Evaluation of Sulforaphane as a Potential Bladder Cancer Chemopreventive Agent

Isothiocyanates (ITC) are a well-known class of chemopreventive phytochemicals found in cruciferous vegetables. The unique in vivo pharmacokinetics of orally ingested ITCs makes bladder, perhaps the most exposed organ to ITCs and their bioactive metabolites in vivo. Consumption of raw cruciferous vegetables, particularly broccoli, is inversely associated with bladder cancer (BC) risk and improved survival. Sulforaphane (SF), an ITC that exists exclusively in broccoli sprouts, may be the active ingredient with most promising chemopreventive properties. The present research is focused on the pharmacokinetics of SF and its cancer chemopreventive activities in prevention of BC recurrence and progression. We demonstrate that SF and its metabolites are selectively delivered to the bladder, especially the bladder epithelium that gives rise to majority of BC, via urinary excretion. Evaluation of pharmacodynamics biomarkers, glutathione S-transferase (GST) and NAD(P)H:quinone oxidoreductase 1 (NQO1), suggested that SF is most responsive in the bladder. In vitro, SF exerts potent antiproliferative activities against human BC cells, regardless of the degree of malignancy, while being less toxic to transformed normal human bladder cells. By using MTT assay, we showed that SF inhibited BC cell proliferation at low microM concentrations (6.6--15 microM), which appear to be readily achievable in vivo. Tobacco smoke, a main source of human exposure, is known to influence Cox-2 expression in urothelial tissues of BC patients. Cox-2 is an oncogene and over-expression of Cox-2 is an important step in bladder tumorigenesis. To assess the effect of SF on 4-aminobiphenol (4-ABP), a major human bladder carcinogen found in cigarette smoke, human BC RT4 cells were co-treated with SF, 4-ABP and S9. We have shown that SF significantly downregulated 4-ABP-induced Cox-2 in human BC RT4 cells. Further, we showed that SF targets Cox-2 in three human BC cells when treated with SF for 24 hours. SF also showed to activation of apoptosis via Bcl-2 phosphorylation in vitro under similar treatment conditions. In an orthotopic BC mouse model, SF modestly inhibited BC growth and progression. Molecular changes such as Cox-2 downregulation and pBcl-2 phosphorylation in bladder tumors by SF were not observed in spite of high urinary concentration (5-18 mM at 24h of orally dosed SF), perhaps due to the orthotopic model inefficiency. Thus our pharmacokinetic and cell studies indicate that SF is a highly promising agent for BC prevention and/or treatment.