Development of an optimized activatable MMP-14 targeted SPECT imaging probe

Center for Molecular and Functional Imaging, Department of Radiology and Biomedical Imaging, University of California, San Francisco, 185 Berry Street, Suite 350, Box 0946, San Francisco, CA 94107, United States.
Bioorganic & medicinal chemistry (Impact Factor: 2.79). 01/2009; 17(2):653-9. DOI: 10.1016/j.bmc.2008.11.078
Source: PubMed


Matrix metalloproteinase-14 (MT1-MMP or MMP-14) is a membrane-associated protease implicated in a variety of tissue remodeling processes and a molecular hallmark of select metastatic cancers. The ability to detect MMP-14 in vivo would be useful in studying its role in pathologic processes and may potentially serve as a guide for the development of targeted molecular therapies. Four MMP-14 specific probes containing a positively charged cell penetrating peptide (CPP) d-arginine octamer (r(8)) linked with a MMP-14 peptide substrate and attenuating sequences with glutamate (8e, 4e) or glutamate-glycine (4eg and 4egg) repeating units were modeled using an AMBER force field method. The probe with 4egg attenuating sequence exhibited the highest CPP/attenuator interaction, predicting minimized cellular uptake until cleaved. The in vitro MMP-14-mediated cleavage studies using the human recombinant MMP-14 catalytic domain revealed an enhanced cleavage rate that directly correlated with the linearity of the embedded peptide substrate sequence. Successful cleavage and uptake of a technetium-99m labeled version of the optimal probe was demonstrated in MMP-14 transfected human breast cancer cells. Two-fold reduction of cellular uptake was found in the presence of a broad spectrum MMP inhibitor. The combination of computational chemistry, parallel synthesis and biochemical screening, therefore, shows promise as a set of tools for developing new radiolabeled probes that are sensitive to protease activity.

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    • "The resulting imaging probe was a kind of smart probe containing a MMP-2 peptide substrate with quenched nearinfrared fluorochromes that are cleaved upon recognition by the MMP [88]. Recently, an activatable SPECT imaging probe specific for MMP- 14 using a cell penetrating peptide as the retention moiety in the cells after MMP recognition was reported to be partly successful in in vitro experiments [89]. "
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    • "In another strategy, a MT1-MMP-activated single photon emission computed tomography (SPECT) imaging probe was constructed by fusing a radionuclide to an inhibited cell penetrating peptide (CPP) to selectively target MT1-MMP expressing cells. However, the probe was also activated in cells that do not express MT1-MMP, indicating non-specific cleavage of the MT1-MMP substrate by other MMPs (Watkins et al., 2009). Thus the specific detection of MT1-MMP activity in cell culture and in vivo will require substrates with improved activity and selectivity. "
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