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




A comparison of 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging subcutaneous HER2-positive tumor xenografts in athymic mice using microSPECT-CT or microPET-CT - Download this document for free, or read online. Document in PDF available to download.

EJNMMI Research

, 1:15

First Online: 17 August 2011Received: 06 July 2011Accepted: 17 August 2011

Abstract

BackgroundOur objective was to compare In- or Cu-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 receptor-2 HER2 expression using microSPECT-CT or microPET-CT.

MethodsTrastuzumab Fab were labeled with In or Cu by conjugation to 1,4,7,10-tetraazacyclododecane N, N-, N-, N-tetraacetic acid DOTA. The purity of In- and Cu-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 × 10 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 × 10 receptors-cell, MDA-MB-361 tumors with intermediate 5.1 × 10 receptors-cell or SKOV-3 xenografts with high HER2 expression 1.2 × 10 receptors-cell at 24 h p.i. of 70 MBq 10 μg of In-DOTA-trastuzumab Fab or 22 MBq 10 μg of Cu-DOTA-trastuzumab Fab or irrelevant In- or Cu-DOTA-rituximab Fab. Tumor and normal tissue uptake were quantified in biodistribution studies.

ResultsIn- and Cu-DOTA-trastuzumab were > 98% radiochemically pure and bound HER2 with high affinity Kd = 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- and Cu-DOTA-trastuzumab Fab. Significantly higher tumor-blood T-B ratios were found for In-DOTA-trastuzumab Fab than In-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-DOTA-trastuzumab Fab was significantly higher than Cu-DOTA-rituximab Fab in MDA-MB-361 tumors but no direct association with HER2 expression was found. Both In- and Cu-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-DOTA-trastuzumab Fab than In-DOTA-trastuzumab Fab.

ConclusionsWe conclude that In-DOTA-trastuzumab Fab was more specific than Cu-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-DOTA-trastuzumab Fab which disrupted the relationship between HER2 density and T-B ratios. Use of alternative chelators that more stably bind Cu may improve the association between T-B ratios and HER2 density for Cu-labeled trastuzumab Fab.

Keywordsindium-111 copper-64 HER2 MicroSPECT MicroPET DOTA trastuzumab Fab breast cancer ovarian cancer Electronic supplementary materialThe online version of this article doi:10.1186-2191-219X-1-15 contains supplementary material, which is available to authorized users.

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Author: Conrad Chan - Deborah A Scollard - Kristin McLarty - Serena Smith - Raymond M Reilly

Source: https://link.springer.com/







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