Background: 5'-Nitro-indirubinoxime (5'-NIO) is a new derivative of indirubin that exhibits anti-cancer activity in a variety of human cancer cells. However, its mechanism has not been fully clarified.
Methods: Human salivary gland adenocarcinoma (SGT) cells were used in this study. Western blot and RT-PCR analyses were performed to determine cellular Notch levels. The cell cycle stage and level of apoptosis were analyzed using flow cytometry analysis.
Results: 5'-NIO significantly inhibited the mRNA levels of Notch-1 and Notch-3 and their ligands (Delta1, 2, 3, and Jagged-2) in SGT cells. Immunocytochemistry analysis showed that 5'-NIO specifically decreased the level of Notch-1 in the nucleus. In addition, 5'-NIO induced G1 cell cycle arrest by reducing levels of CDK4 and CDK6 in SGT cells. Using flow cytometry and immunoblotting analysis, we found that 5'-NIO induces apoptosis following the secretion of cytochrome c and the activation of caspase-3 and caspase-7. Intracellular Notch-1 overexpression led to a decrease in G1 phase arrest and an inhibition of 5'-NIO-induced apoptosis.
Conclusion: These observations suggest that 5'-NIO induces cell cycle arrest and apoptosis by down-regulating Notch-1 signaling.
General significance: This study identifies a new mechanism of 5'-NIO-mediated anti-tumor properties. Thus, 5'-NIO could be used as a candidate for salivary gland adenocarcinoma therapeutics.
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