Data from <i>In Vivo</i> Positron Emission Tomography Imaging of Protease Activity by Generation of a Hydrophobic Product from a Noninhibitory Protease Substrate

Abstract

<div>Abstract<p><b>Purpose:</b> To develop an imaging technology for protease activities in patients that could help in prognosis prediction and in design of personalized, protease-based inhibitors and prodrugs for targeted therapy.</p><p><b>Experimental Design:</b> Polyethylene glycol (PEG) was covalently attached to the N-terminus of a hydrophilic peptide substrate (GPLGVR) for matrix metalloproteinase (MMP) to increase hydrophilicity. PEG-peptide was then linked to a hydrophobic tetramethylrhodamine (TMR) domain and labeled with <sup>18</sup>F to form a PEG-peptide-<sup>18</sup>F-TMR probe. Specific cleavage of the probe by MMP2 was tested <i>in vitro</i> by matrix-assisted laser desorption/ionization–time-of-flight (MALDI-TOF). <i>In vivo</i> imaging of MMP2-expressing tumors was evaluated by micro-PET.</p><p><b>Results:</b> The hydrophobic TMR fragment (948 Da) was specifically generated by MMP2 enzymes and MMP-expressing HT1080 cells but not control MCF-7 cells. MMP-expressing HT1080 cells and tumors selectively accumulated the hydrolyzed, hydrophobic TMR fragment at sites of protease activity. Importantly, we found that <sup>18</sup>F-labeled probe (<sup>18</sup>F-TMR) preferentially localized in HT1080 tumors but not control MCF-7 tumors as shown by micro-PET. Uptake of the probe in HT1080 tumors was 18.4 ± 1.9-fold greater than in the MCF-7 tumors 30 minutes after injection. These results suggest that the PEG-peptide-<sup>18</sup>F-TMR probe displays high selectivity for imaging MMP activity.</p><p><b>Conclusions:</b> This strategy successfully images MMP expression <i>in vivo</i> and may be extended to other proteases to predict patient prognosis and to design personalized, protease-based inhibitors and prodrug-targeted therapies. <i>Clin Cancer Res; 18(1); 238–47. ©2011 AACR</i>.</p></div>