Sci. Adv. Today 3 (2017) 25273  
  Research Article  
Targeting the atypical chemokine receptor ACKR3/CXCR7: phase 2 - cell line studies  
  R. D. Vestala, D. R. LaJeunessea and E. W. Taylorb  
a Department of Nanoscience, University of North Carolina at Greensboro (UNCG), Greensboro, North Carolina 27401, USA
b Department of Chemistry and Biochemistry, University of North Carolina at Greensboro (UNCG), Greensboro, North Carolina 27412, USA

  The efficiency of current anticancer therapies can be increased by directly targeting cell membrane components including chemokine receptors expressed on the external surface of tumor cells. We have identified three heptameric peptide sequences, P-20, P-9, and P-3, which bind a synthesized portion of the N-terminus region of ACKR3/CXCR7, have different physical and chemical properties, and are predicted to mimic three different regions of the endogenous ligand SDF1/CXCL12 [1]. These peptides were shown to have no effect on the viability or proliferation of MCF-7 (breast) or U87-MG (glioblastoma) cancer cells. Additionally, the peptides were observed to significantly bind these same cells using a whole-cell ELISA protocol. The ability of these cancer cell types to bind and internalize the peptides as well as their affinity for ACKR3/CXCR7 was verified using 3D confocal microscopy and a co-localization assay with the known anti-ACKR3/CXCR7 mAb RDC1. Receptor binding specificity was necessary given the cell surface receptors ACKR3/CXCR7 and CXCR4 are known to form heterodimers, bind the same endogenous ligand CXCL12/SDF1a, and are both highly co-expressed in multiple tumor types including glioblastoma [1]. Due to this, binding specificity was established using cell lines known to either express only ACKR3/CXCR7 (MCF-7 cells pos. control) or CXCR4 (THP-1 cells neg. control) on the cell membrane surface. The peptides were shown to bind MCF-7 cells and were also shown to have no affinity for THP-1 cells. Activation of a functional ACKR3/CXCR7 receptor in modified CHO-K1 cells was confirmed via exposure to varying concentrations of SDF1a and a luminescence assay to measure the corresponding increase in levels of ß-arrestin. The peptides did not activate the receptor and had no effect on levels of ß-arrestin. The inability to activate the receptor is an integral part of our desired targeting moiety system. Based on the data presented here, the three recovered peptides P-20, P-9, and P-3 are specific for the N-terminus of ACKR3/CXCR7 and may be used to target cancer cells expressing this receptor and reduce the effects of systemic applications of anticancer therapies.  
  Cite this article as:  
  R. D. Vestal, D. R. LaJeunesse and E. W. Taylor, Targeting the atypical chemokine receptor ACKR3/CXCR7: phase 2 - cell line studies, Sci. Adv. Today 3 (2017) 25273.