Positron emission tomography imaging of CD105 expression with 89Zr-Df-TRC105
High tumor microvessel density correlates with a poor prognosis in multiple solid tumor types. The clinical gold standard for assessing microvessel density is CD105 immunohistochemistry on paraffin-embedded tumor specimens. The goal of this study was to develop an 89Zr-based PET tracer for noninvasive imaging of CD105 expression.
TRC105, a chimeric anti-CD105 monoclonal antibody, was conjugated to p-isothiocyanatobenzyl-desferrioxamine (Df-Bz-NCS) and labeled with 89Zr. FACS analysis and microscopy studies were performed to compare the CD105 binding affinity of TRC105 and Df-TRC105. PET imaging, biodistribution, blocking, and ex-vivo histology studies were performed on 4T1 murine breast tumor-bearing mice to evaluate the pharmacokinetics and tumor-targeting of 89Zr-Df-TRC105. Another chimeric antibody, cetuximab, was used as an isotype-matched control.
FACS analysis of HUVECs revealed no difference in CD105 binding affinity between TRC105 and Df-TRC105, which was further validated by fluorescence microscopy. 89Zr labeling was achieved with high yield and specific activity. Serial PET imaging revealed that the 4T1 tumor uptake of 89Zr-Df-TRC105 was 6.1 ± 1.2, 14.3 ± 1.2, 12.4 ± 1.5, 7.1 ± 0.9, and 5.2 ± 0.3 %ID/g at 5, 24, 48, 72, and 96 h after injection, respectively (n = 4), higher than all organs starting from 24 h after injection, which provided excellent tumor contrast. Biodistribution data as measured by gamma counting were consistent with the PET findings. Blocking experiments, control studies with 89Zr-Df-cetuximab, and ex-vivo histology all confirmed the in vivo target specificity of 89Zr-Df-TRC105.
We report here the first successful PET imaging of CD105 expression with 89Zr as the radiolabel. Rapid, persistent, CD105-specific uptake of 89Zr-Df-TRC105 in the 4T1 tumor was observed.
KeywordsCD105/endoglin Positron emission tomography (PET) Tumor angiogenesis 89Zr RadioimmunoPET TRC105
This work was supported in part by the University of Wisconsin Carbone Cancer Center, the NIH through the UW Radiological Sciences Training Program 5 T32 CA009206-32, NCRR 1UL1RR025011, a DOD BCRP Postdoctoral Fellowship, and a DOD PCRP IDEA Award. The authors also thank Dr. Jason P. Holland and Dr. Jason S. Lewis for sharing their expertise on 89Zr production and radiochemistry, Dr. Anna Wu and Dr. David M. Goldenberg for helpful discussions, Dr. Martin Shafer at the University of Wisconsin State Hygiene Laboratory for performing the ICPMS study, and Dr. Jamey P. Weichert and Mohammed Farhoud for their help with the PET scans.
Conflicts of interest
B.R.L. is an employee of TRACON Pharmaceuticals, Inc. The other authors declare no conflicts of interest.
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