Endothelin-A-receptor antagonism with atrasentan exhibits limited activity on the KU-19-19 bladder cancer cell line in a mouse model.

PURPOSE: The endothelin axis consists of endothelin-1 (ET-1) and its two receptors, ET(A)- and ET(B)-receptor (ET(A)-R and ET(B)-R). In several tumor entities, the ET(A)-R plays a significant role as a drug target. In our study, we investigated whether inhibition of ET(A)-R with atrasentan leads to an antitumor effect in urinary bladder carcinoma as well. MATERIALS AND METHODS: Twenty nude mice with thymic aplasia were subcutaneously administered 2 x 10(6) KU-19-19 bladder cancer cells in the right flank. Starting on the 22nd day after the injection, ten animals were treated with atrasentan (2.5 mg/kg BW intraperitoneally), and another ten animals were treated with placebo. During treatment, absolute tumor growth and relative growth rate over time were determined. After the end of treatment, the mitosis and necrosis rates, microvessel density, and receptor density in the tumor tissue were analyzed by immunohistochemistry. In addition, the expression intensities of ET-1, ET(A)-R, and ET(B)-R were evaluated semiquantitatively and compared between the groups. RESULTS: No significant differences between the active-treatment and placebo groups were detected, either with respect to absolute tumor growth (P = 0.333) or mitosis rate (P = 0.217). In the analysis of the necrosis rate and receptor density for ET(A)-R, a trend toward higher values in the active-treatment group (mean necrosis rate = 63.67%, receptor density: 1.417) than in the placebo group (mean necrosis rate = 46.25%, receptor density: 1.270) was found; however, neither difference was statistically significant (P = 0.08 and 0.219, respectively). CONCLUSIONS: ET(A)-R blockade with atrasentan in a bladder cancer xenograft model shows no significant antitumor effect.