Synergistic growth inhibition mediated by dual PI3K/mTOR pathway targeting and genetic or direct pharmacological AKT inhibition in human glioblastoma models

Molecular genetic aberrations in the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway are common in human cancers including glioblastoma, yet, novel therapeutic approaches targeting this pathway in glioblastoma have not been successful. We hypothesized that molecular profiling in combination with in vitro drug sensitivity testing allows to identify signatures associated with sensitivity or resistance to PI3K/mTOR pathway inhibition. We analyzed the molecular mechanisms determining sensitivity to PI3K/mTOR inhibition using gene silencing or pharmacological target inhibition and proliferation, clonogenicity, or spherogenicity as readouts, in human long-term glioma cell (LTC) lines and glioma-initiating cells (GIC). Cultured glioma cells were universally sensitive to growth inhibition induced by PQR309, a novel, dual pan-PI3K/mTOR antagonist. Cells exhibited profound growth arrest, but little apoptotic or necrotic cell death as confirmed by electron microscopy; yet, there was evidence of senescence. Cell lines with high basal levels of phosphorylated (active) AKT, low levels of phosphorylated (inactive) protein translation repressor eukaryotic initiation factor (eIF) 4E-binding protein 1 (p4E-BP1), and high levels of Ser9-phosphorylated (inactive) glycogen synthase kinase 3 beta (pGSK3β) were more sensitive to PQR309. Accordingly, the activity of PQR309 was synergistically enhanced by AKT gene silencing or direct pharmacological AKT inhibition. In vivo studies confirmed the anti-glioma activity of PQR309 alone or in combination with AKT inhibition in the orthotopic LN-229 glioma xenograft model in nude mice. These data justify to explore combined targeted therapy approaches in glioblastoma that aim at down-regulating AKT function to enhance the therapeutic potential of dual PI3K/mTOR inhibitors.

Conference Scene: Neuro-oncology: a selected review of ASCO 2013 abstracts

ASCO 2013 Annual Meeting, Chicago, IL, USA, 31 May–4 June 2013

The American Society of Clinical Oncology (ASCO) is the largest clinical oncology meeting in the USA that meets annually, and is an exciting forum in which new cancer clinical trials and research data are presented. The ASCO 2013 CNS tumors section comprising of 3 days of posters, oral presentations and over 100 abstracts provided a current overview of neuro-oncology, including both metastatic diseases of the CNS, as well as primary brain tumors. This brief overview selectively highlights presentations featured at this year’s meeting in a manner that will hopefully provide a portrait of a large and multifaceted meeting.