Abstract 4745: Multivalent dendrimeric peptides as new biomarker probes for the detection of cancer metastasis
Authors: Coulup Sara K. , Saludes Jonel P. , Yin Hang 
Published: August 2012

Malignant tumor cells overexpress and release lipid vesicles called exosomes into the body fluids to facilitate their movement and metastasis to other parts of the body. It was found that an increased secretion of exosomes in the peripheral blood is correlated with lung cancer and melanoma metastasis. The hallmarks of exosomes are their highly curved surface (d = ∼30-100 nm) that is distinct from other extracellular lipid vesicles and their enrichment with the anionic lipid phosphatidylserine (PS) in the outer leaflet of the membrane bilayer. These properties provide an opportunity in selectively targeting exosomes as potential cancer biomarkers. Current clinical methods that are being used to classify metastatic patients are not accurate or reproducible, are often problematic, and do not indicate whether or not treatment is reducing metastasis. Furthermore, these methods involve invasive procedures. We aim to develop a novel, minimally invasive, peptide-based diagnostic tool to detect and visualize exosomes and measure exosome oversecretion in cancer patients. The successful creation of this diagnostic tool for cancer metastasis will help in the proper diagnosis and therapy for cancer patients. We chose the small peptide Bradykinin (BK) as our core molecule because it was recently reported that this peptide differentially interacts with nanometer size synthetic lipid vesicles, with preferential binding for vesicles with higher anionic lipid composition. Our earlier studies on a BK analogue showed that it selectively binds to synthetic lipid vesicles with d = 55 +/− 5 nm, dimensions that mimic the size of exosomes. We hypothesized that by creating a library of multivalent, dendrimeric analogues of BK, we could increase its binding affinity to lipid vesicle models that would translate to the detection of exosomes in body fluids. The peptide was prepared by microwave-assisted solid phase synthesis, was modified with Lys-Gly spacers, the epsilon-amino of the Lys residue was deprotected and converted into an azide, and the peptide was labeled with a fluorophore, cleaved from the resin, and purified by high performance liquid chromatography. We also synthesized a series of dendrimer-type, alkyne functionalized, aromatic small molecules as scaffolds in the preparation of the multivalent dendrimeric peptides. The azide-functionalized BK analogue was conjugated to the scaffolds using solution phase Copper-catalyzed azide-alkyne cycloaddition reaction (‘Click’ chemistry). We investigated the curvature sensing ability of the peptides using synthetic liposomes and exosomes from the plasma of a rat model using a combination of spectroscopic techniques. The lipid vesicle detecting properties of these peptides and their potential as new diagnostic tool for cancer metastasis shall be reported herein.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4745. doi:1538-7445.AM2012-4745