Inhibition of glioma growth by minocycline is mediated through endoplasmic reticulum stress-induced apoptosis and autophagic cell death

Background. Wehavereported thatminocycline (Mino) induced autophagic death in glioma cells. In the present study, we characterize the upstream regulators that controlautophagyandswitchcelldeathfromautophagic to apoptotic. Methods. Western blotting and immunofluorescence were used to detect the expressions of eukaryotic translation initiation factor 2a (eIF2a), transcription factor GADD153 (CHOP), and glucose-regulated protein 78 (GRP78). Short hairpin (sh)RNA was used to knock down eIF2a or CHOP expression. Autophagy was assessed by the conversion of light chain (LC)3-I to LC3-II andgreenfluorescentproteinpunctaformation.Anintracranial mouse model and bioluminescent imaging were usedtoassesstheeffectofMinoontumorgrowthandsurvival time of mice. Results. The expression of GRP78 in glioma was high, whereas in normal glia it was low. Mino treatment increased GRP78 expression and reduced binding of GRP78 with protein kinase-like endoplasmic reticulum kinase. Subsequently, Mino increased eIF2a phosphorylation and CHOP expression. Knockdown of eIF2a or CHOP reduced Mino-induced LC3-II conversion and glioma cell death. When autophagy was inhibited, Mino induced cell death in a caspase-dependent manner. Rapamycin in combination with Mino produced synergistic effects on LC3 conversion, reduction of the Akt/ mTOR/p70S6K pathway, and glioma cell death. Bioluminescent imaging showed that Mino inhibited the growth of glioma and prolonged survival time and that these effects were blocked by shCHOP. Conclusions. Minoinducedautophagybyelicitingendoplasmic reticulum stress response and switched cell death from autophagy to apoptosis when autophagy was blocked. These results coupled with clinical availability and a safe track record make Mino a promising agent for the treatment of malignant gliomas.