Identifying drugs for the treatment of glioblastoma (GBM), a rapidly fatal disease, has been challenging. Most screening efforts have been conducted with immortalized cell lines grown with fetal bovine serum, which have little relevance to the genomic features found in GBM patients. Patient-derived neurosphere cultures, while being more physiologically relevant, are difficult to screen and therefore are only used to test a few drug candidates after initial screening efforts. Laminin has been used to generate two-dimensional cell lines from patient tumors, preserving the genomic signature and alleviating some screening hurdles. We present here the first side-by-side comparison of inhibitor sensitivity of laminin and neurosphere-grown patient-derived GBM cell lines and show that both of these culture methods result in the same pattern of inhibitor sensitivity. We used these screening methods to evaluate the dependencies of seven patient-derived cell models: three grown on laminin and four grown as neurospheres, against 56 agents in 17-point dose-response curves in 384-well format in triplicate. This allowed us to establish differential sensitivity of chemotherapeutic agents across the seven patient-derived models. We found that MEK inhibition caused patient-sample-specific growth inhibition and that bortezomib, an FDA-approved proteasome inhibitor, was potently lethal in all patient-derived models. Furthermore, the screening results led us to test the combination of the Bcl-2 inhibitor ABT-263, and the mTOR inhibitor AZD-8055, which we found to be synergistic in a subset of patient-derived GBM models. Thus, we have identified new candidate therapeutics and developed a high-throughput screening system using patient-derived GBM samples.