Relatively low expression of multidrug resistance-1 (MDR-1) and its possible clinical implication in gastric cancers

New insights into the mechanisms of gastric cancer multidrug resistance and future perspectives

Gastric cancer is still the second leading cause of cancer death worldwide. Chemotherapy is one of the major treatment options for advanced gastric cancer. The efficacy of chemotherapy for gastric cancer is poor due to insensitivity and the development of multidrug resistance (MDR). Gastric cancer MDR involves a large number of molecules and complex mechanisms. Classical drug-resistant molecules, such as P-glycoprotein/ABCB1 and MRP1/ABCC1, have been found to play important roles in mediating MDR in some gastric cancers. In recent years, new molecules and mechanisms have been found to be associated with the development of gastric cancer MDR and might provide new targets for tackling gastric cancer MDR. Combined use of molecularly targeted therapy with chemotherapy may offer improved outcomes for gastric cancer patients and might provide new threads of hope for gastric cancer treatment.

Development of multidrug resistance due to multiple factors including P-glycoprotein overexpression underK-selection afterMYC andHRAS oncogene activation

Multistep tumorigenesis is a form of microevolution consisting of mutation and selection. To clarify the role of selection modalities in tumor development, we examined two alternative evolutionary conditions, r-selection in sparse culture, which allows cells to proliferate rapidly, and K-selection in confluent culture, in which overcrowding constrains cell proliferation. Using MYC- and EJ-RAS-transformed rat embryo fibroblasts, we found that K-selected cells acquired and stably maintained multidrug resistance (MDR) to DOX, VCR, MTX and Ara-C. Then, we examined the involvement of a number of factors potentially causal of the development of MDR, that is, ploidy, Tp53 mutation, doubling time and the expression levels of genes related to drug resistance. Although ploidy status and Tp53 mutations did not correlate with MDR, we found that Abcb1/Mdr1, encoding P-glycoprotein (Pgp), was significantly upregulated after K-selection. Cyclosporin A, a competitive inhibitor of Pgp, increased the intracellular accumulation of DOX and reduced the resistance to it. Indeed, the population of Pgp-transfected cells significantly expanded under K-, but not under r-selection. In addition to Pgp upregulation, altered expression of other genes such as Cda/cytidine deaminase and Slc29a1/equilibrative nucleoside transporter 1 and prolonged doubling times were associated with MDR. This system reproduces events associated with MDR in vivo and would be useful for analysis of MDR development.

Prognostic value of multidrug resistance 1, glutathione-S-transferase-pi and p53 in advanced nasopharyngeal carcinoma treated with systemic chemotherapy

OBJECTIVE

Nasopharyngeal carcinoma (NPC) is one of the dominant cancers in South China and Taiwan. Although NPC is highly chemosensitive, the use of chemotherapy for treating patients with recurrent or metastatic NPC has not been very successful. The emergence of drug resistance may be one of the major reasons. However, the mechanisms of drug resistance of NPC have never been addressed before. In this study, we sought to clarify the role of classical drug resistance markers in predicting the chemosensitivity and the prognosis of patients with advanced NPC.

METHODS

In a cohort of 202 consecutive patients diagnosed at the Department of Pathology of the National Taiwan University Hospital, 44 patients with adequately preserved pretreatment tumor tissues and complete clinical information regarding the details of chemotherapy and tumor response were identified. The expression of multidrug resistance (MDR1), glutathione-S-transferase-pi (GSTpi), and p53 were determined by immunohistochemistry. Tumor response to chemotherapy and survival of the patients were the endpoints of this analysis.

RESULTS

Thirty-four patients received cisplatin-based regimens, and 28 of them were enrolled in a prospective trial using a doxorubicin-containing regimen. The overall response rate was 70%. Expression of MDR1 was seen in only 5 cases (11%) and was associated with a significantly worse overall survival, yet did not appear to predict chemoresistance to the doxorubicin-containing regimen. Overexpression of p53 was seen in 22 patients, and surprisingly, was correlated with chemoresponse and a trend towards better survival. GSTpi expression was demonstrated in 13 cases (30%) and was not correlated with chemoresistance to cisplatin-containing regimens and overall survival.

CONCLUSION

In this relatively small cohort, positive MDR1 immunostaining predicted a poor overall survival for recurrent or metastatic NPC patients receiving chemotherapy. Overexpression of p53 by immunohistochemical staining, however, was associated with a better response rate to systemic chemotherapy and a trend towards better survival.

Differential display of vincristine-resistance-related genes in gastric cancer SGC7901 cell

AIM: To isolate and clone the vincristine-resistine-related genes in gastric cancer SGC7901 cell line and to clarify the multidrug-resistant molecular mechanism of gastric cancer cells.

METHODS: The modified differential-display polymerase chain reaction (DD-PCR) was used to examine the differences in the mRNA composition of Vincristine-resistant gastric cancer SGC 7901 cells (SGC7901/VCR), induced by vincristine sulfate versus SGC7901 cells. The differentially expressed cDNA fragments were confirmed by reverseNorthern analysis, sequencing, BLAST analysis and Northern bolt analysis.

RESULTS: DD-PCR identified that 54 cDNA fragments were preferentially expressed in SGC 7901/VCR cells. When these cDNA fragments were analyzed by reverse Northern blot, 20 were reproducibly expressed at a high level in SGC7901/VCR. Sequencing and BLAST analysis revealed that seven of the genes were known genes: ADP-ribosylation factor 4, Cytochrome oxidase subunit II, Ss-A/Ro ribonucleoprtein autoantigen 60kd subunit, ribosomal protein S13, galaectin-8 gene, oligophrenin 1 mRNA, ribosomal protein L23 mRNA; thirteen of the genes were unknown genes. The length and abundance of the four unknown genes mRNA were further confirmed by Northern blot analysis.

CONCLUSION: The twenty differential known and unknown genes may be related to the vincristine-resistant mechanism in human gastric cancer SGC7901 cell line.

High expression of multidrug resistance-1 (MDR-1) and its relationship with multiple prognostic factors in gastric carcinomas in patients in Turkey

Drug resistance remains a major problem in the treatment of gastric cancer. In Turkey, gastric carcinoma is the second most common cancer and, because the rate of early diagnosis is low, chemotherapy plays an important role in the treatment of the disease. We aimed to investigate expression of the multidrug resistance-1 gene (MDR-1) and its relationship with multiple prognostic factors in gastric cancers. Between 1996 and 1998, a total of 55 patients (37 men and 19 women; median age 55 years) were studied. Sections from specimens of gastric carcinomas were immunohistochemically stained to detect P-glycoprotein (which is associated with MDR-1 expression). We found MDR-1 expression in 48 (87%) of the patients. None of the multiple prognostic factors, including histological type of tumour, correlated with expression of MDR-1. Patients who had low MDR-1 expression had better survival. We conclude that the expression of MDR-1 in gastric cancer is high in Turkey, and this may be related to poor prognosis.