In vitro evaluation of adenosine 5′-monophosphate as an imaging agent of tumor metabolism

Steve Y. Cho, Josh Polster, James M. Engles, John Hilton, Edward H. Abraham, Richard L. Wahl

Research output: Contribution to journalArticlepeer-review

Abstract

Adenosine appears to play an important role in tumor growth and metastasis. Synthesized 11C-adenosine 5′-monophosphate (AMP) has recently been reported as a potential tumor-imaging radiotracer. Methods: A variety of human tumor cell lines (SKOV-3, SCC-15, U251, U87, Raji, and Daudi) were incubated with 3.7 kBq (0.1 μCi) of [2-3H]AMP (3H-AMP), [5,6-3H]FDG (3H-FDG), or [2-3H]adenosine (3H-adenosine) in low-physiologicglucose serum-free medium. Selected cells were exposed to caffeine, dipyridamole, adenosine 5′-(α, β-methylene)diphosphate (APCP), or unlabeled adenosine before exposure to the radiotracer. R-phycoerythrin-conjugated mouse antihuman monoclonal antibody to human CD73 was used for immunophenotyping. High-performance liquid chromatography was used to characterize the intracellular metabolites of 3H-AMP after intracellular uptake. Results: Intracellular uptake of 3H-AMP was significant - 10 to 100 times the uptake of 3H-FDG, depending on the particular tumor cell line. Preexposure of SKOV-3 cells to caffeine, a competitive inhibitor of adenosine receptors, did not affect cellular uptake ofv 3H-AMP. However, preexposure of SKOV-3 cells to dipyridamole, an equilibrative nucleoside transporter inhibitor; APCP, a CD73 (ecto-5′-nucleotidase) inhibitor; or cold adenosine significantly inhibited cellular uptake of 3H-AMP. SKOV-3 uptake of 3H-adenosine was inhibited by dipyridamole but not APCP. U251 uptake of 3H-AMP was significantly inhibited by dipyridamole and APCP. U87 uptake of 3H-AMP was only partially inhibited by dipyridamole and APCP. However, Raji and Daudi cells had significantly lower uptake of 3H-AMP than of 3H-FDG but had significantly increased uptake of 3H-adenosine, whichwas inhibited by dipyridamole.Raji and Daudi cells were negative, but the SKOV-3 cells positive, for CD73 cell-surface expression. 3H-Adenosine metabolites were persistently retained after influx into the cell, predominantly as 3H-adenosine triphosphate and 3H-adenosine diphosphate. Conclusion: Cancer cell lines evaluated in vitro had significantly elevated uptake of radiolabeled AMP, on the order of 10- to100-fold, in comparison to radiolabeled FDG. The mechanism of intracellular uptake depends predominantly on equilibrative nucleoside transporters after conversion of AMP to adenosine by CD73 in SKOV-3, SCC-15, and U251 cells. Intracellular retention is due to phosphorylation to adenosine triphosphate and adenosine diphosphate. Raji and Daudi cells have low uptake of radiolabeled AMP because of a lack of CD73 expression. This in vitro evaluation using 3H-AMP with tumor cell lines supports thepotential of 11C-AMP for use in targeting the nucleoside transport pathway in PET imaging of tumors.

Original languageEnglish (US)
Pages (from-to)837-845
Number of pages9
JournalJournal of Nuclear Medicine
Volume47
Issue number5
StatePublished - May 1 2006

Keywords

  • Cancer cells
  • In vitro
  • Nucleoside transporter
  • Oncology
  • PET
  • [2-H]adenosine 5′-monophosphate

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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