Impact of Molecular Weight on Pharmacokinetics, Biodistribution, and Renal Deposition of the Drug Delivery Biopolymer Elastin‐Like Polypeptide
Authors: Kuna Marija , Mahdi Fakhri , McGowan Jeremy W. D. , Bidwell Gene L. 
Published: November 2023

Chronic kidney disease (CKD) and end‐stage renal disease (ESRD) are on the rise in the United States, with one in ten American adults having some form of CKD. A surge in patient number will result in an increased need for resources, dialysis and transplant. CKD and ESRD are often caused by renal vascular disease (RVD) which affects the circulation of the kidney and may cause tissue damage, hypertension and kidney failure. Even with the current treatment regimens, which include antihypertensive medications, a statin, an antiplatelet agent, and sometimes percutaneous transluminal renal angioplasty with stent placement (PTRAS), RVD still progresses in a large number of patients. Therefore, identification of novel therapies to slow down, stop or reverse the progression of the disease is of great importance. Our lab is focused on the development of a kidney‐targeted drug delivery system. This drug delivery system is based on a bioengineered protein polymer called elastin‐like polypeptide (ELP). ELPs have a long plasma half‐life and can be easily modified. ELPs alone have an increased accumulation in kidneys when compared to other tissues, and the kidney deposition can be further amplified by fusion of ELP with a kidney‐targeting peptide. ELPs can be additionally fused to therapeutic peptides/proteins (TP) to target processes such as inflammation or angiogenesis for treatment of RVD. Given our focus on the development of ELP for kidney‐targeted drug delivery, the aim of this study is to investigate how the physical characteristics of ELP, including its molecular weight (MW) and hydrodynamic radius, affect its plasma clearance, biodistribution, kidney accumulation, and intrarenal distribution. Utilizing recursive directional ligation, we synthesized ELP expression constructs coding for ELP proteins ranging in size from 25 kDa to 110 kDa. Proteins were purified by inverse transition cycling, each protein was characterized for purity by SDS‐PAGE, and its hydrodynamic radius and transition temperature measured by dynamic light scattering and turbidity assays, respectively. ELPs were fluorescently labeled and administered to SKH1‐Elite hairless mice. Plasma clearance and total body fluorescence was determined after bolus intravenous injection to define the plasma pharmacokinetics and tissue clearance kinetics of the proteins. After acute administration of fluorescently labeled proteins, the biodistribution of each ELP construct was determined by whole‐organ ex vivo fluorescence imaging, and the intrarenal distribution was determined by confocal microscopy. Increasing the ELP MW from 25 kDa to 110 kDa resulted in an increase of the hydrodynamic radius from 5.7 to 7.02 nm. Turbidity assays showed that with an increase in MW, the ELP transition temperature decreased from 80 to 58°C. These data approach an asymptote where further increase in MW does not result in a change in radius or transition temperature. Ongoing experiments are examining the effect of MW on ELPs plasma half‐life, biodistribution and renal deposition.Support or Funding InformationSupported by NIH Grant R01HL121527 (GLB).