Mechanism exploration of the therapeutic and preventive effects of dietary compound isoliquiritigenin on breast cancer

Breast cancer is by far the most frequent cancer and the second leading cause of cancer death among women worldwide. Breast cancer can be triggered by multiple factors including tumor microenvironment (angiogenesis), cancer stem cells (CSCs), genetic and epigenetic abnormalities, and etc. In this study, we investigated the therapeutic and preventive effects and mechanisms of dietary compound isoliquiritigenin (ISL) on breast cancer. Firstly, we explored the anti-angiogenic activities of ISL. A series of angiogenesis processes including proliferation, tube formation, invasion and migration abilities of human umbilical vein endothelial cells (HUVECs) were interrupted by ISL in vitro. Mechanisms study revealed that ISL could directly inhibit VEGFR-2 kinase activity as well as the activation of its downstream signaling cascades. In vivo studies further showed that ISL administration could inhibit breast cancer growth and neoangiogenesis accompanying with suppressed VEGFR-2 signaling, elevated apoptosis ratio and little toxicity effects. Secondly, studies of ISL for chemosensitization against breast cancer are next warranted. ISL had synergistic effects with chemotherapeutic drugs to inhibit breast cancer cell proliferation and colony formation. In addition, ISL could significantly limit CSC ratios in breast cancer cells, accompanied by inhibited self-renewal and multi-differentiation abilities. A mechanistic study revealed that ISL could inhibit β-catenin/ABCG2 signaling by activating the proteasome degradation pathway. The drug affinity responsive target stability (DARTS) strategy further identified GRP78 as the direct target of ISL. Subsequent functional studies demonstrated that ISL could dock into the ATP domain of GRP78 and thereby inhibit its ATPase activity, resulting in its dissociation from β-catenin. An in vivo study also suggested that ISL could chemosensitize breast CSCs via the GRP78/β-catenin/ABCG2 pathway, with little toxicity in normal tissues and mammary stem cells. Thirdly, the anti-CSC properties also endow ISL as a natural demethylation agent targeting WIF1 for the prevention of breast cancer. ISL administration suppressed in vivo breast cancer initiation and progression, accompanied by reduced CSC-like populations. A global gene expression profile assay further identified WIF1 as the main response gene of ISL treatment, accompanied by the simultaneous downregulation of β-catenin signaling and G0/G1 phase arrest in breast CSCs. In addition, WIF1 inhibition significantly relieved the CSC-limiting effects of ISL, suggesting the central role of WIF1 in mediating the bioactivity of ISL. Notably, methylation-specific polymerase chain reaction (MSP) and bisulfite genomic sequencing (BGS) analyses further revealed that ISL enhanced WIF1 gene expression via promoting the demethylation of its promoter, which was closely correlated with the inhibition of DNMT1 activity following ISL treatment. Collectively, we found that ISL could target different phases and molecules and exert therapeutic and preventive effects on breast cancer. Our study also shed light on the potential application of ISL as a novel natural inhibitor against breast cancer.