111In-CHX-A”-Diethylenetriamine pentaacetic acid-(ZEGFR:955)2

111In-CHX-A”-DTPA-(ZEGFR:955)2

Leung K.

Publication Details

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Table

In vitro Rodents

Background

[PubMed]

Epidermal growth factor (EGF) is a cytokine that comprises 53 amino acids (6.2 kDa) and is secreted by ectodermic cells, monocytes, kidneys, and duodenal glands (1). EGF stimulates growth of epidermal and epithelial cells. EGF and at least seven other growth factors and their transmembrane receptor kinases play important roles in cell proliferation, survival, adhesion, migration, and differentiation. The EGF receptor (EGFR) family consists of four transmembrane receptors: EGFR (HER1/erbB-1), HER2 (erbB-2/neu), HER3 (erbB-3), and HER4 (erbB-4) (2). HER1, HER3, and HER4 operate in three major functional domains: an extracellular ligand-binding domain, a hydrophobic transmembrane domain, and a cytoplasmic tyrosine kinase domain. No ligand has been clearly identified for HER2; however, HER2 can be activated as a result of ligand binding to other HER receptors with the formation of receptor homodimers and/or heterodimers (3). HER1 and HER2 are overexpressed on many solid tumor cells such as breast, non-small cell lung, head and neck, and colon cancers (4-6). The high levels of HER1 and HER2 expression on cancer cells are associated with a poor prognosis (7-10).

Cetuximab is a humanized IgG1 monoclonal antibody (mAb) against the extracellular domain of recombinant HER1 (11). Various labeled cetuximab probes have been developed for imaging human breast cancer in small animal tumor models (12-14). However, the pharmacokinetics of the intact radiolabeled mAb, with high liver uptake and slow blood elimination, are generally not ideal for imaging. Smaller antibody fragments, such as Fab or F(ab´)2, have better imaging pharmacokinetics because they are rapidly excreted by the kidneys. A novel class of recombinant affinity ligands (Affibody molecules) for HER1, based on the Z-domain residues (58 amino acids) from one of the IgG-binding domains of staphylococcal protein A, was constructed (15). The Affibody molecule (ZEGFR:955)2 exhibits a high binding affinity (Kd) to HER-expressing cells (Kd = 1 nM) (16). (ZEGFR:955)2 was labeled with 111In via CHX-A”-diethylenetriamine pentaacetic acid (DTPA) to form 111In-CHX-A”-DTPA-(ZEGFR:955)2 for single-photon emission computed tomography (SPECT) imaging in nude mice bearing human tumors (17).

Synthesis

[PubMed]

CHX-A”-DTPA and (ZEGFR:955)2 (1:1 molar ratio) were incubated for 20 h at 37°C in sodium borate buffer (pH 9.2). CHX-A”-DTPA-(ZEGFR:955)2 was isolated from the incubation mixture with a NAP-5 column. CHX-A”-DTPA-(ZEGFR:955)2 (0.2 M ammonium acetate buffer (pH 5.25)) was mixed with a predetermined amount of 111InCl3. The mixture was incubated for 1 h at room temperature. A non-binding Affibody was also labeled similarly as a control. No data of labeling efficiency, radiochemical purity, and specific activity for 111In-CHX-A”-DTPA-(ZEGFR:955)2 were reported (17).

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

In vitro binding specificity tests showed that binding of 111In-CHX-A”-DTPA-(ZEGFR:955)2 to human epithelial cancer A431 cells expressing HER1 was mediated by the receptors because saturation of receptors by preincubation with non-labeled (ZEGFR:955)2 markedly decreased binding of 111In-CHX-A”-DTPA-(ZEGFR:955)2 (17). The cell-bound radioactivity remained at 38% of the initially bound activity for up to 72 h. 125I-(ZEGFR:955)2 was internalized as shown previously with confocal microscopy (18).

Animal Studies

Rodents

[PubMed]

Nordberg et al. (17) performed biodistribution studies of 0.25 MBq (6.7 μCi) 111In-CHX-A”-DTPA-(ZEGFR:955)2 in nude mice bearing A431 xenografts (n = 4 mice/group). The tracer accumulation values in the A431 tumors were 3.8 ± 1.4% injected dose per gram (ID/g) at 4 h after injection and 2.0 ± 0.5% ID/g at 8 h after injection. The kidneys (86.4% ID/g) and liver (16.5% ID/g) were the only organs that had higher accumulation than the tumor. Blood level was <0.4% ID/g at 4 h, providing a tumor/blood ratio of 9.1. The tumor uptake of the 111In-CHX-A”-DTPA-(Zabeta3:C228S)2 control Affibody was <0.3% ID/g at 4 h. Pre-administration of excess (ZEGFR:955)2 decreased liver accumulation by 8.2-fold at 4 h after injection, but kidney uptake was approximately doubled. SPECT analysis was performed in nude mice bearing the A431 tumors after intravenous injection of 5 MBq (135 μCi) 111In-CHX-A”-DTPA-(ZEGFR:955)2. The tumor was clearly visualized at 4 h along with the kidneys and liver. Pre-administration of excess (ZEGFR:955)2 blocked the uptake in the tumor.

Other Non-Primate Mammals

[PubMed]

No publication is currently available.

Non-Human Primates

[PubMed]

No publication is currently available.

Human Studies

[PubMed]

No publication is currently available.

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