Vascular endothelial growth factor selectively targets boronated dendrimers to tumor vasculature

• Published in: Molecular cancer therapeutics 2005-09, Vol.4 (9), p.1423-1429
• Main Authors: Backer, Marina V, Gaynutdinov, Timur I, Patel, Vimal, Bandyopadhyaya, Achintya K, Thirumamagal, B T S, Tjarks, Werner, Barth, Rolf F, Claffey, Kevin, Backer, Joseph M
• Format: Article
• Language: English
• Subjects: Animals; BNCT; Boron Compounds - chemistry; Boron Compounds - pharmacokinetics; Boron Neutron Capture Therapy; Cell Proliferation - drug effects; Endothelium, Vascular - drug effects; Female; Humans; Mammary Neoplasms, Experimental - blood supply; Mammary Neoplasms, Experimental - metabolism; Mice; Mice, Inbred BALB C; Near-IR imaging; Neovascularization, Pathologic - drug therapy; Neovascularization, Pathologic - metabolism; Polyamines - chemistry; Polyamines - pharmacokinetics; Receptors, Vascular Endothelial Growth Factor - metabolism; Recombinant Fusion Proteins - administration & dosage; Recombinant Fusion Proteins - pharmacology; targeted delivery; Tumor Cells, Cultured; Vascular Endothelial Growth Factor A - administration & dosage; Vascular Endothelial Growth Factor A - pharmacology
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-05-0161

Tumor neovasculature is a potential but, until very recently, unexplored target for boron neutron capture therapy (BNCT) of cancer. In the present report, we describe the construction of a vascular endothelial growth factor (VEGF)–containing bioconjugate that potentially could be used to target up-regulated VEGF receptors (VEGFR), which are overexpressed on tumor neovasculature. A fifth-generation polyamidoamine dendrimer containing 128 reactive amino groups was reacted with 105 to 110 decaborate molecules to produce a macromolecule with 1,050 to 1,100 boron atoms per dendrimer. This was conjugated to thiol groups of VEGF at a 4:1 molar ratio using the heterobifunctional reagent sulfo-LC-SPDP. In addition, the boronated dendrimer was tagged with a near-IR Cy5 dye to allow for near-IR fluorescent imaging of the bioconjugate in vitro and in vivo . As would be predicted, the resulting VEGF-BD/Cy5 bioconjugate was not cytotoxic to HEK293 cells engineered to express 2.5 × 10 6 VEGFR-2 per cell. Furthermore, it showed binding and activation of VEGFR-2 comparable with that of native VEGF. Internalization of VEGF-BD/Cy5 by PAE cells expressing 2.5 × 10 5 VEGFR-2 per cell was inhibited by excess VEGF, indicating a VEGFR-2-mediated mechanism of uptake. Near-IR fluorescent imaging of 4T1 mouse breast carcinoma revealed selective accumulation of VEGF-BD/Cy5, but not BD/Cy5, particularly at the tumor periphery where angiogenesis was most active. Accumulation of VEGF-BD/Cy5 in 4T1 breast carcinoma was diminished in mice pretreated with a toxin-VEGF fusion protein that selectively killed VEGFR-2-overexpressing endothelial cells. Our data lay the groundwork for future studies using the VEGF-BD/Cy5 bioconjugate as a targeting agent for BNCT of tumor neovasculature.