Systemic Effect of Human Growth Hormone after Intramuscular Injection of a Single Dose of a Muscle-Specific Gene Medicine

Abstract

A muscle-specific gene medicine is described that provides for long-term secretion of biologically active human growth hormone (hGH) from skeletal muscle into the systemic circulation. The hGH gene medicine is composed of a muscle-specific hGH plasmid expression system complexed with a protective, interactive, non-condensing (PINC™) delivery system. The muscle-specific gene expression system, pSK-hGH-GH, was constructed by linking the promoter/enhancer regions of chicken skeletal α-actin to hGH gene. C₂C₁₂ myoblast transfection with pSK-hGH-GH resulted in the synthesis of hGH in a muscle-specific manner. Direct injection into rat tibialis cranialis muscle of pSK-hGH-GH complexed with a polymeric PINC delivery system, polyvinylpyrrolidone (PVP), produced hGH levels in muscle that were 10- to 15-fold higher compared with plasmid formulated in saline at 14 days post-injection. Intratracheal instillation in rat lung of pSK-hGH-GH did not produce significantly detectable levels of hGH. In hypophysectomized rats, a single intramuscular dose of the pSK-hGH-GH/PVP complex resulted in hGH expression and a subsequent increase in serum levels of rat IGF-I and growth. hGH expression and effects on rat serum IGF-I levels were detectable up to 28 days after injection of formulated plasmid and effects on growth were detectable unto 21 days. Anti-hGH antibodies were detectable in serum at 14 days post-injection, reached a plateau at 21 days, and remained elevated through the study period. Cyclosporin treatment of the pSK-hGH-GH/PVP-injected animals completely inhibited the antibody response and resulted in increased hGH expression. A muscle-specific gene medicine composed of a plasmid-based human growth hormone (hGH) gene expression system and a polymeric PINC delivery system, was developed to achieve systemic effects of biologically active hGH after intramuscular injection. Muscle injection of a single dose of hGH gene medicine results in sustained levels of hGH in muscle and that these levels are 10- to 15-fold higher than pSK-hGH-GH formulated in isotonic saline. The expression of pSK-hGH-GH was muscle-specific when examined both in vitro and in vivo. The hGH produced in the muscle was biologically active and secreted into the systemic circulation. The expression and biological effects of hGH persisted for up to 21 days after plasmid injection. The loss of hGH effect over time was coincidental with the appearance of hGH antibodies. The inhibition of hGH antibody response and increase in hGH expression by immunosuppressive dose of cyclosporin suggest that the expression and biological effects of hGH gene medicine were modified by immunological processes.