Allicin Overcomes Hypoxia Mediated Cisplatin Resistance in Lung Cancer Cells through ROS Mediated Cell Death Pathway and by Suppressing Hypoxia Inducible Factors

Background/aims: The hypoxic microenvironment in NSCLC has been widely accepted as a contributor to both therapeutic resistance and tumor progression. In this study, we have explored Allicin, a key organosulfur compound present in garlic for its previously unreported effectiveness in the heterogeneous hypoxic tumor microenvironment of NSCLC.

Methods: The effect of Allicin on the viability of NSCLC cells was determined by MTT assay. To determine the migration rate of treated cells compared to the control, scratch and transwell migration assays were performed. Flowcytometry was done to explore cell cycle distribution, apoptosis and ROS production in cells. Fluorescence microscopy was used to examine autophagy and DNA damage in cells. Dot blot was done to check genome wide methylation. RNA expression was detected by RT-PCR and protein expression by western blotting.

Results: Allicin significantly decreases cell viability, proliferation and migration of NSCLC cells in both normoxia and hypoxia. It elicits both apoptosis and autophagy pathway in A549 cells by ROS accumulation and facilitating S/G2-M phase arrest in both normoxia as well as hypoxia. We suggest that ROS/MAPK and ROS/JNK signaling pathway together govern the cytotoxic effect of allicin in NSCLC cells. Notably, allicin suppresses the expression of HIF-1α and HIF-2α in hypoxic cells, pointing towards a mechanism of its effectiveness in hypoxia. A long term passive demethylation was observed, with decreased mC and no change in TET expression, thereby ruling out active demethylation by allicin. Furthermore, allicin synergistically enhances growth inhibitory activity of low dose cisplatin to effectively overcome hypoxia induced cisplatin resistance in A549 cells.

Conclusion: Altogether, our results elucidate a potential use of allicin in sensitizing hypoxic and chemoresistant NSCLC to cisplatin-based chemotherapy and provide new, affordable therapeutic strategy with reduced side effects.

Keywords: NSCLC; Hypoxia; Allicin; Reactive Oxygen Species (ROS); Cisplatin.