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DNA replication stress underpins the vulnerability to oxidative phosphorylation inhibition in colorectal cancer
Xiao Hong Zhao1, Man Man Han2,3, Qian Qian Yan2,3
1School of Biomedical Sciences and Pharmacy, The University of Newcastle, Newcastle, NSW, Australia.
Abstract:
Mitochondrial oxidative phosphorylation (OXPHOS) is a therapeutic vulnerability in glycolysis-deficient cancers. Here we show that inhibiting OXPHOS similarly suppresses the proliferation and tumorigenicity of glycolytically competent colorectal cancer (CRC) cells in vitro and in patient-derived CRC xenografts. While the increased glycolytic activity rapidly replenished the ATP pool, it did not restore the reduced production of aspartate upon OXPHOS inhibition. This shortage in aspartate, in turn, caused nucleotide deficiencies, leading to S phase cell cycle arrest, replication fork stalling, and enrichment of the p53 pathway, manifestations of replication stress. The addition of purine nucleobases adenine and guanine along with the pyrimidine nucleoside uridine restored replication fork progression and cell proliferation, whereas the supplementation of exogenous aspartate recovered the nucleotide pool, demonstrating a causal role of the aspartate shortage in OXPHOS inhibition-induced nucleotide deficiencies and consequently replication stress and reductions in proliferation. Moreover, we demonstrate that glutamic-oxaloacetic transaminase 1 (GOT1) is critical for maintaining the minimum aspartate pool when OXPHOS is inhibited, as knockdown of GOT1 further reduced aspartate levels and rendered CRC cells more sensitive to OXPHOS inhibition both in vitro and in vivo. These results propose GOT1 targeting as a potential avenue to sensitize cancer cells to OXPHOS inhibitors, thus lowering the necessary doses to efficiently inhibit cancer growth while alleviating their adverse effects.
Insights
Inhibiting mitochondrial oxidative phosphorylation (OXPHOS) suppresses colorectal cancer growth by causing aspartate deficiency, leading to replication stress. Targeting GOT1 enhances this effect, offering a novel therapeutic strategy.
Area of Science:
- Biochemistry
- Cancer Biology
- Metabolic Pathways
Background:
- Mitochondrial oxidative phosphorylation (OXPHOS) is a key metabolic pathway in cancer.
- While some cancers rely on glycolysis, others maintain OXPHOS.
- OXPHOS inhibition is a potential cancer therapy, but its effects on glycolytically competent cancers require further study.
Purpose of the Study:
- To investigate the effects of OXPHOS inhibition on colorectal cancer (CRC) cells.
- To identify the metabolic consequences of OXPHOS inhibition in CRC.
- To explore potential therapeutic targets to enhance OXPHOS inhibition efficacy.
Main Methods:
- In vitro and in vivo studies using CRC cell lines and patient-derived xenografts.
- Metabolic analysis to assess ATP production, aspartate levels, and nucleotide pools.
- Assessment of cell proliferation, replication stress markers, and p53 pathway activation.
- Gene knockdown experiments targeting GOT1.
Main Results:
- OXPHOS inhibition suppressed CRC cell proliferation and tumorigenicity, despite increased glycolysis.
- Aspartate deficiency, not ATP depletion, was identified as the cause of nucleotide deficiencies and replication stress.
- Supplementation with purine nucleobases and uridine, or exogenous aspartate, restored proliferation and nucleotide pools.
- GOT1 was found to be critical for maintaining aspartate levels during OXPHOS inhibition, and its knockdown sensitized CRC cells to OXPHOS inhibition.
Conclusions:
- Aspartate shortage is a key mediator of replication stress and proliferation defects upon OXPHOS inhibition in CRC.
- GOT1 plays a crucial role in maintaining aspartate homeostasis under OXPHOS inhibition.
- Targeting GOT1 in combination with OXPHOS inhibitors presents a promising therapeutic strategy for colorectal cancer.
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