The effect of size, charge, and peptide ligand length on kidney targeting by small, organic nanoparticles

Chronic kidney disease (CKD) affects 15% of the US adult population. However, most clinically available drugs for CKD show low bioavailability to the kidneys and non-specific uptake by other organs which results in adverse side effects. Hence, a targeted, drug delivery strategy to enhance kidney drug delivery is highly desired. Recently, our group developed small, organic nanoparticles called peptide amphiphile micelles (PAM) functionalized with the zwitterionic peptide ligand, (KKEEE)₃K, that passage through the glomerular filtration barrier for kidney accumulation. Despite high bioavailability to the kidneys, these micelles also accumulated in the liver to a similar extent. To further optimize the physicochemical properties and develop design rules for kidney-targeting micelles, we synthesized a library of PAMs of varying size, charge, and peptide repeats. Specifically, variations of the original (KKEEE)₃K peptide including (KKEEE)₂K, (KKEEE)K, (EEKKK)₃E, (EEKKK)₂E, (EEKKK)E, KKKKK, and EEEEE were functionalized onto nanoparticles, and peptide surface density and PEG linker molecular weight were altered. After characterization with transmission electron microscopy (TEM) and dynamic light scattering (DLS), nanoparticles were intravenously administered into wildtype mice, and biodistribution was assessed through ex vivo imaging. All micelles localized to the kidneys, but nanoparticles that are positively-charged, close to the renal filtration size cut-off, and consisted of additional zwitterionic peptide sequences generally showed higher renal accumulation. Upon immunohistochemistry, micelles were confirmed to bind to the multiligand receptor, megalin, and histological analyses showed no tissue damage. Our study provides insight into the design of micelle carriers for kidney targeting and their potential for future therapeutic application.