Marine-derived pharmaceuticals for photodynamic therapy of cancer and microbial infections

Photodynamic therapy (PDT) is an established light-based modality that combines a photosensitizer, molecular oxygen and targeted illumination to achieve localized cytotoxicity with limited systemic toxicity. Despite decades of research, the clinical repertoire of photosensitizers remains narrow and consists mainly of synthetic or semi-synthetic compounds. Marine organisms, marine microorganisms and marine-derived natural product scaffolds represent an underexplored source of structurally diverse chromophores, including porphyrinoids, chlorins, phorbides and perylenequinone-type metabolites. Several validated representatives display properties relevant to PDT, such as red-light absorption, efficient reactive oxygen species generation and light-dependent biological activity, whereas many structurally related marine pigments still require direct photodynamic validation. This review summarizes current knowledge on marine-derived photosensitizing chromophores and natural product scaffolds relevant to PDT. It focuses on their structural diversity, photophysical and photochemical mechanisms and translational potential in oncology and antimicrobial PDT. Particular attention is given to ecological and technological challenges that currently limit development, including low natural yields, complex extraction procedures, compound instability and limited scalability. The article concludes by highlighting marine natural products as a promising but unevenly validated foundation for the development of next-generation photodynamic agents, provided that their light-dependent activity, ROS generation, pharmacological properties and sustainable production are systematically established.