Identification of Novel integrin antagonists

描述(由申请人提供)：整合素是异二聚体黏附受体，在发育过程中的肾脏形成和成人肾脏在炎症或血管损伤后的再生中发挥重要作用。然而，整合素功能异常可导致炎症、自身免疫和血栓形成障碍，影响肾脏和血管系统，从而使整合素成为重要的治疗靶点。现有的配体模拟单抗(MAbs)和小分子(基于天然配体的结构形成)通过与整合素配体结合部位(如亲本生理配体)发挥激动剂样的特性，从而诱导细胞黏附反应，这些药物旨在预防这些药物，并强调了针对疾病中整合素的新方法的必要性。整合素包括两个亚群，取决于在一半的整合素亚基中是否存在von Willebrand因子A-结构域(？A-或I结构域)。？A介导整合素配体(或类似配体的药物)的天冬氨酸(Asp)或谷氨酸(Glu)残基在其金属离子依赖的黏附部位(MIDAS)依赖于镁离子的结合。缺乏A的整合素通过其亚基中存在的类A结构域(类A或类I)与配体结合。配体Asp/Gu与镁离子以单齿形式结合，形成一个围绕金属离子的八面体配位球。Mg2+-Asp(或Glu)键的形成触发整合素的构象变化，导致细胞黏附，这是现有整合素拮抗剂具有激动剂样特性的原因。在解决类似配体的单抗的晶体结构时，它结合在A结构域的MIDAS处，但阻止整合素的构象转换(即作为纯粹的拮抗剂)，我们发现钙离子在MIDAS处七配位，这是由单抗衍生的天冬氨酸不寻常的对称双齿连接的结果。稳定的Ca~(2+)七配位阻断了通常由MIDAS配体占位引起的构象转换。因此，我们假设基于我们的晶体结构设计基于结构的环化肽拮抗剂应该是可行的，并且将配体Asp的配位从单齿结合模式切换到双齿结合模式，从而稳定那里的钙离子，在缺乏A的整合素中也将达到类似的结果。本提案代表了一种由细胞、结构生物学和药物化学小组参与的多学科方法。这些研究的结果将是开发新的探针来评估这些动态受体的结构-活性关系，并可能提供新的治疗策略，以治疗影响肾脏和血管系统的广泛疾病状态。 公共卫生相关性：整合素的不当激活在多种疾病中起着关键作用，包括炎症、肾脏和血管系统的自身免疫性疾病以及癌症转移。目前针对这些受体的药物已经导致了不良的自身免疫反应和死亡率的增加，这是由于整合素不经意地激活的结果。确定保持整合素处于非活性状态的药物是非常可取的，也是本提案的主题。

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.