Applications of Melanin and Melanin-Like Nanoparticles in Cancer Therapy: A Review of Recent Advances

SIMPLE SUMMARY: Therapeutic vaccines represent an attractive strategy for cancer patients but have not yet achieved significant efficacy. Many strategies are currently being explored to improve their efficacy and, notably, different types of adjuvants are under development. Nanoparticle systems are promising adjuvants as they act as carriers for antigens to target antigen-presenting cells in lymph nodes. Among them, melanin-based nanoparticles are particularly interesting since they efficiently carry antigens into draining lymphoid tissues and display immunomodulatory properties. In addition, melanin-based nanoparticles can also play an active role in triggering anti-cancer responses in the context of photothermal therapy. This review summarizes the promising results of the melanin-based cancer vaccines recently reported in preclinical models. ABSTRACT: Thanks to the growing knowledge about cancers and their interactions with the immune system, a huge number of therapeutic cancer vaccines have been developed in the past two decades. Despite encouraging results in pre-clinical models, cancer vaccines have not yet achieved significant clinical efficacy. Several factors may contribute to such poor results, including the difficulty of triggering a strong immune response and the immunosuppressive tumor microenvironment. Many strategies are currently being explored. Different types of adjuvants have been incorporated into vaccine formulations to improve their efficacy, as cancer antigens are usually poorly immunogenic. Nanoparticle systems are promising tools as they act as carriers for antigens and can be surface-modified so that they specifically target antigen-presenting cells in lymph nodes. Bioinspired nanomaterials are ideal candidates thanks to their biocompatibility. Recently, melanin-based nanoparticles were reported to efficiently localize into draining lymphoid tissues and trigger immune responses against loaded antigens. In addition, by virtue of their photochemical properties, melanin-based nanoparticles can also play an immunomodulatory role to promote anti-cancer responses in the context of photothermal therapy. In this review, we discuss the above-mentioned properties of melanin, and summarize the promising results of the melanin-based cancer vaccines recently reported in preclinical models.