gms | German Medical Science

Objective: The PI3K/Akt signaling pathway and its downstream effector mTOR are known to play an important role in the regulation of cell growth and have recently been evaluated as a target for the treatment of a variety of tumors. Increasing evidence suggests its involvement in glioma cell survival, but to date little is known about mTOR in more benign tumor diseases like meningiomas. This study aims to further elucidate the role of the pro-survival PI3K/Akt/mTOR pathway in the proliferation of human meningiomas, and to assess the use of specific mTOR inhibitors as novel therapeutic agents.

Method: MTT and BrdU assays of primary human meningioma cell cultures and the permanent meningioma cell lines BenMen 1, and HBL 52 were used to investigate the viability and proliferation inhibitory effects of the mTOR inhibitors Everolimus and Temsirolimus, respectively. Apoptosis analysis proceeded by detecting the cleavage of caspase-3 and PARP, whereas autophagy was analyzed by detection of cleaved LC3B-II. The levels of proteins were determined by Western blotting. Furthermore, nuclear fragmentation analysis after mTOR-inhibition was conducted by immunofluorescence.

Results: Inhibition of mTOR and its active isoform phos-mTOR by Everolimus and Temsirolimus led to a significant reduction of viability as well as inhibition of proliferation of human meningioma cells in a time and concentration-dependent manner. There was no relevant difference of efficacy of mTOR inhibition concerning primary cell cultures and permanent cell lines. mTOR inhibition in meningioma cells induced apoptosis in a caspase-dependent manner. Apoptosis was accompanied by defective autophagy, demonstrated in nuclear fragmentation analysis and proven by the detection of cleaved LC3B-II.

Conclusions: The ability of Everolimus and Temsirolimus to abrogate phos-mTOR activation and by this to interrupt PI3K/Akt signaling in human meningiomas, leading to proliferation inhibition and induction of apoptosis, warrants mTOR to be investigated as a potent target in anti-meningioma therapy.