Detection of the Prodrug-Activating Enzyme Carboxypeptidase G2 Activity with Chemical Exchange Saturation Transfer Magnetic Resonance

• Published in: Molecular imaging and biology Vol. 16; no. 2; pp. 152 - 157
• Main Authors: Jamin, Yann, Eykyn, Thomas R., Poon, Evon, Springer, Caroline J., Robinson, Simon P.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.04.2014; Springer Nature B.V
• Subjects: Benzoates - metabolism; Brief Article; Cell Line, Tumor; gamma-Glutamyl Hydrolase - metabolism; Humans; Imaging; Magnetic Resonance Spectroscopy - methods; Mechlorethamine - chemistry; Mechlorethamine - metabolism; Medicine; Medicine & Public Health; Prodrugs - chemistry; Prodrugs - metabolism; Radiology; Signal Processing, Computer-Assisted; Solutions; CEST MRI; GDEPT; Gene therapy; Carboxypeptidase G2
• ISSN: 1536-1632; 1860-2002
• DOI: 10.1007/s11307-013-0680-5

Purpose 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. Procedures 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. Conclusion 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 .