Bioassay using epidermal keratinocytes to determine phosphorylation status of the epidermal growth factor receptor in distant neoplasms.

We developed a bioassay to evaluate the phosphorylation status of a fibrosarcoma following systemic administration of the protein tyrosine kinase inhibitor PKI 166. Samples of subcutaneous fibrosarcomas and distant skin were fixed in formalin, sectioned, and stained with several fluorescent antibodies against the epidermal growth factor receptor (EGF-R) and phosphorylated EGF-R. In mice given different doses of PKI 166, the dose-dependent inhibition of phosphorylation of EGF-R in epidermal keratinocytes paralleled that in fibrosarcomas growing subcutaneously, suggesting that skin biopsies can be used as surrogate tissues for distant neoplasms to determine the phosphorylation status of protein tyrosine kinase receptors.