P-glycoprotein expression in primary and metastatic transitional cell carcinoma of the bladder

To determine the expression of P-glycoprotein in pre- and post-chemotherapy tumor tissue samples from patients with transitional cell carcinomas treated with M-VAC (methotrexate, vinblastine, adriamycin and cisplatin).

Fresh frozen tissue sections of primary and metastatic urothelial tumors were stained with mouse monoclonal antibody HYB-241 which recognized an external epitope of P-glycoprotein, using an avidin-biotin immunohistochemical technique. Immunoreactivity was scored separately in tumor cells and endothelial cells.

Untreated primary lesions showed immunostaining in 6 of 46 cases (13%), while 6 of 16 (38%) post-therapy primary tumors were immunoreactive. None of the untreated metastases (0 of 17) were positive, however, 6 of 11 (55%) post-therapy specimens showed varied percentages of positivity for p-glycoprotein (p = 0.002). The highest percentage, 50%-70% of tumor cells stained, was observed in metastatic lesions from patients who had received 6 or more chemotherapy cycles. No difference in the proportion of endothelial cells stained was observed in pre- and post-therapy specimens. However, 3 of 6 post-therapy samples obtained from 5 individual patients showed MDR1 up-regulation on endothelial cells.

The data show that an increase in the proportion of cells expressing P-glycoprotein occurs after exposure to a combination chemotherapy program containing drugs known to select for P-glycoprotein expression in vitro. The observation of increased immunoreactive endothelial cells suggests transactivation of the MDR1 in these cells. While data are preliminary, P-glycoprotein expression in capillary endothelial cells may contribute to drug resistance. Taken together, these mechanisms may contribute to therapeutic failure in patients with bladder tumors treated with chemotherapy.