ABSTRACT
Clofarabine (CLO), a purine nucleoside analog with promising efficacy in acute myeloid leukemia (AML), inhibits the ribonucleotidereductase, p53R2. We have shown that p53R2 mRNA is up-regulated by decitabine (DEC), another drug with promising activity in AML. We developed a pharmacodynamic model to characterize the interaction between CLO and DEC on an AML cell line and down-regulated p53R2 protein to understand its role. These results confirm a role for p53R2 in both CLO and DEC mechanism of action, demonstrate synergism between these two drugs in this AML model and support the use of this combination in a future clinical trial.
Subject(s)
Adenine Nucleotides/pharmacology , Arabinonucleosides/pharmacology , Azacitidine/analogs & derivatives , Cell Cycle Proteins/metabolism , Ribonucleotide Reductases/metabolism , Azacitidine/pharmacology , Blotting, Western , Cell Line, Tumor , Cell Survival/drug effects , Clofarabine , Decitabine , Drug Synergism , Humans , Protein Biosynthesis/drug effectsABSTRACT
PURPOSE: Signal transducer and activator of transcription 3 (STAT3) has been shown to be constitutively active in approximately 50% of patients with acute myeloid leukemia and is associated with worse outcome. Arsenic trioxide (ATO) synergizes with the heat shock protein (HSP) 90 inhibitor, 17-DMAG, to down-regulate STAT3 activity. However, both agents up-regulate HSP70, an anti-apoptotic protein. We therefore examined whether down-regulating HSP70 with short interference (si) RNA will affect ATO and 17-DMAG effects on constitutive STAT3 activity. EXPERIMENTAL DESIGN: A semi-mechanistic pharmacodynamic model was used to characterize concentration-effect relationships of ATO and 17-DMAG effects on constitutive STAT3 activity and HSP70 expression with or without siRNA against HSP70 in a cell line model. RESULTS: Treatment with siRNA for HSP70 resulted in a stronger degree of synergism on down-regulation of STAT3 activity by ATO and 17-DMAG. However, treatment with siRNA for HSP70 resulted in less synergism on up-regulation of HSP70 by the two drugs. CONCLUSIONS: Down-regulation of HSP70 improves ATO and 17-DMAG effects on constitutive STAT3 activity. These results further provide a basis for studying the combined role of ATO with a HSP90 inhibitor such as 17-DMAG in AML with constitutive STAT3 activity.