Intra-tumor ROS amplification by melatonin interferes in the apoptosis-autophagy-inflammation-EMT collusion in the breast tumor microenvironment

Abstract

Epidemiological as well as experimental studies have established that the pineal hormone melatonin has inhibitory effects on different types of cancers. Several mechanisms have been proposed for the anticancer activities of melatonin, but the fundamental molecular pathways still require clarity. We developed a mouse model of breast cancer using Ehrlich's ascites carcinoma (injected in the 4th mammary fat pad of female Swiss albino mice) and investigated the possibility of targeting the autophagy-inflammation-EMT colloquy to restrict breast tumor progression using melatonin as intervention. Contrary to its conventional antioxidant role, melatonin was shown to augment intracellular ROS and initiate ROS-dependent apoptosis in our system, by modulating the p53/JNK & NF-κB/pJNK expressions/interactions. Melatonin-induced ROS promoted SIRT1 activity. Interplay between SIRT1 and NF-κB/p65 is known to play a pivotal role in regulating the crosstalk between autophagy and inflammation. Persistent inflammation in the tumor microenvironment and subsequent activation of the IL-6/STAT3/NF-κB feedback loop promoted EMT and suppression of autophagy through activation of PI3K/Akt/mTOR signaling pathway. Melatonin disrupted NF-κB/SIRT1 interactions blocking IL-6/STAT3/NF-κB pathway. This led to reversal of pro-inflammatory bias in the breast tumor microenvironment and augmented autophagic responses. The interactions between p62/Twist1, NF-κB/Beclin1 and NF-κB/Slug were altered by melatonin to strike a balance between autophagy, inflammation and EMT, leading to tumor regression. This study provides critical insights into how melatonin could be utilized in treating breast cancer via inhibition of the PI3K/Akt/mTOR signaling and differential modulation of SIRT1 and NF-κB proteins, leading to the establishment of apoptotic and autophagic fates in breast cancer cells.