Lemons are a widely used citrus crop and have shown several potential health benefits. In the present study, the mechanism and effectiveness of the anti-
cancer and anti-
aromatase properties of
limonoids were investigated for the first time. Defatted lemon (Citrus lemon L. Burm) seed
powder was extracted with
ethyl acetate (EtOAc) and
methanol (MeOH) for 16 h each, successively. These extracts were fractionated using 1D (
silica) and 2D (ion exchange and SP-70 columns) column chromatography to obtain nine
limonoids. The compounds were identified by TLC, HPLC, and LC-MS techniques. A panel of 9 purified
limonoids, including
limonin,
nomilin,
obacunone,
limonexic acid (LNA), isolimonexic
acid (ILNA), nomilinic
acid glucoside (NAG), deacetyl nomilinic
acid glucoside (DNAG),
limonin glucoside (LG) and
obacunone glucoside (OG) as well as 4 modified compounds such as
limonin methoxime (LM),
limonin oxime (LO), defuran
limonin (DL), and defuran
nomilin (DN), were screened for their cytotoxicity on
estrogen receptor (ER)-positive (MCF-7) or ER-negative (MDA-MB-231) human
breast cancer cells. We further tested the mechanism of the anti-proliferative activity of
limonoids using an in vitro
aromatase enzyme assay and western blot with anti-caspase-7. Among the tested
limonoids, 11
limonoids exhibited cytotoxicity on MCF-7 whereas 8
limonoids showed cytotoxicity against the MDA-MB-231 cell lines. Although most of the
limonoids showed anti-
aromatase activity, the inhibition of proliferation was not related to the anti-
aromatase activity. On the other hand, the anti-proliferative activity was significantly correlated with
caspase-7 activation by
limonoids. Our findings indicated that the citrus
limonoids may have potential for the prevention of
estrogen-responsive
breast cancer (MCF-7) via
caspase-7 dependent pathways.