ABSTRACT
Glioblastoma (GBM) remains an incurable disease, requiring more effective therapies. Through interrogation of publicly available CRISPR and RNAi library screens, we identified the α-ketoglutarate dehydrogenase (OGDH) gene, which encodes an enzyme that is part of the tricarboxylic acid (TCA) cycle, as essential for GBM growth. Moreover, by combining transcriptome and metabolite screening analyses, we discovered that loss of function of OGDH by the clinically validated drug compound CPI-613 was synthetically lethal with Bcl-xL inhibition (genetically and through the clinically validated BH3 mimetic, ABT263) in patient-derived xenografts as well neurosphere GBM cultures. CPI-613-mediated energy deprivation drove an integrated stress response with an upregulation of the BH3-only domain protein, Noxa, in an ATF4-dependent manner, as demonstrated by genetic loss-of-function experiments. Consistently, silencing of Noxa attenuated cell death induced by CPI-613 in model systems of GBM. In patient-derived xenograft models of GBM in mice, the combination treatment of ABT263 and CPI-613 suppressed tumor growth and extended animal survival more potently than each compound on its own. Therefore, combined inhibition of Bcl-xL along with disruption of the TCA cycle might be a treatment strategy for GBM.
Subject(s)
Aniline Compounds , Caprylates , Glioblastoma , Ketoglutarate Dehydrogenase Complex , Sulfides , Sulfonamides , Synthetic Lethal Mutations , Xenograft Model Antitumor Assays , bcl-X Protein , Animals , Humans , Mice , Activating Transcription Factor 4/metabolism , Activating Transcription Factor 4/genetics , Aniline Compounds/pharmacology , bcl-X Protein/metabolism , bcl-X Protein/genetics , Brain Neoplasms/pathology , Brain Neoplasms/metabolism , Brain Neoplasms/genetics , Brain Neoplasms/drug therapy , Cell Line, Tumor , Citric Acid Cycle/drug effects , Glioblastoma/pathology , Glioblastoma/genetics , Glioblastoma/metabolism , Glioblastoma/drug therapy , Ketoglutarate Dehydrogenase Complex/metabolism , Ketoglutarate Dehydrogenase Complex/genetics , Ketoglutarate Dehydrogenase Complex/antagonists & inhibitors , Proto-Oncogene Proteins c-bcl-2/metabolism , Proto-Oncogene Proteins c-bcl-2/genetics , Sulfonamides/pharmacologyABSTRACT
The positive transcription elongation factor b (P-TEFb) is a critical coactivator for transcription of most cellular and viral genes, including those of HIV. While P-TEFb is regulated by 7SK snRNA in proliferating cells, P-TEFb is absent due to diminished levels of CycT1 in quiescent and terminally differentiated cells, which has remained unexplored. In these cells, we found that CycT1 not bound to CDK9 is rapidly degraded. Moreover, productive CycT1:CDK9 interactions are increased by PKC-mediated phosphorylation of CycT1 in human cells. Conversely, dephosphorylation of CycT1 by PP1 reverses this process. Thus, PKC inhibitors or removal of PKC by chronic activation results in P-TEFb disassembly and CycT1 degradation. This finding not only recapitulates P-TEFb depletion in resting CD4+ T cells but also in anergic T cells. Importantly, our studies reveal mechanisms of P-TEFb inactivation underlying T cell quiescence, anergy, and exhaustion as well as proviral latency and terminally differentiated cells.