Disclosed are: an inhibitor of the expression of matrix metalloproteinase-9 gene； a therapeutic agent for a disease associated with matrix metalloproteinase-9； and a carcinostatic agent. Each of the agents comprises a pyrrole-imidazole polyamide having an N-methylpyrrole unit, an N-methylimidazole unit and a ³-aminobutyric acid unit. The pyrrole-imidazole polyamide can be folded at the site of the ³-aminobutyric acid unit to form a U-shaped conformation in a minor groove of a double-stranded domain comprising a part or the whole of a specific nucleotide sequence (SEQ ID NO:2, SEQ ID NO:4) included in a human matrix metalloproteinase-9 gene promoter and a strand complementary to the part or the whole of the specific nucleotide sequence. In the U-shaped conformation, a Py-Im pair, an Im/Py pair and a Py/Py pair in the pyrrole-imidazole polyamide target a C-G base pair, a G-C base pair, and both of an A-T base pair and a T-A base pair in the minor groove, respectively.
