Fellow University of Toronto Toronto, Ontario, Canada
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Participants should be aware of the following financial/non-financial relationships:
Shelly Luu, MD, PhD: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Introduction: Despite improvements in surgical technique and perioperative adjuvant therapy for gastric adenocarcinoma (GCa), the case-fatality of GCa remains high. In a search for novel molecular markers and targets, we recently identified the non-canonical RNA polymerase FAM46C as a tumor suppressor in GCa. Here we investigated downstream molecular mediators of this tumor suppressor activity.
Methods: Consecutive patients who underwent curative-intent resection for primary GCa from 2001-2017 were identified from an institutional database. Disease-specific survival (DSS) was estimated by the Kaplan-Meier method and hazard ratios estimated with Fine-Gray competing risk modeling. RNA was extracted from banked primary tumor (T) and paired normal mucosa (NM) and subjected to qPCR and RNA-seq analysis. Functional clustering of Gene Ontology terms analysis was performed with GOrilla on differentially expressed genes (DEGs). Cell viability was measured via calcein/ethidium stain.
Results: In the study cohort of 158 patients who underwent curative-intent resection of GCa, FAM46C expression was markedly reduced in T vs paired NM (median T/NM = 0.24, IQR 0.09-0.43). In multivariable analysis, loss of FAM46C independently predicted inferior DSS (HR 1.7, p< 0.05). Biologic process analysis of DEGs (T vs NM) following RNA-sequencing of tumors with low FAM46C expression identified enrichment for ion channel-related pathways. Depletion of FAM46C in AGS GCa cells via 2 independent FAM46C shRNAs caused dysregulation of several ion channels, including the principle K+/H+ exchanger, KCNQ1. In addition, FAM46C-depleted AGS cells retained viability in a high K+ microenvironment. KCNQ1 expression was significantly reduced in T vs NM in the patient cohort (median T/NM = 0.15, IQR 0.04-0.38), and correlated with FAM46C expression.
Conclusions: Loss of FAM46C is common in GCa, and resultant ion channelopathy may promote GCa viability and progression. Upregulation of FAM46C by norcantharidin, a synthetic derivative of the Mylabris beetle extract cantharidin, could restore ion homeostasis and overcome resistance to therapy.
Learning Objectives:
discuss the need for novel molecular markers and targets in gastric adenocarcinoma
describe the tumor suppressor FAM46C as it relates to predicting survival and recurrence following resection of gastric adenocarcinoma
describe the potential downstream molecular mechanisms of FAM46C’s tumor suppressor activity in relation to ion channelopathy