High affinity ligands for precise tumor diagnosis

Abstract

Selective tumor targeting in vivo can be achieved by monoclonal antibodies, which specifically bind to target receptors. However, most antibodies are immunogenic and have long plasma half-life rendering them suboptimal for molecular imaging. Small peptides and biomolecules are therefore preferred for biological imaging because of their low immunogenicity, reduced barriers to topical delivery, high affinity and selectivity for receptors, and desirable pharmacokinetic properties.
Cyclic RGD peptides are small molecules that bind αvβ3 integrin with high affinity. For this reason, a variety of RGD containing peptides has been developed for targeting tumor-induced angiogenic blood vessels or tumor-associated integrin. Conjugation of these peptides to imaging agents or drugs affords bioactive molecules for cancer imaging and targeted therapy, respectively. However, the cyclic RGD structure requires complicated peptide synthesis leading to increase in production cost and difficulty in quality control. Also, recent studies have demonstrated the strong binding affinity of RGD-containing peptides not only to αvβ3 integrin receptor but also to αvβ5 and α5β1 integrins. Therefore, efforts to develop alternative small linear peptides with similar or even higher affinity and specificity to αvβ3 integrin than cyclic RGD motif peptide have attracted much attention.
Computer-assisted virtual screening is an effective method for drug discovery of small molecules with binding affinity to target receptors. Structure-based pharmacophore strategy has been successfully used to screen small molecule leading compounds in drug development. Molecular docking and dynamic simulation are also considered practical methods to analyze the intermolecular interaction and explain the binding affinity and stability. Therefore, the combination of pharmacophore models with molecular docking will render more efficient hits. Although the compounds obtained from virtual screening have the potential specificity for the targets,it is necessary to confirm the feasibility of this approach by in vitro and in vivo experiments. In this study, we have integrated structure-based pharmacophore method with molecular docking to screen the linear bioactive peptides for identifying αvβ3 integrin. Two novel small linear peptides (RWr, RWrNM) were selected with strong molecular interactions with αvβ3 integrin. To evaluate the affinity of these two peptides to αvβ3, cell lines with different expression levels of αvβ3 were cultured with fluorescence dye-labeled RWr and RWrNM. Confocal imaging and flow cytometry were used to identify their affinity and specificity to αvβ3. Microscale thermophoresis (MST) was performed to quantify affinity of both peptides to αvβ3 integrin. Furthermore, the effects of RWrNM and RWr on cell migration, angiogenesis, and downstream signaling pathways of αvβ3 were investigated. The tumor targeting ability and the therapeutic efficacy of peptide conjugates were further studied.

Speaker

Yueqing GU
Department of engineering, China pharmaceutical university
China

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