TAMI-17. INDUCTION OF SYNTHETIC LETHALITY BY ACTIVATION OF MITOCHONDRIAL CLPP AND INHIBITION OF HDAC1/2 IN GLIOBLASTOMA

Abstract

Abstract Activation of the mitochondrial ClpP protease is an innovative therapeutic concept and the identification of synthetic lethal interactions may foster the development of novel therapies for glioblastoma (GBM). By integration of a transcriptome, metabolite and U-13C-glucose tracing analyses, we showed that activation of the mitochondrial ClpP protease through constitutively active ClpP (Y118A) or utilization of second-generation imipridone compounds (ONC206 and ONC212) in combination with genetic interference of HDAC1 and HDAC2 as well as with global (Panobinostat) and selective (Romidepsin) HDAC inhibitors caused synergistic reduction of viability in established, neuro-sphere and patient-derived xenograft (PDX) cultures of human GBM, which was mediated by interference with tricarboxylic acid cycle activity and GBM cell respiration. Notably, human astrocytes were significantly less susceptible to the combination treatment of HDAC-inhibitors and ClpP activators. The reduction of GBM viability occurred independent of TP53 status and was accompanied by activation of cell death with apoptotic features along with cleavage of caspases regulated chiefly by Bcl-xL and Mcl-1. Importantly, knockdown of the ClpP protease or ectopic expression of a ClpP D190A mutant almost completely rescued from the inhibition of oxidative energy metabolism as well as from the reduction of cellular viability by ClpP activators and the combination treatment, suggesting critical involvement of this protein. Finally, utilizing GBM PDX models, we demonstrated that the combination treatment of HDAC-inhibitors and imipridones reduced tumor growth and prolonged host survival more potently than single treatments or vehicle in vivo. Collectively, these observations suggest that the efficacy of HDAC inhibitors might be significantly enhanced through ClpP activators in model systems of human GBM.