Exploring the involvement of the unfolded protein response (UPR) in proteasome and histone deacetylase inhibitor induced cytotoxicity in glioblastoma

Abstract

Glioblastomas (GB) are neoplasms of the Central Nervous System characterised by diffusely infiltrative growth, high aggressiveness and poor prognosis, which mainly affect the adult population, imposing low survival rates. The unfolded protein response (UPR) could be an important mechanism that sustains GB cell survival and aggressiveness. Activated by a process related to ER stress, the UPR transduces signals for the regulation of downstream transcription factors aimed at reducing stress or inducing pro-apoptotic programs. The UPR mechanism consists of three main branches, which are initiated by ER transmembrane proteins: IRE1, PERK, and ATF6. PERK is a kinase that phosphorylates eIF2±, decreasing protein synthesis when ER stress occurs and to restore proteostasis. In addition to this mechanism, recent studies in the Kruyt lab have shown a role for PERK in regulating GB stem cell (GSC) differentiation and cell adhesion processes crucial for cell invasion, proliferation and therapy resistance. Recent studies in our lab showed antiglioma activity of proteasome inhibitors in HOG and T98G, GB cell lines, with activation of UPR genes. Furthermore, changes in cell-cell interaction and increased function of metalloproteases, mainly MMP2 and MMP9, are directly related to tumour invasiveness, in which the role of these enzymes is crucial for tumour cells to create new tumour niches. Based on these results, the aim of this project is to evaluate the therapeutic potential of the combination of the proteasome inhibitor, marizomib, and the novel dual inhibitors of histone deacetylase and metalloproteinases (molecules related to PCI-34041 and CGS-25966) in the available GSC models, including upon implantation in zebrafish larvae. Moreover, we will examine the contribution of UPR sensors, IRE1, PERK, and ATF6 in drug cytotoxicity. Furthermore, since drug sensitivity was shown to also depend on cell-cell interactions between GB cells as well as with neuronal and astrocytic cells in the tumour microenvironment, the impact of the drugs on cellular network formation will also be investigated. (AU)