Intravesical drug delivery approaches for improved therapy of urinary bladder diseases

Diseases of the urinary bladder have high incidence rates and burden healthcare costs. Their pharmacological treatment involves systemic and local drug administration. The latter is generally accomplished through instillation of liquid formulations and requires repeated or long-term catheterization that is associated with discomfort, inflammation and bacterial infections. Consequently, compliance issues and dropouts are frequently reported. Moreover, instilled drugs are progressively diluted as the urine volume increases and rapidly excreted. When penetration of drugs into the bladder wall is needed, the poor permeability of the urothelium has also to be accounted for. Therefore, much research effort is spent to overcome these hurdles, thereby improving the efficacy of available therapies. Particularly, indwelling delivery systems suited for i) insertion into the bladder through the urethra, ii) intra-organ retention and prolonged release for the desired time lapse, iii) final elimination, either spontaneous or by manual removal, have been proposed to reduce the number of catheterization procedures and reach higher drug levels at the target site. Vesical retention of such devices is allowed by the relevant expansion that can either be triggered from the outside or achieved exploiting elastic and purposely 4D printed shape memory materials. In this article, the main rationales and strategies for improved intravesical delivery are reviewed.

Chitosan-coated nanodiamonds: Mucoadhesive platform for intravesical delivery of doxorubicin

Nanodiamonds (NDs) are an emerging delivery system with a massive surface area qualifying them for efficient loading with various drugs. However, NDs easily scavenge ions upon mixing with physiological media leading to rapid aggregation. Herein, chitosan was employed to endue steric stabilization to NDs and confer adhesiveness to the particles improving their retention in the urinary bladder. The effect of chitosan molecular weight and pH on the particle size and surface charge of chitosan-coated doxorubicin-loaded NDs (Chi-NDX) was investigated. Selected formula exhibited high drug loading efficiency (>90 %), small particle size (<150 nm), good colloidal stability, acid-favored drug release but limited stability in cell culture media. After further stabilization with TPP or dextran sulfate, selected TPP-treated formula displayed more potent cytotoxic effect compared with free doxorubicin and uncoated nanoparticles, and higher drug retention in ex vivo bovine bladder. Therefore, TPP-Chi-NDX is suggested as a promising system for mucosal anticancer delivery.

Enhancement of transduction efficiency using Adeno-associated viral vectors by chemical pretreatment to mice bladder urothelium

Adeno-associated virus (AAV) vectors have been recognized as promising tools for gene delivery. The bladder is a seemingly ideal organ for virus transfer, with easy access through the urethra enabling organ-specific delivery. However, achieving adequate transduction efficiency in the urothelium has been a major challenge because of the barrier function of the glycosaminoglycan (GAG) layer. We investigated optimal pretreatments of the bladder urothelium to maximize transduction efficiency by AAV vectors in vivo. Murine bladders were pretreated with five different chemical agents followed by transurethral instillation with an AAV2 vector encoding a tdTOMATO reporter. After 7 days, transduction efficiency of the urothelium was evaluated. Bladder urothelia pretreated with HCl showed clear evidence of AAV infection and gene delivery. Mice treated with 0.1 N HCl for 4 min showed significantly higher survival rates (nearly 80 %) compared with mice receiving other pretreatment regimens. AAV vector transduction in the urothelium was observed in seven of 20 mice (35 %), and the mean transduction efficiency in these mice was 14.5 %. Thus, HCl pretreatment enhanced transduction efficiency of the mice bladder urothelium by an AAV vector in vivo. Pretreatment with 0.1 N HCl for 4 min was the optimal condition to maximize survival and transduction efficiency of the urothelium.