| Background and Objective: The gastric carcinoma is one of the most common carcinomas in China. The main therapeutic method is surgical operation followed by chemotherapy, but the therapy is frequently going failure due to the development of tolerance to drug of tumor cells. The tumor cell drug resistance is the tolerance of tumor cells to chemical drugs, and also becomes a popular topic in the current tumor research fields. At present, the main mechanism about the drug resistance development of tumor cells has been considered as multi-drug resistance (MDR), which mainly involves of drug extraction, drug detoxification, drug target change and apoptosis of tumor cells. However, by now the widespread effective method to invert tumor drug resistance has not been established not only in clinic but also in research laboratory. These results let us to explain the problem by a new pathway. Gene mutation is an important way of cells adapting to environment change. Whether can tumor cells escape drug attack by gene mutations of themselves? The main function of mismatch repair system (MMR) is to find and repair the mismatch bases which escape proofreading subunit of DNA polymerase during DNA replication, and avoids the mutation accumulation of hereditary and assures the high fidelity of DNA replication in different cells. In recent years, it was reported that MMR-deficient tumor cells were able to tolerate to methylating drug and selection of cells for drug resistance frequently resulted in loss of MMR, and that the drug resistance could be inverted when the MMR function restored. This suggested that the development of tumor cell drug resistance might relate to the expression of mismatch repair genes. In the past, the study in this field was mainly focused on colon and ovary carcinomas. But the similar change has not been reported in gastric carcinoma. Here we used cisplatin to induce human cell line BGC-823 to become BGC-823/cDDP which was resistant to cisplatin and some other chemical drugs, and then made it as carrier for studying the change of biological characteristics including the development of drug resistance and the protein expressions of LRP, GST-Ï€, hMLH1, hMSH2 of the new cell line. Our goal is to explore the relationship between the development of tumor cells drug resistance and the expressions of mismatch repair gene proteins as hMLH1 and hMSH2, and then to certify that the loss of mismatch repair gene function is an important mechanism to develop drug resistance of tumor cell. We hope to give some helpful results to invert drug resistance in tumor cells.Method: 1.Establishment of a cisplatin-induced human gastric carcinoma drug-resistant cell line BGC-823/cDDP and observation of its biological characteristics. The cell line was established by gradually increasing dose of cisplatin and intermittent administration. Resistance index (RI) and cross-resistance was detected by MTT method. The changes of biological characteristics between two cell lines were observed with light microscopy, and population doubling time, cell cycle distribution, chromosome karyotype analysis were processed to make sure the establishment of drug-resistance cell line. 2. Detection of multi-drug resistance relating proteins and mismatch repair proteins. Immunocytochemistry method was used to detect the protein expressions of LRP,GST-Ï€, hMLH1 and hMSH2 in situ, and protein immunoblot method was used to detect the change of protein expressions of hMLH1 and hMSH2 in order to find out the changes of them between BGC-823/cDDP and BGC-823 cells.Result: 1. BGC-823/cDDP cell line with stable resistance to cisplatin was developed after 8 months and its resistance index was 3.93; BGC-823/cDDP cells exhibited cross-resistance to other chemotherapeutic agents including 5-Fuorouracil, vincristine, icamptothecine and the resistance indexes were 1.87, 2.03 and 2.77, respectively. The morphology changed; population doubling-time prolonged(P<0.01); the cell number of G0/G1 and G2/M decreased while in S phase increased; the chro... |
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