Bacillus thuringiensis Cry5B protein as a new pan-hookworm cure

Abstract

Hookworms are intestinal nematode parasites that infect nearly half a billion people and are globally one of the most important contributors to iron-deficiency anemia. These parasites have significant impacts in developing children, pregnant women and working adults. Of all the soil-transmitted helminths or nematodes (STNs), hookworms are by far the most important, with disease burdens conservatively estimated at four million DALYs (Disability-Adjusted Life Years) and with productivity losses of up to US$139 billion annually. To date, mainly one drug, albendazole is used for hookworm therapy in mass drug administration, which has on average ∼80% cure rate that is lower (<40%) in some places. Given the massive numbers of people needing treatment, the threat of parasite resistance, and the inadequacy of current treatments, new and better cures against hookworms are urgently needed. Cry5B, a pore-forming protein produced by the soil bacterium Bacillus thuringiensis (Bt) has demonstrated good efficacy against Ancylostoma ceylanicum hookworm infections in hamsters. Here we broaden studies of Cry5B to include tests against infections of Ancylostoma caninum hookworms in dogs and against infections of the dominant human hookworm, Necator americanus, in hamsters. We show that Cry5B is highly effective against all hookworm parasites tested in all models. Neutralization of stomach acid improves Cry5B efficacy, which will aid in practical application of Cry5B significantly. Importantly, we also demonstrate that the anti-nematode therapeutic efficacy of Cry5B is independent of the host immune system and is not itself negated by repeated dosing. This study indicates that Bt Cry5B is a pan-hookworm anthelmintic with excellent properties for use in humans and other animals.

Recombinant Paraprobiotics as a New Paradigm for Treating Gastrointestinal Nematode Parasites of Humans

“…8). The single dose efficacy seen (53% reduction single dose 40 mg/kg Cry5B) was superior to that shown in previous studies with this parasite (31,45).…”

“…We therefore set out to deliver Cry5B, without purification of the protein, as part of a dead bacterial product (or "paraprobiotic" (50)). To make a Cry5B paraprobiotic, we initially turned to and produced Cry5B spore-crystal lysates, which have been used for most published in vivo studies of Cry5B anthelmintic efficacy as well as all Bt insecticidal production and use (31,33,34,43,45). We attempted to inactivate (kill) the spores without losing activity of the crystal protein using gamma irradiation (51).…”

“…Hamsters were infected with A. ceylanicum, and the infestations were allowed to proceed to mature adults with the appearance of parasite eggs (fecundity) excreted into the hamster feces (31,33,44). These hamsters were then treated with IBaCC produced in our laboratory containing 10 mg/kg Cry5B ( Figure 5A) or treated with IBa (vector-only control produced at the same time and processed identically to Cry5B…”

“…We also tested Cry5B IBaCC against the most common hookworms of humans, N. americanus, which can be maintained and studied in immunosuppressed hamsters (31).…”

“…More than a dozen different 3D-Cry proteins have been tested and found to be completely safe to vertebrates at doses of >>1000 mg/kg, and are FDA/EPA-approved for ingestion (28,29). The 3D-Cry protein Cry5B is related to the 3D-Cry proteins used as insecticides but targets nematodes instead., When administered orally as spore-crystal lysates or SCLs (a mix of Bt spores and Cry protein crystals as they naturally occur), Cry5B is highly effective against GIN infections in hamsters, pigs, and dogs (30)(31)(32)(33)(34).…”