Enhanced photo/chemo combination efficiency against bladder tumor by encapsulation of DOX and ZnPC into in situ-formed thermosensitive polymer hydrogel

BACKGROUND: Chemotherapy after transurethral resection is commonly recommended for bladder cancer. However, studies have shown that chemotherapy solely can hardly decrease progression rates of bladder cancer. The combination of chemotherapeutic agents with photo-dynamic therapy (PDT), a new promising localized therapy, may become a workable strategy for combating bladder cancer. This study reports the combination of doxorubicin (DOX)-based chemotherapy and zinc phthalocyanine (ZnPC)-based PDT using in situ-formed thermal-responsive copolymer hydrogel. MATERIALS AND METHODS: The copolymer was synthesized by polymerization of 3-caprolactone, 1,4,8-trioxa[4.6]spiro-9-undecanone and poly(ethylene glycol) and was abbreviated as PCL-PTSUO-PEG. The thermal-responsive nanoparticles (TNPs) were prepared by the nanoprecipitation technology. The thermal-responsive hydrogel was formed after 37°C heating of TNP solution. The size, morphology and dynamic viscosity of hydrogel were detected. The in vitro drug release profile of TNP/DOX/ZnPC was performed. Cell uptake, cell inhibition and ROS generation of TNP/DOX/ZnPC were studied in 5637 cells. The in vivo antitumor activity of TNP/DOX/ZnPC was evaluated in nude mice bearing 5637 cells xenograft. RESULTS: TNP/DOX and TNP/ZnPC had an average diameter of 102 and 108 nm, respectively. After being heated at 37°C for 5 minutes, TNP/DOX and TNP/ZnPC solution turned uniform light red and dark green hydrogel. ZnPC encapsulation designed by TNP could significantly improve its aqueous solubility to 1.9 mg/mL. Cell inhibition showed that the best cell inhibition was found, with cell viability of 18.5%, when the weight ratio of DOX and ZnPC encapsulated in the TNP reached about 1:5. TNP/DOX/ZnPC generated relative high level of ROS with 4.8-fold of free ZnPC and 1.6-fold of TNP/ZnPC. TNP/DOX/ZnPC showed only 8-fold of relative tumor growth without obvious toxicity to the mice. CONCLUSION: Thermosensitive thermal-responsive hydrogel reported in this contribution are promising in situ-formed matrix for DOX- and ZnPC-based photo/chemo combination treatment for bladder cancer therapy.