Effect of the CDK4/CDK6 inhibitor PD 0332991 on the functional properties of the MCL cells. (A) Cell proliferation as determined by 3-hour BrdU incorporation after 21-hour exposure of the MCL cell lines to the drug at the listed concentrations. (B) Cell cycle progression in MCL cell lines (i) and patient samples (ii) as determined by changes in the percentage of cells in the S phase after cell exposure to 200 nM PD 0332991 for the indicated lengths of time. (C) Effect of PD 0332991 on highly purified primary MCL cells. (i) Flow cytometry analysis with an anti-CD20 antibody of cells from 2 MCL patients after cell purification with a mixture of anti-non-B-cell antibodies (see “Materials and methods”). (ii) BrdU incorporation by the purified MCL cells exposed to medium alone or to 200 nM PD 0332991. (D) Cell apoptosis as determined by DNA fragmentation (TUNEL) assay after 24-hour cell exposure to 200 nM PD 0332991. Results are representative of at least 2 independent experiments. Error bars indicate standard deviation.