Tumor detection by imaging proteolytic activity.
The cell surface protease membrane-type serine protease-1 (MT-SP1), also known as matriptase, is often upregulated in epithelial cancers. We hypothesized that dysregulation of MT-SP1 with regard to its cognate inhibitor hepatocyte growth factor activator inhibitor-1 (HAI-1), a situation that increases proteolytic activity, might be exploited for imaging purposes to differentiate malignant from normal tissue. In this study, we show that MT-SP1 is active on cancer cells and that its activity may be targeted in vivo for tumor detection. A proteolytic activity assay with several MT-SP1-positive human cancer cell lines showed that MT-SP1 antibodies that inhibit recombinant enzyme activity in vitro also bind and inhibit the full-length enzyme expressed on cells. In contrast, in the same assay, MT-SP1-negative cancer cell lines were inactive. Fluorescence microscopy confirmed the cell surface localization of labeled antibodies bound to MT-SP1-positive cells. To evaluate in vivo targeting capability, 0.7 to 2 nmoles of fluorescently labeled antibodies were administered to mice bearing tumors that were positive or negative for MT-SP1. Antibodies localized to MT-SP1-positive tumors (n = 3), permitting visualization of MT-SP1 activity, whereas MT-SP1-negative tumors (n = 2) were not visualized. Our findings define MT-SP1 activity as a useful biomarker to visualize epithelial cancers using a noninvasive antibody-based method.
Graduate Group in Biophysics, Department of Pharmaceutical Chemistry, Helen Diller Family Comprehensive Cancer Center, University of California, San Francisco, San Francisco, California 94158, USA.
Molly R
MR
Darragh
Eric L
EL
Schneider
Jianlong
J
Lou
Paul J
PJ
Phojanakong
Christopher J
CJ
Farady
James D
JD
Marks
Byron C
BC
Hann
Charles S
CS
Craik
D000818:Animals; D000906:Antibodies; D000918:Antibody Specificity; D014408:Biomarkers, Tumor / Q000276:immunology / Q000378:metabolism; D003952:Diagnostic Imaging / Q000379:methods*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005455:Fluorescent Antibody Technique / Q000379:methods; D019073:HT29 Cells; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000175:diagnosis* / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012697:Serine Endopeptidases / Q000276:immunology / Q000378:metabolism*; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D000906:Antibodies; D014408:Biomarkers, Tumor; D004791:Enzyme Inhibitors; D012697:Serine Endopeptidases; C485596:ST14 protein, human