Decline in exogenous gene expression in primate brain following intravenous administration is due to plasmid degradation.

PURPOSE: Nonviral gene transfer to the brain of adult Rhesus monkeys is possible with a single intravenous administration of plasmid DNA that is encapsulated in the interior of pegylated immunoliposomes, which are targeted across membrane barriers in vivo with a monoclonal antibody to the human insulin receptor.
METHODS: The present studies measure the rate of decay of luciferase gene expression in the Rhesus monkey with luciferase enzyme assays, Southern blotting, and real-time polymerase chain reaction.
RESULTS: Luciferase enzyme activity in frontal cortex, cerebellum, and liver decays with a t(1/2) of 2.1 +/- 0.1, 2.6 +/- 0.2, and 1.7 +/- 0.01 days, respectively. Luciferase plasmid in brain and liver was detectable by Southern blotting at 2 days, but not at 7 or 14 days. The concentration of luciferase plasmid DNA in brain and liver was measured by real-time polymerase chain reaction, and decayed with t(1/2) of 1.3 +/- 0.3 and 2.7 +/- 0.5 days, respectively.
CONCLUSIONS: The maximal concentration of luciferase plasmid DNA in Rhesus monkey brain was 3-4 molecules/cell following an i.v. administration of 12 microg/kg pegylated immunoliposome encapsulated plasmid DNA. These results demonstrate that the rate of loss of exogenous gene expression in the primate in vivo correlates with the rate of DNA degradation of the exogenous plasmid DNA.