Mechanism of Tumor Inhibitory Potential of Abrus Agglutinin in Oral Squamous Cell Carcinoma

Abstract

Abrus agglutinin (AGG), isolated from Abrus precatorious, a medicinal plant induces antitumor activity in oral squamous cell carcinoma in vitro and in vivo. P53 being mutated in oral cancer, the focus of our study represented to p73, the sibling of p53 and its regulation in DNA damage mediated programed cell death in AGG treated FaDu cells. AGG effectively inhibited the cell viability of different oral squamous cell carcinoma with IC50 value 1-10 μg/ml. AGG selectively inhibited growth and, caused cell cycle arrest and mitochondrial apoptosis through reactive oxygen species (ROS) mediated ATM-p73 dependent pathway in FaDu cells. AGG-induced ROS accumulation was identified as chief mechanism of its effect on apoptosis, DNA damage and DNA-damage response which significantly reversed by ROS scavenger N-acetylcysteine (NAC). Moreover, AGG found to interact with mitochondrial manganese-dependent superoxide dismutase which might inhibit its activity and upshot ROS in FaDu cells. Further, AGG was found to inhibit epithelial-mesenchymal transition (EMT) in p73 dependent manner in epithelial growth factor (EGF) stimulated FaDu cells. Importantly, AGG induced Snail degradation through ubiqutination and Snail overexpression rescued suppression of EMT phenotypes. Confocal imaging and immunoprecipitation data elaborated about the Snail interaction with p73 in EGF stimulated FaDu cells and AGG found to inhibit the interaction of Snail and p73 through Snail degradation. In addition, our work demonstrated the efficiency of AGG on cancer stem-like cells which has high tumorigenic capacity in tumor population. We showed that AGG has a potential role as an integrative therapeutic approach for combating oral cancer by eliminating self-renewal capacity accompanied with apoptosis in orospheres of FaDu cells. Importantly, AGG induced ROS accumulation in orospheres and pretreatment of NAC inhibited AGG mediated caspase-3 activity and β-catenin expression. The present study provided deep insight into the mechanism of AGG-mediated tumor inhibition and elucidated the further scope for the development of cancer therapeutics against oral squamous cell carcinoma.