Cariporide Enhances the DNA Damage and Apoptosis in Acid-tolerable Malignant Mesothelioma H-2452 Cells

Intracellular Acidification in a Rat C6 Glioma Model following Cariporide Injection Investigated by CEST-MRI

Acidification of cancerous tissue induced pharmacologically may slow tumor growth and can be detected using magnetic resonance imaging. Numerous studies have shown that pharmacologically inhibiting specific transporters, such as the Na⁺/H⁺ exchanger 1 (NHE1), can alter glycolitic metabolism and affect tumor acidosis. The sodium proton exchanger inhibitor Cariporide can acidify U87MG gliomas in mice. This study aimed to determine whether Cariporide could acidify C6 glioma tumors in rats with an intact immune system. C6 glioma cells were implanted in the right brain hemisphere of ten rats. Chemical exchange saturation transfer (CEST) MRI (9.4T) was acquired on days 7-8 and 14-15 after implantation to measure in vivo tissue intracellular pH (pH_i) within the tumors and on the contralateral side. pH_i was basic relative to contralateral tissue at both time points assessed using the amine and amide concentration-independent detection (AACID) value. On day 14-15, measurements were made before and up to 160 min after Cariporide injection (N = 6). Twenty minutes after drug injection, the average AACID value in the tumor significantly increased by ∼6.4% compared to pre-injection, corresponding to 0.31 ± 0.20 lower pH_i, while in contralateral tissue, AACID value increased significantly by ∼4.3% compared to pre-injection, corresponding to 0.22 ± 0.19 lower pH_i. Control rats without tumors showed no changes following injection of Cariporide dissolved in 10% or 1% DMSO and diluted in PBS. This study demonstrates the sensitivity of CEST-based pH-weighted imaging for monitoring the response of tumors to pharmacologically induced acidification.

Colorectal cancer extracellular acidosis decreases immune cell killing and is partially ameliorated by pH-modulating agents that modify tumor cell cytokine profiles

Tumor cells upregulate myriad proteins that are important for pH regulation, resulting in the acidification of the extracellular tumor microenvironment (TME). Abnormal pH is known to dampen immune function, resulting in a worsened anti-tumor immune response. Understanding how extrinsic alterations in pH modulate the interactions between immune cells and tumors cells will help elucidate opportunities for new therapeutic approaches. We observed that pH impacts the function of immune cells, both natural killer (NK) and T cells, which is relevant in the context of a highly acidic TME. Decreased NK and T cell activity was correlated with decreasing pH in a co-culture immune cell-mediated tumor cell-killing assay. The addition of pH-modulating drugs cariporide, lansoprazole, and acetazolamide to the co-culture assay was able to partially mitigate this dampened immune cell function. Treatment of colorectal cancer (CRC) cells with NHE1 inhibitor cariporide increased CRC cell-secreted cytokines involved in immune cell recruitment and activation and decreased cytokines involved in epithelial-mesenchymal transition (EMT). Cariporide treatment also decreased CRC cell shed TRAIL-R2, TRAIL-R3, and PD-L1 which is relevant in the context of immunotherapy. These experiments can help inform future investigations into how the pH of the tumor microenvironment may be extrinsically modulated to improve anti-tumor immune response in solid tumors such as colorectal cancer.

Akt regulates RSK2 to alter phosphorylation level of H2A.X in breast cancer

Histone H2AX (H2A.X) is a variant of the histone H2A family. Phosphorylation of H2A.X is a marker of DNA strand breaks and the presence or absence of H2A.X is closely related to tumor susceptibility and drug resistance. The present study found that the activity of the serine/threonine kinase Akt was negatively associated with H2A.X phosphorylated at the Ser16 site (H2A.X S16ph), but the mechanism of the inverse relationship remains elusive. The aim of the present study was to elucidate the mechanism of action between Akt and H2A.X S16ph and the exact role of this mechanism. Western blot analysis was performed to detect the regulatory association between p-Akt and H2A.X S16ph/p-RSK2, and immunoprecipitation and chromatin immunoprecipitation were performed to prove that Akt, RSK2 and H2A.X combine and interact in human breast cancer cells. The changes of cellular proliferation and migration induced by the interaction of Akt, RSK2 and H2A.X was determined by MTT, soft agar colony formation and cell migration experiments. The effect of interaction of Akt, RSK2 and H2A.X on cancer-promoting genes, such as PSAT-1 was determined via reverse transcription-quantitative PCR analysis. The current study indicated that the serine/threonine kinase ribosomal S6 kinase 2 (RSK2) as a kinase of H2A.X could be phosphorylated by Akt at Ser19 site. Moreover, Akt positively regulated the phosphorylation of RSK2 to inhibit phosphorylation of H2A.X, thereby affecting the affinity between RSK2 and substrate histone, promoting the survival and migration of breast cancer cells. In conclusion, Akt-mediated phosphorylation of RSK2 regulated the phosphorylation of H2A.X, thereby promoting oncogenic activity. This finding provides new insights to understand the pathogenesis and treatment mechanisms of breast cancer.

Targeting the pH Paradigm at the Bedside: A Practical Approach

The inversion of the pH gradient in malignant tumors, known as the pH paradigm, is increasingly becoming accepted by the scientific community as a hallmark of cancer. Accumulated evidence shows that this is not simply a metabolic consequence of a dysregulated behavior, but rather an essential process in the physiopathology of accelerated proliferation and invasion. From the over-simplification of increased lactate production as the cause of the paradigm, as initially proposed, basic science researchers have arrived at highly complex and far-reaching knowledge, that substantially modified that initial belief. These new developments show that the paradigm entails a different regulation of membrane transporters, electrolyte exchangers, cellular and membrane enzymes, water trafficking, specialized membrane structures, transcription factors, and metabolic changes that go far beyond fermentative glycolysis. This complex world of dysregulations is still shuttered behind the walls of experimental laboratories and has not yet reached bedside medicine. However, there are many known pharmaceuticals and nutraceuticals that are capable of targeting the pH paradigm. Most of these products are well known, have low toxicity, and are also inexpensive. They need to be repurposed, and this would entail shorter clinical studies and enormous cost savings if we compare them with the time and expense required for the development of a new molecule. Will targeting the pH paradigm solve the "cancer problem"? Absolutely not. However, reversing the pH inversion would strongly enhance standard treatments, rendering them more efficient, and in some cases permitting lower doses of toxic drugs. This article's goal is to describe how to reverse the pH gradient inversion with existing drugs and nutraceuticals that can easily be used in bedside medicine, without adding toxicity to established treatments. It also aims at increasing awareness among practicing physicians that targeting the pH paradigm would be able to improve the results of standard therapies. Some clinical cases will be presented as well, showing how the pH gradient inversion can be treated at the bedside in a simple manner with repurposed drugs.

Pifithrin-μ induces necroptosis through oxidative mitochondrial damage but accompanies epithelial-mesenchymal transition-like phenomenon in malignant mesothelioma cells under lactic acidosis

Heat shock protein 70 (HSP70), a chaperone protein associated with tumorigenesis and chemoresistance, has attracted significant attention as a potential therapeutic target for the development of anticancer drugs. Here, the effects of pifithrin-μ, an effective dual inhibitor of HSP70 and p53, on anticancer activities and epithelial-mesenchymal transition (EMT) were investigated in malignant mesothelioma (MM) cells. MSTO-211HAcT cells, pre-incubated in a medium containing lactic acid, showed more potent resistance to cisplatin and gemcitabine, compared with their acid-sensitive parental MSTO-211H cells. Pifithrin-μ treatment induced both apoptosis and necroptosis, which were accompanied by an EMT-like phenomenon, as evidenced by an elongated cell morphology, decreased levels of epithelial cell markers including E-cadherin, claudin-1, and β-catenin, increased levels of mesenchymal markers including Snail, Slug, and vimentin, and increased cell migratory property. Moreover, pifithrin-μ increased intracellular ROS levels, which is associated with mitochondrial dysfunction and decreased cellular ATP content. A series of changes caused by pifithrin-μ treatment were effectively restored by lowering the ROS level through pretreatment with N-acetylcysteine. Collectively, our results suggest that pifithrin-μ may promote the metastatic behavior of surviving cells by triggering the EMT, despite its effective cell-killing action against MM cells, possibly linked to oxidative mitochondrial dysfunction and ATP depletion.