Abstract B167: Targeting glioblastoma invasion with GSK-3 inhibitors: Rapid effects on vimentin dynamics.

Abstract

Abstract Tumor cell invasion of surrounding normal brain remains a formidable obstacle to the effective treatment of the lethal brain tumor glioblastoma. Moreover, invasion may be enhanced by radiation and bevacizumab, which are important clinical agents in glioblastoma treatment. At present there are no agents available clinically that specifically target the invading tumor cell population. We previously identified that small molecule inhibitors of the protein kinase GSK-3 (glycogen synthase kinase-3), are able to specifically block glioblastoma invasion in vitro and in vivo, where they also prolong survival in animal models bearing intracranial invasive orthotopic glioblastoma xenografts. GSK-3 is a ubiquitous multifunctional serine/threonine protein kinase involved in many signaling pathways. To better understand the functions of GSK-3 in glioblastoma we used proteomics and gene/microRNA expression profiling to determine the molecular effects of GSK-3 inhibition in glioblastoma cells with the inhibitors Lithium chloride and 6-bromoindirubin-3’-oxime (BIO). This revealed distinct and overlapping effects of each compound, including the expected upregulation of β-catenin targets such as Axin2. Proteomics revealed major changes in the cytoskeleton, with downregulation of the EMT marker vimentin as the most significant alteration. Vimentin is an intermediate filament protein that functions as an organizer of a number of critical proteins involved in attachment, migration, and cell signaling. The downregulation of vimentin was rapid and due to alterations in its dynamics in response to GSK-3 inhibition. GSK-3 and vimentin were shown to associate with each other in glioblastoma cells, and reduction in phosphorylation of vimentin serine 38 was observed in response to treatment with inhibitors. We showed that vimentin is highly expressed in patient glioblastoma samples and higher levels of vimentin are associated with poorer prognosis in glioblastoma patients. Vimentin knockdown also reduced glioblastoma cell migration. The mechanism of action of GSK-3 inhibition in the context of glioblastoma invasion and the potential of developing a therapeutic strategy based on these observations will be discussed. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B167. Citation Format: Sean E. Lawler, Michal O. Nowicki, E. Antonio Chiocca. Targeting glioblastoma invasion with GSK-3 inhibitors: Rapid effects on vimentin dynamics. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B167.