Drug repurposing for skin pigmentation disorders: Discovery of novel tyrosinase inhibitors.

Skin pigmentation disorders present a significant therapeutic challenge, often arising from disturbances in melanin metabolism that lead to uneven pigmentation and skin damage. Tyrosinase (TYR), the key enzyme in melanin biosynthesis, serves as a crucial therapeutic target for managing hyperpigmentation and pigmentary skin diseases. In this study, we performed structure-based virtual screening of a comprehensive library of FDA-approved drugs and chemical active agents against tyrosinase and selected top-ranked compounds based on predicted binding affinities and favorable binding poses for experimental validation. In vitro assays confirmed that nine compounds inhibited mushroom tyrosinase (mTYR) with IC50 values of 6.3-23.4 μM. Among them, rosmarinic acid (compound 1) and ferulic acid (compound 3) also inhibited human tyrosinase (hTYR) with IC50 values of 7.8 ± 0.4 and 9.3 ± 0.5 μM, respectively. Enzyme kinetic analysis indicated a competitive inhibition mechanism against mTYR for the most active compounds. In α-melanocyte stimulating hormone (MSH)-stimulated B16F10 cells, the selected hits produced measurable anti-melanogenic effects within the tested concentration range, with cellular IC50 = 37.8-108.1 μM. Additionally, molecular dynamics simulations of rosmarinic acid in complex with hTYR confirmed a stable binding mode characterized by persistent coordination within the dicopper active site. These findings identify repurposable small-molecule scaffolds with tyrosinase-inhibitory activity and highlight rosmarinic acid as a promising lead for further development. Although the present study is limited to in vitro enzymatic and cellular evaluation, it provides a useful foundation for future validation in human skin-derived systems and in vivo models.