Plasmodium falciparum parasites overexpressing farnesyl diphosphate synthase/geranylgeranyl diphosphate synthase are more resistant to risedronate

Emerging Drug Targets for Antimalarial Drug Discovery: Validation and Insights into Molecular Mechanisms of Function

Approximately 619,000 malaria deaths were reported in 2021, and resistance to recommended drugs, including artemisinin-combination therapies (ACTs), threatens malaria control. Treatment failure with ACTs has been found to be as high as 93% in northeastern Thailand, and parasite mutations responsible for artemisinin resistance have already been reported in some African countries. Therefore, there is an urgent need to identify alternative treatments with novel targets. In this Perspective, we discuss some promising antimalarial drug targets, including enzymes involved in proteolysis, DNA and RNA metabolism, protein synthesis, and isoprenoid metabolism. Other targets discussed are transporters, Plasmodium falciparum acetyl-coenzyme A synthetase, N-myristoyltransferase, and the cyclic guanosine monophosphate-dependent protein kinase G. We have outlined mechanistic details, where these are understood, underpinning the biological roles and hence druggability of such targets. We believe that having a clear understanding of the underlying chemical interactions is valuable to medicinal chemists in their quest to design appropriate inhibitors.

A Trypanosoma brucei ORFeome-Based Gain-of-Function Library Identifies Genes That Promote Survival during Melarsoprol Treatment

Trypanosoma brucei is an early branching protozoan parasite that causes human and animal African trypanosomiasis. Forward genetics approaches are powerful tools for uncovering novel aspects of trypanosomatid biology, pathogenesis, and therapeutic approaches against trypanosomiasis. Here, we have generated a T. brucei cloned ORFeome consisting of >90% of the targeted 7,245 genes and used it to make an inducible gain-of-function parasite library broadly applicable to large-scale forward genetic screens. We conducted a proof-of-principle genetic screen to identify genes whose expression promotes survival in melarsoprol, a critical drug of last resort. The 57 genes identified as overrepresented in melarsoprol survivor populations included the gene encoding the rate-limiting enzyme for the biosynthesis of an established drug target (trypanothione), validating the tool. In addition, novel genes associated with gene expression, flagellum localization, and mitochondrion localization were identified, and a subset of those genes increased melarsoprol resistance upon overexpression in culture. These findings offer new insights into trypanosomatid basic biology, implications for drug targets, and direct or indirect drug resistance mechanisms. This study generated a T. brucei ORFeome and gain-of-function parasite library, demonstrated the library's usefulness in forward genetic screening, and identified novel aspects of melarsoprol resistance that will be the subject of future investigations. These powerful genetic tools can be used to broadly advance trypanosomatid research.IMPORTANCE Trypanosomatid parasites threaten the health of more than 1 billion people worldwide. Because their genomes are highly diverged from those of well-established eukaryotes, conservation is not always useful in assigning gene functions. However, it is precisely among the trypanosomatid-specific genes that ideal therapeutic targets might be found. Forward genetics approaches are an effective way to identify novel gene functions. We used an ORFeome approach to clone a large percentage of Trypanosoma brucei genes and generate a gain-of-function parasite library. This library was used in a genetic screen to identify genes that promote resistance to the clinically significant yet highly toxic drug melarsoprol. Hits arising from the screen demonstrated the library's usefulness in identifying known pathways and uncovered novel aspects of resistance mediated by proteins localized to the flagellum and mitochondrion. The powerful new genetic tools generated herein are expected to promote advances in trypanosomatid biology and therapeutic development in the years to come.

New directions in antimalarial target validation

Introduction: Malaria is one of the most prevalent human infections worldwide with over 40% of the world's population living in malaria-endemic areas. In the absence of an effective vaccine, emergence of drug-resistant strains requires urgent drug development. Current methods applied to drug target validation, a crucial step in drug discovery, possess limitations in malaria. These constraints require the development of techniques capable of simplifying the validation of Plasmodial targets.Areas covered: The authors review the current state of the art in techniques used to validate drug targets in malaria, including our contribution - the protein interference assay (PIA) - as an additional tool in rapid in vivo target validation.Expert opinion: Each technique in this review has advantages and disadvantages, implying that future validation efforts should not focus on a single approach, but integrate multiple approaches. PIA is a significant addition to the current toolset of antimalarial validation. Validation of aspartate metabolism as a druggable pathway provided proof of concept of how oligomeric interfaces can be exploited to control specific activity in vivo. PIA has the potential to be applied not only to other enzymes/pathways of the malaria parasite but could, in principle, be extrapolated to other infectious diseases.

Farnesyl pyrophosphate synthase is essential for the promastigote and amastigote stages in Leishmania major

Isoprenoid synthesis provides a diverse class of biomolecules including sterols, dolichols, ubiquinones and prenyl groups. The enzyme farnesyl pyrophosphate synthase (FPPS) catalyzes the formation of farnesyl pyrophosphate, a key intermediate for the biosynthesis of all isoprenoids. In Leishmania, FPPS is considered the main target of nitrogen containing bisphosphonates, yet the essentiality of this enzyme remains untested. Using a facilitated knockout approach, we carried out the genetic analysis of FPPS in Leishmania major. Our data indicated that chromosomal null mutants for FPPS could only be generated in presence of an episomally expressed FPPS. Long-term retention of the episome by the chromosomal FPPS-null mutants in culture and in infected BALB/c mice suggests that FPPS is indispensable. In addition, applying negative selection pressure failed to induce the loss of ectopic FPPS in the chromosomal FPPS-null mutants, although it led to significant growth delay in culture and in mice. Together, our findings have confirmed the essentiality of FPPS in both promastigotes and amastigotes in L. major and thus validate its potential as a drug target for the treatment of cutaneous leishmaniasis.