Resveratrol (RV) is a natural component of red wine and grapes that has been shown to be a potential chemopreventive and anticancer agent. However, the molecular mechanisms underlying RV's anticancer and chemopreventive effects are incompletely understood. Here we show that RV treatment inhibits the clonogenic growth of non-small cell lung cancer (NSCLC) cells in a dose-dependent manner. Interestingly, the tumor-suppressive effect of low dose RV was not associated with any significant changes in the expression of cleaved PARP and activated caspase-3, suggesting that low dose RV treatment may suppress tumor cell growth via an apoptosis-independent mechanism. Subsequent studies reveal that low dose RV treatment induces a significant increase in senescence-associated β–galactosidase (SA-β-gal) staining and elevated expression of p53 and p21 in NSCLC cells. Furthermore, we show that RV-induced suppression of lung cancer cell growth is associated with a decrease in the expression of EF1A. These results suggest that RV may exert its anticancer and chemopreventive effects through the induction of premature senescence. Mechanistically, RV-induced premature senescence correlates with increased DNA double strand breaks (DSBs) and reactive oxygen species (ROS) production in lung cancer cells. Inhibition of ROS production by N-acetylcysteine (NAC) attenuates RV-induced DNA DSBs and premature senescence. Furthermore, we show that RV treatment markedly induces NAPDH oxidase-5 (Nox5) expression in both A549 and H460 cells, suggesting that RV may increase ROS generation in lung cancer cells through upregulating Nox5 expression. Together, these findings demonstrate that low dose RV treatment inhibits lung cancer cell growth via a previously unappreciated mechanism, namely the induction of premature senescence through ROS-mediated DNA damage.

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Radiotherapy is routinely used for the treatment of lung cancer. However, the mechanisms underlying ionizing radiation (IR)-induced senescence and its role in lung cancer treatment are poorly understood. Here, we show that IR suppresses the proliferation of human non-small cell lung cancer (NSCLC) cells via an apoptosis-independent mechanism. Further investigations reveal that the anticancer effect of irradiation correlates well with IR-induced premature senescence, as evidenced by increased senescence-associated β-glactosidase (SA-β-gal) staining, decreased BrdU incorporation and elevated expression of p16INK4a (p16) in irradiated NSCLC cells. Mechanistic studies indicate that the induction of senescence is associated with activation of the p53-p21 pathway, and that inhibition of p53 transcriptional activity by PFT-α attenuates IR-induced tumor cell killing and senescence. Gain-of-function assays demonstrate that restoration of p53 expression sensitizes H1299 cells to irradiation, whereas knockdown of p53 expression by siRNA inhibits IR-induced senescence in H460 cells. Furthermore, treatment with Nutlin-3a, a small molecule inhibitor of MDM2, enhances IR-induced tumor cell killing and senescence by stabilizing the activation of the p53-p21 signaling pathway. Taken together, these findings demonstrate for the first time that pharmacological activation of p53 by Nutlin-3a can sensitize lung cancer cells to radiation therapy via promoting IR-induced premature senescence.

Curcumin is known to exhibit anticancer effects on various cancers with selective cytotoxicity in tumor cells. In the present study, the effects of curcumin‑induced multiple PCDs on human non‑small cell lung cancer (NSCLC) cells and the potential molecular mechanisms of apoptosis and autophagy triggered by curcumin via the PI3K/Akt/mTOR signaling pathway were explored, further confirmed by co‑culture of curcumin with mTOR blocker rapamycin and PI3K/Akt inhibitor LY294002. The anti‑proliferation effect of different stimulus was measured by MTT assay. Apoptosis was detected by flow cytometry. Autophagy induction was detected by MDC labeling and western blotting of Beclin1, LC3, and p62 expression. The mRNA and protein expression levels of Akt and mTOR were assayed by real‑time fluorescence quantitative (qRT‑PCR) technique and western blotting. Our results showed that curcumin inhibited the viability of A549 cells time‑ and dose‑dependently. In addition, a dosage-dependent A549 cell apoptosis‑induction phenomena was observed by the curcumin intervention. Moreover, obvious autophagy was induced after curcumin‑treatment, characterized by the formation of fluorescent particles [autophagic vesicles (AVs)] and significant increase in ratio of LC3‑Ⅱ/LC3‑Ⅰ and Beclin1 as well as decreased p62 expression. Furthermore, the effect of curcumin on a substantial downregulation of phosphatidylinositol 3‑kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was observed. It is worth noting that the inhibition of mTOR by rapamycin or of PI3K/Akt by LY294002 augmented curcumin‑induced apoptosis and autophagy, leading to significant inhibition of cell proliferation. From these findings, it can be speculated that curcumin potently inhibit the cell growth of NSCLC A549 cells through inducing both apoptosis and autophagy by inhibition of the PI3K/Akt/mTOR pathway. These results support the potential use of curcumin as a novel candidate in treatment of human lung cancer.

MicroRNAs (miRNAs) are a new class of gene expression regulators that have been implicated in tumorigenesis and modulation of the responses to cancer treatment including that of human non-small cell lung cancer (NSCLC). However, the role of miR-34a in ionizing radiation (IR)-induced senescence in NSCLC cells remains poorly understood. Here we report that IR-induced premature senescence correlates with upregulation of miR-34a expression in NSCLC cells. Ectopic overexpression of miR-34a by transfection with synthetic miR-34a mimics markedly enhances IR-induced senescence, whereas inhibition of miR-34a by transfection with a synthetic miR-34a inhibitor attenuates IR-induced senescence. Clonogenic assays reveal that treatment with miR-34a mimics augments IR-induced cell killing in human NSCLC cells. Mechanistically, we found that the senescence-promoting effect of miR-34a is associated with a dramatic down-regulation of c-Myc (Myc) expression, suggesting that miR-34a may promote IR-induced senescence via targeting Myc. In agreement with this suggestion, knockdown of Myc expression by RNAi recapitulates the senescence-promoting effect of miR-34a and enhances IR-induced cell killing in NSCLC cells. Collectively, these results demonstrate a previously unrecognized role for miR-34a in modulating IR-induced senescence in human NSCLC cells and suggest that pharmacological intervention of miR-34a expression may represent a new therapeutic strategy for improving the efficacy of lung cancer radiotherapy.