Characteristics of Selenazolidine Prodrugs of Selenocysteine:  Toxicity and Glutathione Peroxidase Induction in V79 Cells

Abstract

Novel selenazolidine prodrugs of selenocysteine are being developed as potential selenium delivery agents for cancer chemoprevention and other clinical uses. The 2-unsubstituted compound, selenazolidine-4(R)-carboxylic acid (L-SCA), and the 2-oxo- and 2-methyl analogues possessing D-stereochemistry (D-OSCA and D-MSCA, respectively) were synthesized and chemically characterized. L/D pairs, along with other organoselenium compounds and common inorganic forms, were studied in cultured V79 cells to understand their inherent toxicity and their ability to induce selenium-dependent glutathione peroxidase (GPx) activity, which indicates the provision of biologically available selenium. All of the selenazolidines were much less toxic to the cells than was sodium selenite (IC(50) approximately 17 microM) or the parent selenolamines, L- or D-selenocystine (IC(50) approximately 34 or 39 microM, respectively); OSCA was less toxic than MSCA. The stereoisomers of OSCA produced very different IC(50) values (L-OSCA, approximately 451 microM; D-OSCA, >3000 microM), while the IC(50) values derived for the stereoisomers of MSCA were of the same order of magnitude (L-MSCA, approximately 79 microM; D-MSCA, approximately 160 microM). Compounds possessing L-stereochemistry were at least as active with respect to GPx induction as was sodium selenite (2.2-fold increase at 15 microM). L-Selenocystine produced a 4.2-fold increase in GPx activity at 30 microM, while L-SCA produced a 5.9-fold increase, followed by L-OSCA (4.6-fold) and L-MSCA (2.1-fold), all at 100 microM. Compounds possessing D-stereochemistry showed minimal ability to induce GPx activity (D-selenocystine, 1.0-fold increase; D-OSCA, 1.4-fold increase; D-MSCA, 1.3-fold increase).

Murine hepatoma (Hepa1c1c7) cells: A responsive in vitro system for chemoprotective enzyme induction by organoselenium compounds

“…This differential concurs with studies in Chinese hamster lung fibroblasts (V79) where IC50 values for selenite, 2-methylSCA, and SCA were 17, 79, and 317 μ M, respectively (Short et al, 2003). With IC values of 550 μ M and >1mM for 2-methylSCA and SCA respectively in Hepa 1c1c7cells, hepatoma cells appear more resistant to selenocompound toxicity than fibroblasts.…”

“…Several available cell lines have been utilized but most studies have concerned themselves with only a single, or a very narrow range of enzymes and often only a single or very limited number of selenium compounds. The most extensively studied compound has been inorganic selenite which has been investigated for effects on two protective enzymes (glutathione peroxidase, thioredoxin reductase) in human HepG2 (Helmy et al, 2000, Morgan et al, 2002, et al, 2003a, Zhang et al, 2003 and in mouse Hepa1c1c7 (Hintze et al, 2003a) hepatoma cell lines, in a Chinese hamster lung fibroblast (V79) cell line (Short et al, 2003), and a mouse fibrosarcoma WEHI 164 cell line (Reszka et al, 2005). In addition to the hepatoma cells, selenite effects in human cell lines have been investigated in colon cancer (HT-29; Berggren et al, 1997), breast cancer (MCF-7) and lung cancer (A549) cells and Jurkat and HL-60 leukemia cells .…”

“…In addition to the hepatoma cells, selenite effects in human cell lines have been investigated in colon cancer (HT-29; Berggren et al, 1997), breast cancer (MCF-7) and lung cancer (A549) cells and Jurkat and HL-60 leukemia cells . Of the organoselenium-compounds, selenium-containing amino acids and some derivatives have been examined for thioredoxin reductase changes in HT-29 human colon cancer cells , for glutathione peroxidase changes in V79 Chinese hamster lung fibroblasts (Short et al, 2003), and for glutathione transferase changes in rat H35 Reuber rat hepatoma cells (t'Hoen et al, 2002). 1,4 Phenylenebis(methylene)selenocyanate has been examined for glutathione transferase changes in mouse hepatoma (Hepa1c1c7) cells (Lee et al, 1999), human lung adenocarcinoma cells (El -Bayoumay et al, 2006) and alongside unsubstituted, 2-oxo-and 2-methyl-selenazolidine 4-carboxylic acids, for glutathione peroxidase changes in the V79 Chinese hamster lung fibroblasts (Short et al, 2003).…”

“…Of the organoselenium-compounds, selenium-containing amino acids and some derivatives have been examined for thioredoxin reductase changes in HT-29 human colon cancer cells , for glutathione peroxidase changes in V79 Chinese hamster lung fibroblasts (Short et al, 2003), and for glutathione transferase changes in rat H35 Reuber rat hepatoma cells (t'Hoen et al, 2002). 1,4 Phenylenebis(methylene)selenocyanate has been examined for glutathione transferase changes in mouse hepatoma (Hepa1c1c7) cells (Lee et al, 1999), human lung adenocarcinoma cells (El -Bayoumay et al, 2006) and alongside unsubstituted, 2-oxo-and 2-methyl-selenazolidine 4-carboxylic acids, for glutathione peroxidase changes in the V79 Chinese hamster lung fibroblasts (Short et al, 2003). Methylseleninic acid has been examined for its effects on enzyme expression in a human prostate cancer cell line (LNCaP) and increases in several Phase 2 enzymes, most notably NQO1 were identified (Zhao et al, 2004).…”

The antimutagenicity of 2-substituted selenazolidine-4-(R)-carboxylic acids

“…B[a]P, acridine orange, 7-ethoxyresorufin, and NADPH were obtained from Sigma (St Louis, MO). SCA was synthesized as described by Short et al, [36], 2-oxoSCA and 2-methylSCA as described by Xie et al, [35] and the four other 2-substituted selenazolidines were synthesized in a similar manner to 2-methylSCA except the appropriate carbonyl compound was substituted for acetaldehyde in the synthesis. S9 mix consisted of filter-sterilized NADPH (1.25 mM) and hepatic S9 fraction (4 mg protein/ml) prepared from male Sprague Dawley rats treated three days previously with a single dose (25 mg/kg, i.p.…”