Studies on the mechanisms of action of minocycline as a novel anti-glioma drug

• Main Authors: Wei-TingLiu, 劉威廷
• Other Authors: Po-Wu Gean
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/14180499317193435297

博士 === 國立成功大學 === 基礎醫學研究所 === 101 === Malignant gliomas are among the most devastating cancers. Despite advances in the diagnosis and treatment, the prognosis of patients with malignant gliomas remains very poor. Therefore, exploration of a new approach is timely needed. Minocycline (Mino), a second-generation tetracycline, has marked neuroprotective properties in various models of neurological diseases. Besides its neuroprotection, it has also been demonstrated that Mino has antiangiogenic properties to inhibit tumor growth. This study aims to investigate whether Mino can be used as a potential anticancer agent for malignant glioma and to study the underlying mechanisms of Mino. Two parts are included in my thesis. (1) To investigate whether Mino has the probability of tumor suppression. Cell viability assay showed that Mino induced cell death in malignant glioma cells. Immunostaining indicated that Mino treatment did not induce apoptosis or necrosis, whereas increased autophagic vacuoles in the cytoplasm revealed that the glioma cell death was mediated by autophagy activation in response to Mino treatment. Autophagy has been identified as programmed cell death type II. Besides, AKT/mTOR pathway was suppressed and ERK1/2 pathway was activated in glioma cells upon treatment with Mino. Moreover, Mino effectively inhibited tumor growth in the xenograft tumor model of glioma cells. These results suggest that Mino may kill glioma cells by inducing autophagic cell death. Thus, Mino is a promising agent in the treatment of malignant gliomas. However, when autophagy was inhibited, Mino still induced cell death through the activation of apoptosis. It suggests that unknown mechanisms are involved in the autophagy-apoptosis switch which is induced by Mino. (2) To investigate whether Mino induces autophagy and apoptosis through ER stress and clarify the relationships between autophagy and apoptosis. Endoplasmic reticulum (ER) has emerged as a major site of cellular homeostatic regulation in cancer. We found that Mino activated PERK, an ER stress sensor, in a short time and subsequently increased eIF2α phosphorylation and the expression of CHOP, which are markers of ER stress. It suggested that Mino induced ER stress in prior to activation of autophagy. We also found that ER stress regulator, GRP78 was upregulated in glioma. Mino treatment increased GRP78 expression and reduced the binding of GRP78 with PERK, leading to ER stress. Besides, inhibition of ER stress attenuated the Mino-induced glioma cell death. When autophagy was inhibited, Mino still activated ER stress and induced apoptosis in glioma cells. However, autophagy but not Mino-suppressed AKT/mTOR pathway was attenuated by autophagy inhibitor. These results suggest that Mino induces autophagic cell death primarily by eliciting ER stress response. Autophagy inhibition switches cell death to apoptosis due to the suppression of AKT/mTOR cascades by Mino. In the orthotopic glioma model, bioluminescent imaging showed that Mino inhibited the growth of glioma and prolonged the survival of mice. Inhibition of ER stress but not autophagy attenuated Mino-induced anti-proliferation in vivo. Taken together, these results suggest that Mino triggers apoptosis and autophagic cell death by inducing ER stress. Minocycline has superior penetration across the blood-brain barrier to facilitate the effect of treatment and does not cause damage on normal neuron or glia cells. Coupled to clinical availability and safe track record, this thesis strongly suggested that minocycline is a potential therapeutic agent for malignant glioma.