Targeting Galectin-3 with novel drugs for treatment of eczema

Summary

Principal Investigator: Fu Tong Liu
Abstract: Eczema affects a wide population age group, and prevalence of the disease has increased two- to three-fold during the past three decades in industrialized countries, where the current incidence in children is estimated to be 15-20%. Studies suggest that eczema is a complex disease, involving multiple immunologic and inflammatory pathways that include T cells, dendritic cells, mast cells and eosinophils, as well as keratinocytes. Treatment of eczema continues to be a challenge, especially in patients with severe disease. Current therapies include topical application of glucocorticoids and calcineurin inhibitors (immunomodulators), and systemic treatment with glucocorticoids, immunosuppressants and calcineurin inhibitors. Due to significant health concerns of long-term use of glucocorticoids and immunosuppressants, topical immunomodulators gained wide acceptance. However, safety issues raised by the FDA may limit use of these immunomodulators. A family of animal lectins, called galectins, is beta-galactoside-binding animal lectins with conserved carbohydrate-recognition domains. They are evolutionarily highly conserved (found in nematodes and mammals), and some show wide tissue distribution, while others are more selectively expressed by tissue. Galectins have no signal sequence and no transmembrane domain and are found in the cytosol and nucleus, but also in extracellular spaces. Galectins function intracellularly by binding to other proteins through protein-protein interactions. Typical expression of galectin- 3 includes epithelia and immune and inflammatory cells. Galectin-3 is unique among others in possessing chimeric structure consisting of an N-terminal region that contains proline-rich repeats and a C-terminal carbohydrate-recognition domain. Galectin-3 forms oligomers through its N-terminal domain upon binding to multivalent saccharides. Through extensive studies of transgenic mice and human tissues, we have identified galectin-3 as a key molecule involved in skin inflammation. We have begun to characterize drugs targeting galectin-3 for treatment of eczema. These molecules are a newly-established, but growing class of drugs called aptamers (RNA oligonucleotides), and may offer improved safety and specificity over traditional therapies. PUBLIC HEALTH RELEVANCE: Atopic dermatitis is a common chronic inflammatory skin disease. In the US, 15-20% of the population born after 1980 is affected by this disease. Treatment of atopic dermatitis continues to be a challenge and new therapies are clearly needed. The current model suggests that atopic dermatitis is attributable to a Th2-mediated inflammatory response in the acute phase, and both T cells and dendritic cells play important roles. Galectin-3 is a member of a family of animal lectins defined by their affinity for 2-galactosides and consensus amino acid sequences. It is expressed by a number of cell types, including T cells and dendritic cells. Like other galectins, galectin-3 does not have a classical signal sequence and is present inside the cells, but it can be secreted. A number of extracellular functions have been demonstrated by using exogenously added galectin-3, which can induce transmembrane signal transduction by crosslinking cell surface glycans. In addition, a great deal of evidence implicates endogenous galectin-3 in the regulation of various cellular functions through intracellular actions (in the absence of protein secretion). We have obtained important information on the functions of endogenous galectin-3 by studying galectin-3-deficient (gal3-/-) mice, and demonstrated that galectin-3 promotes allergic inflammation. In particular, we have data demonstrating a critical role for galectin-3 in a mouse model of human atopic dermatitis: Gal3-/- mice exhibit Th1-polarized responses and significantly reduced disease Thus, we believe that galectin-3 is a target for treatment of atopic dermatitis, as well as other allergic diseases. Here we propose developing galectin-3 specific RNA aptamers as novel drugs for treatment of atopic dermatitis. We have chosen this technology, because RNA aptamers are more likely to have higher affinity for galectin-3 and more specific for galectin-3 over other galectins than low molecular weight compounds. Moreover, RNA aptamers can be used to target either extracellular or intracellular galectin-3 and may be applied topically. Specific Aim 1: Develop galectin-3-specific RNA aptamers as potent inhibitors Specific Aim 2: Demonstrate the potency of galectin-3 aptamers in suppressing galectin-3 functions in vitro 1. Selection of galectin-3 RNA aptamers that can inhibit galectin-3 functions in vitro 2. Determine the potency of galectin-3 RNA aptamers in inhibition of human Th2 responses in vitro Specific Aim 3: Determine the efficacy of galectin-3 aptamers for treatment of allergic skin inflammation by using a mouse model of human atopic dermatitis 1. Determine whether targeting extracellular galectin-3 is effective in suppressing allergic dermatitis 2. Evaluate the in vivo effects of galectin-3 RNA aptamers in a mouse model. We hope the proposed studies will definitively validate galectin-3 as a target for treating atopic dermatitis and lead to the development of a novel therapy for this disease.
Funding Period: ----------------2009 - ---------------2011-
more information: NIH RePORT