Pharmacologic CDK6 blockade reduces the clonogenicity of primary ITD+ AML patient biopsies. (A) Fold change in FLT3 gene expression upon pharmacologic CDK6 inhibition (#1, 1 µM; #2, 0.3 µM) relative to vehicle computed from qPCR experiments in primary patient CD34+ cells. (B) FLT3-ITD AML patient material was subjected to palbociclib (#1, 3 µM; #4, 1 µM; #2, 0.3 µM), stained with FLT3 phycoerythrin antibody, and analyzed by flow cytometry for FLT3 mean fluorescence intensity. (C) Viability measurements upon CDK6 kinase inhibition (1 µM) were conducted by using the CTG Assay. Analysis was carried out in triplicate. Two-tailed unpaired Student t test was used for statistical comparison. (D) Patient AML samples (n = 6) were embedded in methylcellulose with recombinant cytokines and erythropoietin (MethoCult H4434) in the presence of CDK6 inhibitor (palbociclib) or FLT3 kinase inhibitor (TCS-359). Colonies were counted 10 days after seeding. Representative data are depicted (magnification: ×4). *P < .05; **P < .01; ***P < .001; ****P < .0001. n.s., not significant.