Abstract PR01: Novel role of ketone body metabolism in acquired gemcitabine resistance

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 noninvasive 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 is a synthetic pyrimidine nucleoside prodrug, without a known mechanism for resistance. 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 = 2.3 × 10-3 and TCGA, P = 6.5 × 10-4. 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 expression, as well as PGC1a and SIRT1 involved in mitochondrial biogenesis. 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 among parental and resistant cells with Seahorse. Surprisingly, resistant cells were found to be metabolically quiescent. We evaluated the role OXCT1 has on cancer 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. We identified bone morphogenic protein (BMP) signaling to be induced in promoting SOX9 expression, in OXTC1-dependent manner. Gene expression analysis further corroborated the novel role of ketone metabolism in stemness and therapeutic resistance. This abstract is also being presented as Poster B28. Citation Format: Krizia Rohena-Rivera, Neil Bhowmick. Novel role of ketone body metabolism in acquired gemcitabine resistance [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2019 May 18-21; Denver, CO. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(15_Suppl):Abstract nr PR01.