Validation of a novel imaging technique to detect early osteoarthritis using an antibody specific for post-translationally modified collagen type II

随着世界人口年龄的增加，骨关节炎(OA)正成为迄今为止最常见的关节疾病，也是慢性疼痛和残疾的主要原因。骨性关节炎是一种整个关节的疾病，但一个主要特征是关节软骨的破坏，关节软骨是一层光滑的组织，保护骨骼的末端，使关节能够无摩擦地运动。目前还没有预防软骨破坏的治疗方法，患者必须依靠简单的止痛药、物理治疗和最终的手术关节置换。近年来，已经确定了治疗骨性关节炎的新疗法(如分解组织的关键酶的抑制剂)，但此类疗法的引入一直受到阻碍，因为缺乏能够发现早期疾病(治疗最有可能成功的地方)的具体测试，以及在治疗后发现疾病进展的轻微变化(以便进行临床试验)。目前评估骨性关节炎的黄金标准是普通X射线和磁共振成像，前者不敏感，后者更敏感和特异，但价格昂贵，更难获得。坏消息是，尽管大型制药公司已经开发出安全有效的药物用于个人骨性关节炎，但他们选择目前不在临床试验中测试这些化合物。因此，迫切需要开发一种简单而灵敏的工具来检测人的软骨损伤。我们已经开发出一种与受损软骨强烈结合的人抗体，我们相信这种抗体可以作为早期骨性关节炎的成像标志物。我们已经用荧光标记标记了我们的抗体，并表明它是炎症性关节炎(也有软骨损伤)小鼠关节的家园。我们目前的建议是在OA的小鼠模型中测试这种抗体，在该模型中，通过手术切除内侧半月板(导致关节不稳定)来诱导OA。将进行两项改进，以提高染色强度。首先，我们计划使用一种近红外(NIR)荧光探针，它具有更好的组织穿透性，同时也减少了背景信号。其次，我们将两个抗体片段融合在一起，这将改善抗体与受损软骨的结合，并增加抗体片段携带的荧光量。如果成功，我们将在患者身上测试这种成像技术(在随后的应用中)。将这个项目翻译到人类身上的能力是很容易处理的，特别是因为抗体最初是针对改良的人类软骨提出的，并对人类和小鼠关节炎关节的受损组织进行了染色。将这一项目转化为人类可能会对开发、验证和引入新的治疗OA的方法产生重大影响。

As the age of the world's population increases, osteoarthritis (OA) is becoming by far the most common joint condition and is a major cause of chronic pain and disability. OA is a disease of the whole joint but one major characteristic is the breakdown of the articular cartilage, a smooth layer of tissue that protects the ends of bones and enables frictionless movement of the joint.Currently there are no treatments that prevent the breakdown of cartilage and patients must depend upon simple pain killers, physiotherapy and ultimately surgical joint replacement. In recent years new therapies for treating OA have been identified (such as inhibitors of the key enzymes that break down the tissue), but the introduction of such treatments, has been hampered by the lack of specific tests capable of detecting early disease (where treatment is most likely to be successful), and discerning modest changes in disease progression following treatment (in order to conduct clinical trials). The current gold standard of OA assessment is by plain X-ray which is insensitive, and MRI which is a more sensitive and specific radiographic tool but costly and harder to access. The bad news is that although large pharmaceutical companies have developed 'safe' and effective drugs to use in individuals with OA, they have chosen not to test these compounds in clinical trials at the current time. There is therefore an urgent unmet need to develop a simple and sensitive tool to detect cartilage damage in man.We have developed a human antibody that binds strongly and specifically to damaged cartilage and we believe that this antibody could be developed as an imaging marker for early OA. We have labelled our antibody with a fluorescent marker and shown that it homes to the joints of mice with inflammatory arthritis (where there is also cartilage damage). Our current proposal is to test this antibody in a mouse model of OA in which OA has been induced by surgically cutting the medial meniscus (leading to joint destabilisation). Two refinements will be made to improve the intensity of staining. Firstly we plan to use a near infra red (NIR) fluorescent probe, which has better tissue penetration and which also reduces background signal. Secondly, we will fuse two antibody fragments together which will improve binding of the antibody to the damaged cartilage and increase the amount of fluorescence that the antibody fragment will carry. If successful we will test this imaging technique in patients (in a subsequent application). The ability to translate this project to humans is tractable especially as the antibody was originally raised against modified human cartilage, and stains damaged tissues from human as well as murine arthritic joints. Translation of this project to the human is likely to have a significant impact on the development, validation and introduction of new treatments for OA.