Bivalent 14-mer peptide ligands of CXCR4 with polyproline linkers with anti-chemotactic activity against Jurkat cells

Distance-Dependent Cellular Uptake of Oligoproline-Based Homobivalent Ligands Targeting GPCRs-An Experimental and Computational Analysis

Tumor targeting with bivalent radiolabeled ligands for GPCRs is an attractive means for cancer imaging and therapy. Here, we studied and compared the distance dependence of homobivalent ligands for the human gastrin-releasing peptide receptor (hGRP-R) and the somatostatin receptor subtype II (hSstR_2a). Oligoprolines were utilized as molecular scaffolds to enable distances of 10, 20, or 30 Å between two identical, agonistic recognition motifs. In vitro internalization assays revealed that ligands with a distance of 20 Å between the recognition motifs exhibit the highest cellular uptake in both ligand series. Structural modeling and molecular dynamics simulations support an optimal distance of 20 Å for accommodating ligand binding to both binding sites of a GPCR dimer. Translation of these findings to the significantly higher complexity in vivo proved difficult and showed only for the hGRP-R increased tumor uptake of the bivalent ligand.

Inhibition of EGFR Activation by Bivalent Ligands Based on a Cyclic Peptide Mimicking the Dimerization Arm Structure of EGFR

The epidermal growth factor receptor (EGFR) is a receptor in the ErbB family, and is overexpressed in some cancer cells. Recent research has shown that, since clustering of the EGFR increases the possibility of its dimerization and activation, the dimerization state of the EGFR on the cell surface is important for the recognition of the EGFR. In case a bivalent inhibitor has an optimized linker length, the clusters of the EGFR could be recognized with high affinity and kinase activation, which depends on EGF, could be suppressed. Peptide 1, which is derived from the dimerization arm of the EGFR, has been found previously to inhibit autophosphorylation of the EGFR. In this study, bivalent ligands based on peptide 1 with linkers of poly(L-proline) or poly-[(glycine)₄(L-serine)] have been designed and synthesized. Bivalent ligands with polyproline linkers could maintain the distance between the ligand moieties. The inhibitory activity of these bivalent ligands against EGFR autophosphorylation was measured and was found to increase as the linker enlarges up to a 15-mer proline linker. The inhibitory activity of a bivalent ligand 7b is significantly higher compared to the corresponding monomeric peptide 2a. This suggests that bivalent EGFR ligands with optimal and rigid linkers could recognize the clusters of the EGFR with higher affinity and suppress kinase activation involving EGF.