Effects of EGFR‐TKI on epidermal melanin unit integrity: Therapeutic implications for hypopigmented skin disorders

Abstract Epidermal melanin unit integrity is crucial for skin homeostasis and pigmentation. Epidermal growth factor (EGF) receptor (EGFR) is a pivotal player in cell growth, wound healing, and maintaining skin homeostasis. However, its influence on skin pigmentation is relatively unexplored. This study investigates the impact and underlying mechanisms of EGFR inhibitors on skin pigmentation. We evaluated EGF and EGFR expression in various skin cells using quantitative real‐time PCR, Western blot, and immunofluorescence. EGF and EGFR were predominantly expressed in epidermal keratinocytes, and treatment with the EGFR tyrosine kinase inhibitors (EGFR‐TKIs) gefitinib and PD153035 significantly increased stem cell factor (SCF) and endothelin‐1 (ET‐1) expression in cultured keratinocytes. Enhanced melanocyte migration and proliferation were observed in co‐culture, as evidenced by time‐lapse live imaging and single‐cell tracking assays. Furthermore, topical application of gefitinib to guinea pig dorsal skin induced increased pigmentation and demonstrated efficacy in mitigating rhododendrol‐induced leukoderma. Suppression of EGF signaling indirectly enhanced skin pigmentation by upregulating SCF and ET‐1 in epidermal keratinocytes. This novel mechanism highlights the pivotal role of EGF signaling in regulating skin pigmentation, and topical EGFR‐TKI therapy at an appropriate dose may be a promising approach for depigmentation disorder management.