BONE TARGETED DELIVERY OF ANABOLIC AGENTS

描述(申请人提供)：骨质疏松症是一种主要的公共健康威胁。目前，估计有4400万50岁及以上的男性和女性患有骨质疏松症，占美国该年龄段人口的55%。除了巨大的医疗费用外，这种情况还会导致死亡率的大幅增加。提出了一种治疗骨质疏松症和其他肌肉骨骼疾病的新方法，即以骨为靶向的水溶性聚合物结合物作为合成代谢剂前列腺素E1的载体的靶向给药系统。以往的实验已经证明，D-Asp8靶向的偶联物优先结合到骨吸收表面。这为将药物靶向活跃的骨吸收部位提供了一个独特的机会。另一个令人鼓舞的结果是观察到，在单次注射结合物后，骨形成的增加可以持续至少一个月。这项研究的主要目的是设计新的、有效的结合物来治疗骨质疏松症。我们设计了新的可生物降解的N-(2-羟丙基)甲基丙烯酰胺(HPMA)共聚物共轭化合物。一个重要的设计特征是将可降解键插入到聚合物主链(主链)中。因此，可以使用比不可降解载体更高的分子量，从而导致循环时间较长，并且由于血管泄漏和每条链上靶向部分的数量增加而增加了在骨中的蓄积。新设计的主要特点如下：a)新型可生物降解的HPMA基聚合物载体将由含有PGE1和靶向部分的短遥螺旋HPMA共聚物链段组成，通过使用叠氮官能化链转移剂进行RAFT(可逆加成-断裂链转移)聚合制备。这些片段将通过与酶可降解(乙炔官能化的)寡肽的高效点击化学反应延伸到高分子量(长循环)载体中；b)靶向D-Asp8基团将通过组织蛋白K敏感间隔区与聚合物主干结合；c)PGE1将通过乙醚键与聚合物主链结合；它将通过1，6-消除基团和组织蛋白K敏感间隔区与载体连接。以前使用的酯键在人类中是稳定的，但在大鼠和小鼠血浆中容易被水解，这使得偶联物的优化变得复杂。新的设计将避免这些困难。为了优化治疗方案，将进行剂量递增研究、时间序列研究和多剂量研究。将进行大量的分析，以确定结合物对各种骨指数的影响，即骨密度、骨矿含量、骨生物力学、生物形态计量学和组织形态计量学特性。以骨吸收部位为靶点的(主链)可生物降解HPMA共聚物药物载体的概念为设计治疗肌肉骨骼疾病的有效药物提供了新的范例。公共卫生相关性该提案解决了骨质疏松症治疗的一个重要问题，即将(合成代谢)药物输送到骨吸收部位。所建议的药物释放系统的优点是：选择性地吸附到骨组织中具有较高骨转换率的组织，将合成代谢剂(前列腺素E_1)定位于有利于骨形成的骨骼部位，减少全身给药引起的副作用，以及设计原则适用于其他药物的释放。

DESCRIPTION (provided by applicant): Osteoporosis is a major public health threat. Currently, osteoporosis is present in an estimated 44 million men and women aged 50 and older, which represent 55 percent of the population in that age group in the USA. In addition to the enormous medical costs, this condition leads to a substantial increase in mortality. A new approach for the treatment of osteoporosis and other musculoskeletal diseases is proposed a targeted drug delivery system employing bone targeted; water-soluble polymer conjugates as carriers for the anabolic agent, prostaglandin E1. Previous experiments have demonstrated that D-Asp8-targeted conjugates are preferentially incorporated onto bone resorption surfaces. This offers a unique opportunity to target drugs to sites of active bone resorption. Another encouraging result was the observation that increases in bone formation could be sustained for at least a month following a single injection of the conjugate. The main aim of the proposed research is to design novel, effective conjugates for the treatment of osteoporosis. We designed new, biodegradable N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates. An important design characteristic is the insertion of degradable bonds into the polymer main chain (backbone). Consequently, a higher molecular weight than with nondegradable carriers may be used, resulting in long circulation times and enhanced accumulation in bone due to leaky vasculature and increased number of targeting moieties per chain. Main features of the new design are as follows: a) The new biodegradable HPMA-based polymeric carrier will be composed of short telechelic HPMA copolymer segments, containing PGE1 and targeting moieties, prepared by RAFT (reversible addition-fragmentation chain transfer) polymerization using an azido-functionalized RAFT chain transfer agent. These segments will be extended into high molecular weight (long-circulating) carriers by a highly efficient click chemistry reaction with enzymatically degradable (acetylene functionalized) oligopeptides; b) The targeting D-Asp8 group will be bound to the polymer backbone via a cathepsin K sensitive spacer; c) PGE1 will be bound to the polymer backbone via an ether bond; it will be connected to the carrier via an 1,6-elimination group and a cathepsin K sensitive spacer. The previously used ester bond was stable in humans, but susceptible to hydrolysis in rat and mouse plasma, which complicated the optimization of the conjugate. The new design will avoid these difficulties. To optimize the therapeutic protocol a dose escalation study, a time sequence study, and a multiple dose study will be performed. Numerous analyses will be performed to determine the effect of the conjugates on various bone indices, namely bone mineral density, bone mineral content, bone biomechanical, biomorphometric, and histomorphometric properties. The concept of (main chain) biodegradable HPMA copolymer drug carriers targeted to bone resorption sites is a new paradigm for the design of efficient drugs for the treatment of musculoskeletal diseases. PUBLIC HEALTH RELEVANCE The proposal addresses one of the important problems of osteoporosis treatment delivery of (anabolic) drugs to sites of bone resorption. The advantages of the proposed drug delivery systems are: selective adsorption to the tissues in bone with higher rates of bone turnover, localization of the anabolic agent (prostaglandin E1) in skeletal sites where bone formation would be beneficial, the reduction of side-effects resulting from systemic administration of free drugs, and applicability of design principles to the delivery of other drugs.