In vitro and in vivo investigation of matrix metalloproteinase expression in metastatic tumor models.
BACKGROUND
Overexpression of matrix metalloproteinases (MMPs), particularly MMP-2 and MMP-9, has been correlated with poor prognosis in several cancer types including lung, colon and breast. Noninvasive detection of MMP expression might allow physicians to better determine when more aggressive cancer therapy is appropriate. The peptide CTT (CTTHWGFTLC) was identified as a selective inhibitor of MMP-2/9 that inhibits the growth of MDA-MB-435 human breast cancer xenografts.


METHODS
CTT was conjugated with the bifunctional chelator DOTA (1,4,7,10-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid) for radiolabeling with (64)Cu (t(1/2)=12.7 h, 17.4% beta(+), 39% beta(-)), a radionuclide suitable for positron emission tomography (PET). In vitro affinity was determined in a fluorogenic substrate assay. Tumor gelatinase targeting was evaluated in both biodistribution and microPET imaging studies.


RESULTS
Cu(II)-DOTA-CTT inhibited hMMP-2 (EC(50)=8.7 microM) and mMMP-9 (EC(50)=18.2 microM) with similar affinity to CTT (hMMP-2 EC(50)=13.2 microM; mMMP-9 EC(50)=11.0 microM). In biodistribution and microPET imaging studies, (64)Cu-DOTA-CTT was taken up by MMP-2/9-positive B16F10 murine melanoma tumors. Subsequently, imaging studies using (64)Cu-DOTA-CTT were performed on MDA-MB-435 tumor-bearing mice. With zymography, tumor MMP-2/9 expression in this model was shown to be inconsistent, resulting in microPET detection of the MDA-MB-435 tumor in only 1 of 24 imaged mice. Following limited imaging success, (64)Cu-DOTA-CTT was shown to have poor in vivo stability.


CONCLUSIONS
Despite some evidence for selective uptake of (64)Cu-DOTA-CTT by gelatinase-expressing tumors, the low affinity for MMP-2 and MMP-9 and in vivo instability make this an inadequate radioligand for in vivo tumor evaluation.
Sprague
Jennifer E
JE
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
Li
Wen Ping
WP
Liang
Kexian
K
Achilefu
Samuel
S
Anderson
Carolyn J
CJ
D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism*; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D008545:Melanoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000556:secondary*; D008657:Metabolic Clearance Rate; D051379:Mice; D008810:Mice, Inbred C57BL; D009842:Oligopeptides / Q000502:physiology*; D009942:Organometallic Compounds; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D014408:Biomarkers, Tumor; C513749:Cu-DOTA-CTT; D009842:Oligopeptides; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9