Combined inhibition of Bcl-2/Bcl-xL and Usp9X/Bag3 overcomes apoptotic resistance in glioblastoma in vitro and in vivo

// Georg Karpel-Massler 1 , Chang Shu 1 , Lily Chau 1 , Matei Banu 2 , Marc-Eric Halatsch 3 , Mike-Andrew Westhoff 4 , Yulian Ramirez 5 , Alonzo H. Ross 5 , Jeffrey N. Bruce 2 , Peter Canoll 1 and Markus D. Siegelin 1 1 Department of Pathology and Cell Biology, Columbia University Medical Center, New York, USA 2 Department of Neurosurgery, Columbia University Medical Center, New York, USA 3 Department of Neurosurgery, Ulm University Medical Center, Ulm, Germany 4 Department of Pediatrics and Adolescent Medicine, Ulm University Medical Center, Ulm, Germany 5 Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Massachusetts, USA Correspondence to: Markus D. Siegelin, email: // Keywords : glioblastoma, BH3-mimetic, apoptotic resistance, ABT263, GX15-070 Received : March 12, 2015 Accepted : April 10, 2015 Published : May 04, 2015 Abstract Despite great efforts taken to advance therapeutic measures for patients with glioblastoma, the clinical prognosis remains grim. The antiapoptotic Bcl-2 family protein Mcl-1 is overexpressed in glioblastoma and represents an important resistance factor to the BH-3 mimetic ABT263. In this study, we show that combined treatment with ABT263 and GX15-070 overcomes apoptotic resistance in established glioblastoma cell lines, glioma stem-like cells and primary cultures. Moreover, this treatment regimen also proves to be advantageous in vivo . On the molecular level, GX15-070 enhanced apoptosis by posttranslational down-regulation of the deubiquitinase, Usp9X, and the chaperone Bag3, leading to a sustained depletion of Mcl-1 protein levels. Moreover, knock-down of Usp9X or Bag3 depleted endogenous Mcl-1 protein levels and in turn enhanced apoptosis induced through Bcl-2/Bcl-xL inhibition. In conclusion, combined treatment with ABT263 and GX15-070 results in a significantly enhanced anti-cancer activity in vitro as well as in vivo in the setting of glioblastoma. Both drugs, ABT263 and GX15-070 have been evaluated in clinical studies which facilitates the translational aspect of taking this combinatorial approach to the clinical setting. Furthermore we present a novel mechanism by which GX15-070 counteracts Mcl-1 expression which may lay a foundation for a novel target in cancer therapy.