Goldstein Margi E, Cao Yang, Fiedler Tracey, Toyn Jeremy, Iben Lawrence, Barten Donna M, Pierdomenico Maria, Corsa Jason, Prasad C V C, Olson Richard E, Li Yu-Wen, Zaczek Robert, Albright Charles F
Research and Development, Neuroscience Drug Discovery, Bristol-Myers Squibb Co., Wallingford, CT 06492, USA.
J Pharmacol Exp Ther. 2007 Oct;323(1):102-8. doi: 10.1124/jpet.107.125492. Epub 2007 Jul 19.
Reduction of brain beta-amyloid peptide (Abeta) synthesis by gamma-secretase inhibitors is a promising approach for the treatment of Alzheimer's disease. However, measurement of central pharmacodynamic effects in the Alzheimer's disease patient will be a challenge. Determination of drug occupancy may facilitate the analysis of efficacy of gamma-secretase inhibitors in a clinical setting. In this study, the relationship of gamma-secretase site occupancy and brain Abeta40 reduction by gamma-secretase inhibitors was examined in Tg2576 mice. 3H-2-Isobutyl-N1-((S)-1-methyl-2-oxo-5-phenyl-2,3-dihydro-1H-benzo[e][1,4]diazepin-3-yl)-3-propylsuccinamide (IN973) was used as a gamma-secretase radioligand, since it has been shown to bind to gamma-secretase in rat, rhesus, and human brains with high affinity and specificity. We extended these findings by showing that [3H]IN973 bound to gamma-secretase in Tg2576 brains with an affinity, specificity, and regional localization very similar to the other species. To quantify gamma-secretase occupancy by gamma-secretase inhibitors, an ex vivo binding assay was developed using [3H]IN973 and frozen brain sections from drug-treated mice. Gamma-secretase occupancy and brain Abeta40 reduction were found to be highly correlated in animals dosed with either 2-[(1R)-1-[4-chlorophenyl)-sulfonylamino] ethyl]-5-fluoro-benzenepropanoic acid (BMS-299897) or (S)-2-((S)-2-(3,5-difluorophenyl)-2-hydroxyacetamido)-N-((S,Z)-3-methyl-4-oxo-4,5-dihydro-3H-benzo[d][1,2]diazepin-5-yl)propanamide (BMS-433796) over a wide range of doses and times postdose, with the exception of the earliest times postdose. This lag in Abeta40 response to gamma-secretase inhibition is probably related to the delayed clearance of previously produced Abeta40. The excellent correlation between brain Abeta40 and gamma-secretase occupancy suggests that a positron emission tomography ligand for gamma-secretase could be a valuable biomarker to determine whether gamma-secretase inhibitors bind to their target in humans.
γ-分泌酶抑制剂降低脑β-淀粉样肽（Aβ）的合成是治疗阿尔茨海默病的一种很有前景的方法。然而，在阿尔茨海默病患者中测量中枢药效学效应将是一项挑战。确定药物占有率可能有助于分析γ-分泌酶抑制剂在临床环境中的疗效。在本研究中，在Tg2576小鼠中研究了γ-分泌酶位点占有率与γ-分泌酶抑制剂降低脑Aβ40之间的关系。3H-2-异丁基-N1-((S)-1-甲基-2-氧代-5-苯基-2,3-二氢-1H-苯并[e][1,4]二氮杂卓-3-基)-3-丙基琥珀酰胺（IN973）被用作γ-分泌酶放射性配体，因为已证明它能以高亲和力和特异性与大鼠、恒河猴和人类大脑中的γ-分泌酶结合。我们扩展了这些发现，表明[3H]IN973在Tg2576大脑中与γ-分泌酶结合的亲和力、特异性和区域定位与其他物种非常相似。为了通过γ-分泌酶抑制剂定量γ-分泌酶占有率，使用[3H]IN973和来自药物处理小鼠的冷冻脑切片开发了一种体外结合测定法。发现在给予2-[(1R)-1-[(4-氯苯基)-磺酰基氨基]乙基]-5-氟苯丙酸（BMS-299897）或(S)-2-((S)-2-(3,5-二氟苯基)-2-羟基乙酰胺)-N-((S,Z)-3-甲基-4-氧代-4,5-二氢-3H-苯并[d][1,2]二氮杂卓-5-基)丙酰胺（BMS-433796）后的广泛剂量和给药后时间内，γ-分泌酶占有率与脑Aβ40降低高度相关，但给药后最早的时间除外。Aβ40对γ-分泌酶抑制反应的这种滞后可能与先前产生的Aβ40清除延迟有关。脑Aβ40与γ-分泌酶占有率之间的良好相关性表明，用于γ-分泌酶的正电子发射断层扫描配体可能是一种有价值的生物标志物，可用于确定γ-分泌酶抑制剂在人体内是否与其靶点结合。
