Screening for peptides targeted to IL-7Rα for molecular imaging of rheumatoid arthritis synovium

Abstract

BackgroundInterleukin-7 receptor alpha (IL-7Rα) represents a biomarker with potential applications in rheumatoid arthritis (RA) diagnosis and therapy. We have therefore searched by phage display potential IL-7Rα specific peptides with the primary goal being to develop in vivo molecular imaging tools.MethodsIL-7Rα-targeted peptides were searched within a disulfide-constrained combinatorial phage displayed library of random linear heptapeptides. The apparent dissociation constant (Kd) and half maximal inhibition constant (IC50) were estimated for phage clones and synthesized peptides by ELISA. We used 5-Aza-2’-deoxycytidine (ADC)-stimulated Jurkat cells and human synovial tissue from patients with RA for in vitro characterization of peptides. For molecular imaging studies performed by magnetic resonance imaging (MRI), experimental arthritis was induced in DBA/1 male mice by immunization with an emulsion of complete Freund’s adjuvant and type II collagen from chicken sternal cartilage.ResultsAfter several steps of phage display and peptide screening, two IL-7Rα-specific heptapeptides (P258 and P725) were selected from the initial library, based on their affinity for the target (extracellular domain of IL-7Rα, which contains a fibronectin type III repeat-like sequence). P258 (a linear peptide obtained by removing the Cys-constraint) had the lowest affinity for fibronectin itself and was therefore proposed for molecular imaging. After grafting to ultra-small superparamagnetic particles of iron oxide (USPIO), P258 produced a strong negative contrast on MRI in mice with collagen-induced arthritis (CIA), even at 2 hours post injection. The co-localization of USPIO-P258 with IL-7Rα-expressing cells in the synovial tissue from CIA mice and its ability to discriminate the level of IL-7R expression and the disease severity confirmed its efficacy as an in vivo IL-7Rα imaging agent. Interestingly, the cyclic peptide (P725), which was less adequate for molecular imaging because of higher affinity for fibronectin, had a strong ability to compete with IL-7 for the IL-7Rα binding sites, making it a potential candidate for blocking applications. Accordingly, P725 prevented the signal transducer and activator of transcription 5 (STAT5) activation induced by IL-7 in ADC-stimulated Jurkat cells.ConclusionsThe two peptides identified in this work demonstrate that IL-7Rα targeting in RA presents potential applications for in vivo molecular imaging and putative blocking purposes.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-1133-8) contains supplementary material, which is available to authorized users.

Molecular Imaging of Galectin-1 Expression as a Biomarker of Papillary Thyroid Cancer by Using Peptide-Functionalized Imaging Probes

“…In addition, the circulating concentration of gal-1-targeted USPIO is too low due to the liver and spleen capture ( Figure 5). Indeed, our previous research on nanoparticles has shown a plasma concentration greater than 1000 µmol Fe/L at 90-120 min post-injection [54][55][56], whereas during this work, values ranging from about 400 µmol Fe/L (for USPIO-P1) to 700 µmol Fe/L (for USPIO-P7) were found.…”

Imaging of Human Insulin Secreting Cells with Gd-DOTA-P88, a Paramagnetic Contrast Agent Targeting the Beta Cell Biomarker FXYD2γa

“…As shown by MRI and biodistribution data, the pattern of renal clearance of both Gd-DOTA-P88 and Gd-DOTA-Scramble is not significantly different, which suggests that xenograft enhancement by the specific compound is not a consequence of its delayed blood clearance. On the other hand, Gd-DOTA-P88 is less efficient in terms of NMR efficacy (i.e., relaxivity: r 1 of 4.57 s −1 mM −1 at 300 MHz and 37 °C for Gd-DOTA-P88) than superparamagnetic agents (i.e., r 2 of 92.93 s −1 mM −1 at 300 MHz and 37 °C for USPIO-P88 [ 14 , 15 ]), but the binding of functionalized paramagnetic compounds to their targeted biomarkers contributes to a substantial enhancement of their relaxivity due to the increase in the rotational correlation time [ 21 , 22 ]. Finally, the binding specificity of P88 was evaluated by using an in vitro competitive assay.…”

“…This initial study, however, was (1) restricted to a non-physiological cell model, unrelated to beta cells [ 13 ], and (2) P88 was conjugated to a contrast agent (CA) that produces a negative contrast on MRI. This CA is partially excreted via the reticuloendothelial system (RES) despite a poly (ethylene glycol) (PEG) coating [ 14 , 15 ]. This RES uptake, in combination with the well-known macrophage infiltration of pancreatic islets, may cause an inaccurate BCM reading [ 15 ].…”

Targeted Molecular Magnetic Resonance Imaging Detects Brown Adipose Tissue with Ultrasmall Superparamagnetic Iron Oxide

“…Furthermore, recent studies have verified that specific peptide can be linked with USPIO for molecular MR imaging and the peptide properties and functionality as well as the relaxation abilities of USPIO nanoparticles can also be remained [ 28 ]. Our research also demonstrated that the targeted peptide (CKGGRAKDC-NH2) conjugated with USPIO can also retain its affinity for BAT.…”