Babich J W, Tompkins R G, Graham W, Barrow S A, Fischman A J
Department of Radiology, Massachusetts General Hospital, Boston 02114, USA.
J Nucl Med. 1997 Aug;38(8):1316-22.
The infection imaging properties of a high-affinity 99mTc-labeled chemotactic peptide receptor agonist (N-formyl-methionyl-leucyl-phenylalanine-lysine; N-For-MLFK) were compared with a low-affinity agonist (N-Acetyl-MLFK; N-Ac-MLFK), a moderate-affinity antagonist (N-isobutyloxycarbonyl-MLFK; N-IBoc-MLFK) and non-specific inflammation imaging agents.
All peptides were prepared by solid-phase methods and purified by high-performance liquid chromatography. The products were assayed in vitro for N-formyl-methionyl-leucyl-phenylalanine receptor binding and superoxide production. Three types of studies were performed in rabbits with Escherichia coli infection: (Study A) Four groups of six animals were coinjected with 99mTc-N-For-MLFK-hydrazinonicotinamide (N-For-MLFK-HYNIC) plus 111In-immunoglobulin G, 111In-red blood cells or 111In-diethylene triamine pentaacetic acid. (Study B) Three groups of six rabbits were coinjected with 111In-leukocytes plus 99mTc-N-For-MLFK-HYNIC, 99mTc-N-Ac-MLFK-HYNIC or 99mTc-N-IBoc-MLFK-HYNIC. (Study C) Two groups of six rabbits were injected with 99mTc-N-For-MLFK-HYNIC and 111In-leukocytes with and without an excess of antagonist. In all three studies, the radiopharmaceuticals were injected 24 hr after infection and dual photon (99mTc and 111In) gamma camera images were acquired at 2-3 and 16-18 hr later. Target-to-background (T/B) ratios were calculated for regions of interest drawn over the infected and contralateral normal tissue.
N-For-MLFK, N-Ac-MLFK and N-IBoc-MLFK had EC50s for receptor binding of 2.0, 830 and 150 nM, respectively. The corresponding EC50s for superoxide production were 20.0, approximately 10(3) and > 10(4). Study A demonstrated that the T/B for 99mTc-N-For-MLFK-HYNIC was higher than for any of the nonspecific imaging agents (p < 0.001), and 111In-immunoglobulin G had a higher T/B ratio than 111In-diethylenetriamine pentaacetic acid (p < 0.01) or 111In-red blood cells (p = NS). Study B showed that 99mTc-N-For-MLFK-HYNIC had a higher T/B ratio than the other peptides (p < 0.001). 111In-leukocytes and 99mTc-N-IBoc-MLFK-HYNIC had comparable T/B ratios, which were higher than for 99mTc-N-Ac-MLFK-HYNIC (p < 0.05). Study C demonstrated that coinjection with an antagonist resulted in a significant reduction in the T/B ratio for 99mTc-N-For-MLFK-HYNIC (p < 0.001), but did not affect the T/B ratio for 111In-leukocytes.
Nonspecific mechanisms contribute minimally to the localization of 99mTc-chemotactic peptide analogs at sites of infection and the majority of the accumulation appears to be receptor mediated. Also, chemotactic peptide receptor antagonists can be used for infection imaging. These results provide important new insights for future radiopharmaceutical development.
将一种高亲和力的99mTc标记趋化肽受体激动剂（N-甲酰基-甲硫氨酰-亮氨酰-苯丙氨酸-赖氨酸；N-For-MLFK）的感染成像特性与一种低亲和力激动剂（N-乙酰基-MLFK；N-Ac-MLFK）、一种中等亲和力拮抗剂（N-异丁氧基羰基-MLFK；N-IBoc-MLFK）以及非特异性炎症显像剂进行比较。
所有肽均通过固相方法制备，并通过高效液相色谱法纯化。对产物进行体外N-甲酰基-甲硫氨酰-亮氨酰-苯丙氨酸受体结合和超氧化物生成检测。对感染大肠杆菌的兔子进行了三种类型的研究：（研究A）四组，每组六只动物，同时注射99mTc-N-For-MLFK-肼基烟酰胺（N-For-MLFK-HYNIC）加111In-免疫球蛋白G、111In-红细胞或111In-二乙三胺五乙酸。（研究B）三组，每组六只兔子，同时注射111In-白细胞加99mTc-N-For-MLFK-HYNIC、99mTc-N-Ac-MLFK-HYNIC或99mTc-N-IBoc-MLFK-HYNIC。（研究C）两组，每组六只兔子，分别注射99mTc-N-For-MLFK-HYNIC和111In-白细胞，其中一组同时注射过量拮抗剂。在所有三项研究中，感染后24小时注射放射性药物，并在2 - 3小时和16 - 18小时后采集双光子（99mTc和111In）γ相机图像。计算感染组织和对侧正常组织上感兴趣区域的靶本比（T/B）。
N-For-MLFK、N-Ac-MLFK和N-IBoc-MLFK的受体结合EC50分别为2.0、830和150 nM。相应的超氧化物生成EC50分别为20.0、约10³和>10⁴。研究A表明，99mTc-N-For-MLFK-HYNIC的T/B高于任何一种非特异性显像剂（p<0.001），且111In-免疫球蛋白G的T/B比高于111In-二乙三胺五乙酸（p<0.01）或111In-红细胞（p = 无显著差异）。研究B显示，99mTc-N-For-MLFK-HYNIC的T/B比高于其他肽（p<0.001）。111In-白细胞和99mTc-N-IBoc-MLFK-HYNIC的T/B比相当，均高于99mTc-N-Ac-MLFK-HYNIC（p<0.05）。研究C表明，同时注射拮抗剂会使99mTc-N-For-MLFK-HYNIC的T/B比显著降低（p<0.001），但不影响111In-白细胞的T/B比。
非特异性机制对99mTc趋化肽类似物在感染部位的定位贡献极小，大部分聚集似乎是受体介导的。此外，趋化肽受体拮抗剂可用于感染成像。这些结果为未来放射性药物的开发提供了重要的新见解。
