title: Noninvasive detection of carboxypeptidase G2 activity in vivo.
abstract: The pseudomonad protein, carboxypeptidase G2 (CPG2), is a prodrug-activating enzyme utilized in the targeted chemotherapy strategies of antibody- and gene-directed enzyme prodrug therapy (ADEPT and GDEPT). We have developed a noninvasive imaging approach to monitor CPG2 activity in vivo that will facilitate the preclinical and clinical development of CPG2-based ADEPT and GDEPT strategies. Cleavage of the novel reporter probe, 3,5-difluorobenzoyl-L-glutamic acid (3,5-DFBGlu), by CPG2, in human colon adenocarcinoma WiDr xenografts engineered to stably express CPG2, was monitored using (19)F MRSI. The high signal-to-noise ratio afforded by the two MR-equivalent (19)F nuclei of 3,5-DFBGlu, and the 1.4 ppm (19)F chemical shift difference on CPG2-mediated cleavage, enabled the dynamics and quantification of the apparent pharmacokinetics of 3,5-DFBGlu and its CPG2-mediated cleavage in the tumor to be evaluated. In addition, the apparent rate of increase of 3,5-difluorobenzoic acid concentration could also provide a biomarker of CPG2 activity levels in tumors of patients undergoing CPG2-based therapies, as well as a biomarker of treatment response. The addition of in vivo reporter probes, such as 3,5-DFBGlu, to the armamentarium of prodrugs cleaved by CPG2 affords new applications for CPG2 as a gene reporter of transgene expression.
authors.affiliation: Cancer Research UK and EPRSC Cancer Imaging Centre, The Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK.
authors.forename: Yann
authors.initials: Y
authors.lastname: Jamin
authors.forename: Lynette
authors.initials: L
authors.lastname: Smyth
authors.forename: Simon P
authors.initials: SP
authors.lastname: Robinson
authors.forename: Evon S C
authors.initials: ES
authors.lastname: Poon
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Eykyn
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Springer
authors.forename: Martin O
authors.initials: MO
authors.lastname: Leach
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Payne
mesh_terms: D000818:Animals; D019817:Benzoic Acid / Q000737:chemistry / Q000378:metabolism; D045744:Cell Line, Tumor; D005260:Female; D005461:Fluorine / Q000378:metabolism; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D051379:Mice; D023041:Xenograft Model Antitumor Assays; D011623:gamma-Glutamyl Hydrolase / Q000378:metabolism*
chemical_list: D005461:Fluorine; D018698:Glutamic Acid; D019817:Benzoic Acid; D011623:gamma-Glutamyl Hydrolase