Effects of vitamin D (calcitriol) on transitional cell carcinoma of the bladder in vitro and in vivo

Purpose: Vitamin D (calcitriol) has significant antiproliferative effects o n various tumor cells in vitro and in vivo. In the clinical situation a maj or impediment to systemic administration of calcitriol is the side effect o f hypercalcemia. To test the potential usefulness of calcitriol for bladder cancer treatment, we studied the antiproliferative effect of vitamin D on 2 human bladder cancer cell lines, 253j and T-24, in vitro. We also examine d the in vivo effects of calcitriol in an animal model of bladder cancer us ing intravesical administration to avoid the toxicity of systemic calcitrio l therapy. Materials and Methods: The presence of vitamin D receptors in normal and ne oplastic human bladder tissue, and tumor cells T-24 and 253j was determined by immunoblot analysis. Tumor cell proliferation in the presence or absenc e of calcitriol was determined using a crystal violet assay. Calcitriol ind uced apoptosis was determined by morphology, polyadenosine diphosphate ribo se polymerase cleavage and annexin V binding. In vivo studies were performe d by weekly intravesical instillation of calcitriol in female Fischer 344 r ats after induction of tumors by N-methyl nitrosourea. Calcitriol administr ation was started 3 weeks after tumor induction for 7 doses at weekly inter vals. Results: Normal and neoplastic human bladder tissue, and the cell lines exp ressed vitamin D receptors. In the 253j and T-24 cell lines proliferation w as significantly inhibited by calcitriol. Progressive cleavage of full leng th polyadenosine diphosphate ribose polymerase was observed in calcitriol t reated cells starting as early as 4 hours after exposure. Similar changes w ere not observed in the control cells treated with vehicle (ethanol) alone. After 24 hours of treatment with calcitriol 45.8% of 253j cells bound anne xin compared to 16.5% of control cells (chi-square p <0.001). Of the contro l animals 66% developed bladder tumors and 55% of the animals treated with calcitriol early (3 weeks) after tumor induction developed bladder tumors. Almost all of the tumors that developed in the calcitriol group were unifoc al, and only 20% were invasive compared to 50% of those in the control anim als. Conclusions: These results demonstrate that calcitriol inhibits proliferati on and induces apoptosis in human bladder tumor cells in vitro, and may hav e therapeutic potential in bladder cancer. In vivo studies using an N-methy lnitrosourea induced model of bladder cancer demonstrate that early institu tion of intravesical calcitriol therapy after carcinogen exposure results i n fewer tumors, which are also less likely to be multifocal, high grade or invasive. With our protocol a short course of intravesical calcitriol admin istration did not result in any significant toxicity.