Glioblastoma Multiforme (GBM) is the most common type of malignant glioma and patients currently have a poor prognosis. This is due to the current therapy regimen, which consists of surgery, radiotherapy and Temozolomide, being ineffective as patients ultimately develop treatment resistance and disease recurrence. In this study we analysed 1172 FDA approved agents to identify novel therapeutics that are effective at reducing GBM cell proliferation. This screen revealed several effective, novel agents belonging to a variety of drug classes. Next, we selected a number of these promising agents for further validation at low concentrations and identified Carfilzomib (CFZ), a 20S proteasome inhibitor, to be capable of reducing GBM cell viability even at 1nM. Furthermore, CFZ is able to suppress GBM cell MMP-2 expression, migration and invasion. Finally, CFZ was also able to enhance radiotherapy and Temozolomide cytotoxicity while the combination of radiotherapy with CFZ was much more lethal to some GBM cell lines compared to radiotherapy coupled with Temozolomide. To identify novel biomarkers for GBM resistance we analysed the expression of 800 microRNAs in GBM cells that were sensitive and resistant to treatment with radiotherapy and Temozolomide. This analysis allowed us to identify several novel miRNAs that were highly dysregulated in resistant cells which may play a part in the treatment resistance seen in the GBM clinical setting. In conclusion, this study showed that the novel agent CFZ is capable in reducing GBM tumourogenicity in vitro and that a number of key microRNAs may be key players in contributing to the pathology of GBM.