Bim and Bad mediate imatinib-induced killing of Bcr/Abl ⁺ leukemic cells, and resistance due to their loss is overcome by a BH3 mimetic

Abstract

Cell killing is a critical pharmacological activity of imatinib to eradicate Bcr/Abl + leukemias. We found that imatinib kills Bcr/Abl + leukemic cells by triggering the Bcl-2-regulated apoptotic pathway. Imatinib activated several proapoptotic BH3-only proteins: bim and bmf transcription was increased, and both Bim and Bad were activated posttranslationally. Studies using RNAi and cells from gene-targeted mice revealed that Bim plays a major role in imatinib-induced apoptosis of Bcr/Abl + leukemic cells and that the combined loss of Bim and Bad abrogates this killing. Loss of Bmf or Puma had no effect. Resistance to imatinib caused by Bcl-2 overexpression or loss of Bim (plus Bad) could be overcome by cotreatment with the BH3 mimetic ABT-737. These results demonstrate that Bim and Bad account for most, perhaps all, imatinib-induced killing of Bcr/Abl + leukemic cells and suggest previously undescribed drug combination strategies for cancer therapy.

Apoptosis-based dual molecular targeting by INNO-406, a second-generation Bcr-Abl inhibitor, and ABT-737, an inhibitor of antiapoptotic Bcl-2 proteins, against Bcr-Abl-positive leukemia

“…To identify the apoptotic pathway that is stimulated by INNO-406, we examined the effect of INNO-406 on genetically engineered K562 subclones that overexpressed human Bcl-2 (K562/Bcl-2) or a dominant-interfering mutant of Fasassociated death domain (FADD)/MORT1 (K562/FADD-DN), which inhibits death receptor-induced apoptosis; both molecules were labeled with an N-terminal Flag tag (Figure 1c). [21][22][23] We found that Bcl-2 overexpression blocked INNO-406-induced K562 cell death, whereas FADD-DN had no effect. Moreover, BV173R, a subclone of BV173, which expresses higher levels of Bcl-2 than parental BV173 cells, was less sensitive to INNO-406-induced cell death than BV173 (Figure 1c, d).…”

“…22,26 Treatment with INNO-406 also increased the levels of Bmf and Bik. Although INNO-406 did not change the overall levels of Bad, it induced Bad dephosphorylation ( Figure 2c).…”

The BCL-2 protein family, BH3-mimetics and cancer therapy

“…150,151 Furthermore, BMF as well as BIM are critical for the killing of non-transformed lymphoid cells as well as certain lymphoma cells by inhibitors of histone deacetylases. 110,135 BIM (with BAD and BMF also contributing) is critical for the killing of tumour cells that are dependent on oncogenic kinases by therapeutic agents that block their activity, such as inhibitors of MEK (acting downstream of mutant B-RAF in melanoma or colon carcinoma), 152 EGFR (lung cancer), [153][154][155] BCR-ABL (CML) 156,157 and VEGFR signalling (tumour angiogenesis). 158 Notably, a gene polymorphism that impairs the expression of BIM was found to explain the de novo resistance of BCR-ABL-driven CML to Gleevec and mutant EGFR-driven lung cancer to Iressa/ Tarceva in East Asian populations.…”

“…152,153,157,166,167 Such combinatorial therapeutic strategies would effectively neutralise all pro-survival BCL-2 family proteins and thereby efficiently activate apoptosis in malignant cells.…”

New frontiers in promoting tumour cell death: targeting apoptosis, necroptosis and autophagy

“…In vitro, ABT-737 has also been reported to synergise with conventional chemotherapy, g-irradiation and tyrosine kinase inhibitors, imatinib and gefitinib to reverse drug resistance and kill cancer cells (Cragg et al, 2009). Interestingly, imatinib-and gefitinib-induced death requires the upregulation of BH3-only proapoptotic protein, Bim (Kuroda et al, 2006;Cragg et al, 2007). It is likely that the synergistic death achieved by tyrosine kinase inhibitor co-treatment with ABT-737 is caused by ABT-737 liberation of Bim, which has been observed by Cragg et al (2008).…”