A Systematic Review of the Anticancer Properties of Compounds Isolated from Licorice (Gancao).

Licorice (Gancao in Chinese) has been used worldwide as a botanical source in medicine and as a sweetening agent in food products for thousands of years. Triterpene saponins and flavonoids are its main ingredients that exhibit a variety of biological activities, including hepatoprotective, antiulcer, anti-inflammatory, antiviral and anticancer effects among others. This review attempts to summarize the current knowledge on the anticancer properties and mechanisms of the compounds isolated from licorice and obtain new insights for further research and development of licorice. A broad spectrum of in vitro and in vivo studies have recently demonstrated that the mixed extracts and purified compounds from licorice exhibit evident anticancer properties by inhibition of proliferation, induction of cell cycle arrest, apoptosis, autophagy, differentiation, suppression of metastasis, angiogenesis, and sensitization of chemotherapy or radiotherapy. A combined treatment of licorice compounds and clinical chemotherapy drugs remarkably enhances anticancer effects and reduces the side effects of chemotherapeutics. Furthermore, glycyrrhizic acid and glycyrrhetinic acid in licorice have been indicated to present obvious liver-targeting effects in targeted drug delivery systems for hepatocellular carcinoma treatment.

Glycyrrhetinic Acid triggers a protective autophagy by activation of extracellular regulated protein kinases in hepatocellular carcinoma cells.

Glycyrrhetinic acid (GA), one of the main constituents of the famous Chinese medicinal herb and food additive licorice (Glycyrrhiza uralensis Fisch), has been indicated to possess potential anticancer effects and is widely utilized in hepatocellular carcinoma (HCC) targeted drug delivery systems (TDDS) due to the highly expressed target binding sites of GA on HCC cells. This study found that GA reduced the cell viability, increased the release of lactate dehydrogenase, and enhanced the expression of Bax, cleaved caspase-3, and LC3-II in HCC cells. The GA-triggered autophagy has been further confirmed by monodansylcadaverine staining as well as transmission electron microscopy analysis. The cell viability was obviously decreased whereas the expression of cleaved caspases was significantly increased when inhibition of autophagy by choloroquine or bafilomycin A1, suggesting that GA triggered a protective autophagy. Extracellular regulated protein kinase (ERK) was activated after treatment with GA in HepG2 cells and pretreatment with U0126 or PD98059, the MEK inhibitors, reversed GA-triggered autophagy as evidenced by decreased expression of LC3-II and formation of autophagosomes, respectively. Furthermore, GA-induced cell death and apoptosis were enhanced after pretreatment with PD98059. This is the first report that GA triggers a protective autophagy in HCC cells via activation of ERK, which might attenuate the anticancer effects of GA or chemotherapeutic drugs loaded with GA-modified TDDS.

Pseudolarix acid B, a new tubulin-binding agent, inhibits angiogenesis by interacting with a novel binding site on tubulin.

Tubulin-binding agents have received considerable interest as potential tumor-selective angiogenesis-targeting drugs. Herein, we report that pseudolarix acid B (PAB), isolated from the traditional Chinese medicinal plant Pseudolarix kaempferi Gordon, is a tubulin-binding agent. We further demonstrate that PAB significantly and dose-dependently inhibits proliferation, migration, and tube formation by human microvessel enthothelial cells. It is noteworthy that PAB eliminated newly formed endothelial tubes and microvessels both in vitro and in vivo. In addition, PAB dramatically arrested the cell cycle at G2/M phase. PAB also induced endothelial cell retraction, intercellular gap formation, and promoted actin stress fiber formation in conjunction with disruption of the tubulin and actin cytoskeletons. All of these effects occurred at noncytotoxic concentrations of PAB. We found that these effects of PAB are attributable to depolymerization of tubulin by direct interaction with a distinct binding site on tubulin compared with those of colchicine and vinblastine. Taken together, these findings show that PAB is a candidate antiangiogenic agent for use in cancer therapy, and they provide proof of principle for targeting this novel binding site on tubulin as a new strategy for treating cancer.