Targeted Photodynamic Activity of a Hyaluronic Acid–Protoporphyrin IX Complex via Receptor‐Mediated Endocytosis

ABSTRACT Hyaluronic acid (HA) is not only biocompatible, biodegradable, stable in vivo, nontoxic, and non‐immunogenic, but also specifically binds to the cluster of differentiation 44 (CD44) receptor, which is overexpressed in many solid tumors. Therefore, we investigated unmodified HA as a drug carrier. In this study, protoporphyrin IX ( 1 ) was water‐solubilized at high concentrations through complexation with unmodified HA using a high‐speed vibration milling apparatus without the use of organic solvents. The resulting HA– 1 complex formed a stable aqueous solution that remained intact for at least one week. Cellular uptake studies revealed approximately five times greater internalization of 1 from the HA– 1 complex in human lung cancer cells (A549) than in murine fibroblast‐like cells (L929). Its selectivity index ( = half maximal inhibitory concentration [IC 50 ] in normal cells (L929)/IC 50 in cancer cells [A549]) was approximately 10.3, demonstrating strong selectivity toward cancer cells. Further, the uptake of HA– 1 in A549 cells was suppressed following the addition of free HA, indicating that its internalization occurred through CD44‐receptor‐mediated endocytosis. Moreover, the HA– 1 complex exhibited better photodynamic activity against CD44‐overexpressing cancer cells than both poly‐L‐lysine– 1 complex and Photofrin, underscoring its potential as a targeted photosensitizer for photodynamic therapy.