Rational Targeting of the Urokinase Receptor (uPAR): Development of Antagonists and Non-Invasive Imaging Probes

Finsen Laboratory, Copenhagen Biocenter, Rigshospitalet, Copenhagen, Denmark.
Current drug targets (Impact Factor: 3.02). 06/2011; 12(12):1711-28. DOI: 10.2174/138945011797635812
Source: PubMed


In the last two decades, the urokinase-type plasminogen activator receptor (uPAR) has been implicated in a number of human pathologies such as cancer, bacterial infections, and paroxysmal nocturnal hemoglobinuria. The primary function of this glycolipid-anchored receptor is to focalize uPA-mediated plasminogen activation at the cell surface, which is accomplished by its high-affinity interaction with the growth factor-like domain of uPA. Detailed insights into the molecular basis underlying the interactions between uPAR and its two bona fide ligands, uPA and vitronectin, have been obtained recently by X-ray crystallography and surface plasmon resonance studies. Importantly, these structural studies also define possible druggable target sites in uPAR for small molecules and provide guidelines for the development of reporter groups applicable for non-invasive molecular imaging of uPAR expression in vivo by positron emission tomography. In this review, we will discuss recent advances in our perception of the structure-function relationships of uPAR ligation and how these may assist translational research in preclinical intervention studies of uPAR function.

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    • "Defines the structure of a closed, active conformation of native uPAR wt without covalent modifications; defines a topographic epitope landscape on uPAR for 6 different bins of anti-uPAR mAbs; establish that occupancy of the Vn-binding site by mAbs drives uPAR into to its closed conformation; data defining this interdomain flexibility are important for functional studies on uPAR biology; and for the future design of uPAR-targeted intervention studies in human disease [1] [7] [8] [9]. "
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    ABSTRACT: The urokinase-type plasminogen activator receptor (uPAR or CD87) is a glycolipid-anchored membrane protein often expressed in the microenvironment of invasive solid cancers and high levels are generally associated with poor patient prognosis [1]. uPAR is organized as a dynamic modular protein structure composed of three homologous Ly6/uPAR domains (LU).This internally flexible protein structure of uPAR enables an allosteric regulation of the interactions with its two principal ligands: the serine protease urokinase-type plasminogen activator (uPA) and the provisional matrix protein vitronectin (Vn) [2–4]. The data presented here relates to the non-covalent trapping of one of these biologically relevant uPAR-conformations by a novel class of monoclonal antibodies (Zhao et al in the Journal of Molecular Biology [5]) and to the general mapping of the topographic epitope landscape on uPAR. The methods required to achieve these data include: (1) recombinant expression and purification of a uPAR-hybrid protein trapped in the desired conformation [patent; WO 2013/020898 A12013]; (2) developing monoclonal antibodies with unique specificities using this protein as antigen; (3) mapping the functional epitope on uPAR for these mAbs by surface plasmon resonance with a complete library of purified single-site uPAR mutants [5,6]; and finally (4) solving the three-dimensional structures for one of these mAbs by X-ray crystallography alone and in complex with uPAR [deposited in the PDB database as 4QTH and 4QTI, respectively].
    Full-text · Article · Sep 2015
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    • "Based on the small linear peptide AE105 with high affinity for uPAR, 64 Cu-DOTA-AE105 is one of several promising uPAR PET tracers recently developed in our group [15] [16] [17] [18] [19]. Before considering translation into human use, estimates of human dosimetry are important. "
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    ABSTRACT: (64)Cu-DOTA-AE105 is a novel positron emission tomography (PET) tracer specific to the human urokinase-type plasminogen activator receptor (uPAR). In preparation of using this tracer in humans, as a new promising method to distinguish between indolent and aggressive cancers, we have performed PET studies in mice to evaluate the in vivo biodistribution and estimate human dosimetry of (64)Cu-DOTA-AE105. Five mice received iv tail injection of (64)Cu-DOTA-AE105 and were PET/CT scanned 1, 4.5 and 22h post injection. Volume-of-interest (VOI) were manually drawn on the following organs: heart, lung, liver, kidney, spleen, intestine, muscle, bone and bladder. The activity concentrations in the mentioned organs [%ID/g] were used for the dosimetry calculation. The %ID/g of each organ at 1, 4.5 and 22h was scaled to human value based on a difference between organ and body weights. The scaled values were then exported to OLINDA software for computation of the human absorbed doses. The residence times as well as effective dose equivalent for male and female could be obtained for each organ. To validate this approach, of human projection using mouse data, five mice received iv tail injection of another (64)Cu-DOTA peptide-based tracer, (64)Cu-DOTA-TATE, and underwent same procedure as just described. The human dosimetry estimates were then compared with observed human dosimetry estimate recently found in a first-in-man study using (64)Cu-DOTA-TATE. Human estimates of (64)Cu-DOTA-AE105 revealed the heart wall to receive the highest dose (0.0918mSv/MBq) followed by the liver (0.0815mSv/MBq), All other organs/tissue were estimated to receive doses in the range of 0.02-0.04mSv/MBq. The mean effective whole-body dose of (64)Cu-DOTA-AE105 was estimated to be 0.0317mSv/MBq. Relatively good correlation between human predicted and observed dosimetry estimates for (64)Cu-DOTA-TATE was found. Importantly, the effective whole body dose was predicted with very high precision (predicted value: 0.0252mSv/Mbq, Observed value: 0.0315mSv/MBq) thus validating our approach for human dosimetry estimation. Favorable dosimetry estimates together with previously reported uPAR PET data fully support human testing of (64)Cu-DOTA-AE105.
    Full-text · Article · Mar 2014 · Nuclear Medicine and Biology
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    • "The resulting 9-mer core peptide AE105 (D-Cha-F-s-r-Y-L-W-S) 9 demonstrated specific, high-affinity binding to human uPAR (Kd ≈ 0.4 nM). Later on, AE105 and its derivatives, AE120 [(D-Cha-F-s-r-Y-L-W-S)2 -βA-Kc] and AE170 (K-S-D-Cha-F-s-k-CHg-L-W-S-S-K) have been applied in a variety of experimental settings 10. To date, most uPAR-targeted imaging and therapy studies are based on AE105 and its corresponding derivatives. "
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    ABSTRACT: Urokinase-type plasminogen activator receptor (uPAR) is a glycosylphosphatidylinositol (GPI)-anchored protein. Besides regulating proteolysis, uPAR could also activate many intracellular signaling pathways that promote cell motility, invasion, proliferation, and survival through cooperating with transmembrane receptors. uPAR is overexpressed across a variety of tumors and is associated with cancer invasion and metastasis. In order to meet the demand for a rapid development and potential clinical application of anti-cancer therapy based on uPA/uPAR system, it is desirable to develop non-invasive imaging methods to visualize and quantify uPAR expression in vivo. In this review, we will discuss recent advances in the development of uPAR-targeted nuclear imaging and radionuclide therapy agents. The successful development of molecular imaging probes to visualize uPAR expression in vivo would not only assist preclinical researches on uPAR function, but also eventually impact patient management.
    Full-text · Article · Jun 2013 · Theranostics
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