Dynamic ROS-responsive hyperbranched polymer-based neuroprotective drug delivery system for pathogenesis-adaptive...

The limited delivery efficiency of most therapeutic drugs is a major challenge for effective treatment of ischemic stroke. Herein, we synthesized a ROS-cleavable thioacetal (TA)-linked precursor with multiple reactivities from scratch using a simple, rapid (<1 h), and efficient one-step 'thiol-alkyne' click chemistry approach. This precursor served as the structural framework for producing a three-dimensional, highly hyperbranched polymer (HBP_(TA)) via a mutual esterification cross-linking reaction. Following surface conjugation with brain-targeted borneol-PEG (Bo), the polymer self-assembled into Bo-HBP_(TA) NPs through a kinetically controlled assembly process, effectively encapsulating rapamycin. This nanoformulation administered intravenously in MCAO mice efficiently across the blood-brain barrier (BBB) to reach the targeted lesion and allowed for dynamically ROS-responsive on-demand release of payload under fluctuating pathophysiological conditions, achieving drug accumulation in the brain of up to 12.1 %ID/g of total administered dosage. The structural disintegration of NPs competitively scavenged intrinsic ROS, while the released rapamycin effectively activated mitophagy and restored autophagy flux (Beclin-1/Atg5/LC3/p62 axis) to remove dysfunctional mitochondria, thereby mitigating ongoing ROS production and inhibiting mitochondrial apoptosis (Bcl-2/Bax/Cleaved-Caspase-3 axis), leading to a 96.9 % reduction in apoptotic neurons. Furthermore, it remodeled the cerebral neuro-inflammatory microenvironment by promptly reprogramming microglia towards an anti-inflammatory phenotype (increased by 10.7-fold) and lowering pro-inflammatory cytokine secretion (TNF-α/IL-6/IL-1β decreased by 60 %). Consequently, the treatment significantly declined the infarction area from 46.2 % to 1.1 %, effectively normalized neurological structure and function, restored BBB integrity, and inhibited the microvascular leakage into the brain parenchyma during late reperfusion, offering a pathogenesis-adaptive sequential anti-stroke treatment strategy with huge clinical translational potential.