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Proc Natl Acad Sci U S A. 2016 Apr 12;113(15):4027-32. doi: 10.1073/pnas.1524212113. Epub 2016 Mar 28.

[18F]CFA as a clinically translatable probe for PET imaging of deoxycytidine kinase activity.

Author information

1
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095;
2
Abcam, Cambridge, MA 02139-1517;
3
Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095; Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095;
4
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095;
5
CellSight Technologies, Inc., San Francisco, CA 94107;
6
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Crump Institute for Molecular Imaging, University of California, Los Angeles, CA 90095;
7
Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607;
8
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095; The Pasarow Mass Spectrometry Laboratory, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095; Department of Psychiatry and Biobehavioral Sciences, University of California, Los Angeles, CA 90095;
9
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Department of Microbiology, Immunology, & Molecular Genetics, University of California, Los Angeles, CA 90095; Howard Hughes Medical Institute, University of California, Los Angeles, CA 90095; Eli & Edythe Broad Center of Regenerative Medicine and Stem Cell Research, University of California, Los Angeles, CA 90095;
10
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095; Department of Surgery, David Geffen School of Medicine, University of California, Los Angeles, CA 90095;
11
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Crump Institute for Molecular Imaging, University of California, Los Angeles, CA 90095; cradu@mednet.ucla.edu mphelps@mednet.ucla.edu.
12
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095; Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, CA 90095.
13
Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA 90095; Ahmanson Translational Imaging Division, University of California, Los Angeles, CA 90095; cradu@mednet.ucla.edu mphelps@mednet.ucla.edu.

Abstract

Deoxycytidine kinase (dCK), a rate-limiting enzyme in the cytosolic deoxyribonucleoside (dN) salvage pathway, is an important therapeutic and positron emission tomography (PET) imaging target in cancer. PET probes for dCK have been developed and are effective in mice but have suboptimal specificity and sensitivity in humans. To identify a more suitable probe for clinical dCK PET imaging, we compared the selectivity of two candidate compounds-[(18)F]Clofarabine; 2-chloro-2'-deoxy-2'-[(18)F]fluoro-9-β-d-arabinofuranosyl-adenine ([(18)F]CFA) and 2'-deoxy-2'-[(18)F]fluoro-9-β-d-arabinofuranosyl-guanine ([(18)F]F-AraG)-for dCK and deoxyguanosine kinase (dGK), a dCK-related mitochondrial enzyme. We demonstrate that, in the tracer concentration range used for PET imaging, [(18)F]CFA is primarily a substrate for dCK, with minimal cross-reactivity. In contrast, [(18)F]F-AraG is a better substrate for dGK than for dCK. [(18)F]CFA accumulation in leukemia cells correlated with dCK expression and was abrogated by treatment with a dCK inhibitor. Although [(18)F]CFA uptake was reduced by deoxycytidine (dC) competition, this inhibition required high dC concentrations present in murine, but not human, plasma. Expression of cytidine deaminase, a dC-catabolizing enzyme, in leukemia cells both in cell culture and in mice reduced the competition between dC and [(18)F]CFA, leading to increased dCK-dependent probe accumulation. First-in-human, to our knowledge, [(18)F]CFA PET/CT studies showed probe accumulation in tissues with high dCK expression: e.g., hematopoietic bone marrow and secondary lymphoid organs. The selectivity of [(18)F]CFA for dCK and its favorable biodistribution in humans justify further studies to validate [(18)F]CFA PET as a new cancer biomarker for treatment stratification and monitoring.

KEYWORDS:

PET imaging; cancer; deoxycytidine kinase; nucleotide metabolism

PMID:
27035974
PMCID:
PMC4839461
DOI:
10.1073/pnas.1524212113
[Indexed for MEDLINE]
Free PMC Article

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