In VivoPositron Emission Tomography Imaging of Protease Activity by Generation of a Hydrophobic Product from a Noninhibitory Protease Substrate

Abstract

Purpose: 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.Experimental Design: 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 18 F to form a PEG-peptide-18 F-TMR probe. Specific cleavage of the probe by MMP2 was tested in vitro by matrixassisted laser desorption/ionization-time-of-flight (MALDI-TOF). In vivo imaging of MMP2-expressing tumors was evaluated by micro-PET.Results: 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 18 F-labeled probe ( 18 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 AE 1.9-fold greater than in the MCF-7 tumors 30 minutes after injection. These results suggest that the PEG-peptide-18 F-TMR probe displays high selectivity for imaging MMP activity.Conclusions: This strategy successfully images MMP expression in vivo and may be extended to other proteases to predict patient prognosis and to design personalized, protease-based inhibitors and prodrugtargeted therapies.

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Novel 19F Activatable Probe for the Detection of Matrix Metalloprotease-2 Activity by MRI/MRS

“…13−17 However, optical imaging has limited translational potential into clinical practice due to the shallow penetration of the excitation/emission light, and the scattering of light in living subjects. 25 …”

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