Autophagy Inhibition with Monensin Enhances Cell Cycle Arrest and Apoptosis Induced by mTOR or Epidermal Growth Factor Receptor Inhibitors in Lung Cancer Cells / 결핵및호흡기질환

BACKGROUND: In cancer cells, autophagy is generally induced as a pro-survival mechanism in response to treatment-associated genotoxic and metabolic stress. Thus, concurrent autophagy inhibition can be expected to have a synergistic effect with chemotherapy on cancer cell death. Monensin, a polyether antibiotic, is known as an autophagy inhibitor, which interferes with the fusion of autophagosome and lysosome. There have been a few reports of its effect in combination with anticancer drugs. We performed this study to investigate whether erlotinib, an epidermal growth factor receptor inhibitor, or rapamycin, an mammalian target of rapamycin (mTOR) inhibitor, is effective in combination therapy with monensin in non-small cell lung cancer cells. METHODS: NCI-H1299 cells were treated with rapamycin or erlotinib, with or without monensin pretreatment, and then subjected to growth inhibition assay, apoptosis analysis by flow cytometry, and cell cycle analysis on the basis of the DNA contents histogram. Finally, a Western blot analysis was done to examine the changes of proteins related to apoptosis and cell cycle control. RESULTS: Monensin synergistically increases growth inhibition and apoptosis induced by rapamycin or erlotinib. The number of cells in the sub-G1 phase increases noticeably after the combination treatment. Increase of proapoptotic proteins, including bax, cleaved caspase 3, and cleaved poly(ADP-ribose) polymerase, and decrease of anti-apoptotic proteins, bcl-2 and bcl-xL, are augmented by the combination treatment with monensin. The promoters of cell cycle progression, notch3 and skp2, decrease and p21, a cyclin-dependent kinase inhibitor, accumulates within the cell during this process. CONCLUSION: Our findings suggest that concurrent autophagy inhibition could have a role in lung cancer treatment.

Dual Inhibition of PI3K/Akt/mTOR Pathway and Role of Autophagy in Non-Small Cell Lung Cancer Cells / 결핵및호흡기질환

BACKGROUND: The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling axis has emerged as a novel target for cancer therapy. Agents that inhibit this pathway are currently under development for lung cancer treatment. In the present study, we have tested whether dual inhibition of PI3K/Akt/mTOR signaling can lead to enahnced antitumor effects. We have also examined the role of autophagy during this process. METHODS: We analyzed the combination effect of the mTOR inhibitor, temsirolimus, and the Akt inhibitor, GSK690693, on the survival of NCI-H460 and A549 non-small cell lung cancer cells. Cell proliferation was determined by MTT assay and apoptosis induction was evaluated by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Autophagy induction was also evaluated by acridine orange staining. Changes of apoptosis or autophagy-related proteins were evaluated by western blot analysis. RESULTS: Combination treatment with temsirolimus and GSK690693 caused synergistically increased cell death in NCI-H460 and A549 cells. This was attributable to increased induction of apoptosis. Caspase 3 activation and poly(ADP-ribose) polymerase cleavage accompanied these findings. Autophagy also increased and inhibition of autophagy resulted in increased cell death, suggesting its cytoprotective role during this process. CONCLUSION: Taken together, our results suggest that the combination of temsirolimus and GSK690693 could be a novel strategy for lung cancer therapy. Inhibition of autophagy could also be a promising method of enhancing the combination effect of these drugs.