The Mechanisms and Applications of Imiquimod-Induced Cell Death

• Main Authors: Shi-Wei Huang, 黃士維
• Other Authors: 謝政哲
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/92652711231336863614

博士 === 國立中興大學 === 生物醫學研究所 === 103 === Imiquimod (IMQ), a synthetic Toll-like receptor (TLR) 7/8 ligand, exerts its anti-tumor activity directly by inducing cell death in cancer cells and/or indirectly by activating cellular immune responses against tumor cells. IMQ is currently clinical used as a topical, non-invasive therapy for skin malignancies. However, the mechanisms of IMQ-induced cell death were still unknown. In this study, we investigated the mechanisms of IMQ-induced cell death and generated novel strategies to enhance the anti-tumor activity of IMQ. We demonstrated that IMQ simultaneously induced autophagy and apoptosis in the same cell. Inhibition of IMQ-induced autopahgy enhanced apoptosis and suppression of IMQ-induced apoptosis accelerated autophagy in tumor cells. Both IMQ-induced apoptosis and auotphagy were cooperated for inducing cell death. IMQ-induced the energy sensor AMPK activation might cause translation inhibition and rapidly depleted the anti-apoptotic Bcl-2 family member Mcl-1, but not Bcl-2 or Bcl-xL, to promote intrinsic apoptosis. So that overexpression of Mcl-1 in tumor cells were relative resistant to IMQ-induced apoptosis, but not modulated IMQ-induced autophagy. Furthermore, we also demonstrated that IMQ switched glucose metabolism toward aerobic glycolysis by up-regulation and activation of HIF-1? in tumor cells. This effect was through activation of STAT3 and Akt pathways by increase of intracellular ROS production. The induction of HIF-1? maintained Mcl-1 to protect cell from IMQ-induced apoptosis, thereby targeting of aerobic glycolysis and HIF-1? by 2-DG, 17-AAG, chetomin and YC-1 enhanced the anti-tumor activity of IMQ both in vitro and in vivo. In addition, we also observed that pharmacological inhibition of STAT3 phosphorylation not only reduced IMQ-induced autophagy, but also enhanced IMQ-induced apoptosis in tumor cells. Depletion of ROS suppressed both IMQ-induced autophagy and STAT3 phosphorylation. Thus the activation of STAT3-associated autophagy might attribute to IMQ-induced intracellular ROS. Importantly, these biological effects of IMQ were independent on TLR7 and TLR8. Taken together, our observations provided the possible mechanisms of IMQ-induced autophagy and apoptosis, we also suggested to improve the anti-tumor activity of IMQ by targeting aerobic glycolysis and HIF-1?. Thus, we believe this knowledge of IMQ-induced cell death and the strategies for enhancing anti-tumor activity of IMQ may be used as novel methods to apply in clinical trials in the future.