Epidermal growth factor receptor activation and inhibition in 3D in vitro models of normal skin and human cutaneous squamous cell carcinoma.

The transmembrane tyrosine kinase epidermal growth factor receptor (EGFR) is considered a key player in the development of cutaneous squamous cell carcinoma (SCC), which is the second most common malignancy in white populations. Inhibition of EGFR with the small molecule tyrosine kinase inhibitor erlotinib is currently under clinical investigation in cutaneous SCC patients. In this study, we investigated the effects of EGFR activation and inhibition on normal and malignant in vitro human skin equivalents (HSEs). In healthy HSEs, increasing EGF concentrations ranging from 5 to 50 ng/mL resulted in a dramatic decrease in epidermal proliferation as immunohistochemically assessed by Ki67 and increased epidermal stress as assessed by K17 after 2 weeks of air-exposed culture. Also, higher concentrations of EGF induced remarkable epidermal disorganization with loss of proper stratification. Similar effects were observed in HSEs generated with cutaneous SCC cell lines SCC-12B2 and SCC-13. Treatment of both healthy and SCC-HSEs with 10 μM erlotinib resulted in efficient reduction of epidermal thickness from 10 to 3 viable cell layers and counteracted EGF-induced epidermal stress. Remarkably, erlotinib treatment caused severe desquamation in healthy HSEs, reminiscent of xerosis as a known side-effect in patients treated with erlotinib. The presented three-dimensional organotypic SCC models appear suitable for further investigations on the morphological and functional impacts of modifying EGFR signaling in cutaneous SCC, without burdening patients or mice. The effective inhibition of epidermal growth by erlotinib in our HSEs confirms the therapeutic potential of this tyrosine kinase inhibitor for cutaneous SCC patients.