SCYX-7158, an oxaborole, is currently in Phase I clinical trials for the treatment of human
African trypanosomiasis. Here we investigate possible modes of action against Trypanosoma
brucei using orthogonal chemo-proteomic and genomic approaches. SILAC-based
proteomic studies using an oxaborole analogue immobilised onto a resin was used either in
competition with a soluble oxaborole or an immobilised inactive control to identify thirteen
proteins common to both strategies. Cell-cycle analysis of cells incubated with sub-lethal
concentrations of an oxaborole identified a subtle but significant accumulation of G2 and
>G2 cells. Given the possibility of compromised DNA fidelity, we investigated long-term
exposure of T. brucei to oxaboroles by generating resistant cell lines in vitro. Resistance
proved more difficult to generate than for drugs currently used in the field, and in one of our
three cell lines was unstable. Whole-genome sequencing of the resistant cell lines revealed
single nucleotide polymorphisms in 66 genes and several large-scale genomic aberrations.
The absence of a simple consistent mechanism among resistant cell lines and the diverse
list of binding partners from the proteomic studies suggest a degree of polypharmacology
that should reduce the risk of resistance to this compound class emerging in the field. The
combined genetic and chemical biology approaches have provided lists of candidates to be
investigated for more detailed information on the mode of action of this promising new drug
class
© 2015 Jones et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.