The hepatocyte growth factor (HGF) is the only known ligand of the mesenchymal-epithelial transition factor (c-Met) (also known as the HGF receptor) that has an important function, including cell development, proliferation, scattering, migration, and angiogenesis, all of which are necessary for the survival and repair of tissues (2). c-Met is known to mediate its activity through an intracellular tyrosine kinase (TK) that activates different signal transduction pathways, leading to initiation of the various cell processes (3). Also, deregulation of c-Met activity due to paracrine/autocrine activation, overexpression, or mutation promotes the development of a neoplastic cell phenotype (3). Overexpression of c-Met and HGF has been associated with a poor prognosis and survival of the patient (4), suggesting that the c-Met receptor may be a suitable target for the detection of cancers at an early stage, which could help in the development of an appropriate treatment regimen to improve patient prognosis (5). c-Met is the target of several drugs under evaluation in clinical trials approved by the United States Food and Drug Administration.
Because the overexpression of HGF and c-Met in malignant gliomas indicates a poor prognosis for the patient, c-Met is a tumor marker of interest for the detection and diagnosis of this disease (1, 6). Although brain lesions are quite easily detected when a contrast agent (CA) is used in conjunction with magnetic resonance imaging (MRI), this technique cannot determine the molecular basis for development of the lesion (1). However, an antibody or a ligand can be used to target a gadolinium (Gd)-based CA for use with MRI to detect and possibly quantify a specific cell-surface component or antigen that may have an important role in the development of a malignancy. Using this approach, investigators were successful in using Gd linked to diethylenetriamine pentaacetic acid and conjugated to a folate-containing dendrimer to quantify folate receptor expression in xenograft tumors on mice (7). In another study, SCID mice bearing xenograft tumors expressing the Her-2/neu receptor were pre-exposed to a biotinylated anti–Her-2/neu monoclonal antibody (MAb), and the animals were subsequently treated with an avidin-Gd-DTPA conjugate (8). Using MRI, the investigators obtained tumor images and determined the level of Her-2/neu receptor expression in the tumor tissue. On the basis of these studies, Towner et al. evaluated the use of Gd-DTPA-albumin coupled to an anti-c-Met MAb (anti-c-Met-Gd-DTPA-albumin) for the visualization of c-Met overexpression in an intracranial rat glioma model (1).
The synthesis of anti-c-Met-Gd-DTPA-albumin has been discussed in detail by Towner et al. (1). Briefly, biotinylated bovine serum albumin (BSA) was first linked to Gd-DTPA to obtain biotin-BSA-Gd-DTPA (the number of Gd attached to each molecule of biotib-BSA was not reported), and this complex was then conjugated to a mouse anti-c-Met MAb to obtain anti-c-Met-Gd-DTPA-albumin, the MRI CA. Biotinylated BSA was used to facilitate detection of anti-c-Met-Gd-DTPA-albumin with immunofluorescence staining using Cy3-streptavidin. The final product was freeze-dried and stored at 4°C until required. The freeze-dried anti-c-Met-Gd-DTPA-albumin was reconstituted in phosphate-buffered saline (pH not reported) before treating the animals. Using a similar procedure, rat IgG-biotin-BSA-Gd-DTPA was also prepared for use as a control CA. The stability of the various CAs after reconstitution was not reported.
In Vitro Studies: Testing in Cells and Tissues
The overexpression of c-Met in rat gliomas compared with normal rat brain tissue was detected with Western blot analysis by Towner et al. (1). After immunofluorescence staining with Cy3-streptavidin, an increased fluorescence was observed in the gliomas compared with the normal brain tissue, which confirmed the overexpression of c-Met in the tumors as noted with the Western blots (1).
Rats (the number of animals used was not reported) bearing gliomas were treated with the control IgG CAs, the c-Met–directed CAs, or the Gd-DTPA-BSA CAs, and T1-weighted images of the animal brains were obtained before and 3 h after injection of the CAs through the tail vein (1). Several 1H-MRI image slices were taken in the transverse plane with a multi-spin echo, multi-slice sequence using a repetition time of 2.4 s and echo times of 17.4 (T1-weighted) and 63.9 (T2-weighted) (1). The T1-weighted images revealed the anatomical details of the brain, whereas the T2-weighted images provided contrast to detect the tumors. A decrease in T1 relaxation with a simultaneous increase in the MRI signal intensity indicated specific binding of anti-c-Met-Gd-DTPA-albumin to areas within the glioma tumors.
On the basis of the T1 maps obtained 3 h after treatment and the signal intensities from various regions of the brain, it was reported that a significantly increased signal intensity and concentration (P = 0.01–0.05) of the c-Met–specific CA on the glioma tumor periphery and interior of animals treated with anti-c-Met-Gd-DTPA-albumin was observed compared with the signal intensity and concentration of the CAs in tumors obtained from animals treated with Gd-DTPA-BSA or control IgG CAs and the normal brain. The binding specificity of anti-c-Met-Gd-DTPA-albumin to the tumors was confirmed with immunofluorescence staining. In addition, the T1 values for the tumors were reported to decrease over a 3-h period with an increase in the contrast signal during that time, however during the same period the T1 and the contrast signal values returned to precontrast treatment levels in the normal brain tissue. No blocking studies were reported.
From these studies, the investigators concluded that anti-c-Met-Gd-DTPA-albumin could be used for the detection of c-Met in rodents under in vivo conditions (1).
Other Non-Primate Mammals
No references are currently available.
No references are currently available.
No references are currently available.
No information is currently available.
Some studies presented in this chapter were funded by a National Institutes of Health grant 5RO3CA121359-2.
- Naran S., Zhang X., Hughes S.J. Inhibition of HGF/MET as therapy for malignancy. Expert Opin Ther Targets. 2009;13(5):569–81. [PubMed: 19397476]
- Birchmeier C., Birchmeier W., Gherardi E., Vande Woude G.F. Met, metastasis, motility and more. Nat Rev Mol Cell Biol. 2003;4(12):915–25. [PubMed: 14685170]
- Kim E.M., Park E.H., Cheong S.J., Lee C.M., Jeong H.J., Kim D.W., Lim S.T., Sohn M.H. In vivo imaging of mesenchymal-epithelial transition factor (c-Met) expression using an optical imaging system. Bioconjug Chem. 2009;20(7):1299–306. [PubMed: 19534520]
- Lamszus K., Laterra J., Westphal M., Rosen E.M. Scatter factor/hepatocyte growth factor (SF/HGF) content and function in human gliomas. Int J Dev Neurosci. 1999;17(5-6):517–30. [PubMed: 10571413]
- Konda S.D., Aref M., Wang S., Brechbiel M., Wiener E.C. Specific targeting of folate-dendrimer MRI contrast agents to the high affinity folate receptor expressed in ovarian tumor xenografts. Magma. 2001;12(2-3):104–13. [PubMed: 11390265]
- Artemov D., Mori N., Ravi R., Bhujwalla Z.M. Magnetic resonance molecular imaging of the HER-2/neu receptor. Cancer Res. 2003;63(11):2723–7. [PubMed: 12782573]
Created: September 15, 2009; Last Update: October 26, 2009.
National Center for Biotechnology Information (US), Bethesda (MD)
Chopra A. Mouse anti-cMet monoclonal antibody linked to gadolinium diethylenetriamine pentaacetic acid conjugated to biotinylated bovine serum albumin. 2009 Sep 15 [Updated 2009 Oct 26]. In: Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.