Overexpression of Human Methylmalonyl CoA Mutase in Mice after In Vivo Gene Transfer with Asialoglycoprotein/Polylysine/DNA Complexes

Methylmalonic acidemia resulting from genetic deficiency of methylmalonyl CoA mutase (MCM) is an often fatal metabolic disease. Somatic gene therapy for this disorder may require gene replacement in the liver. We describe overexpression of MCM in the liver of mice after in vivo gene delivery using asialoglycoprotein/polylysine/DNA (ASO/PL/DNA) targeted delivery to the liver of plasmids expressing recombinant MCM. After intravenous administration of the ASO/PL/DNA complex, the vector sequences are cleared from the blood with t1/2 = 2.5 min and >95% of the vector is taken up by the liver. Vector sequences are cleared from the liver with t1/2 = 1.0–1.3 hr. MCM enzyme activity in the liver increases to levels 30–40% over baseline 6–24 hr after injection. No acute or chronic toxicity was observed. This net level of expression is likely to be therapeutic for MCM if the complex could be administered repetitively to treat acute episodes of life-threatening acidosis or establish a steady-state level of MCM activity. Repetitive administration of the ASO/PL/DNA complexes in mice was associated with formation of antibodies against asialo-orosomucoid and the asialo-orosomucoid complex but not against DNA. Methylmalonic acidemia is an often fatal inborn error of metabolism that might be effectively treated by repetitive administration of a gene therapy with a short duration of action such as methods described for delivery of DNA expression vectors to the liver using asialoglycoprotein/DNA complexes. The present work describes studies of the pharmacokinetics and short-term toxicology of gene delivery using these methods, demonstrating that therapeutic levels of the enzyme methylmalonyl CoA mutase can be established in the liver, and illustrating the pharmacokinetic and toxicological challenges that remain in developing clinically applicable therapies.