PLASMID DELIVERY TO MUSCLE - RECENT ADVANCES IN POLYMER DELIVERY SYSTEMS

Preclinical studies involving intramuscular injection of plasmid into animals have revealed at least four significant variables that effect levels of gene expression (i.e., > fivefold effect over controls), inc luding the formulation, injection technique, species and pretreatment of the muscle with myotoxic agents to induce muscle damage. The uptake of plasmid formulated in saline has been shown to be a saturable proc ess, most likely via a receptor-mediated event involving the T tubules and caveolae. Pharmacokinetic studies have demonstrated that the bioa vailability of injected plasmid to muscle cells is very low, due to ra pid and extensive plasmid degradation by extracellular nucleases. We h ave developed protective, interactive, non-condensing (PINC) delivery systems designed to complex plasmids and to (i) protect plasmids from rapid nuclease degradation, (ii) disperse and retain intact plasmid in the muscle and (iii) facilitate the uptake of plasmid by muscle cells . PINC systems result in up to at least a one log increase in both the extent and levels of gene expression over plasmid formulated in salin e. We have combined the PINC delivery systems with two different muscl e-specific expression plasmids. After direct intramuscular injection o f these gene medicines, we have shown both local myotrophic and neurot rophic effects of expressed human insulin-like growth factor (hIGF-I) and the secretion of biologically active human growth hormone (hGH) in to the systemic circulation. (C) 1998 Elsevier Science B.V.