Figure 3. CDK4 inhibition partially restores G₁-S arrest and reduces cell viability upon drug treatment in MYCN-amplified cells. (A and B) Cells were transiently transfected with one of two different CDK4 siRNAs or one of two unrelated control siRNAs, then treated with doxo 24 h after transfection. Knockdown efficacies of both CDK4 siRNAs (%) are shown in the western blot (A), in addition to flow cytometric cell cycle analyses performed 48 h after doxo treatment (B). (C) Flow cytometric cell cycle analyses after 48 h of treatment with doxo and/or the CDK4 inhibitor, RO0505124. (D) Cell viability was assessed after doxo and/or RO0505124 treatment at the indicated time points using the alamarBlue assay. Data shown in (B–D) are presented as mean ± SD of triplicates.