The chemopreventive effects of orally administered dexamethasone in Strain A/J mice following cessation of smoke exposure.

Male Strain A/J mice were exposed for 6 mo, 6 h/d, 5d/wk to a mixture of cigarette sidestream and mainstream smoke with an average total suspended particulate concentration of 156 mg/m3. They then were removed into air and fed diet AIN93M containing 0.5 mg/kg of dexamethasone until killed 4 mo later for the evaluation of lung tumor multiplicities. In animals kept in air, an average of 1.3 tumors per lung was found, and in tobacco-smoke-exposed animals the average number of tumors per lung was 2.2 (p<.05). Addition of dexamethasone to the diet reduced lung tumor multiplicities in the tobacco smoke exposed animals to 1.4 (64% of control values), not quite statistically significant. In animals not exposed to tobacco smoke, however, dexamethasone significantly decreased lung tumor multiplicities to 46% of control values. In animals injected with the tobacco-smoke-specific carcinogen NNK [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone], dietary dexamethasone significantly reduced lung tumor multiplicities to 38% of controls. It is concluded that the dietary intake of dexamethasone against full tobacco smoke might show improved chemopreventive activity when combined with other agents.