Development and Characterization of Clinical-Grade ⁸⁹Zr-Trastuzumab for HER2/neu ImmunoPET Imaging

Abstract

The anti-human epidermal growth factor receptor 2 (HER2/neu) antibody trastuzumab is administered to patients with HER2/ neu-overexpressing breast cancer. Whole-body noninvasive HER2/neu scintigraphy could help to assess and quantify the HER2/neu expression of all lesions, including nonaccessible metastases. The aims of this study were to develop clinical-grade radiolabeled trastuzumab for clinical HER2/neu immunoPET scintigraphy, to improve diagnostic imaging, to guide antibodybased therapy, and to support early antibody development. The PET radiopharmaceutical 89 Zr-trastuzumab was compared with the SPECT tracer 111 In-trastuzumab, which we have tested in the clinic already. Methods: Trastuzumab was labeled with 89 Zr and (for comparison) with 111 In. The minimal dose of trastuzumab required for optimal small-animal PET imaging and biodistribution was determined with human HER2/neu-positive or -negative tumor xenograft-bearing mice. Results: Trastuzumab was efficiently radiolabeled with 89 Zr at a high radiochemical purity and specific activity. The antigen-binding capacity was preserved, and the radiopharmaceutical proved to be stable for up to 7 d in solvent and human serum. Of the tested protein doses, the minimal dose of trastuzumab (100 mg) proved to be optimal for imaging. The comparative biodistribution study showed a higher level of 89 Zr-trastuzumab in HER2/neu-positive tumors than in HER2/neu-negative tumors, especially at day 6 (33.4 6 7.6 [mean 6 SEM] vs. 7.1 6 0.7 percentage injected dose per gram of tissue). There were good correlations between the small-animal PET images and the biodistribution data and between 89 In-trastuzumab uptake in tumors (R 2 5 0.972). Conclusion: Clinical-grade 89 Zr-trastuzumab showed high and HER2/neu-specific tumor uptake at a good resolution.

Tissue Distribution Studies of Protein Therapeutics Using Molecular Probes: Molecular Imaging

“…It is already proven with numerous antibodies (39,(70)(71)(72)(73)(74) and other proteins (75,76) through the efforts of groups in The Netherlands where it has been developed in both preclinical and, with good manufacturing practices (GMP) production for tracer production and validation, in clinical settings. Although Zr-89 does have an extraneous high-energy gamma ray (909 keV), the image quality is good and the overall radiation burden is well tolerated (77).…”

Improved decision making for prioritizing tumor targeting antibodies in human xenografts: Utility of fluorescence imaging to verify tumor target expression, antibody binding and optimization of dosage and application schedule

“…Numerous studies with radiolabeled antibodies or fragments thereof have been conducted to determine their PK behavior and TAA expression using non-invasive positron emission tomography (PET) imaging or ex vivo tumor tissue autoradiography. [64][65][66][67][68] Although both imaging modalities are widely used for preclinical and clinical applications, they possess clear limitations for TAA analysis, such as long acquisition time, restricted half-life of radioactive isotopes, which limit long-term investigations, and the missing multispectral ability of in vivo PET imaging. In addition, the ex vivo autoradiography analysis possesses insufficient spatial resolution to detect drug-target interaction on a cellular level.…”

PET-CT Imaging in Breast Cancer Patients: New Tracers, Future Directions

“…The 89 Zr-labeled trastuzumab revealed to be also a suitable agent for HER2-imaging [43,44], and also seemed to be advantageous in metastatic, HER2-positive breast cancer patients. The feasibility study of Dijkers et al [45]-performed in 14 metastatic breast cancer patients-demonstrated the good visualization of HER-2 positive lesions with an appropriate 50 mg dose of 89 Zr-labeled trastuzumab in trastuzumab-naïve and 10 mg in pretreated patients.…”