Repurposing Tamoxifen as Potential Host-Directed Therapeutic For Tuberculosis

The global burden of tuberculosis (TB) is aggravated by the continuously increasing emergence of drug resistance, highlighting the need for innovative therapeutic options. The concept of host-directed therapy (HDT) as adjunctive to classical antibacterial therapy with antibiotics represents a novel and promising approach for treating TB. Here, we have focused on repurposing the clinically used anticancer drug tamoxifen, which was identified as a molecule with strong host-directed activity against intracellular Mycobacterium tuberculosis (Mtb). Using a primary human macrophage Mtb infection model, we demonstrate the potential of tamoxifen against drug-sensitive as well as drug-resistant Mtb bacteria. The therapeutic effect of tamoxifen was confirmed in an in vivo TB model based on Mycobacterium marinum infection of zebrafish larvae. Tamoxifen had no direct antimicrobial effects at the concentrations used, confirming that tamoxifen acted as an HDT drug. Furthermore, we demonstrate that the antimycobacterial effect of tamoxifen is independent of its well-known target the estrogen receptor (ER) pathway, but instead acts by modulating autophagy, in particular the lysosomal pathway. Through RNA sequencing and microscopic colocalization studies, we show that tamoxifen stimulates lysosomal activation and increases the localization of mycobacteria in lysosomes both in vitro and in vivo, while inhibition of lysosomal activity during tamoxifen treatment partly restores mycobacterial survival. Thus, our work highlights the HDT potential of tamoxifen and proposes it as a repurposed molecule for the treatment of TB. Overall design: Zebrafish embryos and their were manually dechorionated at 24 hours post fertilisation (hpf) and at 30 hpf they were infected by injecting 200 colony forming units of M. marinum strain M into the blood island. After injections embryos were transferred into fresh egg water containing Tamoxifen (10uM), Amiodarone (10uM), or DMSO (equal v/v as treatments) incubated for 2 days at 28,5°C. After the incubation period, infected and uninfected embryos and their controls (10 per sample) were snap-frozen in liquid nitrogen and RNA was isolated for Illumina RNAseq analysis.