Table 2.

Characteristics of published tau protein tracers updated from (Villemagne et al. 2015)

Tracer name	Chemical structure	Features
Pyridinyl-butadienyl-benzothiazole derivative
[11C]-PBB3 (Maruyama et al. 2013; Hashimoto et al. 2014)		• Selectively binds to tau
		• Retention of 11C-PBB3 in the venous sinuses
		• Retention of tracer in basal ganglia in patient with corticobasal degeneration suggests that it might bind to non-AD tauopathies
Dialkylamino-naphthylethylidene derivative
[18F] FDDNP (Kepe et al. 2013; Thompson et al. 2009; Small et al. 2013; Shoghi-Jadid et al. 2002; Smid et al. 2013)		• First 18F-tracer with tau binding
		• Lack of selectivity for tau; nanomolar binding affinity to Aβ
		• Very limited dynamic range
		• Regional brain retention used for differentiating Aβ and tau
Benzimidazole derivatives
[11C]-N-Methyl-Lansoprazole (Shao et al. 2012; Fawaz et al. 2014)		• In vitro binding to paired helical filament-tau demonstrated
		• No brain uptake in mice (P-glycoprotein substrate)
		• Brain uptake in non-human primates
		• No human studies reported
[18F]-N-Methyl-Lansoprazole (Fawaz et al. 2014)
Quinoline derivatives
[18F]-THK-523 (Harada et al. 2013)		• Slow kinetics
		• Non-specific binding (white matter, brain stem)
		• No detection of non-AD tauopathies (Pick’s disease; three-repeat tauopathy)
[18F]-THK-5105 (Okamura et al. 2013; Okamura et al. 2014)		• Faster kinetics and higher contrast than 18F-THK-523
		• Non-specific binding (white matter, brain stem)
[18F]-THK-5117 (Okamura et al. 2013; Okamura et al. 2015)
[18F]-THK-5351 (Harada et al. 2015)		• Faster kinetics and higher contrast than THK-523
		• Lower white matter retention
		• Higher signal-to-noise ratio compared with 18F-THK-5105 and 18F-THK-5117
6,5,6 Tricyclic pyrimidines and indoles
[18F]-T807 (Chien et al. 2013; Xia et al. 2013)		• Tracer with broadest clinical data package
		• Cortical retention consistent with the known distribution of tau in AD brain
		• Strong correlation with disease severity
		• Slower kinetics than 18F-T808
		• Off-target activity (striatum, choroid plexus)
[18F]-T808 (Chien et al. 2014)		• Faster kinetics than 18F-T807
		• Substantial defluorination
Pyrrolo-pyridine-isoquinolineamine
[18F]-MK-6240 (Walji et al. 2016)		• Good in vitro binding affinity to NFTs, high selectivity to β-amyloid, and excellent physicochemical properties for brain penetration and cellular permeability.
		• No off-target binding and suitable in vivo pharmacokinetics
		• Clinical studies are currently underway

AD alzheimer’s disease