PROBLEM TO BE SOLVED: To provide (+)-1,4-dihydro-7-[(3S,4S)-3-methoxy-4-(methylamino)-1-pyrrolidinyl]-4-oxo-1-(2-thiazolyl)-1,8-naphthyridine-3-carboxylic acid (SNS-595) represented by the following formula, and to provide methods of treating cancer using the agent.SOLUTION: The present invention provides a method of treating cancer in which a therapeutically effective amount of a second agent, such as DNA-PK inhibitor, ligase IV inhibitor or apoptosis-enhancer, through DNA dependent protein kinase (DNA-PK) pathway in cancer cells to be treated is used in combination with SNS-595.SELECTED DRAWING: None【課題】下式で表される（＋）－１，４－ジヒドロ－７[（３Ｓ，４Ｓ）－３－メトキシ－４－（メチルアミノ）－１－ピロリジニル]－４－オキソ－１－（２－チアゾイル）１，８－ナフチリジン－３－カルボン酸（ＳＮＳ－５９５）及び該剤を使用するガンの治療方法の提供。【解決手段】ＳＮＳ－５９５と一緒に、治療すべき癌細胞におけるＤＮＡ依存性プロテインキナーゼ（ＤＮＡ－ＰＫ）経路を媒介した、治療的有効量の、ＤＮＡ－ＰＫ阻害剤、リガーゼIV阻害剤又はアポトーシス増進剤等の２番目の薬剤を組み合わせて使用するガンの治療方法。【選択図】なし
