Nano‐Mediated PDT as a Multifunctional Immunomodulatory Agent in the Intricate Milieu of Melanoma

Abstract

Abstract The complexity of the tumor microenvironment (TME) and nutrient competition represent the main causes of therapy resistance in cancers, including malignant melanoma (MM). Photodynamic therapy (PDT), through a cascade of events including its ability to induce significant immune responses, causes tumor eradication. However, the high pigmentation level of melanoma, lack of adequate accumulation of photosensitizers (PSs) in the target tissue as well as their nonspecific toxicity represent three main obstacles to obtaining satisfactory responses in melanoma. To prevail over these challenges, this study employs a depigmentation strategy followed by a nano‐mediated topical application of PDT using a chlorophyllin derivative as PS, focusing on the evaluation of the immunomodulatory and metabolic regulatory axes of PDT in melanoma. Photo‐immunomodulation is assessed in a melanoma mouse model using a nanocarrier system of the PS. Markers of the immunosuppressive microenvironment and T cell exhaustion, as independent immune hallmarks, are quantified. The histopathology of the spleen and skin/tumor is evaluated. The amino acid profile is quantified from normal skin or tumor biopsies using UHPLC‐MS/MS. Around 80% of the 300 nm transethosomal ferrous chlorophyllin (fC‐TEs) are retained in the tumor over 24 h upon topical application. Arbutin 2% gel not only decreased the melanin content of tumors but also regulated the expression of interleukin 12 (IL‐12), IL‐10, transforming growth factor beta (TGF‐β), and tumor necrosis factor‐alpha (TNF‐α). Additionally, the nano‐mediated PDT strategy decreased the expression of programmed cell death protein 1 (PD‐1) and its ligand 1 (PD‐L1) and reduces the activity of arginase 1 (Arg1) through an upregulation of miRNA155. A mild recruitment of megakaryocytes (MKs) is observed in the spleen of the PDT group. This special localization of MKs depicts effector immune properties. Lastly, the combination of PDT and arbutin restores the normal tissue levels of arginine (Arg), and glutamine (Gln) and lavished those of tryptophan (Trp). Nano‐mediated PDT represents a novel immunotherapeutic approach in melanoma by a triple modulation of the immune suppressive TME, immune checkpoint signaling, and reprogrammed tumor metabolism.