Abstract 5720: MicroRNA deregulation of the serine synthesis pathway controls intrinsic and non-cell autonomous mechanism of resistance to Regorafenib in metastatic colorectal cancer (mCRC)
Authors: Hedayat Somaieh , Lampis Andrea , Vlachogiannis George , Khan khurum , Marchetti Silvia , Fassan Matteo , Ghidini Michele , Begum Ruwaida , Schirripa Marta , Passalacqua Rodolfo , Cunningham David , Loupakis Fotios , Valeri Nicola 
Published: September 2020

Abstract
Background: MicroRNAs (miRs) are small non-coding RNAs involved in cell homeostasis. miR dysregulation has been linked with activation of oncogenic pathways, cancer progression and clinical outcome in 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 patient stratification and identification of mechanisms of resistance.
Methods: Serial liquid biopsies were obtained at baseline (BL) and monthly until disease progression (PD) in 43 patients treated with regorafenib for chemo-refractory mCRC in the context of a phase II clinical trial (PROSPECT-R). Tissue biopsies were obtained at BL, after 2 months and at PD within the same trial and used to establish Patient-Derived Organoids (PDOs) and for molecular analyses. PDOs co-cultures and PDO-xenotransplants were generated to study primary and acquired resistance to regorafenib. Liquid biopsies were also obtained from an additional cohort (n=97) of mCRC patients treated with regorafenib. MiR profiling was performed on baseline seras using NanoString nCounter platform and significant miRs were validated with digital droplet (dd)PCR in serum, plasma, PDOs and by In Situ Hybridization (ISH) in matching tissue biopsies. Functional experiments were performed in PDOs, PDO co-cultures and PDO-xenotransplants.
Results: MiR expression was tested in 43 BL in the PROSPECT-R trial. Up-regulation of miR-652-3p was associated with poor PFS and OS. These results were validated by ddPCR on the same serum samples, matching plasmas and organoids. ISH confirmed upregulation of this miR in sequential tissues biopsies, PDOs and PDO-xenotransplants of patients with primary and acquired resistance to regorafenib. The same findings were confirmed in the validation cohort.
Functional experiments showed that miR-652-3p upregulation has significant effects on cancer cell migration. Up and down-regulation of miR-652-3p upon regorafenib treatment translated in a significant effect on cell viability in PDO co-cultures and liver PDO-xenotransplants. RNA-sequencing analysis of miR-652-3p over-expressing organoids showed downregulation of several components of the serine synthesis pathway. Among them, phosphoserine aminotransferase (PSAT1) was validated as a miR-652-3p direct target. Rescue experiments confirmed that PSAT1 over-expression and silencing lead to increase sensitivity and resistance to regorafenib respectively via cell and non-cell autonomous regulation of autophagy.
Conclusions: Our data suggest that miR-652-3p may be uses as a prognostic/predictive biomarker for the selection of treatment and provide mechanics insight on regorafenib resistance.
Citation Format: Somaieh Hedayat, Andrea Lampis, George Vlachogiannis, khurum Khan, Silvia Marchetti, Matteo Fassan, Michele Ghidini, Ruwaida Begum, Marta Schirripa, Rodolfo Passalacqua, David Cunningham, Fotios Loupakis, Nicola Valeri. MicroRNA deregulation of the serine synthesis pathway controls intrinsic and non-cell autonomous mechanism of resistance to Regorafenib in metastatic colorectal cancer (mCRC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5720.