Novel Targeting of Transcription and Metabolism in Glioblastoma

Abstract

Purpose: Glioblastoma (GBM) is highly resistant to treatment, largely due to disease heterogeneity and resistance mechanisms. We sought to investigate a promising drug that can inhibit multiple aspects of cancer cell survival mechanisms and become an effective therapeutic for GBM patients.Experimental Design: To investigate TG02, an agent with known penetration of the blood-brain barrier, we examined the effects as single agent and in combination with temozolomide, a commonly used chemotherapy in GBM. We used human GBM cells and a syngeneic mouse orthotopic GBM model, evaluating survival and the pharmacodynamics of TG02. Mechanistic studies included TG02-induced transcriptional regulation, apoptosis, and RNA sequencing in treated GBM cells as well as the investigation of mitochondrial and glycolytic function assays.Results: We demonstrated that TG02 inhibited cell proliferation, induced cell death, and synergized with temozolomide in GBM cells with different genetic background but not in astrocytes. TG02-induced cytotoxicity was blocked by the overexpression of phosphorylated CDK9, suggesting a CDK9-dependent cell killing. TG02 suppressed transcriptional progression of antiapoptotic proteins and induced apoptosis in GBM cells. We further demonstrated that TG02 caused mitochondrial dysfunction and glycolytic suppression and ultimately ATP depletion in GBM. A prolonged survival was observed in GBM mice receiving combined treatment of TG02 and temozolomide. The TG02-induced decrease of CDK9 phosphorylation was confirmed in the brain tumor tissue.Conclusions: TG02 inhibits multiple survival mechanisms and synergistically decreases energy production with temozolomide, representing a promising therapeutic strategy in GBM, currently under investigation in an ongoing clinical trial.

Profound, durable and MGMT‐independent sensitivity of glioblastoma cells to cyclin‐dependent kinase inhibition

“…These observations indicate that – theoretically – tumors sensitive to TG02 may not easily develop efficient escape strategies in vivo . Our study complements and extends another recent study exploring the activity of TG02 in different glioma models in vitro and in vivo that focused on synergy with TMZ and changes in energy metabolism . These authors confirmed CDK9 as the main target of TG02 and hypothesized that mitochondrial dysfunction and ATP depletion were the proximate cause of cell death, consistent with our assumption that caspase inhibition delays cell death, but that cell death induced by TG02 can proceed in a caspase‐independent manner.…”

“…TG02 and hypothesized that mitochondrial dysfunction and ATP depletion were the proximate cause of cell death, consistent with our assumption that caspase inhibition delays cell death, but that cell death induced by TG02 can proceed in a caspaseindependent manner. While Su et al observed no activity of TG02 alone in the GL-261 mouse glioma model, 32 we observed moderate single agent activity in two human glioma models, including one GIC model ( Figs. 1g and 1h).…”

“…While Su et al . observed no activity of TG02 alone in the GL‐261 mouse glioma model, we observed moderate single agent activity in two human glioma models, including one GIC model (Figs. g and 1 h ).…”

“…Our study complements and extends another recent study exploring the activity of TG02 in different glioma models in vitro and in vivo that focused on synergy with TMZ and changes in energy metabolism. 32 These authors confirmed CDK9 as the main target of Figure 6. Explorative studies of acquired resistance to TG02.…”

Mitigating Temozolomide Resistance in Glioblastoma via DNA Damage-Repair Inhibition

“…Over-expression of both MGMT and APNG have been linked to resistance to alkylating agents, and are associated with lower survival rates in patients [10,11], while MGMT methylation (a mark of reduced average expression) has been linked to improved survival. Consequently, it has been hypothesized that MGMT and APNG expression or methylation may be used as biomarkers for glioma response to treatment with alkylating agents such as TMZ [12,13,14].…”