Technetium-99m radiolabeling using a phage-derived single-chain Fv with a C-terminal cysteine.
Single-chain Fv (scFv) antibody fragments have potential for clinical imaging because of their rapid tumor penetration and high tumor-to-tissue ratios at early time points. ScFvs clear rapidly from the circulation so radiolabels such as 99mTc which have short half-lives are desirable, but the free thiol groups necessary for labeling with 99mTc are not normally found on these molecules.


METHODS
We constructed a vector which enabled a free cysteine to be linked to the C-terminus of scFvs. MFE-23, a scFv directed against carcinoembryonic antigen (CEA), was cloned into this vector and cys-tagged MFE-23 was labeled with 99mTc using a D-glucarate transfer method.


RESULTS
The radiolabeled product was stable in vivo and in vitro and showed favorable tumor-to-blood ratios in vivo at early time points (4:1 at 24 hr and 8:1 at 48 hr), although high kidney levels were also detected.


CONCLUSIONS
Our study demonstrates an effective method to enable scFvs radiolabeling with 99mTc and also shows the potential of using a 99mTc-labeled scFv for clinical imaging studies.
Verhaar
M J
MJ
CRC Laboratories, Department of Clinical Oncology, Royal Free Hospital School of Medicine, London, United Kingdom.
Keep
P A
PA
Hawkins
R E
RE
Robson
L
L
Casey
J L
JL
Pedley
B
B
Boden
J A
JA
Begent
R H
RH
Chester
K A
KA
D000230:Adenocarcinoma / Q000000981:diagnostic imaging; D000818:Animals; D003110:Colonic Neoplasms / Q000000981:diagnostic imaging; D006801:Humans; D007128:Immunoglobulin Fragments; D007553:Isotope Labeling; D051379:Mice; D009368:Neoplasm Transplantation; D016719:Radioimmunodetection; D013667:Technetium; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D007128:Immunoglobulin Fragments; D013667:Technetium