ENHANCED ANTITUMOR EFFECT OF INTRAVESICAL GEMICITABINE THERAPY PLUS BCG IN AN ORTHOTOPIC MURINE BLADDER CANCER MODEL

Abstract

INTRODUCTION AND OBJECTIVES: Intravesical immunotherapy with bacillus Calmette-Guerin (BCG) is the most successful adjuvant agent for superficial bladder tumors. However, tumors recur in 60 to 70% of the cases, and 30 % of these recurrent tumors present with a higher grade with invasive properties.Gemicitabine is a strong and specific deoxycytidine analog with activity in bladder tumors. To treat superficial bladder tumors that are resistant, we evaluated the combination treatment strategies with intravesical BCG plus Gemicitabine for bladder tumors in a model of orthotopic murine bladder cancer(MBT-2). METHODS: Superficial murine bladder cancer was established by simple instillation of 1 x 106 MBT-2 cells into the lumen of the bladder of female C3H mouse. To assess the antitumoral effect of gemicitabine, intravesical gemicitabine therapy was administered at various doseescalating concentrations; 0(control), 1mg, 2mg, 4 mg and 8mg (n = 8 for each group). Intravesical therapy was administered at 3-days intervals starting on day 5 and repeated 6 times. Next, comparative evaluation of tumor growth among the control group, Gemicitabine-alone group, Gemicabine plus BCG group and BCG-alone group were performed (n= 16 for each group). On day 60 after the initial implantation of the MBT-2 cells, all the surviving mice were sacrificed and necropsied. To evaluate the proliferative activity among the group, Ki67 staining of the tumor cells was performed following corresponding single intavesical administration in an orthotopic bladder tumor model. RESULTS: In the Gemicitabine-only groups of 8 mice each at the dose of 0(control), 1mg, 2mg, 4 mg and 8mg, one, four, four, four, five and four of the mice, respectively, survived. In the 8mg group, three of the eight mice were died due to adverse events. There was no significant difference in the tumor growth rate between any doses of Gemicitabine groups. There was a significant survival advantage in the Gemecitabine plus BCG group (54.1 ± 9.4 days) as compared with that in the BCG-alone group (39.0 ± 16.4 days) (p = 0.02). The Ki67 expression level as the proliferation index was significantly decreased in the Gemecitabine plus BCG group as compared with that in the BCG-alone group (p <0.05). CONCLUSIONS: Our results suggest that intravesical BCG plus Gemicitabine exhibited augmented antitumor effect against bladder tumors. Combined BCG plus Gemicitabine therapy was associated with a reduced proliferation rate as compared to BCG-alone therapy in the orthotopic bladder tumor model.