Bacillus thuringiensis Cry5B protein as a new pan-hookworm cure

Authors: HU, YAN - University Of Massachusetts; NGUYEN, THANH-THANH - University Of Massachusetts; LEE, ALICE - Cornell University; Urban, Joseph; MILLER, MELANIE - University Of San Diego; ZHAN, BIN - Baylor College Of Medicine; KOCH, DAVID - University Of Massachusetts; NOON, JASON - University Of Massachusetts; ABRAHAM, AMBILY - University Of Massachusetts; FUJIWARA, TOSHIO - Federal University Of Minas Gerais

Submitted to: International Journal for Parasitology: Drugs and Drug Resistance
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2018
Publication Date: 5/4/2018
Citation: Hu, Y., Nguyen, T., Lee, A.C., Urban Jr, J.F., Miller, M.M., Zhan, B., Koch, D.J., Noon, J., Abraham, A., Fujiwara, T. 2018. Bacillus thuringiensis Cry5B protein as a new pan-hookworm cure. International Journal for Parasitology: Drug and Drug Resistance. 8:287-294. https://doi.org/10.1016/j.ijpddr.2018.05.001
DOI: https://doi.org/10.1016/j.ijpddr.2018.05.001

Interpretive Summary: Roundworms are one of the most important of the soil-transmitted helminths (parasitic worms) of humans and livestock where they cause considerable morbidity and economic losses. Strategies to control infection rely mostly on anti-parasitic drugs, but drug resistance is a growing problem. Thus, development of additional treatment options are urgently needed. One such promising option is Cry5B, a bacterial derived three-domain crystal (Cry) protein that has been shown to be effective against worm infection in rodent models. Cry5B is also efficacious against large roundworms in pigs and against important veterinary targets in cell culture studies. The Cry proteins are generally considered non-toxic and safe to mammals and are used globally to control insects that damage crops and carry disease. They are EPA/FDA approved for human ingestion and are a significant part of our food chain, e.g., >80% of all corn grown in the U.S. expresses a Cry protein. Cry5B is also mechanistically safe because mammals lack the receptors that convey reactivity of this compound. However, to be effective as a human and livestock therapeutic against these globally important parasites, it is important to establish if Cry5B is broadly active against parasitic worms within different mammalian hosts. Therefore Cry5B efficacy was tested against hookworms in multiple host species to examine three key issues that included 1) if the anti-parasitic activity of Cry5B requires the immune system to expel parasites; 2) if a host response to Cry5B builds up after repeated doses that would inhibit the ability of the protein to subsequently function; and 3) whether neutralization of stomach acid improves protein efficacy in order to allow for lower costs and significant reductions in dosing. The results of all three objectives confirmed the efficacy of Cry5B supporting further studies to broadly explore more practical use of this compound for the control of parasitic worms in humans and livestock. This work is relevant and important to clinicians that study parasitic disease in humans and to producers of livestock that expect better control options for producing more cost effective and healthy livestock.

Technical 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.