Effect of 17-AAG on antiproliferative effects of cytarabine in colony-forming assays. (A,C-D) Freshly isolated mononuclear cells from 3 newly diagnosedAML patients were treated for 24 hours with diluent or 100 nM cytarabine (Ara-C) as indicated in the panels. Diluent or 17-AAG was then added to the indicated final concentration for an additional 24 hours. At the completion of the drug treatment, samples were washed and plated in Methocult medium to permit growth and quantitation of leukemic colonies. Bars indicate relative colony counts observed after the indicated treatment; ○, relative colony counts predicted from the effects of the individual agents using the fractional product method.⁶⁶  (B) Combination index values calculated from the data in panel A and additional results from the same clonogenic assay under the assumption that effects of 17-AAG and cytarabine are mutually exclusive (⬡).⁸²  Other symbols indicate combination index values from clonogenic assays performed in 4 additional AML samples as described in the text. A combination index level below 1.0 indicates synergy.