Circulating microRNA-652-3p as a biomarker of regorafenib resistance in metastatic colorectal cancer patients

Abstract

MicroRNAs (miRNAs) are small non-coding RNAs involved in cell homeostasis. MiRNAs dysregulation has been linked with activation of oncogenic pathways, cancer progression and clinical outcome in metastatic colorectal cancer (mCRC). Chemo-refractory mCRC patients are often treated with regorafenib, a multi-tyrosine kinase inhibitor with anti-angiogenic effect. Given the limited clinical benefits of regorafenib in unselected patient populations, there is an unmet need for better patients' stratification and identification of mechanisms of resistance. Serial liquid and tissue biopsies were obtained in 41 patients treated with regorafenib for chemo-refractory mCRC in the context of a phase II clinical trial (PROSPECT-R). Liquid biopsies were also obtained from an additional cohort (n=85) of mCRC patients treated with regorafenib. MiRNA profiling was performed and significant deregulated miRNAs were validated with digital droplet (dd) PCR in serum, plasma, patient-derived organoids (PDOs) and by In Situ Hybridization (ISH) in matching tissue biopsies, including up-regulation of miRNA-652-3p that was associated with poor progression free survival (PFS) and overall survival (OS). The same findings were confirmed in the validation cohort. RNA-sequencing analysis of miRNA-652-3p over-expressing organoids, showed downregulation of phosphoserine aminotransferase (PSAT1) a key enzyme involved in the serine synthesis pathway. PSAT1 was validated as a miRNA-652-3p direct target and in vivo experiments confirmed that PSAT1 over-expression could restore sensitivity to regorafenib. Our data suggest the miRNA-652-3p may be used as a prognostic/predictive biomarker for patients' stratification for regorafenib treatment and provide biological mechanisms that might explain regorafenib acquired resistance.