In order to probe for factors which might support supra-additive killing of AML cells by the combination of GO and tipifarnib, a preliminary study was carried out in which the expression of 46 known human phospho-kinase proteins was measured in the CD34+CD38- TF-1a cell line after incubation with tipifarnib, GO and the combination. Here, CD34 is linked to acute myeloid leukemia.