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

Na+/H+-exchange inhibition by cariporide is compensated via Na+,HCO3--cotransport and has no net growth consequences for ErbB2-driven breast carcinomas

Defense against intracellular acidification of breast cancer tissue depends on net acid extrusion via Na+,HCO3--cotransporter NBCn1/Slc4a7 and Na+/H+-exchanger NHE1/Slc9a1. NBCn1 is increasingly recognized as breast cancer susceptibility protein and promising therapeutic target, whereas evidence for targeting NHE1 is discordant. Currently, selective small molecule inhibitors exist against NHE1 but not NBCn1. Cellular assays-with some discrepancies-link NHE1 activity to proliferation, migration, and invasion; and disrupted NHE1 expression can reduce triple-negative breast cancer growth. Studies on human breast cancer tissue associate high NHE1 expression with reduced metastasis and-in some molecular subtypes-improved patient survival. Here, we evaluate Na+/H+-exchange and therapeutic potential of the NHE1 inhibitor cariporide/HOE-642 in murine ErbB2-driven breast cancer. Ex vivo, cariporide inhibits net acid extrusion in breast cancer tissue (IC50 = 0.18 μM) and causes small decreases in steady-state intracellular pH (pHi). In vivo, we deliver cariporide orally, by osmotic minipumps, and by intra- and peritumoral injections to address the low oral bioavailability and fast metabolism. Prolonged cariporide administration in vivo upregulates NBCn1 expression, shifts pHi regulation towards CO2/HCO3--dependent mechanisms, and shows no net effect on the growth rate of ErbB2-driven primary breast carcinomas. Cariporide also does not influence proliferation markers in breast cancer tissue. Oral, but not parenteral, cariporide elevates serum glucose by ∼1.5 mM. In conclusion, acute administration of cariporide ex vivo powerfully inhibits net acid extrusion from breast cancer tissue but lowers steady-state pHi minimally. Prolonged cariporide administration in vivo is compensated via NBCn1 and we observe no discernible effect on growth of ErbB2-driven breast carcinomas.

A systematic review on the culture methods and applications of 3D tumoroids for cancer research and personalized medicine

Cancer is a highly heterogeneous disease, and thus treatment responses vary greatly between patients. To improve therapy efficacy and outcome for cancer patients, more representative and patient-specific preclinical models are needed. Organoids and tumoroids are 3D cell culture models that typically retain the genetic and epigenetic characteristics, as well as the morphology, of their tissue of origin. Thus, they can be used to understand the underlying mechanisms of cancer initiation, progression, and metastasis in a more physiological setting. Additionally, co-culture methods of tumoroids and cancer-associated cells can help to understand the interplay between a tumor and its tumor microenvironment. In recent years, tumoroids have already helped to refine treatments and to identify new targets for cancer therapy. Advanced culturing systems such as chip-based fluidic devices and bioprinting methods in combination with tumoroids have been used for high-throughput applications for personalized medicine. Even though organoid and tumoroid models are complex in vitro systems, validation of results in vivo is still the common practice. Here, we describe how both animal- and human-derived tumoroids have helped to identify novel vulnerabilities for cancer treatment in recent years, and how they are currently used for precision medicine.

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.

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.

MiR-598-5p inhibits breast cancer tumor growth and lung metastasis by targeting PPAPDC1A

This study aimed to explore the effects of PPAPDC1A on the malignant phenotype of breast cancer (BC) in vivo and in vitro. PPAPDC1A expression was examined in BC tissues and cell lines by real-time polymerase chain reaction and Western blot. In this article, cell proliferation was evaluated by Cell Counting Kit-8 assay and colony formation assay, and cell migration and invasion were evaluated by wound healing assay and transwell assays. Furthermore, in vivo cell growth and pulmonary metastasis experiments were also performed using nude mice. The results showed that compared with normal tissues and cells, the PPAPDC1A expression in BC tissues and cell lines were both significantly increased. The PPAPDC1A targeting sequence significantly inhibited the PPAPDC1A expression and cell proliferation, migration, and invasion. The results of xenograft showed that knockdown of PPAPDC1A inhibited tumor growth and lung metastasis of BC. Then, the Dual-Luciferase Reporter Assay confirmed that miR-598-5p targeted the regulation of PPAPDC1A expression. In addition, the miR-598-5p expression in BC tissues was lower than that in the normal tissues. The rescue experiment showed that PPAPDC1A overexpression reversed the inhibitory effect of miR-598-5p mimic on cell proliferation, migration, and invasion. In conclusion, PPAPDC1A was highly expressed in BC tissues and cell lines, and miR-598-5p inhibited the malignant phenotype of BC by targeting PPAPDC1A.