Abstract 369: The retinoblastoma protein regulates glucose metabolism in lung cancer
Authors: Reynolds Lindsey , Dougherty Susan , Kruer Traci , Clem Brian 
Published: August 2018

Abstract
Lung cancer is among the most frequently diagnosed cancers and is the leading cause of cancer-related deaths in the United States. Of its subtypes, non-small cell lung cancer (NSCLC) accounts for 85% of all lung cancer diagnoses. The retinoblastoma protein (Rb) is a tumor suppressor which functions to regulate cell cycle progression by altering the transcriptional activity of the E2F family of transcription factors. In most NSCLC cases, Rb inactivation occurs via hyperphosphorylation due to loss of upstream regulatory mechanisms including overexpression of cyclin D1 or loss of p16INK4A. Although the canonical fucntions of Rb have been well established, advances in our understanding of Rb have highlighted additional cellular processes regulated by this tumor suppressor in both normal and transformed cells. Increased glucose utilization has become a hallmark of transformed cells and is driven in part by specific genetic alterations in various oncogenes or tumor suppressors. In preliminary studies, we demonstrate a role for Rb in regulating glucose metabolism in both in vitro and in vivo models of lung cancer. Using A549 lung adenocarcinoma cells, which harbor a p16 deletion that allows CDK4/6 inactivation of Rb, we performed in vitro metabolic assays, including glucose uptake and glycolysis as well as measured the expression of key enzymes within glycolysis and downstream metabolic pathways. Each assay was performed following treatment with vehicle control or Palbociclib, a CDK4/6 inhibitor which inhibits the phosphorylation and subsequent inactivation of Rb. Following treatment with Palbociclib, A549 cells show decreased glycolysis and expression of glycolytic genes, without altering glucose uptake. To define the metabolic fates of glucose in vitro, we performed stable isotope resolved metabolomics (SIRM) analysis of 13C-glucose in A549 cells. Consistent with in vitro metabolic assays and gene expression data, SIRM analysis revealed treatment with Palbociclib decreases glucose-derived carbons into glycolytic intermediates and other metabolic pathways. To determine if Rb1 loss results in an altered metabolic phenotype in an in vivo model of lung cancer, we have crossed Rb1lox/lox mice with Kras+/LSLG12D mice to generate Kras+/LSLG12D/Rb1lox/lox and Kras+/LSLG12D/Rb1+/+ mice. Rb1 KO mice exhibit increased tumor burden as well as decreased overall survival compared to Rb1 WT mice. Additionally, SIRM analysis of 13C-glucose incorporation into lung tumors of Kras+/LSLG12D/Rb1+/+ and Kras+/LSLG12D/Rb1lox/lox mice revealed increased glycolysis in lung tumors of Rb1 KO mice compared to Rb1 WT mice. Lastly, immunohistochemistry was performed to determine the metabolic transporter/enzyme expression profile in these tumors. We have observed increased levels of glycolytic genes in Rb1 KO lung tumors compared to Rb1 WT. Taken together, these data indicate that Rb may regulate the metabolic reprogramming of lung cancer.
Citation Format: Lindsey Reynolds, Susan Dougherty, Traci Kruer, Brian Clem. The retinoblastoma protein regulates glucose metabolism in lung cancer [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 369.