Phenethyl Isothiocyanate and Sulforaphane and their N-Acetylcysteine Conjugates Inhibit Malignant Progression of Lung Adenomas Induced by Tobacco Carcinogens in A/J Mice

Abstract

We have shown previously that naturally occurring isothiocyanates derived from cruciferous vegetables and their N-acetylcysteine conjugates inhibit lung adenoma formation induced by tobacco carcinogens in A/J mice at the postinitiation stage. The tumor-inhibitory activity by these compounds is linked with activation of activator protein and induction of apoptosis in lung tissues, suggesting that these compounds may also inhibit the development of adenomas to adenocarcinomas in lung. In this study, the chemopreventive activity of phenethyl isothiocyanate and sulforaphane and their N-acetylcysteine conjugates during progression of lung adenomas to malignant tumors was investigated in A/J mice. Mice were divided into 14 groups and treated with a mixture of 3 Mmol benzo(a)pyrene [B(a)P] and 3 Mmol 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) given by gavage once weekly for 8 weeks. Twenty weeks after the beginning of carcinogen administration, a total of 20 mice in the treatment groups were sacrificed with an average yield of 7.3 F 4.5 lung adenomas per mouse. The remaining mice in each group were fed diets containing phenethyl isothiocyanate (3 and 1.5 mmol/kg diet), sulforaphane (3 and 1.5 mmol/kg diet), phenethyl isothiocyanate-N-acetylcysteine (8 and 4 mmol/kg diet), sulforaphane-N-acetylcysteine (8 and 4 mmol/kg diet) during weeks 21 to 42. Four mice in each of the high-dose treatment groups were sacrificed during weeks 28 and 36 and the bioassay was terminated during week 42; lung tissues were harvested for histopathologic examination of tumors and for cell proliferation (proliferating cell nuclear antigen) and apoptosis (caspase-3) assays using immunohistochemical staining. At termination, the incidence of adenocarcinoma in the 3 mmol/kg diet phenethyl isothiocyanate group and 8 mmol/kg diet phenethyl isothiocyanate-N-acetylcysteine group was reduced to 19% and 13%, respectively, compared with 42% in the carcinogen-treated control group. At the lower doses, phenethyl isothiocyanate and its N-acetylcysteine conjugate also inhibited the incidences of lung adenocarcinoma, however, the decreases were not statistically significant. The lung tumor incidences in groups treated with sulforaphane-N-acetylcysteine in the diet were also significantly reduced to 11% or 16%. Furthermore, the malignant lung tumor multiplicity was significantly reduced from 1.0 tumor/ mouse in the carcinogen-treated control group to 0.3 in the sulforaphane low-dose group, 0.3 and 0.4 in the two sulforaphane-N-acetylcysteine groups, and 0.4 in the phenethyl isothiocyanate high-dose group. The malignant tumor multiplicities in other treatment groups were also reduced (0.5-0.8 tumors/mouse), but not significantly. Unlike lung adenocarcinomas, both incidences and multiplicities of lung adenomas were not much affected by treatment with isothiocyanates or their conjugates. Immunohistochemical examination of the lung tumors from all time points indicated that significant reduction in proliferating cell nuclear antigen and induction...

Modulation of rat pulmonary carcinogen-metabolising enzyme systems by the isothiocyanates erucin and sulforaphane

“…Phenethyl isothiocyanate anatagonised the carcinogenicity of the tobacco carcinogen NNK and inhibited DNA-adduct formation in rat [9]. Finally, the malignant progression of lung adenomas induced by a mixture of benzo[a]pyrene and NNK was inhibited by sulforaphane (1-isothiocyanato-4-(methylsulphinyl) butane) and phenethyl isothiocyanate [10].…”

Electrophilic tuning of the chemoprotective natural product sulforaphane

“…The plant product sulforaphane [1-isothiocyanato-4-(methylsulfinyl)butane], derived from glucosinolates present in broccoli and other cruciferous vegetables (3), has served as a prototype for our understanding of chemoprotection by induction of phase 2 cytoprotective enzymes including NAD(P)H:quinone oxidoreductase (NQO1) (4). A broad series of animal and human studies has demonstrated the potential of sulforaphane to protect against the onset, or reduce the severity, of cancer (5)(6)(7)(8), retinal disease (9), and skin damage (10)(11)(12) resulting from oxidative or electrophile damage (5,6,8), UV irradiation (10,11), or genetic predisposition (9,13).…”

Handbook of Plant Food Phytochemicals

“…One potential use of Brassica wastes based on the antimicrobial properties of glucosinolates and their isothiocyanate breakdown products has been as a biofumigation agent for control of soil borne pathogens as an alternative to methyl bromide soil fumigation. Approaches using both dried and fresh material, and in the use of Brassica species as green manures have been investigated in a number of studies (reviewed in [32]). A commercial green manure BQ Mulch TM consisting of a mixture of Brassica species has been developed and marketed in New Zealand for control of soil nematodes and soil pathogens such as Phytophthora and Pythium [98,166] and there are approaches to develop Brassica derived biocidal dried plant pellets for biofumigation [88].…”