Investigation of the anti-migratory properties of GSK-3 inhibitors in glioblastoma
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Glioblastoma is the most malignant form of brain cancer. Due to its aggressive nature, extensive research has been performed, but little progress has been made in identifying effective treatment options. Glycogen synthase kinase-3 (GSK-3) is a ubiquitous, multifaceted protein kinase. Previous studies have shown that small molecule inhibitors of GSK-3 block the migration of glioblastoma cells and may prevent spread of tumor in the brain. However, these studies were performed using non-selective GSK-3 inhibitors (LiCl and an indirubin derivative, BIO); thus, it was unclear whether GSK-3 was the most important target. In this study, we used recently generated highly selective GSK-3 inhibitors (CHIR99021, AZD1080, and AZD2858, as well as BIO) to investigate these questions. These were applied to four glioblastoma cell lines: G30, G9, U251, and U1242, in three migration assays: transwell, spheroid, and wound healing (scratch) assay to further assess the suitability of GSK-3 as a target in glioblastoma. We also utilized the ATP Luciferase reporter assay for cell viability to assess the influence of our panel of drugs on cell migration versus viability. In addition, the TOPFlash Luciferase reporter assay was performed as an indicator of the level of GSK-3 inhibition. The TOPFlash assay showed that all GSK-3 inhibitors were able to increase luciferase levels. This indicates that GSK-3 was inhibited in our cells after drug treatment. The transwell assays showed us that the GSK-3 inhibitors were able to block migration significantly in all cell lines tested in a dose-dependent manner. The effectiveness of GSK-3 inhibition in the three-dimensional collagen spheroid assays was cell line-dependent, with the non-selective GSK-3 inhibitor BIO showing the most potent effects. Cell migration was not blocked by any of the three selective GSK-3 inhibitors in the wound healing scratch assay. Thus we have found that the three distinct highly selective inhibitors of GSK-3 block glioblastoma cell migration, but only work consistently in the transwell assay. Therefore, we conclude that GSK-3 might be important in the contraction and morphological changes necessary for glioblastoma cells to migrate through the 8 micron pores in the transwell. Further investigation into this observation is necessary. Though results were variable between assays, we conclude that the inhibition of GSK-3 is a promising potential therapeutic strategy for glioblastoma treatment.