In vitro and in vivo evaluation of [99mTc]-labeled tricarbonyl His-annexin A5 as an imaging agent for the detection of phosphatidylserine-expressing cells.
BACKGROUND
Apoptosis is one of the mechanisms behind successful chemotherapy and radiation treatment. Radiolabeled annexin A5 has been demonstrated to be a successful tool in the detection of apoptosis following chemotherapy in vivo.


METHODS
His-tagged annexin A5 was labeled with [(99m)Tc]-tricarbonyl and evaluated as apoptosis imaging radiotracer in vitro and in vivo. The binding of the radiotracer was evaluated in Colo205 cells stimulated with 5-FU (1 mM) for 4 and 24 h, and confirmed by flow cytometry. Biodistribution and dosimetric studies were performed in healthy nude mice (n=5) via planar scintigraphy. [(99m)Tc]-(CO)(3) His-annexin A5 was also evaluated for in vivo imaging of spontaneous apoptosis in Colo205-bearing mice (n=12).


RESULTS
The labeling procedure yielded a compound with 95-99% radiochemical purity and good in vitro stability. In vitro binding experiments indicated that the radiotracer retained its PS-binding activity. [(99m)Tc]-(CO)(3) His-annexin A5 rapidly cleared from the blood and predominantly accumulated in the kidneys. Absorbed dose (per organ) was found to be 116 ± 64 μGy/MBq for the kidneys and 10.38 ± 0.50 μGy/MBq for the liver. The effective dose was 7.00 ± 0.28 μSv/MBq. Spontaneous apoptosis in Colo205-bearing mice was visualised by [(99m)Tc]-(CO)(3) His-annexin A5 SPECT and correlated well with caspase-3 immunostaining (R=0.867, P<.01).


CONCLUSIONS
[(99m)Tc]-(CO)(3) His-annexin A5 may be a useful novel radioligand for the in vivo detection of cell death associated with PS expression. A simple, noninvasive way of detecting apoptosis in vivo could have many applications including a better understanding of the extent and timing of apoptosis in response to cancer therapies and assessment of early tumor response.
Department of Gastroenterology, Ghent University Hospital, 9000-B Ghent, Belgium. christel.vangestel@ugent.be
Christel
C
Vangestel
Marc
M
Peeters
Ruth
R
Oltenfreiter
Yves
Y
D'Asseler
Steven
S
Staelens
Magali
M
Van Steenkiste
Jan
J
Philippé
Dennis
D
Kusters
Chris
C
Reutelingsperger
Nancy
N
Van Damme
Christophe
C
Van de Wiele
D000818:Animals; D017304:Annexin A5 / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D017209:Apoptosis; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006639:Histidine / Q000737:chemistry*; D006801:Humans; D051379:Mice; D015609:Organotechnetium Compounds; D010718:Phosphatidylserines / Q000378:metabolism*; D011874:Radiometry; D015899:Tomography, Emission-Computed, Single-Photon
D017304:Annexin A5; D015609:Organotechnetium Compounds; D010718:Phosphatidylserines; D006639:Histidine