Antiestrogenic and anti-HER2 activities of allspice (Pimenta dioica L., Myrtaceae) extracts in MCF-7 and SK-BR3 breast cancer cells

Abstract

Human epidermal growth factor 2 (HER2) is a trans-membrane tyrosine kinase that is over expressed in 20% of breast cancers. Overexpression of HER2 has been linked to tumor proliferation and poor prognosis. Numerous studies have focused on targeting HER2 for breast cancer treatment. The leaves of Pimenta dioica (L.) Merr. (Myrtaceae), commonly known as allspice, are used in Costa Rican traditional medicine for women's health. A MeOH extract of allspice leaves collected in Costa Rica, inhibited the growth of MCF-7 (ER+, low HER2) cell proliferation with IC50 of 50 µg/ml, but were more active in SK-Br3 (ER-, high HER2) cells with an IC50 of 12.5µg/ml. In a panel of fifteen receptor tyrosine kinases (RTKs), the extract and partition inhibited two erbB RTKs, namely EGFR (HER1) and HER2 RTKs. Chromatographic separation of the EtOAc partition on a 2L C18 reversed phase silica gel column with methanol/water afforded 20 fractions. Using a high-throughput 96-well HER2 assay, the active fraction was determine to be a 50% methanol/water fraction, which also inhibited the activity of HER2 RTK. Two C-methylated flavonoids, (being new 2-phenoxychromones) were the most active with an IC50 of 1 and 5.1 µg/ml, respectively. Further preliminary data demonstrated that the 50% MeOH fraction of allspice down-regulated the expression of the HER-2 receptor protein in Western blotting and using qPCR the fraction also down-regulated the expression of the HER2 mRNA in SK-Br3 cells.