An object of the present invention is to provide a
small molecule compound (IL-17 activity inhibitor) having a more potent
inhibitory effect on IL-17 activity than conventional compounds. The IL-17RA inhibitor of the present invention is, for example, a
small molecule compound surrounded by Phe60, Gln87, Asp121, Pro122, Asp123, Gln124, Asp153, Cys154, Glu155, Lys160, Pro164, Cys165, Ser167, Ser168, Gly169, Ser170, Leu171, Trp172, Asp173, Pro174, Pro254, Phe256, Ser258, Cys259, Asp262, Cys263, Leu264, and His266, which are contained in the
extracellular domain of human
interleukin-17
receptor A (IL-17RA). The compound contains a compound having the effect of inhibiting the binding of
interleukin-17A (IL-17A) to IL-17RA in humans, etc., or a pharmaceutically acceptable salt, solvate, or
prodrug thereof, which can bind to IL-17RA through non-covalent interactions, including van der Waals forces acting between at least 13 of these
amino acid residues in the space defined by the compound, and preferably further including at least one type of
intermolecular interaction selected from the group consisting of ionic bond,
hydrogen bond, C-H-π interaction, and hydrophobic interaction acting between predetermined ones of the
amino acid residues.