A water-soluble phosphorescent conjugated polymer brush for tumor-targeted photodynamic therapy

Photodynamic therapy (PDT) has become a promising treatment approach against cancer due to low side effects and high therapeutic efficacy. However, the limitations of photosensitizers such as poor water solubility and lack of targeting ability hindered the clinical application of PDT. Here, we synthesized a phosphorescent conjugated polymer brush (PPF-Ir-g-(POEGMA-b-PGal)) in which a small photosensitizer iridium(iii) complex was covalently attached to the conjugated backbone. A further hydrophilic polymer (POEGMA) and glycopolymer polygalactose (PGal), which has a specific binding ability with Hep G2 tumors, were grafted from the conjugated backbone via atom transfer radical polymerization (ATRP) and click reaction. The brush structure rendered PPF-Ir-g-(POEGMA-b-PGal) exhibited excellent water solubility. Meanwhile, PPF-Ir-g-(POEGMA-b-PGal) showed efficient properties of producing singlet oxygen. The photodynamic effect of the PPF-Ir-g-(POEGMA-b-PGal) photosensitizer was evaluated in Hep G2 cells via the MTT assay and flow cytometry and the results indicated that this photosensitizer can efficiently cause the death of cancer cells. Additionally, an antitumor study of PPF-Ir-g-(POEGMA-b-PGal) was conducted in vivo with Hep G2 tumor bearing nude mice, and the results show that the xenograft tumors were significantly inhibited. In summary, PPF-Ir-g-(POEGMA-b-PGal) exhibited fine water solubility and high PDT efficiency both in vitro and in vivo. Our study may further encourage the applications of conjugated polymer brush based photosensitizers for PDT in tumor treatment.