The engagement of Ras/Raf/MEK/ERK and PLCγ1/PKC pathways regulated by TrkB receptor in resistance of glioma cells to elimination upon apoptosis induction

Abstract

The most aggressive tumors of human central nervous system are anaplastic astrocytoma (AA, III grade) and glioblastoma multiforme (GBM, IV grade) with an extremely bad prognosis. Their malignant character and resistance to standard therapy are correlated to the over-expression of survival pathways such as Ras/Raf/MEK/ERK and PLCγ1/PKC regulated by TrkB receptor. Therefore, the aim of this study was to investigate the engagement of those pathways in human glioma cells resistance for apoptosis induction by Temozolomide treatment. Two cancer MOGGCCM (AA) and T98G (GBM) and normal human astrocytes (NHA) cell lines were utilized. The tested inhibitors single and simultaneous action with Temozolomide affection on apoptosis induction was analyzed by MTT, microscopic observations and flow cytometry. Bcl-2:beclin-1 complexes occurrence was also assessed. siRNAs were used for direct proof of tested pathways engagement in gliomas resistance to apoptosis elimination. The most effective in eliminating gliomas with minimal astrocyte damage was 5 μM PLCγ1 inhibitor (U-73122) for MOGGCCM and 15 μM for T98G cells, and 1 μM LOXO-101 for all cancer cells. Sorafenib, Temozolomide, U-73122, and LOXO-101 effectively eliminate cancer cells. Single applications of sorafenib and Temozolomide were effective, but had lower efficiency than U-73122 and LOXO-101. These drugs induced apoptosis, affecting mitochondrial membrane potential and caspases 3, 8, and 9 activity. The study found that a Bcl-2:beclin-1 complex formation was observed when apoptosis was dominant. Inhibiting the pathways regulated by TrkB receptor combined with Temozolomide action, led to successful gliomas elimination. Those results might serve as basis for modern targeted treatment development.