title: Detection of the prodrug-activating enzyme carboxypeptidase G2 activity with chemical exchange saturation transfer magnetic resonance.
abstract: OBJECTIVE
  The purpose of this study is to evaluate if the differential exchange rates with bulk water between amine and amide protons can be exploited using chemical exchange saturation transfer magnetic resonance (CEST-MR) to monitor the release of glutamate induced by carboxypeptidase G2 (CPG2), an enzyme utilized in cancer gene therapy.
  
  
  METHODS
  Z spectra of solutions of the CPG2 substrate, 3,5-difluorobenzoyl-L-glutamate (amide), and glutamate (amine) were acquired at 11.7 T, 37 °C, across different pH (5-8). The ability of CEST-MR to monitor CPG2-mediated release of glutamate was assessed in extracts of CPG2-expressing cancer cells and purified solution of CPG2.
  
  
  RESULTS
  The addition of CPG2 to a solution containing 3,5-difluorobenzoyl-L-glutamate led to a marked and progressively increasing CEST effect (+3 ppm), concomitant with the time-dependent release of glutamate induced by CPG2.
  
  
  CONCLUSIONS
  CEST-MR allows the detection of CPG2 activity in vitro and supports the translation of CEST-MRI to assess CPG2-based gene therapy in vivo.
authors: Cancer Research UK and EPRSC Cancer Imaging Centre, Division of Radiotherapy and Imaging, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust, 15 Cotswold Road, Sutton, Surrey, SM2 5NG, UK, yann.jamin@icr.ac.uk.
authors: Yann
authors: Y
authors: Jamin
authors: Thomas R
authors: TR
authors: Eykyn
authors: Evon
authors: E
authors: Poon
authors: Caroline J
authors: CJ
authors: Springer
authors: Simon P
authors: SP
authors: Robinson
mesh_terms: D001565:Benzoates / Q000378:metabolism; D045744:Cell Line, Tumor; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008466:Mechlorethamine / Q000737:chemistry / Q000378:metabolism; D011355:Prodrugs / Q000737:chemistry / Q000378:metabolism*; D012815:Signal Processing, Computer-Assisted; D012996:Solutions; D011623:gamma-Glutamyl Hydrolase / Q000378:metabolism*
chemical_list: D001565:Benzoates; D011355:Prodrugs; D012996:Solutions; D008466:Mechlorethamine; D011623:gamma-Glutamyl Hydrolase
references: Cancer Res. 2007 May 15;67(10):4949-55
references: 17510425
references: Magn Reson Med. 2009 Nov;62(5):1300-4
references: 19780183
references: Methods Mol Med. 2004;90:161-202
references: 14657564
references: Cancer Res. 2005 Jun 15;65(12):5003-8
references: 15958540
references: Cancer Res. 2009 Jun 1;69(11):4918-25
references: 19458066
references: Drug Deliv Transl Res. 2012 Feb 1;2(1):22-30
references: 23646292
references: Nat Biotechnol. 1997 Dec;15(13):1373-7
references: 9415889
references: Magn Reson Med. 2011 Apr;65(4):927-48
references: 21337419
references: J Am Chem Soc. 2011 Oct 19;133(41):16326-9
references: 21919523
references: NMR Biomed. 2011 May;24(4):343-50
references: 20891022
references: Nat Rev Cancer. 2007 Nov;7(11):870-9
references: 17943135
references: Nat Med. 2012 Jan 22;18(2):302-6
references: 22270722