Abstract 7052: p53 underpins a dependence on oxidative phosphorylation in glycolysis-competent colorectal cancer
Authors: Zhao Xiao Hong , Han Man Man , Yan Qian Qian , Yue Yi Meng , Ye Kai Hong , Zhang Yuan Yuan , Teng Liu , Xu Liang , Shi Xiao Jing , La Ting , Feng Yu Chen , Xu Ran , Narayana Vinod K. , De Souza David P. , Liu Tao , Baker Mark , Thorne Rick F. , Zhang Xu Dong , Chen Song , Jin Lei 
Published: March 2024

Abstract
The use of mitochondrial inhibitors to target oxidative phosphorylation (OXPHOS) in cancer treatment presents a challenge due to dose-limiting toxicities. Moreover, while glycolysis-deficient cancers are vulnerable to OXPHOS inhibition in preclinical models, the full extent of phenotypical and mechanistic consequences of inhibiting OXPHOS in cancers capable of glycolysis is not yet well understood. Our results presented here offer promising insights into potential therapeutic gains from combining p53 restoration strategies with OXPHOS inhibitors, even when applied to glycolysis-competent CRC cells. Treatment with mitochondrial complex I inhibitors did not cause energy stress in CRC cells capable of glycolysis. It does, however, induce DNA replication stress, apparent through an observed cell cycle arrest at the S phase, enrichment of the G2/M DNA-damage checkpoint regulation pathway, and replication fork slowdown. Intriguingly, CRC cells harboring wildtype p53 exhibited more severe replication stress than those carrying mutant p53. Furthermore, siRNA knockdown of p53 attenuates replication stress and reduces cell cycle arrest, underlining the important role of p53 in CRC cell responses to OXPHOS inhibition. Our targeted metabolomics analysis reveals that OXPHOS inhibition results in reductions in the purine nucleotides, adenine monophosphate (AMP) and guanine monophosphate (GMP), as well as the pyrimidine nucleotide, uridine monophosphate (UMP), in CRC cells, regardless of their p53 mutational status. By supplementing cell culture mediums with the purine nucleobases adenine and guanine, and the pyrimidine nucleoside uridine, we observed a partial reversal of the replication fork slowdown and reductions in cell viability. This suggests nucleotide deficiencies are involved in the induction of DNA replication stress caused by OXPHOS inhibition. The nucleotide deficiencies were associated with a decrease in the nucleobase precursor aspartate. By adding aspartate at a supraphysiological concentration, to overcome the low expression of the excitatory amino acid transporter 1 required for cellular import of aspartate, we were able to restore the levels of nucleotides. Collectively, our findings suggest broader potential cancer treatment paradigms via OXPHOS targeting, extending beyond glycolysis-deficient cancers. Our data uncovers that CRC cells, which commonly exhibit the glycolytic phenotype, are susceptible to OXPHOS inhibition, with those carrying wildtype p53 showing heightened sensitivity. Therefore, p53 status could serve as a biomarker for predicting CRC responses to OXPHOS inhibitors. Moreover, our findings suggest that combined strategies of restoring p53 function, using small molecules such as APR-246, might enable reduced dosage of OXPHOS inhibitors in CRC treatment, thereby mitigating their dose-limiting toxicities.
Citation Format: Xiao Hong Zhao, Man Man Han, Qian Qian Yan, Yi Meng Yue, Kai Hong Ye, Yuan Yuan Zhang, Liu Teng, Liang Xu, Xiao Jing Shi, Ting La, Yu Chen Feng, Ran Xu, Vinod K. Narayana, David P. De Souza, Tao Liu, Mark Baker, Rick F. Thorne, Xu Dong Zhang, Song Chen, Lei Jin. p53 underpins a dependence on oxidative phosphorylation in glycolysis-competent colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7052.