Emodin modulates PI3K-AKT pathway to inhibit proliferation, invasion and induce apoptosis in glioma cells

Glioma is a type of tumor that begins in glial cells and occurs in the brain and spinal cord. Glioma forms a major health challenge worldwide. They are hard to treat, not only because of the deregulation in multiple signaling transduction pathways affecting various cellular processes but also because they are not contained in a well-defined mass with clear borders. One of the main pathways deregulated in glioma is PI3K-AKT and its associated downstream targets like NF-ĸB which affects different proteins/transcription factors influencing many aspects of gliomagenesis like epithelial to mesenchymal transition (EMT). A combination of in-silico and in-vitro approaches targeted against specific catalytic isoform (p110δ) of Class IA PI3K with potent and selective inhibitors would maximize the chances of tumor regression. We adopted an in-silico approach to screen a range of natural molecules for a potent p110δ inhibitor and among them, “emodin” was found to be a potential candidate. In vitro, emodin treatment inhibits proliferation, induces apoptosis, modulates astrocytic phenotype, and decreases cell density of glioma cells. Emodin induces changes in the astrocytic phenotype of glioma cells to elongated form with rounded-off, shrunken-down morphology. Emodin was found to contribute to ROS production which leads to apoptosis of glioma cells. The apoptosis induced by emodin was confirmed by propidium iodide staining and ascertained by FACS analysis. We evaluated the effect of emodin on various proteins of PI3K-AKT and downstream targets. We found that emodin treatment decreases the expression of p-AKT, increases expression levels of Iĸ-B, inhibits nuclear translocation of NF-ĸB, and upregulates the phosphorylated form of GSK-3β. Changes at the molecular level of these proteins result in the inhibition/degradation of downstream proteins and transcription factors associated with the growth and proliferation of glioma cells. Inhibition of nuclear translocation of NF-ĸB also inhibits nuclear activation of various protumorigenic signaling pathway mediators involved in EMT such as N-cadherin, β-catenin, Claudin-1. These EMT markers promote invasion, proliferation, migration, and growth in glioma cells. Emodin treatment resulted in changed expression profiles of these EMT markers involved in promoting gliomagenesis. In essence these results suggest that in-vitro emodin treatment remarkably reduces the proliferation of glioma cells possibly targeting multiple pathways involved in tumor growth, proliferation, and development, supporting the rationale and relevance of using multipronged strategies for effective treatment of glioma.