Mechanisms of chemopreventive effects of 8-methoxypsoralen against 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced mouse lung adenomas

• Published in: Carcinogenesis (New York) 2005-11, Vol.26 (11), p.1947-1955
• Main Authors: Miyazaki, Masafumi, Yamazaki, Hiroshi, Takeuchi, Hijiri, Saoo, Kousuke, Yokohira, Masanao, Masumura, Ken-ichi, Nohmi, Takehiko, Funae, Yoshihiko, Imaida, Katsumi, Kamataki, Tetsuya
• Format: Article
• Language: English
• Subjects: 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; ABC; Adenoma - chemically induced; Adenoma - enzymology; Adenoma - prevention & control; Animals; Antineoplastic Agents - therapeutic use; Aryl Hydrocarbon Hydroxylases - metabolism; avidin-biotin complex; Biological and medical sciences; Carcinogenesis, carcinogens and anticarcinogens; Carcinogens - toxicity; Chemical agents; Chemoprevention; Coumarins - therapeutic use; CPR; CYP; Cytochrome P-450 CYP2A6; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System - metabolism; Cytochrome P450 Family 2; ENU; Escherichia coli Proteins; ethylnitrosourea; Female; general term for cytochrome P450; Humans; individual forms of cytochrome P450 (EC 1.14.14.1); Lung Neoplasms - chemically induced; Lung Neoplasms - enzymology; Lung Neoplasms - prevention & control; Medical sciences; Methoxsalen - therapeutic use; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microsomes - drug effects; Microsomes - enzymology; Mixed Function Oxygenases - metabolism; Mutation - genetics; NADPH-cytochrome P450 reductase (EC 1.6.2.4; NADPH:ferrihemoprotein reductase; Nitrosamines - toxicity; NNK; P450; PCR; Pentosyltransferases; polymerase chain reaction; Proteins - genetics; Proteins - physiology; reverse transcriptase; Salmonella typhimurium; Salmonella typhimurium - drug effects; Salmonella typhimurium - enzymology; Salmonella typhimurium - growth & development; Steroid Hydroxylases - metabolism; Tumors
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgi156

Recently we reported that the occurrence of lung adenoma caused by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was completely prevented by pretreatment of female A/J mice with 8-methoxypsoralen, a potent inhibitor of cytochrome P450 (P450 or CYP) 2A [Takeuchi et al. (2003) Cancer Res., 63, 7581–7583]. Thus, the aim of this study was to confirm that 8-methoxypsoralen exhibits chemopreventive effects by inhibiting CYP2A in the mouse lung. The involvement of CYP2A in the metabolic activation of NNK in the lung was first evidenced by the fact that the mutagenic activation of NNK by mouse lung microsomes was inhibited by 8-methoxypsoralen, coumarin and antibodies to rat CYP2A1. Supporting this, the mutagenic activation of NNK was efficiently catalyzed by mouse CYP2A4 and CYP2A5 co-expressed with NADPH-P450 reductase in a genetically engineered Salmonella typhimurium YG7108. The expression of mRNA for CYP2A5, but not for CYP2A4 or CYP2A12, in the mouse lung was proven by reverse transcriptase–polymerase chain reaction, probably indicating that CYP2A5 present in the mouse lung was involved in the metabolic activation of NNK. In accordance with these in vitro data, treatment of gpt delta transgenic mice with 8-methoxypsoralen prior to NNK completely inhibited the mutation of the gpt delta gene. The in vivo chemopreventive effects of 8-methoxypsoralen towards NNK-induced adenoma was seen only when the agent was given to female A/J mice prior to, but not posterior to, NNK, lending support to the idea that NNK is activated by CYP2A5 in the mouse lung as an initial step to cause adenoma. The inhibition by 8-methoxypsoralen of NNK-induced adenoma was seen in a dose-dependent manner: the dose to show apparent 50% suppression was calculated to be 1.0 mg/kg. To our surprise, CYP2A protein(s) was expressed in the lesion of NNK-induced lung adenomas, probably suggesting that 8-methoxypsoralen could inhibit the possible occurrence of further mutation of the adenoma cells induced by NNK. Based on these lines of evidence, we propose that 8-methoxypsoralen inhibits the CYP2A5-mediated metabolic activation of NNK in the mouse lung, leading to the prevention of NNK-induced adenoma.