Amiloride and guggulsterone suppression of esophageal cancer cell growth in vitro and in nude mouse xenografts

Hypoxic regulation of extracellular vesicles: Implications for cancer therapy

Extracellular vesicles (EVs) play a pivotal role in intercellular communication and have been implicated in cancer progression. Hypoxia, a pervasive hallmark of cancer, is known to regulate EV biogenesis and function. Hypoxic EVs contain a specific set of proteins, nucleic acids, lipids, and metabolites, capable of reprogramming the biology and fate of recipient cells. Enhancing the intrinsic therapeutic efficacy of EVs can be achieved by strategically modifying their structure and contents. Moreover, the use of EVs as drug delivery vehicles holds great promise for cancer treatment. However, various hurdles must be overcome to enable their clinical application as cancer therapeutics. In this review, we aim to discuss the current knowledge on the hypoxic regulation of EVs. Additionally, we will describe the underlying mechanisms by which EVs contribute to cancer progression in hypoxia and outline the progress and limitations of hypoxia-related EV therapeutics for cancer.

Vista of the Future: Novel Immunotherapy Based on the Human V-Set Immunoregulatory Receptor for Digestive System Tumors

While gastrointestinal tumors remain a multifactorial and prevalent group of malignancies commonly treated surgically in combination with chemotherapy and radiotherapy, advancements regarding immunotherapeutic approaches continue to occur. Entering a new era of immunotherapy focused on overcoming resistance to preceding therapies caused the emergence of new therapeutic strategies. A promising solution surfaces with a V-domain Ig suppressor of T-cell activation (VISTA), a negative regulator of a T-cell function expressed in hematopoietic cells. Due to VISTA's ability to act as both a ligand and a receptor, several therapeutic approaches can be potentially developed. A broad expression of VISTA was discovered on various tumor-growth-controlling cells, which proved to increase in specific tumor microenvironment (TME) conditions, thus serving as a rationale behind the development of new VISTA-targeting. Nevertheless, VISTA's ligands and signaling pathways are still not fully understood. The uncertain results of clinical trials suggest the need for future examining inhibitor agents for VISTA and implicating a double immunotherapeutic blockade. However, more research is needed before the breakthrough can be achieved. This review discusses perspectives and novel approaches presented in the current literature. Based on the results of the ongoing studies, VISTA might be considered a potential target in combined therapy, especially for treating gastrointestinal malignancies.

Mouse organoid culture is a suitable model to study esophageal ion transport mechanisms

Altered esophageal ion transport mechanisms play a key role in inflammatory and cancerous diseases of the esophagus, but epithelial ion processes have been less studied in the esophagus because of the lack of a suitable experimental model. In this study, we generated three-dimensional (3D) esophageal organoids (EOs) from two different mouse strains and characterized the ion transport processes of the EOs. EOs form a cell-filled structure with a diameter of 250-300 µm and were generated from epithelial stem cells as shown by FACS analysis. Using conventional PCR and immunostaining, the presence of Slc26a6 Cl-/HCO3- anion exchanger (AE), Na+/H+ exchanger (NHE), Na+/HCO3- cotransporter (NBC), cystic fibrosis transmembrane conductance regulator (CFTR), and anoctamin 1 Cl- channels was detected in EOs. Microfluorimetric techniques revealed high NHE, AE, and NBC activities, whereas that of CFTR was relatively low. In addition, inhibition of CFTR led to functional interactions between the major acid-base transporters and CFTR. We conclude that EOs provide a relevant and suitable model system for studying the ion transport mechanisms of esophageal epithelial cells, and they can be also used as preclinical tools to assess the effectiveness of novel therapeutic compounds in esophageal diseases associated with altered ion transport processes.

Inhibition of NHE-1 Increases Smoke-Induced Proliferative Activity of Barrett's Esophageal Cell Line

Several clinical studies indicate that smoking predisposes its consumers to esophageal inflammatory and malignant diseases, but the cellular mechanism is not clear. Ion transporters protect esophageal epithelial cells by maintaining intracellular pH at normal levels. In this study, we hypothesized that smoking affects the function of ion transporters, thus playing a role in the development of smoking-induced esophageal diseases. Esophageal cell lines were treated with cigarettesmoke extract (CSE), and the viability and proliferation of the cells, as well as the activity, mRNA and protein expression of the Na+/H+ exchanger-1 (NHE-1), were studied. NHE-1 expression was also investigated in human samples. For chronic treatment, guinea pigs were exposed to tobacco smoke, and NHE-1 activity was measured. Silencing of NHE-1 was performed by using specific siRNA. CSE treatment increased the activity and protein expression of NHE-1 in the metaplastic cells and decreased the rate of proliferation in a NHE-1-dependent manner. In contrast, CSE increased the proliferation of dysplastic cells independently of NHE-1. In the normal cells, the expression and activity of NHE-1 decreased due to in vitro and in vivo smoke exposure. Smoking enhances the function of NHE-1 in Barrett's esophagus, and this is presumably a compensatory mechanism against this toxic agent.

Roles of Ion and Water Channels in the Cell Death and Survival of Upper Gastrointestinal Tract Cancers

Ion and water channels were recently shown to be involved in cancer cell functions, and various transporter types have been detected in upper gastrointestinal tract (UGI) cancers. Current information on the expression and roles of these channels and transporters in the death and survival of UGI cancer cells was reviewed herein, and the potential of their regulation for cancer management was investigated. Esophageal cancer (EC) and gastric cancer (GC) cells and tissues express many different types of ion channels, including voltage-gated K⁺, Cl^-, and Ca²⁺, and transient receptor potential (TRP) channels, which regulate the progression of cancer. Aquaporin (AQP) 1, 3, and 5 are water channels that contribute to the progression of esophageal squamous cell carcinoma (ESCC) and GC. Intracellular pH regulators, including the anion exchanger (AE), sodium hydrogen exchanger (NHE), and vacuolar H⁺-ATPases (V-ATPase), also play roles in the functions of UGI cancer cells. We have previously conducted gene expression profiling and revealed that the regulatory mechanisms underlying apoptosis in ESCC cells involved various types of Cl^- channels, Ca²⁺ channels, water channels, and pH regulators (Shimizu et al., 2014; Ariyoshi et al., 2017; Shiozaki et al., 2017, 2018a; Kobayashi et al., 2018; Yamazato et al., 2018; Konishi et al., 2019; Kudou et al., 2019; Katsurahara et al., 2020, 2021; Matsumoto et al., 2021; Mitsuda et al., 2021). We have also previously demonstrated the clinicopathological and prognostic significance of their expression in ESCC patients, and shown that their pharmacological blockage and gene silencing had an impact on carcinogenesis, indicating their potential as targets for the treatment of UGI cancers. A more detailed understanding of the molecular regulatory mechanisms underlying cell death and survival of UGI cancers may result in the application of cellular physiological methods as novel therapeutic approaches.

Advances in research on the regulatory mechanism of NHE1 in tumors

Tumors pose a major threat to human health and present with difficulties that modern medicine has yet to overcome. It has been demonstrated that the acid-base balance of the tumor microenvironment is closely associated with the dynamic balance in the human body and that it regulates several processes, such as cell proliferation and differentiation, intracellular enzyme activity, and cytoskeletal assembly and depolymerization. It has been well established that the regulation of intra- and extracellular pH depends on a series of functional ion transporters and hydrogen ion channels, such as the Na⁺/H⁺ exchanger (NHE) protein and thee Cl/HCO₃- exchange protein, among which the NHE1 member of the NHE family has been attracting increasing attention in recent years, particularly in studies on the correlation between pH regulation and tumors. NHE1 is a housekeeping gene encoding a protein that is widely expressed on the surface of all plasma membranes. Due to its functional domain, which determines the pHi at its N-terminus and C-terminus, NHE1 is involved in the regulation of the cellular pH microenvironment. It has been reported in the literature that NHE1 can regulate cell volume, participate in the transmembrane transport of intracellular and extracellular ions, affect cell proliferation and apoptosis, and regulate cell behavior and cell cycle progression; however, research on the role of NHE1 in tumorigenesis and tumor development in various systems is at its early stages. The aim of the present study was to review the current research on the correlation between the NHE family proteins and various systemic tumors, in order to indicate a new direction for antitumor drug development with the pH microenvironment as the target.

VISTA: A Mediator of Quiescence and a Promising Target in Cancer Immunotherapy

V-domain Ig suppressor of T cell activation (VISTA) is a B7 family member that maintains T cell and myeloid quiescence and is a promising target for combination cancer immunotherapy. During inflammatory challenges, VISTA activity reprograms macrophages towards reduced production of proinflammatory cytokines and increased production of interleukin (IL)-10 and other anti-inflammatory mediators. The interaction of VISTA with its ligands is regulated by pH, and the acidic pH ~6.0 in the tumor microenvironment (TME) facilitates VISTA binding to P-selectin glycoprotein ligand 1 (PSGL-1). Targeting intratumoral pH might be a way to reduce the immunoinhibitory activity of the VISTA pathway and enhance antitumor immune responses. We review differences among VISTA therapeutics under development as candidate immunotherapies, focusing on VISTA binding partners and the unique structural features of this interaction.

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.

Potential of guggulsterone, a farnesoid X receptor antagonist, in the prevention and treatment of cancer

Cancer is one of the most dreadful diseases in the world with a mortality of 9.6 million annually. Despite the advances in diagnosis and treatment during the last couple of decades, it still remains a serious concern due to the limitations associated with currently available cancer management strategies. Therefore, alternative strategies are highly required to overcome these glitches. The importance of medicinal plants as primary healthcare has been well-known from time immemorial against various human diseases, including cancer. Commiphora wightii that belongs to Burseraceae family is one such plant which has been used to cure various ailments in traditional systems of medicine. This plant has diverse pharmacological properties such as antioxidant, antibacterial, antimutagenic, and antitumor which mostly owes to the presence of its active compound guggulsterone (GS) that exists in the form of Z- and E-isomers. Mounting evidence suggests that this compound has promising anticancer activities and was shown to suppress several cancer signaling pathways such as NF-κB/ERK/MAPK/AKT/STAT and modulate the expression of numerous signaling molecules such as the farnesoid X receptor, cyclin D1, survivin, caspases, HIF-1α, MMP-9, EMT proteins, tumor suppressor proteins, angiogenic proteins, and apoptotic proteins. The current review is an attempt to summarize the biological activities and diverse anticancer activities (both in vitro and in vivo) of the compound GS and its derivatives, along with its associated mechanism against various cancers.

OEsophageal Ion Transport Mechanisms and Significance Under Pathological Conditions

Ion transporters play an important role in several physiological functions, such as cell volume regulation, pH homeostasis and secretion. In the oesophagus, ion transport proteins are part of the epithelial resistance, a mechanism which protects the oesophagus against reflux-induced damage. A change in the function or expression of ion transporters has significance in the development or neoplastic progression of Barrett’s oesophagus (BO). In this review, we discuss the physiological and pathophysiological roles of ion transporters in the oesophagus, highlighting transport proteins which serve as therapeutic targets or prognostic markers in eosinophilic oesophagitis, BO and esophageal cancer. We believe that this review highlights important relationships which might contribute to a better understanding of the pathomechanisms of esophageal diseases.

(Patho-)Physiology of Na+/H+ Exchangers (NHEs) in the Digestive System

Na⁺/H⁺ exchangers (NHEs) are expressed in virtually all human tissues and organs. Two major tasks of those NHE isoforms that are located in plasma membranes are cell volume control by Na⁺-uptake and cellular pH regulation by H⁺-extrusion. Several NHEs, particularly NHE 1–4 and 8, are involved in the pathogenesis of diseases of the digestive system such as inflammatory bowel disease (ulcerative colitis, Crohn’s disease) and gastric and colorectal tumorigenesis. In the present review, we describe the physiological purposes, possible malfunctions and pathophysiological effects of the different NHE isoforms along the alimentary canal from esophagus to colon, including pancreas, liver and gallbladder. Particular attention is paid to the functions of NHEs in injury repair and to the role of NHE1 in Barrett’s esophagus. The impact of NHEs on gut microbiota and intestinal mucosal integrity is also dealt with. As the hitherto existing findings are not always consistent, sometimes even controversial, they are compared and critically discussed.

Googling the Guggul (Commiphora and Boswellia) for Prevention of Chronic Diseases

Extensive research during last 2 decades has revealed that most drugs discovered today, although costs billions of dollars for discovery, and yet they are highly ineffective in their clinical response. For instance, the European Medicines Agency has approved 68 anti-cancer drugs, and out of which 39 has reached the market level with no indication of increased survival nor betterment of quality of life. Even when drugs did improve survival rate compared to available treatment strategies, most of these were found to be clinically insignificant. This is a fundamental problem with modern drug discovery which is based on thinking that most chronic diseases are caused by alteration of a single gene and thus most therapies are single gene-targeted therapies. However, extensive research has revealed that most chronic diseases are caused by multiple gene products. Although most drugs designed by man are mono-targeted therapies, however, those designed by "mother nature" and have been used for thousands of years, are "multi-targeted" therapies. In this review, we examine two agents that have been around for thousands of years, namely "guggul" from Commiphora and Boswellia. Although we are all familiar with the search engine "google," this is another type of "guggul" that has been used for centuries and being explored for its various biological activities. The current review summarizes the traditional uses, chemistry, in vitro and in vivo biological activities, molecular targets, and clinical trials performed with these agents.

Hypoxia-induced exosome secretion promotes survival of African-American and Caucasian prostate cancer cells

African American men in the United States have higher mortality due to prostate cancer (PCa) compared to other races. One reason for this disparity is the lack of in-depth understanding of the PCa biology in African Americans. For example, hypoxia in prostate tumor microenvironment is associated with adverse prognosis; still, no hypoxia-related studies have been reported in African Americans. Here, we compared African-American and Caucasian PCa cells for exosome secretion under normoxic (21% O2) and hypoxic (1% O2) conditions. All cell lines showed higher exosome secretion under hypoxia but it was clearly more prominent in African-American PCa cells. Further, under hypoxia, Rab5 (a biomarker for early endosome) was clustered in perinuclear region; and CD63 (a biomarker for exosomes and multivesicular endosomes) showed greater co-localization with actin cytoskeleton especially in African American PCa cells. Importantly, exosome biogenesis inhibitors GW4869 (10-20 µM) or DMA (10-20 µg/ml) significantly decreased cell viability and clonogenicity in PCa cells. Interestingly, we also observed higher level of lactic acid loaded in exosomes secreted under hypoxia. Overall, under chronic hypoxia, PCa cells secrete more exosomes as a survival mechanism to remove metabolic waste.

Role of Proton Pumps in Tumorigenesis

One of the differences between normal and cancer cells is lower pH of the extracellular space in tumors. Low pH in the extracellular space activates proteases and stimulates tumor invasion and metastasis. Tumor cells display higher level of the HIF1α transcription factor that promotes cell switch from mitochondrial respiration to glycolysis. The terminal product of glycolysis is lactate. Lactate formation from pyruvate is catalyzed by the specific HIF1α-dependent isoform of lactate dehydrogenase A. Because lactate accumulation is deleterious for the cell, it is actively exported by monocarboxylate transporters. Lactate is cotransported with proton, which acidifies the extracellular space. Another protein that contributes to proton concentration increase in the extracellular space is tumor-specific HIF1α-dependent carbonic anhydrase IX, which generates a proton in the reaction between carbon dioxide and water. The activity of Na+/H+ exchanger (another protein pump) is stimulated by stress factors (e.g. osmotic shock) and proliferation stimuli. This review describes the mechanisms of proton pump activation and reviews results of studies on effects of various proton pump inhibitors on tumor functioning and growth in cell culture and in vivo. The prospects of combined application of proton pump inhibitors and cytostatics in cancer therapy are discussed.

Potential therapeutic targets of Guggulsterone in cancer

Natural compounds capable of inducing apoptosis in cancer cells have always been of considerable interest as potential anti-cancer agents. Many such compounds are under screening and development with their potential evolution as a clinical drug benefiting many of the cancer patients. Guggulsterone (GS), a phytosterol isolated gum resin of the tree Commiphora mukul has been widely used in Indian traditional medicine as a remedy for various diseses. GS has been shown to possess cancer chemopreventive and therapeutic potential as established by in vitro and in vivo studies. GS has been shown to target constitutively activated survival pathways such as PI3-kinase/AKT, JAK/STAT, and NFκB signaling pathways that are involved in the regulation of growth and inflammatory responses via regulation of antiapoptotic and inflammatory genes. The current review focuses on the molecular targets of GS, cellular responses, and the animal model studies in various cancers. The mechanistic action of GS in different types of cancers also forms a part of this review. The perspective of translating this natural compound into a clinically approved drug with its pros and cons is also discussed.

Value of pH regulators in the diagnosis, prognosis and treatment of cancer

Altered metabolism, associated with acidification of the extracellular milieu, is one of the major features of cancer. As pH regulation is crucial for the maintenance of all biological functions, cancer cells rely on the activity of lactate exporters and proton transporters to regulate their intracellular pH. The major players in cancer pH regulation are proton pump ATPases, sodium-proton exchangers (NHEs), monocarboxylate transporters (MCTs), carbonic anhydrases (CAs) and anion exchangers (AEs), which have been shown to be upregulated in several human malignancies. Thanks to the activity of the proton pumps and transporters, tumours acidify their microenvironment, becoming more aggressive and resistant to therapy. Thus, targeting tumour pH may contribute to more effective anticancer strategies for controlling tumour progression and therapeutic resistance. In the present study, we review the role of the main pH regulators expressed in human cancer cells, including their diagnostic and prognostic value, as well as their usefulness as therapeutic targets.

Inhibition of monocarboxylate transporter 1 suppresses the proliferation of glioblastoma stem cells

Recent evidence suggests that a minor subset of cancer cells, termed cancer stem cells (CSCs), have self-renewal and tumorigenic potential. Therefore, the characterization of CSCs is important for developing therapeutic strategies against cancer. Cancer cells rely on anaerobic glycolysis to produce ATP even under normoxic conditions, resulting in the generation of excess acidic substances. Cancer cells maintain a weakly alkaline intracellular pH to support functions. Glioblastoma is an aggressive malignancy with a poor 5-year survival rate. Based on the hypothesis that ion transport-related molecules regulate the viability and function of CSCs, we investigated the expression of ion transport-related molecules in glioblastoma CSCs (GSCs). Quantitative RT-PCR analysis showed that monocarboxylate transporter1 (MCT1) were upregulated in GSCs, and inhibition of MCT1 decreased the viability of GSCs compared with that of non-GSCs. Our findings indicate that MCT1 is involved in the maintenance of GSCs and is a promising therapeutic target for glioblastoma.