title: Cell-specific targeting by heterobivalent ligands.
abstract: Current cancer therapies exploit either differential metabolism or targeting to specific individual gene products that are overexpressed in aberrant cells. The work described herein proposes an alternative approach--to specifically target combinations of cell-surface receptors using heteromultivalent ligands ("receptor combination approach"). As a proof-of-concept that functionally unrelated receptors can be noncovalently cross-linked with high avidity and specificity, a series of heterobivalent ligands (htBVLs) were constructed from analogues of the melanocortin peptide ligand ([Nle(4), dPhe(7)]-α-MSH) and the cholecystokinin peptide ligand (CCK-8). Binding of these ligands to cells expressing the human Melanocortin-4 receptor and the Cholecystokinin-2 receptor was analyzed. The MSH(7) and CCK(6) were tethered with linkers of varying rigidity and length, constructed from natural and/or synthetic building blocks. Modeling data suggest that a linker length of 20-50 Å is needed to simultaneously bind these two different G-protein coupled receptors (GPCRs). These ligands exhibited up to 24-fold enhancement in binding affinity to cells that expressed both (bivalent binding), compared to cells with only one (monovalent binding) of the cognate receptors. The htBVLs had up to 50-fold higher affinity than that of a monomeric CCK ligand, i.e., Ac-CCK(6)-NH(2). Cell-surface targeting of these two cell types with labeled heteromultivalent ligand demonstrated high avidity and specificity, thereby validating the receptor combination approach. This ability to noncovalently cross-link heterologous receptors and target individual cells using a receptor combination approach opens up new possibilities for specific cell targeting in vivo for therapy or imaging.
authors.affiliation: Department of Chemistry & Biochemistry, 1306 E. University Blvd., The University of Arizona, Tucson, Arizona 85721, United States.
authors.forename: Jatinder S
authors.initials: JS
authors.lastname: Josan
authors.forename: Heather L
authors.initials: HL
authors.lastname: Handl
authors.forename: Rajesh
authors.initials: R
authors.lastname: Sankaranarayanan
authors.forename: Liping
authors.initials: L
authors.lastname: Xu
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Lynch
authors.forename: Josef
authors.initials: J
authors.lastname: Vagner
authors.forename: Eugene A
authors.initials: EA
authors.lastname: Mash
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Hruby
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Gillies
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry* / Q000378:metabolism*; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D011485:Protein Binding; D043887:Receptor, Cholecystokinin B / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D044105:Receptor, Melanocortin, Type 4 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D003432:Cross-Linking Reagents; D008024:Ligands; C470072:MC4R protein, human; D043887:Receptor, Cholecystokinin B; D044105:Receptor, Melanocortin, Type 4