Effect of alpha‐Synuclein on the binding of [18F]MK‐6240 and [18F]AV‐1451

Abstract Background Binding in alpha‐synuclein containing brain regions have been described for both Flortaucipir ([18F]AV‐1451) and [18F]MK‐6240. Here we assessed whether alpha‐Synuclein constitutes a target for these tau imaging agents. Method We used autoradiographic dot blot to validate specific and evaluate off‐target interactions of [18F]MK‐6240 and [18F]AV‐1451 using sarkosyl‐insoluble extracts from PSP, CBD, PiD, and AD cortical tissue which contain fibrillar forms of tau. Tissue concentrations of alpha‐Synuclein are orders of magnitude lower than NFTs leading us to use recombinant alpha‐Synuclein PFFs to evaluate potential off‐target interactions. Briefly, 1:100 dilutions of each preparation were incubated with 82 fmol of mass in a 30uL total volume. Samples were incubated for 90 minutes at 37°C. Reactions were terminated by pipetting the solution in triplicate onto a glass fiber filter held within a 96‐well dot‐blot aspiration device and the samples were immobilized. Unbound ligand was washed three times with ice cold PBS. The glass fiber filters were transferred to a cassette for exposure to autoradiographic film for 90 minutes and the activity in photostimulated luminescence units per mm 2 was calculated using ImageJ software v.1.8.0. Result Disintegrations were corrected for decay and normalized to cerebellar extracts for both ligands. [18F]MK‐6240 demonstrated high specificity, binding in AD extracts and AD extracts subject to trypsin treatment. [18F]AV‐1451 demonstrated similar binding in both native and trypsinized AD extracts, while also showing overlapping binding profiles in human alpha‐synuclein PFFs but not in mouse alpha‐synuclein PFFs. Conclusion [18F]AV‐1451 binds to recombinant human alpha‐Synuclein PFFs as it does to native AD‐tau PHFs. Future experiments should assess patient derived alpha‐Synuclein aggregates as a potential off target binding to [18F]AV‐1451.