Anti-cancer drug Tamoxifen interferes withMycobacterium tuberculosisPhoPR mediated signaling and inhibits mycobacterial growth

Abstract

Two-component signaling (TCS) systems empower all bacteria, including intracellular pathogens likeMycobacterium tuberculosis (M. tb)to regulate key pathways governing growth, physiology and virulence. Amongst allM. tbTCS systems, PhoPR and DevRS have been studied extensively for their roles in regulating persistence and virulence. Here, we report that besides its cognate response regulator PhoP, the PhoR sensor kinase displays several non-cognate interactions that augment its role in pathogenesis. We demonstrate that PhoR phosphorylates the DevR response regulator and furthermore, is itself subjected toO-phosphorylation by PknK, a Ser/Thr protein kinase (STPK), connecting TCS pathways with “eukaryotic-like” STPK driven phosphosignaling. This intersection of non-canonical regulatory pathways and the coregulation of PhoP and DevR regulons makeM. tbPhoR a potentially attractive drug target. We rationalized that disruption of PhoPR signaling cascade and the resulting dysregulation may result in decreased virulence ofM. tb. We tested this hypothesis by performing a high-throughput screen for compounds that inhibit autophosphorylation of PhoR sensor kinase. Screening of pharmacologically active, small molecule libraries yielded 11 potential inhibitors, of which one compound, Tamoxifen was able to attenuate PhoR autophosphorylation at micromolar concentrationsin vitroandin vivo. Tamoxifen not only inhibited growth ofMycobacterium bovisBCG in culture but also interrupted PhoPR-mediated downstream signaling. Quantitative expression analysis revealed suppression of target gene,aprAunder acidic conditions. Our findings highlight TCS sensor kinases as promising drug targets and underscore the applicability of clinically relevant anti-cancer drug tamoxifen as a repurposed anti-TB drug.