A comparison of In-111- or Cu-64-DOTA-trastuzumab Fab fragments for imaging subcutaneous HER2-positive tumor xenografts in athymic mice using microSPECT/CT or microPET/CT

作者：Chan Conrad; Scollard Deborah A; McLarty Kristin; Smith Serena; Reilly Raymond M^*

来源：EJNMMI Research, 2011, 1: 15.

DOI：10.1186/2191-219X-1-15

• indium-111
• copper-64
• HER2
• MicroSPECT
• MicroPET
• DOTA
• trastuzumab Fab
• breast cancer
• ovarian cancer

Background: Our objective was to compare In-111- or Cu-64-DOTA-trastuzumab Fab fragments for imaging small or large s.c. tumor xenografts in athymic mice that display a wide range of human epidermal growth factor receptor2 (HER2) expression using microSPECT/CT or microPET/CT.
Methods: Trastuzumab Fab were labeled with In-111 or Cu-64 by conjugation to 1,4,7,10-tetraazacyclododecane N, N', N '', N'''-tetraacetic acid (DOTA). The purity of In-111- and Cu-64-DOTA-trastuzumab Fab was measured by SDS-PAGE and HPLC. HER2 binding affinity was determined in saturation radioligand binding assays using SKBR-3 cells (1.3 x 106 HER2/cell). MicroSPECT/CT and microPET/CT were performed in athymic mice bearing s.c. BT-20 and MDA-MB-231 xenografts with low (0.5 to 1.6 x 10(5) receptors/cell), MDA-MB-361 tumors with intermediate (5.1 x 10(5) receptors/cell) or SKOV-3 xenografts with high HER2 expression (1.2 x 10(6) receptors/cell) at 24 h p.i. of 70 MBq (10 mu g) of In-111-DOTA-trastuzumab Fab or 22 MBq (10 mu g) of Cu-64-DOTA-trastuzumab Fab or irrelevant In-111- or Cu-64-DOTA- rituximab Fab. Tumor and normal tissue uptake were quantified in biodistribution studies.
Results: In-111- and Cu-64-DOTA-trastuzumab were >98% radiochemically pure and bound HER2 with high affinity (K-d = 20.4 +/- 2.5 nM and 40.8 +/- 3.5 nM, respectively). MDA-MB-361 and SKOV-3 tumors were most clearly imaged using In-111- and Cu-64-DOTA-trastuzumab Fab. Significantly higher tumor/blood (T/B) ratios were found for In-111-DOTA-trastuzumab Fab than In-111-DOTA-rituximab Fab for BT-20, MDA-MB-231 and MDA-MB-361 xenografts, and there was a direct association between T/B ratios and HER2 expression. In contrast, tumor uptake of Cu-64-DOTA-trastuzumab Fab was significantly higher than Cu-64-DOTA-rituximab Fab in MDA-MB-361 tumors but no direct association with HER2 expression was found. Both In-111- and Cu-64-DOTA-trastuzumab Fab imaged small (5 to 10 mm) or larger (10 to 15 mm) MDA-MB-361 tumors. Higher blood, liver, and spleen radioactivity were observed for Cu-64-DOTA-trastuzumab Fab than In-111-DOTA-trastuzumab Fab.
Conclusions: We conclude that In-111-DOTA-trastuzumab Fab was more specific than Cu-64-DOTA-trastuzumab Fab for imaging HER2-positive tumors, especially those with low receptor density. This was due to higher levels of circulating radioactivity for Cu-64-DOTA-trastuzumab Fab which disrupted the relationship between HER2 density and T/B ratios. Use of alternative chelators that more stably bind Cu-64 may improve the association between T/B ratios and HER2 density for Cu-64-labeled trastuzumab Fab.

• 出版日期2011