Validation of DXS as an attractive drug target in mycobacteria

A rapid emergence in the incidences of Tuberculosis (TB) drug resistance undermines efforts to eradicate the disease and strengthens calls for development of new drugs with novel mechanisms of action. In drug discovery, finding an attractive drug target is as important as finding a good drug candidate. Hence more efforts are made to identify, validate and prioritize drug targets in TB drug discovery. Here, using CRISPRi technology, we showed that dxs1 transcriptional knockdown attenuated growth of both Mycobacterium smegmatis and Mycobacterium tuberculosis cultures, and the effect was more profound in the latter. Chemical supplementation of the growth medium with 10 uM of isoprenoid pyrophosphates, thiamine and thiamine pyrophosphate failed to rescue growth of M. smegmatis cultures, while partial rescue was observed with addition of menatetrenone, a menaquinone derivative with four isoprenyl groups. Similarly, culture growth could not be rescued by the addition of prenol and isoprenol, which suggested the lack of isoprenoid salvage pathway in mycobacteria.  Importantly, and in the context of drug discovery, dxs1 depleted mutants displayed four-fold more sensitive towards a mixture of isoniazid, rifampicin and ethambutol, suggesting that inhibitors of DXS1 or other MEP pathway enzymes could potentiate antimycobacterial effect of the first-line TB drugs. Additionally, dxs1 depletion increased growth retardation of the mutant in acidic pH and under oxidative stress, conditions that are encountered in activated macrophage compartments. Taken together, our results validated DXS1 as an attractive drug target that should be prioritized for developments on new antitubercular agents.