Metformin Sensitizing Colon Cancer Cells To Atmospheric Pressure Low Temperature Plasma

Plasma,the fourth state of matter after solid,liquid and gas,consists of electrons,ions and neutral particles,etc.Atmospheric non-thermal plasma(NTP),produced under normal atmosphere,has been proved to selectively kill cancer cells,cause DNA damage,cell cycle arrest,induce apoptosis of a variety of cancer cells,.inhibit the proliferation,infiltration and migration of cancer cells,inhibit the growth of cancer cells in vivo,reduce tumor size and prolong the life of tumor bearing mice.And NTP has a significant killing effect on a variety of tumor cells,such as skin cancer,colon cancer,breast cancer,cervical cancer,lung cancer and liver cancer.It has been considered that NTP is a new method of cancer treatment in the future.Metformin,a member of the biguanide family,is the most commonly used oral hypoglycemic drug in the treatment of type 2 diabetes.Recent studies have shown that metformin can not only reduce the risk of cancer in patients with type 2 diabetes,but also inhibit the proliferation of breast cancer cells by activating AMPK and inhibiting mTOR.So far,two main effects of metformin have been reported:(1)inhibition of mitochondrial electron transport chain complex;(2)liver kinase B1(LKB1)dependent and independent activation of AMPK.This study explored the sensitization of metformin on NTP killing colon cancer cells and the possible mechanisms.The results showed that as bellow:(1)Metformin significantly enhanced NTP-induced colon cancer cell death,and metformin itself has little effect on cell viability;metformin pretreatment significantly enhances NTP-induced mitochondrial membrane potential depolarization and apoptosis rate,and apoptosis related protein caspase 3/9 activation increased significantly,suggesting that metformin pretreatment effectively promote NTP-induced apoptosis.(2)Metformin effectively reduced cellular aerobic respiration and enhanced glycolysis;metformin pretreatment promoted the reduction of NTP-induced oxidative phosphorylation and enhanced glycolysis,and significantly reduces the production of ATP,suggesting that metformin pretreatment led to the decrease of mitochondrial energy supply.(3)Pretreatment with metformin significantly enhanced the expression of p-AMPK after NTP exposure.When siRNA interfered with the expression of AMPK,the killing effect and apoptosis of colon cancer cells were significantly inhibited,suggesting that AMPK plays a key role in the combination killing effect of metformin and NTP.(4)NTP exposure led to significant increase in the production of superoxide anion in colon cancer cells.After NTP exposure,the production of superoxide anion in cells treated with metformin is significantly higher than those without metformin treatment.The synergistic effect of metformin and NTP(AMPK activation and apoptosis)was significantly alleviated by the treatment of NAC,a kind of ROS scavenger.This study demonstrates that metformin can significantly enhance the mitochondrial oxidative damage induced by NTP,promote apoptosis through the activation of AMPK,showing the synergistic effect of metformin and NTP on colon cancer cells,providing a new method for clinical treatment of colon cancer.