Stimuli-Responsive Polymeric Conjugates of Tacrolimus: A pH/Redox-Triggered Approach toward Precision Drug Delivery

A dual pH- and redox-responsive macromolecular prodrug of tacrolimus (TAC; FK506) was strategically developed through a stepwise approach involving the conjugation of hyaluronic acid (HA) with cystamine, followed by hydrazide functionalization and final coupling with succinate-modified tacrolimus. The resulting conjugate HA-cystamine-hydrazide-tacrolimus (HA-ss-NHNH₂-TAC or HSNT), confirmed by ¹H NMR, spontaneously formed stable micellar nanostructures as observed under a transmission electron microscope (TEM). The developed micelles possess an average particle size of about 200 nm, as measured by dynamic light scattering (DLS) and exhibited an acceptable polydispersity index, suggesting a relatively uniform and consistent size distribution. The developed system exhibited a high drug loading capacity (10.24%). Cellular uptake studies demonstrated that pretreatment of HCT-116 cells with excess HA to block CD44 receptors significantly reduced intracellular fluorescence, confirming receptor-mediated endocytosis of TAC/HSNT micelles. Further, hemolysis analysis showed less than 5% hemolysis upon incubation with red blood cells, highlighting the nonhemolytic and biocompatible nature of the micelles at the tested concentrations. The dual responsive polymeric micelles have the potential for further translational studies.