Nucleic acid construct for expressing active substances which can be activated by proteases, and preparation and use

A nucleic acid construct for expressing an active substance which is activated by an enzyme which is released from mammalian cells, wherein said construct comprises the following nucleic acid sequences in the following order:

• a) at least one promoter element operably linked to;
• b) at least one nucleic acid sequence which encodes an active compound, wherein said active compound is endogenous to mammals, operably linked to;
• c) at least one nucleic acid sequence which encodes an amino acid sequence cleavable specifically by an enzyme which is released from a mammalian cell, operably linked to;
• d) at least one DNA sequence which encodes a polypeptide which is bound to said active compound by said cleavable amino acid sequence and inhibits the activity of said active compound, and wherein said nucleic acid component c) does not naturally occur as operably linking said nucleic acid sequence b) to said nucleic acid d).