Abstract
Recent experimental data showed that the PI3K pathway contributes to resistance to temozolomide (TMZ) in paediatric glioblastoma and that this effect is reversed by combination treatment of TMZ with a PI3K inhibitor. Our aim is to assess whether this combination results in metabolic changes that are detectable by nuclear magnetic resonance (NMR) spectroscopy, potentially providing metabolic biomarkers for PI3K inhibition and TMZ combination treatment. Using two genetically distinct paediatric glioblastoma cell lines, SF188 and KNS42, in vitro 1H-NMR analysis following treatment with the dual pan-Class I PI3K/mTOR inhibitor PI-103 resulted in a decrease in lactate and phosphocholine (PC) levels (P<0.02) relative to control. In contrast, treatment with TMZ caused an increase in glycerolphosphocholine (GPC) levels (P≤0.05). Combination of PI-103 with TMZ showed metabolic effects of both agents including a decrease in the levels of lactate and PC (P<0.02) while an increase in GPC (P<0.05). We also report a decrease in the protein expression levels of HK2, LDHA and CHKA providing likely mechanisms for the depletion of lactate and PC, respectively. Our results show that our in vitro NMR-detected changes in lactate and choline metabolites may have potential as non-invasive biomarkers for monitoring response to combination of PI3K/mTOR inhibitors with TMZ during clinical trials in children with glioblastoma, subject to further in vivo validation.
Highlights
Glioblastomas are very aggressive tumours and are one of the leading causes of brain tumour-related deaths in children [1]
In glioblastoma cells not expressing MGMT, resistance to TMZ was shown to be associated with a PI3K–mediated HOX/stem cell gene signature, and this resistance was reversed by inhibition of the PI3K signalling pathway using the dual pan-class I PI3K/mTOR inhibitor PI-103 [13,14,15]
KNS42 cells were treated for 48 h with the dual pan-Class I PI3K/mTOR inhibitor PI-103 [13,14,15] (2xGI50, GI50 = 1.4 μM), TMZ (2xGI50, GI50 = 900 μM), or simultaneously with both PI-103 and TMZ
Summary
Glioblastomas (grade IV astrocytomas) are very aggressive tumours and are one of the leading causes of brain tumour-related deaths in children [1] These tumours are morphologically similar to malignant gliomas that arise in adults, increasing evidence indicates that the molecular pathways activated in brain neoplasms in children substantially differ from those in adults [2,3,4,5,6]. Results from one study [12] showed that, as in adults, in the majority of paediatric glioblastoma cell lines TMZ resistance was linked to a lack of promoter methylation of the gene encoding the repair protein DNA methyltransferase MGMT (O6-methylguanine-DNA-methyl-transferase). Combination of TMZ with PI3K inhibition may provide one therapeutic strategy for those children who tumours either have innate resistance to, or which acquire resistance to, TMZ treatment
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