pH-Sensitive graphene oxide conjugate purpurin-18 methyl ester photosensitizer nanocomplex in photodynamic therapy

Abstract

Graphene oxide (GO) has been widely recognized as a good drug delivery vector due to its special properties and biocompatibility. Herein, a promising chlorophyll-a derivative photosensitizer, purpurin-18 methyl ester (Pu18), was introduced onto the surface of GO to investigate the drug loading and release properties. Pu18 is considered to be more suitable for the treatment of deeper tissues due to its strong absorption in the near infrared region (Q(0,0) band at 699 nm). The graphene oxide loaded Pu18 nanomaterial (GO–Pu18) was obtained via simple ultrasonic agitation and presented pH-sensitive drug release behavior. Pu18 could be released more easily from the GO–Pu18 composite in a weak acid environment than that in a neutral environment, suggesting that GO–Pu18 could be applied in tumor treatment due to the weak acid environment around tumor tissues. Moreover, GO–Pu18 showed an increased singlet oxygen (¹O₂) quantum yield (Φ_Δ = 62.60%) compared to free Pu18 (Φ_Δ = 58.82%) and showed remarkable photostability in phosphate buffer saline (PBS). In vitro experiments on HepG-2 cells showed that the GO–Pu18 composite possessed excellent photocytotoxicity and negligible dark toxicity. Cell morphological changes after PDT treatment also showed that GO–Pu18 could lead to remarkable damage of cancer cells under light, during which Type I (the generation of hydroxyl radicals) and Type II (the generation of singlet oxygen) photodynamic reactions occurred simultaneously, yet the Type II reaction might play a predominant role. The research has disclosed that the new composite GO–Pu18a is a favorable prospect in the treatment of PDT.