An Imidazoquinolone as a Novel Oral Agent for Treatment of Metastatic Renal Cell Carcinoma in a Mouse Model.
Michael J. Schwartz, Huixian Liu, Hideki Kawamoto, Eric B. Smith, Xueke You and Douglas S. Scherr
Department of Urology, New York Presbyterian Hospital, Weill Medical College of Cornell University
INTRODUCTION AND OBJECTIVE: The treatment of metastatic renal cell carcinoma has historically relied on immunomodulation, the mainstays of therapy being IL-2 and interferon. Imidazoquinolones, toll-like receptor-7 (TLR-7) agonists currently used as topical agents for treatment of several benign and malignant skin lesions, stimulate a pro-inflammatory immune response with anti-tumor activity. We evaluated the in vitro and in vivo effects of imidazoquinolones in renal cell carcinoma (RCC) cell lines and in a mouse model of metastatic RCC.
METHODS: In vitro experiments were carried out using mouse (RENCA) and human (Caki-1, Caki-2, and A-498) RCC cell lines. TLR-7 expression in RCC cell lines was assessed by Western blot. In addition, we assessed the ability of imidazoquinolones (3M Pharmaceuticals, St. Paul, MN) to induce apoptosis (TUNEL assay) and inhibit cell proliferation (cell counts and tetrazolium dye colorimetric assay) in vitro. For in vivo experiments, 2 x 105 RENCA cells were injected into the tail vein of syngeneic Balb/cJ mice. Two weeks after injection, mice were given oral imidazoquinolone (15mg/kg/day) or placebo for 14 days. The mice were then sacrificed and lungs were harvested and inspected for tumor nodules.
RESULTS: TLR-7 was expressed in all cell lines tested, with RENCA cells showing the highest level of expression. Imidazoquinolones inhibited in vitro proliferation of RENCA cells in a time and dose-dependent manner. Proliferation was also inhibited significantly in the Caki-2 and A-498 cell lines, but not in Caki-1. Interestingly, Caki-1 also showed the lowest TLR-7 expression. Apoptosis was most significantly induced in RENCA cells. Oral imidazoquinolone for 14 days started 2 weeks after tail vein inoculation with RENCA cells significantly reduced the number of pulmonary metastasis.
CONCLUSIONS: Imidazoquinolones inhibit cell proliferation and cause DNA fragmentation leading to apoptosis in RCC cell lines, potentially working via the TLR-7 which all cell lines expressed. In addition, preliminary in vivo data suggests anti-tumor effects in a mouse model of metastatic RCC.