This Monday 30/09/2024 at 11:00h Mr. Bernardo Queralt has made the reading of his doctoral thesis entitled: ‘Phenotyping of NRAS mutations in colorectal cancer: clinical-molecular characterization and search for new therapies’ directed by Dr. Joan Brunet and Dr. Javier Menéndez.

ABSTRACT

Mutation of the KRAS gene is the best-characterized biomarker for predicting the lack of response of metastatic colorectal cancer (mCRC) to the EGFR-targeted therapies cetuximab and panitumumab. However, it is largely unknown how mutations in the NRAS gene, which are a minority (3-5%) compared to the more common KRAS (30-40%), contribute to the initiation, progression, and response to treatment of mCRC. Our study hypothesized that characterizing the cellular phenotypes specifically activated by mutations in the NRAS gene and causally involved in cetuximab resistance, as well as studying the prognostic and predictive value of KRAS versus NRAS mutational status in routine clinical practice of patients with mCRC, could reveal new clinical-molecular strategies more effective in the therapeutic management of the subgroup of mCRC patients with mutated NRAS.

First, using CRISPR-Cas9 gene-edited cell models harboring a single-allelic point mutation in the NRAS gene (Q61K), we characterized the molecular mechanisms used by mutant NRAS to escape the therapeutic effects of the anti-EGFR agent cetuximab in vitro. Second, on the basis of the discovered escape mechanisms, we developed and preclinically validated novel therapeutic combinations capable of (re)sensitizing NRAS-mutant mCRC cells to the anti-proliferative and pro-apoptotic effects of cetuximab. Third, we performed a retrospective review of clinical registries of more than 200 consecutive patients with mCRC who were genotyped for KRAS and NRAS mutations to evaluate the impact of different therapeutic approaches to mCRC in routine clinical practice (real-world data).

Our studies have revealed two novel molecular mechanisms involved in the maintenance of the cetuximab-refractory phenotype of NRAS-mutant mCRC cells, namely: constitutive hyperactivation of the MEK/ERK pathway and dysregulation of the ephrin signaling axis and its Eph receptors. The simultaneous combination of cetuximab with pharmacological inhibitors of MEK1/2 (trametinib, selumetinib, pimasertib, binimetinib) results in a synthetic lethal interaction. This interaction synergistically multiplies the anti-proliferative and pro-apoptotic activity of the drugs used separately. NRAS mutant cells can be resensitized to the anti-proliferative activity of cetuximab by treatment with recombinant ephrin eA1-Fc, which can restore the tumor suppressor function of the ephA2 receptor. The pre-treatment functional status as defined by the ECOG scale, the local treatment of metastatic disease and the presence of a high histologic grade were independent factors that were significantly associated with the survival of patients with mCRC.

Our study provides molecular evidence to support the use of MEK/ERK and eph/ephrin pathways as novel molecular targets for clinical evaluation as precision strategies in the therapeutic management of patients with NRAS-mutated mCRC. The acquisition of molecular-clinical data in the real-world setting may guide clinical practice in a complementary manner to the genotyping of KRAS and NRAS mutations and may favor the rational use of therapies in patients with mCRC.