Purpose: Expression of the mdr-1 gene has been correlated with the chemoresistance mechanisms of some cancer models. In the present study, we tried to evaluate mdr-1 gene expression in transitional cell carcinoma (TCC) in both cultured cells and clinical tumors. The expression status of mdr-1 was further correlated with the response to chemotherapy in both systemic and intravesical models.
Materials and methods: We evaluated mdr-1 expression levels by reverse transcription polymerase chain reaction and Southern blotting (RT-PCR-SB) and the activity of P-glycoprotein (P-gp) by flow cytometric rhodamine-123 retention and efflux study in 10 TCC cell lines, 2 doxorubicin-resistant sublines (RLs), T24/A and NTUB1/A, and 2 cisplatin-RLs, T24/P and NTUB1/P. Eighty-eight clinical tumors with their benign counterparts were also assayed by RT-PCR-SB to determine mdr-1 expression status. Of the 88 TCC cases, 28 were treated with systemic and 60 with intravesical chemotherapy. Response to chemotherapy in either form was correlated with mdr-1 expression status.
Results: By RT-PCR-SB, mdr-1 expression signals were observed in only 2 of the 10 TCC cell lines; only 1 of these had a strong signal and active P-gp function. The other, bearing a weak signal, was negative for active P-gp function. All of the 4 RLs studied showed elevated mdr-1 transcript levels as compared with their mdr-1 negative parental cell lines. Doxorubicin-RLs showed much stronger expression signals than cisplatin-RLs. Active P-gp functions were observed in the 2 doxorubicin-RLs but not in the 2 cisplatin-RLs. The efflux of rhodamine-123 in cells with active P-gp function can be significantly inhibited by 10 microM. verapamil. Of the 88 clinical tumors, 62 (70.5%) were positive and 26 (29.5%) were negative for mdr-1 expression by RT-PCR-SB. All benign counterparts of the 88 tumors were positive for mdr-1 expression. However, no differences in chemotherapy responses were found between the positive and negative mdr-1 expression groups in either systemic chemotherapy (p = 0.32, one-tailed Fisher's exact test) or intravesical chemotherapy (p = 0.52, Cox-Mantel log rank test).
Conclusions: Expression of mdr-1 was not commonly seen in TCC cell lines but can be significantly induced by chronic exposure to doxorubicin. Benign transitional cell epithelia seemed to universally express the mdr-1 gene. However, clinical TCCs lost mdr-1 transcript expressions in about 30% of cases. Most important, it appeared that mdr-1 expression status did not correlate with the response to chemotherapy in either systemic or intravesical models.