Does Cysteine Rule (CysR) Complete the CendR Principle? Increase in Affinity of Peptide Ligands for NRP-1 Through the Presence of N-Terminal Cysteine

Structure-activity relationship studies and biological properties evaluation of peptidic NRP-1 ligands: Investigation of N-terminal cysteine importance

Neuropilin-1 (NRP-1) is a major co-receptor of vascular endothelial growth factor receptor-2 (VEGFR-2). It may also stimulate tumour growth and metastasis independently of VEGF-A165. These functions make VEGF-A165/NRP-1 complex formation and its inhibition of great interest, where NRP-1 is the target for which effective ligands are sought. Design of peptide-like inhibitors represent a strategy with great potential in the treatment of NRP-1-related disorders. Here, we present the synthesis, molecular modelling, structure-activity relationship studies as well as biological evaluation of peptides with the branched sequences H2N-X-Lys(hArg)-Dab-Oic-Arg-OH and H2N-Lys(X-hArg)-Dab-Oic-Arg-OH. Two of the designed peptides, in which Cys was inserted in X position, expressed high affinity (∼40 nM value) for NRP-1 and were resistant to enzymatic digestion in human serum. Moreover, peptide/NRP-1 complex promoted fast intracytoplasmic protein trafficking towards the plasma membrane in breast cancer cells. Our results suggest that these compounds might be good candidates for further development of VEGF-A165/NRP-1 inhibitors.

tLyp-1: A peptide suitable to target NRP-1 receptor

Targeting vascular endothelial growth factor receptor (VEFGR) and its co-receptor neuropilin-1 (NRP-1) is an interesting vascular strategy. tLyp-1 is a tumor-homing and penetrating peptide of 7 amino acids (CGNKRTR). It is a truncated form of Lyp-1 (CGNKRTRGC), which is known to target NRP-1 receptor, with high affinity and specificity. It is mediated by endocytosis via C-end rule (CendR) internalization pathway. The aim of this study is to evaluate the importance of each amino acid in the tLyp-1 sequence through alanine-scanning (Ala-scan) technique, during which each of the amino acid in the sequence was systematically replaced by alanine to produce 7 different analogues. In silico approach through molecular docking and molecular dynamics are employed to understand the interaction between the peptide and its analogues with the NRP-1 receptor, followed by in vitro ligand binding assay study. The C-terminal Arg is crucial in the interaction of tLyp-1 with NRP-1 receptor. Substituting this residue dramatically reduces the affinity of this peptide which is clearly seen in this study. Lys-4 is also important in the interaction, which is confirmed via the in vitro study and the MM-PBSA analysis. The finding in this study supports the CendR, in which the presence of R/K-XX-R/K motif is essential in the binding of a ligand with NRP-1 receptor. This presented work will serve as a guide in the future work pertaining the development of active targeting agent towards NRP-1 receptor.

Synthesis, Physicochemical and Biological Study of Gallium-68- and Lutetium-177-Labeled VEGF-A165/NRP-1 Complex Inhibitors Based on Peptide A7R and Branched Peptidomimetic

Neuropilin-1 (NRP-1) is a surface receptor found on many types of cancer cells. The overexpression of NRP-1 and its interaction with vascular endothelial growth factor-165 (VEGF₁₆₅) are associated with tumor growth and metastasis. Therefore, compounds that block the VEGF₁₆₅/NRP-1 interaction represent a promising strategy to image and treat NRP-1-related pathologies. The aim of the presented work was to design and synthesize radioconjugates of two known peptide-type inhibitors of the VEGF₁₆₅/NRP-1 complex: A7R peptide and its shorter analog, the branched peptidomimetic Lys(hArg)-Dab-Pro-Arg. Both peptide-type inhibitors were coupled to a radionuclide chelator (DOTA) via a linker (Ahx) and so radiolabeled with Ga-68 and Lu-177 radionuclides, for diagnostic and therapeutic uses, respectively. The synthesized radioconjugates were tested for their possible use as theranostic-like radiopharmaceuticals for the imaging and therapy of cancers that overexpress NRP-1. The obtained results indicate good efficiency of the radiolabeling reaction and satisfactory stability, at least 3t_1/2 for the ⁶⁸Ga- and 1t_1/2 for the ¹⁷⁷Lu-radiocompounds, in solutions mimicking human body fluids. However, enzymatic degradation of both the studied inhibitors caused insufficient stability of the radiocompounds in human serum, indicating that further modifications are needed to sufficiently stabilize the peptidomimetics with inhibitory properties against VEGF₁₆₅/NRP-1 complex formation.

The Role of VEGF Receptors as Molecular Target in Nuclear Medicine for Cancer Diagnosis and Combination Therapy

Simple Summary

The rapid development of diagnostic and therapeutic methods of the cancer treatment causes that these diseases are becoming better known and the fight against them is more and more effective. Substantial contribution in this development has nuclear medicine that enables very early cancer diagnosis and early start of the so-called targeted therapy. This therapeutic concept compared to the currently used chemotherapy, causes much fewer undesirable side effects, due to targeting a specific lesion in the body. This review article discusses the possible applications of radionuclide-labelled tracers (peptides, antibodies or synthetic organic molecules) that can visualise cancer cells through pathological blood vessel system in close tumour microenvironment. Hence, at a very early step of oncological disease, targeted therapy can involve in tumour formation and growth.

Abstract

One approach to anticancer treatment is targeted anti-angiogenic therapy (AAT) based on prevention of blood vessel formation around the developing cancer cells. It is known that vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEGFRs) play a pivotal role in angiogenesis process; hence, application of angiogenesis inhibitors can be an effective approach in anticancer combination therapeutic strategies. Currently, several types of molecules have been utilised in targeted VEGF/VEGFR anticancer therapy, including human VEGF ligands themselves and their derivatives, anti-VEGF or anti-VEGFR monoclonal antibodies, VEGF binding peptides and small molecular inhibitors of VEGFR tyrosine kinases. These molecules labelled with diagnostic or therapeutic radionuclides can become, respectively, diagnostic or therapeutic receptor radiopharmaceuticals. In targeted anti-angiogenic therapy, diagnostic radioagents play a unique role, allowing the determination of the emerging tumour, to monitor the course of treatment, to predict the treatment outcomes and, first of all, to refer patients for AAT. This review provides an overview of design, synthesis and study of radiolabelled VEGF/VEGFR targeting and imaging agents to date. Additionally, we will briefly discuss their physicochemical properties and possible application in combination targeted radionuclide tumour therapy.

Urea-Peptide Hybrids as VEGF-A165/NRP-1 Complex Inhibitors with Improved Receptor Affinity and Biological Properties

Neuropilin-1 (NRP-1), the major co-receptor of vascular endothelial growth factor receptor-2 (VEGFR-2), may also independently act with VEGF-A₁₆₅ to stimulate tumour growth and metastasis. Therefore, there is great interest in compounds that can block VEGF-A165/NRP-1 interaction. Peptidomimetic type inhibitors represent a promising strategy in the treatment of NRP-1-related disorders. Here, we present the synthesis, affinity, enzymatic stability, molecular modeling and in vitro binding evaluation of the branched urea–peptide hybrids, based on our previously reported Lys(hArg)-Dab-Oic-Arg active sequence, where the Lys(hArg) branching has been modified by introducing urea units to replace the peptide bond at various positions. One of the resulting hybrids increased the affinity of the compound for NRP-1 more than 10-fold, while simultaneously improving resistance for proteolytic stability in serum. In addition, ligand binding to NRP-1 induced rapid protein stock exocytotic trafficking to the plasma membrane in breast cancer cells. Examined properties characterize this compound as a good candidate for further development of VEGF₁₆₅/NRP-1 inhibitors.