TARGETING GLIOBLASTOMA METABOLISM THROUGH mTOR AND MITOCHONDRIAL INHIBITION

PENAO is a potent mitochondrial inhibitor, currently in a Phase 1 clinical trial in Australia as a pan-cancer treatment. Temsirolimus is an inhibitor of the mTOR pathway, a pathway that is highly upregulated in glioblastoma, and has also been shown to interfere with mitochondrial metabolism. The aim of this study is to combine both PENAO and temsirolimus, both potent inhibitors of mitochondrial metabolism, to synergistically impede glioblastoma growth, particularly in patients with an unmethylated MGMT promoter. PENAO and temsirolimus were tested in vitro as single agents and in combination using patient-derived cell lines (PDCLs). Additionally, in an orthotopic mouse model in which the animals were implanted with the PDCL RN1, we combined PENAO (3 mg/kg/day) and temsirolimus (1 mg/kg/day or 5 mg/kg/day). In vitro drug cytotoxic assays using a panel of PDCLs showed promising synergistic effects with PENAO and temsirolimus. IC50 dose of PENAO and temsirolimus combined showed 11- to 20-fold decrease in cell viability. Annexin V-PI assay revealed that the drug combination induced apoptosis in ~90% of the cell population. Unfortunately, in vivo results showed no significant difference between treatment and control groups, and did not extend survival. Although the combination of PENAO and temsirolimus was highly effective in PDCLs in vitro, it did not translate into a significant survival improvement in vivo. Ongoing studies have identified that the concentration levels of PENAO reaching the brain were inadequate to deliver the synergistic effects observed in vitro. Future studies will investigate mechanisms of enhancing drug delivery of PENAO to the brain and mimic the synergistic effect we observed in vitro.