Multi‐Stage Regulated Peptide Microneedle for Enhancing Ferroptosis in Melanoma Therapy

ABSTRACT Microneedle (MN)‐based nanodrug delivery strategies have shown considerable promise for the localized treatment of melanoma. However, current MN systems frequently neglect three critical delivery bottlenecks: (1) insufficient intratumoral drug penetration; (2) low subcellular targeting efficiency; and (3) short intracellular retention time. These sequential bottlenecks significantly restrict their therapeutic efficacy. Herein, this study develops a multi‐stage regulated peptide microneedle system (Cel‐FLPM/PF@MN) that integrates a paeoniflorin (PF)‐based matrix and a mitochondria‐targeted, enzyme‐responsive celastrol (Cel) nanoformulation (Cel‐FLPM). In contrast to traditional MN systems, Cel‐FLPM/PF@MN executes a programmed cascade regulation: First, PF released from the rapidly degradable MN matrix modulates the extracellular matrix to create pathways for the deep intratumoral penetration of Cel‐FLPM. Second, Cel‐FLPM targets mitochondria specifically via its 3‐(3‐methylpyridin‐3‐yl)alanine (MP) group after intracellular uptake. Third, the leucine aminopeptidase (LAP)‐triggered in situ morphological transformation of Cel‐FLPM prolongs the intracellular drug retention time. In vitro and in vivo results demonstrate that Cel‐FLPM/PF@MN significantly enhances the induction of ferroptosis, effectively inhibits the growth and metastasis of melanoma, and induces long‐term immune memory. Overall, this study emphasizes the importance of multi‐stage regulation during the MN delivery process, overcomes critical sequential delivery barriers present in current MN systems, and provides a new paradigm for efficient melanoma therapy.