Tau PET imaging: present and future directions

Table 1 Preclinical properties of the tau-specific PET tracers

		PBB3	THK5117			THK5351	AV-1451
Radiotracer		¹¹C	cold	¹⁸F	³H	¹⁸F	¹⁸F	³H
In vitro binding	Brain tissue	Kd₁ = 2.5 [28] Bmax₁ = 25nM [28] Kd₂ = 100 [28] Bmax₂ = 300nM [28]		Kd = 5.19 [15]; 11.5 [14] Bmax = 338 [15]	Kd₁ = 2.2^a; 3.1^b [24] Kd₂ = 23.6^a; 34.6^b [24] Bmax₁ = 250^a; 250^b [24] Bmax₂ = 1416^a; 1226^b [24]	Kd = 2.9 [26] Bmax = 368.3 [26]	15^f [22]	Kd = 1.4–3.72^c; 0.63–1.70^d [23] Bmax = 15–62.5nM^c; 46.9–119.7nM^d [23]
In vitro binding	Ki	Ki₁ = 1.3^b; 5.9^e [33] Ki₂ = 23.5^b [33]	Ki₁ = 0.001^a; 0.0005^b [24] Ki₂ = 27.4 [14]; 16^a [24]; 10.5 [15] Ki₃ = 750^a; 800^b [24]				Ki₁ = 0.3^b; 3.3^e [33] Ki₂ = 97.2^b [33]
Ex vivo biodistribution	LogP			2.32 [15]		1.5 [26]		1.67 [18]
Ex vivo biodistribution	Uptake in mouse brain (2 min)			6.06%ID/g [15]		4.36%ID/g [26]	7.5%ID/g [29]

^aTissue from hippocampal region; ^btissue from temporal region; ^ctissue from frontal cortex; ^dtissue from entorhinal cortex; ^etissue from motor cortex in a case of progressive supranuclear palsy; ^fdetermined by autoradiography. Aβ beta-amyloid, Bmax receptor density, ID injected dose, Kd dissociation constant, Ki binding affinity, LogP partition coefficient. Ki and Kd values in nM and Bmax values in pmol/g (unless stated otherwise)

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