b) Dosedependent activation of LepR by leptin and combinatorial antibody ligands Ab06, Ab08, Ab11, and H6 via chemiluminescent detection (luminescence) of STAT3 phosphorylation in LepR or nonLepR expressed luciferase reporter cell lines. therapy A full agonist antibody against leptin receptor is usually discovered using a functionguided approach from a combinatorial antibody library. It shows identical biochemical properties and functional profiles as leptin both in vitro and in vivo. Furthermore, it activates several leptin receptor mutants which cannot be activated by leptin, indicating promising therapeutic applications. The selection strategy can be applied to other cellular targets. == 1. Wnt-C59 Introduction == Growth factors and cytokines are critical modulators of physiological processes important to the body’s homeostasis.[1,2,3]They are external signaling molecules exerting physiological functions through interaction with their cognate receptors on cell surfaces. Based on their functions and structures, growth factors are categorized into different protein families such as, interleukins, interferons, tumor necrosis factors (TNFs), fibroblast growth factors (FGFs), epidermal growth factors (EGFs), vascular endothelial growth factors (VEGFs), hepatocyte growth factors (HGFs), transforming growth factors (TGFs), hematopoietic factors, and neurotrophic factors, to name a few.[4]The first approved recombinant growth factor drug is a glycemic regulatory factor, insulin, developed by Genentech in 1982.[5]Since then, growth factor replacement therapy using recombinant proteins or enzymes, or other similar surrogates, has experienced rapid growth and development. For the last three decades, growth factors have been used as replacement therapy for a number of deficiency syndromes, including those associated with hematologic, oncologic, and cardiovascular diseases.[6,7,8] Recombinant growth factors, in spite of being at center stage in current replacement therapy, encounter significant challenges when used chronically in the clinical setting, including Wnt-C59 short serum halflife, low bioavailability, doselimiting toxicity, and immunogenicity.[9,10]For example, low molecular weight growth factors often require modification to extend their halflife.[11,12,13,14]These modifications, in turn, increase their immunogenicity. Growth factors with poor bioavailability often fail to meet desired endpoints due to their hydrophobicity. Growth factors with multiple cognate receptors other than the target often require high dosage PIK3C3 treatment leading to doselimiting toxicities. Last but not the least, tolerance to recombinant growth factors is usually often terminated over the course of treatment,[15]leading to an immune response against both the recombinant and natural growth factors. Combinatorial antibodies named because of their selection from combinatorial antibody libraries,[16,17]on the other hand, have been successful in clinical intervention in a wide variety of diseases, including cancer, chronic inflammatory diseases, autoimmunity, and metabolic syndromes.[18,19]As one of the fastest growing therapeutics, and taking advantage of the infinite diversity of combinatorial antibodies, various innovative strategies and applications have been developed targeting challenging pharmaceutical targets such as G ProteinCoupled Receptor (GPCRs), ionchannels, etc.[20,21,22,23]In addition to conventional neutralization, combinatorial antibodies have shown mechanismbased modulation of various signaling pathways,[16,17,24]and in some cases, function beyond the scope of native ligands.[25,26,27]As they are themselves immunoglobulins, loss of immunetolerance would be less of a concern for chronic administration of antibodies. Leptin, a key physiological modulator of energy balance, was first discovered in 1994 by Friedman and coworkers using a positional cloning strategy. [28]Leptin is usually released into Wnt-C59 the bloodstream by white adipose tissue at a level proportional to body fat. After entering the brain it activates sets of hypothalamic neurons expressing the leptin receptor (LepR), which results in inhibition of food intake and stimulation of energy expenditure.[29,30,31,32]The leptin receptor is a member of the class I cytokine receptor family, and shares structural homology with many important hematopoietic factor receptors, such as glycoprotein 130, leukemia inhibitory factor receptor, oncostatin M receptor, ciliary neurotrophic factor receptor, and others.[33,34,35]Its downstream signaling pathway, transduced via Janus kinase (JAK) and signaltransducerandactivator of transcription (STAT) factor, regulates subsequent kinase activities including.
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