| Gastric cancer continues to be a significant health issue, which is second only to lung cancer as a leading cause of cancer deaths worldwide. The incidence of gastric cancer is reported to be especially high in Asia, South America, and Eastern Europe. Surgery remains the mainstay of any curative treatment, however, approximately two-thirds of patients diagnosed with gastric cancer have unresectable locally advanced and/or metastatic disease. But In this way, for stage IV, unradical correction, recurrence and metastasis, chemotherapy has been the main therapeutic approach for preventing relapse and improving survival ratio. Nevertheless, patient prognosis remains very poor, and therapy-associated toxicity remains a problem,the main reasons including the anti-tumor effects of traditional agents is low, leading to the disability of inhibiting the proliferation of cancer cells, and the heterogeneity of tumors induces chemotherapeutic failure of patients for standard chemotherapeutic agents and regimens. Thus, it is necessary to find new compounds and optimized chemotherapeutic agents or regimens for improving the clinical outcomes of gastric cancer patients. The aim of the first chapter of this dissertation: To investigate the anti-tumor and chemosensitizing effects of luteolin on AGS gastric cancer cell, and elucidate the mechanisms. Methods: Gastric cancer AGS cells were treated with luteolin or/and other chemotherapeutic agents. Cell growth was assessed by MTT assay, cell cycle, apoptosis and mitochondrial membrane potential were assessed by flow-cytometric analysis, the expression of major proteins regulating cell cycle and apoptosis was also detected by western blot, the combination index were analyzed by Chou–Talalay equation, and the mechanisms of chemosensitizing effects were explored by molecular virtual docking. Results: Luteolin inhibited the growth of gastric cancer cells in a dose- and time-dependent manner. Flow cytometry revealed that the percentage of cells at G2/M phase increased dose-dependently. The protein levels of Cdc2, cyclin B1 and Cdc25C were reduced and p21/cip1 was up-regulated after the treatment with luetolin. Furthermore, luteolin induced apoptosis in gastric cancer AGS cells. Western blotting showed that luteolin treatment significantly increased the levels of pro-apoptotic proteins, including Caspase-3, 6, 9, Bax and p53, and decreased the levels of anti-apoptotic protein Bcl-2, thus shifting the Bax/Bcl ratio in favor of apoptosis. It was also demonstrated that a combinational treatment of cisplatin and luteolin induced more effectively cell growth inhibition and apoptosis, compared to cisplatin treatment alone, and the molecular docking and western blotting revelaed that stabilizing the p53 might be the mechanism of chemosensitizing effect . Conclusions: These findings indicate the antiproliferative and chemosensitizing effects of luteolin on human gastric cancer AGS cells and luteolin may be a promising candidate agent used in the treatment of gastric cancer. The aim of the second chapter: To investigate the radiosensitizing effects of luteolin in gastric cancer cell line SGC-7901. Methods: Gastric cancer SGC-7901 cells were treated with luteolin or/and irradiation. Cell survival fraction was assessed by colony-forming assay, cell apoptosis were analyzed by EB/AO staining and TUNEL assay, the expression of major proteins involving in apoptosis and radiosensitization were detected by western blot, the activity of Caspase-3 and 9 were analyzed by fluorometric assay, the production of PGE2 were analyzed by ELISA, and the rediosensitizing effect were further assessed on nude mice model. Results: Luteolin could enhance irradiation-induced clonogenic inhibition. EB/AO staining and TUNEL assay also showed synergistic effect of luteolin on irradiation-induced apoptosis.Compared to irradiation only, the activities of Caspase-3 and 9 were also be enhanced by luteolin at various times. Westen blot analysis showed that there were remarkably changes of downregulation of Bcl-2, VEGF, Ang1 and HIF-1α, upregulation of Ang2, and induction of Cytochrome C from mitochondria to the cytosol after co-treatment with luteolin and irradiation. In addition, significantly decreased production of PGE2 was observed in luteolin plus radiation treatment by ELISA. Finally, luteolin significantly enhances the radioresponse of human tumors transplanted into nude mice and can decreases the tumor microvascular density. Conclusions: Our results provide the molecular mechanism of synergistic effect of luteolin combining with irradiation in human gastric cancer cells and indicate luteolin may be a promising radiosensitizer for use in treatment for gastric cancer.The aim of the third and fourth chapters: To determine the predictive clinical values of in vitro MTT chemosensitivity testing for directing chemotherapy in patients with gastric cancer. Methods: (1) The results of MTT chemosensitivity testing on gastric cancer were collected, and the inhibitory and efficacy rates of 16 chemotherapeutic agents were analyzed by different TNM stages and histological types, the clinical data of 353 consecutive patients with gastric cancer treated with MTT-directed chemotherapy or physician's choice chemotherapy from July 1997 to April 2003 were reviewed and analyzed retrospectively, the overall survival were analyzed by Kaplan-Meire method, and the Cox proportional-hazards model was used to calculate the hazard ratios; (2) Studies eligible for systematic review were independent quality assessment and data extraction, data were pooled for meta-analysis on overall survival, morbidity and mortality. Results: (1) The higher inhibitory ratio agents in 16 drugs on gastric cancer specimen were 5-Fu, PY, CDDP, EPI and ACM, and the efficacy rates among different TNM stages and histological types were no significant statistical difference (P>0.05);(2)The 5-year overall survival probability of MSG and CG groups was 47.5% and 45.1%, respectively, the results of subgroup analysis with Cox proportional-hazards model were favored to MSG group. But statistically significant differences in survival probability were not observed between two groups; (3) Seven reports of controlled trials were included for quality data extraction and meta-analysis, a significant improvement in overall survival, morbidity and mortality was associated with MTT chemosensitivity testing based chemotherapy in total patients or subgroup TNM III stage patients (P<0.01), but in TNM IV patients, the overall survival was also higher than control groups (P<0.05), but the morbidity and mortality was not show significant statistical difference (P>0.05). Conclusions: The present meta-analysis indicates that MTT chemosensitivity testing have the predictive clinical values for optimizing selection of chemotherapeutic agents on gastric cancer patients. However, more randomized controlled trials are needed to confirm the results. |
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