Background

[PubMed]

Integrins are a broad family of glycoprotein, transmembrane cell surface receptors that are formed by the association of an α and a β subunit. These receptors are involved in cell-matrix interactions and also play a role in cell signaling and migration (1, 2). Because of their role in cell migration, the α_vβ₃ integrin (that binds proteins such as vitronectin, fibronectin, thrombospondin, collagen, osteopontin, etc.) is a target of interest for the investigation of cancer metastasis and angiogenesis (3). Normally this receptor is expressed at low levels on epithelial and mature endothelial cells, but the expression is significantly upregulated during wound repair, cancer metastasis, and in neoplastic tumor vasculature (4-6). However, the exact role of α_vβ₃ integrin in angiogenesis is unclear because the inhibition of this receptor inhibits tumor angiogenesis, but knockout mice lacking the β₃ integrins were shown to develop larger than normal and extremely vascularized tumors (7, 8).

Visualization of small solid tumors has often helped in early detection of cancer and resulted in a favorable prognosis for the patient (9). Using magnetic resonance imaging with nanoparticles (NP) that target the α_vβ₃ integrin, investigators have obtained high-resolution images of even minute tumors, but this technique requires knowledge of the exact location of the tumor to set up the equipment for imaging (10). Although a variety of radiolabeled compounds such as peptides, antibodies, and other α_vβ₃ integrin antagonists have been used to visualize tumors in animals, these radiochemicals have limitations because of nonspecific binding (11, 12). Perfluorocarbon NP was shown to biodistribute primarily to the reticuloendothelial organs (lungs, liver, and spleen), and Hu et al. investigated the use of these NP with a radionuclide payload to detect budding tumors and their vasculature in different regions of the body, including the brain, head, neck, prostate, and breasts (10). The investigators developed an α_vβ₃ integrin anatagonist labeled with indium (¹¹¹In) on a perfluorocarbon NP (α_vβ₃-targeted ¹¹¹In/NP) and used the NP to visualize neoplastic tumor vasculature (10). The α_vβ₃ integrin antagonist used to prepare the α_vβ₃-targeted ¹¹¹In/NP was TA138 (known as 3-sulfon-N-[[4,7,10-tris(carboxymethyl)1,4,7,10-tetraaza-cyclododec-1-yl]acetyl]-L-alanyl-N-[2-[4-[[[(1S)-1-carboxy-2[[[1,4-dihydro-7-[(1H-imidazol-2-ylamino]methyl]-1-methyl-4-oxo-3-quinolinyl] carbonyl]amino]ethyl]amino]sulfonyl]-3,5-dimethylphenoxy]-1-oxobutyl]amino]ethyl]-3-sulfo-L-alaninamide) (10).

Synthesis

[PubMed]

The perfluorocarbon NP were produced as detailed by Hu et al. (10). A mixture of perfluorooctylbromide (PFOB), a surfactant commixture, with glycerin and water was evaporated under reduced pressure and dried overnight at 50°C in a vacuum oven. The commixture consisted of lecithin, dipalmitoyl-L-α-ethanolamine, cholesterol, methoxy-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-caproyl-phosphatidylethanolamine and TA138 conjugated to polyethylene glycol 2000 dissolved in chloroform (13-15). The dried mixture was then suspended in water by sonication to produce a liposomal suspension (14). The liposomes were blended with PFOB and distilled, deionized water and emulsified at 20,000 psi for 4 minutes. The completed emulsion was aliquoted into a vial, sealed under nitrogen, and stored until use. The exact storage conditions were not provided in the publication. The NP size was determined with a laser light–scattering submicron particle size analyzer to be nominally 242 nm with a polydispersity index of 0.231 at 37°C (10).

The synthesis of TA138 was described by Liu et al. (16). For this, 2-{[(4-{3-[N-(2-{(2R)-2-[(2R)-3-sulfo-2-(2-{1,4,7,10-tetraaza-4,7,10-tris[(tert-butoxycarbonyl)methyl] cyclododecyl}acetylamino)propyl]-3-sulfopropyl}ethyl)carbamoyl]propoxy}-2,6-dimethylphenyl) sulfonyl]amino}(2S)-3-{[1-methyl-4-oxo-7-({[1-(triphenylmethyl)imidazol-2-yl]-amino}methyl)(3-hydroquinolyl)]carbonylamino}propanoic acid (DPC-AG1613) was dissolved in trifluoroacetic acid and triethylsilane, heated at 70°C under nitrogen for 60 min, and concentrated under vacuum to obtain an oily solid. The solid was partitioned between diethyl ether and aqueous acetonitrile (ACN). The ether layer was once again extracted with aqueous ACN, and the two aqueous extractions were pooled for freeze-drying to obtain crude TA138 (16). Pure TA138 was obtained by several runs of the crude preparation on high-performance liquid chromatography using a Vydac C₁₈ pharmaceutical column. The salt was subsequently extracted in ACN and water and then freeze-dried to obtain pure TA138 as a fluffy solid (16).

Coupling of ¹¹¹In to α_vβ₃ integrin–targeted perfluorocarbon NP was done at two different concentrations of the radionuclide (to produce particles with ~1 and ~10 radionuclides per NP, respectively), and it was achieved in citrate buffer (pH 5.7) (10). Briefly, α_vβ₃ integrin–targeted perfluorocarbon NP was combined with [¹¹¹In]indium chloride (in hydrochloric acid) in citrate buffer and incubated overnight at 40°C in a shaker water bath. The reaction was stopped by adding free diethylenetriamine pentaacetic acid for 5 min to remove all the free ¹¹¹In. Coupling efficiency was determined by thin-layer chromatography at room temperature. It ranged from 50% to 70% for the ~10 nuclides/NP and 85% to 90% for the ~1 nuclide/NP. The specific activity and radiochemical purity of the final product were not reported by the investigators (10)

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

No publications are currently available.

Animal Studies

Human Studies

[PubMed]

No publications are currently available.

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Elkin E.B. , Hudis C. , Begg C.B. , Schrag D. The effect of changes in tumor size on breast carcinoma survival in the U.S.: 1975-1999. Cancer. 2005; 104 (6):1149–57. [PubMed: 16088887]

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