Luteolin is a natural flavonoid with strong anti-oxidative properties that is 
reported to have an anti-cancer effect in several malignancies other than 
bladder cancer. In this study, we describe the effect of luteolin on a human 
bladder cancer cell line, T24, in the context of the regulation of p21, 
thioredoxin-1 (TRX1) and the mechanistic target of rapamycin (mTOR) pathway. 
Luteolin inhibited cell survival and induced G2/M cell-cycle arrest, p21 
upregulation and downregulation of phospho(p)-S6, which is downstream of mTOR 
signaling. Luteolin also upregulated TRX1 and reduced intracellular reactive 
oxygen species production. In a subcutaneous xenograft mouse model using the rat 
bladder cancer cell line, BC31, tumor volumes were significantly decreased in 
mice orally administered luteolin compared to control. Immunohistochemical 
analysis revealed that increased p21 and decreased p-S6 expression were induced 
in the luteolin treatment group. Moreover, in another in vivo 
N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced rat bladder cancer model, 
the oral administration of luteolin led to a trend of decreased bladder tumor 
dimension and significantly decreased the Ki67-labeling index and p-S6 
expression. Furthermore, the major findings on the metabolism of luteolin 
suggest that both plasma and urine luteolin-3'-O-glucuronide concentrations are 
strongly associated with the inhibition of cell proliferation and mTOR 
signaling. Moreover, a significant decrease in the squamous differentiation of 
bladder cancer is attributed to plasma luteolin-3'-glucuronide concentration. In 
conclusion, luteolin, and in particular its metabolized product, may represent 
another natural product-derived therapeutic agent that acts against bladder 
cancer by upregulating p21 and inhibiting mTOR signaling.