Lactate Promotes Tunneling Nanotube Formation and Reduces Temozolomide Sensitivity in Glioblastoma Cells

Tunneling nanotubes (TNTs) mediate intercellular communication and contribute to cancer progression. Tumour cells produce excess lactate through increased glycolysis, but whether lactate regulates TNT formation has not been studied. Here, we show that lactate promotes TNT formation in U-87 MG glioblastoma (GBM) cells under both glucose-restricted and glucose-replete conditions, with a similar effect in MDA-MB-231 breast cancer cells. This effect depends on lactate uptake and metabolism rather than receptor-mediated signalling: inhibition of monocarboxylate transporter 1 (MCT1) or lactate dehydrogenase (LDH) reduced TNT formation, while exogenous lactate restored TNT formation during LDH inhibition. 3-chloro-5-hydroxybenzoic acid, an agonist of the plasma membrane-localized lactate receptor (GPR81/HCAR1), did not reproduce the effect of lactate. Lactate also increased intercellular mitochondrial transfer, attenuated temozolomide (TMZ)-induced growth suppression of GBM spheroids, and increased expression of the TNT-associated genes CDC42, MYO10 and FSCN1. Inhibition of p300/CBP-mediated lactylation with A-485 reduced both protein lactylation and TNT formation, implicating lactylation in TNT biogenesis. Lactate increased basal and ATP-linked respiration that persisted during MCT1 inhibition and reduced on LDH inhibition, indicating that the effects of lactate on respiration and on TNT formation are at least partly separable. Together, these findings identify lactate as a regulator of TNT formation and link tumour metabolism to intercellular connectivity and TMZ response, highlighting lactate metabolism and lactylation as potential therapeutic targets.