No abstract

the na + /H + exchanger-1 (NHE1) supports tumour growth, making NHE1 inhibitors of interest in anticancer therapy, yet their molecular effects are incompletely characterized. Here, we demonstrate that widely used pyrazinoylguanidine-type NHE1 inhibitors potently inhibit growth and survival of cancer cell spheroids, in a manner unrelated to NHE1 inhibition. Cancer and non-cancer cells were grown as 3-dimensional (3D) spheroids and treated with pyrazinoylguanidine-type (amiloride, 5-(N-ethyl-Nisopropyl)-amiloride (EIPA), 5-(N,N-dimethyl)-amiloride (DMA), and 5-(N,N-hexamethylene)-amiloride (HMA)) or benzoylguanidine-type (eniporide, cariporide) NHE1 inhibitors for 2-7 days, followed by analyses of viability, compound accumulation, and stress-and death-associated signalling. EIPA, DMA and HMA dose-dependently reduced breast cancer spheroid viability while cariporide and eniporide had no effect. Although both compound types inhibited NHE1, the toxic effects were NHE1-independent, as inhibitor-induced viability loss was unaffected by NHE1 CRISPR/Cas9 knockout. EIPA and HMA accumulated extensively in spheroids, and this was associated with marked vacuolization, apparent autophagic arrest, ER stress, mitochondrial-and DNA damage and poly-ADP-ribose-polymerase (PARP) cleavage, indicative of severe stress and paraptosis-like cell death. Pyrazinoylguanidine-induced cell death was partially additive to that induced by conventional anticancer therapies and strongly additive to extracellular-signal-regulated-kinase (ERK) pathway inhibition. Thus, in addition to inhibiting NHE1, pyrazinoylguanidines exert potent, NHE1-independent cancer cell death, pointing to a novel relevance for these compounds in anticancer therapy.

The mechanisms linking tumor microenvironment acidosis to disease progression are not understood. Here, we used mammary, pancreatic, and colon cancer cells to show that adaptation to growth at an extracellular pH (pH e ) mimicking acidic tumor niches is associated with upregulated net acid extrusion capacity and elevated intracellular pH at physiological pH e , but not at acidic pH e . Using metabolic profiling, shotgun lipidomics, imaging and biochemical analyses, we show that the acid adaptation-induced phenotype is characterized by a shift toward oxidative metabolism, increased lipid droplet-, triacylglycerol-, peroxisome content and mitochondrial hyperfusion. Peroxisome proliferator-activated receptor-α (PPARA, PPARα) expression and activity are upregulated, at least in part by increased fatty acid uptake. PPARα upregulates genes driving increased mitochondrial and peroxisomal mass and β-oxidation capacity, including mitochondrial lipid import proteins CPT1A, CPT2 and SLC25A20, electron transport chain components, peroxisomal proteins PEX11A and ACOX1, and thioredoxin-interacting protein (TXNIP), a negative regulator of glycolysis.

No abstract

Solid tumours are often highly acidic compared to normal tissue, and tumour extracellular acidosis contributes to multiple aspects of cancer progression. Now, Anemone et al. in this issue of the British Journal of Cancer provide in vivo evidence that the degree to which various breast cancer cell lines acidify their environment correlates with their ability to metastasise to the lungs. This indicates that measurements of tumour extracellular acidosis have the potential to become a clinical tool for assessing the risk of metastasis.