Involvement of PI3K Pathway in Glioma Cell Resistance to Temozolomide Treatment

Abstract

The aim of the study was to investigate the anticancer potential of LY294002 (PI3K inhibitor) and temozolomide using glioblastoma multiforme (T98G) and anaplastic astrocytoma (MOGGCCM) cells. Apoptosis, autophagy, necrosis, and granules in the cytoplasm were identified microscopically (fluorescence and electron microscopes). The mitochondrial membrane potential was studied by flow cytometry. The activity of caspases 3, 8, and 9 and Akt was evaluated fluorometrically, while the expression of Beclin 1, PI3K, Akt, mTOR, caspase 12, and Hsp27 was determined by immunoblotting. SiRNA was used to block Hsp27 and PI3K expression. Cell migration and localization of Hsp27 were tested with the wound healing assay and immunocytochemistry, respectively. LY294002 effectively diminished the migratory potential and increased programmed death of T98G and MOGGCCM. Autophagy was dominant in MOGGCCM, while apoptosis was dominant in T98G. LY294002 with temozolomide did not potentiate cell death but redirected autophagy toward apoptosis, which was correlated with ER stress. A similar effect was observed after blocking PI3K expression with siRNA. Transfection with Hsp27 siRNA significantly increased apoptosis related to ER stress. Our results indicate that inhibition of the PI3K/Akt/mTOR pathway sensitizes glioma cells to apoptosis upon temozolomide treatment, which was correlated with ER stress. Hsp27 increases the resistance of glioma cells to cell death upon temozolomide treatment.

YTHDF2 promotes temozolomide resistance in glioblastoma by activation of the Akt and NF‐κB signalling pathways via inhibiting EPHB3 and TNFAIP3

“…As previously described, EPHB3 could inhibit lung cancer cell migration and suppress PI3K/Akt signalling in GBM 27,28 . The decreased EPHB3 expression was correlated with the reduced survival rate of GBM patients, and blocking the PI3K/Akt/mTOR pathway sensitised GBM cells to apoptosis upon TMZ treatment 29 . We next discovered that the overexpression of YTHDF2 decreased the protein and mRNA levels of EPHB3 in T98G and LN229 cells, and the knockdown of YTHDF2 enhanced these levels in T98G/TR and LN229/TR cells (Figure 3a, b).…”

“…27,28 The decreased EPHB3 expression was correlated with the reduced survival rate of GBM patients, and blocking the PI3K/Akt/mTOR pathway sensitised GBM cells to apoptosis upon TMZ treatment. 29 We next discovered that the overexpression of YTHDF2 decreased the protein and mRNA levels of EPHB3 in T98G and LN229 cells, and the knockdown of YTHDF2 enhanced these levels in T98G/TR and LN229/TR cells (Figure 3a, b). According to RIP experiment, we found that YTHDF2 could bind to the mRNA of EPHB3 (Figure 3c).…”

Prognostic and Predictive Biomarkers in Gliomas

“…Moreover, PI3K inhibitors, such as XL765, a dual mTOR and PI3K oral inhibitor, are currently examined in glioblastoma patients and a phase I trial is underway [ 135 ]. The recent study conducted by Zając et al proved that inhibition of the PI3K/Akt/mTOR pathway sensitizes glioma cells to apoptosis upon temozolomide treatment [ 137 ]. Furthermore, epigenetic alterations also play a role in the development of the resistance to EGFR inhibitors.…”

Regulation of temozolomide resistance via lncRNAs: Clinical and biological properties of lncRNAs in gliomas (Review)

“…Supporting this, the pan-PI3K inhibitor, PX-866, has been found to block TMZ-induced autophagy, whilst promoting GBM cell death (103). In addition, the activation of PTEN/PI3K/AKT signaling has been reported to be an essential step in the development of TMZ resistance in GBM cells in a MGMT-dependent manner (104)(105)(106).…”