RasGRP1 is a potential biomarker for stratifying anti-EGFR therapy response in colorectal cancer
Oghenekevwe M. Gbenedio, Caroline Bonnans, Delphine Grun, Chih-Yang Wang, Ace J. Hatch, Michelle R. Mahoney, David Barras, Mary Matli, Yi Miao, K. Christopher Garcia, Sabine Tejpar, Mauro Delorenzi, Alan P. Venook, Andrew B. Nixon, Robert S. Warren, Jeroen P. Roose, Philippe Depeille
Oghenekevwe M. Gbenedio, Caroline Bonnans, Delphine Grun, Chih-Yang Wang, Ace J. Hatch, Michelle R. Mahoney, David Barras, Mary Matli, Yi Miao, K. Christopher Garcia, Sabine Tejpar, Mauro Delorenzi, Alan P. Venook, Andrew B. Nixon, Robert S. Warren, Jeroen P. Roose, Philippe Depeille
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Research Article Gastroenterology Therapeutics

RasGRP1 is a potential biomarker for stratifying anti-EGFR therapy response in colorectal cancer

Abstract

Colorectal cancer (CRC) is the third most frequent neoplastic disorder and is a main cause of tumor-related mortality, as many patients progress to stage IV metastatic CRC. Standard care consists of combination chemotherapy (FOLFIRI or FOLFOX). Patients with WT KRAS typing are eligible to receive anti-EGFR therapy combined with chemotherapy. Unfortunately, predicting efficacy of CRC anti-EGFR therapy has remained challenging. Here we uncovered that the EGFR pathway component RasGRP1 acts as a CRC tumor suppressor in the context of aberrant Wnt signaling. We found that RasGRP1 suppresses EGF-driven proliferation of colonic epithelial organoids. Having established that RasGRP1 dosage levels impact biology, we next focused on CRC patients. Mining 5 different data platforms, we establish that RasGRP1 expression levels decrease with CRC progression and predict poor clinical outcome of patients. Last, deletion of 1 or 2 Rasgrp1 alleles made CRC spheroids more susceptible to EGFR inhibition. Retrospective analysis of the CALGB 80203 clinical trial showed that addition of anti-EGFR therapy to chemotherapy significantly improved outcome for CRC patients when tumors expressed low levels of RasGRP1 suppressor. In sum, our data support RasGRP1 as a biomarker in the EGFR pathway that has potential relevance to anti-EGFR therapy for CRC patients.

Authors

Oghenekevwe M. Gbenedio, Caroline Bonnans, Delphine Grun, Chih-Yang Wang, Ace J. Hatch, Michelle R. Mahoney, David Barras, Mary Matli, Yi Miao, K. Christopher Garcia, Sabine Tejpar, Mauro Delorenzi, Alan P. Venook, Andrew B. Nixon, Robert S. Warren, Jeroen P. Roose, Philippe Depeille

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Figure 2

RasGRP1 is a critical suppressor of EGF-induced growth in the colon.

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RasGRP1 is a critical suppressor of EGF-induced growth in the colon. (A)...
(A) Pipeline of colonic organoid generation. (B) Schematic representation of Wnt surrogate ligands simultaneously triggering LDL receptor-related protein 5 and 6 (LRP5/6) and Frizzled (FZD) as well as R-spondin (RSPO) contributing to sustained, canonical Wnt signaling. (C) Colonic organoids from individual WT and Rasgrp1–/– mice. Each image is a representative example of 12 wells of organoids per genotype from 3 independent experiments (n = 3 mice per genotype; n = 9 total). Scale bars: 200 μm. (D). Detection of Egfr and Sos1 expression by Western blot analysis in growing organoids from WT and Rasgrp1–/– mice (n = 2 mice per genotype). β-Actin served as protein loading control. Panels are representative of 2 independent organoid experiments. (E) Proliferation of developing organoids (represented in C) evaluated in growth media containing R-spondin and Wnt surrogate ligand over 5 days. Each point represents the average of 2 wells in triplicate (n = 3 mice per genotype). (F) Organoids were treated with erlotinib at different doses (0.2, 0.5, 2 μM) for 1, 3, and 5 days. All values were normalized to untreated on similar developing day. Data are representative of 3 independent experiments (n = 3 mice per genotype) with 2 wells per condition. We analyzed growth of organoids on day 3, when these were in the exponential growth phase. *P < 0.05, **P < 0.01, ****P < 0.01, NS not significant (1-way ANOVA, Bonferroni’s multiple-comparisons test). Data are mean ± SEM.