Elevated Hsp90 expression is reported in several resistant leukemia subtypes such as BCR-ABL1 + CML/BCP-ALL, FLT3-ITD-driven AML, and Ph-like BCP-ALL. Besides that, client proteins of Hsp90 include several kinases (e.g., AKT, BCR-ABL1, BRAF, EGFR2, HER2, and JAK1/2), growth and steroid receptors, and apoptotic factors (e.g., BCL-2 and mutant p53), which are often aberrantly regulated in several malignancies. Therefore, we determined the efficacy of 5b on therapy-resistant cell lines obtained from different leukemia subtypes (B-ALL, T-ALL, CML, and AML), including imatinib (IM), multi TKI-resistant and bortezomib (BTZ)-resistant leukemic cell lines. Average IC 50 values of 5b in these cell lines were determined using ATP-based viability assay and plotted in a clustered heat map, indicating the superior efficacy against BCR-ABL1+ and AML leukemic cell lines, when compared to T-ALL cell lines (Figure ).