Presentation Authors: Taichi Mizushima, Guiyang Jiang, Rochester, NY, Takashi Kawahara, Yokohama, Japan, Peng Li, Shanghai, China, People's Republic of, Bin Han, Shenyang, China, People's Republic of, Satoshi Inoue*, Rochester, NY, Hiroki Ide, Tokyo, Japan, Mehrsa Jalalizadeh, Baltimore, MD, Hiroji Uemura, Yokohama, Japan, Leonardo Reis, Campinas, Brazil, Hiroshi Miyamoto, Rochester, NY
Introduction: A significant number of patients with non-muscle-invasive bladder cancer fail to respond to intravesical BCG immunotherapy. Interestingly, in a few studies, male patients have been shown to be less likely to respond to BCG therapy, compared with female patients. Meanwhile, emerging preclinical evidence suggests the involvement of androgen receptor (AR) signaling in urothelial tumorigenesis and cancer progression. This study aimed to investigate whether and how AR signals have an impact on the direct cytotoxic effects of BCG on bladder cancer cell growth.
Methods: We compared the inhibitory effects of BCG on bladder cancer cell viability or colony formation between AR-positive versus AR-knockdown lines or between AR-positive lines with versus without treatment with androgen (e.g. R1881) and/or anti-androgen (e.g. hydroxyflutamide). We also knocked down Rab27b, a GTPase known to mediate bacterial exocytosis (e.g. E. coli from urothelial cells), in bladder cancer cells to compare the cytotoxic effects and intracellular amounts of BCG. Immunohistochemistry of AR and Rab27b was then performed in bladder cancer specimens from patients undergoing BCG therapy.
Results: BCG treatment reduced the numbers of viable cells or colonies of AR-knockdown lines more significantly than those of AR-positive control lines. Similarly, R1881 and hydroxyflutamide lowered and enhanced, respectively, the BCG effects on cell proliferation of AR-positive lines. In addition, R1881 reduced BCG amount in AR-positive cells and up-regulated Rab27b expression. Rab27b knockdown cells contained larger amounts of BCG and were more sensitive to BCG treatment, compared with control cells. Meanwhile, the expression levels of both AR and Rab27b were considerably higher in BCG-resistant sublines than in respective control sublines. Using an orthotopic mouse xenograft model, Rab27b knockdown was also found to increase BCG amount in the tumors and its inhibitory effects on tumor growth. Finally, immunostaining showed positivity of AR and Rab27b in 4 (22%) of 18 responders versus 9 (64%) of 14 non-responders (P=0.016) and in 12 (67%) of 18 responders versus 14 (100%) of 14 non-responders (P=0.017), respectively.
Conclusions: AR activity likely correlates with resistance to BCG treatment in bladder cancer, presumably via up-regulating Rab27b expression, leading to promotion of exocytosis of BCG from urothelial cells. Accordingly, anti-androgenic drugs may function as sensitizers of BCG therapy especially in male patients with AR-positive bladder cancer.