Seliciclib inhibits Mcl-1 transcription, at least in part, by inhibiting IL-6 transcription in the BM microenvironment. (A) Seliciclib inhibits MM1.S cell adhesion induced IL-6 secretion by BMSCs at 24 hours, assessed by ELISA. Data represent the mean ± standard deviation of triplicate cultures. (B) IL-6 transcripts were also down-regulated, as shown by RT-PCR. (C) Addition of exogenous IL-6 (10 ng/mL) resulted in up-regulation of Mcl-1, which was down-regulated by seliciclib (25 μM for 6 hours). (D) Addition of IL-6 neutralizing antibody (10 μg/mL) partially down-regulated Mcl-1 expression.