Modulation of glioma cell migration and invasion using Cl- and K+ ion channel blockers

Human malignant gliomas are highly invasive tumors. Mechanisms that allow g lioma cells to disseminate, migrating through the narrow extracellular brai n spaces are poorly understood. We recently demonstrated expression of larg e voltage-dependent chloride (Cl-) currents, selectively expressed by human glioma cells in vitro and in situ (Ullrich et al., 1998). Currents are sen sitive to several Cl- channel blockers, including chlorotoxin (Ctx), (Ullri ch and Sontheimer, 1996; Ullrich et al., 1996), tetraethylammonium chloride (TEA), and tamoxifen (Ransom and Sontheimer, 1998). Using Transwell migrat ion assays, we show that blockade of glioma Cl- channels specifically inhib its tumor cell migration in a dose-dependent manner. Ctx (5 mu M), tamoxife n (10 mu M), and TEA (1 mM) also prevented invasion of human glioma cells i nto fetal rat brain aggregates, used as an in vitro model to assess tumor i nvasiveness. Anion replacement studies suggest that permeation of chloride ions through glioma chloride channel is obligatory for cell migration. Osmo tically induced cell swelling and subsequent regulatory volume decrease (RV D) in cultured glioma cells were reversibly prevented by 1 mM TEA, 10 mu M tamoxifen, and irreversibly blocked by 5 mu M CtX added to the hypotonic me dia. Cl- fluxes associated with adaptive shape changes elicited by cell swe lling and RVD in glioma cells were inhibited by 5 mu M Ctx, 10 mu M tamoxif en, and I mM TEA, as determined using the Cl--sensitive fluorescent dye 6-m ethoxy-N-ethylquinolinium iodide. Collectively, these data suggest that chl oride channels in glioma cells may enable tumor invasiveness, presumably by facilitating cell shape and cell volume changes that are more conducive to migration and invasion.