Growth arrest and Apoptosis of Dioscoreanone from Dioscorea membranacea against Human non-small cell lung cancer A549 cells

Dioscoreanone (DN), 1, 4-Phenanthraquinone, has been previously isolated from the ethanolic extract of Dioscorea membranacea Pierre rhizome, and has shown to be potently cytotoxic to lung and breast cancer cells (1). This study further explored its cytotoxicity against two types of lung cancer cells including non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), and also elucidated its molecular mechanisms. Cytotoxicity studies revealed that DN was specifically toxic to all three subtypes of NSCLC, but not to SCLC and normal lung fibroblast cells. The human lung adenocarcinoma cell line A549, one of the three NSCLC subtypes, was used to investigate the cytotoxic mechanisms of DN. The CFSE cell division assay showed that A549 cells treated with 15µM and 30µM DN proliferated more slowly than did control cells. Analysis of cell cycle distribution also indicated that both concentrations caused cell cycle arrest at the G2/M phase with the highest percentage of cells after 48h incubation. Moreover, treatment of these cells with 30µM DN for 72h resulted in a 12 fold-increase in a sub-G1 peak corresponding to apoptotic cells as compared with control cells. With Annexin V/PI assay, phosphatidylserine translocation to the cell surface required for the early apoptotic cells was detected within 24h, and progressively increased in a dose- and time-dependent manner. Importantly, such apoptosis was activated via caspase activation cascade because the highest activity of caspase 3 was found in A549 cells after treatment with 30µM DN for 24h. Moreover, the general caspase inhibitor Z-VAD-FMK completely suppressed DN-induced apoptosis in these cells, thus ascertaining caspase-dependent apoptosis as a major mode of cell death. This study disclosed the molecular mechanisms of DN for the first time and suggests that it may be a potential, natural apoptosis-inducing agent for NSCLC.

References:

[1] Itharat, A. et al. (2003) Org. Lett. 5, 2879 – 2882