We have shown in a murine model of treatment with intermittent androgen ablation therapy of prostate cancer that when dutasteride is given during the regrowth phase (off-phase) of intermittent therapy, that tumor growth is inhibited and that survival is improved. We have also shown that testosterone is a more potent inducer of certain tumor suppressor androgen response genes than dihydrotestosterone. In this murine model, we showed that use of a 5-alpha reductase inhibitor (dutasteride) resulted in significant hyperinduction of the U19 tumor suppressor androgen response gene during the regrowth phase of treatment. In the current clinical trial, we will determine if use of dutasteride in men with advanced prostate cancer during the off-phase of intermittent androgen ablation therapy will also result in hyperinduction of these tumor suppressor androgen response genes. Gene expression will be measured in tumor tissue obtained by prostate biopsies during the off-phase when the testosterone level has normalized. Prostate-specific antigen (PSA) levels will also be measured to determine the PSA doubling time during the off-phase to determine the effect of dutasteride on PSA kinetics.
