Glucocorticoids Induce Drug Resistance To Chemotherapy By Blunting Cellular Senescence In Non-Small-Cell Lung Cancer

Lung cancer is the leading cause of cancer-related mortality worldwide, with nearly1.4million death each year. Non-small cell lung cancer (NSCLC), which includes adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and bronchioloalveolar carcinoma, accounting for nearly85%of all cases of lung cancer. Pemetrexed (PEM) is a novel and multitargeted antifolate used as an antineoplastic agent for NSCLC and pleural mesothelioma. As one of the "third-generation" cytotoxic agents, PEM has demonstrated efficacy when given in combination with a platinum compound in patients with advanced NSCLC. And in patients with adenocarcinoma histology, the PEM and DDP regimen was associated with a superior median survival, thus setting the precedent for histology-based treatment selection for patients with NSCLC. Generally, dexamethasone(DEX) would be recommended at each cycle and administered orally for3days, beginning1day before PEM and DDP administration. However, some patients unavoidably caused disease progression after a period of progression-free survival. The mechanisms of PEM+DDP resistance have gained great attention. Recent studies have shown that DEX could render cancer cells more insensitive to cytotoxic drug therapy. So we are wondering whether DEX co-medication is associated with PEM and DDP resistance to some extent.The tumor microenvironment is a complex tissue comprising variabel numbers of tumor cells and stromal cells, such as fibroblasts and endothelial cells. Cytokines are key molecules controlling autocrine or paracrine communications within and between these individual cell types. There is accumulating evidence that the tumor microenvironment contributes to tumor growth, progression and drug resistance. Therapy induced senescence (TIS) is an alternative strategy which permanently disables the proliferative capacity of cells without inducing cancer cell death. Senescent cells also secrete factors which named senescence associated secretory phenotypes (SASPs) that alter tissue microenvironments. Some cytotoxic drugs can induce DNA damage and TIS during the therapy course. So we need to know whether PEM and DDP can induce therapy induced cellular senescence in NSCLC and whether DEX co-medication could influence TIS and the secretory of SASPs.Bear this in mind, in the following study, we evaluated the influence of DEX co-medication when combined with PEM or DDP, respectively. Also, we detected the changes of cellular senescence in the presence or absence of DEX. Part One:Dexamethasone reduces sensitivity to cisplatin by blunting p53-dependent cellular senescence in Non-Small Cell Lung CancerIntroduction:Dexamethasone (DEX) co-treatment has proved beneficial in NSCLC patients, improving clinical symptoms by the reduction of side effects after chemotherapy. However, recent studies have shown that DEX could render cancer cells more insensitive to cytotoxic drug therapy, but it is not known whether DEX co-treatment could influence therapy-induced senescence, and unknown whether it is in a p53-dependent or p53-independent manner.Methods:We examined in different human NSCLC cells lines and detected cellular senescence after cisplatin treatment in the presence or absence of DEX. The in vivo effect of the combination of DEX and cisplatin was assessed by tumor growth experiments using human lung cancer cell lines growing as xenograft tumors in nude mice.Results:Co-treatment with DEX during chemotherapy in NSCLC resulted in increased tumor cell viability and inhibition of TIS compared with cisplatin treated group. DEX co-treatment cells exhibited the decrease of DNA damage signaling pathways proteins, the lower expression of p53and p21CIP1, the lower cellular secretory program and down-regulation of NF-κB and its signaling cascade. DEX also significantly reduced cisplatin sensitivity in vivo.Conclusions:Our results underscore that DEX reduces chemotherapy sensitivity by blunting therapy induced cellular senescence after chemotherapy in NSCLC, which may, at least in part, in a p53-dependent manner. These data therefore raised concerns about the widespread combined use of GCs with antineoplastic drugs in the clinical management of cancer patients. Part Two:Senescence-Associated Secretory Phenotype Mediates the Cytotoxic Activity of Pemetrexed in Non-Small-Cell Lung CancerIntroduction:Pemetrexed (PEM) is a novel and multitargeted antifolate used as an antineoplastic agent for non-small cell lung cancer (NSCLC) and pleural mesothelioma. Although dexamethasone (DEX) is recommended to be co-administered with PEM during the chemotherapy to reduce toxicity, it has been reported to induce drug resistance. However, it is not clear yet whether DEX co-administration could affect PEM efficacy or not on chemotherapy.Methods:We established NSCLC cell lines and examined the effects of DEX on PEM sensitivity in vitro and in xenograft models.Results:DEX co-adminstration promoted cell growth and weakened senescence growth arrest, such as altered secretions of proinflammatory and mitogenic cytokines, reminiscent of a senescence associated secretory phenotype (SASP). We showed that DEX co-adminstration altered SASP expression in NSCLC after PEM treatment. We also identified traits similar to those of cancer stem cells (CSCs) following SASP signaling. CSCs in DEX co-adminstration group were subsequently found to be less sensitive towards PEM treatment as measured by cell proliferation and generation of tumor spheres in the presence of PEM. Survival molecule Bcl-2may involve in this process and blockage of Bcl-2could reverse altered senescence and CSCs abilities, thus alleviated PEM insensitivity.Conclusion:As such, DEX might suppress the antitumor activity of PEM through alterd SASP level which had induced traits simliar to CSCs. Extra caution need to be required when PEM and DEX were jointly adminstered in NSCLC patients chemotherapy.