The invention provides a method of inhibiting binding between acetylated histone and a bromodomain-containing protein in a mammal, as well as a method of shrinking or killing of cancer cells expressing a bromodomain-containing protein or inhibiting the growth of cancer cells expressing a bromodomain-containing protein in a mammal. The methods involve administering an effective amount of (S)-2-[4-(4-chlorophenyl)-2,3,9-trimethyl-6H-thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepin-6-yl]-N-(4-hydroxyphenyl)acetamide or a dihydrate thereof to the mammal.