Two major human diseases caused by filariid nematodes are onchocerciasis, or river blindness, and lymphatic filariasis, which can lead to elephantiasis. The drugs ivermectin, diethylcarbamazine (DEC), and albendazole are used in control programs for these diseases, but are mainly effective against the microfilarial stage and have minimal or no effect on adult worms. Adult Onchocerca volvulus and Brugia malayi worms (macrofilariae) can live for up to 15 years, reproducing and allowing the infection to persist in a population. Therefore, to support control or elimination of these two diseases, effective macrofilaricidal drugs are necessary, in addition to current drugs. In an effort to identify macrofilaricidal drugs, we screened an FDA-approved library with adult worms of Brugia spp. and Onchocerca ochengi, third-stage larvae (L3s) of Onchocerca volvulus, and the microfilariae of both O. ochengi and Loa loa. We found that auranofin, a gold-containing drug used for rheumatoid arthritis, was effective in vitro in killing both Brugia spp. and O. ochengi adult worms and in inhibiting the molting of L3s of O. volvulus with IC₅₀ values in the low micromolar to nanomolar range. Auranofin had an approximately 43-fold higher IC₅₀ against the microfilariae of L. loa compared with the IC₅₀ for adult female O. ochengi, which may be beneficial if used in areas where Onchocerca and Brugia are co-endemic with L. loa, to prevent severe adverse reactions to the drug-induced death of L. loa microfilariae. Further testing indicated that auranofin is also effective in reducing Brugia adult worm burden in infected gerbils and that auranofin may be targeting the thioredoxin reductase in this nematode. Onchocerciasis or river blindness, and lymphatic filariasis, which can lead to disfiguring elephantiasis, are two neglected tropical diseases that affect millions of people, primarily in developing countries. Both diseases are caused by filariid nematodes; onchocerciasis is caused by Onchocerca volvulus and lymphatic filariasis is caused by Brugia malayi, B. timori, and Wuchereria bancrofti. Currently, there are no drugs available that are highly efficacious against adult worms; existing drugs mainly kill the first-stage larvae (microfilariae). While these drugs can reduce the transmission of infections in a population, the adult filariids (macrofilariae) can continue to produce microfilariae and perpetuate the cycle of infection. Finding a drug that could kill the adult worms would be an important tool in eliminating onchocerciasis and lymphatic filariasis. To identify potential macrofilaricidal drugs, we developed a high throughput screening method to test FDA-approved drugs on adult Brugia spp., which serves as a model for O. volvulus. Using this screening method, we identified a drug called auranofin that kills adult Onchocerca and adult Brugia spp. in vitro, inhibits the molting of O. volvulus L3s, and reduces the worm burden in an in vivo gerbil-B. pahangi model system. Auranofin is known to inhibit a critical enzyme called thioredoxin reductase in some parasite species, and subsequent testing of the effects of auranofin on the thioredoxin reductase of Brugia indicates that this may be auranofin’s mode of action in this nematode as well.

Neglected parasitic diseases remain a major public health issue worldwide, especially in tropical and subtropical areas. Human parasite diversity is very large, ranging from protozoa to worms. In most cases, more effective and new drugs are urgently needed. Previous studies indicated that the gold(I) drug auranofin (Ridaura^®) is effective against several parasites. Among new gold(I) complexes, the phosphole-containing gold(I) complex {1-phenyl-2,5-di(2-pyridyl)phosphole}AuCl (abbreviated as GoPI) is an irreversible inhibitor of both purified human glutathione and thioredoxin reductases. GoPI-sugar is a novel 1-thio-β-d-glucopyranose 2,3,4,6-tetraacetato-S-derivative that is a chimera of the structures of GoPI and auranofin, designed to improve stability and bioavailability of GoPI. These metal-ligand complexes are of particular interest because of their combined abilities to irreversibly target the essential dithiol/selenol catalytic pair of selenium-dependent thioredoxin reductase activity, and to kill cells from breast and brain tumors. In this work, screening of various parasites—protozoans, trematodes, and nematodes—was undertaken to determine the in vitro killing activity of GoPI-sugar compared to auranofin. GoPI-sugar was found to efficiently kill intramacrophagic Leishmania donovani amastigotes and adult filarial and trematode worms.

Helminths represent a diverse category of parasitic organisms that can thrive within a host for years, if not decades, in the absence of treatment. As such, they must establish mechanisms to subsist off their hosts, evade the immune system, and develop a niche among the other cohabiting microbial communities. The complex interplay of biologically small molecules (collectively known as the metabolome) derived from, utilized by, or in response to the presence of helminths within a host is an emerging field of study. In this Perspective, we briefly summarize the current existing literature, categorize key host–pathogen–microbiome interfaces that could be studied in the context of the metabolome, and provide background on mass spectrometry-based metabolomic methodology. Overall, we hope to provide a comprehensive guide for utilizing metabolomics in the context of helminthic disease.

Antibiotic treatment has emerged as a promising strategy to sterilize and kill filarial nematodes due to their dependence on their endosymbiotic bacteria, Wolbachia. Several studies have shown that novel and FDA-approved antibiotics are efficacious at depleting the filarial nematodes of their endosymbiont, thus reducing female fecundity. However, it remains unclear if antibiotics can permanently deplete Wolbachia and cause sterility for the lifespan of the adult worms. Concerns about resistance arising from mass drug administration necessitate a careful exploration of potential Wolbachia recrudescence. In the present study, we investigated the long-term effects of the FDA-approved antibiotic, rifampicin, in the Brugia pahangi jird model of infection. Initially, rifampicin treatment depleted Wolbachia in adult worms and simultaneously impaired female worm fecundity. However, during an 8-month washout period, Wolbachia titers rebounded and embryogenesis returned to normal. Genome sequence analyses of Wolbachia revealed that despite the population bottleneck and recovery, no genetic changes occurred that could account for the rebound. Clusters of densely packed Wolbachia within the worm’s ovarian tissues were observed by confocal microscopy and remained in worms treated with rifampicin, suggesting that they may serve as privileged sites that allow Wolbachia to persist in worms while treated with antibiotic. To our knowledge, these clusters have not been previously described and may be the source of the Wolbachia rebound. Onchocerciasis (river blindness) and lymphatic filariasis (elephantiasis) are two neglected tropical diseases caused by filarial nematodes, which harbor the endosymbiotic bacteria, Wolbachia. Major efforts to discover new drugs to treat these diseases have led to the discovery of novel compounds including those that target Wolbachia. We investigated the long-term effects of rifampicin on the filarial nematode, Brugia pahangi, and its endosymbiont, Wolbachia, in an in vivo rodent model of infection. Initially, Wolbachia titers were significantly reduced by 95% and female fecundity was impaired shortly after treatment. 8 months later however, Wolbachia rebounded and embryogenesis returned to normal. Sequence analysis of the Wolbachia genome revealed that despite the population bottleneck and recovery, no genetic changes occurred that could account for the rebound. Clusters of Wolbachia were observed within the ovaries of female worms throughout the entire 8-month study. These clusters may sequester Wolbachia and allow the bacteria to persist during antibiotic treatment, thereby enabling them to repopulate ovarian tissues and ensuring their vertical transmission to future generations of microfilariae.

Filarial worms cause multiple debilitating diseases in millions of people worldwide, including river blindness. Currently available drugs reduce transmission by killing larvae (microfilariae), but there are no effective cures targeting the adult parasites (macrofilaricides) which survive and reproduce in the host for very long periods. To identify effective macrofilaricides, we carried out phenotypic screening of a library of 2121 approved drugs for clinical use against adult Brugia pahangi and prioritized the hits for further studies by integrating those results with a computational prioritization of drugs and associated targets. This resulted in the identification of 18 hits with anti-macrofilaricidal activity, of which two classes, azoles and aspartic protease inhibitors, were further expanded upon. Follow up screening against Onchocerca spp. (adult Onchocerca ochengi and pre-adult O. volvulus) confirmed activity for 13 drugs (the majority having IC₅₀ < 10 μM), and a counter screen of a subset against L. loa microfilariae showed the potential to identify selective drugs that prevent adverse events when co-infected individuals are treated. Stage specific activity was also observed. Many of these drugs are amenable to structural optimization, and also have known canonical targets, making them promising candidates for further optimization that can lead to identifying and characterizing novel anti-macrofilarial drugs.