Tipping the Noxa/Mcl-1 Balance Overcomes ABT-737 Resistance in Chronic Lymphocytic Leukemia

Purpose: The lymph node microenvironment promotes resistance to chemotherapy in chronic lymphocytic leukemia (CLL), partly through induction of BCL2 family prosurvival proteins. Currently available inhibitors do not target all BCL2 family prosurvival proteins and their effectiveness is also modified by proapoptotic BCL2 homology domain 3 (BH3) only protein expression. The goal of this study was to evaluate synergy between the eIF4E/eIF4G interaction inhibitor, 4EGI-1, and the BH3 mimetic, ABT-737.Experimental Design: CLL cells were cultured in conditions to mimic the lymph node microenvironment. Protein synthesis and cap-complex formation were determined. Polysome association of mRNAs from BCL2 family survival genes was analyzed by translational profiling. The effects of 4EGI-1 and the BCL2/ BCL2L1 antagonist, ABT-737, on CLL cell apoptosis were determined.Results: Protein synthesis was increased approximately 6-fold by stromal cell/CD154 culture in a phosphoinositide 3-kinase a (PI3Ka)-specific manner and was reduced by 4EGI-1. PI3K inhibitors and 4EGI-1 also reduced cap-complex formation but only 4EGI-1 consistently reduced BCL2L1 and BCL2A1 protein levels. 4EGI-1, but not PI3K inhibitors or rapamycin, induced an endoplasmic reticulum stress response including proapoptotic NOXA and the translation inhibitor phosphorylated eIF2a. 4EGI-1 and ABT-737 synergized to cause apoptosis, independent of levels of prosurvival protein expression in individual patients.Conclusions: Overall protein synthesis and cap-complex formation are induced by microenvironment stimuli in CLL. Inhibition of the cap-complex was not sufficient to repress BCL2 family prosurvival expression, but 4EGI-1 inhibited BCL2A1 and BCL2L1 while inducing NOXA through cap-dependent and -independent mechanisms. 4EGI-1 and ABT-737 synergized to produce apoptosis, and these agents may be the basis for a therapeutically useful combination.

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“…that knockdown of NOXA enhances resistance to ABT-737 in primary B cells and induction of NOXA by fludarabine synergizes with ABT-737 in CLL (7).…”

Section: Discussionmentioning

confidence: 92%

Cap-Translation Inhibitor, 4EGI-1, Restores Sensitivity to ABT-737 Apoptosis through Cap-Dependent and -Independent Mechanisms in Chronic Lymphocytic Leukemia

Willimott

Beck

Ahearne

et al. 2013

Clinical Cancer Research

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“…These results suggest that inhibition of Mcl-1 in TNBC could resensitize tumors following acquired resistance to Bcl-2 family chemotherapeutics, as is seen in other cancer types. 26,27,41 We next sought to understand why some (but not all) cell lines responded to Mcl-1 knockdown. Each cell line in this TNBC panel expresses executioner proteins Bak, Bax and BH3-only proteins, and their mitochondria depolarizes in response to Bim.…”

Section: Discussionmentioning

confidence: 99%

Myeloid cell leukemia-1 is an important apoptotic survival factor in triple-negative breast cancer

et al. 2015

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Breast cancer is the second-most frequently diagnosed malignancy in US women. The triple-negative breast cancer (TNBC) subtype, which lacks expression of the estrogen receptor, progesterone receptor and human epidermal growth factor receptor-2, afflicts 15% of patients and is refractory to current targeted therapies. Like many cancers, TNBC cells often deregulate programmed cell death by upregulating anti-apoptotic proteins of the B-cell CLL/lymphoma 2 (Bcl-2) family. One family member, myeloid cell leukemia-1 (Mcl-1), is commonly amplified in TNBC and correlates with a poor clinical prognosis. Here we show the effect of silencing Mcl-1 and Bcl-2-like protein 1 isoform 1 (Bcl-xL) expression on viability in a panel of seventeen TNBC cell lines. Cell death was observed in a subset upon Mcl-1 knockdown. In contrast, Bcl-xL knockdown only modestly reduced viability, indicating that Mcl-1 is a more important survival factor. However, dual silencing of both Mcl-1 and Bcl-xL reduced viability in most cell lines tested. These proliferation results were recapitulated by BH3 profiling experiments. Treatment with a Bcl-xL and Bcl-2 peptide had only a moderate effect on any of the TNBC cell lines, however, co-dosing an Mcl-1-selective peptide with a peptide that inhibits Bcl-xL and Bcl-2 was effective in each line tested. Similarly, the selective Bcl-xL inhibitor WEHI-539 was only weakly cytotoxic across the panel, but sensitization by Mcl-1 knockdown markedly improved its EC 50 . ABT-199, which selectively inhibits Bcl-2, did not synergize with Mcl-1 knockdown, indicating the relatively low importance of Bcl-2 in these lines. Mcl-1 sensitivity is not predicted by mRNA or protein levels of a single Bcl-2 family member, except for only a weak correlation for Bak and Bax protein expression. However Breast cancer is the second-most frequently diagnosed malignancy in US women with 230 000 new cases and 40 000 deaths in 2011. The triple-negative breast carcinoma (TNBC) subtype, which does not express the estrogen receptor (ER) and progesterone receptor (PR) and lacks overexpression of human epidermal growth factor receptor-2 (HER2), afflicts nearly 15% of all breast cancer patients and remains refractory to currently available endocrine and HER2-directed therapies.1,2 The current standard of care for TNBC is radiation and neoadjuvant cytotoxic chemotherapy, and carries a poor clinical prognosis. [3][4][5] As with most cancers, TNBC cells are under metabolic and oncogenic stress and require inhibition of the intrinsic apoptotic pathway for survival. 6 Under normal physiological conditions, this pathway is tightly regulated by both pro-and anti-apoptotic members of the B-cell CLL/lymphoma 2 (Bcl-2) family. Stressors such as DNA damage, hypoxia or oncogenic signaling, cause increased expression or translocation of proapoptotic Bcl-2 family members, such as Bim, Bad and Noxa, to the mitochondria. 7 These proteins subsequently trigger pore formation in the mitochondrial outer membrane via induced multimerization of Bak or Bax, a proc...

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“…The transfected cells were evaluated for their sensitivity to a panel of therapies, including mitoxantrone, ABT-737, and CXL017. Mitoxantrone was selected for evaluation as a standard therapy, whereas ABT-737 was selected because overexpression of Mcl-1 is known to induce resistance to ABT-737 (Oltersdorf et al, 2005;Lucas et al, 2012;Mazumder et al, 2012;Tromp et al, 2012). CXL017 was evaluated to explore whether Mcl-1 may be less effective in conferring resistance to CXL017.…”

Section: Resultsmentioning

confidence: 99%

Overexpression of Mcl-1 Confers Multidrug Resistance, Whereas Topoisomerase IIβDownregulation Introduces Mitoxantrone-Specific Drug Resistance in Acute Myeloid Leukemia

Hermanson

Das

et al. 2013

Mol Pharmacol

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Drug resistance is a serious challenge in cancer treatment and can be acquired through multiple mechanisms. These molecular changes may introduce varied extents of resistance to different therapies and need to be characterized for optimal therapy choice. A recently discovered small molecule, ethyl-2-amino-6-(3,5-dimethoxyphenyl)-4-(2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate) (CXL017), reveals selective cytotoxicity toward drug-resistant leukemia. A drug-resistant acute myeloid leukemia cell line, HL60/MX2, also failed to acquire resistance to CXL017 upon chronic exposure and regained sensitivity toward standard therapies. In this study, we investigated the mechanisms responsible for HL60/MX2 cells' drug resistance and the molecular basis for its resensitization. Results show that the HL60/MX2 cell line has an elevated level of Mcl-1 protein relative to the parental cell line, HL60, and its resensitized cell line, HL60/ MX2/CXL017, whereas it has a reduced level of topoisomerase IIb. Mcl-1 overexpression in HL60/MX2 cells is mainly regulated through phospho-extracellular signal-regulated protein kinases 1 and 2-mediated Mcl-1 stabilization, whereas the reduction of topoisomerase IIb in HL60/MX2 cells is controlled through genetic downregulation. Upregulating Mcl-1 introduces multidrug resistance to standard therapies, whereas its downregulation results in significant cell death. Downregulating topoisomerase IIb confers resistance specifically to mitoxantrone, not to other topoisomerase II inhibitors. Overall, these data suggest that Mcl-1 overexpression is a critical determinant for cross-resistance to standard therapies, whereas topoisomerase IIb downregulation is specific to mitoxantrone resistance.

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Tipping the Noxa/Mcl-1 Balance Overcomes ABT-737 Resistance in Chronic Lymphocytic Leukemia

Cited by 84 publications

References 38 publications

Cap-Translation Inhibitor, 4EGI-1, Restores Sensitivity to ABT-737 Apoptosis through Cap-Dependent and -Independent Mechanisms in Chronic Lymphocytic Leukemia

Cap-Translation Inhibitor, 4EGI-1, Restores Sensitivity to ABT-737 Apoptosis through Cap-Dependent and -Independent Mechanisms in Chronic Lymphocytic Leukemia

Myeloid cell leukemia-1 is an important apoptotic survival factor in triple-negative breast cancer

Overexpression of Mcl-1 Confers Multidrug Resistance, Whereas Topoisomerase IIβDownregulation Introduces Mitoxantrone-Specific Drug Resistance in Acute Myeloid Leukemia

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