Changes in P-glycoprotein expression in gastric carcinoma with respect to distant gastric mucosa may be influenced by p53.

BACKGROUND: The effectiveness of some chemotherapeutic agents used to treat gastric carcinoma patients may be impaired by the presence of P-glycoprotein (P-gp) and the status of p53. A modulation of P-gp expression by p53 or other alterations during tumorigenesis have been reported. The authors analyzed P-gp expression in relation to p53 and histopathologic features in gastric carcinoma. METHODS: Forty-one resected gastric carcinomas and mucosa distant from the tumor were assessed for P-gp expression by immunohistochemistry with C494 and JSB-1 antibodies. p53 expression was also immunohistochemically assessed by DO7 antibody in tumor samples. P-gp and p53 expression were semiquantitatively analyzed according to the percentage of stained cells. Histologic type, grade, vessel invasion, and stage were also studied. RESULTS: Moderate or high P-gp expression was detected in gastric carcinoma in 29 cases (71%) and in gastric mucosa remote from the tumor in 36 cases (88%). This reduction in P-gp expression was observed in 22% of the carcinomas, all but 1 being p53 immunonegative tumors. Thus, 8 (42%) of the p53 immunonegative carcinomas showed a loss of P-gp expression compared with their distant gastric mucosa. All p53 immunopositive carcinomas coexpressed P-gp. No correlation between P-gp expression and histologic type, grade, vessel invasion, or stage was found. CONCLUSIONS: P-gp expression in gastric carcinomas is frequent and coexpression with p53 is found. The analysis of P-gp expression in carcinomas and distant mucosa show that it is not regulated by p53, but a loss of P-gp detected in some of these carcinomas is mainly associated with a lack of p53 protein accumulation.

Detection of P-glycoprotein in frozen and paraffin-embedded gastric adenocarcinoma tissues using a panel of monoclonal antibodies.

AIMS: Most chemotherapeutic regimens used against gastric carcinoma include anthracyclines whose effectiveness can be impaired by the presence of P-glycoprotein. In order to obtain a reliable pattern of P-glycoprotein expression in these tumours an immunohistochemical study using a panel of anti-P-glycoprotein antibodies was performed in frozen and paraffinized tissues. METHODS AND RESULTS: Frozen and paraffinized samples from 25 gastric carcinomas were immunohistochemically analysed using a panel of four anti-P-glycoprotein monoclonal antibodies including C219, MRK16, JSB-1 and C494. Semiquantitative analysis indicated that moderate or high P-glycoprotein levels were detected in 40% to 76% of gastric adenocarcinomas, depending on the anti-P-glycoprotein antibody used. The antibody C494 was the most sensitive in detecting P-glycoprotein in both frozen and paraffinized gastric carcinoma samples. Moreover, C494 showed a pattern of staining exclusively associated with the plasma membrane, in contrast to the cytoplasmic with reinforcement of plasma membrane pattern displayed by the other three antibodies. Significant differences in P-glycoprotein levels were obtained when C494 and MRK16 were used in frozen tissues. Finally, detection of P-glycoprotein in frozen samples did not improve when compared to paraffinized ones. CONCLUSIONS: It appears that P-glycoprotein is frequently expressed in gastric adenocarcinomas, and the use of C494 complemented by JSB-1 is recommended for reliable detection of P-glycoprotein in this neoplasm.