Mechanisms of Glioblastoma Replication: Ca²⁺ Flares and Cl⁻ Currents

Glioblastoma (GBM) is amongst the deadliest types of cancers, with no resolutive cure currently available. GBM cell proliferation in the patient’s brain is a complex phenomenon controlled by multiple mechanisms. The aim of this study was to determine whether the ionic fluxes controlling cell duplication could represent a target for GBM therapy. In this work, we combined multi-channel Ca²⁺ and Cl⁻ imaging, optical tweezers, electrophysiology, and immunohistochemistry to describe the role of ion fluxes in mediating the cell volume changes that accompany mitosis of U87 GBM cells. We identified three main steps: (i) in round GBM cells undergoing mitosis, during the transition from anaphase to telophase and cytokinesis, large Ca²⁺ flares occur, reaching values of 0.5 to 1 μmol/L; (ii) these Ca²⁺ flares activate Ca²⁺-dependent Cl⁻ channels, allowing the entry of Cl⁻ ions; and (iii) to maintain osmotic balance, GBM cells swell to complete mitosis. This sequence of steps was validated by electrophysiological experiments showing that Cl⁻ channels are activated either directly or indirectly by Ca²⁺, and by additional live-cell imaging experiments. Cl⁻ channel blockers with different molecular structures, such as niflumic acid and carbenoxolone, blocked GBM replication by arresting GBM cells in a round configuration. These results describe the central role of Ca²⁺ flares and Cl⁻ fluxes during mitosis and show that inhibition of Ca²⁺-activated Cl⁻ channels blocks GBM replication, opening the way to new approaches for the clinical treatment of GBM.

Implications: Our work identifies ionic fluxes occurring during cell division as targets for devising novel therapies for glioblastoma treatment.