The importance of MCL-1 in leukemogenesis has prompted development of MCL-1 antagonists e.g.,S63845,MIK665.However,their effectiveness in acute myeloid leukemia(AML)is limited by compensatory MCL-1 accumulation via th...The importance of MCL-1 in leukemogenesis has prompted development of MCL-1 antagonists e.g.,S63845,MIK665.However,their effectiveness in acute myeloid leukemia(AML)is limited by compensatory MCL-1 accumulation via the ubiquitin proteasome system.Here,we investigated mechanisms by which kinase inhibitors with Src inhibitory activity e.g.,bosutinib(SKI-606)might circumvent this phenomenon.MCL-1 antagonist/SKI-606 co-administration synergistically induced apoptosis in diverse AML cell lines.Consistently,Src or MCL-1 knockdown with shRNA markedly sensitized cells to MCL-1 inhibitors or SKI-606 respectively,while ectopic MCL-1 expression significantly diminished apoptosis.Mechanistically,MCL-1 antagonist exposure induced MCL-1 up-regulation,an event blocked by Src inhibitors or Src shRNA knock-down.MCL-1 down-regulation was associated with diminished transcription and increased K48-linked degradative ubiquitination.Enhanced cell death depended functionally upon down-regulation of phosphorylated STAT3(Tyr705/Ser727)and cytoprotective downstream targets c-Myc and BCL-xL,as well as BAX/BAK activation,and NOXA induction.Importantly,the Src/MCL-1 inhibitor regimen robustly killed primary AML cells,including primitive progenitors,but spared normal hematopoietic CD34+cells and human cardiomyocytes.Notably,the regimen significantly improved survival in an MV4-11 cell xenograft model,while reducing tumor burden in two patient-derived xenograft(PDX)AML models and increased survival in a third.These findings argue that Src inhibitors such as SKI-606 potentiate MCL-1 antagonist anti-leukemic activity in vitro and in vivo by blocking MCL-1 antagonist-mediated cytoprotective MCL-1 accumulation by promoting degradative ubiquitination,disrupting STAT-3-mediated transcription,and inducing NOXA-mediated MCL-1 degradation.They also suggest that this strategy may improve MCL-1 antagonist efficacy in AML and potentially other malignancies.展开更多
基金funding from NIH-NCI Cancer Center Support Grant P30 CA016059supported by P30 CA16059,5UM1CA186644,CA205607.
文摘The importance of MCL-1 in leukemogenesis has prompted development of MCL-1 antagonists e.g.,S63845,MIK665.However,their effectiveness in acute myeloid leukemia(AML)is limited by compensatory MCL-1 accumulation via the ubiquitin proteasome system.Here,we investigated mechanisms by which kinase inhibitors with Src inhibitory activity e.g.,bosutinib(SKI-606)might circumvent this phenomenon.MCL-1 antagonist/SKI-606 co-administration synergistically induced apoptosis in diverse AML cell lines.Consistently,Src or MCL-1 knockdown with shRNA markedly sensitized cells to MCL-1 inhibitors or SKI-606 respectively,while ectopic MCL-1 expression significantly diminished apoptosis.Mechanistically,MCL-1 antagonist exposure induced MCL-1 up-regulation,an event blocked by Src inhibitors or Src shRNA knock-down.MCL-1 down-regulation was associated with diminished transcription and increased K48-linked degradative ubiquitination.Enhanced cell death depended functionally upon down-regulation of phosphorylated STAT3(Tyr705/Ser727)and cytoprotective downstream targets c-Myc and BCL-xL,as well as BAX/BAK activation,and NOXA induction.Importantly,the Src/MCL-1 inhibitor regimen robustly killed primary AML cells,including primitive progenitors,but spared normal hematopoietic CD34+cells and human cardiomyocytes.Notably,the regimen significantly improved survival in an MV4-11 cell xenograft model,while reducing tumor burden in two patient-derived xenograft(PDX)AML models and increased survival in a third.These findings argue that Src inhibitors such as SKI-606 potentiate MCL-1 antagonist anti-leukemic activity in vitro and in vivo by blocking MCL-1 antagonist-mediated cytoprotective MCL-1 accumulation by promoting degradative ubiquitination,disrupting STAT-3-mediated transcription,and inducing NOXA-mediated MCL-1 degradation.They also suggest that this strategy may improve MCL-1 antagonist efficacy in AML and potentially other malignancies.
