Pennogenin-3-O-α-L-Rhamnopyranosyl-(1→2)-[α-L-Rhamnopyranosyl-(1→3)]-β-D-Glucopyranoside (Spiroconazol A) Isolated from Dioscorea bulbifera L. var. sativa Induces Autophagic Cell Death by p38 MAPK Activation in NSCLC Cells

In our previous study, we reported the isolation of pennogenin-3-O-α-L-rhamnopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→3)]-β-D-glucopyranoside (spiroconazol A), a steroidal saponin, from the flowers of Dioscorea bulbifera L. var. sativa. In the present study, we aimed to investigate the effects of spiroconazol A on autophagy and its underlying mechanisms in A549 and NCI-H358 human non-small cell lung cancer (NSCLC) cells. Spiroconazol A inhibited the proliferation of NSCLC cells in a concentration- and time-dependent manner. To determine the type of programmed cell death induced by spiroconazol A, we performed a characterization of apoptosis in spiroconazol A-treated A549 cells. Our results showed that spiroconazol A significantly suppressed A549 cell viability but did not influence cell apoptosis because phosphatidylserine and caspase activation were not detected. Furthermore, spiroconazol A treatment upregulated the expression of LC3-II and autophagy-related Beclin-1 protein, suggesting that spiroconazol A induces autophagy in A549 cells. Moreover, spiroconazol A activated the phosphorylation of p38 mitogen-activated protein kinase (MAPK) but did not affect the phosphorylation of Janus kinase or ERK1/2. Notably, SB203580, a p38 MAPK inhibitor, had a significant inhibitory effect on spiroconazol A-induced autophagic cell death in A549 cells. Our results indicated that spiroconazol A-induced autophagy is dependent on p38 MAPK signaling and has potential as a therapeutic target in NSCLC.