Deoxypodophyllotoxin induces cytoprotective autophagy against apoptosis via inhibition of PI3K/AKT/mTOR pathway in osteosarcoma U2OS cells

Background: A natural compound deoxypodophyllotoxin (DPT) possesses potent anti-proliferative and anti-tumor properties on several Cancer types. It triggers cell cycle arrest followed by Apoptosis through various cellular processes. However, it is limited to the action mechanism of DPT-mediated cell death modes via Apoptosis and Autophagy.

Methods: Cell viability assay, morphological changes, annexin-V/propidium iodide (PI) assay, Reactive Oxygen Species (ROS), acridine orange staining, and Western blot analyses were evaluated.

Results: We demonstrated that DPT induced both Apoptosis and Autophagy via production of mitochondrial Reactive Oxygen Species (ROS). DPT suppressed the PI3K/Akt/mTOR signaling cascades to lead Autophagy process, resulting from conversion of LIGHT chain 3-I (LC3-I) into LC3-II and acidic vesicular organelles (AVOs) formation. Even if DPT-induced ROS were occurred in both Apoptosis and Autophagy, inhibition of ROS generation enhanced cell viability. Otherwise, 3-methyladeine (3-MA) impeding on Autophagy accelerated an apoptotic response caused by DPT. Therefore, these findings suggest that DPT triggers cytoprotective Autophagy against cytotoxic Apoptosis.

Conclusion: Autophagy is required for cell survival by inhibition of Apoptosis through down-regulation of PI3K/Akt/mTOR pathway against DPT-induced Apoptosis in U2OS cells.