Abstract 2373: Expression of exosomal let-7g in biofluids and outcome in colon cancer patient treated with anti-EGFR therapy

Introduction: Monoclonal antibodies against the Epidermal Growth Factor Receptor (EGFR) such as cetuximab or panitumumab are used for the treatment of metastatic colorectal cancer (mCRC) patients. Unfortunately, most patients develop resistance against these therapies within months. Several studies have shown that aberrations in the RAS pathway are responsible for resistance. However, even in metastases that are refractory to anti-EGFR treatment a significant fraction of RAS wild-type (wt) cells remain. These findings suggest a cross-talk between RAS mutant and wt cells in mediating resistance in the wt compartment. Methods: Mouse and patient-derived organoids from mCRC as well as CRC cell lines were used to test the contribution of extracellular vesicles in mediating resistance in RAS wt cells. Using conditioned media, transfection experiments and liquid biopsies (plasma and urine) from patients differential expression of the let-7g microRNA was demonstrated in microvesicles from cetuximab sensitive and resistant cells. Changes in expression of let-7g were further analyzed by in-situ hybridization in tissues. Results: Conditioned media from RAS mutant organoids rendered RAS wt organoids resistant against cetuximab treatment. Basal let-7g expression from pre-treatment plasma and urine samples of RAS wt patients correlated with clinical outcome and changes in let-7g circulating levels mirrored clinical behavior. In-situ hybridization in tissues confirmed changes in expression of the let-7g microRNA observed in plasma and urine samples. Conclusions: Our data suggest that let-7g microRNA might function as a paracrine mediator of anti-EGFR resistance and might be exploited as a non-invasive biomarker of resistance to cetuximab treatment. Further work is ongoing to characterize the molecular mechanisms underpinning let-7g mediated effect on anti-EGFR sensitivity in RAS wt CRC cells. Citation Format: Jens C. Hahne, Andrea Lampis, Michele Ghidini, Margherita Ratti, Chiara Senti, Rodolfo Passalacqua, Luciano Cascione, Chiara Braconi, Owen Sansom, Matteo Fassan, Nicola Valeri. Expression of exosomal let-7g in biofluids and outcome in colon cancer patient treated with anti-EGFR therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2373.