Pharmacologic inhibition of CDK6 in human AML cells. (A) Colony formation of AML cell lines treated with PD-0332991. (B) Effects of CDK4 suppression in AML cell lines. (C) Relative colony numbers of primary human MLL-rearranged AML specimens cultured in the presence of PD-0332991. (D) Cumulative analysis of normalized colony data shown in panel C. (E) Flow cytometric analysis of myeloid differentiation in AML cell lines treated with PD-0332991. Numbers indicate percentages of cells. (F) Microscopic analysis of May-Grünwald-Giemsa–stained cytospin preparations of AML cell lines treated with PD-0332991. Original magnification, ×400. Insets show twofold magnified details of the corresponding photographs.