MOHAPATRA, A. K. | Search bioRxiv

bioRxiv2023

Chemical inhibition of histidine biosynthesis curtails M. tuberculosis infection

To overcome the drug resistance crisis and shorten the current duration of human tuberculosis (TB) therapy, new anti-TB molecules is required. In an earlier study, we have shown that Mycobacterium tuberculosis (Mtb), the causative agent of TB, with a fractured de novo histidine biosynthesis fails to mount TB infection in mouse model, emboldening that disrupting the function of this pathway may constitute a novel strategy to curtailing TB infection. In this study, through a target based approach we have designed a number of triazole scaffold molecules specific to imidazole glycerol phosphate dehydratase (IGPD; HisB) of this pathway and have delineated atomic level interactions between the enzyme and inhibitors which pinpointed the specificity and the inhibitory mechanism. Importantly, these molecules exhibited significant potency against free as well as macrophage-internalized wild-type and drug-resistant clinical isolates in culture medium. Notably, a couple of these compounds showed efficacy in reducing the bacterial burden in Mtb-infected mouse model. The chemical inhibition of IGPD induces histidine auxotrophy in Mtb and brings in new prospects to the area of anti-TB drug discovery.

biochemistry↗

bioRxiv2023

Iron chelation by deferoxamine as useful adjunct therapeutics in murine tuberculosis.

Dysregulated iron metabolism is reported in tuberculosis patients; therefore, it represents an opportunity for developing host-directed therapeutics. This study monitored the antimycobacterial properties of an iron chelator, i.e., Deferoxamine (DFO/D), and its impact on the transcript and metabolite levels of Mycobacterium tuberculosis (Mtb) in vitro. For in vivo validation, a group of mice received ferric carboxymaltose to create an iron overload condition, and controls were aerosol-infected with Mtb H37Rv. Mtb-infected mice received isoniazid (INH/H) and rifampicin (RIF/R) in combination with or without DFO before tissue-specific CFU assay, liver metabolite screening and iron quantification using mass spectrometry. DFO showed antimycobacterial properties comparable to INH in vitro. DFO treatment deregulated (log2DFO/control>{+/-}1.0) Mtb transcript (n=137) levels, the majority of which encode for iron-containing proteins and proteins involved in stress response. DFO treatment up-regulated Rv3622c (PE32), Rv2353c (PPE39) and Rv3022A (PE29) genes and conditional knocking down of ABC transporter like irtA by anhydrotetracycline (Atc) inducible CRISPR interference (CRISPRi) approach compromised Mtb growth showing their potential involvement in iron metabolism. Global Mtb metabolite analysis using GC-MS identified a set of 5 deregulated metabolites indicating a perturbed pentose phosphate pathway and inositol phosphate metabolism in the host upon DFO treatment. Iron-overloaded mice exhibited significantly higher tissue mycobacterial burden at two weeks post-infection, and the efficacy of INH and RIF were compromised, corroborating with previous reports. Iron chelation by DFO or combined with/adjunct to RIF and INH significantly reduced the lung/tissue mycobacterial burden at four weeks post-treatment, specifically in the first ([~]0.5 log) and second weeks ([~]0.5 log) of treatment. The intracellular pro-inflammatory cytokine levels in the lung CD4+ T cells of INH and RIF-treated groups with or without DFO were similar, suggesting DFO has a direct role in Mtb survival and metabolism rather than improved infection, and the efficacy of INH and RIF were compromised, corroborating with previous reports. DFO adjunct to RIF and INH treatment significantly altered liver arginine biosynthesis, which directly neutralizes ammonia and is immune-supportive. Conventionally, DFO is used for treating acute iron toxicity that is common in thalassemic patients, and this study demonstrates DFO has potential as adjunct therapeutics for tuberculosis. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/543389v3_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@5066fdorg.highwire.dtl.DTLVardef@99a292org.highwire.dtl.DTLVardef@80426dorg.highwire.dtl.DTLVardef@892436_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗