Ye Liang, Morgenstern Jennifer L, Gee Antony D, Hong Guizhu, Brown John, Lockhart Andrew
Translational Medicine and Genetics, GlaxoSmithKline Research and Development, Addenbrookes Hospital, Cambridge, CB2 2GG, United Kingdom.
J Biol Chem. 2005 Jun 24;280(25):23599-604. doi: 10.1074/jbc.M501285200. Epub 2005 Apr 26.
A range of imaging agents for use in the positron emission tomography of Alzheimer's disease is currently under development. Each of the main compound classes, derived from thioflavin T (PIB), Congo Red (BSB), and aminonaphthalene (FDDNP) are believed to bind to mutually exclusive sites on the beta-amyloid (Abeta) peptide fibrils. We recently reported the presence of three classes of binding sites (BS1, BS2, BS3) on the Abeta fibrils for thioflavin T derivatives and now extend these findings to demonstrate that these sites are also able to accommodate ligands from the other chemotype classes. The results from competition assays using [3H]Me-BTA-1 (BS3 probe) indicated that both PIB and FDDNP were able to displace the radioligand with Ki values of 25 and 42 nM, respectively. BSB was unable to displace the radioligand tracer from the Abeta fibrils. In contrast, each of the compounds examined were able to displace thioflavin T (BS1 probe) from the Abeta fibrils when evaluated in a fluorescence competition assay with Ki values for PIB, FDDNP, and BSB of 1865, 335, and 600 nM, respectively. Finally, the Kd values for FDDNP and BSB binding to Abeta fibrils were directly determined by monitoring the increases in the ligand intrinsic fluorescence, which were 290 and 104 nM, respectively. The results from these assays indicate that (i) the three classes of thioflavin T binding sites are able to accommodate a wide range of chemotype structures, (ii) BSB binds to two sites on the Abeta fibrils, one of which is BS2, and the other is distinct from the thioflavin T derivative binding sites, and (iii) there is no independent binding site on the fibrils for FDDNP, and the ligand binds to both the BS1 and BS3 sites with significantly lower affinities than previously reported.
目前正在研发一系列用于阿尔茨海默病正电子发射断层扫描的成像剂。源自硫黄素T（PIB）、刚果红（BSB）和氨基萘（FDDNP）的每一类主要化合物，据信都能与β-淀粉样蛋白（Aβ）肽纤维上相互排斥的位点结合。我们最近报道了硫黄素T衍生物在Aβ纤维上存在三类结合位点（BS1、BS2、BS3），现在扩展这些发现以证明这些位点也能够容纳来自其他化学类型类别的配体。使用[3H]Me-BTA-1（BS3探针）的竞争试验结果表明，PIB和FDDNP都能够取代放射性配体，其Ki值分别为25和42 nM。BSB无法从Aβ纤维上取代放射性配体示踪剂。相比之下，在荧光竞争试验中评估时，所检测的每种化合物都能够从Aβ纤维上取代硫黄素T（BS1探针），PIB、FDDNP和BSB的Ki值分别为1865、335和600 nM。最后，通过监测配体内在荧光的增加直接测定了FDDNP和BSB与Aβ纤维结合的Kd值，分别为290和104 nM。这些试验结果表明：（i）硫黄素T的三类结合位点能够容纳广泛的化学类型结构；（ii）BSB与Aβ纤维上的两个位点结合，其中一个是BS2，另一个与硫黄素T衍生物结合位点不同；（iii）纤维上不存在FDDNP的独立结合位点，该配体与BS1和BS3位点结合的亲和力明显低于先前报道。
