An SS31-rapamycin conjugate via RBC hitchhiking for reversing acute kidney injury

Mitochondrial dysfunction plays a major role in driving acute kidney injury (AKI) via alteration in energy and oxygen supply, which creates further ROS and inflammatory responses. However, mitochondrial targeting medicine in recovering AKI is challenging. Herein, we conjugated SS31, a mitochondria-targeted antioxidant tetrapeptide connecting a cleavable linker to rapamycin (Rapa), which provided specific interaction with FK506-binding protein (FKBP) in the RBCs. Once entering the bloodstream, SS31-Rapa could be directed to the intracellular space of RBCs, allowing the slow diffusion of the conjugate to tissues via the concentration gradient. The new RBC hitchhiking strategy enables the encapsulation of conjugate into RBC via a less traumatic and more natural and permissive manner, resulting in prolonging the t_1/2 of SS31 by 6.9 folds. SS31-Rapa underwent the direct cellular uptake, instead of the lysosomal pathway, released SS31 in response to activated caspase-3 stimulation in apoptotic cells, favoring the mitochondrial accumulation of SS31. Combined with autophagy induction associated with Rapa, a single dose of SS31-Rapa can effectively reverse cisplatin and ischemia reperfusion-induced AKI. This work thus highlights a simple and effective RBC hitchhiking strategy and a clinically translatable platform technology to improve the outcome of other mitochondrial dysfunctional related diseases.