Therapeutic Combination of Novel Mitochondrial Hsp90 Inhibitors, Gamitrinibs, with Phosphatidylinositol 3-Kinase Inhibitors Exerts Therapeutic Activity Against Glioblastoma In Vivo and In Vitro without Significant Toxicity
Markus D Siegelin, Dario C Altieri. Columbia University College of Physicians & Surgeons, New York, NY; The Wistar Institute Cancer Center, Philadelphia, PA
Background: The identification of novel effective treatment strategies for glioblastoma WHO IV remains a challenge. Recent data demonstrated that Heat-shock-protein 90 (Hsp90) is preferentially over-expressed in tumor mitochondria. Gamitrinibs are a novel class of Hsp90 inhibitors that inhibit mitochondrial Hsp90 activity. As many primary glioblastomas harbor well characterized genetic alterations of molecules of the phosphatidylinositol 3-kinase (PI3-Kinase) pathway, a combinatorial targeted approach of the PI3-kinase and mitochondrial Hsp90 might be a worthwhile treatment strategy for high-grade gliomas.
Design: Glioma cell lines were treated with Gamitrinibs, PI3-Kinase inhibitors or the combination of both. Apoptosis and caspase-activity were analysed by Annexin V/PI staining and immunoblotting, respectively. U87 glioblastoma cells stably transfected with a luciferase expression plasmid were stereotactically intracranially implanted in the right striatum of nude mice. Animals with established tumors were randomized in 4 groups (4 animals/group) and started on sterile vehicle (cremophor), Gamitrinib, NVP-BEZ235 (PI3-Kinase inhibitor), or the combination of Gamitrinib-G4 and NVP-BEZ235.
Results: The combination of PI3-kinase inhibitors with suboptimal dosages of Gamitrinibs resulted in rapid apoptosis induction in glioblastoma cells. Mechanistically, the combination treatment enhanced the activation of caspases. Similarly vector-driven forced expression of a dominant negative PI3-Kinase construct in U251 glioma cells sensitized glioblastoma cells to Gamitrinib mediated apoptosis. Moreover, in an orthotopic intracranial xenograft mouse model the combination of Gamitrinib-G4 with NVP-BEZ235 (PI3-Kinase inhibitor) significantly reduced proliferation of tumor cells and significantly extended animal survival in the combination group (Gamitrinib+NVP-BEZ235) as compared to vehicle-treated, Gamitrinib-G4 and NVP-BEZ235 single treated animals. Most important, the combination of Gamitrinib and NVP-BEZ235 did not reveal significant signs of toxicity in vivo.
Conclusions: Gamitrinibs are powerful mitochondrial Hsp90 inhibitors that in combination with PI3-Kinase inhibitors reveal significant anti-glioma activity both in vitro and in vivo.
Monday, March 19, 2012 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 279, Monday Morning