructed by electroporation and then added to macrophage cells on RPMI. The effect of CRISPR/Cas9 constructs on GP63 mutation, viability, and status of L. major was investigated by counting phagocytic parasites into macrophages and DNA sequence analysis. Our data validate that the use of CRISPR/Cas9 in L. major creates a new stop codon and disrupts the frame sheet of the gene by creating a new insertion (thymine), which prevents its expression. In addition, the parasite count was significantly different in the case and control of infected macrophages (P < 0.05). This study shows the successfully targeted manipulation of the L. major GP63 gene via the adaptation of the CRISPR/Cas9 editing tool. The manipulation of GP63 revealed a reduction in the infection load compared to wild-type parasite infection. Therefore, more studies are necessary for this field to help achieve a new method for the prevention and treatment of CL disease.

In vitro cultivation of Trypanosoma congolense bloodstream forms: State of the art and advances

Animal African Trypanosomosis (AAT or Nagana) is a severe vector-borne disease caused by protozoan parasites belonging to the Trypanosomatidae family and is usually cyclically transmitted by blood-sucking tsetse flies. AAT remains a major problem in sub-Saharan Africa. Among the main AAT causative agents, Trypanosoma congolense (T. congolense or Tc) is one of the most important trypanosome species, in terms of economic and animal health impacts, infecting cattle and a wide range of animal hosts as well. To advance in AAT prevention and control, it is essential to better understand trypanosome biology and pathogenesis using bloodstream form (BSF) in vitro culture. The in vitro cultivation of T. congolense IL3000 BSF strain is already well established and widely used in research studies and drug activity assays. However, it may probably no longer truly reflect the reality of field trypanosome strains, due to decades of use and subsequent modifications. Here, we propose a novel culture protocol that supports the long-term in vitro growth of the animal-infective BSFs of three Savannah and Forest types of T. congolense strains, including T. congolense clone IL1180, which is not only a field strain but also a commonly-used reference strain in experimental animal assays. We established a homemade culture medium which made it possible to sustain T. congolense IL1180 growth from infected mouse blood for 18 days in axenic conditions. Moreover, we developed an efficient freezing/thawing system that allowed, for the first time, T. congolense IL1180 BSF growth within 30 days after thawing. Our results on T. congolense adaptation to in vitro culture are encouraging for future gene studies using new molecular tools or for new therapeutic drug assays.

Barcode sequence could be a good target for developing a species-specific anti-parasite agent based on CRISPR-Cas9

Parasitic infections are a severe issue in many regions of the world. We assume that if a chemical can destroy a DNA barcode sequence, then this chemical could be developed as a species-specific parasiticidal agent. To test this hypothesis, we designed sgRNAs that target the sequences of both a DNA barcode (ITS-2) and a control (5.8S rDNA) in Cryptocaryon irritans. In in vivo tests, we found that exposure to Cas9 mRNA mixed with sgRNAs was able to significantly reduce the hatching rate of tomont and the survival rate of theront. Quantitative Real-time PCR demonstrated that the DNAs of tomont and theront exposed to sgRNAs and Cas9 mRNA were significantly disrupted, no matter whether they were exposed to a single sgRNA or a mixture of two sgRNAs. DNA sequencing also suggested the test group that was exposed to a single sgRNA mixed with Cas9-induced mutation at sgRNA targeted fragments and the test group exposed to two sgRNAs combined with Cas9-induced deletion of large pieces. The findings and principles provided by this study contribute to the development of novel nucleic acid therapeutic drugs for cryptocaryoniasis and other parasitic diseases and provide insight into the development of species-specific parasiticidal agents.