E. M. Bahnson1, H. Kassam1, K. T. Nennig3, M. J. Avram2,3, M. R. Kibbe1 1Feinberg School Of Medicine – Northwestern University,Vascular Surgery,Chicago, IL, USA 2Feinberg School Of Medicine – Northwestern University,Anesthesiology,Chicago, IL, USA 3Northwestern University,Donnelley Clinical Pharmacology Core,Chicago, IL, USA
Introduction: Nanoscale carriers that incorporate targeting information are emerging as a promising modality of delivering a therapeutic load with high efficacy and minimal toxicity to the vasculature. However there is little information about the pharmacokinetic properties of such compounds. To prevent neointimal hyperplasia, we developed a novel targeted therapy capable of delivering a therapeutic agent to the site of vascular injury via systemic administration, using a highly customizable peptide amphiphile (PA). The goal of this project is to study the disposition of the collagen-targeted PA and develop a pharmacokinetic model for it. We hypothesize that the targeted nanofibers will exhibit a pharmacokinetic behavior distinct from that of classic small molecule drugs.
Methods: PAs were synthesized using solid-phase peptide synthesis, and purified by preparative reverse-phase HPLC. Male Sprague Dawley rats received a single dose (2.5 mg) of PA via tail vein injection. Blood was collected for analysis at various times over three days (0.1, 0.2, 0.25, 0.5, 0.45, 1, 1.5, 2, 3, 4, 6, 8, 16, 24, 48, and 72 h; n=3/time point). After addition of a PA internal standard, samples were reduced with 5 mM tris(2-carboxyethyl)phosphine. Proteins were precipitated with acetonitrile before HPLC injection. Concentrations of the PA were determined by HPLC with mass spectrometry detection (Lower Limit of Quantification = 1 ng/ml). A multicompartmental pharmacokinetic model was then developed for the PA nanofibers.
Results: A 3-compartment pharmacokinetic model fit yielded the parameters shown in Figure 1. Estimate of the central volume is consistent with the volume of plasma and interstitial space in rats. The concentration of the nanofibers in plasma decreased two orders of magnitude in the first hour. The first fast exponential phase generally corresponds to distribution clearance of rapidly equilibrating tissues. However, for the PA nanofibers, this first exponential phase corresponded to elimination clearance, that is a process that removes the nanofibers from plasma irreversibly within the time frame of the study. The ex-vivo stability of the nanofibers in plasma revealed that this rapid process is not due to rapid degradation by plasma components. The very fast elimination clearance could be due to organ sequestration or irreversible conjugation.
Conclusions: We describe an unusual 3-compartment pharmacokinetic model of a targeted nanofiber that clearly differs from classic small molecule pharmacokinetics. This information becomes essential when trying to understand the differential properties of nanocarrier-based drugs. Further work is required in order to elucidate the mechanism responsible for the very fast elimination clearance.
