Combination therapy using ascochlorin derivative

A method for treating or preventing a cancer, comprising administrating to a subject in need thereof a therapeutically effective amount of a compound represented by formula (I):

• wherein
• R1 is formyl, or —CH═N—O—Y, in which Y is a hydrogen atom or C1-6 alkyl;
• R2 is C1-6 alkyl that may be substituted with 1 to 5 fluorine atoms;
• R3 is a hydrogen atom or C1-6 alkyl;
• R4 is hydroxy, C1-6 alkylamino, C3-7 cycloalkylamino, or 3- to 7-membered heterocycloalkylamino which contains —O—, —S—, —NR6—, —SO— or —SO2— as a ring atom, or
• R3 and R4 together with the carbon atom to which they are attached form >C═N—O—Z;
• Z is a hydrogen atom, C1-6 alkyl, —CO(CH2)n—R5 or —(CH2)n—R5;
• n is an integer selected from 1 to 4;
• R5 is —CO2R6, —CONH2, —CONR7R8, —OCONR7R8, —SO2NR7R8, —SO2R9, hydroxy, —NHSO2R9, or —NR7R8;
• R6, R7 and R8 are each independently selected from a group consisting of a hydrogen atom, C1-6 alkyl, and C3-7 cycloalkyl;
• or R7 and R8 together with the nitrogen atom to which they are attached form a nitrogen-containing 3- to 7-membered heterocyclic ring which may further contain —O—, —S—, —NR6—, —SO— or —SO2— as a ring atom, in which the heterocyclic ring may be substituted with one or more substituents selected from hydroxy and C1-6 alkyl;
• R9 is C1-6 alkyl, or C3-7 cycloalkyl;
• a pharmaceutically acceptable salt or a solvate thereof,
• in combination with administration of an immune checkpoint inhibitor.