Hitting drug-resistant malaria infection with triazole-linked flavonoid-chloroquine hybrid compounds

Background: Malaria represents the major parasitic disease in tropical regions, and the development of new potent drugs is of pivotal importance. In this study, a series of hybrid molecules were designed by linking the 7-chloroquinoline core of chloroquine to different fluorinated flavonoid-related scaffolds. Materials & methods: Compounds were prepared by exploiting the click chemistry approach, allowing the introduction of a 1,2,3-triazole, a privileged structural motif in antiparasitic dug discovery. Results: Compounds 1b and 1c were the most interesting and were endowed with the highest in vitro activity, mainly against a resistant Plasmodium falciparum strain. They also inhibited hemozoin formation, and 1c was more effective than chloroquine against stage V gametocytes. Conclusion: The homoisoflavone core is a new, promising antimalarial scaffold that deserves further investigation.

Exploring a Tetrahydroquinoline Antimalarial Hit from the Medicines for Malaria Pathogen Box and Identification of its Mode of Resistance as PfeEF2

New antimalarial treatments with novel mechanism of action are needed to tackle Plasmodium falciparum infections that are resistant to first-line therapeutics. Here we report the exploration of MMV692140 (2) from the Pathogen Box, a collection of 400 compounds that was made available by Medicines for Malaria Venture (MMV) in 2015. Compound 2 was profiled in in vitro models of malaria and was found to be active against multiple life-cycle stages of Plasmodium parasites. The mode of resistance, and putatively its mode of action, was identified as Plasmodium falciparum translation elongation factor 2 (PfeEF2), which is responsible for the GTP-dependent translocation of the ribosome along mRNA. The compound maintains activity against a series of drug-resistant parasite strains. The structural motif of the tetrahydroquinoline (2) was explored in a chemistry program with its structure-activity relationships examined, resulting in the identification of an analog with 30-fold improvement of antimalarial asexual blood stage potency.

Beta-globin gene haplotypes and selected Malaria-associated variants among black Southern African populations

Partial carrier-resistance to Plasmodium falciparum malaria conferred by the sickle cell (HbS) mutation has resulted in the local amplification and positive selection of sickle cell disease (SCD) in malaria-endemic regions and particularly in sub-Saharan Africa (SSA). The present study investigated the β-globin gene haplotypes, and selected malaria-associated variants among three cohorts of Bantu-speaking individuals from Malawi, Zimbabwe and South Africa compared with reports with data from others SSA populations. The data suggest a south-ward frequency decrease of malaria-associated variants in SSA linked to the evolutionary dynamics of various African populations’ genomes through selective pressure of malaria. These selected genomics differences, positive selection of SCD in malaria-endemic regions among ‘Bantus’ from various part of Africa emphasise the evidence of the dissociation between genetics, anthropology and culture. The present study also showed a relatively prevalent Benin haplotype, which is mostly found in West Africa, among Southern African Blacks and very low Bantu haplotype, which could suggest a major migration route, of Southern Africa Bantu, along the African west coast, post-occurrence of the Sickle cell mutation, which date remain to be fully elucidated.

The "pushmi-pullyu" of resistance to chloroquine in malaria

Malarial infection continues to impart devastating health problems in the developing world. Treatment of malaria has involved chemotherapy since 168 BC, with the most prevalent and successful forms using plant alkaloids. Perhaps the greatest treatment success against malaria was by chloroquine, a synthetic derivative of the quinines found in the Cinchona tree bark. Chloroquine is able to kill parasites by interfering with haem metabolism in the parasite's digestive vacuole. The widespread use of chloroquine predictably resulted in the development of drug-resistant malaria and the most highly implicated resistance mediators are the transporter proteins P-glycoprotein (P-gp) homologue 1 (P-gh1) and Plasmodium falciparum chloroquine-resistance transporter (PfCRT), which reside on the parasite's digestive vacuole. The presence of PfCRT and P-gh1 on the vacuole membrane is analogous to the two-headed fictional creature known as the "Pushmi-Pullyu". P-gh1 (Pushmi) increases influx of chloroquine into the vacuole, while PfCRT (Pullmi) causes efflux of chloroquine from the vacuole. This review describes how drug-resistant malarial parasites co-ordinate chloroquine distribution through adaptive mutations to promote their survival in the presence of this cytotoxic drug.

Molecular Farming in Artemisia annua, a Promising Approach to Improve Anti-malarial Drug Production

Malaria is a parasite infection affecting millions of people worldwide. Even though progress has been made in prevention and treatment of the disease; an estimated 214 million cases of malaria occurred in 2015, resulting in 438,000 estimated deaths; most of them occurring in Africa among children under the age of five. This article aims to review the epidemiology, future risk factors and current treatments of malaria, with particular focus on the promising potential of molecular farming that uses metabolic engineering in plants as an effective anti-malarial solution. Malaria represents an example of how a health problem may, on one hand, influence the proper development of a country, due to its burden of the disease. On the other hand, it constitutes an opportunity for lucrative business of diverse stakeholders. In contrast, plant biofarming is proposed here as a sustainable, promising, alternative for the production, not only of natural herbal repellents for malaria prevention but also for the production of sustainable anti-malarial drugs, like artemisinin (AN), used for primary parasite infection treatments. AN, a sesquiterpene lactone, is a natural anti-malarial compound that can be found in Artemisia annua. However, the low concentration of AN in the plant makes this molecule relatively expensive and difficult to produce in order to meet the current worldwide demand of Artemisinin Combination Therapies (ACTs), especially for economically disadvantaged people in developing countries. The biosynthetic pathway of AN, a process that takes place only in glandular secretory trichomes of A. annua, is relatively well elucidated. Significant efforts have been made using plant genetic engineering to increase production of this compound. These include diverse genetic manipulation approaches, such as studies on diverse transcription factors which have been shown to regulate the AN genetic pathway and other biological processes. Results look promising; however, further efforts should be addressed toward optimization of the most cost-effective biofarming approaches for synthesis and production of medicines against the malaria parasite.

Molecular analysis of markers associated with chloroquine and sulfadoxine/pyrimethamine resistance in Plasmodium falciparum malaria parasites from southeastern Côte-d'Ivoire by the time of Artemisinin-based Combination Therapy adoption in 2005

PURPOSE

Artemisin-based combination therapies became the recommended therapy in Côte-d'Ivoire in 2005, but both chloroquine (CQ) and sulfadoxine/pyrimethamine (SP) have been heavily used for many decades. Despite this long history, little is known about the geographical distribution of drug resistance-conferring genotypes outside the capital city of Abidjan. In this work, we compared the prevalence of drug-resistant genotypes in Bonoua, an urban area, and Samo, a rural agricultural area, in southeastern Côte-d'Ivoire, about 59 km from Abidjan.

PATIENTS AND METHODS

Samples were collected from symptomatic patients in both sites during the rainy season in 2005. Genomic DNA was isolated and codons associated with resistance to CQ and SP were analyzed: pfcrt codons Cys-72-Ser, Val-73-Val, Met-74-Ile, Arg-75-Glu, Lys-76-Thr; pfdhfr codons Ala-16-Val, Arg-51-Ile, Cys-59-Arg, Ser-108-Arg/Thr, and Ile-164-Leu; pfdhps codons Ser-436-Ala, Ala-437-Gly, Lys-540-Glu, Ala-581-Gly, and Ala-613-Thr/Ser.

RESULTS

A limited number of genotypes were found in Bonoua compared with Samo. In both sites, the triple-mutant allele CVIET of pfcrt predominated: 100% in Bonoua and 86.2% in Samo. The wild-type allele, NCSI of pfdhfr, was common - 50% in Bonoua and 38.7% in Samo - but the triple-mutant IRNI and double-mutant NRNI were also frequent (IRNI, 32.6% in Bonoua and 19.4% in Samo; NRNI, 15.2% in Bonoua and 9.7% in Samo). In Samo, a wide range of different genotypes of Pfdhps was observed, with alleles carrying the Gly-437 codon fixed in Bonoua and comprising 73% of the isolates in Samo.

CONCLUSION

Although these two sites are only 8 km apart, they belonged to very different ecological environments. The overall prevalence of alleles of single-nucleotide polymorphisms associated with resistance to CQ and SP in both locations was among the highest of the region by 2005, although the more rural site showed a more diverse set of alleles and mixed infections. Continued surveillance of these markers will be a useful tool for drug policy, as both CQ and SP are still frequently used years after withdrawal, and SP is recommended by the World Health Organization for intermittent preventive therapy for pregnant women and infants. Data analyzed herein are among the first to be generated during the year of artemisin-based combination-therapy introduction in Côte-d'Ivoire and could be of some interest for malaria policy-makers.