An Engineered Cysteine-Modified Diabody for Imaging Activated Leukocyte Cell Adhesion Molecule (ALCAM)-Positive Tumors
The purpose of this study was to generate and evaluate a positron emission tomography (PET) radiotracer targeting activated leukocyte cell adhesion molecule (ALCAM).
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 64Cu-DOTA-CysDb were evaluated in mice bearing human pancreatic adenocarcinoma xenografts (HPAF-II or BxPC-3).
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).
Successful imaging with 64Cu-DOTA-CysDb in animal models suggests further investigation of ALCAM as an imaging biomarker is warranted.
Key wordsActivated leukocyte cell adhesion molecule (ALCAM) Biomarker Diabody Pancreatic cancer Positron emission tomography (PET)
Funding support was provided by the National Cancer Institute through the UCLA in vivo Cellular and Molecular Imaging Center (NIH CA 86306), the Stanford Center for Nanotechnology Excellence (NIH CA 119367), and the UCLA Small Animal Imaging Resource Program (NIH CA 92865), and a Dr. Ursula Mandel Scholarship. We thank Dr. Noah Federman for his help with the immunofluorescence experiments and Waldemar Ladno for his assistance with the animal studies. We would also like to acknowledge the UCLA Translational Pathology Core Laboratory for their antibody optimization and immunostaining services. Flow cytometry was performed in the UCLA Jonsson Comprehensive Cancer Center (JCCC) and Center for AIDS Research Flow Cytometry Core Facility, supported by NIH awards CA-16042 and AI-28697.
Conflict of Interest
Anna M. Wu owns stock and is a consultant to ImaginAb, Inc. James D. Marks own stock, is a member of the Scientific Advisory Board, and is a consultant to ImaginAb, Inc. The other authors declare they have no conflicts of interest.
- 39.Liu K, Lepin EJ, Wang M-W, Guo F, Lin W-Y, Chen Y-C, Sirk SJ, Olma S, Phelps ME, Zhao X-Z, Tseng H-R, van Dam RM, Wu AM, Shen CK-F (2011) Microfluidic-based 18F labeling of biomolecules for immuno-positron emission tomography. Molecular Imaging 10:168–176. doi: 10.2310/7290.2010.00043 PubMedGoogle Scholar
- 40.Horner MJ RL, Krapcho M, Neyman N, Aminou R, Howlader N, Altekruse SF, Feuer EJ, Huang L, Mariotto A, Miller BA, Lewis DR, Eisner MP, Stinchcomb DG, Edwards BK (eds) SEER Cancer Statistics Review, 1975–2006, National Cancer Institute. Bethesda, MD, based on November 2008 SEER data submission, posted to the SEER web site, 2009. Available at http://seer.cancer.gov/csr/1975_2006/