Progress in Retinal and Eye Research xxx (xxxx) xxx Contents lists available at ScienceDirect Progress in Retinal and Eye Research journal homepage: www.elsevier.com/locate/preteyeres Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration Inge Van Hove a,1, Tjing-Tjing Hu a,1, Karen Beets a, Tine Van Bergen a, Isabelle Etienne a, Alan W. Stitt a,b,*, Elke Vermassen a, Jean H.M. Feyen a a Oxurion NV, Gaston Geenslaan 1, 3001, Heverlee, Belgium b Wellcome-Wolfson Institute for Experimental Medicine, Queen’s University Belfast, Northern Ireland, UK ARTICLE INFO ABSTRACT Keywords: Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. RGD-binding integrin Dysregulation of integrins has been implicated in many pathological processes and consequently, they are Diabetic retinopathy attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins Neovascular age-related macular degeneration play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye Retina disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg- Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specificallyinflammation, vascular leakage, angiogenesis and fibrosis.Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multi­ factorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases. proliferation and survival with clear linkage to pathological processes, including inflammation, vascular leakage, neovascularization and 1. Introduction fibrosis( Eklund et al., 2017; Fu et al., 2007; Hammes et al., 1996; Kanda et al., 2012; Koch and Distler, 2007; Santulli et al., 2008; Umeda et al., Integrin receptors are transmembrane heterodimeric adhesion pro­ 2006; Wilkinson-Berka et al., 2006; Zahn et al., 2009). The teins that play an essential role in integrating the extracellular to the multi-facetted role integrins play in cell pathophysiology is still being intracellular environment. In the mid-eighties, the firstintegrin receptor investigated and deciphering the precise nature of integrin-linked mo­ was discovered based on its engagement with specific motifs on extra­ lecular mechanisms in health and disease remains a significant and cellular matrix (ECM) protein fibronectin( Pierschbacher and Ruoslahti, relevant research challenge. 1984; Tamkun et al., 1986). Since then, a vast number of articles on In the last few years, there has been renewed interest in integrins and integrins have been published on a regular basis (on average ~2000 new especially drugs that target arginyl-glycyl-aspartic acid (Arg-Gly-Asp; publications per year and ~27,000 to date) and it is established that RGD) -binding integrins in tissues of the eye. This reinvigoration in the these receptors are involved in various cellular processes such as area has been driven, at least in part, by recent preclinical and clinical adhesion, differentiation, shape, migration, signalling, invasion, * Corresponding author. McCauley Chair of Experimental Ophthalmology, Wellcome-Wolfson Institute for Experimental Medicine, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7AE, Northern Ireland, UK. E-mail addresses: [email protected] (I. Van Hove), [email protected] (T.-T. Hu), [email protected] (K. Beets), Tine.VanBergen@ oxurion.com (T. Van Bergen), [email protected] (I. Etienne), [email protected] (A.W. Stitt), [email protected] (E. Vermassen), Jean. [email protected] (J.H.M. Feyen). 1 These authors contributed equally to the work. https://doi.org/10.1016/j.preteyeres.2021.100966 Received 8 January 2021; Received in revised form 15 March 2021; Accepted 19 March 2021 Available online 26 March 2021 1350-9462/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Please cite this article as: Inge Van Hove, Progress in Retinal and Eye Research, https://doi.org/10.1016/j.preteyeres.2021.100966 I. Van Hove et al. Progress in Retinal and Eye Research xxx (xxxx) xxx List of abbreviations IL Interleukin IPL Inner plexiform layer AMD Age-related macular degeneration IVT Intravitreal Ang Angiopoietin LAP Latency-associated peptide ANGPTL Angiopoietin-like protein MCP Monocyte chemoattractant protein BBB Blood-brain barrier MMP Matrix metalloproteinase BCVA Best corrected visual acuity nvAMD Neovascular age-related macular degeneration bFGF Basic fibroblast growth factor NF-κB Nuclear factor kappa B CAM Chick chorioallantoic membrane NLRP3 NACHT, LRR and PYD domains-containing protein 3 CNV Choroidal neovascularization PDR Proliferative diabetic retinopathy CST Central subfield thickness PI3K Phosphoinositide-3-kinase CTGF Connective tissue growth factor PlGF Placental growth factor DME Diabetic macular edema POS Photoreceptor outer segments DR Diabetic retinopathy RGC Retinal ganglion cell EC Endothelial cell RGD Arginyl-glycyl-aspartic acid ECM Extracellular matrix ROP Retinopathy of prematurity EGF Epidermal growth factor RPE Retinal pigment epithelial EMT Epithelial-to-mesenchymal transition SMA Smooth muscle actin EndoMT Endothelial-to-mesenchymal transition STZ Streptozotocin ERK Extracellular signal-regulated kinase TGF Transforming growth factor FAK Focal adhesion kinase TNF Tumour necrosis factor HUVEC Human umbilical vein endothelial cell uPA Urokinase-type plasminogen activator IGFBP Insulin-like growth factor-binding protein VEGF Vascular endothelial growth factor studies which demonstrated promising results in retinal diseases such as Reddy, 2012). Integrins are obligate heterodimeric receptors consisting diabetic retinopathy (DR), diabetic macular edema (DME) and neo­ of an α- and a β-subunit. Currently, 18 α-subunits and eight β-subunits vascular age-related macular degeneration (nvAMD) (Askew et al., are known, and various combinations thereof constitute the family of 24 2018; Shaw et al., 2020; Tolentino et al., 2016). The main goal of this heterodimeric integrin members (Humphries et al., 2006; Pan et al., review is to highlight preclinical as well as clinical knowledge on the 2016). The classification of the integrin receptor family into four role of mainly RGD-binding integrins in DR, DME, proliferative DR different classes is based on their structure similarity and ligand recog­ (PDR) and nvAMD. In addition, we will endeavour to provide compre­ nition pattern: 1) RGD-binding, 2) collagen-binding, 3) hensive information on the intricate cellular and molecular mechanisms leukocyte-specific and 4) laminin-binding integrin receptors (Fig. 1). of RGD-binding integrin signalling in the main disease hallmarks of The first subgroup recognizes the tripeptide sequence RGD in their these vision-threatening retinal disorders. natural ligands (e.g. fibronectin)and consists of eight different integrins: αvβ1, αvβ3, αvβ5, αvβ6, αvβ8, αIIbβ3, α5β1 and α8β1. However, it is now 2. Classification and function of integrins known that RGD-binding integrins also bind to many other ECM proteins (e.g. vitronectin, fibrinogenand osteopontin) as well as growth factors, Integrins constitute a family of ubiquitously expressed trans­ cytokines, enzymes, bacterial proteins and hormones (LaFoya et al., membrane receptors that regulate cell-cell and cell-ECM interactions 2018; Ruoslahti, 1996; Wu and Reddy, 2012). (Bouvard et al., 2013; LaFoya et al., 2018; Moser et al., 2009; Wu and Integrin receptors are activated upon binding to their cognate Fig. 1. Classification of the integrin receptor family. 2 I. Van Hove et al. Progress in Retinal and Eye Research xxx (xxxx) xxx ligands. The affinity and activation state can be influenced by engage­ et al., 1990; Chu and Grunwald, 1991; Elner and Elner, 1996; Li et al., ment of intracellular proteins, such as talin and kindlin, to the integrin 2009). In chick and rat retina, adhesion of RPE cells to Bruch’s mem­ cytoplasmic domains. This outside-in and inside-out signalling enables brane was found to involve an integrin-fibronectin interaction (Philp integrins to 1) carry signals from the extracellular microenvironment and Nachmias, 1987). The apical microvilli of the RPE cells expressed and 2) respond to changes from inside the cell to induce a conforma­ αvβ5 which is essential for phagocytosis and internalization of the shed tional change and modulate their affinity for extracellular ligands POS-αvβ5 complex (Finnemann et al., 1997; Li et al., 2009; Lin and (Bouvard et al., 2013; Dalton et al., 2016; Klapholz and Brown, 2017). Clegg, 1998). Furthermore,