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

BACKGROUND: Interleukin-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. METHODS: IL-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. RESULTS: After 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. CONCLUSIONS: The 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.

Development of a peptide-functionalized imaging nanoprobe for the targeting of (FXYD2)γa as a highly specific biomarker of pancreatic beta cells.

Diabetes is characterized by a progressive decline of the pancreatic beta cell mass (BCM), which is responsible for insufficient insulin secretion and hyperglycaemia. There are currently no reliable methods to measure non-invasively the BCM in diabetic patients. Our work describes a phage display-derived peptide (P88) that is highly specific to (FXYD2)γa expressed by human beta cells and is proposed as a molecular vector for the development of functionalized imaging probes. P88 does not bind to the exocrine pancreas and is able to detect down to ~156 human pancreatic islets/mm(3) in vitro after conjugation to ultra-small particles of iron oxide (USPIO), as proven by the R2 measured on MR images. For in vivo evaluation, MRI studies were carried out on nude mice bearing Capan-2 tumours that also express (FXYD2)γa. A strong negative contrast was obtained subsequent to the injection of USPIO-P88, but not in negative controls. On human histological sections, USPIO-P88 seems to be specific to pancreatic beta cells, but not to duodenum, stomach or kidney tissues. USPIO-P88 thus represents a novel and promising tool for monitoring pancreatic BCM in diabetic patients. The quantitative correlation between BCM and R2 remains to be demonstrated in vivo, but the T2 mapping and the black pixel estimation after USPIO-P88 injection could provide important information for the future pancreatic BCM evaluation by MRI.

Immunoassay-based proteome profiling of 24 pancreatic cancer cell lines.

Pancreatic ductal adenocarcinoma is one of the most deadly forms of cancers, with a mortality that is almost identical to incidence. The inability to predict, detect or diagnose the disease early and its resistance to all current treatment modalities but surgery are the prime challenges to changing the devastating prognosis. Also, relatively little is known about pancreatic carcinogenesis. In order to better understand relevant aspects of pathophysiology, differentiation, and transformation, we analysed the cellular proteomes of 24 pancreatic cancer cell lines and two controls using an antibody microarray that targets 741 cancer-related proteins. In this analysis, 72 distinct disease marker proteins were identified that had not been described before. Additionally, categorizing cancer cells in accordance to their original location (primary tumour, liver metastases, or ascites) was made possible. A comparison of the cells' degree of differentiation (well, moderately, or poorly differentiated) resulted in unique marker sets of high relevance. Last, 187 proteins were differentially expressed in primary versus metastatic cancer cells, of which the majority is functionally related to cellular movement.