The present invention relates to a modified polypeptide comprising a non-cytotoxic protease, a translocation domain, a destructive protease cleavage site and a Targeting Moiety that binds to a Binding Site on a nerve cell, wherein after cleavage of the destructive cleavage site the polypeptide has reduced potency. The destructive cleavage site is recognised and cleaved by a protease present at or in an off-site target cell, and, in one embodiment, the polypeptide is a modified clostridial neurotoxin. The present invention also relates to the use of said polypeptides for treating a range of conditions, and to nucleic acids encoding said polypeptides.