Technetium-99m labeling and biodistribution of anti-TAC disulfide-stabilized Fv fragment.
We used a preformed 99mTc chelate approach to label a genetically engineered disulfide-bonded Fv fragment of anti-Tac monoclonal antibody (dsFv). The biodistribution of this 99mTc-labeled dsFv was evaluated in athymic mice with IL-2 alpha-receptor-positive ATAC4 tumor xenografts.


METHODS
Benzoylmercaptoacetyl-triglycine (BzMAG3) was first labeled with 99mTc, and the carboxy group of 99mTc-MAG3 was then activated to the corresponding tetrafluorophenyl ester. This activated ester was purified with a Sep-Pak C18 column and conjugated to dsFv. The resulting 99mTc-MAG3-dsFv was purified with PD-10 size-exclusion chromatography. The immunoreactivity of 99mTc-MAG3-dsFv was 76% +/- 9%. When incubated in serum at 37 degrees C for 24 hr, there was no appreciable dissociation of 99mTc. The mice were co-injected with 125I-dsFv labeled by the Iodo-Gen method as a control. The mice were killed at 15 to 720 min for analysis of biodistribution and radiocatabolites.


RESULTS
The tumor uptake of 99mTc-MAG3-dsFv was similar to that of 125I-dsFv. The tumor uptake of 99mTc-MAG3-dsFv was rapid with tumor-to-blood or tumor-to-organ ratio higher than 1 for all organs except the kidneys. The peak tumor value of 5.1% injected dose per gram was obtained at 45 min, and the tumor-to-organ ratios increased steadily over time; a ratio of 15, 11, 7, 95 and 0.10 resulted at 6 hr for blood, liver, stomach, muscle and kidney. The radioactivity was primarily excreted through kidneys.


CONCLUSIONS
The rapid achievement of high tumor-to-blood and -tissue ratios makes 99mTc-MAG3-dsFv a promising agent for scintigraphic detection of various hematological malignancies that express IL-2 alpha receptors.
Yoo
T M
TM
Department of Nuclear Medicine, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Bethesda, Maryland, USA.
Chang
H K
HK
Choi
C W
CW
Webber
K O
KO
Le
N
N
Kim
I S
IS
Eckelman
W C
WC
Pastan
I
I
Carrasquillo
J A
JA
Paik
C H
CH
D000818:Animals; D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000378:metabolism; D005260:Female; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000378:metabolism; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics; D016719:Radioimmunodetection; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015375:Receptors, Interleukin-2 / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D015375:Receptors, Interleukin-2; C104214:technetium-99m-MAG3-dsFV