Folate chitosan conjugated doxorubicin and pyropheophorbide acid nanoparticles (FCDP–NPs) for enhance photodynamic therapy

Abstract

We prepared new folate chitosan conjugated doxorubicin (DOX) and pyropheophorbide acid (PPa) nanoparticles (FCDP–NPs) using an ionic gelation method with tripolyphosphate (TPP) to enhance photodynamic therapy activity, based on the considerations of the long absorption wavelength (683 nm) of pyropheophorbide acid (PPa) in water and the excellent chemotherapeutic characteristics of doxorubicin (DOX) in cancer therapy. The obtained FCDP–NPs demonstrated a typical spherosome structure, a strong near infrared (NIR) absorption (705 nm) and significantly improved stability and dispersity in PBS (pH = 5, 7, 9); as well as a high singlet oxygen quantum yield (Φ_Δ = 64%) compared to free PPa (Φ_Δ = 59.1%). In addition, the in vitro cell experiments suggested that FCDP–NPs could be uptaken by HepG2 cells quickly and were mainly located in the cell nucleus. FCDP–NPs showed improved PDT efficiency over pure PPa and DOX at the same concentration after irradiation. Specifically, FCDP–NPs could lead to a 92% inhibition rate on HepG2 cells at 40 μg mL⁻¹ (equal to 6 μg mL⁻¹ DOX). However, the pure DOX showed little cytotoxicity at 6 μg mL⁻¹, which suggests that a small amount of DOX could effectively enhance the PDT activities of PPa and lead to little “dark” cytotoxicity. Moreover, cell morphological changes after PDT treatment further indicated that FCDP–NPs could induce damage and apoptotic cell death efficiently. Finally, the photochemical mechanism of FCDP–NPs during PDT process was investigated by using specific quenching agents sodium azide (SA, a single oxygen quencher) and D-mannitol (DM, a hydroxyl radicals quencher), respectively. The results suggested that Type I and Type II photodynamic reactions can occur simultaneously, yet Type I reaction (the generation of hydroxyl radicals) might play a more important role. All these studies indicated that the FCDP–NPs could be potential nanoparticles in photodynamic cancer treatment.