Seminars

Recently, we proposed a four-group functional classification of Glioblastoma Multiforme (GBM) that included proliferative/progenitor (PPR), neuronal (NEU), mitochondrial (MTC), and glycolytic/plurimetabolic (GPM) subtypes with prognostic and therapeutic implications as the mitochondrial subtype carries the best survival and exhibits distinct sensitivity to mitochondrial OXPHOS inhibitors. Over the past few years, it has become evident that restricting attention to individual genes and pathways is not beneficial to most cancer patients and the integrated convergence of multi-omics datasets towards druggable targets (i.e., protein kinases) driving the identity of individual tumors and/or tumor subtypes must be charted. To uncover novel therapeutic targets for each functional GBM subtype, we focused on protein kinases for their attractive features as both drivers and drug targets. We designed an unbiased integrative, machine learning-based proteomics/phosphoproteomics network for the identification of Master Kinases (MKs) responsible for effecting key phenotypic hallmarks of each of the four GBM subtypes. We performed the identification and validation of protein kinase C delta (PKCd) and DNA-PKcs as MKs that sustain the GPM and PPR GBM subtypes, respectively. Moreover, we validate the efficacy of specific inhibitor for PKCd and DNA-PK. Functional assessment of the plurimetabolic hallmarks of GPM PDOs, namely glucose uptake and lipid accumulation showed that both activities were significantly compromised by silencing of PKCd which is crucial therapeutic target in the GPM subtype of GBM. For the PPR subtype, DNA-PKcs, one of the three members of the family of phosphatidylinositol 3-kinase related kinases (PIKKs) with principal role in activating various forms of DDR, was experimentally validated as the essential MK. The striking synergistic and lethal effect of inhibition of DNA-PKcs and irradiation in PPR PDOs but not in GPM provided the mechanistic interpretation of therapy resistance in this GBM subtype. As DNA-PKcs inhibitors have been introduced into clinical trials, our findings support the notion that pre-selection of patient with PPR tumors is likely to enhance therapeutic success. It can be used in retrospective studies to evaluate the association of therapeutic response with GBM subtypes or as tool for patient selection in prospective clinical trials.