Acid-base transporters and pH dynamics in human breast carcinomas predict proliferative activity, metastasis, and survival

The electroneutral Na+-HCO3- cotransporter NBCn1 (SLC4A7) modulates colonic enterocyte pHi, proliferation, and migration

NBCn1 (SLC4A7) is one of the two major Na+-HCO3- cotransporters in the human colonic epithelium, expressed predominantly in the highly proliferating colonocytes at the cryptal base. Increased NBCn1 expression levels are reported in tumors, including colorectal cancer. The study explores its importance for maintenance of the intracellular pH (pHi), as well as the proliferative, adhesive, and migratory behavior of the self-differentiating Caco2BBe colonic tumor cell line. In the self-differentiating Caco2BBe cells, NBCn1 mRNA was highly expressed from the proliferative stage until full differentiation. The downregulation of NBCn1 expression by RNA interference affected proliferation and differentiation and decreased intracellular pH (pHi) of the cells in correlation with the degree of knockdown. In addition, a disturbed cell adhesion and reduced migratory speed were associated with NBCn1 knockdown. Murine colonic Nbcn1-/- enteroids also displayed reduced proliferative activity. In the migrating Caco2BBe cells, NBCn1 was found at the leading edge and in colocalization with the focal adhesion markers vinculin and paxillin, which suggests that NBCn1 is involved in the establishment of cell-matrix adhesion. Our data highlight the physiological significance of NBCn1 in modulating epithelial pH homeostasis and cell-matrix interactions in the proliferative region of the colonic epithelium and unravel the molecular mechanism behind pathological overexpression of this transporter in human colorectal cancers.NEW & NOTEWORTHY The transporter NBCn1 plays a central role in maintaining homeostasis within Caco2BBe colonic epithelial cells through its regulation of intracellular pH, matrix adhesion, migration, and proliferation. These observations yield valuable insights into the molecular mechanism of the aberrant upregulation of this transporter in human colorectal cancers.

MCT4 knockdown by tumor microenvironment-responsive nanoparticles remodels the cytokine profile and eradicates aggressive breast cancer cells

Breast cancer is a wide-spread threat to the women's health. The drawbacks of conventional treatments necessitate the development of alternative strategies, where gene therapy has regained hope in achieving an efficient eradication of aggressive tumors. Monocarboxylate transporter 4 (MCT4) plays pivotal roles in the growth and survival of various tumors, which offers a promising target for treatment. In the present study, pH-responsive lipid nanoparticles (LNPs) based on the ionizable lipid,1,2-dioleoyl-3-dimethylammonium propane (DODAP), were designed for the delivery of siRNA targeting MCT4 gene to the breast cancer cells. Following multiple steps of characterization and optimization, the anticancer activities of the LNPs were assessed against an aggressive breast cancer cell line, 4T1, in comparison with a normal cell line, LX-2. The selection of the helper phospholipid to be incorporated into the LNPs had a dramatic impact on their gene delivery performance. The optimized LNPs enabled a powerful MCT4 silencing by ∼90 % at low siRNA concentrations, with a subsequent ∼80 % cytotoxicity to 4T1 cells. Meanwhile, the LNPs demonstrated a 5-fold higher affinity to the breast cancer cells versus the normal cells, in which they had a minimum effect. Moreover, the MCT4 knockdown by the treatment remodeled the cytokine profile in 4T1 cells, as evidenced by 90 % and ∼64 % reduction in the levels of TNF-α and IL-6; respectively. The findings of this study are promising for potential clinical applications. Furthermore, the simple and scalable delivery vector developed herein can serve as a breast cancer-targeting platform for the delivery of other RNA therapeutics.

Antibodies toward Na+,HCO3--cotransporter NBCn1/SLC4A7 block net acid extrusion and cause pH-dependent growth inhibition and apoptosis in breast cancer

BACKGROUND

Na+,HCO3--cotransporter NBCn1/Slc4a7 accelerates murine breast carcinogenesis. Lack of specific pharmacological tools previously restricted therapeutic targeting of NBCn1 and identification of NBCn1-dependent functions in human breast cancer.

METHODS

We develop extracellularly-targeted anti-NBCn1 antibodies, screen for functional activity on cells, and evaluate (a) mechanisms of intracellular pH regulation in human primary breast carcinomas, (b) proliferation, cell death, and tumor growth consequences of NBCn1 in triple-negative breast cancer, and (c) association of NBCn1-mediated Na+,HCO3--cotransport with human breast cancer metastasis.

RESULTS

We identify high-affinity (KD ≈ 0.14 nM) anti-NBCn1 antibodies that block human NBCn1-mediated Na+,HCO3--cotransport in cells, without cross-reactivity towards human NBCe1 or murine NBCn1. These anti-NBCn1 antibodies abolish Na+,HCO3--cotransport activity in freshly isolated primary organoids from human breast carcinomas and lower net acid extrusion effectively in primary breast cancer tissue from patients with macrometastases in axillary lymph nodes. Inhibitory anti-NBCn1 antibodies decelerate tumor growth in vivo by ~50% in a patient-derived xenograft model of triple-negative breast cancer and pH-dependently reduce colony formation, cause G2/M-phase cell cycle accumulation, and increase apoptosis of metastatic triple-negative breast cancer cells in vitro.

CONCLUSIONS

Inhibitory anti-NBCn1 antibodies block net acid extrusion in human breast cancer tissue, particularly from patients with disseminated disease, and pH-dependently limit triple-negative breast cancer growth.

Acid-base transporters in the context of tumor heterogeneity

The copious metabolic acid production and -extrusion by cancer cells render poorly vascularized regions of solid tumors highly acidic. A growing list of proton - and bicarbonate transporters has been suggested to contribute to net acid extrusion from cancer cells, and/or been shown to be dysregulated and favor malignant development in various cancers. The great majority of these roles have been studied at the level of the cancer cells. However, recent advances in understanding of the cellular and physicochemical heterogeneity of solid tumors both enable and necessitate a reexamination of the regulation and roles of acid-base transporters in such malignancies. This review will briefly summarize the state-of-the-art, with a focus on the SLC9A and SLC4A families, for which most evidence is available. This is followed by a discussion of key concepts and open questions arising from recent insights and of the challenges that need to be tackled to address them. Finally, opportunities and challenges in therapeutic targeting of the acid-base transportome in cancers will be addressed.

Co-Expression Network Analysis Unveiled lncRNA-mRNA Links Correlated to Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitor Resistance and/or Intermediate Epithelial-to-Mesenchymal Transition Phenotypes in a Human Non-Small Cell Lung Cancer Cellular Model System

We investigated mRNA-lncRNA co-expression patterns in a cellular model system of non-small cell lung cancer (NSCLC) sensitive and resistant to the epithelial growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) erlotinib/gefitinib. The aim of this study was to unveil insights into the complex mechanisms of NSCLC targeted therapy resistance and epithelial-to-mesenchymal transition (EMT). Genome-wide RNA expression was quantified for weighted gene co-expression network analysis (WGCNA) to correlate the expression levels of mRNAs and lncRNAs. Functional enrichment analysis and identification of lncRNAs were conducted on modules associated with the EGFR-TKI response and/or intermediate EMT phenotypes. We constructed lncRNA-mRNA co-expression networks and identified key modules and their enriched biological functions. Processes enriched in the selected modules included RHO (A, B, C) GTPase and regulatory signaling pathways, apoptosis, inflammatory and interleukin signaling pathways, cell adhesion, cell migration, cell and extracellular matrix organization, metabolism, and lipid metabolism. Interestingly, several lncRNAs, already shown to be dysregulated in cancer, are connected to a small number of mRNAs, and several lncRNAs are interlinked with each other in the co-expression network.

Chitosan nanoplatform for the co-delivery of palbociclib and ultra-small magnesium nanoclusters: dual receptor targeting, therapy and imaging

Theranostic nanoparticles have gained significant attention in cancer diagnosis and therapy. In this study, estrone (ES) and folic acid (FA) functionalized single and dual receptor targeted theranostic chitosan nanoparticles were developed for breast cancer imaging and therapy. These nanoparticles (NPs) were loaded with palbociclib (PB) and ultra-small magnesium nanoclusters (UMN). The developed nontargeted theranostic NPs (PB-UMN-CS-NPs), estrogen receptor targeted theranostic NPs (PB-UMN-CS-ES-NPs), folate receptor targeted theranostic NPs (PB-UMN-CS-FA-NPs), and dual targeted theranostic NPs (PB-UMN-CS-ES-FA-NPs) have particle sizes of 178.4 ± 1.21 nm, 181.6± 1.35 nm, 185.1± 1.33 nm, and 198.2± 1.43 nm with surface charges of +19.02± 0.382 mV, +13.89±0.410 mV, +16.72±0.527 mV and +15.23±0.377 mV, respectively. Cytotoxicity studies on estrogen receptor (ER) and folate receptor (FR) expressing breast cancer cells revealed that dual-targeted theranostic NPs (PB-UMN-CS-FA-ES-NPs) were more effective, inhibiting cell growth by 54.17 and 42.23 times in MCF-7 and T-47D cells compared to free PB, respectively. Additionally, developed NPs were capable of inhibiting the cell cycle progression of MCF-7 cells from the G1 phase to the S phase more efficiently compared to free PB. Ultrasound and photoacoustic (USG/PA) imaging demonstrated that dual targeted theranostic NPs were capable of effectively reducing hypoxic tumor volume and significantly suppressing tumor vascularity compared to free PB, nontargeted, FR targeted and ER targeted NPs. Moreover, in vivo optical imaging demonstrated tumor specific accumulation of the dual-targeted theranostic NPs. Furthermore, in vitro hemocompatibility and histopathological studies confirmed the biocompatibility of developed nanoformulations.

How protons pave the way to aggressive cancers

Cancers undergo sequential changes to proton (H+) concentration and sensing that are consequences of the disease and facilitate its further progression. The impact of protonation state on protein activity can arise from alterations to amino acids or their titration. Indeed, many cancer-initiating mutations influence pH balance, regulation or sensing in a manner that enables growth and invasion outside normal constraints as part of oncogenic transformation. These cancer-supporting effects become more prominent when tumours develop an acidic microenvironment owing to metabolic reprogramming and disordered perfusion. The ensuing intracellular and extracellular pH disturbances affect multiple aspects of tumour biology, ranging from proliferation to immune surveillance, and can even facilitate further mutagenesis. As a selection pressure, extracellular acidosis accelerates disease progression by favouring acid-resistant cancer cells, which are typically associated with aggressive phenotypes. Although acid-base disturbances in tumours often occur alongside hypoxia and lactate accumulation, there is now ample evidence for a distinct role of H+-operated responses in key events underpinning cancer. The breadth of these actions presents therapeutic opportunities to change the trajectory of disease.

Optimized strategies of ROS-based nanodynamic therapies for tumor theranostics

Reactive oxygen species (ROS) play a crucial role in regulating the metabolism of tumor growth, metastasis, death and other biological processes. ROS-based nanodynamic therapies (NDTs) are becoming attractive due to non-invasive, low side effects and tumor-specific advantages. NDTs have rapidly developed into numerous branches, such as photodynamic therapy, chemodynamic therapy, sonodynamic therapy and so on. However, the complexity of the tumor microenvironment and the limitations of existing sensitizers have greatly restricted the therapeutic effects of NDTs, which heavily rely on ROS levels. To address the limitations of NDTs, various strategies have been developed to increase ROS yield, which is an urgent aspect for the positive development of NDTs. In this review, the nanodynamic potentiation strategies in terms of unique properties and universalities of NDTs are comprehensively outlined. We mainly summarize the current dilemmas faced by each NDT and the respective solutions. Meanwhile, the NDTs universalities-based potentiation strategies and NDTs-based combined treatments are elaborated. Finally, we conclude with a discussion of the key issues and challenges faced in the development and clinical transformation of NDTs.

In Situ Insonation of Alkaline Buffer Containing Liposomes Leads to a Net Improvement of the Therapeutic Outcome in a Triple Negative Breast Cancer Murine Model

Breast cancer is characterized by an acidic micro-environment. Acidic extracellular pH gives cancer cells an evolutionary advantage, hence, neutralization of the extracellular pH has been considered as a potential therapeutic strategy. To address the issue of systemic pH alteration, an approach based on the targeted delivery of the buffering solution to the tumor region is investigated. The method relies on the use of low frequency ultrasound and sono-sensitive liposomes loaded with buffers at alkaline pH (LipHUS). After the i.v. injection of LipHUS, the application of ultrasound (US) at the sites of the pathology induces a local increase of pH that results highly effective in i) inhibiting primary tumor growth, ii) reducing tumor recurrence after surgery, and iii) suppressing metastases' formation. The experiments are carried out on a triple negative breast cancer mouse model. The results obtained demonstrate that localized and triggered release of bicarbonate or PBS buffer from sonosensitive liposomes represents an efficient therapeutic tool for treating triple-negative breast cancer. This approach holds promise for potential clinical translation.

IDH1 K224 acetylation promotes colorectal cancer via miR-9-5p/NHE1 axis-mediated regulation of acidic microenvironment

The acidic microenvironment is considered an important factor in colorectal cancer (CRC) that contributes to malignant transformation. However, the underlying mechanism remains unclear. In a previous study, we confirmed that IDH1 K224 deacetylation promotes enzymatic activity and the production of α-KG. Here, we further investigate the effect of IDH1 hyperacetylation on the CRC acidic microenvironment. We demonstrate that increased α-KG affects hydroxylation of Ago2 and mediates miR-9-5p targeting NHE1 protein. Knockdown of NHE1 dramatically attenuates CRC cell proliferation and migration by restricting transport of intracellular H⁺ out of cells. Furthermore, we show that miR-9-5p is the microRNA with the most significant difference in the alteration of IDH1 K224 acetylation and can downregulate NHE1 mRNA. Our data also indicate that hydroxylation stabilizes Ago2, which in turn promotes miR-9-5p activity. Taken together, our results reveal a novel mechanism through which IDH1 deacetylation regulates the cellular acidic microenvironment and inhibits CRC metastasis.

Chitosan-g-estrone Nanoparticles of Palbociclib Vanished Hypoxic Breast Tumor after Targeted Delivery: Development and Ultrasound/Photoacoustic Imaging

Breast cancer is the leading cause of death among women globally. Approximately 80% of all breast cancers diagnosed are overexpressed with estrogen receptors (ERs). In this study, we have developed an estrone (Egen)-grafted chitosan-based polymeric nanocarrier for the targeted delivery of palbociclib (PLB) to breast cancer. The nanoparticles (NPs) were prepared by solvent evaporation using the ionic gelation method and characterized for particle size, zeta potential, polydispersity, surface morphology, surface chemistry, drug entrapment efficiency, cytotoxicity assay, cellular uptake, and apoptosis study. The developed PLB-CS NPs and PLB-CS-g-Egen NPs had a particle size of 116.3 ± 1.53 nm and 141.6 ± 1.97 nm, respectively. The zeta potential of PLB-CS NPs and PLB-CS-g-Egen NPs was found to be 18.70 ± 0.416 mV and 12.45 ± 0.574 mV, respectively. The morphological analysis demonstrated that all NPs were spherical in shape and had a smooth surface. An in vitro cytotoxicity assay was performed in estrogen receptor (ER)-expressing MCF7 cells and T47D cells, which suggested that targeted NPs were 57.34- and 30.32-fold more cytotoxic compared to the pure PLB, respectively. Additionally, cell cycle analysis confirmed that cell cycle progression from the G1 into S phase was blocked more efficiently by targeted NPs compared to nontargeted NPs and PLB in MCF7 cells. In vivo pharmacokinetic studies demonstrated that entrapment of the PLB in the NPs improved the half-life and bioavailability by ∼2-3-fold. Further, ultrasound and photoacoustic imaging of DMBA induced breast cancer in the Sprague-Dawley (SD) rat showed that targeted NPs completely vanished breast tumor, reduced hypoxic tumor volume, and suppressed tumor angiogenesis more efficiently compared to the nontargeted NPs and free PLB. Further, in vitro hemocompatibility and histopathology studies suggested that NPs were biocompatible and safe for clinical use.

Sodium channels and the ionic microenvironment of breast tumours

Cancers of epithelial origin such as breast, prostate, cervical, gastric, colon and lung cancer account for a large proportion of deaths worldwide. Better treatment of metastasis, the main cause of cancer deaths, is therefore urgently required. Several of these tumours have been shown to have an abnormally high concentration of Na+ ([Na+ ]) and emerging evidence points to this accumulation being due to elevated intracellular [Na+ ]. This poses intriguing questions about the cellular mechanisms underlying Na+ dysregulation in cancer, and its pathophysiological significance. Elevated intracellular [Na+ ] may be due to alterations in activity of the Na+ /K+ -ATPase, and/or increased influx via Na+ channels and Na+ -linked transporters. Maintenance of the electrochemical Na+ gradient across the plasma membrane is vital to power many cellular processes that are highly active in cancer cells, including glucose and glutamine import. Na+ channels are also upregulated in cancer cells, which in turn promotes tumour growth and metastasis. For example, ENaC and ASICs are overexpressed in cancers, increasing invasion and proliferation. In addition, voltage-gated Na+ channels are also upregulated in a range of tumour types, where they promote metastatic cell behaviours via various mechanisms, including membrane potential depolarisation and altered pH regulation. Together, recent findings relating to elevated Na+ in the tumour microenvironment and how this may be regulated by several classes of Na+ channels provide a link between altered Na+ handling and poor clinical outcome. There are new opportunities to leverage this altered Na+ microenvironment for therapeutic benefit, as exemplified by several ongoing clinical trials.

Hyperoxia induces glucose metabolism reprogramming and intracellular acidification by suppressing MYC/MCT1 axis in lung cancer

The perils and promises of inspiratory hyperoxia (IH) in oncology are still controversial, especially for patients with lung cancer. Increasing evidence shows that hyperoxia exposure is relevant to the tumor microenvironment. However, the detailed role of IH on the acid-base homeostasis of lung cancer cells remains unclear. In this study, the effects of 60% oxygen exposure on intra- and extracellular pH were systematically evaluated in H1299 and A549 cells. Our data indicate that hyperoxia exposure reduces intracellular pH, which might be expected to reduce the proliferation, invasion, and epithelial-to-mesenchymal transition of lung cancer cells. RNA sequencing, Western blot, and PCR analysis reveal that monocarboxylate transporter 1 (MCT1) mediates intracellular lactate accumulation and intracellular acidification of H1299 and A549 cells at 60% oxygen exposure. In vivo studies further demonstrate that MCT1 knockdown dramatically reduces lung cancer growth, invasion, and metastasis. The results of luciferase and ChIP-qPCR assays further confirm that MYC is a transcription factor of MCT1, and PCR and Western blot assays confirm that MYC is downregulated under hyperoxic conditions. Collectively, our data reveal that hyperoxia can suppress the MYC/MCT1 axis and cause the accumulation of lactate and intracellular acidification, thereby retarding tumor growth and metastasis.

Carbonic anhydrases reduce the acidity of the tumor microenvironment, promote immune infiltration, decelerate tumor growth, and improve survival in ErbB2/HER2-enriched breast cancer

BACKGROUND

Carbonic anhydrases catalyze CO₂/HCO₃^- buffer reactions with implications for effective H⁺ mobility, pH dynamics, and cellular acid-base sensing. Yet, the integrated consequences of carbonic anhydrases for cancer and stromal cell functions, their interactions, and patient prognosis are not yet clear.

METHODS

We combine (a) bioinformatic analyses of human proteomic data and bulk and single-cell transcriptomic data coupled to clinicopathologic and prognostic information; (b) ex vivo experimental studies of gene expression in breast tissue based on quantitative reverse transcription and polymerase chain reactions, intracellular and extracellular pH recordings based on fluorescence confocal microscopy, and immunohistochemical protein identification in human and murine breast cancer biopsies; and (c) in vivo tumor size measurements, pH-sensitive microelectrode recordings, and microdialysis-based metabolite analyses in mice with experimentally induced breast carcinomas.

RESULTS

Carbonic anhydrases-particularly the extracellular isoforms CA4, CA6, CA9, CA12, and CA14-undergo potent expression changes during human and murine breast carcinogenesis. In patients with basal-like/triple-negative breast cancer, elevated expression of the extracellular carbonic anhydrases negatively predicts survival, whereas, surprisingly, the extracellular carbonic anhydrases positively predict patient survival in HER2/ErbB2-enriched breast cancer. Carbonic anhydrase inhibition attenuates cellular net acid extrusion and extracellular H⁺ elimination from diffusion-restricted to peripheral and well-perfused regions of human and murine breast cancer tissue. Supplied in vivo, the carbonic anhydrase inhibitor acetazolamide acidifies the microenvironment of ErbB2-induced murine breast carcinomas, limits tumor immune infiltration (CD3⁺ T cells, CD19⁺ B cells, F4/80⁺ macrophages), lowers inflammatory cytokine (Il1a, Il1b, Il6) and transcription factor (Nfkb1) expression, and accelerates tumor growth. Supporting the immunomodulatory influences of carbonic anhydrases, patient survival benefits associated with high extracellular carbonic anhydrase expression in HER2-enriched breast carcinomas depend on the tumor inflammatory profile. Acetazolamide lowers lactate levels in breast tissue and blood without influencing breast tumor perfusion, suggesting that carbonic anhydrase inhibition lowers fermentative glycolysis.

CONCLUSIONS

We conclude that carbonic anhydrases (a) elevate pH in breast carcinomas by accelerating net H⁺ elimination from cancer cells and across the interstitial space and (b) raise immune infiltration and inflammation in ErbB2/HER2-driven breast carcinomas, restricting tumor growth and improving patient survival.

Bicarbonate transporter SLC4A7 promotes EMT and metastasis of HNSCC by activating the PI3K/AKT/mTOR signaling pathway

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Currently, therapeutic modalities such as surgery, chemotherapy, radiotherapy, and immunotherapy are being used to treat HNSCC. However, the treatment outcomes of most patients are dismal because they are already in middle or advanced stage by the time of diagnosis and poorly responsive to treatments. It is therefore of great interest to clarify mechanisms that contribute to the metastasis of cells to identify possible targets for therapy. In this study, we identified the Na⁺ -coupled bicarbonate transporter, SLC4A7, play essential roles in the metastasis of HNSCC. Our results showed that the relative expression of SLC4A7 messenger RNA was highly expressed in HNSCCs samples from TCGA, and compared with precancerous cells of human oral mucosa (DOK), SLC4A7 was highly expressed in HNSCC cell lines. In vitro and in vivo experiments showed that dysregulation of SLC4A7 had minor influence on the proliferation of HNSCC but impacted HNSCC's migration and invasion. Meanwhile, SLC4A7 could promote epithelial-mesenchymal transition (EMT) in HNSCC. RNA-seq, KEGG pathway enrichment analysis and Western blot further revealed that downregulation of SLC4A7 in HNSCC cells inhibited the PI3K/AKT pathway. These findings were further validated via rescue experiments using a small molecule inhibitor of PI3K/mTOR (GDC-0980). Our findings suggest that SLC4A7 promotes EMT and metastasis of HNSCC through the PI3K/AKT/mTOR signaling pathway, which may be a valuable predictive biomarker and potential therapeutic target in HNSCC.

The mTORC1-SLC4A7 axis stimulates bicarbonate import to enhance de novo nucleotide synthesis

Bicarbonate (HCO3-) ions maintain pH homeostasis in eukaryotic cells and serve as a carbonyl donor to support cellular metabolism. However, whether the abundance of HCO3- is regulated or harnessed to promote cell growth is unknown. The mechanistic target of rapamycin complex 1 (mTORC1) adjusts cellular metabolism to support biomass production and cell growth. We find that mTORC1 stimulates the intracellular transport of HCO3- to promote nucleotide synthesis through the selective translational regulation of the sodium bicarbonate cotransporter SLC4A7. Downstream of mTORC1, SLC4A7 mRNA translation required the S6K-dependent phosphorylation of the translation factor eIF4B. In mTORC1-driven cells, loss of SLC4A7 resulted in reduced cell and tumor growth and decreased flux through de novo purine and pyrimidine synthesis in human cells and tumors without altering the intracellular pH. Thus, mTORC1 signaling, through the control of SLC4A7 expression, harnesses environmental bicarbonate to promote anabolic metabolism, cell biomass, and growth.

Loss of RPTPγ primes breast tissue for acid extrusion, promotes malignant transformation and results in early tumour recurrence and shortened survival

BACKGROUND

While cellular metabolism and acidic waste handling accelerate during breast carcinogenesis, temporal patterns of acid-base regulation and underlying molecular mechanisms responding to the tumour microenvironment remain unclear.

METHODS

We explore data from human cohorts and experimentally investigate transgenic mice to evaluate the putative extracellular HCO₃^--sensor Receptor Protein Tyrosine Phosphatase (RPTP)γ during breast carcinogenesis.

RESULTS

RPTPγ expression declines during human breast carcinogenesis and particularly in high-malignancy grade breast cancer. Low RPTPγ expression associates with poor prognosis in women with Luminal A or Basal-like breast cancer. RPTPγ knockout in mice favours premalignant changes in macroscopically normal breast tissue, accelerates primary breast cancer development, promotes malignant breast cancer histopathologies, and shortens recurrence-free survival. In RPTPγ knockout mice, expression of Na⁺,HCO₃^--cotransporter NBCn1-a breast cancer susceptibility protein-is upregulated in normal breast tissue but, contrary to wild-type mice, shows no further increase during breast carcinogenesis. Associated augmentation of Na⁺,HCO₃^--cotransport in normal breast tissue from RPTPγ knockout mice elevates steady-state intracellular pH, which has known pro-proliferative effects.

CONCLUSIONS

Loss of RPTPγ accelerates cellular net acid extrusion and elevates NBCn1 expression in breast tissue. As these effects precede neoplastic manifestations in histopathology, we propose that RPTPγ-dependent enhancement of Na⁺,HCO₃^--cotransport primes breast tissue for cancer development.

Research Progress on Improving the Efficiency of CDT by Exacerbating Tumor Acidification

In recent years, chemodynamic therapy (CDT) has received extensive attention as a novel means of cancer treatment. The CDT agents can exert Fenton and Fenton-like reactions in the acidic tumor microenvironment (TME), converting hydrogen peroxide (H₂O₂) into highly toxic hydroxyl radicals (·OH). However, the pH of TME, as an essential factor in the Fenton reaction, does not catalyze the reaction effectively, hindering its efficiency, which poses a significant challenge for the future clinical application of CDT. Therefore, this paper reviews various strategies to enhance the antitumor properties of nanomaterials by modulating tumor acidity. Ultimately, the performance of CDT can be further improved by inducing strong oxidative stress to produce sufficient ·OH. In this paper, the various acidification pathways and proton pumps with potential acidification functions are mainly discussed, such as catalytic enzymes, exogenous acids, CAIX, MCT, NHE, NBCn1, etc. The problems, opportunities, and challenges of CDT in the cancer field are also discussed, thereby providing new insights for the design of nanomaterials and laying the foundation for their future clinical applications.

Amplified Ca2+ dynamics and accelerated cell proliferation in breast cancer tissue during purinergic stimulation

Intracellular Ca²⁺ dynamics shape malignant behaviors of cancer cells. Whereas previous studies focused on cultured cancer cells, we here used breast organoids and colonic crypts freshly isolated from human and murine surgical biopsies. We performed fluorescence microscopy to evaluate intracellular Ca²⁺ concentrations in breast and colon cancer tissue with preferential focus on intracellular Ca²⁺ release in response to purinergic and cholinergic stimuli. Inhibition of the sarco‐/endoplasmic reticulum Ca²⁺ ATPase with cyclopiazonic acid elicited larger Ca²⁺ responses in breast cancer tissue, but not in colon cancer tissue, relative to respective normal tissue. The resting intracellular Ca²⁺ concentration was elevated, and ATP, UTP and acetylcholine induced strongly augmented intracellular Ca²⁺ responses in breast cancer tissue compared with normal breast tissue. In contrast, resting intracellular Ca²⁺ levels and acetylcholine‐induced increases in intracellular Ca²⁺ concentrations were unaffected and ATP‐ and UTP‐induced Ca²⁺ responses were smaller in colon cancer tissue compared with normal colon tissue. In accordance with the amplified Ca²⁺ responses, ATP and UTP substantially increased proliferative activity—evaluated by bromodeoxyuridine incorporation—in breast cancer tissue, whereas the effect was minimal in normal breast tissue. ATP caused cell death—identified with ethidium homodimer‐1 staining—in breast cancer tissue only at concentrations above the expected pathophysiological range. We conclude that intracellular Ca²⁺ responses are amplified in breast cancer tissue, but not in colon cancer tissue, and that nucleotide signaling stimulates breast cancer cell proliferation within the extracellular concentration range typical for solid cancer tissue.

Regulation of proton partitioning in kinase-activating acute myeloid leukemia and its therapeutic implication

Gain-of-function kinase mutations are common in AML and usually portend an inferior prognosis. We reported a novel mechanism whereby kinase mutants induced intracellular alkalization characteristic in oncogenesis. Thirteen kinases were found to activate sodium/hydrogen exchanger (NHE1) in normal hematopoietic progenitors, of which FLT3-ITD, KRAS^G12D, and BTK phosphorylated NHE1 maintained alkaline intracellular pH (pHi) and supported survival of AML cells. Primary AML samples with kinase mutations also showed increased NHE1 phosphorylation and evidence of NHE1 addiction. Amiloride enhanced anti-leukemic effects and intracellular distribution of kinase inhibitors and chemotherapy. Co-inhibition of NHE1 and kinase synergistically acidified pHi in leukemia and inhibited its growth in vivo. Plasma from patients taking amiloride for diuresis reduced pHi of leukemia and enhanced cytotoxic effects of kinase inhibitors and chemotherapy in vitro. NHE1-mediated intracellular alkalization played a key pathogenetic role in transmitting the proliferative signal from mutated-kinase and could be exploited for therapeutic intervention in AML.

Anagliptin promotes apoptosis in mouse colon carcinoma cells via MCT-4/lactate-mediated intracellular acidosis

Cancer cells frequently exhibit an acidic extracellular microenvironment, where inversion of the transmembrane pH gradient is associated with tumor proliferation and metastasis. To elucidate a new therapeutic target against cancer, the current study aimed to determine the mechanism by which the dipeptidyl peptidase-4 inhibitor anagliptin regulates the cellular pH gradient and concomitant extracellular acidosis during cancer progression. A total of 5x10⁵ CT-26 cells (resuspended in phosphate buffer saline) were injected subcutaneously in the right flank of male BALB/c mice (weighing 25-28 g). The tumor samples were harvested, and lactate was detected using a lactate assay kit. Immunohistochemistry was used to detect the Ki67 and PCNA. MTT assay and flow cytometric were used to detect cell viability. Intracellular pH was detected by fluorescence pH indicator. The results revealed that anagliptin effectively reduced tumor growth, but did not affect the body weight of treated mice. Anagliptin reduced the accumulation of lactate in tumor sample. Treatment with anagliptin stimulated the apoptosis of CT-26 cells. And lactate excretion inhibition is accompanied by an increase in extracellular pH (pHe) after treatment with anagliptin. Furthermore, anagliptin induced intracellular acidification and reversed the low pHe gradient via monocarboxylate transporter-4 (MCT-4)-mediated lactate excretion. Additionally, anagliptin reversed the aberrant transmembrane extracellular/intracellular pH gradient by suppressing MCT-4-mediated lactate excretion, while also reducing mitochondrial membrane potential and inducing apoptosis. These data revealed a novel function of anagliptin in regulating lactate excretion from cancer cells, suggesting that anagliptin may be used as a potential treatment for cancer.

Permissive role of Na+/H+ exchanger isoform 1 in migration and invasion of triple-negative basal-like breast cancer cells

In breast cancer, it is the resulting metastasis that is the primary cause of fatality. pH regulatory proteins and the tumor microenvironment play an important role in metastasis of cancer cells and acid-extruding proteins are critical in this process. There are several types of breast cancer and triple-negative breast cancer tends to be more metastatic and invasive and is itself is composed of several types. MDA-MB-468 are a triple-negative breast cancer cell line and are classified as basal-like and basal tumors account for up to 15% of breast cancers. Here we examined the effect of removal of the acid-extruding protein, the Na⁺/H⁺ exchanger isoform one, from MDA-MB-468 cells. NHE1 was deleted from these cells using the CRISPR/Cas9 system. Western blotting and measurement of activity confirmed the absence of the protein. In wounding/cell migration experiments, deletion of NHE1 reduced the rate of cell migration in the presence of low- or high-serum concentrations. Anchorage-dependent colony formation was also greatly reduced by deletion of the NHE1 protein. Cell proliferation was not affected by knockout of NHE1. The results demonstrate that NHE1 has an important role in migration and invasion of basal-like triple-negative breast cancer cells.

Hypoxia enhances motility and EMT through the Na+/H+ exchanger NHE-1 in MDA-MB-231 breast cancer cells

Breast cancer metastasis is the leading cause of cancer-related deaths. Hypoxia in the tumor mass is believed to trigger cell migration, which is involved in a crucial process of breast cancer metastasis. However, the molecular mechanisms underlying aggressive behavior under hypoxic conditions have not been fully elucidated. Here, we demonstrate the significant motility of MDA-MB-231 cells cultured under hypoxic conditions compared to that of cells cultured under normoxic conditions. MDA-MB-231 cells under hypoxic conditions showed a significant increase in Na⁺/H⁺ exchanger isoform 1 (NHE1) expression level, which was observed to co-locate in lamellipodia formation. Inhibition of NHE1 significantly suppressed the intracellular pH and the expression of mesenchymal markers, thereby blocking the high migration activity in hypoxia. Moreover, treatment with ciglitazone, a potent and selective peroxisome proliferator-activated receptor γ (PPARγ) agonist, modulated hypoxia-enhanced motion in cells via the repression of NHE1. These findings highlight that NHE1 is required for migratory activity through the enhancement of epithelial-mesenchymal transition (EMT) in MDA-MB-231 cells under hypoxic conditions, and we propose new drug repurposing strategies targeting hypoxia based on NHE1 suppression by effective usage of PPARγ agonists.