Inhibition of c-erbB-2 expression an activity in human ovarian carcinoma cells by hypericin

The c-erbB-2 oncogene encodes a tyrosine kinase that constitutes the internal and transmembrane part of the epidermal growth factor receptor (EGFR). ErbB-2 overexpression has been reported in 20% to 30% of human adenocarcinomas of the breast and ovary, and has been linked to an unfavorable prognosis in patients. Hypericin is a protein tyrosine kinase inhibitor that has been exploited in models for anti-tumor and anti-viral activity. In this study, we investigated the effects of hypericin on the activity of the c-erbB-2 oncoprotein and its downstream kinases. We also investigated the effect of hypericin on metastasis. We used ovarian SK-OV-3 cells as a model to determine whether hypericin-induced cell death was associated with inhibition of c-erbB-2 expression and activation. The IC50 of hypericin after 72 hrs exposure was 7.5 microM as determined by the MTT assay. Apoptosis, which was assessed by morphological changes and a flow cytometric assay, was observed at 24 h after continuous exposure to 5 microM hypericin. Inhibition of expression of the c-erbB-2 protein was detected, using a monoclonal anti-erbB-2 antibody after 12-48 hrs of exposure to hypericin. Hypericin was found to inhibit autophosphorylation of the erbB-2 protein and downstream kinases such as MEK and ERK1/2. We also found up-regulation of p21WAF1 expression and down-regulation of Bcl-2 in hypericin treated cells. An invasion assay showed that hypericin inhibited the movement of SK-OV-3 cells into the Matrigel. However, gelatin zymography showed that hypericin had no effect on the secretion of matrix metalloproteinases (MMPs) in SK-OV-3 cells. From these results, we conclude that hypericin inhibits the growth of SK-OV-3 ovarian cancer cells, inhibits the autophosphorylation of c-erbB-2, induces apoptosis, and may inhibit invasion.