Sulforaphane increases the efficacy of anti-androgens by rapidly decreasing androgen receptor levels in prostate cancer cells

Abstract

Prostate cancer (PCa) cells utilize androgen for their growth. Hence, androgen deprivation therapy (ADT) using anti-androgens, e.g. bicalutamide (BIC) and enzalutamide (ENZ), is a mainstay of treatment. However, the outgrowth of castration resistant PCa (CRPC) cells remains a significant problem. These CRPC cells express androgen receptor (AR) and utilize the intratumoral androgen towards their continued growth and invasion. Sulforaphane (SFN), a naturally occurring isothiocyanate found in cruciferous vegetables, can decrease AR protein levels. In the present study, we tested the combined efficacy of anti-androgens and SFN in suppressing PCa cell growth, motility and clonogenic ability. Both androgen-dependent (LNCaP) and androgen-independent (C4-2B) cells were used to monitor the effects of BIC and ENZ, alone and in combination with SFN. Co-exposure to SFN significantly (p<0.005) enhanced the anti-proliferative effects of anti-androgens and downregulated expression of the AR-responsive gene, prostate specific antigen (PSA) (p<0.05). Exposure to SFN decreased AR protein levels in a time- and dose-dependent manner with almost no AR detected at 24 h with 15 µM SFN (p<0.005). This rapid and potent AR suppression by SFN occurred by both AR protein degradation, as suggested by cycloheximide (CHX) co-exposure studies, and by suppression of AR gene expression, as evident from quantitative RT-PCR experiments. Pre-exposure to SFN also reduced R1881-stimulated nuclear localization of AR, and combined treatment with SFN and anti-androgens abrogated the mitogenic effects of this AR-agonist (p<0.005). Wound-healing assays revealed that co-exposure to SFN and anti-androgens can significantly (p<0.005) reduce PCa cell migration. In addition, long-term exposures (14 days) to much lower concentrations of these agents, SFN (0.2 µM), BIC (1 µM) and/or ENZ (0.4 µM) significantly (p<0.005) decreased the number of colony forming units (CFUs). These findings clearly suggest that SFN may be used as a promising adjunct agent to augment the efficacy of anti-androgens against aggressive PCa cells.

Stevia Eupatoria and Stevia Pilosa Extracts Inhibit the Proliferation and Migration of Prostate Cancer Cells

“…Quercetin is able to reduce the migration and invasion of human skin melanoma cells SK-MEL-28, increasing the expression of epithelial markers and decreasing mesenchymal markers [32]. The combination of Stevia pilosa and Stevia eupatoria with enzalutamide did not induce an antagonist effect on the migration of cells, which is consistent with wound-healing assay with enzalutamide alone reported by Khurana, et al [33], and different from the antagonist effect reported by the same group with enzalutamide and sulforaphane in resistant cells [34]. Based on the above, we suggest that the extracts could affect some of these mechanisms, however, additional studies are needed.…”

Effects of 3-butenyl isothiocyanate on phenotypically different prostate cancer cells

“…The association between AR and tubulin, and the preferential binding of microtubules to AR can recruit AR to determine apoptotic-signaling promotion and tumor growth inhibition (54). SFN can decrease the expression of AR in a dose-and time-dependent manner in PC cells (55). The chemical structure of this ITC determines this effect.…”

Epigenetic modulators as therapeutic targets in prostate cancer

“…Romidepsin combined with docetaxel not only demonstrated superior cytotoxic effects in CRPC cell lines but it also significantly reduced tumor growth in mice [ 268 ]. A combination of sulforaphane, bicalutamide, and enzalutamide enhanced the anti-proliferative effects, decreased tumor cell migration, and reduced PSA and AR expression in LNCaP and C4-2B cells [ 269 ].…”