Delphinidin: A Novel Agent for Inhibition of Breast Tumor Kinase Signaling by Targeting EGFR

摘要

Abnormalities in the expression and signaling pathways downstream of the epidermal growth factor receptor (EGFR) contribute to the progression, invasion, and maintenance of the malignant phenotype in breast cancer. EGFR is expressed at high levels in at least 25% of breast cancers and is associated with poor prognosis. Upon epidermal growth factor (EGF)-stimulation, breast tumor kinase (Brk) is recruited to the EGFR, and this event activates the catalytic activity of Brk, which in turn phosphorylates paxillin a binding partner and substrate for Brk. The phosphorylation of paxillin promotes the activation of Rac1, thereby stimulating cell migration and invasion in response to EGF. Many synthetic inhibitors of EGFR are known, but their use is limited because of their unacceptable cytotoxic effects on normal cells. Therefore, identification of a natural, nontoxic agent(s) as an inhibitor of EGFR is of utmost importance. Delphinidin, a major anthocyanin known to be present in pigmented fruits and vegetables, inhibits constitutive and EGF-induced phosphorylation of EGFR, activation of PI3K, phosphorylation of AKT, and MAPK. We also found that delphinidin treatment inhibits constitutive and EGF-induced activation of Brk signaling mediated through EGFR. Furthermore, treatment of breast cancer cells with delphindin inhibited cell growth and induced apoptosis. In summary this study identifies an abundant fruits and vegetables based anthocyanin delphinidin as an effective blocker of EGFR signaling at least in breast cancer cells that act through novel Brk signaling pathway.