Pretreatment with 8-methoxypsoralen, a potent human CYP2A6 inhibitor, strongly inhibits lung tumorigenesis induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in female A/J mice.

Human CYP2A6 has been recognized as being involved in the mutagenic activation of promutagens such as the tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Methoxsalen (8-methoxypsoralen) was reported to inhibit CYP2A6. In the present study, the inhibitory effects of methoxsalen on NNK-induced lung tumorigenesis in female A/J mice were examined. Female A/J mice were treated with methoxsalen at doses of 50 or 12.5 mg/kg body weight, given by stomach tube, daily for 3 days. One h after the final treatment, NNK was injected i.p. at a dose of 2 mg/mouse. The experiments were terminated 16 weeks after the first methoxsalen treatment, and lung adenomas were analyzed. Pretreatment of methoxsalen significantly reduced tumor incidence from 93.8% to 16.7% (50 mg/kg) and 20.0% (12.5 mg/kg), and tumor multiplicity from 5.97 to 0.23 (50 mg/kg) and 0.25 (12.5 mg/kg) tumors/mouse. These results clearly demonstrated that methoxsalen, a potent human CYP2A6 inhibitor, is a strong chemopreventive agent against NNK-induction of lung tumorigenesis.