Mp61-05 Intravesical Instillation of Exogenous Microrna-145 as a Therapy for Mouse Orthotopic Human Bladder Cancer Xenograft

Abstract

INTRODUCTION AND OBJECTIVES: Cancer cells generate a significant proportion of ATP by glycolysis, even in the presence of oxygen (Warburg effect). Lactate transporters are of utmost importance for regulation of metabolism. Recently, the significance of lactate transporters has been recognized in various cancer types, but their role in urothelial carcinoma (UC) remains mostly unknown. The aim of the present study was to investigate the functional importance of the lactate transporters MCT1 and MCT4 and their chaperone CD147 (Basigin) in preclinical models of UC.METHODS: MCT1, MCT4 and CD147 protein expression was assessed in 12 UC cell lines, and in benign and malignant tissue from 180 patients with muscle invasive UC of the bladder. MCT1, MCT4 and CD147 expression were correlated with molecular subtypes in The Cancer Genome Atlas (TCGA) dataset and validated using gene expression microarray data from an independent cohort of 65 patients with muscle invasive UC. Transient silencing of MCT1, MCT4 and CD147 was performed using small-interfering RNAs (siRNAs) in three UC cell lines. Cell viability in varying concentrations of oxygen and glucose was assessed using MTS assay. We measured apoptosis and production of reactive oxygen species by flow cytometry. Moreover, intra-and extracellular lactate, extracellular acidification and the oxygenconsumption rate were determined. In vivo effects of MCT4 silencing were assessed in an orthotopic xenograft model. RESULTS: Protein expression of MCT1, MCT4 and CD147 was significantly increased in cancer tissue. A high expression of MCT1, MCT4 and CD147 was associated with poor disease-specific survival after radical cystectomy. Analysis of the TCGA data as well as our own cohort of 65 UC revealed a significantly higher expression of MCT1 and MCT4 in the basal subtype. In vitro silencing of MCT4 led to a significant reduction in cell growth, a significant induction of apoptosis and an increased synthesis of reactive oxygen species. Moreover, silencing of MCT4 resulted in intracellular accumulation of lactate and reduced extracellular acidification. In vivo, stable knockdown of MCT4 significantly reduced tumor growth.CONCLUSIONS: The expression of lactate transporters in UC is associated with features of aggressive tumor biology and portends a poor prognosis. Inhibition of MCT4 induces intracellular accumulation of lactate and results in decreased tumor growth in vitro and in vivo. Targeting lactate metabolism via MCT4 therefore provides a promising therapeutic approach for invasive UC.