Mechanistic study on liver tumor promoting effects of flutamide in rats.

Mohammad Monir Tawfeeq, Hitomi Hayashi, Keisuke Shimamoto, Kazuhiko Suzuki, Makoto Shibutani, Hisashi Inokuma, Kunitoshi Mitsumori

Laboratory of Veterinary Pathology, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.

Archives of toxicology 2012 Mar

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Flutamide (FLU), a nonsteroidal anti-androgen, is used for the treatment of prostate cancer but is also a cytochrome P450 (CYP) 1A inducer. Some CYP1A inducers are known to exert hepatocellular tumor-promoting activities in rodents, and reactive oxygen species (ROS) produced by CYP1A1 induction via a metabolism of FLU is probably involved in the liver tumor promotion. In the present study, to clarify the possible liver tumor promoting effect of FLU, a two-stage liver carcinogenesis assay was performed using male F344 rats. Rats received an intraperitoneal (ip) injection of 200 mg/kg body weight of N-diethylnitrosamine (DEN) and fed a diet containing 0, 0.1 or 0.2% FLU for 6 weeks. After 2 weeks of DEN treatment, all rats were subjected to two-thirds partial hepatectomy. Animals were killed 8 weeks after ip injection of DEN. Immunohistochemically, the number and area of glutathione S-transferase placental form (GST-P)-positive foci significantly increased in the liver of rats given 0.2% FLU as compared with the control. Ki-67-positive cell ratio also increased in rats given FLU at both concentrations. ROS generation in the microsomal fraction and production of thiobarbituric acid-reactive substance [TBARS] and 8-hydroxy-2'-deoxyguanosine (8-OHdG) content in the liver did not increase in any of the FLU-treated groups. The results of microarray and real-time RT-PCR revealed that phase 1 drug-metabolizing enzymes such as CYP1A1, Ugt1a61 and Nqo1 and phase II drug-metabolizing enzymes such as Yc2, Akr1b7, Akr1b8, Akr1b10, Aldh1a1, Gpx2 and Me1 were up-regulated in rats treated with FLU. In addition, the MAPK pathway family-related genes such as Prkcα, Mek1, Rafb, Myc, Mek2, Raf1 and Egfr were also up-regulated in FLU-treated groups. The results of the present study indicate that FLU is a CYP1A inducer but does not cause any production of microsomal ROS in the liver and suggest that microsomal ROS is not involved in the liver tumor promoting effect of FLU.

Citation

Mohammad Monir Tawfeeq, Hitomi Hayashi, Keisuke Shimamoto, Kazuhiko Suzuki, Makoto Shibutani, Hisashi Inokuma, Kunitoshi Mitsumori. Mechanistic study on liver tumor promoting effects of flutamide in rats. Archives of toxicology. 2012 Mar;86(3):497-507