Ethosomes and lipid-coated chitosan nanocarriers for skin delivery of a chlorophyll derivative: A potential treatment of squamous cell carcinoma by photodynamic therapy

Photodynamic therapy (PDT) is a localized treatment strategy used for skin cancers such as squamous cell carcinoma (SCC), the second most common form of skin cancer. PDT combines a photosensitizer, laser source and tissue oxygen. In this study, the selected photosensitizer, ferrous chlorophyllin (Fe-CHL) was loaded in ethosomes and lipid coated chitosan (PC/CHI) nanocarriers to enhance skin delivery of Fe-CHL for potential PDT of squamous carcinoma. The nanocarrier formulations were characterized and studied for their skin retention and penetration depth of Fe-CHL across mouse skin ex vivo using high performance liquid chromatography and confocal microscopy. Confocal microscope images of mouse skin showed deeper penetration of ethosomes down to the dermis when compared to PC/CHI that was confined to the epidermis, although they showed no significant difference in skin retention. Immunohistochemistry (IHC) staining with ki67 and TUNEL show maintained skin structure and no cytotoxic effects of the nanocarrier gel formulations before laser exposure to mouse skin. The nanocarriers were also studied for their PDT effect against human SCC monolayer and three-dimensional (3-D) spheroids. When compared to ethosomes, PC/CHI showed higher cytotoxicity in MTT assay and live confocal microscopy showed cell disintegration after laser exposure. For 3-D spheroids, PC/CHI also showed higher cytotoxicity using acid phosphatase assay and a decrease in spheroid size was observed using light microscopy. In conclusion, both types of nanocarriers can be used for their potential treatment of SCC using PDT depending on the tumour localization in the skin.