Background

[PubMed]

Extracellular matrix (ECM) adhesion molecules consist of a complex network of fibronectins, collagens, chondroitins, laminins, glycoproteins, heparin sulfate, tenascins, and proteoglycans that surround connective tissue cells, and they are mainly secreted by fibroblasts, chondroblasts, and osteoblasts (1). Cell substrate adhesion molecules are considered essential regulators of cell migration, differentiation, and tissue integrity and remodeling. These molecules play an important role in inflammation and atherogenesis, but they also participate in the process of invasion and metastasis of malignant cells in the host tissue (2). Invasive tumor cells adhere to the ECM, which provides a matrix environment for permeation of tumor cells through the basal lamina and underlying interstitial stroma of the connective tissue. Overexpression of matrix metalloproteinases (MMPs) and other proteases by tumor cells allows intravasation of tumor cells into the circulatory system after degradation of the basement membrane and ECM (3). Several families of proteases are involved in atherogenesis, myocardial infarction, angiogenesis, and tumor invasion and metastasis (4-7).

Gadolinium (Gd), a lanthanide metal ion with seven unpaired electrons, has been shown to be very effective in enhancing proton relaxation because of its high magnetic moment and water coordination (8, 9). Gd-Labeled diethylenetriaminepentaacetic acid (Gd-DTPA) was the first intravenous magnetic resonance imaging (MRI) contrast agent used clinically, and a number of similar Gd chelates have been developed in an effort to further improve clinical use. However, these low molecular weight Gd chelates have short blood and tissue retention times, which limit their use as imaging agents in the vasculature and cancer. Various macromolecular Gd complexes have demonstrated superior contrast enhancement for MRI of the vasculature and carcinomas (10-12); however, these Gd complexes cannot proceed into further clinical development because of high tissue accumulation and slow excretion of toxic Gd ions. Furthermore, they are largely nonspecific. Gly-Pro-D-Leu-D-Ala-NHOH was found to be a broad-spectrum inhibitor of MMP-1, -2, -3, -8, -9, and -13 (13). Gd-1,4,7,10-tetraazacyclododecane-N',N'',N''',N''''-tetraacetic acid (DOTA)-Gly-Pro-D-Leu-D-Ala-NHOH (P947) has been developed to detect MMP activities in atherosclerotic plaques.

Synthesis

[PubMed]

P947 was prepared by coupling Gly-Pro-D-Leu-D-Ala-NHOH to DOTA (13). P947 is a Gd(III) complex of a bi-functional DOTA chelate conjugated via a phenylbutyric linker with a thiourea function to the tetrapeptidyl hydroxamic acid Gly-Pro-D-Leu-D-Ala-NHOH. It has a molecular weight of 1,210 Da and the r1 relaxivity value of 5.5 mM^-1 s^-1 in water at 1.5 T and 37°C, whereas Gd-DOTA has the r1 relaxivity value of 3.7 mM^-1 s^-1.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

P947 exhibited 50% inhibition concentration (IC₅₀) values of 100 µM for MMP-14, 10 µM for MMP-3 and MMP-9, 1 µM for MMP-1, MMP-2, and MMP-13, and 0.1 µM for MMP-8 (13). Immunohistochemical measurements of human and rabbit atherosclerotic aortas revealed the presence of various MMPs in the aortas with higher P947 accumulation than Gd-DOTA. Gly-Pro-D-Leu-D-Ala-NHOH blocked P947 accumulation in the rabbit experiments.

Animal Studies

Human Studies

[PubMed]

No publication is currently available.

NIH Support

HL78667, R01 HL71021

References

1.

Bosman F.T. , Stamenkovic I. Functional structure and composition of the extracellular matrix. J Pathol. 2003; 200 (4):423–8. [PubMed: 12845610]

2.

Jiang W.G. , Puntis M.C. , Hallett M.B. Molecular and cellular basis of cancer invasion and metastasis: implications for treatment. Br J Surg. 1994; 81 (11):1576–90. [PubMed: 7827878]

3.

Albelda S.M. Role of integrins and other cell adhesion molecules in tumor progression and metastasis. Lab Invest. 1993; 68 (1):4–17. [PubMed: 8423675]

4.

Keppler D. , Sameni M. , Moin K. , Mikkelsen T. , Diglio C.A. , Sloane B.F. Tumor progression and angiogenesis: cathepsin B & Co. Biochem Cell Biol. 1996; 74 (6):799–810. [PubMed: 9164649]

5.

Liu J. , Sukhova G.K. , Sun J.S. , Xu W.H. , Libby P. , Shi G.P. Lysosomal cysteine proteases in atherosclerosis. Arterioscler Thromb Vasc Biol. 2004; 24 (8):1359–66. [PubMed: 15178558]

6.

Berchem G. , Glondu M. , Gleizes M. , Brouillet J.P. , Vignon F. , Garcia M. , Liaudet-Coopman E. Cathepsin-D affects multiple tumor progression steps in vivo: proliferation, angiogenesis and apoptosis. Oncogene. 2002; 21 (38):5951–5. [PubMed: 12185597]

7.

Brix, K., A. Dunkhorst, K. Mayer, and S. Jordans, Cysteine cathepsins: Cellular roadmap to different functions. Biochimie, 2007. [PubMed: 17825974]

8.

Brasch R.C. New directions in the development of MR imaging contrast media. Radiology. 1992; 183 (1):1–11. [PubMed: 1549653]

9.

Runge V.M. , Gelblum D.Y. Future directions in magnetic resonance contrast media. Top Magn Reson Imaging. 1991; 3 (2):85–97. [PubMed: 2025435]

10.

Schmiedl U. , Ogan M. , Paajanen H. , Marotti M. , Crooks L.E. , Brito A.C. , Brasch R.C. Albumin labeled with Gd-DTPA as an intravascular, blood pool-enhancing agent for MR imaging: biodistribution and imaging studies. Radiology. 1987; 162 (1 Pt 1):205–10. [PubMed: 3786763]

11.

Gossmann A. , Okuhata Y. , Shames D.M. , Helbich T.H. , Roberts T.P. , Wendland M.F. , Huber S. , Brasch R.C. Prostate cancer tumor grade differentiation with dynamic contrast-enhanced MR imaging in the rat: comparison of macromolecular and small-molecular contrast media--preliminary experience. Radiology. 1999; 213 (1):265–72. [PubMed: 10540670]

12.

Preda A. , van Vliet M. , Krestin G.P. , Brasch R.C. , van Dijke C.F. Magnetic resonance macromolecular agents for monitoring tumor microvessels and angiogenesis inhibition. Invest Radiol. 2006; 41 (3):325–31. [PubMed: 16481916]

13.

Lancelot E. , Amirbekian V. , Brigger I. , Raynaud J.S. , Ballet S. , David C. , Rousseaux O. , Le Greneur S. , Port M. , Lijnen H.R. , Bruneval P. , Michel J.B. , Ouimet T. , Roques B. , Amirbekian S. , Hyafil F. , Vucic E. , Aguinaldo J.G. , Corot C. , Fayad Z.A. Evaluation of matrix metalloproteinases in atherosclerosis using a novel noninvasive imaging approach. Arterioscler Thromb Vasc Biol. 2008; 28 (3):425–32. [PubMed: 18258820]