Inflammatory fibroblasts mediate resistance to neoadjuvant therapy in rectal cancer

Standard cancer therapy targets tumor cells without considering the possible collateral damage on the tumor microenvironment that could impair therapy response. Employing patient-derived tumor organoids and primary stroma cells or a novel murine rectal cancer model, we show that interleukin-1 (IL-1 dependent inflammatory cancer-associated fibroblast (iCAF) polarization triggers oxidative DNA damage in iCAFs leading to p53-mediated therapy-induced senescence associated with changes in matrisome composition, chemoradiotherapy resistance and disease progression. IL-1 inhibition, prevention of iCAF senescence or senolytic therapy sensitizes mice to irradiation. In rectal cancer patients a dominant iCAF gene signature as well as lower IL-1 receptor antagonist (IL-1RA) serum levels correlate with poor prognosis. Moreover, conditioned supernatant from patient tumor organoids renders fibroblasts susceptible to radiation-induced senescence in an IL-1-dependent manner. Collectively, we unravel a critical role for iCAFs in therapy resistance and identify IL-1 signaling as an attractive target for stroma-repolarization and prevention of CAF senescence.