PROBLEM TO BE SOLVED: To provide a photoacoustic-imaging contrast agent which has high clustering properties to a tumor, leaves little residue in blood, and is capable of administration into blood.SOLUTION: The invention provides a photoacoustic-imaging contrast agent consisting of a conjugate (A) of a pigment and a polyethylene glycol, the pigment having, as a basic skeleton, a bisindole structure constructed by binding a methine chain to a five-membered ring comprising N at both ends of the methine chain and additives (B), such as cyclodextrin, which interact with the conjugate. After the administration into blood, the aggregate of (A) and (B) is transferred from blood to a tumor, while the aggregate remaining in blood is dissolved and discharged from the body.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2016,JPO&INPIT【課題】腫瘍への集積性が高く、血中への残存が少なく、血中へ投与可能な光音響イメージング用造影剤の提供。【解決手段】メチン鎖と該メチン鎖の両端にNを含む5員環が結合してなるビスインドール構造を基本骨格として有する色素とポリエチレングリコールの結合体(A)及び、結合体と相互作用するシクロデキストリン等の添加剤(B)からなる光音響イメージング用造影剤。血中に投与された後に、血中から(A)と(B)の凝集体が腫瘍へ移行し、一方、その間に血中に残存している凝集体は分解し、体内から排出される前記造影剤の投与方法。【選択図】図1
