The present invention provides methods of proteolytically converting a precursor
protein (e.g. tau) to a product fragment (e.g., a 12 kd fragment) in a
stable cell line, wherein the precursor
protein is associated with a
disease state in which the precursor
protein aggregates pathologically (e.g. a
tauopathy), and the methods comprise: (a) providing a
stable cell line transfected with
nucleic acid encoding: (i) a template fragment of the precursor protein such that the template fragment is constitutively expressed in the
cell at a level which is not toxic to the
cell; and (ii) the precursor protein, which protein is inducibly expressed in the
cell in response to a stimulus, whereby interaction of the template fragment with the precursor protein causes a
conformational change in the precursor protein such as to cause aggregation and proteolytic
processing of the precursor protein to the product fragment. The method is preferably used to screen for modulators of the aggregation process by monitoring production (or modulation of production) of the product band or bands. Also provided are materials for used in the assays, plus medicaments, and related uses and processes, based on compounds which show
high activity in the
assay of the invention e.g. reduced diaminophenothiazines.