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An engineered cysteine-modified diabody for imaging activated leukocyte cell adhesion molecule (ALCAM)-positive
Katelyn E McCabe1, Bin Liu, James D Marks
1Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA, USA. kmccabe@ucla.edu
Purpose:
The purpose of this study was to generate and evaluate a positron emission tomography (PET) radiotracer targeting activated leukocyte cell adhesion molecule (ALCAM).
Procedures:
A human anti-ALCAM single chain variable fragment was reformatted to produce a covalent dimer, termed a cys-diabody (CysDb). Purified CysDb was characterized by gel electrophoresis and size exclusion chromatography, and immunoreactivity was assessed by flow cytometry and immunofluorescence. Targeting and imaging of ALCAM-positive tumors using (64)Cu-DOTA-CysDb were evaluated in mice bearing human pancreatic adenocarcinoma xenografts (HPAF-II or BxPC-3).
Results:
CysDb binds specifically to ALCAM-positive cells in vitro with an apparent affinity in the range of 1-3 nM. MicroPET images at 4 h showed specific targeting of positive tumors in vivo, a finding confirmed by biodistribution analysis, with positive/negative tumor ratios of 1.9 ± 0.6 and 2.4 ± 0.6, and positive tumor/blood ratios of 2.5 ± 0.9 and 2.9 ± 0.6 (HPAF-II and BxPC-3, respectively).
Conclusions:
Successful imaging with (64)Cu-DOTA-CysDb in animal models suggests further investigation of ALCAM as an imaging biomarker is warranted.
