Kip1/p27 is up-regulated in response to anti-proliferative signals [35] and [36]. In accordance with these observations, our study also revealed an up-regulation of Kip1/p27 and Cip1/p21, and a

decrease in the levels of CDK2, CDK4, HER2 inhibitor cyclins E1 and D1 proteins. These results provide a mechanism by which NX induces cell cycle arrest that results in a decrease in cell proliferation of liver cancer cells. MAPKs are important upstream regulators of transcription factor activation and their signaling is critical to transduction of a wide variety of extracellular stimuli into intracellular cascades, thereby controlling the cellular events such as proliferation, differentiation and apoptosis [37]. Our results demonstrated that NX treatment blocked the phosphorylation, and hence, activation of MAPKs, including ERK1/2 p38, and JNK in liver cancer cells. These findings

are similar to previous Ruxolitinib chemical structure studies where inhibition of ERK1/2, p38 and JNK by chemopreventive agents are capable of preventing skin carcinogenesis [38] and [39]. Apoptotic cell death represents a universal and exquisitely efficient suicidal pathway and an ideal way for elimination of unwanted cells; however, cancerous cells show dysregulation of this mechanism, which makes the cells virtually immortal and resistant to stress stimuli as well as therapeutic agents [40]. Therefore, the apoptotic pathway is widely studied as a potential target for cancer chemotherapy [41] and [42]. In our study, NX treatment to liver cancer cells resulted in a dose-dependent apoptotic cell death, which would contribute to NX-mediated Vitamin B12 cell growth inhibition. In support these findings, prior studies have shown that various chemotherapeutic phytochemicals possess the ability to induce apoptosis in cancer

cells by arresting the cell cycle progression in various phases of cell division [43], [44] and [45]. Furthermore, NX treatment to liver cancer cells results in significant decrease in the levels of Bcl-2 protein along with an increase in the levels of Bax protein, thus enhancing the Bax/Bcl-2 ratio, which favors apoptosis. Increase in Bax/Bcl-2 ratio acts as a proapoptotic signal resulting in the release of cytochrome c protein from mitochondria to cytoplasm, activating the apoptosome, which further leads to auto-activation of caspase 9 and cleavage of pro-caspase 3 to its activated form caspase 3, the executioner caspase [46], [47] and [48]. Caspases are the mediators of execution mechanism of apoptosis, and their activation results in the cleavage of PARP protein, a DNA repair enzyme in the cell, and subsequent DNA degradation and apoptotic death [21]. Since, caspase 8 was not found to be activated after NX treatment in liver cancer cells, it can be deduced that NX-induced apoptosis is mediated via activation of the intrinsic pathway.