RADIOLABELED CHEMOTACTIC PEPTIDES FOR IMAGING INFECTION

隐匿性炎性病灶的定位常常是必要的 危重病人的治疗管理。电流成像 检查方法包括：CT、超声和MRI主要依靠改变 在组织密度或成分中发生的后期变化 炎症过程。放射性核素程序已经用于 定位早期炎症过程至少需要12小时，并且 通常从注射到成像的时间是24-48小时。显然， 一种快速定位急性炎症部位的方法将非常 对病人管理有帮助。最近，我们开发了一些方法来 制备白细胞趋化多肽的类似物，For-MLF， 可用于外部成像的放射性标记。在体外，这些化合物具有 与中性粒细胞与-MLF受体结合的生物活性和可比性 天然多肽。对动物的初步研究表明， 这些药物在体内与白细胞结合，从循环中清除 在一定程度上快速定位于大肠杆菌感染部位 足以在注射后早期产生外部图像。通过贴标签 该多肽与99mTc具有很高的比活度，可以进行成像 在不会导致大鼠中性粒细胞减少的多肽剂量下进行， 兔子或猴子。对照实验旨在证明 多肽对MLF受体介导的感染定位 相互作用，表现为：1)与本地化试剂相比 非特异性机制引起的炎症(放射性标记的DTPA、RBC和 Ig G)，T/B比值较高； 高亲和力激动剂和极低亲和力激动剂之间的比较 拮抗剂和受体拮抗剂表明T/B明显 与受体亲和力有关。这些研究还证实， 受体拮抗剂定位于感染部位而不是 不良反应的可能性；以及3)感染的定位 共注射受体可阻断99mTc标记的多肽 对抗者。拟议研究的目标是开发一种 快速检测趋化性多肽试剂的最佳条件 感染部位的定位。这些研究将涉及 一系列趋化性多肽类似物的合成，重点是： 高亲和力拮抗剂或部分激动剂的设计；简单， 99mTc快速、高效、高比活度标记 良好的生物分布，并提高了本地化和 病变与背景的对比。每种试剂都将在 体外测定其与白细胞表面For-MLF受体的亲和力 以及它通过以下方式刺激超氧化物生成的能力 粒细胞。在动物体内的生物分布将被确定 感染/炎症。场地本地化的速度和强度 炎症的发生将与体外For-MLF受体相关 亲和力和生物活性数据。组织和细胞分级 技术将被用来确定分布的动力学和 多肽和代谢物的代谢。

Localization of occult inflammatory foci is frequently essential to the therapeutic management of critically ill patients. Current imaging procedures, including: CT, Ultrasound and MRI rely primarily on changes in tissue density or composition that occur late changes in the inflammatory process. Radionuclide procedures that have been used to localize early inflammatory processes require a minimum of 12 hours, and typically 24-48 hours from the time of injection to imaging. Clearly, a method of rapidly localizing sites of acute inflammation would be very helpful for patient management. Recently, we developed methods for preparing analogs of the leukocyte chemoattractant peptide, For-MLF, that can be radiolabeled for external imaging. In vitro, these compounds have bioactivity and neutrophil For-MLF receptor binding comparable to the native peptide. Preliminary studies in animals have demonstrated that these agents bind to leucocytes in vivo, clear from the circulation rapidly and localize at sites of E. coli infection to an extent sufficient to yield external images early after injection. By labeling the peptides with 99mTc at very high specific activity, imaging can be performed at doses of peptide that do not induce neutropenia in rats, rabbits or monkeys. Control experiments designed to establish that infection localization is mediated by peptide-For-MLF receptor interaction, demonstrated: 1) When compared with reagents that localize at inflammation by non-specific mechanisms (radiolabeled DTPA, RBC's and IgG), T/B ratios for 99mTc-labeled peptide were much greater; 2) Comparisons between a high affinity agonist, a very low affinity antagonist and a receptor antagonist demonstrated that T/B is clearly related to receptor affinity. These studies also established that receptor antagonists localize at sites of infection without the possibility of adverse effects; and 3) The infection localization of 99mTc labeled peptide could be blocked by coinjection of a receptor antagonist. The objective of the proposed research is to develop an optimal chemotactic peptide reagent for the rapid detection and localization of focal sites of infection. These studies will involve the synthesis of a series chemotactic peptide analogs with emphasis on: design of a high affinity antagonists or partial agonist; uncomplicated, rapid, efficient and high specific activity labeling with 99mTc, favorable biodistribution, and enhanced speed of localization and contrast between lesion and background. Each reagent will be studied in vitro to determine its affinity for the For-MLF receptor on leukocytes and its ability to stimulate the production of superoxide by granulocytes. Biodistribution will be determined in animals with infection/inflammation. The rate and intensity of localization at sites of inflammation will be correlated with the in vitro For-MLF receptor affinity and biological activity data. Tissue and cell fractionation techniques will be used to determine the kinetics of distribution and metabolism of the peptides and metabolites.