Structural Requirements for Dihydrobenzoxazepinone Anthelmintics: Actions against Medically Important and Model Parasites: Trichuris muris, Brugia malayi, Heligmosomoides polygyrus, and Schistosoma mansoni

Scaffolds imparting anthelmintic activity: recent advancements and SAR studies

Helminthiasis, affecting billions globally, poses a significant health concern, especially in impoverished regions with inadequate sanitation. The intricate anatomical complexity of helminths requires specialized treatment approaches. There is currently no effective vaccine against helminth infections. Anthelmintics, crucial for combating these infections, target neuromuscular functions in parasites without harming the host. However, the emergence of resistance to existing anthelmintics, notably benzimidazoles, presents a growing global challenge. This review delves into the structure-activity relationship of previously synthesized core anthelmintic scaffolds-Benzimidazole, coumarin, pyrazoline, triazole, and others-to elucidate their promising anthelmintic activities. Understanding the structure-activity relationship of these novel benzimidazole derivatives, Coumarin derivatives, and others is crucial in designing potent anthelmintics, overcoming resistance, and optimizing efficacy to combat the escalating global burden of helminth infections. In the present review, we cover recently studied compounds (from the year 2019 to till date) which have promising anthelmintic activity. This review will be useful for the pharmacology and medicinal chemistry researchers working in the area anthelmintics with various scaffolds like aminobenzothiazole, benzimidazole, benzothiazole, coumarin, chromene, spiroketal, pyrazoline, triazole, etc. to design novel potent anthelmintic compound.

Discovery of Human PIM Kinase Inhibitors as a Class of Anthelmintic Drugs to Treat Intestinal Nematode Infections

Soil-transmitted helminth (STH) infections affect one-fourth of the global population and pose a significant threat to human and animal health, with limited treatment options and emerging drug resistance. Trichuris trichiura (whipworm) stands out as a neglected disease, necessitating new drugs to address this unmet medical need. We discovered that several different chemical series of related human Provirus Integration sites for Moloney murine leukemia virus (PIM) family kinase inhibitors possess potent anthelmintic activity by using whole-worm motility assays. Systematic structure-activity relationship (SAR) studies based on the pan-PIM kinase inhibitor CX-6258 were conducted to identify compounds displaying improved in vitro motility inhibition of both adult hookworm (Ancylostoma ceylanicum) and adult whipworm (Trichuris muris) nematodes. A broad kinase selectivity screen of >450 human kinases confirms PIM1 kinase and others as potential targets for CX-6258 and analogues thereof. In addition, we demonstrated that CX-6258 significantly reduced worm burden and egg counts in the T. muris infection model of mice, establishing it as a new oral small molecule anthelmintic therapeutic.

Small Molecule Ligands of the BET-like Bromodomain, SmBRD3, Affect Schistosoma mansoni Survival, Oviposition, and Development

Schistosomiasis is a disease affecting >200 million people worldwide, but its treatment relies on a single agent, praziquantel. To investigate new avenues for schistosomiasis control, we have conducted the first systematic analysis of bromodomain-containing proteins (BCPs) in a causative species, Schistosoma mansoni. Having identified 29 putative bromodomains (BRDs) in 22 S. mansoni proteins, we selected SmBRD3, a tandem BRD-containing BCP that shows high similarity to the human bromodomain and extra terminal domain (BET) family, for further studies. Screening 697 small molecules identified the human BET BRD inhibitor I-BET726 as a ligand for SmBRD3. An X-ray crystal structure of I-BET726 bound to the second BRD of SmBRD3 [SmBRD3(2)] enabled rational design of a quinoline-based ligand (15) with an ITC Kd = 364 ± 26.3 nM for SmBRD3(2). The ethyl ester pro-drug of compound 15 (compound 22) shows substantial effects on sexually immature larval schistosomula, sexually mature adult worms, and snail-infective miracidia in ex vivo assays.

Another decade of Trichuris muris research: An update and application of key discoveries

The mouse whipworm, Trichuris muris, has been used for over 60 years as a tractable model for human trichuriasis, caused by the related whipworm species, T. trichiura. The history of T. muris research, from the discovery of the parasite in 1761 to understanding the lifecycle and outcome of infection with different doses (high versus low dose infection), as well as the immune mechanisms associated with parasite expulsion and chronic infection have been detailed in an earlier review published in 2013. Here, we review recent advances in our understanding of whipworm biology, host-parasite interactions and basic immunology brought about using the T. muris mouse model, focussing on developments from the last decade. In addition to the traditional high/low dose infection models that have formed the mainstay of T. muris research to date, novel models involving trickle (repeated low dose) infection in laboratory mice or infection in wild or semi-wild mice have led to important insights into how immunity develops in situ in a multivariate environment, while the use of novel techniques such as the development of caecal organoids (enabling the study of larval development ex vivo) promise to deliver important insights into host-parasite interactions. In addition, the genome and transcriptome analyses of T. muris and T. trichiura have proven to be invaluable tools, particularly in the context of vaccine development and identification of secreted products including proteins, extracellular vesicles and micro-RNAs, shedding further light on how these parasites communicate with their host and modulate the immune response to promote their own survival.

Discovery of N-methylbenzo[d]oxazol-2-amine as new anthelmintic agent through scalable protocol for the synthesis of N-alkylbenzo[d]oxazol-2-amine and N-alkylbenzo[d]thiazol-2-amine derivatives

We discovered a lead compound, N-methylbenzo[d]oxazol-2-amine (2a), which had comparable potency to albendazole, an orally administered anthelminticdrug, against Gnathostoma spinigerum, Caenorhabditis elegans and Trichinella spiralis. Compound 2a showed about 10 times lower cytotoxicity towards normal human cell line (HEK293) than albendazole. Moreover, we have developed new processes for the synthesis of N-alkylbenzo[d]oxazol-2-amine and N-alkylbenzo[d]thiazol-2-amine derivatives via metal-free conditions. This protocol could serve as a robust and scalable method, especially, to synthesize N-methylbenzo[d]oxazol-2-amine and N-methylbenzo[d]thiazol-2-amine derivatives which were difficult to prepare using other metal-free conditions. The method employed benzoxazole-2-thiol or benzothiazole-2-thiol as the substrate. The reaction was triggered by methylation of the thiol functional group to form the methyl sulfide intermediate, a crucial tactic, which facilitated in a smooth nucleophilic addition-elimination reaction with gaseous methylamine generated in situ from N-methylformamide. In addition, the proteomic analysis of compound 2a was also studied in this work.

Medicinal Plant Preparations Administered by Botswana Traditional Health Practitioners for Treatment of Worm Infections Show Anthelmintic Activities

Schistosomiasis and soil-transmitted helminths are some of the priority neglected tropical diseases (NTDs) targeted for elimination by the World Health Organization (WHO). They are prevalent in Botswana and although Botswana has begun mass drug administration with the hope of eliminating soil-transmitted helminths as a public health problem, the prevalence of schistosomiasis does not meet the threshold required to warrant large-scale interventions. Although Botswana has a modern healthcare system, many people in Botswana rely on traditional medicine to treat worm infections and schistosomiasis. In this study, ten plant species used by traditional health practitioners against worm infections were collected and tested against Ancylostoma ceylanicum (zoonotic hookworm), Heligmosomoides polygyrus (roundworm of rodents), Necator americanus (New World hookworm), Schistosoma mansoni (blood fluke) [adult and newly transformed schistosomula (NTS)], Strongyloides ratti (threadworm) and Trichuris muris (nematode parasite of mice) in vitro. Extracts of two plants, Laphangium luteoalbum and Commiphora pyaracanthoides, displayed promising anthelmintic activity against NTS and adult S. mansoni, respectively. L. luteoalbum displayed 85.4% activity at 1 μg/mL against NTS, while C. pyracanthoides displayed 78.5% activity against adult S. mansoni at 10 μg/mL.

A mouse infection model and long-term lymphatic endothelium co-culture system to evaluate drugs against adult Brugia malayi

The development of new drugs targeting adult-stage lymphatic filarial nematodes is hindered by the lack of a robust long-term in vitro culture model. Testing potential direct-acting and anti-Wolbachia therapeutic candidates against adult lymphatic filariae in vitro requires their propagation via chronic infection of gerbils. We evaluated Brugia malayi parasite burden data from male Mongolian gerbils compared with two immune-deficient mouse strains highly susceptible to B. malayi: CB.17 Severe-Combined Immmuno-Deficient (SCID) and interleukin-4 receptor alpha, interleukin-5 double knockout (IL-4Rα-/-IL-5-/-) mice. Adult worms generated in IL-4Rα-/-IL-5-/- mice were tested with different feeder cells (human embryonic kidney cells, human adult dermal lymphatic endothelial cells and human THP-1 monocyte differentiated macrophages) and comparative cell-free conditions to optimise and validate a long-term in vitro culture system. Cultured parasites were compared against those isolated from mice using motility scoring, metabolic viability assay (MTT), ex vivo microfilariae release assay and Wolbachia content by qPCR. A selected culture system was validated as a drug screen using reference anti-Wolbachia (doxycycline, ABBV-4083 / flubentylosin) or direct-acting compounds (flubendazole, suramin). BALB/c IL-4Rα-/-IL-5-/- or CB.17 SCID mice were superior to Mongolian gerbils in generating adult worms and supporting in vivo persistence for periods of up to 52 weeks. Adult females retrieved from BALB/c IL-4Rα-/-IL-5-/- mice could be cultured for up to 21 days in the presence of a lymphatic endothelial cell co-culture system with comparable motility, metabolic activity and Wolbachia titres to those maintained in vivo. Drug studies confirmed significant Wolbachia depletions or direct macrofilaricidal activities could be discerned when female B. malayi were cultured for 14 days. We therefore demonstrate a novel methodology to generate adult B. malayi in vivo and accurately evaluate drug efficacy ex vivo which may be adopted for drug screening with the dual benefit of reducing overall animal use and improving anti-filarial drug development.

Actions of Camptothecin Derivatives on Larvae and Adults of the Arboviral Vector Aedes aegypti

Mosquito-borne viruses including dengue, Zika, and Chikungunya viruses, and parasites such as malaria and Onchocerca volvulus endanger health and economic security around the globe, and emerging mosquito-borne pathogens have pandemic potential. However, the rapid spread of insecticide resistance threatens our ability to control mosquito vectors. Larvae of Aedes aegypti were screened with the Medicines for Malaria Venture Pandemic Response Box, an open-source compound library, using INVAPP, an invertebrate automated phenotyping platform suited to high-throughput chemical screening of larval motility. We identified rubitecan (a synthetic derivative of camptothecin) as a hit compound that reduced A. aegypti larval motility. Both rubitecan and camptothecin displayed concentration dependent reduction in larval motility with estimated EC50 of 25.5 ± 5.0 µM and 22.3 ± 5.4 µM, respectively. We extended our investigation to adult mosquitoes and found that camptothecin increased lethality when delivered in a blood meal to A. aegypti adults at 100 µM and 10 µM, and completely blocked egg laying when fed at 100 µM. Camptothecin and its derivatives are inhibitors of topoisomerase I, have known activity against several agricultural pests, and are also approved for the treatment of several cancers. Crucially, they can inhibit Zika virus replication in human cells, so there is potential for dual targeting of both the vector and an important arbovirus that it carries.

Automated phenotyping of mosquito larvae enables high-throughput screening for novel larvicides and offers potential for smartphone-based detection of larval insecticide resistance

Pyrethroid-impregnated nets have contributed significantly to halving the burden of malaria but resistance threatens their future efficacy and the pipeline of new insecticides is short. Here we report that an invertebrate automated phenotyping platform (INVAPP), combined with the algorithm Paragon, provides a robust system for measuring larval motility in Anopheles gambiae (and An. coluzzi) as well as Aedes aegypti with the capacity for high-throughput screening for new larvicides. By this means, we reliably quantified both time- and concentration-dependent actions of chemical insecticides faster than using the WHO standard larval assay. We illustrate the effectiveness of the system using an established larvicide (temephos) and demonstrate its capacity for library-scale chemical screening using the Medicines for Malaria Venture (MMV) Pathogen Box library. As a proof-of-principle, this library screen identified a compound, subsequently confirmed to be tolfenpyrad, as an effective larvicide. We have also used the INVAPP / Paragon system to compare responses in larvae derived from WHO classified deltamethrin resistant and sensitive mosquitoes. We show how this approach to monitoring larval response to insecticides can be adapted for use with a smartphone camera application and therefore has potential for further development as a simple portable field-assay with associated real-time, geo-located information to identify hotspots.