Wedelolactone Acts as Proteasome Inhibitor in Breast Cancer Cells.

Wedelolactone is a multi-target natural plant coumestan exhibiting cytotoxicity towards cancer cells. Although several molecular targets of wedelolactone have been recognized, the molecular mechanism of its cytotoxicity has not yet been elucidated. In this study, we show that wedelolactone acts as an inhibitor of chymotrypsin-like, trypsin-like, and caspase-like activities of proteasome in breast cancer cells. The proteasome inhibitory effect of wedelolactone was documented by (i) reduced cleavage of fluorogenic proteasome substrates; (ii) accumulation of polyubiquitinated proteins and proteins with rapid turnover in tumor cells; and (iii) molecular docking of wedelolactone into the active sites of proteasome catalytic subunits. Inhibition of proteasome by wedelolactone was independent on its ability to induce reactive oxygen species production by redox cycling with copper ions, suggesting that wedelolactone acts as copper-independent proteasome inhibitor. We conclude that the cytotoxicity of wedelolactone to breast cancer cells is partially mediated by targeting proteasomal protein degradation pathway. Understanding the structural basis for inhibitory mode of wedelolactone might help to open up new avenues for design of novel compounds efficiently inhibiting cancer cells.

Wedelolactone induces growth of breast cancer cells by stimulation of estrogen receptor signalling.

Wedelolactone, a plant coumestan, was shown to act as anti-cancer agent for breast and prostate carcinomas in vitro and in vivo targeting multiple cellular proteins including androgen receptors, 5-lipoxygenase and topoisomerase IIα. It is cytotoxic to breast, prostate, pituitary and myeloma cancer cell lines in vitro at µM concentrations. In this study, however, a novel biological activity of nM dose of wedelolactone was demonstrated. Wedelolactone acts as agonist of estrogen receptors (ER) α and ß as demonstrated by transactivation of estrogen response element (ERE) in cells transiently expressing either ERα or ERß and by molecular docking of this coumestan into ligand binding pocket of both ERα and ERß. In breast cancer cells, wedelolactone stimulates growth of estrogen receptor-positive cells, expression of estrogen-responsive genes and activates rapid non-genomic estrogen signalling. All these effects can be inhibited by pretreatment with pure ER antagonist ICI 182,780 and they are not observed in ER-negative breast cancer cells. We conclude that wedelolactone acts as phytoestrogen in breast cancer cells by stimulating ER genomic and non-genomic signalling pathways.

Plant coumestans: recent advances and future perspectives in cancer therapy.

Natural products are often used in drug development due to their ability to form unique and diverse chemical structures. Coumestans are polycyclic aromatic plant secondary metabolites containing a coumestan moiety, which consists of a benzoxole fused to a chromen-2-one to form 1-Benzoxolo[3,2-c]chromen-6-one. These natural compounds are known for large number of biological activities. Many of their biological effects can be attributed to their action as phytoestrogens and polyphenols. In the last decade, anticancer effects of these compounds have been described in vitro but there is only limited number of studies based on models in vivo. More information concerning their in vivo bioavailability, stability, metabolism, toxicity, estrogenicity, cellular targets and drug interactions is therefore needed to proceed further to clinical studies. This review focuses on coumestans exhibiting anticancer properties and summarizes mechanisms of their toxicity to cancer cells. Moreover, the possible role of coumestans in cancer prevention is discussed.