Antiproliferative effects of tipifarnib-containing combinations. (A,B) Log-phase HL-60 cells were treated with the indicated concentration of etoposide (○, A), tipifarnib (○, B), or the combination at a 2:1 ratio (●, A,B). (C) Combination index values calculated from the data shown in panels A and B when data were analyzed by the median effect method⁵⁹  as previously described in detail.⁶⁰  (D) Summary of results obtained when tipifarnib was combined with multiple orally bioavailable antileukemic agents. Results are expressed as the mean ± SD of combination index values at the IC₅₀ and IC₉₀ in the indicated number of independent experiments.