Characterization of ⁸⁹Zr-trastuzumab for clinical HER2 immunoPET imaging

Abstract

3508 Background: SPECT imaging with 111In-DTPA-trastuzumab has recently identified new tumor lesions, undetected with conventional staging, in 13/15 patients with HER2++ breast cancers (Perik et al., J Clin Oncol 2006). The aim of this study was to develop an immunoPET label, suitable for clinical use, which would allow excellent detection of HER2 positive tumor lesions and quantification of HER2 expression levels in vivo. Methods: Trastuzumab has essentially been radiolabeled as described by Verel et al. (J Nucl Med 2003). Radiochemical purity (rcp) and stability were determined by SEC-HPLC, immunoreactivity with a Lindmo assay. Biodistribution was performed in nude mice bearing HER2 positive (SKOV3) or HER2 negative (GLC4) xenografts. Five animals per group were co-injected with 111In-ITC-DTPA-trastuzumab and 89Zr-trastuzumab, imaged on a microPET (Focus 220) and sacrificed 144 hours post injection. Results: The immunoreactive fraction of 89Zr-trastuzumab was 0.96, labeling efficiency > 90% and rcp > 95%. 89Zr-trastuzumab was stable for 7 days in buffer at 4 °C and in human serum at 37 °C. MicroPET imaging showed excellent tumor uptake and could easily detect metastases with a size approximating the spatial resolution of the microPET scanner. 89Zr- and 111In-ITC-DTPA-trastuzumab showed similar biodistribution. Highest uptake was found in HER2 positive tumors at 144 hours post injection (40% ID/g tissue for 89Zr-trastuzumab and 47% ID/g for 111In-ITC-DTPA-trastuzumab) compared to 8% ID/g tissue in HER2 negative control tumors. Liver uptake was low (8–12% ID/g tissue). Preliminary results in HER2 positive breast cancer patients show excellent tumor tracer uptake and a resolution unapproachable by 111In-DTPA-trastuzumab. Conclusions: 89Zr-trastuzumab is stable, shows excellent and specific tumor uptake and is suitable for clinical use. Minimal aspecific tracer uptake in the liver allows detection of abdominal metastases. No significant financial relationships to disclose.

Immuno-PET: A Navigator in Monoclonal Antibody Development and Applications

“…Degradation of 76 Br-and 124 I-labeled mAbs upon internalization results in rapid clearance of these radionuclides from the target cells, and therefore the PET image shows less tumor contrast and does not reflect the actual mAb distribution. In contrast, when 68 Ga-, 64 Cu-, 86 Y-, and 89 Zr-labeled mAbs are processed, the positron emitters are trapped intracellularly in lysosomes. This phenomenon of residualization should be taken into account when selecting a positron emitter for immuno-PET applications.…”

“…The most commonly used beta emitters in RIT studies are copper-67 ( 67 During the past few years, appropriate positron emitters and chelates have become commercially available, as well as standardized procedures for the production of optimal quality antibody conjugates (Good Manufacturing Practice). To the best of our knowledge, 18 F, 68 Ga, 64 Cu, 86 Y, and to a lesser extent 124 I are commercially available from a few different vendors at reasonable costs, while 89 Zr will become commercially available shortly. These achievements will open avenues to routine clinical application of immuno-PET.…”

“…In 1995, the anti-colorectal carcinoma m-mAb 1A3 was labeled with the longer-lived positron emitter 64 Cu using a 1,4,8,11-tetraazacyclotetradecanetetraacetic acid chelate and evaluated in 36 patients with suspected advanced primary or metastatic colorectal cancer [34]. Immuno-PET was performed 4 -36 hours p.i.…”

“…Detection of metastases in the liver and lung, the most important sites of this disease, was difficult because of high blood-pool activity at the early imaging time points, which were chosen because of the short half-life of 64 Cu (12.7 hours). Detection of liver metastases was also hampered by accumulation of 64 Cu chelate com-plexes in the liver. These results prompted the search for other 64 Cu chelates and suggest a preference for even longer-living positron emitters when using intact mAbs to enable imaging at late time points.…”

“…Detection of liver metastases was also hampered by accumulation of 64 Cu chelate com-plexes in the liver. These results prompted the search for other 64 Cu chelates and suggest a preference for even longer-living positron emitters when using intact mAbs to enable imaging at late time points.…”