Microwave hyperthermia enhances the sensitivity of lung cancer cells to gemcitabine through reactive oxygen species­induced autophagic death.

The pleiotropic effects of hyperthermia on cancer cells have been well documented, and microwave hyperthermia (MWHT) has been widely applied for multifarious cancer treatment. However, the mechanisms underlying the anticancer effect of MWHT combined with gemcitabine (GEM) remain poorly understood. The aim of the present study was to investigate the role of autophagy in the thermo­chemotherapy of human squamous cell lung carcinoma cells. It was observed that MWHT combined with GEM potently suppressed the viability of NCI­H2170 and NCI­H1703 cells, and induced G0/G1 cell cycle arrest. Notably, MWHT with GEM induced autophagy, as indicated by the formation of autophagic vacuoles, downregulation of p62 and upregulation of light chain 3­II. It was further demonstrated that the autophagy was due to the production of reactive oxygen species (ROS), whereas N­acetyl cysteine, an ROS scavenger, attenuated the level of autophagy. However, when the autophagy inhibitor 3­methyladenine was used, there was no significant change in the production of ROS. Furthermore, it was observed that MWHT combined with GEM downregulated the protein expression levels of phosphoinositide 3­kinase (PI3K), phosphorylated (p)­PI3K, protein kinase B (AKT), p­AKT, mammalian target of rapamycin (mTOR), p­mTOR, phosphorylated S6 (pS6) and p70 S6 kinase, which are associated with autophagy. In addition, the results demonstrated that ROS served as an upstream mediator of PI3K/AKT/mTOR signaling. In light of these findings, the present study provides original insights into the molecular mechanisms underlying the cell death induced by MWHT combined with GEM, and this may be a promising approach for the treatment of human squamous cell lung carcinoma.