Chemopreventive activity of selenocysteine prodrugs against tobacco-derived nitrosamine (NNK) induced lung tumors in the A/J mouse

Prodrugs of L-selenocysteine have potential utility in cancer chemoprevention. This study reports the efficacy of three selenazolidine-4(R)-carboxylic acids, (2-unsubstituted, 2-oxo, and 2-methyl derivatives; SCA, OSCA, and MSCA, respectively) against tobacco-related lung tumorigenesis in a mouse model. Seven days after initiation of an AIN-76A diet supplemented with sodium selenite (5 ppm Se), L-selenomethionine (3.75 ppm Se), Se-methyl-L-selenocysteine (3 ppm Se), L-selenocystine (15 ppm Se), SCA (15 ppm Se), OSCA (15 ppm Se), or MSCA (15 ppm Se), mice received 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; 10 micromol, i.p.). After an additional 16 weeks on the diets, two compounds, OSCA and selenocystine, significantly reduced lung adenoma multiplicity from 7.2 tumors per mouse in the NNK group to 4.5 and 4.6 tumors per mouse, respectively. Neither selenium concentration nor glutathione peroxidase activity in either RBCs or liver served as surrogate indicators of tumor reduction. Hepatic selenium levels were significantly elevated by all selenium-containing compounds except Se-methyl-L-selenocysteine and SCA; RBC selenium levels by all except sodium selenite and MSCA. With the exception of L-selenomethionine, RBC glutathione peroxidase activity was increased along with the elevated selenium levels. Hepatic glutathione peroxidase activity was elevated by all Se-compounds except SCA. The two compounds showing significant tumor reduction (OSCA and selenocystine) were the only two compounds that showed ubiquity of changes, elevating both selenium levels and GPx activity in both liver and RBC.