{
  "abstract": "Background Failure of patients with microsatellite stable (MSS) colorectal cancer (CRC) to respond to T-cell immunotherapies can be contributed by innate immune dysregulation in the tumor microenvironment. We hypothesised that endotoxins from gastrointestinal bacteria may be exploited to reactivate the anti-tumor activity of macrophages against CRC.Methods Lipopolysaccharide (LPS) isoforms were isolated and purified from defined gut bacteria by HPLC/MS or were applied as heat-inactivated lysates (n=6 single species). Macrophages were generated from human monocytic leukemia THP1 cells and ex vivo from peripheral blood mononuclear cells from healthy donors. Human CRC cell lines (BRAFV600E HT29, KRASG12V SW480) and KRAS/APC-mutant MSS patient-derived tumor organoids (PDOs, n=5 cases) were co-cultured with differentiated, polarised, pro-inflammatory M1(LPS/IFNg) vs. anti-inflammatory M2(IL4/IL13) macrophages (n=3 donors per patient) and analysed by microscopy, flow cytometry and viability assays.Results Lysates from pathobionts of the genera Porphyromonas, Peptostreptococcus and Parvimonas micra increased proliferation of PDOs (by ≤40 %, 1wANOVA, *p<0.05 vs. untreated, n=3 replicates per strain), whereas LPS extracted from the gut commensal Akkermansia muciniphila was inert. In contrast, M1-type macrophages reduced growth and viability of PDOs and CRC cell lines (by ~50 %, 1wANOVA, *p<0.05 vs. M2, n=3 co-cultures per line or patient, n=1 donor per replicate). Toll-like receptor-4 (TLR4) ligands derived from LPS of the oral pathobiont Porphyromonas gingivalis and the environmental probiotic Rhodobacter spheroides further mitigated survival of tumor cells in combination with M1-type macrophages (by 25-50 %, 2wANOVA, *p<0.05 vs. M2, n=3). Mechanistically, TLR4 ligands stimulated inflammatory NFkB-STAT1 and survival AKT-ERK1/2 signaling in macrophages, whereas in tumor cells nuclear ERK1/2 positivity and Ki67+ proliferation index were diminished and PARP+ cell death was induced by M1-type macrophages.Conclusions Bacterial endotoxins may be optimised as ‘immune adjuvants’ to promote anti-tumoral effector functions of macrophages, proposing a potential novel therapeutic strategy for MSS colorectal cancer.",
  "authors": [
    {
      "affiliations": [
        "Department of Medicine II, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany"
      ],
      "name": "Elke Burgermeister"
    },
    {
      "affiliations": [
        "Department of Medicine II, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany"
      ],
      "name": "Dominik Kato"
    },
    {
      "affiliations": [
        "Department of Medicine II, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany"
      ],
      "name": "Longfei Cao"
    },
    {
      "affiliations": [
        "Dept. of Medicine II, DKFZ-Hector Institute, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University & Junior Clinical Cooperation Unit Translational Gastrointestinal Oncology and Preclinical Models, DKFZ, Heidelberg, Germany"
      ],
      "name": "Johannes Betge"
    },
    {
      "affiliations": [
        "Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore"
      ],
      "name": "Sunny Hei Wong"
    },
    {
      "affiliations": [
        "Leiden University Center for Infectious Diseases (LUCID), Leiden University Medical Center, Leiden, The Netherlands & Molecular Systems Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany"
      ],
      "name": "Georg Zeller"
    },
    {
      "affiliations": [
        "Department of Medicine II, DKFZ-Hector Institute, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University & Molecular Medicine Partnership Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany"
      ],
      "name": "Matthias P Ebert"
    }
  ],
  "title": "IDDF2026-ABS-0026 Endotoxin adjuvants from commensal bacteria enhance cytotoxic activity of macrophages against KRAS/APC-mutant colorectal cancer",
  "uid": "c98ef8c9-6d64-594f-b4a3-ad1ce382c92e"
}