Acute intermittent porphyria: vector optimization for gene therapy.
BACKGROUND
Acute intermittent porphyria (AIP) is an autosomal dominant disorder caused by the half-normal activity of hydroxymethylbilane synthase (HMB-synthase). Affected individuals can experience episodic, life-threatening, acute neurological attacks that are precipitated by various drugs, dieting, and hormonal changes. Intravenous hematin is used to treat the attacks, but a more effective, preventive therapy is needed, especially for patients with frequent attacks. Since the disease is a hepatic encephalopathy, efforts were focused towards evaluating four different combinations of liver-specific enhancers and promoters for maximal hepatic HMB-synthase expression.


METHODS
Four different mammalian expression vectors, each carrying a unique combination of liver-specific enhancers and promoters driving murine HMB-synthase cDNA expression, were transiently transfected into HepG2 cells. The vectors included: HMBS-1; human alpha1-microglobulin enhancer/alpha1-antityrpsin promoter (alpha1Me/alpha1ATp), HMBS-2; alpha1Me/human serum albumin promoter (alpha1Me/SAp), HMBS-3; human prothrombin enhancer/SAp (PTe/SAp), and HMBS-4; (PTe/alpha1ATp). Each HMB-synthase construct and a luciferase reporter construct were hydrodynamically coinjected into mice with HMB-synthase deficiency and evaluated for hepatic expression 24 h post-injection, the time-point of peak hepatic HMB-synthase expression.


RESULTS
Following transient transfection into HepG2 cells, HMBS-1 (alpha1Me/alpha1ATp) had the highest HMB-synthase expression level, with an approximately 8-fold increase over endogenous cellular activities. Construct HMBS-1 also had the highest hepatic HMB-synthase activity following hydrodynamic delivery into HMB-synthase deficient mice, with a approximately 6-fold increase over saline-treated mice.


CONCLUSIONS
These studies support the use of a gene therapy vector containing the alpha1Me/alpha1ATp combination for preclinical studies of the efficacy and safety of liver-targeted gene therapy for AIP.
Yasuda
Makiko
M
Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, NY 10029, USA.
Domaradzki
Maciej E
ME
Armentano
Donna
D
Cheng
Seng H
SH
Bishop
David F
DF
Desnick
Robert J
RJ
D000818:Animals; D004742:Enhancer Elements, Genetic / Q000235:genetics; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D011163:Hydroxymethylbilane Synthase / Q000235:genetics / Q000378:metabolism; D007267:Injections; D008099:Liver / Q000201:enzymology; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D017118:Porphyria, Acute Intermittent / Q000628:therapy*; D011401:Promoter Regions, Genetic / Q000235:genetics; D014162:Transfection
D008156:Luciferases; D011163:Hydroxymethylbilane Synthase