| Intravesical chemotherapy following transurethral resection of tumors is the gold standard for the treatment of superficial bladder cancer.Intravesical instillation involves the administration of therapeutic agents to the bladder through a catheter. It has a number of potential benefits including high drug concentration in bladder, unconcerned with complicated blood circulation and lymphatic system, and reducing the risk of systemic side effects compared with traditional systematic chemotherapy. However,recurrence rate in patients with NMIBC still remains high. This might be due to the poor penetration of instilled drugs and short drug residence in bladder.Objective:This study was designed to develop a drug delivery system which could enhance the permeability of drug and extend the drug residence time in bladder.Methods:For the development of this drug delivery system,Polyamidoamine (PAMAM) dendrimer was conjugated with polyethylene glyeol (PEG) at first.Then doxorubicin(DOX) was loaded into the relatively hydrophobic interior of the dendrimers by a physical method.Finally,DOX loaded PAMAM (PP-DOX) nanoparticles were incorporated into floating hydrogel to form PP-DOX/Gel drug delivery system,which was expected to extend the drug residence time. DLS and TEM were used to characterize the PP-DOX nanoparticles. Cell toxicity of PAMAM-PEG complexes o T24 human bladder cancer cells was evaluated using cell counting kit(CCK-8) assays. Dialysis bag methods were applied to evaluate the drug release behavior of PP-DOX under different conditions.In vitro release behavior of PP-DOX/Gel complexes under artificial urine was performed by dissolution tester. The release behavior in vivo of PP-DOX and PP-DOX/Gel complexes were assessed by a fluorescence microplate reader to reflect the retention time of the instilled drugs in the bladder.Frozen section and histological examinations were used to evaluate the penetration ability of PP-DOX nanoparticles and their effects on bladder mucous.Results:The average hydrodynamic diameter of PP-DOX was about 13nm,with an average zeta potential of +3.78mV. From the TEM image, the PP-DOX nanoparticles are uniformly dispersed in aqueous solution and have a diameter of 10～15nm. The stability of PP-DOX nanoparticles was evaluated by testing the size change of the nanoparticles in artificial urine and PBS buffer (pH 7.4). The size of nanoparticles remains consistent in both kinds of solution within 24 hours. Cellular toxicity test revealed that PAMAM-PEG was lower toxic to T24 cells compared with unmodified PAMAM. PAMAM-PEG complexes were non-toxic to T24 cells even at a high concentration of 800μg/ml.The release behaviors of DOX from PP-DOX nanoparticles showed that PP-DOX nanoparticles had remarkable sustained-release property and excellent pH-sensitive release property.In the acidic conditions, more DOX was released from the PP-DOX nanoparticles.When PP-DOX nanoparticles were incorporated with floating hydrogel, the release time could extend up to 3.5h.After intravesical instillation of DOX or PP-DOX,the drug concentration in bladder reached maximum value promptly,but dropped dramatically after the first voiding. However,the amount of drugs released from PP-DOX/Gel reached only 13.3% before the first voiding. After that, PP-DOX/Gel could still keep releasing slowly.Permeability studies revealed that PP-DOX could penetrate deeper into the bladder wall compared with DOX.In addition, the residues in PP-DOX/Gel group was more than other three groups.Finally,the bladder mucosa kept intact in NS and DOX groups after intravesical instillation,while the umbrella cells were disrupted in PP-DOX groups.Conclusions:PP-DOX /Gel consisted of PAMAM and floating hydrogel could enhance the permeability of drugs and extend the drug residence time in bladder. This drug delivery system provided a new perspective for effective intravesical therapy and had the potential to be applied as a carrier for treatment of bladder tumor in the future. |
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