title: Vascular endothelial growth factor selectively targets boronated dendrimers to tumor vasculature.
abstract: 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 x 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 x 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.
authors.affiliation: Sibtech, Inc., Newington, CT 06111, USA. mbacker@sibtech.com
authors.forename: Marina V
authors.initials: MV
authors.lastname: Backer
authors.forename: Timur I
authors.initials: TI
authors.lastname: Gaynutdinov
authors.forename: Vimal
authors.initials: V
authors.lastname: Patel
authors.forename: Achintya K
authors.initials: AK
authors.lastname: Bandyopadhyaya
authors.forename: B T S
authors.initials: BT
authors.lastname: Thirumamagal
authors.forename: Werner
authors.initials: W
authors.lastname: Tjarks
authors.forename: Rolf F
authors.initials: RF
authors.lastname: Barth
authors.forename: Kevin
authors.initials: K
authors.lastname: Claffey
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Backer
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000737:chemistry / Q000493:pharmacokinetics*; D016754:Boron Neutron Capture Therapy; D049109:Cell Proliferation / Q000187:drug effects; D004730:Endothelium, Vascular / Q000187:drug effects*; D005260:Female; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009389:Neovascularization, Pathologic / Q000188:drug therapy* / Q000378:metabolism; D011073:Polyamines / Q000737:chemistry / Q000493:pharmacokinetics*; D040262:Receptors, Vascular Endothelial Growth Factor / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000008:administration & dosage / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D001896:Boron Compounds; D011073:Polyamines; D011993:Recombinant Fusion Proteins; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D040262:Receptors, Vascular Endothelial Growth Factor