Bladder tumors have the biological characteristics of easy recurrence, and postoperative treatment with drug intravesical bladder perfusion can significantly improve the prognosis. However, there are still many problems with chemotherapy, among which multidrug resistance (MDR) is one of the important factors of chemotherapy failure, so MDR has become a hot spot in clinical and basic research of tumor in recent years. A variety of factors can cause MDR, among which the P-glycoprotein mechanism has been studied most and widely, and the expression of the protein is affected by a variety of factors.In this experiment, we observe the expression of multidrug resistance gene (MDR-1mRNA) at the level of genes and its effect on clinical biological behavior. 1, Data and Methods 1.1 Study subjects All specimens were taken from surgically resected bladder tumor tissues of patients hospitalized between January 1998 and December 1998 in this undergraduate department, which were found by cystoscopy before surgery and confirmed by pathological examination. Pathologic type: all 30 cases in this group were bladder migratory cell carcinoma, according to WHO pathologic tissue grading: G110 cases, G213 cases, G37 cases. There were 16 cases of primary tumors and 14 cases of recurrent tumors after intravesical instillation of chemotherapeutic agents. Normal controls were normal bladder mucosa beyond 2 cm from the base of the bladder tumor during surgery, all of which were resected intraoperatively and examined histologically as normal. 1.2 Collection and storage of tissue specimens All specimens were collected when the bladder tumors were removed during surgery, and the necrotic tissue in the center of the tumors was avoided during the sampling. Fresh specimens within 2 h after the surgery were used for the experiments, or the specimens were put into an ultra-low-temperature refrigerator at -70 ℃ immediately after the specimens were removed to be preserved for examination. 1.3 Main reagents: AMV reverse transcriptase was purchased from Promega, and TaqDNA polymerase was purchased from the Institute of Genetics, Chinese Academy of Sciences. 1.4 Main instruments Gene Cycler PCR instrument (B10-RAD, USA). 1.5 Detection of the expression level of multidrug resistance gene (MDR1) Quantitative RT-PCR was used. 1.5.1 Tissue total RNA extraction: total RNA extraction in the samples was carried out by the one-step method of isothiocyanic acid, and the extracted total RNA was dissolved by adding 50-100 μL of DEPC deionized water, and then a part of the samples was taken to identify its quality by formaldehyde gel electrophoresis detection and the A260 and A280 were determined by UV spectrophotometry, and A260/A280 was calculated, and the ratios were all greater than 1.8, and its RNA content was calculated based on A260. The ratio of A260/A280 was greater than 1.8, and the RNA content was calculated according to A260. 1.5.2 Synthesis of cDNA by reverse transcription The reverse transcription reaction was carried out in a 50 μL reaction system containing 5 μL of total RNA, 0.5 μg of RNAase inhibitor (Rnasin 40 U, AMV 10 U, dNTP 40 μL), and 0.5 μg of RNAase inhibitor (Rnasin 40 U, AMV 10 U, dNTP 40 μL). 40 μL). The RT was completed in a 42 ℃ water bath for 1 h. The enzyme was inactivated in a 95 ℃ water bath for 5 min and immediately placed in an ice bath, and 50 μL of DEPC was added to prepare a template for the cDNA used for PCR. 1.5.3 PCR amplification reaction: PCR amplification reaction was performed using two pairs of oligonucleotide primers, one of which was the MDR-1mRNAcDNA primer, primer sequence: MDR-1mRNA justice: 5′-CCCATCATTGCAATAGCAGG-3′; antisense: 5′-GTTCAAACTTCTGCTCCTCA-3′. The internal control primer β2-microglobulin was designed with reference to the literature, 5′-ACCCCCCACTGAAAAAGATGA3′-ATCTTCAAACCTCCATGATG. 1.5.4 Judgment of PCR results: after the PCR product was separated by electrophoresis, the positive sample should have three bands with molecular weight sizes of 300 bp and 170 bp, respectively, where 300 bp was the internal standard b2-MG, while the 170 bp product is the MDR-1 mRNA gene. The ratio of the intensity of the two bands (MDR-1mRNA/b2MG) is the relative value of MDR-1mRNA gene expression, according to which the difference in the degree of MDR-1mRNA expression in each sample can be judged. 2. Results The above RT-PCR conditions were applied to 30 bladder tumor specimens and 26 normal bladder mucosa tissues, and the expression of MDR-1mRNA in 26 normal bladder mucosa specimens was 15.4%. 17/30 (56.7%) of the 30 bladder tumors were positive for MDR-1mRNA, and the positivity rates of the G1, G2, and G3 tumors were 40%, 61.5%, 61.5%, and 61.5%, respectively. The positive rates of G1, G2 and G3 tumors were 40%, 61.5% and 71.4%, respectively.The positive rate of 16 primary tumor specimens was 37.5%, and the positive rate of 14 recurrent tumor specimens after chemotherapy was 78.6%. The results suggested that normal bladder mucosal tissues had MDR-1mRNA expression, and the expression of MDR-1mRNA was related to the degree of differentiation of the tumor. There was a significant enhancement of MDR-1mRNA expression in recurrent tumors after chemotherapy. 3, DISCUSSION Resistance of bladder tumor cells to chemotherapeutic agents is a major obstacle to postoperative chemotherapy for bladder tumors. Many tumors in the clinic are still inevitably recurrent in the end after initially effective chemotherapy, and the main reason is the resistance of tumor cells to chemotherapeutic drugs. Commonly used chemotherapeutic drugs related to MDR1 gene include alkylating agents (e.g. BCNU, ME-CCNU, etc.), plant bases (e.g. Vincristine, Vincristine, VM26, etc.), antibiotics (e.g. mitomycin, Adriamycin, Bleomycin, etc.), hormones (e.g. dexamethasone, etc.). These drugs are usually lipophilic compounds with large molecular weights and are commonly used in bladder tumor therapy. When the tumor cells become resistant to one of these drugs, they can simultaneously become cross-tolerant to other types of drugs, therefore, the expression of MDR1 gene in bladder tumors is closely related to the resistance to chemotherapeutic drugs.