Article

Structure-Activity Relationship Analysis of Peptides Targeting the EphA2 Receptor

Sanford-Burnham Medical Research Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA.
Biochemistry (Impact Factor: 3.02). 08/2010; 49(31):6687-95. DOI: 10.1021/bi1006223
Source: PubMed

ABSTRACT

The EphA2 receptor tyrosine kinase has emerged as a promising new therapeutic target in cancer because of its high level of expression in tumors. EphA2-specific antibodies have been used to deliver drugs and toxins to tumor cells, leading to inhibition of tumor growth and metastatic dissemination. We previously identified two related peptides, YSA and SWL, that selectively bind to the ligand-binding domain of EphA2 but not other Eph receptors and could therefore be useful as selective targeting agents. Here we characterize the two peptides and a series of derivatives. On the basis of systematic amino acid replacements, only five YSA residues appear to be critical for high-affinity receptor binding. Furthermore, a peptide comprising only the first five residues of YSA retains selectivity for EphA2. Similar to ephrin-A1, the physiological ligand for EphA2, both YSA and SWL activate EphA2 and inhibit downstream oncogenic signaling pathways in PC3 cancer cells. The two peptides and derivatives are quite stable in conditioned cell culture medium and show promise for delivering drugs and imaging agents to EphA2-expressing tumors.

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    • "More specifically, we selected the Phe111-Leu116 fragment of the G-H loop of ephrin-A1 as query structure. This small peptide fragment has been shown to be fundamental for the binding of ephrin-A1 ligand to EphA2 high affinity site[42]and thus its shape might be effective in retrieving active compounds. In this condition, the EFs were significantly lower than those obtained using UniPR129 as a query. "
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    ABSTRACT: The EphA2 receptor and its ephrin-A1 ligand form a key cell communication system, which has been found overexpressed in many cancer types and involved in tumor growth. Recent medicinal chemistry efforts have identified bile acid derivatives as low micromolar binders of the EphA2 receptor. However, these compounds suffer from poor physicochemical properties, hampering their use in vivo. The identification of compounds able to disrupt the EphA2-ephrin-A1 complex lacking the bile acid scaffold may lead to new pharmacological tools suitable for in vivo studies. To identify the most promising virtual screening (VS) protocol aimed at finding novel EphA2 antagonists, we investigated the ability of both ligand-based and structure-based approaches to retrieve known EphA2 antagonists from libraries of decoys with similar molecular properties. While ligand-based VSs were conducted using UniPR129 and ephrin-A1 ligand as reference structures, structure-based VSs were performed with Glide, using the X-ray structure of the EphA2 receptor/ephrin-A1 complex. A comparison of enrichment factors showed that ligand-based approaches outperformed the structure-based ones, suggesting ligand-based methods using the G-H loop of ephrin-A1 ligand as template as the most promising protocols to search for novel EphA2 antagonists.
    Preview · Article · Sep 2015 · Molecules
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    • "Apart from antibody-based targeting, the synthetic YSA peptide can also efficiently direct various moieties to the EPHA2 receptor. Recently, Mitra et al (2010) elucidated functional properties of the YSA peptide as a specific binding molecule to EPHA2 with subsequent downstream signalling events in a prostate cancer cell line. Dickerson et al (2010) described the use of hydrogel nanoparticles coated with YSA peptide for the specific delivery of siRNA to EPHA2-expressing tumour cells, with the aim of enhancing chemosensitivity. "
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    ABSTRACT: Background: Osteosarcoma (OS) is the most common bone tumour in children and adolescents. Despite aggressive therapy regimens, treatment outcomes are unsatisfactory. Targeted delivery of drugs can provide higher effective doses at the site of the tumour, ultimately improving the efficacy of existing therapy. Identification of suitable receptors for drug targeting is an essential step in the design of targeted therapy for OS. Methods: We conducted a comparative analysis of the surface proteome of human OS cells and osteoblasts using cell surface biotinylation combined with nano-liquid chromatography – tandem mass spectrometry-based proteomics to identify surface proteins specifically upregulated on OS cells. This approach generated an extensive data set from which we selected a candidate to study for its suitability as receptor for targeted treatment delivery to OS. First, surface expression of the ephrin type-A receptor 2 (EPHA2) receptor was confirmed using FACS analysis. Ephrin type-A receptor 2 expression in human tumour tissue was tested using immunohistochemistry. Receptor targeting and internalisation studies were conducted to assess intracellular uptake of targeted modalities via EPHA2. Finally, tissue micro arrays containing cores of human OS tissue were stained using immunohistochemistry and EPHA2 staining was correlated to clinical outcome measures. Results: Using mass spectrometry, a total of 2841 proteins were identified of which 156 were surface proteins significantly upregulated on OS cells compared with human primary osteoblasts. Ephrin type-A receptor 2 was highly upregulated and the most abundant surface protein on OS cells. In addition, EPHA2 was expressed in a vast majority of human OS samples. Ephrin type-A receptor 2 effectively mediates internalisation of targeted adenoviral vectors into OS cells. Patients with EPHA2-positive tumours showed a trend toward inferior overall survival. Conclusion: The results presented here suggest that the EPHA2 receptor can be considered an attractive candidate receptor for targeted delivery of therapeutics to OS.
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    • "Small peptides with affinities for the ephrin binding pocket of Eph receptors can inhibit ephrin binding to EphA2 [138], EphA4 [139], EphB2 [140], and EphB4 [140], and additional uncharacterized peptides show promise as Eph inhibitors [137]. EphA2 targeting peptides inhibit ephrin binding but also induce phosphorylation of EphA2 and modulate EphA2 signaling [141]. However, these peptides do not induce receptor degradation like full-length ephrinAs [138]. "
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    ABSTRACT: Despite significant advancements in treatment regimens, cardiovascular disease remains a worldwide leader of morbidity, mortality, and healthcare cost. A large percentage of cardiovascular disease is directly attributable to the process of atherosclerosis, a chronic inflammatory disease of the vessel wall. In the hunt for novel therapeutic targets in cardiovascular disease, neuronal guidance molecules are emerging as significant regulators of cardiovascular remodeling and inflammation. The Eph family of neuronal guidance molecules comprises the largest family of receptor tyrosine kinases in the mammalian genome. While best characterized in embryogenesis and carcinogenesis, Eph receptors and their ephrin ligands are becoming increasingly recognized as important players in chronic inflammatory diseases and immune function. Herein we discuss the current evidence for how Eph/ephrin interactions, particularly EphA2/ephrinA1 and EphB/ephrinB2, affect inflammation and cardiovascular disease.
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