Effects of naturally occurring and synthetic organoselenium compounds on protein profiling in androgen responsive and androgen independent human prostate cancer cells

Prostate cancer represents a major clinical public health challenge. Both epidemiological and clinical intervention studies support the protective role of selenium against development of prostate cancer. However, the mechanisms responsible for the inhibitory activity by this micronutrient remain elusive. Furthermore, literature reports consistently have shown that the dose and form of selenium are important factors in cancer chemoprevention. Thus, in the present investigation using androgen responsive (AR) lymph node carcinoma of the prostate (LNCaP) and its androgen-independent clone (AI) LNCaP C4-2 human prostate cancer cells, we compared the effects of selenomethionine (SM) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) on cell growth, DNA synthesis, and on proteomic profiles. p-XSC (5-20 μM) significantly inhibited cell growth in both cell types in a dose-dependent manner; SM was also effective but at much higher doses (50-100 μM). We hypothesize that the inhibition of cell growth is due, in part, to selenium interaction with redox-sensitive proteins. Using 2D gel electrophoresis, both organoselenium compounds altered the expression, to a varied extent, of several unrecognized selenium-responsive proteins. Employing matrix-assisted laser-desorption ionization (MALDI) and time-of-flight (TOF; MALDI-TOF) followed by tandem mass spectrometric analysis, we identified the following proteins: cofilin-2, heterogeneous nuclear ribonucleoprotein, single-stranded mitochondrial DNA binding protein, chaperonin 10, nucleoside diphosphate kinase 6, and chain A Horf 6 human peroxidase enzyme. This is the first report showing that SM and p-XSC are capable of altering these proteins; their roles in prostate cancer prevention warrant further investigations.