¹Protiva Biotherapeutics, Burnaby, British Columbia, Canada

Correspondence: Ian MacLachlan, Protiva Biotherapeutics, 100-3480 Gilmore Way, Burnaby, British Columbia, Canada V5G 4Y1. E-mail: ian@protivabio.com

Received 10  2006; Accepted 1 December 2006; Published online 13 February 2007.

Abstract

Using a new controlled mixing process, highly transfection-competent polyplexes were formed and subsequently encapsulated within a lipid bilayer. The resulting "pre-condensed stable plasmid lipid particles" (pSPLPs) have small size (1043 nm) and low surface charge characteristics. The formulation process equally enabled lipid encapsulation of either poly-L-lysine or poly(ethyleneimine) (PEI) condensed DNA, and the endosomolytic benefits of PEI were demonstrated in in vitro gene expression studies. The clearance properties of pSPLP were compared to similar formulations with an uncondensed payload (SPLP) in A/J mice bearing subcutaneous Neuro-2a tumors. Plasma clearance of pSPLP (t_1/2=6.6 h) was similar to SPLP (t_1/2=7.1 h), allowing significant accumulation at distal tumor target sites. Gene expression profiles were evaluated in vivo using the Neuro-2a model, and PEI-pSPLP formulations demonstrated a sixfold increase in reporter gene expression in tumors compared to SPLP. No significant gene expression was observed in the liver, lung, or spleen when mice were treated with either SPLP or pSPLP, and both formulations were equally well tolerated. The results support the lipid encapsulation of polyplex plasmid DNA as a means of changing its pharmacologic properties and enabling systemic delivery. The inclusion of endosomolytic DNA-condensing agents such as PEI greatly improves the potency of SPLP.