Abstract 501: A RET-related microRNA, miR-153-3p, acts as a tumor suppressor in medullary thyroid carcinoma (MTC) via S6K signaling

Abstract

Abstract Background Medullary thyroid carcinoma (MTC), which comprises 3-5% of all thyroid cancers, originates from a small population of neuroendocrine calcitonin C-cells of thyroid gland. Gain-of-function mutations of the human Rearranged during Transfection (RET) proto-oncogene have been recognized as the key driver of MTC tumorigenesis. RET has been targeted by tyrosine kinase inhibitors (TKIs), however with modest efficacy. Many of the microRNAs (miRNAs) identified in human genome have been associated with cancer and have prompted interest in the establishment of miRNA-based therapeutics. However miRNA studies in MTC has been hampered due to the lack of normal C-cell tissue as a differential expression comparator. Aims We aimed to characterize differentially expressed miRNAs, which play fundamental roles in MTC tumorigenesis and in modulation of TKI responses. Methods RET of human MTC cells were silenced using TKI, Cabozantinib, or siRNA. Small RNA sequencing was performed (AGRF) to identify differentially expressed miRNAs before and after RET inhibition. MiRNA effects on cell proliferation (MTS assay), cell cycle and apoptosis (flow cytometry, Western blot) were investigated with gain-of-function studies. For in vivo study, MTC xenografts were established and miRNAs were intravenously delivered using nanoparticle delivery vehicles invented by biotechnology company - EnGeneIC Ltd. Results miR-153-3p was identified to be under-expressed in MTC following RET inhibition. Restoration of miR-153-3p significantly reduced cell proliferation, induced G2 cell arrest and increased cell apoptosis. Furthermore, combined treatment of miR-153-3p and Cabozantinib caused greater cell proliferation inhibition compared to individual treatment. miR-153-3p targets ribosomal protein S6 kinase B1 (RPS6KB1) and reduced phosphorylation of Bcl-2 associated death promoter (BAD) protein. In vivo delivery of miR-153-3p significantly impeded tumor growth compared to scrambled sequence. Combination of miR-153-3p delivery and oral administration of Cabozantinib resulted in further tumor stabilization effect. Conclusion miR-153-3p reveals a significant tumor suppressive role in MTC via S6K signaling, demonstrating its important therapeutic potential for MTC patients. Citation Format: Lauren Jin Suk Joo, Jocelyn Weiss, Anthony J. Gill, Roderick Clifton-Bligh, Himanshu Brahmbhatt, Jennifer A. MacDiarmid, Matti L. Gild, Bruce G. Robinson, Stan B. Sidhu, Jing Ting Zhao. A RET-related microRNA, miR-153-3p, acts as a tumor suppressor in medullary thyroid carcinoma (MTC) via S6K signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 501.