The inhibitory effect of oral
methylseleninic acid or
methylselenocysteine administration on
cancer cell xenograft development in nude mice is well characterized; however, less is known about the efficacy of
selenate and age on
selenium chemoprevention. In this study, we tested whether
selenate and duration on diets would regulate
prostate cancer xenograft in nude mice. Thirty-nine homozygous NU/J nude mice were fed a
selenium-deficient, Torula yeast basal diet alone (Se-) or supplemented with 0.15 (Se) or 1.0 (Se+) mg
selenium/kg (as Na₂SeO₄) for 6 months in Experiment 1 and for 4 weeks in Experiment 2, followed by a 47-day PC-3
prostate cancer cell xenograft on the designated diet. In Experiment 1, the Se- diet enhanced the initial
tumor development on days 11-17, whereas the Se+ diet suppressed
tumor growth on days 35-47 in adult nude mice.
Tumors grown in Se- mice were loosely packed and showed increased
necrosis and
inflammation as compared to those in Se and Se+ mice. In Experiment 2, dietary
selenium did not affect
tumor development or histopathology throughout the time course. In both experiments, postmortem plasma
selenium concentrations in Se and Se+ mice were comparable and were twofold greater than those in Se- mice. Taken together, dietary
selenate at nutritional and supranutritional levels differentially inhibit
tumor development in adult, but not young, nude mice engrafted with PC-3
prostate cancer cells.