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Table 3 Characteristics of published a-synuclein deposition tracers

From: New protein deposition tracers in the pipeline

Tracer name

Chemical structure

Features

Aminothiazolyl-ethenyl-benzoxazole derivatives

 [11C] BF-227 (Kikuchi et al. 2010)

• Non-selective, affinities: see below for 18F-derivative

• Investigated in MSA patients

 [18F] BF-227: (Fodero-Tavoletti et al. 2009)

• Aß1-42 fibrils: KD1 = 1.3 nM

• α-syn fibrils: KD = 9.6 nM

Phenothiazine derivatives

 SIL23 (Bagchi et al. 2013)

• Affinity and selectivity not optimal for in vivo imaging

• Affinity α-synuclein: Ki = 58 nM

• Screening tool

 [18F] 2b (Zhang et al. 2014)

• Affinity α-synuclein: Ki = 49 nM

• Selectivity α -syn vs. Aß: 2-fold

• Selectivity α -syn vs. tau: 2.5-fold

• Crosses blood–brain-barrier in healthy cynomolgus macaques

• Shows sufficient initial uptake and wash-out

• Higher selectivity desired

 [11C] 2a (Zhang et al. 2014)

• Affinity α-synuclein: Ki = 32 nM

• Selectivity α-syn vs. Aß: 3-fold

• Selectivity α-syn vs. tau: 4-fold

• Crosses blood–brain-barrier in cynomolgus macaques

• Shows sufficient initial uptake and wash-out

• Higher selectivity desired

3-(Benzylidene) indolin-2-one derivatives

 [18F] 46a: (Chu et al. 2015)

• Selective for α-synuclein:

  o α-syn Kd = 8.9 nM

  o Aß Kd = 271 nM

  o Tau fibrils: 50 nM

• High logP and presence of nitro group may limit its use for in vivo PET studies

• Potential as secondary lead compound for further SAR studies