IDDF2024-ABS-0109 Peptostreptococcus stomatis binds to colon epithelial cell to promote tumorigenesis and receptor tyrosine kinase inhibitor resistance by activating ERBB2-MAPK

<h3>Background </h3> <i>Peptostreptococcus stomatis (P. </i><i>stomatis)</i> is an oral pathogen enriched in colorectal cancer (CRC) patients, but its causality and translational implication in CRC are unknown. In this study, we investigate the function of <i>P. stomatis</i> in CRC, and its impact on CRC therapy response. <h3>Methods</h3> <i>P. stomatis</i> was identified as a CRC-enriched bacterium from multiple cohorts. The pro-tumorigenic effect of <i>P. stomatis</i> on colorectal carcinogenesis was determined in Apc^Min/+ mice and azoxymethane/Dextran sodium sulfate (AOM-DSS)-treated spontaneous CRC models. <i>In vitro</i>, function of <i>P. stomatis</i> was analysed by cell proliferation, apoptosis, and cell cycle assays. Interplay between <i>P. stomatis</i> and CRC cells was evaluated by fluorescence in situ hybridization (FISH), scanning electron microscopy (SEM), transmission electron microscopy (TEM), adhesion and invasion assays. The interaction between <i>P. stomatis</i> surface protein and the receptor of CRC cells was investigated by far-western, biotin pulldown, glutathione S-transferase (GST) pulldown, co-immunoprecipitation, and microscale thermophoresis (MST) assays. <h3>Results</h3> <i>P. stomatis</i> accelerated colonic tumorigenesis in Apc^Min/+ and AOM-DSS models by inducing cell proliferation, suppressing apoptosis, and impairing gut barrier function. <i>P. stomatis</i> adhered to CRC cells through its surface protein fructose-1,6-bisphosphate aldolase (FBA) that binds to integrin α6/β4 receptor on CRC cells, leading to activation of ERBB2 and downstream MEK-ERK-p90 cascade. Blockade of FBA-integrin α6/β4 abolished ERBB2-MAPK activation and the protumorigenic effect of <i>P. stomatis. P. stomatis</i>-driven ERBB2 activation bypasses receptor tyrosine kinase (RTK) blockade by EGFR inhibitors (Cetuximab, Erlotinib), leading to drug resistance in xenograft and spontaneous CRC models of KRAS-wildtype CRC. <i>P. stomatis</i> also abrogated BRAF inhibitor (Vemurafenib) efficacy in BRAF^V600E-mutant CRC xenografts. <i>E. coli</i> overexpressing FBA phenocopied the effect of <i>P. stomatis</i> in promoting CRC. <i>E. coli</i> overexpressing FBA or recombinant FBA induced ERBB2-MEK-ERK-p90 signaling and promoted resistance to EGFR and BRAF inhibitors. Targeting ERBB2 reversed <i>P. stomatis</i>-associated resistance to EGFR and BRAF inhibitors in CRC cell lines and primary CRC organoids. <h3>Conclusions</h3> We identified <i>P. stomatis</i> as an oncogenic bacterium and a contributory factor for non-responsiveness to RTK inhibitors in CRC.