Real-time imaging of convection-enhanced delivery of viruses and virus-sized particles.
OBJECTIVE
Despite recent evidence showing that convection-enhanced delivery (CED) of viruses and virus-sized particles to the central nervous system (CNS) is possible, little is known about the factors influencing distribution of these vectors with convection. To better define the delivery of viruses and virus-sized particles in the CNS, and to determine optimal parameters for infusion, the authors coinfused adeno-associated virus ([AAV], 24-nm diameter) and/or ferumoxtran-10 (24 nm) by using CED during real-time magnetic resonance (MR) imaging.


METHODS
Sixteen rats underwent intrastriatal convective coinfusion with 4 microl of 35S-AAV capsids (0.5-1.0 x 10(14) viral particles/ml) and increasing concentrations (0.1, 0.5, 1, and 5 mg/ml) of a similar sized iron oxide MR imaging agent (ferumoxtran-10). Five nonhuman primates underwent either convective coinfusion of 35S-AAV capsids and 1 mg/ml ferumoxtran-10 (striatum, one animal) or infusion of 1 mg/ml ferumoxtran-10 alone (striatum in two animals; frontal white matter in two). Clinical effects, MR imaging studies, quantitative autoradiography, and histological data were analyzed.


RESULTS
Real-time, T2-weighted MR imaging of ferumoxtran-10 during infusion revealed a clearly defined hypointense region of perfusion. Quantitative autoradiography confirmed that MR imaging of ferumoxtran-10 at a concentration of 1 mg/ml accurately tracked viral capsid distribution in the rat and primate brain (the mean difference in volume of distribution [Vd] was 7 and 15% in rats and primates, respectively). The Vd increased linearly with increasing volume of infusion (Vi) (R2 = 0.98). The mean Vd/Vi ratio was 4.1 +/- 0.2 (mean +/- standard error of the mean) in gray and 2.3 +/- 0.1 in white matter (p < 0.01). The distribution of infusate was homogeneous. Postinfusion MR imaging revealed leakback along the cannula track at infusion rates greater than 1.5 microl/minute in primate gray and white matter. No animal had clinical or histological evidence of toxicity.


CONCLUSIONS
The CED method can be used to deliver AAV capsids and similar sized particles to the CNS safely and effectively over clinically relevant volumes. Moreover, real-time MR imaging of ferumoxtran-10 during infusion reveals that AAV capsids and similar sized particles have different convective delivery properties than smaller proteins and other compounds.
Szerlip
Nicholas J
NJ
Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1414, USA.
Walbridge
Stuart
S
Yang
Linda
L
Morrison
Paul F
PF
Degen
Jeffrey W
JW
Jarrell
S Taylor
ST
Kouri
Joshua
J
Kerr
P Benjamin
PB
Kotin
Robert
R
Oldfield
Edward H
EH
Lonser
Russell R
RR
D000818:Animals; D001921:Brain / Q000378:metabolism*; D003287:Contrast Media / Q000008:administration & dosage / Q000493:pharmacokinetics*; D018481:Convection; D000229:Dependovirus; D003911:Dextrans; D052203:Ferrosoferric Oxide; D005822:Genetic Vectors / Q000008:administration & dosage / Q000493:pharmacokinetics*; D007091:Image Processing, Computer-Assisted; D007263:Infusions, Parenteral; D007501:Iron / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008252:Macaca fascicularis; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles; D010087:Oxides / Q000008:administration & dosage / Q000493:pharmacokinetics*; D010316:Particle Size; D051381:Rats; D017207:Rats, Sprague-Dawley
D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C097921:ferumoxtran-10; D007501:Iron; D052203:Ferrosoferric Oxide