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Cerenkov Luminescence Imaging as a Modality to Evaluate Antibody-Based PET Radiotracers
Jimson W D'Souza1, Harvey Hensley1, Mohan Doss1,2
1Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania.
Abstract:
Antibodies, and engineered antibody fragments, labeled with radioisotopes are being developed as radiotracers for the detection and phenotyping of diseases such as cancer. The development of antibody-based radiotracers requires extensive characterization of their in vitro and in vivo properties, including their ability to target tumors in an antigen-selective manner. In this study, we investigated the use of Cerenkov luminescence imaging (CLI) as compared with PET as a modality for evaluating the in vivo behavior of antibody-based radiotracers.
Methods:
The anti-prostate-specific membrane antigen (PSMA) huJ591 antibody (IgG; 150 kDa) and its minibody (Mb; 80 kDa) format were functionalized with the chelator 1,4,7-triazacyclononane-1-glutaric acid-4,7-diacetic acid (NODAGA) and radiolabeled with the positron-emitting radionuclide 64Cu (half-life, 12.7 h). Immunoreactive preparations of the radiolabeled antibodies were injected into NCr nu/nu mice harboring PSMA-positive CWR22Rv1 and PSMA-negative PC-3 tumor xenografts. Tumor targeting was evaluated by both PET and CLI.
Results:
64Cu-NODAGA-PSMA-IgG and 64Cu-NODAGA-PSMA-Mb retained the ability to bind cell surface PSMA, and both radiotracers exhibited selective uptake into PSMA-positive tumors. Under the experimental conditions used, PSMA-selective uptake of 64Cu-NODAGA-PSMA-IgG and 64Cu-NODAGA-PSMA-Mb was observed by CLI as early as 3 h after injection, with tumor-to-background ratios peaking at 24 (IgG) and 16 (Mb) h after injection. Targeting data generated by CLI correlated with that generated by PET and necropsy.
Conclusion:
CLI provided a rapid and simple assessment of the targeting specificity and pharmacokinetics of the antibody-based PET radiotracers that correlated well with the behavior observed by standard PET imaging. Moreover, CLI provided clear discrimination between uptake kinetics of an intact IgG and its small-molecular-weight derivative Mb. These data support the use of CLI for the evaluation of radiotracer performance.
Insights
Cerenkov luminescence imaging (CLI) offers a rapid and effective method for evaluating antibody-based radiotracers, correlating well with PET imaging for disease detection.
Area of Science:
- Nuclear Medicine
- Oncology
- Radiochemistry
Background:
- Antibodies and antibody fragments labeled with radioisotopes are crucial for detecting and phenotyping diseases like cancer.
- Characterizing in vitro and in vivo properties, including tumor targeting, is essential for developing antibody-based radiotracers.
- Cerenkov luminescence imaging (CLI) is explored as a complementary modality to Positron Emission Tomography (PET) for evaluating radiotracer behavior.
Purpose of the Study:
- To investigate Cerenkov luminescence imaging (CLI) as a method for evaluating the in vivo behavior of antibody-based radiotracers.
- To compare the performance of CLI with PET in assessing tumor targeting and pharmacokinetics of radiolabeled antibodies.
Main Methods:
- Antibodies targeting prostate-specific membrane antigen (PSMA), huJ591 IgG and its minibody (Mb) format, were functionalized with NODAGA and radiolabeled with 64Cu.
- Radiolabeled antibodies were injected into mice with PSMA-positive and PSMA-negative tumor xenografts.
- Tumor targeting was evaluated using both PET and CLI.
Main Results:
- 64Cu-labeled PSMA IgG and Mb demonstrated selective uptake in PSMA-positive tumors.
- CLI detected PSMA-selective uptake as early as 3 hours post-injection.
- CLI data correlated well with PET imaging and necropsy findings, showing distinct uptake kinetics for IgG and Mb.
Conclusions:
- CLI provides a rapid, simple, and accurate assessment of radiotracer targeting specificity and pharmacokinetics.
- CLI performance correlates strongly with standard PET imaging.
- CLI effectively differentiates uptake kinetics between intact IgG and smaller antibody fragments like minibodies.
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