**2.4.2.2 Quinoline and benzamidizole PET biomarkers**

Investigations into the possibility of using radiolabeled quinoline and benzamidizole derivatives for PET imaging of tau NFTs have been reported recently by Okamura and colleagues (N. Okamura, et al., 2005). Initial experiments, with [11C]BF-126, [11C]BF-158, and [11C]BF-170, demonstrated that these compounds have a high affinity for tau NFTs. Furthermore, these compounds appear to bind specifically to tau, without extensive nonspecific binding to amyloid plaques. Through the use of *in vit*ro staining of AD brain slices, [11C]BF-158 was shown to be the most promising compound for PET imaging of tau NFTs. These radiopharmaceuticals only interact with tau formations in the brains of AD patients. This could prove beneficial for distinguishing early AD from other types of tauopathies. For example, these radiopharmaceuticals do not bind strongly to the tau structures present in the brain slices of patients with Pick's disease and PSP. Although these radiopharmaceuticals have not yet been translated into human clinical trials, the promising pre-clinical data suggest they possess the appropriate properties to make them realistic radiopharmaceuticals for future testing.
