Comparison of In Vitro Cell Transformation Assay Using Murine Fibroblasts and Human Keratinocytes

The in vitro cell transformation assays (CTA) were performed using BALB/3T3 murine fibroblasts and HaCaT human keratinocytes in order to evaluate concordance between both in vitro CTAs and carcinogenicity with compounds differing in their genotoxic and carcinogenic potential. Six test articles were evaluated, two each from three classes of compounds: genotoxic carcinogens (2-amino-5-nitrophenol and 4-nitroquinoline-N-oxide), genotoxic noncarcinogens (8-hydroxyquinoline and benzyl alcohol), and nongenotoxic carcinogens (methyl carbamate and N-nitrosodiphenylamine). Any foci of size ≥ 2 mm regardless of invasiveness and piling was scored as positive in CTA with BALB/3T3. As expected, four carcinogens regardless of their genotoxicity had positive outcomes in two-stage CTA using BALB/3T3 cells. However, of the two genotoxic noncarcinogens, benzyl alcohol was positive CTA finding. We concluded that, of the 6 chemicals tested, the sensitivity for BALB/3T3 system was reasonably high, being 100%. The respective specificity for BALB/3T3 assay was 50%. We also investigated the correlation between results of BALB/3T3 assay and results from HaCaT assay in order to develop a reliable human cell transformation assay. However, evaluation of staining at later time points beyond the confluency stage did not yield further assessable data because most of HaCaT cells were detached after 2~3 days of confluency. Thus, after test article treatment, HaCaT cells were split before massive cell death began. In this modified protocol for this HaCaT system, growing attached colonies were counted instead of transformed foci 3 weeks since last subculture. Compared to BALB/3T3 assay, HaCaT assay showed moderate low sensitivity and high specificity. Despite these differences in specificity and sensitivity, both cell systems did exhibit same good concordance between in vitro CTA and rodent carcinogenicity findings (overall 83% concordant results). At present the major weakness of these in vitro CTA is lack of validation for regulatory acceptance and use. Thus, more controlled studies will be needed in order to be better able to assess and quantitatively estimate in vitro CTA data.

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.