Fabrication and characterization of liposomal drug formulations for lipo-gel depot to treat urological diseases

• Main Author: Yee, Zhen Lin
• Other Authors: Subbu S. Venkatraman
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/76744
• Institution: Nanyang Technological University

Upper tract urothelial carcinoma (UTUC) and ureteral stricture are two of the several urological diseases that plague the ureter. The use of a highly anti-proliferative drug, paclitaxel, to treat and manage these urological disorders have been documented. The highly drug impermeable urothelium however presents a formidable barrier for the effective drug transport. Longer drug residency time through the co-aptation of drug with the urothelial wall have been reported to be capable of increasing the efficiency in drug penetration across the barrier membrane. Achieving a sustained drug delivery system is crucial for the treatment and management of these chronic diseases. More importantly, since the drug absorption by urothelium is expected to be much lower than the drug released due to its impermeable nature, the critical objective is to deliver as much drugs to the target within the tolerable safe dosage. In this project, a novel swellable hydrogel coating loaded with liposome-containing paclitaxel, coated on ureteric stent, is proposed to overcome the limitations on the current clinical methods for ureteric carcinoma and stricture. Herein, candidate liposomal drug formulations for the lipo-gel depot of the swellable drug eluting ureteric stent (SDEUS) were designed and characterized. Liposomes of different lipids, including saturated and unsaturated types, with the addition of additives such as cholesterol and DOTAP, were fabricated by microfluidics. Particle size, drug loading, encapsulation efficiency, stability (size and charge of liposomes as well as drug encapsulated in liposomes) and drug release were evaluated. Results demonstrated that out of the 5 lipid candidates (POPC, EPC, SPC, DMPC, DPPC), only POPC, EPC and DMPC based liposomes could be fabricated successfully without aggregation during the removal of residual ethanol via ultracentrifugation. Moreover, drug loading studies showed loading followed in the order: POPC < EPC < DMPC, with drug loading and encapsulation efficiency of 7.5% and 19.4% for 5% mol and 10% mol of paclitaxel (w.r.t. lipids), respectively. Higher drug loading for DMPC over POPC and EPC was due to the shorter acyl chain length of DMPC (C14) that resulted in weaker van der ii Waals forces, hence higher flexibility to incorporate PTX. Incorporating cholesterol at 30% mol was found to increase drug loading regardless of lipid saturation. Stability studies demonstrated batch-to-batch variations, with the first round of stability study demonstrating much instability in liposome, size and charge whereas a second study demonstrated an overall stable liposomal formulations. Finally, drug release studies conducted under static fluid flow with perfect sink condition fulfilled, demonstrated that EPC-100 (5% mol paclitaxel) released the greatest amount of drug (up to 88%) within the 14 days of release period, whereas EPC-60 released the lowest amount (24%). In contrast to the expected faster rate of release for DMPC based liposomes due to its shorter acyl chain length that facilitates faster drug transport out of the bilayer, DMPC based liposomes had an overall retarded release rate as compared to that of POPC and EPC based liposomes of longer chain length (16C:18C). Such observation could be due to the instability of liposomes due to variations in batch fabrication as observed in the stability studies. Nevertheless, the addition of cholesterol elicited the expected results, in which cholesterol reduced the drug release rate for unsaturated lipids, whereas it increased the drug release rate for saturated lipids, due to the modulation of lipid flexibility. To add on, the release of drug was sustained for all liposomal formulations during the 14-days study period, which is an important feature for the treatment of chronic diseases such as stricture and carcinoma. In addition, for all liposomal formulations, even though the release did not follow a zero order kinetics, the drug released per day was found to be above the minimum effective concentration reported in literature (8.5 ng/mL) which was required to inhibit urothelial bladder cancer cells in-vitro. In conclusion, the study demonstrated liposomes as potential carrier of PTX and provided a preliminary comparative assessments of the tunable liposomal drug formulation candidates required for the subsequent future studies in the formulations and the involvement of hydrogel for the coating formulation on ureteric stent device.