Focal adhesion kinase (FAK) is a central component of focal adhesions that regulate cancer cell proliferation and migration. Here, we studied the effects of FAK inhibition in glioblastoma (GBM), a fast growing brain tumor that has a poor prognosis. Treating GBM cells with the FAK inhibitor PF-573228 induced a proliferative arrest and increased cell size. PF-573228 also reduced the growth of GBM neurospheres. These effects were associated with increased p27/CDKN1B levels and β-galactosidase activity, compatible with acquisition of senescence. Interestingly, FAK inhibition repressed the expression of the autophagy cargo receptor p62/SQSTM-1. Moreover, depleting p62 in GBM cells also induced a senescent-like phenotype through transcriptional upregulation of p27. Our results indicate that FAK inhibition arrests GBM cell proliferation, resulting in cell senescence, and pinpoint p62 as being key to this process. These findings highlight the possible therapeutic value of targeting FAK in GBM.

Mibefradil and NNC-55-0396, tetralol derivatives with a proven -ability to block T-type calcium channels in excitable cells, reduce cancer cell viability in vitro, causing cell death. Furthermore, they reduce tumor growth in preclinical models of Glioblastoma multiforme (GBM), a brain tumor of poor prognosis. Here we found that GBM cells treated with cytotoxic concentrations of NNC-55-0396 paradoxically increased cytosolic calcium levels through the activation of inositol triphosphate receptors (IP₃R) and ER stress. We used pharmacological inhibitors and gene silencing to dissect the cell death pathway stimulated by NNC-55-0396 in GBM cell lines and biopsy-derived cultures. Calcium chelation or IP₃R inhibition prevented NNC-55-0396-mediated cytotoxicity, indicating that ER calcium efflux is the cause of cell death. Upstream of calcium mobilization, NNC-55-0396 activated the IRE1α arm of the Unfolded Protein Response (UPR) resulting in the nuclear translocation of pro-apoptotic CHOP. Consistent with these findings, silencing IRE1α or JNK1 rescued the cell death elicited by NNC-55-0396. Therefore, we demonstrate that activation of IRE1α and calcium signaling accounts for the cytotoxicity of NNC-55-0396 in GBM cells. The delineation of the signaling pathway that mediates the abrupt cell death triggered by this compound can help the development of new therapies for GBM.