White Paper: Benzoxaboroles: A New Potential Drug for African Sleeping Sickness

Human African trypanosomiasis, caused by the kinetoplastid parasite Trypanosoma brucei, affects thousands of people across sub-Saharan Africa, and is fatal if left untreated. Treatment options for this disease, particularly stage 2 disease, which occurs after parasites have infected brain tissue, are limited due to inadequate efficacy, toxicity, and the complexity of treatment regimens.

We have discovered and optimized a series of benzoxaborole- 6-carboxamides to provide trypanocidal compounds that are orally active in murine models of human African trypanosomiasis. A key feature of this series is the presence of a boron atom in the heterocyclic core structure, which is essential to the observed trypanocidal activity. We also report the in vivo pharmacokinetic properties of lead compounds from the series and selection of SCYX-7158 as a preclinical candidate.

Human African trypanosomiasis (HAT), more commonly known as African sleeping sickness, is caused by two subspecies of the kinetoplastid parasite Trypanosoma brucei, Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, which are introduced into the victim through the bite of the tse-tse fly. Endemic across sub-Saharan Africa, tens of thousands of people are infected each year, with millions at risk of contracting the disease. If not treated early in the progression of the disease, the T. brucei parasites migrate across the blood–brain barrier and reside in brain tissue, ultimately causing neuronal death leading to a multitude of neurological symptoms including hallucinations, sleep disorders, coma and, ultimately, death.

Current treatment options for HAT are inadequate due to lack of efficacy, particularly once the parasites have migrated to the brain (stage 2 HAT), toxicity and the complexity of treatment regimens. The most commonly used treatment for stage 2 HAT, melarsoprol is highly toxic, with an estimated 5–10% drug-related mortality. A more recent drug, eflornithine, while effective against T.b. gambiense, is not effective against T.b. rhodesiense, and must be administered in a complex intravenous regime that is impractical in disease-endemic areas.

Consequently, there is an urgent need for new drugs to treat HAT and, in particular, a need for a safe, orally active drug that is effective against all known strains of T. brucei and is effective in stage 2 HAT.

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