CRISPR-induced RASGAP deficiencies in colorectal cancer organoids reveal that only loss of NF1 promotes resistance to EGFR inhibition

// Jasmin B. Post 1, 2 , Nizar Hami 1, 2 , Alexander E.E. Mertens 1, 2 , Suraya Elfrink 1, 2 , Johannes L. Bos 1, 2 and Hugo J.G. Snippert 1, 2 1 Center for Molecular Medicine, Section Molecular Cancer Research, University Medical Center Utrecht, Utrecht, The Netherlands 2 Oncode Netherlands, Institute Netherlands, Office Jaarbeurs Innovation Mile, Utrecht, The Netherlands Correspondence to: Hugo J.G. Snippert, email: H.J.G.Snippert@umcutrecht.nl Keywords: NF1; RASGAP; anti-EGFR therapy resistance; cancer progression; colorectal cancer Received: December 12, 2018      Accepted: February 01, 2019      Published: February 15, 2019 ABSTRACT Anti-EGFR therapy is used to treat metastatic colorectal cancer (CRC) patients, for which initial response rates of 10–20% have been achieved. Although the presence of HER2 amplifications and oncogenic mutations in KRAS, NRAS, and BRAF are associated with EGFR-targeted therapy resistance, for a large population of CRC patients the underlying mechanism of RAS-MEK-ERK hyperactivation is not clear. Loss-of-function mutations in RASGAPs are often speculated in literature to promote CRC growth as being negative regulators of RAS, but direct experimental evidence is lacking. We generated a CRISPR-mediated knock out panel of all RASGAPs in patient-derived CRC organoids and found that only loss of NF1, but no other RASGAPs e.g. RASA1, results in enhanced RAS-ERK signal amplification and improved tolerance towards limited EGF stimulation. Our data suggests that NF1-deficient CRCs are likely not responsive to anti-EGFR monotherapy and can potentially function as a biomarker for CRC progression.