Mechanism of action of adapalene for treating EGFR‐TKI‐induced skin disorder

Background Skin disorders are the most common side effect associated with epidermal growth factor receptor‐tyrosine kinase inhibitor (EGFR‐TKI) therapy. It is important to manage skin lesions. Adapalene has been used to treat skin lesions caused by EGFR‐TKIs in some cases. The aim of this study was to investigate the functional mechanism of adapalene in erlotinib‐induced skin disorder. Methods To analyze the effect of adapalene on skin rash, afatinib and adapalene were administered to mice. The relationship between the concentration of adapalene and skin disorders was also examined by analyzing AQP3 expression. A skin lesion model was experimentally established in human skin keratinocytes (HaCaT) by using erlotinib with TNF‐ α and IL‐1β. We used qRT–PCR to analyze chemokine‐induced inflammation and western blotting to analyze the effects of adapalene on the NF‐κB signaling pathway. Antimicrobial peptides and adhesion factors were also examined using qRT–PCR. Results Mice administered 0.01% adapalene had less skin inflammation than mice treated with afatinib alone. The expression level of AQP3 decreased in an adapalene concentration‐dependent manner. The mRNA levels of proinflammatory cytokines such as CCL2 and CCL27 in HaCaT cells were significantly reduced by adapalene. The expression of an antimicrobial peptide, hBD3, was upregulated after adapalene treatment. Adhesion factors, such as E‐cadherin, were significantly downregulated by EGFR‐TKI and significantly upregulated by adapalene treatment. Western blot analysis suggested that erlotinib‐induced phosphorylation of p65 was decreased by adapalene. Conclusion We suggest that adapalene may be a possible treatment option for skin disorders induced by EGFR‐TKIs.