title: Structural characterization and in vivo evaluation of β-Hairpin peptidomimetics as specific CXCR4 imaging agents.
abstract: The CXCR4 chemokine receptor is integral to several biological functions and plays a pivotal role in the pathophysiology of many diseases. As such, CXCR4 is an enticing target for the development of imaging and therapeutic agents. Here we report the evaluation of the POL3026 peptidomimetic template for the development of imaging agents that target CXCR4. Structural and conformational analyses of POL3026 and two of its conjugates, DOTA (POL-D) and PEG12-DOTA (POL-PD), by circular dichroism, two-dimensional NMR spectroscopy and molecular dynamics calculations are reported. In silico observations were experimentally verified with in vitro affinity assays and rationalized using crystal structure-based molecular modeling studies. [(111)In]-labeled DOTA conjugates were assessed in vivo for target specificity in CXCR4 expressing subcutaneous U87 tumors (U87-stb-CXCR4) through single photon emission computed tomography (SPECT/CT) imaging and biodistribution studies. In silico and in vitro studies show that POL3026 and its conjugates demonstrate similar interactions with different micelles that mimic cellular membrane and that the ε-NH2 of lysine(7) is critical to maintain high affinity to CXCR4. Modification of this group with DOTA or PEG12-DOTA led to the decrease of IC50 value from 0.087 nM for POL3026 to 0.47 nM and 1.42 nM for POL-D and POL-PD, respectively. In spite of the decreased affinity toward CXCR4, [(111)In]POL-D and [(111)In]POL-PD demonstrated high and significant uptake in U87-stb-CXCR4 tumors compared to the control U87 tumors at 90 min and 24 h post injection. Uptake in U87-stb-CXCR4 tumors could be blocked by unlabeled POL3026, indicating specificity of the agents in vivo. These results suggest POL3026 as a promising template to develop new imaging agents that target CXCR4.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University , Baltimore, Maryland 21287, United States.
authors.forename: Wojciech G
authors.initials: WG
authors.lastname: Lesniak
authors.forename: Emilia
authors.initials: E
authors.lastname: Sikorska
authors.forename: Hassan
authors.initials: H
authors.lastname: Shallal
authors.forename: Babak
authors.initials: B
authors.lastname: Behnam Azad
authors.forename: Ala
authors.initials: A
authors.lastname: Lisok
authors.forename: Mrudula
authors.initials: M
authors.lastname: Pullambhatla
authors.forename: Martin G
authors.initials: MG
authors.lastname: Pomper
authors.forename: Sridhar
authors.initials: S
authors.lastname: Nimmagadda
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001702:Biopharmaceutics; D045744:Cell Line, Tumor; D005260:Female; D005909:Glioblastoma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000276:immunology*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D064593:Heterografts; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010456:Peptides, Cyclic / Q000737:chemistry; D057786:Peptidomimetics / Q000737:chemistry*; D011487:Protein Conformation; D019718:Receptors, CXCR4 / Q000378:metabolism*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: C527276:CXCR4 protein, human; D006573:Heterocyclic Compounds, 1-Ring; C516700:POL3026 peptide; D010456:Peptides, Cyclic; D057786:Peptidomimetics; D019718:Receptors, CXCR4; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid
keywords: CXCR4; SPECT/CT; chemokine; chemokine receptor; molecular imaging