1 research outputs found
<sup>64</sup>Cu-Labeled Gp2 Domain for PET Imaging of Epidermal Growth Factor Receptor
This
purpose of this study is to determine the efficacy of a 45-amino
acid Gp2 domain, engineered to bind to epidermal growth factor receptor
(EGFR), as a positron emission tomography (PET) probe of EGFR in a
xenograft mouse model. The EGFR-targeted Gp2 (Gp2-EGFR) and a nonbinding
control were site-specifically labeled with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic
acid (DOTA) chelator. Binding affinity was tested toward human EGFR
and mouse EGFR. Biological activity on downstream EGFR signaling was
examined in cell culture. DOTA-Gp2 molecules were labeled with <sup>64</sup>Cu and intravenously injected (0.6–2.3 MBq) into mice
bearing EGFR<sup>high</sup> (<i>n</i> = 7) and EGFR<sup>low</sup> (<i>n</i> = 4) xenografted tumors. PET/computed
tomography (CT) images were acquired at 45 min, 2 h, and 24 h. Dynamic
PET (25 min) was also acquired. Tomography results were verified with
gamma counting of resected tissues. Two-tailed <i>t</i> tests
with unequal variances provided statistical comparison. DOTA-Gp2-EGFR
bound strongly to human (<i>K</i><sub>D</sub> = 7 ±
5 nM) and murine (<i>K</i><sub>D</sub> = 29 ± 6 nM)
EGFR, and nontargeted Gp2 had no detectable binding. Gp2-EGFR did
not agonize EGFR nor antagonize EGF-EGFR. <sup>64</sup>Cu-Gp2-EGFR
tracer effectively localized to EGFR<sup>high</sup> tumors at 45 min
(3.2 ± 0.5%ID/g). High specificity was observed with significantly
lower uptake in EGFR<sup>low</sup> tumors (0.9 ± 0.3%ID/g, <i>p</i> < 0.001), high tumor-to-background ratios (11 ±
6 tumor/muscle, <i>p</i> < 0.001). Nontargeted Gp2 tracer
had low uptake in EGFR<sup>high</sup> tumors (0.5 ± 0.3%ID/g, <i>p</i> < 0.001). Similar data was observed at 2 h, and tumor
signal was retained at 24 h (2.9 ± 0.3%ID/g). An engineered Gp2
PET imaging probe exhibited low background and target-specific EGFR<sup>high</sup> tumor uptake at 45 min, with tumor signal retained at
24 h postinjection, and compared favorably with published EGFR PET
probes for alternative protein scaffolds. These beneficial <i>in vivo</i> characteristics, combined with thermal stability,
efficient evolution, and small size of the Gp2 domain validate its
use as a future class of molecular imaging agents