Abstract 3239: OXCT1: Role of ketone bodies in acquired gemcitabine resistance in bladder cancer
Authors: Rivera Krizia Rohena , You Sungyoung , Kim Minhyung , Billet Sandrine , Hoeve-Scott Johanna , Gonzales Gabrielle , Huang Chengqun , Heard Ashley , Bhowmick Neil A. 
Published: June 2022

Abstract
Urinary bladder cancer accounts for 81,000 new cases per year and 4.7% of the new cancer diagnosis in the US. Even though most of the patients suffer from non-invasive lesions, around 70% will recur following surgical intervention. Chemotherapy with gemcitabine in combination with cisplatin is a common treatment option for recurrent disease, however 60% of the patients will relapse due to resistance. Gemcitabine (2’,2’-difluoro 2’-deoxycytidine) is classified as an antimetabolite, is commonly administered to BCa patients. This DNA synthesis inhibitor, is also used to treat pancreatic, breast, ovarian, and non-small cell lung cancer patients. Having lower relative toxicity, BCa patients are given gemcitabine as a single agent for intravesical therapy. Resistance mechanisms for gemcitabine have been reported to involve Hedgehog, Wnt, and Notch, signaling as potential means of cancer stem cell programming dependent on the tumor type. In examining mechanisms of resistance, we identified ketone body metabolism to be important. OXCT1, a rate-limiting enzyme in ketone metabolism, was found to be highly associated with bladder cancer death - Hoglund et al. P = 2.3x10-3 and TCGA, P = 6.5x10-4. We measured the expression of OXCT1 in RT4, UMUC3, T24 and 5637 bladder cancer cell lines and observed that expression correlated with gemcitabine resistance. The generation of gemcitabine resistance of otherwise sensitive 5637 cells (5637GR) resulted in elevation of OXCT1. Conversely, the CRISPR/Cas9 knockout of OXCT1 was able to sensitize inherently resistant UMUC3 and generated 5637GR lines. Given that OXCT1 is a rate limiting enzyme in ketone metabolism, we evaluated oxygen consumption rate finding increase metabolic activity. Furthermore we evaluated stemness through sphere forming assays (hanging drop and forced floating methods) to reveal that the OXCT1-KO lines had reduced spheres compared to their parental lines. Keeping in mind that several developmental processes were altered in 5637GR and restored to parental levels in the 5637GR-OXCT1-KO, we evaluated the transcriptomic differences in the cell types to determine the mechanism that led to the metabolic changes induced by gemcitabine resistance. master regulator analysis that revealed three key transcription factors (TFs), TBX2, SOX15 and OVOL1. Analysis of the downstream targets of the three master regulators in the TCGA BCa data (n = 408), the Peter C. Black neoadjuvant chemotherapy data (n = 134) and the Hoglund muscle invasive data (n = 308) demonstrated that OVOL1 is highly associated with recurrence. Moreover, downstream targets of OVOL1 are involved in fatty acid metabolism, survival and differentiation. These data links ketone metabolism and stemness. Additionally, it opens the door for targets in gemcitabine treatment
Citation Format: Krizia Rohena Rivera, Sungyoung You, Minhyung Kim, Sandrine Billet, Johanna Hoeve-Scott, Gabrielle Gonzales, Chengqun Huang, Ashley Heard, Neil A. Bhowmick. OXCT1: Role of ketone bodies in acquired gemcitabine resistance in bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3239.