Identification of Novel integrin antagonists

描述（由申请人提供）：整合素是异二聚体粘附受体，在发育期间的肾脏形成和炎症或血管损伤后的成人肾脏再生中发挥重要作用。然而，异常的整合素功能可导致影响肾脏和脉管系统的炎性、自身免疫性和血栓性疾病，从而使整合素成为重要的治疗靶标。现有的配体模拟单克隆抗体（mAb）和小分子（基于天然配体的结构形成）通过接合整合素配体结合位点（如亲本生理配体）发挥激动剂样性质，从而诱导细胞粘附反应，这些药物被设计用于预防，并强调了对靶向疾病中的整合素的新方法的需要。 整合素包括两个亚组，取决于在一半的整合素亚基中发现的血管性血友病因子A型结构域（vWFA）（<$A或I结构域）的存在或不存在。<$A介导整合素配体（或配体模拟药物）的天冬氨酸（Asp）或谷氨酸（Glu）残基在<$A的金属离子依赖性粘附位点（MIDAS）的Mg 2+依赖性结合。缺乏<$A的整合素通过存在于其<$A亚基中的<$A样结构域（<$A或I样）结合配体。配体Asp/Gu在MIDAS单齿结合Mg 2+，完成金属离子周围的八面体配位球。Mg 2 +- Asp（或Glu）键的形成触发整联蛋白中的激活构象变化，导致细胞粘附，解释了现有整联蛋白拮抗剂的激动剂样性质。 在解决配体模拟mAb的晶体结构时，其结合在Δ A结构域中的MIDAS处，但阻止整联蛋白中的构象转换（即作为纯拮抗剂），我们发现Ca 2+在MIDAS处是七配位的，这是mAb衍生的Asp进行的不寻常的对称双齿连接的结果。稳定的七配位的Ca ~（2+）阻断了MIDAS的配体占据所引起的构象转换。因此，我们假设，根据我们的晶体结构设计基于结构的环化肽拮抗剂对<$A结构域是可行的，并且将配体Asp配位从<$A MIDAS中的单齿结合模式切换到双齿结合模式，从而稳定那里的Ca 2+，也将在<$A缺乏的整合素中实现类似的结果。目前的建议是一个多学科的方法，参与细胞，结构生物学和药物化学组。这些研究的结果将是开发用于评估这些动态受体的结构-活性关系的新探针，并可以提供新的治疗策略来治疗影响肾脏和血管系统的广谱疾病状态。 公共卫生相关性：整合素的不适当活化在多种疾病中起关键作用，包括肾脏和脉管系统的炎性、自身免疫性疾病以及癌症转移。目前靶向这些受体的药物导致不良自身免疫反应和死亡率增加，这是整合素意外激活的结果。鉴定维持整合素处于非活性状态的药物是非常期望的，并且是本提议的主题。

DESCRIPTION (provided by applicant): Integrins are ¿/¿ heterodimeric adhesion receptors that play essential roles in kidney formation during development and in regeneration of the adult kidney following inflammatory or vascular injury. Abnormal integrin function can lead, however, to inflammatory, autoimmune and thrombotic disorders affecting the kidney and the vasculature, thus making integrins important therapeutic targets. Existing ligand-mimetic monoclonal antibodies (mAbs) and small molecules (fashioned based on structures of natural ligands) exert agonist-like properties, by engaging the integrin ligand binding site, like the parent physiologic ligand, thus inducing cell adhesion responses these drugs were designed to prevent, and underscoring the need for novel approaches targeting integrins in disease. Integrins comprise two subgroups, depending on the presence or absence of a von Willebrand's Factor Type A-domain (vWFA) (¿A- or I domain) found in one-half of the integrin ¿-subunits. ¿A mediates Mg2+- dependent binding of an aspartate (Asp) or glutamate (Glu) residue from integrin ligands (or ligand-mimetic drugs) at a metal-ion-dependent-adhesion site (MIDAS) in ¿A. ¿A-lacking integrins bind ligands through an ¿A-like domain (¿A or I-like) present in their ¿-subunits. The ligand Asp/Gu binds the Mg2+ at MIDAS monodentately, completing an octahedral coordination sphere around the metal ion. Formation of the Mg2+- Asp (or Glu) bond triggers activating conformational changes in the integrin leading to cell adhesion, accounting for the agonist-like properties of existing integrin antagonists. In solving the crystal structure of a ligand-mimetic mAb, which binds at MIDAS in the ¿A domain but prevents conformational switching in the integrin (i.e. acting as a pure antagonist), we found that a Ca2+ is heptacoordinated at MIDAS, the result of the unusual symmetric bidentate ligation by the mAb-derived Asp. Stable heptacoordination of Ca2+ blocked the conformational switching normally induced by ligand occupancy of MIDAS. We hypothesize that it should therefore be feasible to design structure-based cyclized peptide antagonists to the ¿A domain based on our crystal structure, and that switching ligand Asp coordination from the monodentate to the bidentate binding mode in the ¿A MIDAS, thus stabilizing a Ca2+ there, will also achieve a similar outcome in the ¿A-lacking integrins. The present proposal represents a multidisciplinary approach with participation by cell-, structural biology and medicinal chemistry groups. An outcome from these studies will be the development of new probes for assessing structure-activity relationships of these dynamic receptors and could provide new therapeutic strategies to treat a wide-spectrum of disease states affecting the kidney and the vasculature. PUBLIC HEALTH RELEVANCE: Improper activation of integrins plays critical roles in a diverse range of diseases including inflammatory, autoimmune diseases of the kidney and the vasculature as well as cancer metastasis. Current drugs targeting these receptors have contributed to adverse autoimmune reactions and to increased mortality, the result of inadvertent activation of integrins. Identifying drugs that maintain the integrin in the inactive state is highly desirable and is the subject of this proposal.