A general tyrosinase-responsive prodrug strategy: design and synthesis of melanoma-selective anticancer agents

Melanoma is highly aggressive with limited therapeutic options for advanced-stage disease, making it the leading cause of skin cancer-related deaths. This study developed a tyrosinase (TYR)-responsive prodrug design strategy by taking TYR-an enzyme specifically overexpressed in melanoma cells-as the endogenous trigger. By introducing a TYR-specific recognition unit into the molecular structures of doxorubicin (DOX) and camptothecin (CPT) and coupling them via a self-immolative linker, two potential prodrugs, TYR-DOX and TYR-CPT, were successfully designed and synthesized. In vitro enzymatic activity assays demonstrated that TYR-DOX could be efficiently activated by TYR in a concentration-dependent manner, and this process was significantly inhibited by a TYR inhibitor, confirming its specific responsiveness to TYR. In contrast, TYR-CPT did not exhibit similar activity. Further cellular assays revealed that, compared with free DOX, TYR-DOX retained potent cytotoxicity against melanoma A375 cells (IC₅₀ = 1.40 μM) while significantly reducing toxicity to normal HEK293 cells (p < 0.0001), indicating markedly enhanced tumor selectivity. Extending this design strategy to seven other clinically used antitumor drugs led to the successful identification of two promising candidates, TYR-GEM and TYR-ETC, demonstrating the general applicability of the strategy. Preliminary structure-activity relationship analysis further suggests that the presence of hydrogen-bond-forming groups within the prodrug structure contributes to enhanced TYR-responsive activity. In summary, the TYR-responsive prodrug design strategy constructed in this study effectively enhances the tumor selectivity of chemotherapeutic agents, and provides a versatile and translatable new approach for the precise targeted therapy of melanoma.