pH-dependent antitumor activity of proton pump inhibitors against human melanoma is mediated by inhibition of tumor acidity.
TL;DR: Preclinical evidence supporting the use of PPI as novel therapeutic strategy for melanoma is shown, providing the proof of concept that PPI target human melanoma modifying tumor pH gradients.
Abstract: Metastatic melanoma is associated with poor prognosis and still limited therapeutic options. An innovative treatment approach for this disease is represented by targeting acidosis, a feature characterizing tumor microenvironment and playing an important role in cancer malignancy. Proton pump inhibitors (PPI), such as esomeprazole (ESOM) are prodrugs functionally activated by acidic environment, fostering pH neutralization by inhibiting proton extrusion. We used human melanoma cell lines and xeno-transplated SCID mice to provide preclinical evidence of ESOM antineoplastic activity. Human melanoma cell lines, characterized by different mutation and signaling profiles, were treated with ESOM in different pH conditions and evaluated for proliferation, viability and cell death. SCID mice engrafted with human melanoma were used to study ESOM administration effects on tumor growth and tumor pH by magnetic resonance spectroscopy (MRS). ESOM inhibited proliferation of melanoma cells in vitro and induced a cytotoxicity strongly boosted by low pH culture conditions. ESOM-induced tumor cell death occurred via rapid intracellular acidification and activation of several caspases. Inhibition of caspases activity by pan-caspase inhibitor z-vad-fmk completely abrogated the ESOM-induced cell death. ESOM administration (2.5 mg kg(-1)) to SCID mice engrafted with human melanoma reduced tumor growth, consistent with decrease of proliferating cells and clear reduction of pH gradients in tumor tissue. Moreover, systemic ESOM administration dramatically increased survival of human melanoma-bearing animals, in absence of any relevant toxicity. These data show preclinical evidence supporting the use of PPI as novel therapeutic strategy for melanoma, providing the proof of concept that PPI target human melanoma modifying tumor pH gradients.
Citations
More filters
TL;DR: Key pH regulators in tumour cells include: isoforms 2, 9 and 12 of carbonic anhydrase, isoforms of anion exchangers, Na+/HCO3− co-transporters, Na+./H+ exchanger, monocarboxylate transporters and the vacuolar ATPase.
Abstract: The high metabolic rate of tumours often leads to acidosis and hypoxia in poorly perfused regions. Tumour cells have thus evolved the ability to function in a more acidic environment than normal cells. Key pH regulators in tumour cells include: isoforms 2, 9 and 12 of carbonic anhydrase, isoforms of anion exchangers, Na+/HCO3- co-transporters, Na+/H+ exchangers, monocarboxylate transporters and the vacuolar ATPase. Both small molecules and antibodies targeting these pH regulators are currently at various stages of clinical development. These antitumour mechanisms are not exploited by the classical cancer drugs and therefore represent a new anticancer drug discovery strategy.
1,331 citations
TL;DR: CO2 from the pentose phosphate pathway is an alternative source of acidity, showing that hypoxia and extracellular acidity are, while being independent from each other, deeply associated with the cellular microenvironment.
Abstract: Acidic extracellular pH is a major feature of tumor tissue, extracellular acidification being primarily considered to be due to lactate secretion from anaerobic glycolysis. Clinicopathological evidence shows that transporters and pumps contribute to H+ secretion, such as the Na+/H+ exchanger, the H+-lactate co-transporter, monocarboxylate transporters, and the proton pump (H+-ATPase); these may also be associated with tumor metastasis. An acidic extracellular pH not only activates secreted lysosomal enzymes that have an optimal pH in the acidic range, but induces the expression of certain genes of pro-metastatic factors through an intracellular signaling cascade that is different from hypoxia. In addition to lactate, CO2 from the pentose phosphate pathway is an alternative source of acidity, showing that hypoxia and extracellular acidity are, while being independent from each other, deeply associated with the cellular microenvironment. In this article, the importance of an acidic extracellular pH as a microenvironmental factor participating in tumor progression is reviewed.
1,000 citations
Cites background from "pH-dependent antitumor activity of ..."
...Therefore, inhibition of the H pump can be a new strategy for cancer treatment [117-119]....
[...]
TL;DR: This Review presents the key pH-regulating systems and synthesizes recent advances in strategies that combine the disruption of pH control with bioenergetic mechanisms and discusses the possibility of exploiting, in rapidly growing tumours, acute cell death by 'metabolic catastrophe'.
Abstract: Intense interest in the 'Warburg effect' has been revived by the discovery that hypoxia-inducible factor 1 (HIF1) reprogrammes pyruvate oxidation to lactic acid conversion; lactic acid is the end product of fermentative glycolysis. The most aggressive and invasive cancers, which are often hypoxic, rely on exacerbated glycolysis to meet the increased demand for ATP and biosynthetic precursors and also rely on robust pH-regulating systems to combat the excessive generation of lactic and carbonic acids. In this Review, we present the key pH-regulating systems and synthesize recent advances in strategies that combine the disruption of pH control with bioenergetic mechanisms. We discuss the possibility of exploiting, in rapidly growing tumours, acute cell death by 'metabolic catastrophe'.
513 citations
TL;DR: It is reported that lowering the environmental pH to values that characterize tumor masses (pH 6-6.5) was sufficient to establish an anergic state in human and mouse tumor-specific CD8(+) T lymphocytes, and this state was characterized by impairment of cytolytic activity and cytokine secretion.
Abstract: Stimulating the effector functions of tumor-infiltrating T lymphocytes (TIL) in primary and metastatic tumors could improve active and adoptive T-cell therapies for cancer. Abnormal glycolysis, high lactic acid production, proton accumulation, and a reversed intra-extracellular pH gradient are thought to help render tumor microenvironments hostile to roving immune cells. However, there is little knowledge about how acidic microenvironments affect T-cell immunity. Here, we report that lowering the environmental pH to values that characterize tumor masses (pH 6-6.5) was sufficient to establish an anergic state in human and mouse tumor-specific CD8(+) T lymphocytes. This state was characterized by impairment of cytolytic activity and cytokine secretion, reduced expression of IL-2Rα (CD25) and T-cell receptors (TCR), and diminished activation of STAT5 and extracellular signal-regulated kinase (ERK) after TCR activation. In contrast, buffering pH at physiologic values completely restored all these metrics of T-cell function. Systemic treatment of B16-OVA-bearing mice with proton pump inhibitors (PPI) significantly increased the therapeutic efficacy of both active and adoptive immunotherapy. Our findings show that acidification of the tumor microenvironment acts as mechanism of immune escape. Furthermore, they illustrate the potential of PPIs to safely correct T-cell dysfunction and improve the efficacy of T-cell-based cancer treatments.
454 citations
TL;DR: T tumor acidity is a central regulator of cancer immunity that orchestrates both local and systemic immunosuppression and that may offer a broad panel of therapeutic targets to potentiate immune-mediated tumor control in cancer patients.
393 citations
References
More filters
Journal Article•
TL;DR: Current knowledge of blood flow and perfusion-related parameters, which usually go hand in hand and in turn define the cellular metabolic microenvironment of human malignancies, are summarized for predicting the acute and/or long-term response of tumors to therapy.
Abstract: The objective of this review article is to summarize current knowledge of blood flow and perfusion-related parameters, which usually go hand in hand and in turn define the cellular metabolic microenvironment of human malignancies. A compilation of available data from the literature on blood flow, oxygen and nutrient supply, and tissue oxygen and pH distribution in human tumors is presented. Whenever possible, data obtained for human tumors are compared with the respective parameters in normal tissues, isotransplanted or spontaneous rodent tumors, and xenografted human tumors. Although data on human tumors in situ are scarce and there may be significant errors associated with the techniques used for measurements, experimental evidence is provided for the existence of a compromised and anisotropic blood supply to many tumors. As a result, O2-depleted areas develop in human malignancies which coincide with nutrient and energy deprivation and with a hostile metabolic microenvironment (e.g., existence of severe tissue acidosis). Significant variations in these relevant parameters must be expected between different locations within the same tumor, at the same location at different times, and between individual tumors of the same grading and staging. Furthermore, this synopsis will attempt to identify relevant pathophysiological parameters and other related areas future research of which might be most beneficial for designing individually tailored treatment protocols with the goal of predicting the acute and/or long-term response of tumors to therapy.
3,379 citations
TL;DR: The Warburg effect of aerobic glycolysis is re-examine and a framework for understanding its contribution to the altered metabolism of cancer cells is established.
2,081 citations
"pH-dependent antitumor activity of ..." refers background in this paper
...Acidity of human solid tumors is involved in tumor progression and malignancy, mostly by inducing a selection of cells adapted through an altered metabolism to survive in hostile conditions.(2) Recent in vivo studies on animal models and also in patients with oral cancer have shown an acidic extracellular pH (pHe) and neutral-to-alkaline intracellular pH (pHi) in tumor lesions....
[...]
...The adaptive response to metabolic stress occurring in cancer cells includes indeed the upregulation of proton extrusion,(2,43,44) which represents a detoxification mechanism significantly contributing to tumor microenvironment acidification.(2) We showed in previous reports that inhibition of proton pumps by PPI impairs Figure 4....
[...]
...Tumor cell metabolism is being nowadays object of renewed consideration for better understanding of cancer biology and therapeutic strategies.(2,43) The adaptive response to metabolic stress occurring in cancer cells includes indeed the upregulation of proton extrusion,(2,43,44) which represents a detoxification mechanism significantly contributing to tumor microenvironment acidification....
[...]
TL;DR: The peculiarities of tumor cell metabolism are reviewed to discuss the alterations in signal transduction pathways and/or enzymatic machineries that account for metabolic reprogramming of transformed cells.
2,007 citations
TL;DR: How the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumormicroenvironment are described.
Abstract: Resistance of human tumors to anticancer drugs is most often ascribed to gene mutations, gene amplification, or epigenetic changes that influence the uptake, metabolism, or export of drugs from single cells. Another important yet little-appreciated cause of anticancer drug resistance is the limited ability of drugs to penetrate tumor tissue and to reach all of the tumor cells in a potentially lethal concentration. To reach all viable cells in the tumor, anticancer drugs must be delivered efficiently through the tumor vasculature, cross the vessel wall, and traverse the tumor tissue. In addition, heterogeneity within the tumor microenvironment leads to marked gradients in the rate of cell proliferation and to regions of hypoxia and acidity, all of which can influence the sensitivity of the tumor cells to drug treatment. In this review, we describe how the tumor microenvironment may be involved in the resistance of solid tumors to chemotherapy and discuss potential strategies to improve the effectiveness of drug treatment by modifying factors relating to the tumor microenvironment.
1,889 citations
"pH-dependent antitumor activity of ..." refers background in this paper
...This may have important consequences not only on the capacity of malignant cells to proliferate and survive in acidic conditions but also on distribution and penetration of chemotherapeutics in tumor microenvironment and tumor cells.(3,5,48) Consistent with the derangement of tumor pH gradients, ESOM clearly inhibited tumor growth and dramatically prolonged survival of melanoma-bearing animals....
[...]
Journal Article•
TL;DR: Measurement of pH in tissue has shown that the microenvironment in tumors is generally more acidic than in normal tissues, and acid conditions in tumors might allow the development of new and relatively specific types of therapy which are directed against mechanisms which regulate pHi under acid conditions.
Abstract: Measurement of pH in tissue has shown that the microenvironment in tumors is generally more acidic than in normal tissues. Major mechanisms which lead to tumor acidity probably include the production of lactic acid and hydrolysis of ATP in hypoxic regions of tumors. Further reduction in pH may be achieved in some tumors by administration of glucose (+/- insulin) and by drugs such as hydralazine which modify the relative blood flow to tumors and normal tissues. Cells have evolved mechanisms for regulating their intracellular pH. The amiloride-sensitive Na+/H+ antiport and the DIDS-sensitive Na+-dependent HCO3-/Cl- exchanger appear to be the major mechanisms for regulating pHi under conditions of acid loading, although additional mechanisms may contribute to acid extrusion. Mitogen-induced initiation of proliferation in some cells is preceded by cytoplasmic alkalinization, usually triggered by stimulation of Na+/H+ exchange; proliferation of other cells can be induced without prior alkalinization. Mutant cells which lack Na+/H+ exchange activity have reduced or absent ability to generate solid tumors; a plausible explanation is the failure of such mutant cells to withstand acidic conditions that are generated during tumor growth. Studies in tissue culture have demonstrated that the combination of hypoxia and acid pHe is toxic to mammalian cells, whereas short exposures to either factor alone are not very toxic. This interaction may contribute to cell death and necrosis in solid tumors. Acidic pH may influence the outcome of tumor therapy. There are rather small effects of pHe on the response of cells to ionizing radiation but acute exposure to acid pHe causes a marked increase in response to hyperthermia; this effect is decreased in cells that are adapted to low pHe. Acidity may have varying effects on the response of cells to conventional anticancer drugs. Ionophores such as nigericin or CCCP cause acid loading of cells in culture and are toxic only at low pHc; this toxicity is enhanced by agents such as amiloride or DIDS which impair mechanisms involved in regulation of pHi. It is suggested that acid conditions in tumors might allow the development of new and relatively specific types of therapy which are directed against mechanisms which regulate pHi under acid conditions.
1,650 citations