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Alkalization of cellular pH leads to cancer cell death by disrupting autophagy and mitochondrial function

Abstract

We previously found that lactic acidosis in the tumor environment was permissive to cancer cell surviving under glucose deprivation and demonstrated that neutralizing lactic acidosis restored cancer cell susceptibility to glucose deprivation. We then reported that alternate infusion of bicarbonate and anticancer agent into tumors via tumor feeding artery markedly enhanced the efficacy of transarterial chemoembolization (TACE) in the local control of hepatocellular carcinoma (HCC). Here we sought to further investigate the mechanism by which bicarbonate enhances the anticancer activity of TACE. We propose that interfering cellular pH by bicarbonate could induce a cascade of molecular events leading to cancer cell death. Alkalizing cellular pH by bicarbonate decreased pH gradient (ΔpH), membrane potential (ΔΨm), and proton motive force (Δp) across the inner membrane of mitochondria; disruption of oxidative phosphorylation (OXPHOS) due to collapsed Δp led to a significant increase in adenosine monophosphate (AMP), which activated the classical AMPK-mediated autophagy. Meanwhile, the autophagic flux was ultimately blocked by increased cellular pH, reduced OXPHOS, and inhibition of lysosomal proton pump in alkalized lysosome. Bicarbonate also induced persistent mitochondrial permeability (MPT) and damaged mitochondria. Collectively, this study reveals that interfering cellular pH may provide a valuable approach to treat cancer.

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Fig. 1: Bicarbonate decreases the ΔpH across the inner membrane of mitochondria, depolarizes ΔΨm, reduces Δp, and disrupts OXPHOS in SK-HEP-1 cells.
Fig. 2: Bicarbonate increases cellular AMP concentration and activates AMPK-mediated autophagy.
Fig. 3: Bicarbonate concentration-dependent effect on lysosome alkalization and autophagic flux blockage.
Fig. 4: Bicarbonate alkalizes lysosome and autolysosome and blocks autophagic flux induced by bicarbonate.
Fig. 5: The effect of Cyclophilin D knockdown on the ΔΨm, MPT, mitochondrial respiration, and autophagy of SK-HEP-1 cells treated with bicarbonate.
Fig. 6: The contribution of bicarbonate-induced autophagy and MPT to cell death and combined effect of bicarbonate with pirarubicin on cell cytotoxicity.
Fig. 7: Contrast-enhanced MRI scans of patients with hepatocellular carcinoma before and after treatment with TILA-TACE or cTACE.
Fig. 8: Bicarbonate induces a cascade of molecular events that lead to cancer cell death.

Data availability

All the data described in the manuscript are contained within the manuscript.

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Acknowledgements

This work has been supported in part by China Natural Sciences Foundation projects (82073038, 81772947 to XH), a key project (2018C03009) funded by Zhejiang Provincial Department of Sciences and Technologies (to XH & MC), and the Fundamental Research Funds for the Central Universities (2017XZZX001-01, 2019FZJD009, to XH), National Ministry of Education, China. We thank Dr. Guo-Hua Fong (University of Connecticut School of Medicine, USA) for critical readings of our manuscript and constructive comments, Dr. Wei Liu (Zhejiang University) for the kind gift of plasmids GFP-LC3, Cherry-GFP-LC3, and Dr. Shanrong Cai for the statistical assistance (Zhejiang University).

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XH conceived the project, designed the study, analyzed the data, wrote the manuscript. CY & CJ. performed the experiments, CY, CJ, SZ. analyzed the data, MC, analysis of MRI images.

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Correspondence to Ming Chao or Xun Hu.

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Ying, C., Jin, C., Zeng, S. et al. Alkalization of cellular pH leads to cancer cell death by disrupting autophagy and mitochondrial function. Oncogene 41, 3886–3897 (2022). https://doi.org/10.1038/s41388-022-02396-6

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