271. Improved Gene Transfer with a New Class of PEG-Peptide Scavenger Receptor Inhibitors

Abstract

Scavenger receptors (SR) found on Kupffer and fenestrated endothelial cells of the recticuloendothelial system (RES) in liver are responsible for the capture and degradation of both viral1 and non viral gene delivery systems 2. SR inhibition using polyinosinic acid (Poly-I) has been shown to improve the gene transfer efficiency of AdV, AAV, and measles virus by blocking rapid metabolism in the liver. While Poly-I is reportedly not toxic to mice, co-administration of Poly-I with AdV decreases the lethal threshold for AdV in mice by an unknown mechanism1, making Poly-I inhibition of SR a clinically unacceptable approach to inhibit viral uptake by the RES in the liver. In the present study, we report the discovery of a new class of PEGylated polylysine peptides that are potent and safe SR inhibitors. PEGylated(30kDa)-Cys-Trp-Lys(N) (where N = 10, 15, 20, 25, and 30) were prepared by solid phase peptide synthesis and administered to mice i.v. with 125I-pGL3. Administration of 1 nmol of PEG-peptide with 1 mg of 125I-pGL3 resulted in capture of 60% of the polyplex dose by the liver. However, dose-escalation of the PEG-peptide revealed a dose-dependent decrease in 125I-pGL3 PEG-peptide polyplex capture by the liver, resulting from SR inhibition. A maximum dose of 80 nmols of PEG(30kDa)-Cys-Trp-Lys25 inhibited SR mediated uptake of 125I-pGL3 by the liver to 10%. The potency of PEG-peptide inhibition of SR was also dependent on the length of the Lys repeat, with Lys30kDa=Lys25Lys20Lys15 Lys10. Application of delayed hydrodynamic (HD)-stimulation at 1 hour post-pGL3 polyplex delivery resulted in potent gene expression only when administering a SR inhibitory dose (80 nmol) of PEG-peptide. The reported PEG-peptides are proposed to function by in situ formation of 30 nm albumin nanoparticles in the blood that bind to SRs. This new class of safe and potent SR inhibitors may have broad applications by improving both viral and non-viral delivery systems by blocking SR-mediated uptake in the liver.