Overcoming Biophysical Barriers in Melanoma Photomedicine: From Photodynamic Therapy to Smart Nanodelivery and Photoimmunotherapy

Malignant melanoma presents formidable therapeutic challenges due to optical shielding and free-radical scavenging by endogenous melanin, profound tumor microenvironment hypoxia, and aggressive metastatic dissemination, rendering conventional photodynamic therapy (PDT) clinically immature. This narrative review comprehensively synthesizes literature across PubMed/MEDLINE, Scopus, and Web of Science evaluating photochemical mechanisms, photosensitizing agents, bioengineered drug delivery systems, and adjacent light-triggered strategies. Preclinical evidence demonstrates that third-generation photosensitizers, targeted organic/inorganic nanoparticles, and transdermal dissolving microneedle (MN) arrays effectively bypass the stratum corneum, enhance drug bioavailability, and alleviate hypoxia-mediated treatment resistance. Furthermore, femtosecond two-photon PDT converts melanin into an active energy-transfer mediator, while nanotechnology-driven photoimmunotherapy (PIT) triggers immunogenic cell death (ICD) and systemic CD8+ cytotoxic T-lymphocyte activation to induce abscopal regression of un-irradiated distant metastases. Nevertheless, critical translational bottlenecks persist, including an overwhelming reliance on static two-dimensional (2D) cell cultures, a lack of validated prognostic or predictive biomarkers, and a complete absence of randomized controlled clinical trials. Ultimately, advancing melanoma photomedicine from bench to bedside requires standardized photophysical dosimetry, systematic evaluation in multicellular three-dimensional (3D) tumor spheroids, and prospective clinical trials defining its role in multimodal dermato-oncology.