Seliciclib has synergistic anti-MM activity when combined with doxorubicin and bortezomib. Increasing concentrations of seliciclib were added with bortezomib (1-4 nM) and doxorubicin (100-500 nM); MM.1S cytotoxicity was assayed by MTT. Synergism was confirmed by applying the Chou-Talalay method to calculate a CI. Data for bortezomib (1 nM) and doxorubicin (100 nM) are represented, with maximum synergism noted at concentrations of 10 to 15 μM seliciclib and a CI of less than 1. Data represent the mean ± standard deviation of triplicate cultures.