PO-049 Egfr blockade induces a paneth cell-like phenotype with rewired signalling dependencies in crc tumoursat maximal response

Introduction Anti-EGFR therapies with the monoclonal antibodies cetuximab and panitumumab have improved survival in colorectal cancer (CRC) patients; nevertheless, incomplete mass obliteration and eventual relapse are a common setback, even after a plateau of maximal response. Preclinical data suggest that tumour recurrence may be fueled by a reservoir of so-called ‘drug-tolerant persisters’ that engage non-mutational routes of adaptation to therapy. Yet, the molecular underpinnings that sustain residual disease, as well as the strategies to oppose it, are largely unexplored. Material and methods The effects of targeted therapies were evaluated in patient-derived xenografts. The biochemical and biological consequences of drug exposure were gauged by immunohistochemistry and morphometric analyses ( in vivo ), and by time-lapse imaging, Western Blot, Cell Titer-Glo and Caspase-Glo assays ( in vitro ). Transcriptional perturbations were assessed by microarray analysis and/or RT-qPCR. The activity of transcriptional modulators was measured by reporter assays in vitro . Results and discussions Residual tumours surviving cetuximab treatment exhibited a quiescent, Wnt-high, and secretory/Paneth cell-like state as a distinctive trait. This pattern outlines that of EGFR-inhibited quiescent stem cells of the normal intestine, suggesting that developmental trajectories are somehow coopted by cancer cells to face external insults. Such phenotype was reversible with drug suspension, pointing to non-genetic plasticity as a determinant of cancer cell reprogramming. Residual tumours also displayed lower expression of EGFR-activating ligands, congruent with reduced EGFR dependency, and showed rewired reliance on compensatory HER2/HER3 activity, as well as persistent PI3K signalling. Mechanistically, the acquisition of Paneth cell-like features was mediated, at least partly, by inactivation of YAP – a key driver of intestinal cell regeneration. Therapeutically, combined blockade of EGFR and PI3K/AKT lessened residual disease burden, but did not lead to long-term disease control. However, treatment with panHER, a mixture of antibodies concurrently targeting EGFR, HER2, and HER3, reduced tumour volumes and delayed tumour relapse after therapy cessation. Conclusion Drug tolerance in cetuximab-sensitive CRC models involves a switch towards a Paneth-cell like state typified by sustained HER2/HER3 and PI3K signalling. Treatment with panHER effectively exhausted residual tumour burden and impeded/delayed late relapse.