Sulforaphane, an
isothiocyanate found in cruciferous vegetables, has been shown to induce phase 2 detoxication
enzymes and inhibit the growth of chemically induced mammary
tumors in rats, although the exact mechanisms of action of
sulforaphane are not understood. In this study, we evaluated the effects of
sulforaphane on cell growth and death in several human
breast cancer cell lines and examined the hypothesis that
sulforaphane acts as a
histone deacetylase (
HDAC) inhibitor in these cell lines.
Sulforaphane treatment inhibited cell growth, induced a G(2)-M cell cycle block, increased expression of
cyclin B1, and induced oligonucleosomal DNA fragmentation in the four human
breast cancer cell lines examined, MDA-MB-231, MDA-MB-468, MCF-7, and T47D cells. Activation of apoptosis by
sulforaphane in MDA-MB-231 cells seemed to be initiated through induction of
Fas ligand, which resulted in activation of
caspase-8,
caspase-3, and
poly(ADP-ribose) polymerase, whereas apoptosis in the other
breast cancer cell lines was initiated by decreased Bcl-2 expression, release of
cytochrome c into the cytosol, activation of
caspase-9 and
caspase-3, but not
caspase-8, and
poly(ADP-ribose) polymerase cleavage.
Sulforaphane inhibited HDAC activity and decreased the expression of
estrogen receptor-alpha,
epidermal growth factor receptor, and human
epidermal growth factor receptor-2 in each cell line, although no change in the acetylation of H3 or H4 was seen. These data suggest that
sulforaphane inhibits cell growth, activates apoptosis, inhibits HDAC activity, and decreases the expression of key
proteins involved in
breast cancer proliferation in human
breast cancer cells. These results support testing
sulforaphane in vivo and warrant future studies examining the clinical potential of
sulforaphane in human
breast cancer.