Title

Dual Inhibition Of Sodium-Mediated Proton And Calcium Efflux Triggers Non-Apoptotic Cell Death In Malignant Gliomas

Author Info

William Harley, University of California - Davis
Candace Floyd, University of Alabama - Birmingham
Tamara Dunn, University of California - Davis
Xiao-Dong Zhang, University of California - Davis
Tsung-Yu Chen, University of California - Davis
Manu Hegde, University of California - San Francisco
Hasan Palandoken, California Polytechnic State University - San Luis ObispoFollow
Michael H. Nantz, University of Louisville
Leonardo Leon, University of California - Davis
K.L. Carraway III, University of California - Davis
Bruce Lyeth, University of California - Davis
Fredric A. Gorin, University of California - Davis

Recommended Citation

Postprint version. Published in Brain Research, Volume 1363, December 6, 2010, pages 159-169.

The definitive version is available at https://doi.org/10.1016/j.brainres.2010.09.059.

Abstract

Malignant glioma cells maintain an elevated intracellular pH (pH_i) within hypoxic–ischemic tumormicroenvironments through persistent activation of sodium–proton transport (McLean et al., 2000). Amiloride has been reported to selectively kill human malignant glioma cell lines but not primary astrocytes (Hegde et al., 2004). While amiloride reduces pH_i of malignant gliomas by inhibiting isoform 1 of sodium–proton exchange (NHE1), direct acidification was shown to be cytostatic rather than cytotoxic. At cytotoxic concentrations, amiloride has multiple drug targets including inhibition of NHE1 and sodium–calciumexchange. Amiloride's glioma cytotoxicity can be explained, at least in part, by dual inhibition of NHE1 and of Na⁺- dependent calcium efflux by isoform 1.1 of the sodium–calcium exchanger (NCX1.1) , which increases [Ca²⁺]_i and initiates glioma cell demise. As a result of persistent NHE1 activity, cytosolic free levels of sodium ([Na⁺]i) in U87 and C6 glioma cells are elevated 3-fold, as compared with normal astrocytes. Basal cytosolic free calciumlevels ([Ca²⁺]i) also are increased 5-fold. 2′, 4′-dichlorobenzamil (DCB) inhibits the sodium-dependent calcium transporter (NCX1.1) much more potently than NHE1. DCB was employed in a concentration-dependent fashion in glioma cells to selectively inhibit the forwardmode of NCX1.1 at ≤1 μM, while dually inhibiting bothNHE1 and NCX1.1 at ≥20 μM. DCB (1 μM) was not cytotoxic to glioma cells,while DCB (20 μM) further increased basal elevated levels of [Ca²⁺]i in glioma cells thatwas followed by cell demise. Cariporide and SEA0400 are more selective inhibitors of NHE1 and NCX1.1 than amiloride or DCB, respectively. Individually, Cariporide and SEA0400 are not cytotoxic, but in combination induced glioma cell death. Like amiloride, the combination of Cariporide and SEA0400 produced glioma cell death in the absence of demonstrable caspase activation.

Disciplines

Biochemistry | Chemistry

Copyright

2010 Elsevier.