Failure of annexin-based apoptosis imaging in the assessment of antiangiogenic therapy effects
Background Molecular apoptosis imaging is frequently discussed to be useful for monitoring cancer therapy. We demonstrate that the sole assessment of therapy effects by apoptosis imaging can be misleading, depending on the therapy effect on the tumor vasculature. Methods Apoptosis was investigated b...
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Published in | EJNMMI research Vol. 1; no. 1; p. 26 |
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Main Authors | , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Berlin/Heidelberg
Springer Berlin Heidelberg
17.11.2011
BioMed Central Ltd Springer |
Subjects | |
Online Access | Get full text |
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Summary: | Background
Molecular apoptosis imaging is frequently discussed to be useful for monitoring cancer therapy. We demonstrate that the sole assessment of therapy effects by apoptosis imaging can be misleading, depending on the therapy effect on the tumor vasculature.
Methods
Apoptosis was investigated by determining the uptake of Annexin Vivo by optical imaging (study part I) and of
99 m
Tc-6-hydrazinonicotinic [HYNIC]-radiolabeled Annexin V by gamma counting (study part II) in subcutaneous epidermoid carcinoma xenografts (A431) in nude mice after antiangiogenic treatment (SU11248). Optical imaging was performed by optical tomography (3D) and 2D reflectance imaging (control,
n
= 7; therapy,
n
= 6). Accumulation of the radioactive tracer was determined
ex vivo
(control,
n
= 5; therapy,
n
= 6). Tumor vascularization was investigated with an optical blood pool marker (study part I) and contrast-enhanced ultrasound (both studies). Data were validated by immunohistology.
Results
A significantly higher apoptosis rate was detected in treated tumors by immunohistological terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining (area fraction: control, 0.023 ± 0.015%; therapy, 0.387 ± 0.105%;
P
< 0.001). However, both 2D reflectance imaging using Annexin Vivo (control, 13 ± 15 FI/cm
2
; therapy, 11 ± 7 FI/cm
2
) and gamma counting using
99 m
Tc-HYNIC-Annexin V (tumor-to-muscle ratio control, 5.66 ± 1.46; therapy, 6.09 ± 1.40) failed in showing higher accumulation in treated tumors. Optical tomography even indicated higher probe accumulation in controls (control, 81.3 ± 73.7 pmol/cm
3
; therapy, 27.5 ± 34.7 pmol/cm
3
). Vascularization was strongly reduced after therapy, demonstrated by contrast-enhanced ultrasound, optical imaging, and immunohistology.
Conclusions
The failure of annexin-based apoptosis assessment
in vivo
can be explained by the significant breakdown of the vasculature after therapy, resulting in reduced probe/tracer delivery. This favors annexin-based apoptosis imaging only in therapies that do not severely interfere with the vasculature. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 2191-219X 2191-219X |
DOI: | 10.1186/2191-219X-1-26 |