RT Journal Article
SR Electronic
T1 Engineered Antibody Fragments with Infinite Affinity as Reporter Genes for PET Imaging
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 1828
OP 1835
DO 10.2967/jnumed.108.054452
VO 49
IS 11
A1 Liu H. Wei
A1 Tove Olafsen
A1 Caius Radu
A1 Isabel J. Hildebrandt
A1 Mark R. McCoy
A1 Michael E. Phelps
A1 Claude Meares
A1 Anna M. Wu
A1 Johannes Czernin
A1 Wolfgang A. Weber
YR 2008
UL http://jnm.snmjournals.org/content/49/11/1828.abstract
AB Reporter gene imaging has great potential for many clinical applications including the tracking of transplanted cells and monitoring of gene therapy. However, currently available reporter gene–reporter probe combinations have significant limitations with the biodistribution of the reporter probe and the specificity and immunogenicity of the reporter gene. The objective of the present study was to evaluate a new approach for reporter gene imaging based on cell surface expression of antibody fragments that can irreversibly bind to radiometal chelates. Methods: We developed a new reporter gene, designated 1,4,7,10-tetraazacyclodocecane-N,N′,N″,N‴-tetraacetic acid (DOTA) antibody reporter 1 (DAbR1), which consists of the single-chain Fv (scFv) fragment of the anti-Y-DOTA antibody 2D12.5/G54C fused to the human T cell CD4 transmembrane domain. The corresponding reporter probe is yttrium-(S)-2-(4-acrylamidobenzyl)-DOTA (*Y-AABD), a DOTA complex that binds irreversibly to a cysteine residue in the 2D12.5/G54C antibody. U-87 glioma cells were stably transfected with a DAbR1 expression vector. Binding of *Y-AABD to transfected and wild-type cells was studied in vitro and in vivo. Results: Flow cytometry revealed high expression of the DAbR1 protein on the cell surface of tumor cells. Uptake of 90Y-AABD in DAbR1-expressing human U-87 glioma xenografts was 6.2 (±1.3) percentage injected dose per gram (%ID/g) at 1 h and 4.9 (±0.62) %ID/g at 24 h after injection. The corresponding tumor-to-plasma ratios were 45:1 and 428:1, respectively. Uptake by U-87 tumors without the DAbR1 gene was 0.16 (±0.02) %ID/g at 1 h and 0.05 (±0.03) %ID/g at 24 h. PET images in mice with 86Y-AABD demonstrated intense uptake in DAbR1-positive tumors and low background activity in the liver. Conclusion: These findings indicate that cell surface expression of radiometal chelate binding antibodies such as 2D12.5/G54C is a promising strategy for reporter gene imaging.