Synthesis of 2′-Deoxy-2′-[18F]Fluoro-9-β-D-Arabinofuranosylguanine: a Novel Agent for Imaging T-Cell Activation with PET

Molecular Imaging Program at Stanford (MIPS), Stanford University, Stanford, CA 94305, USA.
Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging (Impact Factor: 2.77). 10/2011; 13(5):812-8. DOI: 10.1007/s11307-010-0414-x
Source: PubMed


9-(β-D-Arabinofuranosyl)guanine (AraG) is a guanosine analog that has a proven efficacy in the treatment of T-cell lymphoblastic disease. To test the possibility of using a radiofluorinated AraG as an imaging agent, we have synthesized 2'-deoxy-2'-[(18)F]fluoro-9-β-D-arabinofuranosylguanine ([(18)F]F-AraG) and investigated its uptake in T cells.
We have synthesized [(18)F]F-AraG via a direct fluorination of 2-N-acetyl-6-O-((4-nitrophenyl)ethyl)-9-(3',5'-di-O-trityl-2'-O-trifyl-β-D-ribofuranosyl)guanine with [(18)F]KF/K.2.2.2 in DMSO at 85°C for 45 min. [(18)F]F-AraG uptake in both a CCRF-CEM leukemia cell line (unactivated) and activated primary thymocytes was evaluated.
We have successfully prepared [(18)F]F-AraG in 7-10% radiochemical yield (decay corrected) with a specific activity of 0.8-1.3 Ci/μmol. Preliminary cell uptake experiments showed that both a CCRF-CEM leukemia cell line and activated primary thymocytes take up the [(18)F]F-AraG.
For the first time to the best of our knowledge, [(18)F]F-AraG has been successfully synthesized by direct fluorination of an appropriate precursor of a guanosine nucleoside. This approach maybe also useful for the synthesis of other important positron emission tomography (PET) probes such as [(18)F]FEAU, [(18)F]FMAU, and [(18)F]FBAU which are currently synthesized by multiple steps and involve lengthy purification. The cell uptake studies support future studies to investigate the use of [(18)F]F-AraG as a PET imaging agent of T cells.

25 Reads
  • Source
    • "One such PET probe, [(18)F]FAC (1-[2'-deoxy-2'-[(18)F]fluoroarabinofura­nosyl] cytosine), was used to visualize lymphoid organs and localized activation of anti-tumor T cell responses 61. The development of other probes which may selectively image immune activation are currently underway 62. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Immune responses to cancer are dynamic processes which take place through the concerted activity of innate and adaptive cell populations. In order to fully understand the efficacy of immune therapies for cancer, it is critical to understand how the treatment modulates the function of each cell type involved in the anti-tumor immune response. Molecular imaging is a versatile method for longitudinal studies of cellular localization and function. The development of reporter genes for tracking cell movement and function was a powerful addition to the immunologist's toolbox. This review will highlight the advances and challenges in the use of reporter gene imaging to track immune cell localization and function in cancer.
    Theranostics 04/2012; 2(4):355-62. DOI:10.7150/thno.3903 · 8.02 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Positron emission tomography (PET) reporter gene imaging can be used to non-invasively monitor cell-based therapies. Therapeutic cells engineered to express a PET reporter gene (PRG) specifically accumulate a PET reporter probe (PRP) and can be detected by PET imaging. Expanding the utility of this technology requires the development of new non-immunogenic PRGs. Here we describe a new PRG-PRP system that employs, as the PRG, a mutated form of human thymidine kinase 2 (TK2) and 2′-deoxy-2′-18F-5-methyl-1-β-l-arabinofuranosyluracil (l-18F-FMAU) as the PRP. We identified l-18F-FMAU as a candidate PRP and determined its biodistribution in mice and humans. Using structure-guided enzyme engineering, we generated a TK2 double mutant (TK2-N93D/L109F) that efficiently phosphorylates l-18F-FMAU. The N93D/L109F TK2 mutant has lower activity for the endogenous nucleosides thymidine and deoxycytidine than wild type TK2, and its ectopic expression in therapeutic cells is not expected to alter nucleotide metabolism. Imaging studies in mice indicate that the sensitivity of the new human TK2-N93D/L109F PRG is comparable with that of a widely used PRG based on the herpes simplex virus 1 thymidine kinase. These findings suggest that the TK2-N93D/L109F/l-18F-FMAU PRG-PRP system warrants further evaluation in preclinical and clinical applications of cell-based therapies.
    Journal of Biological Chemistry 11/2011; 287(1):446-54. DOI:10.1074/jbc.M111.314666 · 4.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Uncontrolled cell proliferation is an important hallmark of cancer. Cancer treatment with cytostatic chemodrugs usually results in insignificant changes in tumor size, and thus limits the applications of anatomical imaging modalities for determining the therapeutic efficacy. Positron emission tomography (PET) imaging with cell proliferation probes to assess the clinical outcome during or soon after treatment is becoming acceptable. At present, monitoring DNA synthetic pathways with radiolabeled nucleoside probes that are essential for cell proliferation has been considered a more specific approach to predict tumor response. Among the four nucleosides, thymidine analogues, such as (18)F-FLT, have undergone years of development for clinical practice, while cytidine, adenosine and guanosine analogues receive less attention. Recently, several literatures have demonstrated that PET imaging with radiolabeled cytidine and adenosine analogues may have potential to evaluate immune response after chemotherapy, and may enable the prognosis forecast. In this review, we summarize the results of recent preclinical and clinical studies regarding using radiolabeled nucleoside analogues for predicting and monitoring tumor response in cancer treatment. The preparation protocols of these nucleoside scintigraphic probes are also described.
    Current Medicinal Chemistry 05/2012; 19(20):3315-24. DOI:10.2174/092986712801215955 · 3.85 Impact Factor
Show more