Abstract B024: The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity
Authors: Prasad Chandra Bhushan , Oo Adrian , Qiu Zhaojun , Li Na , Singh Deepika , Xin Xiwen , Cho Young-Jae , Li Zaibo , Zhang Xiaoli , Yan Chunhong , Zheng Qingfei , Shao Jimin , Wang Qi-En , Kim Baek , Zhang Junran 
Published: January 2024

Abstract
The replication stress (RS) response protein ataxia telangiectasia and Rad3-related protein (ATR) and its main downstream factor, checkpoint kinase 1 (CHK1), play important roles in cell survival under RS. The inhibitors targeting CHK1 (CHK1i’s) have been shown to be a powerful strategy for treating solid tumors and hematological malignancies in preclinical studies. However, in most clinical trials, including those for treating non-small cell lung cancer (NSCLC), which accounts for 85% of all lung cancer cases, CHKi’s have failed to achieve their primary endpoints and have shown cumulative tissue toxicities in normal tissues. These findings significantly limit the clinical benefit of these agents. Thus, identifying novel combinational strategies that can enhance the sensitivity of tumor cells to CHKi’s, while limiting their toxicities, might be the key to improve the safety and efficacy of these compounds. To explore novel combinational strategies that can overcome these limitations, we performed an unbiased high-throughput screen in a NSCLC cell line and identified thioredoxin1 (Trx1), a major component of the mammalian antioxidant-system, as a novel determinant of CHK1i sensitivity. We established a role for redox recycling of RRM1, the larger subunit of ribonucleotide reductase (RNR), and a depletion of the deoxynucleotide pool in this Trx1-mediated RS. In addition, we also demonstrate that CHK1-mediated E2F1-RRM2 induction was triggered during Trx1 or TrxR1 depletion-induced RS. CHK1 inhibition abrogates the Trx1 or TrxR1 depletion induced RRM2 expression and leads to the more profound dNTP pool scarcity. Further, the TrxR1 inhibitor auronafin, an anti-rheumatoid arthritis drug, shows a synergistic interaction with CHK1i via interruption of the deoxynucleotide pool. In summary, our study reveals an underappreciated mechanism responsible for the Trx or TrxR1 inhibition-induced RS. We propose that increased RRM1 oxidation following Trx system inhibition and the abrogation of RRM2 pathway by CHKi contributes to the synergistic interaction by the severe loss of RNR function. Our findings identify a new pharmacological combination to treat NSCLC that relies on a redox regulatory link between the Trx system and mammalian RNR activity.
Citation Format: Chandra Bhushan Prasad, Adrian Oo, Zhaojun Qiu, Na Li, Deepika Singh, Xiwen Xin, Young-Jae Cho, Zaibo Li, Xiaoli Zhang, Chunhong Yan, Qingfei Zheng, Jimin Shao, Qi-En Wang, Baek Kim, Junran Zhang. The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr B024.