In vitro characterisation of BF227 binding to alpha-synuclein/Lewy bodies

Amyloid-beta (Abeta) plaques are a pathological hallmark of Alzheimer's disease and a current target for positron emission tomography (PET) imaging agents. Whilst [(11)C]-PiB is currently the most widely used PET ligand in clinic, a novel family of benzoxazole compounds have shown promise as Abeta imaging agents; particularly BF227. We characterised the in vitro binding of [(18)F]-BF227 toward alpha-synuclein to address its selectivity for Abeta pathology, to establish whether [(18)F]-BF227 binds to alpha-synuclein/Lewy bodies, in addition to Abeta plaques. In vitro [(18)F]-BF227 saturation studies were conducted with 200 nM alpha-synuclein or Abeta(1-42) fibrils or 100 microg of Alzheimer's disease, pure dementia with Lewy bodies or control brain homogenates. Non-specific binding was established with PiB (1 microM). In vitro binding studies indicated that [(18)F]-BF227 binds with high affinity to two binding sites on Abeta(1-42) fibrils (K(D1) = 1.31 and K(D2) = 80 nM, respectively) and to one class of binding sites on alpha-synuclein fibrils (K(D) = 9.63 nM). [(18)F]-BF227 bound to Abeta-containing Alzheimer's disease brain (K(D) = 25 +/- 0.5 nM), but failed to bind to Abeta-free dementia with Lewy bodies or age-matched control homogenates. Moreover, BF227 labelled both Abeta plaques and Lewy bodies in immunohistochemical/fluorescence analysis of human Alzheimer's disease and Parkinson's disease brain sections, respectively. This study suggests that [(18)F]-BF227 is not Abeta-selective. Evaluation of BF227 as a potential biomarker for Parkinson's disease is warranted.