Abstract
Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults. Currently, treatment is focused on achieving maximal safe resection, followed by chemo- and radiotherapy. Although surgery remains the most important therapeutic component, complete surgical resection is virtually impossible, as GBM cells readily infiltrate the adjacent brain parenchyma. One fundamental mechanism for GBM cell migration is the ability of these cells to use cell volume regulation as a driving force of cell infiltration and potentially interfering with apoptosis and cell cycle progression. In this work, we targeted the master regulators of cell volume, the kinases STE20/SPS1-Related Proline-Alanine-Rich Protein Kinase (SPAK) and Oxidative stress-responsive kinase-1) (OSR1) by using a novel proprietary small molecule inhibitor. In order to study the effects of inhibiting SPAK and OSR1, we analyzed cell proliferation and migration. First, we determined the IC50 using six different patient-derived GBM cell lines; we found IC50 values ranging from 0.2–2μM. Next, cell proliferation was determined by cell cycle analysis through Edu labeling. We found a significant decrease in S phase and cell cycle arrest in G2M (p= 0.001, n=6). In addition, cell migration was determined using boyden chamber assay. We found a dose-dependent reduction in cell migration (p=0.001, n=3). These results correlated with the phenomenon observed in an orthotopic murine model of GBM, in which the inhibitor showed a decrease in tumor growth (p=0.0026, n=4) and greater survival rates in vivo (p=0.0046, n=8). When used in combination with radiation therapy, this small molecule inhibitor was capable of radio-sensitizing GBM cells decreasing clonogenicity (p=0.01, n=3) were observed in vitro. In summary, by targeting the SPAK/OSR1 kinases with a small molecule inhibitor, GBM cells become less aggressive, mainly by interfering with cell migration and proliferation and becoming more sensitive to radiation.