The growth and metastasis of human hepatocellular carcinoma xenografts are inhibited by small interfering RNA targeting to the subunit ATP6L of proton pump

Microenvironmental acidosis in carcinogenesis and metastases: new strategies in prevention and therapy

Much effort is currently devoted to developing patient-specific cancer therapy based on molecular characterization of tumors. In particular, this approach seeks to identify driver mutations that can be blocked through small molecular inhibitors. However, this approach is limited by extensive intratumoral genetic heterogeneity, and, not surprisingly, even dramatic initial responses are typically of limited duration as resistant tumor clones rapidly emerge and proliferate. We propose an alternative approach based on observations that while tumor evolution produces genetic divergence, it is also associated with striking phenotypic convergence that loosely correspond to the well-known cancer “hallmarks”. These convergent properties can be described as driver phenotypes and may be more consistently and robustly expressed than genetic targets. To this purpose, it is necessary to identify strategies that are critical for cancer progression and metastases, and it is likely that these driver phenotypes will be closely related to cancer “hallmarks”. It appears that an antiacidic approach, by targetting a driver phenotype in tumors, may be thought as a future strategy against tumors in either preventing the occurrence of cancer or treating tumor patients with multiple aims, including the improvement of efficacy of existing therapies, possibly reducing their systemic side effects, and controlling tumor growth, progression, and metastasis. This may be achieved with existing molecules such as proton pump inhibitors (PPIs) and buffers such as sodium bicarbonate, citrate, or TRIS.

Spatial profiles of markers of glycolysis, mitochondria, and proton pumps in a rat glioma suggest coordinated programming for proliferation

Background

In cancer cells in vitro, the glycolytic pathway and the mitochondrial tricarboxylic acid (TCA) cycle are programmed to produce more precursor molecules, and relatively less ATP, than in differentiated cells. We address the questions of whether and where these changes occur in vivo in glioblastomas grown from C6 cells in rat brain. These gliomas show some spatial organization, notably in the upregulation of membrane proton transporters near the rim.

Results

We immunolabeled pairs of proteins (as well as DNA) on sections of rat brains containing gliomas, measured the profiles of fluorescence intensity on strips 200 µm wide and at least 3 mm long running perpendicular to the tumor rim, and expressed the intensity in the glioma relative to that outside. On averaged profiles, labeling of a marker of the glycolytic pathway, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), was, as expected, greater in the glioma. Over distances up to 2.5 mm into the glioma, expression of a marker of the TCA cycle, Tom20, a pre-protein receptor on the translocation complex of the mitochondrial outer membrane, was also upregulated. The ratio of upregulation of Tom20 to upregulation of GAPDH was, on average, slightly greater than one. Near the rim (0.4–0.8 mm), GAPDH was expressed less and there was a peak in the mean ratio of 1.16, SEM = 0.001, N = 16 pairs of profiles. An antibody to V-ATPase, which, by pumping protons into vacuoles contributes to cell growth, also indicated upregulation by about 40%. When compared directly with GAPDH, upregulation of V-ATPase was only 0.764, SD = 0.016 of GAPDH upregulation.

Conclusions

Although there was considerable variation between individual measured profiles, on average, markers of the glycolytic pathway, of mitochondria, and of cell proliferation showed coherent upregulation in C6 gliomas. There is a zone, close to the rim, where mitochondrial presence is upregulated more than the glycolytic pathway, in agreement with earlier suggestions that lactate is taken up by cells near the rim.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1191-z) contains supplementary material, which is available to authorized users.

Inhibition of vacuolar ATPase subunit in tumor cells delays tumor growth by decreasing the essential macrophage population in the tumor microenvironment

In cancer cells, vacuolar ATPase (V-ATPase), a multi-subunit enzyme, is expressed on the plasma as well as vesicular membranes and critically influences metastatic behavior. The soluble, cleaved N-terminal domain of V-ATPase a2 isoform is associated with in vitro induction of tumorigenic characteristics in macrophages. This activity led us to further investigate its in vivo role in cancer progression by inhibition of a2 isoform (a2V) in tumor cells and the concomitant effect on tumor microenvironment in the mouse 4T-1 breast cancer model. Results showed that macrophages cocultivated with a2V knockdown (sh-a2) 4T-1 cells produce lower amounts of tumorigenic factors in vitro and have reduced ability to suppress T-cell activation and proliferation compared with control 4T-1 cells. Data analysis showed a delayed mammary tumor growth in Balb/c mice inoculated with sh-a2 4T-1 cells compared with control. The purified CD11b(+) macrophages from sh-a2 tumors showed a reduced expression of mannose receptor-1 (CD206), interleukin-10, transforming growth factor-β, arginase-1, matrix metalloproteinase and vascular endothelial growth factor. Flow cytometric analysis of tumor-infiltrated macrophages showed a significantly low number of F4/80(+)CD11c(+)CD206(+) macrophages in sh-a2 tumors compared with control. In sh-a2 tumors, most of the macrophages were F4/80(+)CD11c(+) (antitumor M1 macrophages) suggesting it to be the reason behind delayed tumor growth. Additionally, tumor-infiltrating macrophages from sh-a2 tumors showed a reduced expression of CD206 compared with control whereas CD11c expression was unaffected. These findings demonstrate that in the absence of a2V in tumor cells, the resident macrophage population in the tumor microenvironment is altered which affects in vivo tumor growth. We suggest that by involving the host immune system, tumor growth can be controlled through targeting of a2V on tumor cells.

TM9SF4 is a novel V-ATPase-interacting protein that modulates tumor pH alterations associated with drug resistance and invasiveness of colon cancer cells

An inverted pH gradient across the cell membranes is a typical feature of malignant cancer cells that are characterized by extracellular acidosis and cytosol alkalization. These dysregulations are able to create a unique milieu that favors tumor progression, metastasis and chemo/immune-resistance traits of solid tumors. A key event mediating tumor cell pH alterations is an aberrant activation of ion channels and proton pumps such as (H+)-vacuolar-ATPase (V-ATPase). TM9SF4 is a poorly characterized transmembrane protein that we have recently shown to be related to cannibal behavior of metastatic melanoma cells. Here, we demonstrate that TM9SF4 represents a novel V-ATPase-associated protein involved in V-ATPase activation. We have observed in HCT116 and SW480 colon cancer cell lines that TM9SF4 interacts with the ATP6V1H subunit of the V-ATPase V1 sector. Suppression of TM9SF4 with small interfering RNAs strongly reduces assembly of V-ATPase V0/V1 sectors, thus reversing tumor pH gradient with a decrease of cytosolic pH, alkalization of intracellular vesicles and a reduction of extracellular acidity. Such effects are associated with a significant inhibition of the invasive behavior of colon cancer cells and with an increased sensitivity to the cytotoxic effects of 5-fluorouracil. Our study shows for the first time the important role of TM9SF4 in the aberrant constitutive activation of the V-ATPase, and the development of a malignant phenotype, supporting the potential use of TM9SF4 as a target for future anticancer therapies.

Expression and role of V1A subunit of V-ATPases in gastric cancer cells

BACKGROUND

Vacuolar-ATPases (V-ATPases) play an important role in maintaining a relatively neutral pHi (internal pH) and are responsible for the progression of cancer. V-ATPases contain different subunits and few studies have been conducted on subunit V1A. This study aimed to investigate the gene expression of V1A subunit of V-ATPases in gastric cancer tissues and explore its role in the progression and prognosis of gastric cancer.

METHODS

The protein expressions of the V1A subunit of V-ATPase gene in 100 normal gastric specimens and 100 gastric cancer tissues were determined by immunohistochemistry. The role of V1A subunit of V-ATPases was studied using a specific small interfering RNA (siRNA).

RESULTS

The positive expression rate of the V1A subunit of V-ATPases was 76 % in gastric cancer tissue samples, much higher than that in normal tissue samples (30 %, P < 0.05), and was correlated with histological grade (P = 0.001), lymph node metastasis (P = 0.002), TNM (P = 0.040), and vascular invasion (P = 0.010), but not with patient age, sex, depth of tumor invasion, tumor size, or histological type. The median overall survival times of 76 patients who had positive staining for tumor cell V1A subunit of V-ATPases and 24 patients who had negative staining were 31.7 and 59.2 months, respectively. When the expression of V1A subunit was knocked down using siRNA, the proliferation and invasion of gastric cancer cells in vitro were significantly inhibited.

CONCLUSIONS

V1A subunit of V-ATPases can be a prognostic indicator for poor outcome and is a therapeutic target in gastric cancer.

Hepatic stellate cells activated by acidic tumor microenvironment promote the metastasis of hepatocellular carcinoma via osteopontin

Extracellular pH of solid tumor is generally acidic due to excessive glycolysis and poor perfusion. But whether acidic tumor microenvironment influenced the stromal cells infiltrating in tumor remains unknown. As the predominant progenitor of stromal cells in liver, the number of activated hepatic stellate cells (HSCs) was found positively correlated to the acidification level in the tumor tissues of HCC patients in our study. Whereas, in vitro acidic culture condition and in vivo co-implanting xenograft model were adopted to study the response of HSCs and its influence on HCC progression. HSCs were activated under acidic culture condition depending on the phosphorylation of cellular signal-regulated kinase (ERK). Acidity-activated HSCs promoted HCC metastasis in vitro and in vivo. Osteopontin (OPN) excretion from HSCs was increased under acidic condition and proved to promote the migration of HCC cells. Furthermore, the expression level of OPN was significantly associated with myofibroblasts and the combination of α-SMA with OPN was a powerful predictor for poor prognosis of HCC patients. Activation of HSCs in acidic tumor microenvironment represents a novel mechanism for HCC metastasis and provides a potential therapeutic strategy for HCC.

Lansoprazole induces sensitivity to suboptimal doses of paclitaxel in human melanoma

Tumor acidity is now considered an important determinant of drug-resistance and tumor progression, and anti-acidic approaches, such as Proton Pump inhibitors (PPIs), have demonstrated promising antitumor and chemo-sensitizing efficacy. The main purpose of the present study was to evaluate the possible PPI-induced sensitization of human melanoma cells to Paclitaxel (PTX). Our results show that PTX and the PPI Lansoprazole (LAN) combination was extremely efficient against metastatic melanoma cells, as compared to the single treatments, both in vitro and in vivo. We also showed that acidity plays an important role on the anti-tumor activity of these drugs, being detrimental for PTX activity, while crucial for the synergistic effect of PTX following pretreatment with LAN, due to its nature of pro-drug needing protonation for a full activation. We obtained straightforward results in a human melanoma xenograft model combining well tolerated LAN doses with suboptimal and poorly toxic doses of PTX. With this study we provide a clear evidence that the PPI LAN may be included in new combined therapy of human melanoma together with low doses of PTX.

Proton channels and exchangers in cancer

Although cancer is characterized by an intratumoral genetic heterogeneity, a totally deranged pH control is a common feature of most cancer histotypes. Major determinants of aberrant pH gradient in cancer are proton exchangers and transporters, including V-ATPase, Na+/H+ exchanger (NHE), monocarboxylate transporters (MCTs) and carbonic anhydrases (CAs). Thanks to the activity of these proton transporters and exchangers, cancer becomes isolated and/or protected not only from the body reaction against the growing tumor, but also from the vast majority of drugs that when protonated into the acidic tumor microenvironment do not enter into cancer cells. Proton transporters and exchangers represent a key feature tumor cells use to survive in the very hostile microenvironmental conditions that they create and maintain. Detoxifying mechanisms may thus represent both a key survival option and a selection outcome for cells that behave as unicellular microorganisms rather than belonging to an organ, compartment or body. It is, in fact, typical of malignant tumors that, after a clinically measurable yet transient initial response to a therapy, resistant tumor clones emerge and proliferate, thus bursting a more malignant behavior and rapid tumor progression. This review critically presents the background of a novel and efficient approach that aims to fight cancer through blocking or inhibiting well characterized proton exchangers and transporters active in human cancer cells. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Silencing of LASS2/TMSG1 enhances invasion and metastasis capacity of prostate cancer cell

Homo sapiens longevity assurance homolog 2 of yeast LAG1 (LASS2), also known as tumor metastasis suppressor gene 1 (TMSG1), was firstly cloned by our laboratory in 1999. However, its antitumor molecular mechanisms are still unclear. LASS2/TMSG-1 could directly interact with the C subunit of Vacuolar H(+) ATPase (V-ATPase), which suggested that LASS2/TMSG1 might inhibit the invasion and metastasis through regulating the function of V-ATPase. In this study, we explored the effect of small hairpin RNA (shRNA) targeting LASS2/TMSG1 on the invasion and metastasis of human prostate carcinoma cell line PC-3M-2B4 with low metastatic potential and its functional interaction with V-ATPase. Silencing of LASS2/TMSG1 gene in PC-3M-2B4 cells increased V-ATPase activity, extracellular hydrogen ion concentration and in turn the activation of secreted MMP-2 and MMP-9, which coincided with enhancing cell proliferation, cell survival, and cell invasion in vitro, as well as acceleration of prostate cancer (PCA) growth and lymph node metastases in vivo. Thus we concluded that silencing of LASS2/TMSG1 enhances invasion and metastasis of PCA cell through increase of V-ATPase activity. These results establish LASS2/TMSG1 as a promising therapeutic target for advanced PCA.

Proton pump inhibitors (PPIs) impact on tumour cell survival, metastatic potential and chemotherapy resistance, and affect expression of resistance-relevant miRNAs in esophageal cancer

Background

Neoadjuvant treatment plays a crucial role in the therapy of advanced esophageal cancer. However, response to radiochemotherapy varies widely. Proton pump inhibitors (PPIs) have been demonstrated to impact on chemotherapy in a variety of other cancers. We analyzed the impact of PPI treatment on esophageal cancer cell lines, and investigated mechanisms that mediate the effect of PPI treatment in this tumour.

Methods

We investigated the effect of esomeprazole treatment on cancer cell survival, adhesion, migration and chemotherapy in human adeno-(OE19) and squamous-cell-carcinoma (KYSE410) cell lines. Furthermore, we investigated the effect of PPI treatment on intra-/extracellular pH and on expression of resistance-relevant miRNAs.

Results

Esomeprazole significantly inhibited tumour cell survival (in a dose-dependent manner), adhesion and migration in both tumour subtypes. Furthermore, esomeprazole augmented the cytotoxic effect of cisplatin and 5-FU in both tumour subtypes. Surprisingly, PPI treatment led to a significant increase of intracellular pH and a decrease of the extracellular pH. Finally, we found esomeprazole affected expression of resistance-relevant miRNAs. Specifically, miR-141 and miR-200b were upregulated, whereas miR-376a was downregulated after PPI treatment in both tumour types.

Conclusion

Our study demonstrates for the first time that PPIs impact on tumour cell survival, metastatic potential and sensitivity towards chemotherapy in esophageal cancer cell lines. Furthermore, we observed that in this tumour entity, PPIs do not lead to intracellular acidification, but affect the expression of resistance-relevant miRNAs.

Iejimalides Show Anti-Osteoclast ActivityviaV-ATPase Inhibition

Iejimalides (IEJLs), 24-membered macrolides, are potent antitumor compounds, but their molecular targets remain to be revealed. In the course of screening, we identified IEJLs as potent osteoclast inhibitors. Since it is known that osteoclasts are sensitive to vacuolar H(+)-ATPase (V-ATPase) inhibitor, we investigated the effect of IEJLs on V-ATPases. IEJLs inhibited the V-ATPases of both mammalian and yeast cells in situ, and of yeast V-ATPases in vitro. A bafilomycin-resistant yeast mutant conferred IEJL resistance, suggesting that IEJLs bind a site similar to the bafilomycins/concanamycins-binding site. These results indicate that IEJLs are novel V-ATPase inhibitors, and that antitumor and antiosteporotic activities are exerted via V-ATPase inhibition.

Lansoprazole induces apoptosis of breast cancer cells through inhibition of intracellular proton extrusion

The increased glycolysis and proton secretion in tumors is proposed to contribute to the proliferation and invasion of cancer cells during the process of tumorigenesis and metastasis. Here, treatment of human breast cancer cells with proton pump inhibitor (PPI) lansoprazole (LPZ) induces cell apoptosis in a dose-dependent manner. In the implantation of the MDA-MB-231 xenografts in nude mice, administration of LPZ significantly inhibits tumorigenesis and induces large-scale apopotosis of tumor cells. LPZ markedly inhibits intracellular proton extrusion, induces an increase in intracellular ATP level, lysosomal alkalinization and accumulation of reactive oxygen species (ROS) in breast cancer cells. The ROS scavenger N-acetyl-l-cysteine (NAC) and diphenyleneiodonium (DPI), a specific pharmacological inhibitor of NADPH oxidases (NOX), significantly abolish LPZ-induced ROS accumulation in breast cancer cells. Our results suggested that LPZ may be used as a new therapeutic drug for breast tumor.

Overexpression of EMMPRIN isoform 2 is associated with head and neck cancer metastasis

Extracellular matrix metalloproteinase inducer (EMMPRIN), a plasma membrane protein of the immunoglobulin (Ig) superfamily, has been reported to promote cancer cell invasion and metastasis in several human malignancies. However, the roles of the different EMMPRIN isoforms and their associated mechanisms in head and neck cancer progression remain unknown. Using quantitative real-time PCR, we found that EMMPRIN isoform 2 (EMMPRIN-2) was the only isoform that was overexpressed in both head and neck cancer tissues and cell lines and that it was associated with head and neck cancer metastasis. To determine the effects of EMMPRIN-2 on head and neck cancer progression, we transfected head and neck cancer cells with an EMMPRIN-2 expression vector and EMMPRIN-2 siRNA to exogenously modulate EMMPRIN-2 expression and examined the functional importance of EMMPRIN-2 in head and neck cancer invasion and metastasis. We found that EMMPRIN-2 promoted head and neck cancer cell invasion, migration, and adhesion in vitro and increased lung metastasis in vivo. Mechanistic studies revealed that EMMPRIN-2 overexpression promoted the secretion of extracellular signaling molecules, including matrix metalloproteinases-2(MMP-2), urokinase-type plasminogen activator(uPA) and Cathepsin B, in head and neck cancer cells. While MMP-2 and uPA have been demonstrated to be important mediators of EMMPRIN signaling, the role of Cathepsin B in EMMPRIN-mediated molecular cascades and tumorigenesis has not been established. We found that EMMPRIN-2 overexpression and Cathepsin B down-regulation significantly inhibited the invasion, migration and adhesion of Tca8133 cells, suggesting that Cathepsin B is required for EMMPRIN-2 enhanced cell migration and invasion in head and neck cancer. The results of our study demonstrate the important role of EMMPRIN-2 in head and neck cancer progression for the first time and reveal that increased extracellular secretion of Cathepsin B may be a novel mechanism underlying EMMPRIN-2 enhanced tumor progression in head and neck cancer.

Nanosecond pulsed electric field (nsPEF) treatment for hepatocellular carcinoma: a novel locoregional ablation decreasing lung metastasis

Hepatocellular carcinoma (HCC) is a highly aggressive malignancy. Nanosecond pulsed electric field (nsPEF) is a new technology destroying tumor cells with a non-thermal high voltage electric field using ultra-short pulses. The study's aim was to evaluate the ablation efficacy of nsPEFs with human HCC cell lines and a highly metastatic potential HCC xenograft model on BALB/c nude mice. The in vivo study showed nsPEFs induced HCC cell death in a dose dependent manner. On the high metastatic hepatocellular carcinoma cell line (HCCLM3) xenograft mice model, tumor growth was inhibited significantly in nsPEF-treated- groups (single dose and multi-fractionated dose). Besides a local effect, the nsPEF treatment reduced pulmonary metastases. The nsPEFs also enhanced HCC cell phagocytosis by human macrophage cell (THP1) in vitro. The nsPEF is efficient in controlling HCC progression and reducing its metastasis. NsPEF treatment may elicit a host immune response against tumor cells. This study suggests nsPEF therapy could be used as a potential locoregional therapy for hepatocellular carcinoma.

Multitargeting and antimetastatic potentials of silibinin in human HepG-2 and PLC/PRF/5 hepatoma cells

Hepatocellular carcinoma (HCC) is the most common sort of primary liver malignancy with poor prognosis. This study aimed at examining the effects of silibinin (a putative antimetastatic agent) on some transcriptional markers mechanistically related to HCC recurrence and metastasis in HepG-2 [hepatitis B virus (HBV)-negative and P53 intact) and PLC/PRF/5 (HBV-positive and P53 mutated) cells. The expression of 27 genes in response to silibinin was evaluated by real-time RT-PCR. The MMP gelatinolytic assay and microculture tetrazolium test (MTT) were tested. Silibinin was capable of suppressing the transcriptional levels of ANGPT2, ATP6L, CAP2, CCR6, CCR7, CLDN-10, cortactin, CXCR4, GLI2, HK2, ID1, KIAA0101, mortalin, PAK1, RHOA, SPINK1, and STMN1 as well as the enzymatic activity of MMP-2 but promoted the transcripts of CREB3L3, DDX3X, and PROX1 in both cells. Some significant differences between the cells in response to silibinin were detected that might be related to the differences of the cells in terms of HBV infection and/or P53 mutation, suggesting the possible influence of silibinin on HCC through biological functions of these 2 prognostic factors. In conclusion, our findings suggest that silibinin could potentially function as a multitargeting antimetastatic agent and might provide new insights for HCC therapy particularly for HBV-related and/or P53-mutated HCCs.

Enhancement of DEN-induced liver tumourigenesis in hepatocyte-specific Lass2-knockout mice coincident with upregulation of the TGF-β1-Smad4-PAI-1 axis

Longevity assurance homolog 2 of yeast LAG1 (Lass2) gene is capable of suppressing the proliferation and metastasis of several types of tumours including liver cancer. In the present study, hepatocyte-specific Lass2-knockout (Lass2 KO) and wild-type (WT) mice were exposed to the carcinogen, diethylnitrosamine (DEN), to induced liver tumours. At week 23 following DEN injection, tumours were produced in 100% of the Lass2 KO mice and 21.4% of the WT mice. At week 40, 100% of the Lass2 KO mice and 78.6% of the WT mice developed tumours, with no distinct significant difference in tumour occurrences between the two genotypes; yet, tumours in the Lass2 KO mouse livers were more numerous and larger in size. Hepatocellular carcinoma (HCC) was confirmed by α-fetoprotein (AFP). PCNA and EdU assays indicated more active proliferation whereas TUNEL assay revealed decreased apoptosis in Lass2 KO livers, when compared with the WT control. The expression of plasminogen activator inhibitor type-1 (PAI-1), a tumour-promoting gene, in the liver tissues of the 2 genotypes was detected using qPCR and western blotting, showing that PAI-1 levels were significantly elevated in Lass2 KO livers at week 40 following DEN introduction. Moreover, the expression of PAI-1-related TGF-β1, Smad-4 and -7 was detected, displaying an elevation in TGF-β1 and Smad-4 (not including Smad-7) in the Lass2 KO livers. Our data demonstrates that i) Lass2 is a protective gene against DEN-induced liver tumourigenesis; and ii) upregulation of the TGF-β1-Smad4-PAI-1 axis may contribute to the vulnerability of Lass2-knockout mice to DEN.

Regulation of endothelial signaling and migration by v-ATPase

The vacuolar ATPase (v-ATPase) is a proton pump, able to acidify intracellular compartments and the pericellular space. v-ATPase has extensively been studied in various functional contexts, e.g., migration of tumor cells, and inhibition of v-ATPase has been proven as intriguing novel therapeutic concept. Since the role of v-ATPase in endothelial cell migration and angiogenesis has scarcely been investigated, we examined the consequences of pharmacological inhibition of v-ATPase (by concanamycin) on proliferation, migration, VEGF-receptor 2 (VEGFR2) trafficking and signaling, as well as Notch-mediated transcription in endothelial cells [human microvascular endothelial cells (HMEC-1) and human umbilical vein endothelial cells (HUVEC)] Treatment of the cells with 3 or 10 nM of the v-ATPase inhibitor concanamycin for 48 h or longer inhibited proliferation and arrested cell cycle in the G2/M phase in HMEC-1, while a G1 phase arrest occurred in HUVEC. Already after 24 h these concentrations reduced migration (scratch assay, chemotactic gradient). Activation of the small GTPase Rac1 in freshly adherent cells was reduced by concanamycin. Downstream signaling of the VEGFR2 (phosphorylation of ERK1/2 and AKT), as well as autophosphorylation of VEGFR2 were inhibited. VEGFR2 on the cell surface was reduced, and sequestered in a lysosomal compartment. In addition, concanamycin blocked transcription of the Notch target genes Hey1 and Hey2 after stimulation with DLL4. Since the impaired signaling pathways (Rac-1, VEGFR2, Notch) all depend on vesicular recycling circuits, we conclude that the disturbance of these is the main mode of action of v-ATPase inhibition in endothelial cells, offering an attractive multi-factorial anti-angiogenic approach.

Chemoresistance to concanamycin A1 in human oral squamous cell carcinoma is attenuated by an HDAC inhibitor partly via suppression of Bcl-2 expression

V-ATPase is involved in the acidification of the microenvironment around/in solid tumors, such as oral squamous cell carcinoma (OSCC). V-ATPase is thought to induce tumor invasion and multi-drug resistance in several malignant tumors, and it also contributes to maintaining the intracellular pH under an acidic microenvironment by inducing proton extrusion into the extracellular medium. However, there is little information regarding the effects of V-ATPase inhibitors on OSCCs. In this study, the effects of a V-ATPase inhibitor, concanamycin A1 (CMA), on the proliferation and apoptosis of OSCC were investigated in vitro. We used four OSCC cell lines, MISK81-5, SAS, HSC-4 and SQUU-B. Acridine orange staining revealed that the red fluorescence was reduced in all of the low concentration CMA-treated OSCC cells, indicating that the acidification of vesicular organelles in the OSCCs was prevented by the treatment with low-concentration of CMA. CMA treatment induced apoptosis in MISK81-5, SAS and HSC-4 cells, but not in SQUU-B cells. The p-p38 expression was not altered in CMA-treated SQUU-B cells, but their levels were increased in the other cells. The Bax/Bcl-2 ratio in CMA-treated SQUU-B cells was dramatically decreased in comparison with that in the other cell lines treated with CMA. However, when the SQUU-B cells were treated with CMA and a histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), the SQUU-B cells became more susceptible to the CMA-induced apoptosis. SAHA treatment led to a significantly decrease in the Bcl-2 expression in CMA-treated SQUU-B cells, resulting in a dramatically increased Bax/Bcl-2 ratio in comparison with that observed in the SQUU-B cells treated with CMA alone. These findings suggest that CMA could have an anti-tumor effect on OSCCs. In addition, combination of CMA with other agents, such as SAHA, could help improve the pro-apoptotic effects of CMA even in CMA-resistant OSCC cells.

V-ATPase inhibition by archazolid leads to lysosomal dysfunction resulting in impaired cathepsin B activation in vivo

The myxobacterial agent archazolid inhibits the vacuolar proton pump V-ATPase. V-ATPases are ubiquitously expressed ATP-dependent proton pumps, which are known to regulate the pH in endomembrane systems and thus play a crucial role in endo- and exocytotic processes of the cell. As cancer cells depend on a highly active secretion of proteolytic proteins in order to invade tissue and form metastases, inhibition of V-ATPase is proposed to affect the secretion profile of cancer cells and thus potentially abrogate their metastatic properties. Archazolid is a novel V-ATPase inhibitor. Here, we show that the secretion pattern of archazolid treated cancer cells includes various prometastatic lysosomal proteins like cathepsin A, B, C, D and Z. In particular, archazolid induced the secretion of the proforms of cathepsin B and D. Archazolid treatment abrogates the cathepsin B maturation process leading to reduced intracellular mature cathepsin B protein abundance and finally decreased cathepsin B activity, by inhibiting mannose-6-phoshate receptor-dependent trafficking. Importantly, in vivo reduced cathepsin B protein as well as a decreased proteolytic cathepsin B activity was detected in tumor tissue of archazolid-treated mice. Our results show that inhibition of V-ATPase by archazolid reduces the activity of prometastatic proteases like cathepsin B in vitro and in vivo.

Role of ion channels in the development and progression of hepatocellular carcinoma

Ion channels are pore-forming membrane proteins which play regulatory roles in a variety of biological processes. Their abnormality in expression or activity has a close relationship with the proliferation and apoptosis of cancer cells. This article will describe the role of four ion channels in the development and progression of hepatocellular carcinoma. Our review suggests that ion channels might be a new therapeutic target for hepatocellular carcinoma.

The influence of pH and hypoxia on tumor metastasis

Rapid malignant proliferation, prior to effective tumor neoangiogenesis, creates a microenvironment around solid cancers, which is predominantly hypoxic and characterized by a high interstitial fluid pressure. Presumably as an adaptive response, tumor cells favor metabolic activity with apparently inefficient energy output, and production of intermediates that promote cellular replication, preferentially through anaerobic glycolysis, a phenomenon that persists even in re-established normoxic conditions (anomalously referred to as 'aerobic glycolysis'). Extrusion of the consequently excessive accumulation of lactate and protons decreases extracellular pH, leading to a microenvironment considered conducive to promotion of tumor motility, invasion and metastasis, and one that will invariably influence response to drug treatment. This review will critically assess the evidence forming the basis of current understanding of the precise pH conditions in the extracellular tumor matrix, its regulation by cancer cells and relationship with hypoxia, its relevance to malignant progression and its exploitation for therapeutic advantage.

Silencing of atp6v1c1 prevents breast cancer growth and bone metastasis

Previous studies have shown that Atp6v1c1, a regulator of the assembly of the V0 and V1 domains of the V-ATPase complex, is up-regulated in metastatic oral tumors. Despite these studies, the function of Atp6v1c1 in tumor growth and metastasis is still unknown. Atp6v1c1's expression in metastatic oral squamous cell carcinoma indicates that Atp6v1c1 has an important function in cancer growth and metastasis. We hypothesized that elevated expression of Atp6v1c1 is essential to cancer growth and metastasis and that Atp6v1c1 promotes cancer growth and metastasis through activation of V-ATPase activity. To test this hypothesis, a Lentivirus-mediated RNAi knockdown approach was used to study the function of Atp6v1c1 in mouse 4T1 mammary tumor cell proliferation and migration in vitro and cancer growth and metastasis in vivo. Our data revealed that silencing of Atp6v1c1 in 4T1 cancer cells inhibited lysosomal acidification and severely impaired 4T1 cell growth, migration, and invasion through Matrigel in vitro. We also show that Atp6v1c1 knockdown with Lenti-c1s3, a lentivirus targeting Atp6v1c1 for shRNA mediated knockdown, can significantly inhibit 4T1 xenograft tumor growth, metastasis, and osteolytic lesions in vivo. Our study demonstrates that Atp6v1c1 may promote breast cancer growth and bone metastasis through regulation of lysosomal V-ATPase activity, indicating that Atp6v1c1 may be a viable target for breast cancer therapy and silencing of Atp6v1c1 may be an innovative therapeutic approach for the treatment and prevention of breast cancer growth and metastasis.

Human voltage-gated proton channel hv1: a new potential biomarker for diagnosis and prognosis of colorectal cancer

Solid tumors exist in a hypoxic microenvironment, and possess high-glycolytic metabolites. To avoid the acidosis, tumor cells must exhibit a dynamic cytosolic pH regulation mechanism(s). The voltage-gated proton channel Hv1 mediates NADPH oxidase function by compensating cellular loss of electrons with protons. Here, we showed for the first time, that Hv1 expression is increased in colorectal tumor tissues and cell lines, associated with poor prognosis. Immunohistochemistry showed that Hv1 is strongly expressed in adenocarcinomas but not or lowly expressed in normal colorectal or hyperplastic polyps. Hv1 expression in colorectal cancer is significantly associated with the tumor size, tumor classification, lymph node status, clinical stage and p53 status. High Hv1 expression is associated significantly with shorter overall and recurrence-free survival. Furthermore, real-time RT-PCR and immunocytochemistry showed that Hv1 is highly expressed in colorectal cancer cell lines, SW620, HT29, LS174T and Colo205, but not in SW480. Inhibitions of Hv1 expression and activity in the highly metastatic SW620 cells by small interfering RNA (siRNA) and Zn²⁺ respectively, markedly decrease the cell invasion and migration, restraint proton extrusion and the intracellular pH recovery. Our results suggest that Hv1 may be used as a potential biomarker for diagnosis and prognosis of colorectal carcinoma, and a potential target for anticancer drugs in colorectal cancer therapy.

A novel tumor metastasis suppressor gene LASS2/TMSG1 interacts with vacuolar ATPase through its homeodomain

LASS2/TMSG1 was a novel tumor metastasis suppressor gene, which was first cloned by our laboratory from non-metastatic and metastatic cancer cell variants of human prostate carcinoma PC-3M using mRNA differential display in 1999. LASS2/TMSG1 could interact with the C subunit of vacuolar ATPase (V-ATPase, ATP6V0C) and regulate V-ATPase activity. In an attempt to provide molecular mechanism of the interaction between LASS2/TMSG1 and V-ATPase, we constructed four variant transfectants containing different functional domain of LASS2/TMSG1 and stably transfected the variants to human prostate cancer cell line PC-3M-1E8 cell with high metastatic potential. Results showed that there were no obvious differences of V-ATPase expression among different transfected cells and the control. However, V-ATPase activity and intracellular pH was significantly higher in the variant transfectants with Homeodomain of LASS2/TMSG1 than that in the control using the pH-dependent fluorescence probe BECEF/AM. Immunoprecipitation, immunofluorescence and immuno-electron microscope alone or in combination demonstrated the direct interaction of Homeodomain of LASS2/TMSG1 and ATP6V0C. Loss of Homeodomain markedly enhanced the proliferation ability but weakened the apoptotic effect of LASS2/TMSG1 in PC-3M-1E8 cells. These lines of results for the first time contribute to the conclusion that LASS2/TMSG1 could regulate V-ATPase activity and intracellular pH through the direct interaction of its Homeodomain and the C subunit of V-ATPase. Their interaction could play important roles in the apoptosis of tumor cells.

Effect of pantoprazole on human gastric adenocarcinoma SGC7901 cells through regulation of phospho‑LRP6 expression in Wnt/β-catenin signaling

Recent studies have found that an acidic tumor microenvironment is the key to managing cancer progression and metastasis. Our previous study found that proton pump inhibitors (PPIs) inhibit the expression of vacuolar-ATPases (V-ATPases) and reverse the transmembrane pH gradient. The present study was conducted to explore the effect of pantoprazole on gastric adenocarcinoma through the regulation of Wnt/β-catenin signaling. We used SGC7901 human gastric cancer cells as an in vitro model to study the effect of pantoprazole. The antiproliferative, pro-apoptotic and anti‑invasive effects of pantoprazole were examined. The effects of pantoprazole on the expression of the Wnt/β-catenin signaling pathway were also studied by western blotting. Our study found that pantoprazole inhibited the proliferation and induced the apoptosis of SGC7901 human gastric cancer cells. The expression of V-ATPases was decreased following treatment with pantoprazole. Further study found that pantoprazole treatment caused a decrease in phospho-LRP6, but not in LRP6. β-catenin in Wnt/β-catenin signaling and its target genes c-Myc and cyclin D1 were also decreased upon the inhibition of V-ATPases. Therefore, pantoprazole could be characterized as a V-ATPase inhibitor for treating gastric cancer by inhibiting the phosphorylation of LRP6 in Wnt/β-catenin signaling.

V-ATPase is a candidate therapeutic target for Ewing sarcoma

Suppression of oxidative phosphorylation combined with enhanced aerobic glycolysis and the resulting increased generation of protons are common features of several types of cancer. An efficient mechanism to escape cell death resulting from intracellular acidification is proton pump activation. In Ewing sarcoma (ES), although the tumor-associated chimeric gene EWS-FLI1 is known to induce the accumulation of hypoxia-induced transcription factor HIF-1α, derangements in metabolic pathways have been neglected so far as candidate pathogenetic mechanisms. In this paper, we observed that ES cells simultaneously activate mitochondrial respiration and high levels of glycolysis. Moreover, although the most effective detoxification mechanism of proton intracellular storage is lysosomal compartmentalization, ES cells show a poorly represented lysosomal compartment, but a high sensitivity to the anti-lysosomal agent bafilomycin A1, targeting the V-ATPase proton pump. We therefore investigated the role of V-ATPase in the acidification activity of ES cells. ES cells with the highest GAPDH and V-ATPase expression also showed the highest acidification rate. Moreover, the localization of V-ATPase was both on the vacuolar and the plasma membrane of all ES cell lines. The acidic extracellular pH that we reproduced in vitro promoted high invasion ability and clonogenic efficiency. Finally, targeting V-ATPase with siRNA and omeprazole treatments, we obtained a significant selective reduction of tumor cell number. In summary, glycolytic activity and activation of V-ATPase are crucial mechanisms of survival of ES cells and can be considered as promising selective targets for the treatment of this tumor.

Vacuolar H+ ATPase expression and activity is required for Rab27B-dependent invasive growth and metastasis of breast cancer

The secretory Rab27B small GTPase promotes invasive growth and metastasis in estrogen receptor (ER) α-positive breast cancer cells by orchestrating the peripheral targeting of vesicles secreting proinvasive growth regulators. Increased Rab27B expression is associated with poor prognosis in breast cancer patients. The molecular mechanisms of peripheral Rab27B secretory vesicle distribution are poorly understood. Mass spectrometry analysis on green fluorescent protein (GFP)-Rab27B vesicles prepared from GFP-Rab27B transfected MCF-7 human breast cancer cells detected eight subunits of the vacuolar H(+)-ATPase (V-ATPase) and the presence of V0a1 and V0d1 subunits was confirmed by Western blot analysis. Reversible inhibition of V-ATPase activity by bafilomycin A1 or transient silencing of V0a1 or V0d1 subunits demonstrated that V-ATPase controls peripheral localization and size of Rab27B vesicles. V-ATPase expression and activity further controls Rab27B-induced collagen type I invasion, cell-cycle progression and invasive growth in the chorioallantoic membrane assay. In agreement, Rab27B-dependent extracellular heat shock protein90α release and matrix metalloprotease-2 activation is markedly reduced by bafilomycin A1 and transient silencing of V0a1 and V0d1 subunits. Poor prognosis ERα-positive primary breast tumors expressing high levels of Rab27B also expressed multiple V-ATPase subunits and showed a strong cytoplasmic and peripheral V-ATPase V1E expression. In conclusion, inhibiting V-ATPase activity by interfering agents and drugs might be an effective strategy for blocking Rab27B-dependent proinvasive secretory vesicle trafficking in ERα-positive breast cancer patients.

Elevated expression of the V-ATPase C subunit triggers JNK-dependent cell invasion and overgrowth in a Drosophila epithelium

The C subunit of the vacuolar H⁺-ATPase or V-ATPase regulates the activity and assembly of the proton pump at cellular membranes. It has been shown to be strongly upregulated in oral squamous cell carcinoma, a highly metastatic epithelial cancer. In addition, increased V-ATPase activity appears to correlate with invasiveness of cancer cells, but the underlying mechanism is largely unknown. Using the Drosophila wing imaginal epithelium as an in vivo model system, we demonstrate that overexpression of Vha44, the Drosophila orthologue of the C subunit, causes a tumor-like tissue transformation in cells of the wing epithelium. Overexpressing cells are excluded from the epithelium and acquire invasive properties while displaying high apoptotic rates. Blocking apoptosis in these cells unmasks a strong proliferation stimulus, leading to overgrowth. Furthermore, we show that excess Vha44 greatly increases acidification of endocytic compartments and interferes with endosomal trafficking. As a result, cargoes such as GFP-Lamp1 and Notch accumulate in highly acidified enlarged endolysosomal compartments. Consistent with previous reports on the endocytic activation of Eiger/JNK signaling, we find that V-ATPase stimulation by Vha44 causes JNK signaling activation whereas downmodulation of JNK signaling rescues the invasive phenotypes. In summary, our in vivo-findings demonstrate that increased levels of V-ATPase C subunit induce a Eiger/JNK-dependent cell transformation within an epithelial organ that recapitulates early carcinoma stages.

Inhibitors of vacuolar ATPase proton pumps inhibit human prostate cancer cell invasion and prostate-specific antigen expression and secretion

Vacuolar ATPases (V-ATPases) comprise specialized and ubiquitously distributed pumps that acidify intracellular compartments and energize membranes. To gain new insights into the roles of V-ATPases in prostate cancer (PCa), we studied the effects of inhibiting V-ATPase pumps in androgen-dependent (LNCaP) and androgen-independent (C4-2B) cells of a human PCa progression model. Treatment with nanomolar concentrations of the V-ATPase inhibitors bafilomycin A or concanamycin A reduced the in vitro invasion in both cell types by 80%, regardless that V-ATPase was prominent at the plasma membrane of C4-2B cells and only traces were detected in the low-metastatic LNCaP parental cells. In both cell types, intracellular V-ATPase was excessive and co-localized with prostate-specific antigen (PSA) in the Golgi compartment. V-ATPase inhibitors reversibly excluded PSA from the Golgi and led to the accumulation of largely dispersed PSA-loaded vesicles of lysosomal composition. Inhibition of acridine orange staining and transferrin receptor recycling suggested defective endosomal and lysosomal acidification. The inhibitors, additionally, interfered with the AR-PSA axis under conditions that reduced invasion. Bafilomycin A significantly reduced steady-state and R1881-induced PSA mRNA expression and secretion in the LNCaP cells which are androgen-dependent, but not in the C4-2B cells which are androgen ablation-resistant. In the C4-2B cells, an increased susceptibility to V-ATPase inhibitors was detected after longer treatments, as proliferation was reduced and reversibility of bafilomycin-induced responses impaired. These findings make V-ATPases attractive targets against early and advanced PCa tumors.

Estimating the rotation rate in the vacuolar proton-ATPase in native yeast vacuolar membranes

The rate of rotation of the rotor in the yeast vacuolar proton-ATPase (V-ATPase), relative to the stator or steady parts of the enzyme, is estimated in native vacuolar membrane vesicles from Saccharomyces cerevisiae under standardised conditions. Membrane vesicles are formed spontaneously after exposing purified yeast vacuoles to osmotic shock. The fraction of total ATPase activity originating from the V-ATPase is determined by using the potent and specific inhibitor of the enzyme, concanamycin A. Inorganic phosphate liberated from ATP in the vacuolar membrane vesicle system, during ten min of ATPase activity at 20 °C, is assayed spectrophotometrically for different concanamycin A concentrations. A fit of the quadratic binding equation, assuming a single concanamycin A binding site on a monomeric V-ATPase (our data are incompatible with models assuming multiple binding sites), to the inhibitor titration curve determines the concentration of the enzyme. Combining this with the known ATP/rotation stoichiometry of the V-ATPase and the assayed concentration of inorganic phosphate liberated by the V-ATPase, leads to an average rate of ~10 Hz for full 360° rotation (and a range of 6-32 Hz, considering the ± standard deviation of the enzyme concentration), which, from the time-dependence of the activity, extrapolates to ~14 Hz (8-48 Hz) at the beginning of the reaction. These are lower-limit estimates. To our knowledge, this is the first report of the rotation rate in a V-ATPase that is not subjected to genetic or chemical modification and is not fixed to a solid support; instead it is functioning in its native membrane environment.

Lysosomotropic properties of weakly basic anticancer agents promote cancer cell selectivity in vitro

Drug distribution in cells is a fundamentally important, yet often overlooked, variable in drug efficacy. Many weakly basic anticancer agents accumulate extensively in the acidic lysosomes of normal cells through ion trapping. Lysosomal trapping reduces the activity of anticancer drugs, since anticancer drug targets are often localized in the cell cytosol or nucleus. Some cancer cells have defective acidification of lysosomes, which causes a redistribution of trapped drugs from the lysosomes to the cytosol. We have previously established that such differences in drug localization between normal and cancer cells can contribute to the apparent selectivity of weakly basic drugs to cancer cells in vitro. In this work, we tested whether this intracellular distribution-based drug selectivity could be optimized based on the acid dissociation constant (pKa) of the drug, which is one of the determinants of lysosomal sequestration capacity. We synthesized seven weakly basic structural analogs of the Hsp90 inhibitor geldanamycin (GDA) with pKa values ranging from 5 to 12. The selectivity of each analog was expressed by taking ratios of anti-proliferative IC₅₀ values of the inhibitors in normal fibroblasts to the IC₅₀ values in human leukemic HL-60 cells. Similar selectivity assessments were performed in a pair of cancer cell lines that differed in lysosomal pH as a result of siRNA-mediated alteration of vacuolar proton ATPase subunit expression. Optimal selectivity was observed for analogs with pKa values near 8. Similar trends were observed with commercial anticancer agents with varying weakly basic pKa values. These evaluations advance our understanding of how weakly basic properties can be optimized to achieve maximum anticancer drug selectivity towards cancer cells with defective lysosomal acidification in vitro. Additional in vivo studies are needed to examine the utility of this approach for enhancing selectivity.

Silencing of a novel tumor metastasis suppressor gene LASS2/TMSG1 promotes invasion of prostate cancer cell in vitro through increase of vacuolar ATPase activity

Homo sapiens longevity assurance homologue 2 of yeast LAG1 (LASS2), also known as tumor metastasis suppressor gene 1 (TMSG1), is a newly found tumor metastasis suppressor gene in 1999. Preliminary studies showed that it not only suppressed tumor growth but also closely related to tumor metastasis, however, its molecular mechanisms is still unclear. There have been reported that protein encoded by LASS2/TMSG-1 could directly interact with the C subunit of Vacuolar ATPase (V-ATPase), which suggested that LASS2/TMSG1 might inhibit the invasion and metastasis through regulating the function of V-ATPase. Thus, in this study, we explored the effect of small interference RNA (siRNA) targeting LASS2/TMSG1 on the invasion of human prostate carcinoma cell line PC-3M-2B4 and its molecular mechanisms associated with the V-ATPase. Real-time fluorogentic quantitative PCR (RFQ-PCR) and Western blot revealed dramatic reduction of 84.5% and 60% in the levels of LASS2/TMSG1 mRNA and protein after transfection of siRNA in PC-3M-2B4 cells. The V-ATPase activity and extracellular hydrogen ion concentration were significantly increased in 2B4 cells transfected with the LASS2/TMSG1-siRNA compared with the controls. The activity of secreted MMP-2 was up-regulated in LASS2/TMSG1-siRNA treated cells compared with the controls; and the capacity for migration and invasion in LASS2/TMSG1-siRNA treated cells was significantly higher than the controls. Thus, we concluded that silencing of LASS2/TMSG1 may promote invasion of prostate cancer cell in vitro through increase of V-ATPase activity and extracellular hydrogen ion concentration and in turn the activation of secreted MMP-2.

The V-ATPase-inhibitor archazolid abrogates tumor metastasis via inhibition of endocytic activation of the Rho-GTPase Rac1

The abundance of the multimeric vacuolar ATP-dependent proton pump, V-ATPase, on the plasma membrane of tumor cells correlates with the invasiveness of the tumor cell, suggesting the involvement of V-ATPase in tumor metastasis. V-ATPase is hypothesized to create a proton efflux leading to an acidic pericellular microenvironment that promotes the activity of proinvasive proteases. An alternative, not yet explored possibility is that V-ATPase regulates the signaling machinery responsible for tumor cell migration. Here, we show that pharmacologic or genetic reduction of V-ATPase activity significantly reduces migration of invasive tumor cells in vitro. Importantly, the V-ATPase inhibitor archazolid abrogates tumor dissemination in a syngeneic mouse 4T1 breast tumor metastasis model. Pretreatment of cancer cells with archazolid impairs directional motility by preventing spatially restricted, leading edge localization of epidermal growth factor receptor (EGFR) as well as of phosphorylated Akt. Archazolid treatment or silencing of V-ATPase inhibited Rac1 activation, as well as Rac1-dependent dorsal and peripheral ruffles by inhibiting Rab5-mediated endocytotic/exocytotic trafficking of Rac1. The results indicate that archazolid effectively decreases metastatic dissemination of breast tumors by impairing the trafficking and spatially restricted activation of EGFR and Rho-GTPase Rac1, which are pivotal for directed movement of cells. Thus, our data reveals a novel mechanism underlying the role of V-ATPase in tumor dissemination.

Expression and functional role of vacuolar H(+)-ATPase in human hepatocellular carcinoma

Tumor cells often exist in a hypoxic microenvironment, which produces acidic metabolites. To survive in this harsh environment, tumor cells must exhibit a dynamic cytosolic pH regulatory system. Vacuolar H(+)-adenosine triphosphatase (V-ATPase) is considered to play an important role in the regulation of the acidic microenvironment of some tumors. In this study, we made an investigation on the expression and functional role of V-ATPase in native human hepatocellular carcinoma (HCC). The results showed that the messenger RNA and protein expression levels of V-ATPase subunit ATP6L in native human HCC tissues were markedly increased, compared with normal liver tissues. Immunohistochemical analysis further confirmed the enhanced expression of V-ATPase ATP6L in human HCC cells and revealed that V-ATPase ATP6L was distributed in the cytoplasm and plasma membrane of HCC cells. The results from immunofluorescence and biotinylation of cell surface protein showed that V-ATPase ATP6L was conspicuously located in the plasma membrane of human HCC cells. Bafilomycin A1, a specific V-ATPase inhibitor, markedly slowed the intracellular pH (pHi) recovery after acid load in human HCC cells and retarded the growth of human HCC in orthotopic xenograft model. These results demonstrated that V-ATPase is up-regulated in human HCC and involved in the regulation of pHi of human HCC cells. The inhibition of V-ATPase can effectively retard the growth of HCC, indicating that V-ATPase may play an important role in the development and progression of human HCC, and targeting V-ATPase may be a promising therapeutic strategy against human HCC.

LASS2 enhances chemosensitivity of breast cancer by counteracting acidic tumor microenvironment through inhibiting activity of V-ATPase proton pump

A main obstacle to overcome during the treatment of tumors is drug resistance to chemotherapy; emerging studies indicate that a key factor contributing to this problem is the acidic tumor microenvironment. Here, we found that LASS2 expression was significantly lower in drug-resistant Michigan Cancer Foundation-7/adriamycin (MCF-7/ADR) human breast cancer cells than the drug-sensitive MCF-7 cells, and low expression of LASS2 was associated with poor prognosis in patients with breast cancer. Our results showed that the overexpression of LASS2 in MCF-7/ADR cells increased the chemosensitivity to multiple chemotherapeutic agents, including doxorubicin (Dox), whereas LASS2 knockdown in MCF-7 cells decreased the chemosensitivity. Cell-cycle analysis revealed a corresponding increase in apoptosis in the LASS2-overexpressing cells following Dox exposure, showing that the overexpression of LASS2 increased the susceptibility to Dox cytotoxicity. This effect was mediated by a significant increase in pHe (extracellular pH) and lysosomal pH, and more Dox entered the cells and stayed in the nuclei of cells. In nude mice, the combination of LASS2 overexpression and Dox significantly inhibited the growth of xenografts. Our findings suggest that LASS2 is involved in chemotherapeutic outcomes and low LASS2 expression may predict chemoresistance.

Clinicopathological and biological significance of human voltage-gated proton channel Hv1 protein overexpression in breast cancer

In our previous work, we showed for the first time that the voltage-gated proton channel Hv1 is specifically expressed in highly metastatic human breast tumor tissues and cell lines. However, the contribution of Hv1 to breast carcinogenesis is not well known. In this study, we showed that Hv1 expression was significantly correlated with the tumor size (p = 0.001), tumor classification (p = 0.000), lymph node status (p = 0.000), clinical stage (p = 0.000), and Her-2 status (p = 0.045). High Hv1 expression was associated significantly with shorter overall (p = 0.000) and recurrence-free survival (p = 0.000). In vitro, knockdown of Hv1 expression in the highly metastatic MDA-MB-231 cells decreased the cell proliferation and invasiveness, inhibited the cell proton secretion and intracellular pH recovery, and blocked the cell capacity of acidifying extracellular milieu. Furthermore, the gelatinase activity in MDA-MB-231 cells that suppressed Hv1 was reduced. In vivo, the breast tumor size of the implantation of the MDA-MB-231 xenografts in nude mice that were knocked down by Hv1 was dramatically smaller than that in the control groups. The results demonstrated that the inhibition of Hv1 function via knockdown of Hv1 expression can effectively retard the cancer growth and suppress the cancer metastasis by the decrease of proton extrusion and the down-regulation of gelatinase activity. Based on these results, we came to the conclusion that Hv1 is a potential biomarker for prognosis of breast cancer and a potential target for anticancer drugs in breast cancer therapy.

Lansoprazole as a rescue agent in chemoresistant tumors: a phase I/II study in companion animals with spontaneously occurring tumors

BACKGROUND

The treatment of human cancer has been seriously hampered for decades by resistance to chemotherapeutic drugs. Mechanisms underlying this resistance are far from being entirely known. A very efficient mechanism of tumor resistance to drugs is related to the modification of tumour microenvironment through changes in the extracellular and intracellular pH. The acidification of tumor microenvironment depends on proton pumps that actively pump protons outside the cells, mostly to avoid intracellular acidification. In fact, we have shown in pre-clinical settings as pre-treatment with proton-pumps inhibitors (PPI) increase tumor cell and tumor responsiveness to chemotherapeutics. In this study pet with spontaneously occurring cancer proven refractory to conventional chemotherapy have been recruited in a compassionate study.

METHODS

Thirty-four companion animals (27 dogs and 7 cats) were treated adding to their chemotherapy protocols the pump inhibitor lansoprazole at high dose, as suggested by pre-clinical experiments. Their responses have been compared to those of seventeen pets (10 dogs and 7 cats) whose owners did not pursue any other therapy than continuing the currently ongoing chemotherapy protocols.

RESULTS

The drug was overall well tolerated, with only four dogs experiencing side effects due to gastric hypochlorhydria consisting with vomiting and or diarrhea. In terms of overall response twenty-three pets out of 34 had partial or complete responses (67.6%) the remaining patients experienced no response or progressive disease however most owners reported improved quality of life in most of the non responders. On the other hand, only three animals in the control group (17%) experienced short lived partial responses (1-3 months duration) while all the others died of progressive disease within two months.

CONCLUSIONS

high dose proton pump inhibitors have been shown to induce reversal of tumor chemoresistance as well as improvement of the quality of life in pets with down staged cancer and in the majority of the treated animals PPI were well tolerated. Further studies are warranted to assess the efficacy of this strategy in patients with advanced cancers in companion animals as well as in humans.

Specific expression of the human voltage-gated proton channel Hv1 in highly metastatic breast cancer cells, promotes tumor progression and metastasis

The newly discovered human voltage-gated proton channel Hv1 is essential for proton transfer, which contains a voltage sensor domain (VSD) without a pore domain. We report here for the first time that Hv1 is specifically expressed in the highly metastatic human breast tumor tissues, but not in poorly metastatic breast cancer tissues, detected by immunohistochemistry. Meanwhile, real-time RT-PCR and immunocytochemistry showed that the expression levels of Hv1 have significant differences among breast cancer cell lines, MCF-7, MDA-MB-231, MDA-MB-468, MDA-MB-453, T-47D and SK-BR-3, in which Hv1 is expressed at a high level in highly metastatic human breast cancer cell line MDA-MB-231, but at a very low level in poorly metastatic human breast cancer cell line MCF-7. Inhibition of Hv1 expression in the highly metastatic MDA-MB-231 cells by small interfering RNA (siRNA) significantly decreases the invasion and migration of the cells. The intracellular pH of MDA-MB-231 cells down-regulated Hv1 expression by siRNA is obviously decreased compared with MDA-MB-231 with the scrambled siRNA. The expression of matrix metalloproteinase-2 and gelatinase activity in MDA-MB-231 cells suppressed Hv1 by siRNA were reduced. Our results strongly suggest that Hv1 regulates breast cancer intracellular pH and exacerbates the migratory ability of metastatic cells.

The a3 isoform vacuolar type H⁺-ATPase promotes distant metastasis in the mouse B16 melanoma cells

Accumulating evidence indicates that the acidic microenvironments critically influence malignant behaviors of cancer including invasiveness, metastasis, and chemoresistance. Because the vacuolar-type H(+)-ATPase (V-ATPase) has been shown to cause extracellular acidification by pumping protons, we studied the role of V-ATPase in distant metastasis. Real-time PCR analysis revealed that the high-metastatic B16-F10 melanoma cells strongly expressed the a3 isoform V-ATPase compared to the low-metastatic B16 parental cells. Consistent with this, B16-F10 cells created acidic environments in lung metastases by acridine orange staining and strong a3 V-ATPase expression in bone metastases by immunohistochemistry. Immunocytochemical analysis showed B16-F10 cells expressed a3 V-ATPase not only in cytoplasm but also plasma membrane, whereas B16 parental cells exhibited its expression only in cytoplasm. Of note, knockdown of a3 V-ATPase suppressed invasiveness and migration with reduced MMP-2 and MMP-9 expression in B16-F10 cells and significantly decreased lung and bone metastases, despite that tumor growth was not altered. Importantly, administration of a specific V-ATPase a3 inhibitor FR167356 reduced bone metastasis of B16-F10 cells. These results suggest that a3 V-ATPase promotes distant metastasis of B16-F10 cells by creating acidic environments via proton secretion. Our results also suggest that inhibition of the development of cancer-associated acidic environments by suppressing a3 V-ATPase could be a novel therapeutic approach for the treatment of cancer metastasis.

Effects of diphyllin as a novel V-ATPase inhibitor on gastric adenocarcinoma

The natural compound diphyllin, a cytostatic lignan isolated from Cleistanthus collinus, can dramatically inhibit the proliferation and induce the apoptosis of human gastric cancer cells, SGC7901. Our study found that diphyllin can inhibit the expression of V-ATPases in a dose-dependent manner, decrease the internal pH (pHi) and reverse the transmembrane pH gradient in SGC7901 cells. Changes of the pH gradient were positively correlated with diphyllin concentration. Further study found that diphyllin treatment caused a decrease in phospho-LRP6, but not in LRP6. β-catenin in Wnt/β-catenin signaling and its target genes, c-myc and cyclin-D1, were also decreased with the inhibition of V-ATPases. Therefore, diphyllin could be characterized as a new V-ATPase inhibitor in treating gastric cancer and inhibiting the phosphorylation of LRP6 in Wnt/β-catenin signaling.

The vacuolar-ATPase modulates matrix metalloproteinase isoforms in human pancreatic cancer

The vacuolar-ATPase (v-ATPase) is a proton transporter found on many intracellular organelles and the plasma membrane (PM). The v-ATPase on PMs of cancer cells may contribute to their invasive properties in vitro. Its relevance to human cancer tissues remains unclear. We investigated whether the expression and cellular localization of v-ATPase corresponded to the stage of human pancreatic cancer, and its effect on matrix metalloproteinase (MMP) activation in vitro. The intensity of v-ATPase staining increased significantly across the range of pancreatic histology from normal ducts to pancreatic intraepithelial neoplasms (PanIN), and finally pancreatic ductal adenocarcinoma (PDAC). Low-grade PanIN lesions displayed polarized staining confined to the basal aspect of the cell in the majority (86%) of fields examined. High-grade PanIN lesions and PDAC showed intense and diffuse v-ATPase localization. In pancreatic cancer cells, PM-associated v-ATPase colocalized with cortactin, a component of the leading edge that helps direct MMP release. Blockade of the v-ATPase with concanamycin or short-hairpin RNA targeting the V₁E subunit reduced MMP-9 activity; this effect was greatest in cells with prominent PM-associated v-ATPase. In cells with detectable MMP-2 activities, however, treatment with concanamycin markedly increased MMP-2's most activated forms. V-ATPase blockade inhibited functional migration and invasion in those cells with predominantly MMP-9 activity. These results indicate that human PDAC specimens show loss of v-ATPase polarity and increased expression that correlates with increasing invasive potential. Thus, v-ATPase selectively modulates specific MMPs that may be linked to an invasive cancer phenotype.

pH control mechanisms of tumor survival and growth

A distinguishing phenotype of solid tumors is the presence of an alkaline cellular feature despite the surrounding acidic microenvironment. This phenotypic characteristic of tumors, originally described by Otto Warburg, arises due to alterations in metabolism of solid tumors. Hypoxic regions of solid tumors develop due to poor vascularization and in turn regulate the expression of numerous genes via the transcription factor HIF-1. Ultimately, the tumor microenvironment directs the development of tumor cells adapted to survive in an acidic surrounding where normal cells perish. The provision of unique pH characteristics in tumor cells provides a defining trait that has led to the pursuit of treatments that target metabolism, hypoxia, and pH-related mechanisms to selectively kill cancer cells. Numerous studies over the past decade involving the cancer-specific carbonic anhydrase IX have re-kindled an interest in pH disruption-based therapies. Although an acidification of the intracellular compartment is established as a means to induce normal cell death, the defining role of acid-base disturbances in tumor physiology and survival remains unclear. The aim of this review is to summarize recent data relating to the specific role of pH regulation in tumor cell survival. We focus on membrane transport and enzyme studies in an attempt to elucidate their respective functions regarding tumor cell pH regulation. These data are discussed in the context of future directions for the field of tumor cell acid-base-related research.

Involvement of acidic microenvironment in the pathophysiology of cancer-associated bone pain

Bone pain is one of the most common complications in cancer patients with bone metastases. Although the mechanism of cancer-associated bone pain is poorly understood, clinical observations that inhibitors of osteoclasts such as bisphosphonates (BPs) efficiently reduce bone pain suggest a potential role of osteoclasts, which play a central role in the development and progression of bone metastasis. Osteoclasts dissolve bone minerals by releasing protons through the a3 isoform of the vacuolar-H(+)-ATPase, creating acidic microenvironments. In addition, cancer cells, inflammatory cells and immune cells that reside in bone metastases also produce acidic conditions by releasing protons. It has been well-known that acidic conditions due to proton release cause pain. Our study showed that the sensory nociceptive neurons innervate bone and these neurons express acid-sensing nociceptors such as the acid-sensing ion channels and transient receptor potential channel-vanilloid subfamily members. Acid signals received by these nociceptors subsequently activate intracellular signaling pathways and transcription factors in sensory neurons. The understanding of the nociceptive events following proton release and subsequent creation of acidic microenvironments leads us to design novel molecular-based approaches for reducing bone pain associated with cancer and inflammation.