Abstract
Heterogeneous upregulation of multiple prosurvival pathways underlies resistance to damage-induced apoptosis in acute lymphoblastic leukemia (ALL) cells despite normal p53 responses. Here, we show that the dual combination of insulin-like growth factor 1 (IGF1)/IGF1 receptor (IGF1/R) and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibition using AG1024 + U0126 can sensitize apoptosis-resistant ALL cells to ionizing radiation-induced DNA damage irrespective of effect of single pathway inhibition in vitro. This AG1024 + U0126 combination also significantly potentiates the ability of the core chemotherapy compounds vincristine, dexamethasone, and daunorubicin to kill ALL cells in vitro. Evidence of the synergistic action of AG1024 + U0126 in samples with variable basal levels of phosphorylated IGF1/Rβ and ERK1/2 suggested additional targets of this drug combination. Consistent with this, gene expression profiling identified 32 "synergy genes" differentially targeted by IGF1/R + MEK inhibition and, among these, Signal transducer and activator of transcription 6 (STAT6) and platelet-derived growth factor-associated protein 1 (PDAP1) were the most differentially downregulated cluster. Pearson correlation analysesrevealed that STAT6 and PDAP1 display significant expression codependency and a common expression pattern linked with other key "synergy" genes, supporting their predicted role in an STAT6-ERK-nuclear factor kappa beta (NF-κB) network. Knockdown studies revealed that loss of STAT6, but not PDAP1, impinges on the cell cycle, causing reduced numbers of viable cells. In combination with daunorubicin, STAT6 loss has an additive effect on cell killing, whereas PDAP1 loss is synergistic, indicating an important role of PDAP1 in the cellular response to this anthracycline. Inhibition of STAT6 or PDAP1 may therefore represent a potential novel therapeutic strategy for resistant ALL by enhancing sensitivity to chemotherapy.
Highlights
TagedPAlthough cure rates for childhood acute lymphoblastic leukemia (ALL) have increased dramatically over recent years through the integration of risk stratification into treatment protocols [1À3], failure of Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.exphem.2018.04.002
We show that the mechanism of this drug combination involves downregulation of signal transducer and activator of transcription 6 (STAT6) and PDGFassociated protein 1 (PDAP1), which appear to function in a predicted STAT6ÀERKÀNF-kB regulatory network that may be implicated in apoptosis resistance in childhood ALL
We identified that the specific combination of AG1024 (IGF1/R inhibitor) and U0126 (MEK inhibitor) was consistently active in sensitizing four DNA damage-resistant ALL to ionizing radiation (IR), whereas dual combinations involving the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 induced more variable responses (Figures 1A and B)
Summary
TagedPAlthough cure rates for childhood acute lymphoblastic leukemia (ALL) have increased dramatically over recent years through the integration of risk stratification into treatment protocols [1À3], failure of Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.exphem.2018.04.002. Preclinical studies on adverse-risk Ph-like ALL, which frequently harbors Janus kinase (JAK) and cytokine receptor-like factor 2 (CRLF2) mutations, indicate sensitivity to JAK inhibition and mammalian target of rapamycin (mTOR)/PI3K inhibitors [10,16,17], whereas plateletderived growth factor beta (PDGFB)- and ABL-rearranged Ph-like disease instead appear to display responsiveness to the tyrosine kinase inhibitors imatinib and dasatinib [8,18,19] Consistent with these findings, our previous work showed that childhood ALL displaying both poor clinical outcome and impaired apoptotic responses to DNA damage in vitro exhibit heterogeneous upregulation of multiple prosurvival pathways, which notably involves the PI3K, insulin-like growth factor 1 (IGF1) and MAPK pathways [20,21]. We show that the mechanism of this drug combination involves downregulation of signal transducer and activator of transcription 6 (STAT6) and PDGFassociated protein 1 (PDAP1), which appear to function in a predicted STAT6ÀERKÀNF-kB regulatory network that may be implicated in apoptosis resistance in childhood ALL
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