tokens: NIK - 247 , tacrine and E - 2020 all strongly inhibited acetylcholinesterase ( AChE ) in human red blood cells ( IC50s = 1 . 0 x 10 ( - 6 ) , 2 . 9 x 10 ( - 7 ) and 3 . 7 x 10 ( - 8 ) M , respectively ) .