Inhibition of autophagy enhances timosaponin AIII-induced lung cancer cell apoptosis and anti-tumor effect in vitro and in vivo

Aims: Timosaponin AIII (TAIII), an active component with anti-tumor activity from Anemarrhena asphodeloides Bunge, can induce both autophagy and apoptosis of cancer cells. The present study aimed to reveal the promoting or inhibiting role of TAIII-induced autophagy on TAIII-induced apoptosis, to determine the respective upstream signaling pathways for TAIII-induced autophagy and apoptosis; and to observe the therapeutic potential of TAIII in human non-small cell lung cancer in vivo.

Methods and materials: WST-1 assay was used to determine the effect of TAIII on cell growth and proliferation. Apoptosis was detected by DAPI staining and flow cytometry. Autophagy was verified by immunofluorescence and transmission electron microscopy. Western blot was used to determine the levels of protein expression. Furthermore, the anti-tumor activity of TAIII was observed in nude mice.

Key findings: TAIII at high concentrations from 10 μM to 30 μM induced both autophagy and apoptosis in human non-small cell lung cancer cells in a time- and concentration-dependent manner. TAIII at low concentration (1 μM) only induced autophagy. The AMP-activated protein kinase (AMPK) signaling pathway was identified to be responsible for TAIII-induced autophagy both at high or low concentrations. The MAPK/Erk1/2 signaling pathway was identified to be responsible for TAIII-induced apoptosis at the high concentration (20 μM). TAIII-induced autophagy protected cancer cells from apoptosis, and combination of TAIII and autophagy inhibitor showed higher anti-cancer activity.

Keywords: Apoptosis; Autophagy; Non-small cell lung cancer; TAIII.