Antitumor Activity of the Cardiac Glycoside αlDiginoside by Modulating Mcl-1 in Human Oral Squamous Cell Carcinoma Cells

We recently isolated a cardiac glycoside (CG), &alpha
L-diginoside, from an indigenous plant in Taiwan, which exhibits potent tumor-suppressive efficacy in oral squamous cell carcinoma (OSCC) cell lines (SCC2095 and SCC4, IC50 &lt
0.2 &micro
M
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays). Here, we report that &alpha
L-diginoside caused Sphase arrest and apoptosis, through the inhibition of a series of signaling pathways, including those mediated by cyclin E, phospho-CDC25C (p-CDC25C), and janus kinase/signal transducer and activator of transcription (JAK/STAT)3. &alpha
L-diginoside induced apoptosis, as indicated by caspase activation and poly (ADP-ribose) polymerase (PARP) cleavage. Equally important, &alpha
L-diginoside reduced Mcl-1 expression through protein degradation, and overexpression of Mcl-1 partially protected SCC2095 cells from &alpha
L-diginoside&rsquo
s cytotoxicity. Taken together, these data suggest the translational potential of &alpha
L-diginoside to foster new therapeutic strategies for OSCC treatment.