Purpose: To develop an intravesical instillation system for the treatment of bladder cancer, rapamycin (Rap) was encapsulated into liposomes and then homogeneously dispersed throughout a poloxamer 407 (P407)-based hydrogel.
Methods: Rap-loaded conventional liposomes (R-CL) and folate-modified liposomes (R-FL) were prepared using a film hydration method and pre-loading technique, and characterized by particle size, drug entrapment efficiency, and drug loading. The cellular uptake behavior in folate receptor-expressing bladder cancer cells was observed by flow cytometry and confocal laser scanning microscopy using a fluorescent probe. In vitro cytotoxic effects were evaluated using MTT assay, colony forming assay, and Western blot. For in vivo intravesical instillation, Rap-loaded liposomes were dispersed in P407-gel, generating R-CL/P407 and R-FL/P407. Gel-forming capacities and drug release were evaluated. Using the MBT2/Luc orthotopic bladder cancer mouse model, in vivo antitumor efficacy was evaluated according to regions of interest (ROI) measurement.
Results: R-CL and R-FL were successfully prepared, at approximately <160 nm, 42% entrapment efficiency, and 57 μg/mg drug loading. FL cellular uptake was enhanced over 2-fold than that of CL; folate receptor-mediated endocytosis was confirmed using a competitive assay with folic acid pretreatment. In vitro cytotoxic effects increased dose-dependently. Rap-loaded liposomes inhibited mTOR signaling and induced autophagy in urothelial carcinoma cells. With gelation time of <30 seconds and gel duration of >12 hrs, both R-CL/P407 and R-FL/P407 preparations transformed into gel immediately after instillation into the mouse bladder. Drug release from the liposomal gel was erosion controlled. In orthotopic bladder cancer mouse model, statistically significant differences in ROI values were found between R-CL/P407 and R-FL/P407 groups at day 11 (P=0.0273) and day 14 (P=0.0088), indicating the highest tumor growth inhibition by R-FL/P407.
Conclusion: Intravesical instillation of R-FL/P407 might represent a good candidate for bladder cancer treatment, owing to its enhanced retention and FR-targeting.
Keywords: antitumor efficacy; autophagy; bladder cancer; enhanced uptake; mTOR signaling; prolonged retention.