Recent advances in the development of Mcl-1 inhibitors for cancer therapy.
Hird Alexander W,Tron Adriana E
Pharmacology & therapeutics
Dysregulation of the mitochondrial apoptotic pathway controlled by members of the Bcl-2 protein family plays a central role in cancer development and resistance to conventional cytotoxic as well as targeted therapies. Hence, selective inhibition of pro-survival Bcl-2 family of proteins to activate apoptosis in malignant cells represents an exciting anti-cancer strategy. The remarkable clinical performance of the selective Bcl-2 antagonist venetoclax has highlighted the potential for selective inhibitors of the other pro-survival members of the Bcl-2 family, particularly Mcl-1. Here we review the latest progress on the discovery and development of selective inhibitors of Mcl-1 that are undergoing clinical evaluation for cancer therapy.
Molecular Comprehension of Mcl-1: From Gene Structure to Cancer Therapy.
Senichkin Viacheslav V,Streletskaia Alena Y,Zhivotovsky Boris,Kopeina Gelina S
Trends in cell biology
Among cell death regulators, members of the Bcl-2 family are of interest because they are highly conserved across species and represent promising targets for anticancer therapy. This family and its associated proteins include more than 25 members, with either anti- or proapoptotic functions. Although the overall regulation of apoptosis by Bcl-2 family proteins is now well understood, targeted therapy requires careful consideration of individual members of the family and their crosstalk. One of the most studied representatives of the Bcl-2 family is antiapoptotic Mcl-1. After 25 years of investigations, a large amount of data regarding Mcl-1's regulation and functions has been compiled. In this review, we summarize current knowledge about Mcl-1, focusing on molecular aspects relevant to Mcl-1-targeted therapies.
MCL-1 inhibitors - where are we now (2019)?
Expert opinion on therapeutic patents
: Myeloid cell leukemia-1 (MCL-1) is an anti-apoptotic member of the B-cell lymphoma-2 (BCL-2) family of proteins that regulates apoptosis. Elevated levels of MCL-1 contribute to tumorigenesis and resistance, not only to conventional chemotherapies but also to targeted therapies, including the BCL-2 selective inhibitor venetoclax. Accordingly, researchers in both the pharmaceutical industry and academia have been actively seeking MCL-1 inhibitors in the quest for new anti-cancer drugs. : This review covers the patent literature on the discovery and development of small-molecule inhibitors of MCL-1 since 2017. : Pharmacologic inhibition of MCL-1's oncogenic activity has certainly come of age with the discovery of numerous inhibitors spanning a variety of chemotypes that selectively inhibit MCL-1 in the picomolar range and with on-target cell activity. Furthermore, seminal research by Servier has demonstrated for the first time that MCL-1 inhibition is tolerable in animal models of cancer, paving the way for the six Phase 1 clinical trials that are currently underway for hematological malignancies, among other cancers. After more than a decade of research, the hurdles and obstacles are mostly behind us, and uncovering the therapeutic impact of disrupting the protein-protein interactions of MCL-1 in humans is imminent.
A-1210477, a selective MCL-1 inhibitor, overcomes ABT-737 resistance in AML.
Wang Qing,Hao Siguo
Acute myeloid leukemia (AML) is one of the most common hematological malignancies. It is difficult to treat since it easily develops resistance to therapeutic drugs. Myeloid cell leukemia 1 (MCL-1), BCL-2 and BCL-XL, which belong to the anti-apoptotic group of proteins in the BCL-2 family, are overexpressed in AML. The effects of inhibitors that target anti-apoptotic proteins of the BCL-2 family in AML were evaluated in the present study. MCL-1 protein levels of HL60, MOLM13, OCI-AML3 and MV4-11 cell lines were investigated. Furthermore, following treatment with MCL-1-selective antagonist A-1210477 and/or BCL-2/BCL-XL antagonist ABT-737, cell viability was detected. The chimera rate of human CD45(+) cells of bone marrow from mouse models was analyzed via flow cytometry and immunohistochemistry using murine tissues (lung, spleen and liver). The data revealed that the HL-60 cell line, which exhibited a low MCL-1 protein level, and MOLM-13 and MV4-11 cell lines, whose MCL level was intermediate, were sensitive to ABT-737, whereas OCI-AML3 cells, which exhibited a high MCL-1 level, were insensitive to ABT-737. However, multiple AML mouse models and AML cell lines were sensitive to the MCL-1-selective antagonist A-1210477. The results of the present study indicated that the MCL-1-selective antagonist could overcome the resistance to the BCL-2/BCL-XL antagonist (ABT-737) and .
AMG-176, an Mcl-1 Antagonist, Shows Preclinical Efficacy in Chronic Lymphocytic Leukemia.
Yi Xue,Sarkar Aloke,Kismali Gorkem,Aslan Burcu,Ayres Mary,Iles LaKesla R,Keating Michael J,Wierda William G,Long James P,Bertilaccio Maria Teresa Sabrina,Gandhi Varsha
Clinical cancer research : an official journal of the American Association for Cancer Research
PURPOSE:Survival of CLL cells due to the presence of Bcl-2 and Mcl-1 has been established. Direct inhibition of Bcl-2 by venetoclax and indirect targeting of Mcl-1 with transcription inhibitors have been successful approaches for CLL. AMG-176 is a selective and direct antagonist of Mcl-1, which has shown efficacy in several hematologic malignancies; however, its effect on CLL is elusive. We evaluated biological and molecular effects of AMG-176 in primary CLL cells. EXPERIMENTAL DESIGN:Using samples from patients ( = 74) with CLL, we tested effects of AMG-176 on CLL and normal hematopoietic cell death and compared importance of CLL prognostic factors on this biological activity. We evaluated CLL cell apoptosis in the presence of stromal cells and identified cell death pathway including stabilization of Mcl-1 protein. Finally, we tested a couplet of AMG-176 and venetoclax in CLL lymphocytes. RESULTS:AMG-176 incubations resulted in time- and dose-dependent CLL cell death. At 100 and 300 nmol/L, there was 30% and 45% cell death at 24 hours. These concentrations did not result in significant cell death in normal hematopoietic cells. Presence of stroma did not affect AMG-176-induced CLL cell death. IGHV unmutated status, high β2M and Mcl-1 protein levels resulted in slightly lower cell death. Mcl-1, but not Bcl-2 protein levels, in CLL cells increased with AMG-176. Low concentrations of venetoclax (1-30 nmol/L) were additive or synergistic with AMG-176. CONCLUSIONS:AMG-176 is active in inducing CLL cell death while sparing normal blood cells. Combination with low-dose venetoclax was additive or synergistic.
Design, synthesis and biological evaluation of tyrosine derivatives as Mcl-1 inhibitors.
Liu Lulu,Liu Renshuai,Yang Xinying,Hou Xuben,Fang Hao
European journal of medicinal chemistry
The upregulation of the protein myeloid cell leukemia-1 (Mcl-1) is closely associated with various human cancers, which can result in the evasion of apoptosis and a low survival rate. Therefore, developing Mcl-1 inhibitors has become a promising paradigm for cancer therapy. Herein, we designed and synthesized a novel series of tyrosine derivatives, among which compounds 5g, 6l and 6c exhibited very high binding affinity to Mcl-1 with K values of 0.18, 0.27 and 0.23 μM, respectively. Interestingly, compound 6l showed not only potent activity against Mcl-1 but also considerable selectivity over Bcl-2 and Bcl-xL, which was rationalized by molecular docking and fragment-centric topographical mapping (FCTM). It is worth noting that compounds 5g, 6l and 6c displayed potent antiproliferative activity against several cancer cell lines and could induce apoptosis of KM3 and HepG2 cells in a dose-dependent manner.
Targeting MCL-1 in hematologic malignancies: Rationale and progress.
Wei Andrew H,Roberts Andrew W,Spencer Andrew,Rosenberg Aaron Seth,Siegel David,Walter Roland B,Caenepeel Sean,Hughes Paul,McIver Zach,Mezzi Khalid,Morrow Phuong Khanh,Stein Anthony
Myeloid cell leukemia sequence 1 (MCL-1) is an antiapoptotic protein that plays a key role in promoting cell survival in multiple myeloma (MM), acute myeloid leukemia (AML), and non-Hodgkin lymphoma (NHL). Overexpression of MCL-1 is associated with treatment resistance and poor prognosis; thus, MCL-1 inhibitors are rational therapeutic options for malignancies depending on MCL-1. Several MCL-1 inhibitors have entered clinical trials, including AZD5991, S64315, AMG 176, and AMG 397. A key area of investigation is whether MCL-1 inhibitors will complement the activity of BCL-2 inhibitors, such as venetoclax, and synergistically enhance anti-tumor efficacy when given in combination with other anti-cancer drugs. Another important question is whether a safe therapeutic window can be found for this new class of inhibitors. In summary, inhibition of MCL-1 shows potential as a treatment for hematologic malignancies and clinical evaluation of MCL-1 inhibitors is currently underway.
Mcl-1 as a "barrier" in cancer treatment: Can we target it now?
Pervushin Nikolay V,Senichkin Viacheslav V,Zhivotovsky Boris,Kopeina Gelina S
International review of cell and molecular biology
During the last two decades, the study of Mcl-1, an anti-apoptotic member of the Bcl-2 family, attracted researchers due to its important role in cancer cell survival and tumor development. The significance of Mcl-1 protein in resistance to chemotherapeutics makes it an attractive target in cancer therapy. Here, we discuss the diverse possibilities for indirect Mcl-1 inhibition through its downregulation, for example, via targeting for proteasomal degradation or blockage of translation and transcription. We also provide an overview of the direct blocking of protein-protein interactions with pro-apoptotic Bcl-2 family proteins, including examples of the most promising regulators of Mcl-1 and selective BH3-mimetics, which at present are under clinical evaluation. Moreover, several approaches for the co-targeting of Mcl-1 and other proteins (e.g., CDKs) are also presented. In addition, we highlight the broad spectrum of problems that accompanied the discovery and development of effective Mcl-1 inhibitors.
[Expression and Clinical Sgnificance of IL-6, IL-6R and MCL-1 in Patients with Multiple Myeloma].
Wang Bi-Wei,Sun Hui,Chen Xi,Li Xiao-Long,Liu Hong-Tao,Chai Tie
Zhongguo shi yan xue ye xue za zhi
OBJECTIVE:To study the expression level and clinical significance of serum interleukin-6 (IL-6), its receptor (IL-6R) and myeloid cell leukemin-1(MCL-1) in patients with multiple myeloma（MM）. METHODS:Ninety-eight cases of MM treated in our hospital from January 2014 to January 2019 were selected, and the patients were divided into three groups according to their DS stage: stage I (27 cases), stage II (34 cases) and stage III (37 cases). The expression levels of IL-6, IL-6R and MCL-1 in patients at different DS stages were compared, and the prognostic-related factors were analyzed. RESULTS:The expression levels of IL-6 and MCL-1 in patients rised with DS stages, and the difference showed statistical significance (P<0.05), but the level of IL-6R in three groups showed no significant difference (P>0.05). The prognosis of patients with different levels of IL-6 and MCL-1 was compared and the results were as follows, the median survival time of 41 patients with IL-6≥80 pg/ml was 33.0 months, and that of 57 patients with IL-6 <80 pg/ml was 33.5 months, which showed no significant difference (P>0.05). The median survival time of 45 patients with MCL-1≥200 pg/ml was 30.5 months, and that of 53 patients with MCL-1 <200 pg/ml was 37.0 months, and their difference was statistically significant (P<0.05). Sex, age, β2-MG and Hb not significantly correlated with prognosis of patients (P>0.05), however, DS stage, IL-6 and MCL-1 correlated with prognosis of patients（r=2.261，r=1.754，r=1.905）. CONCLUSION:The levels of IL-6 and MCL-1 in patients with multiple myeloma correlate with the DS stage and prognosis of patients.
MCL-1 is essential for survival but dispensable for metabolic fitness of FOXP3 regulatory T cells.
Teh Charis E,Robbins Alissa K,Henstridge Darren C,Dewson Grant,Diepstraten Sarah T,Kelly Gemma,Febbraio Mark A,Gabriel Sarah S,O'Reilly Lorraine A,Strasser Andreas,Gray Daniel H D
Cell death and differentiation
FOXP3 regulatory T (Treg) cells are essential for maintaining immunological tolerance. Given their importance in immune-related diseases, cancer and obesity, there is increasing interest in targeting the Treg cell compartment therapeutically. New pharmacological inhibitors that specifically target the prosurvival protein MCL-1 may provide this opportunity, as Treg cells are particularly reliant upon this protein. However, there are two distinct isoforms of MCL-1; one located at the outer mitochondrial membrane (OMM) that is required to antagonize apoptosis, and another at the inner mitochondrial membrane (IMM) that is reported to maintain IMM structure and metabolism via ATP production during oxidative phosphorylation. We set out to elucidate the relative importance of these distinct biological functions of MCL-1 in Treg cells to assess whether MCL-1 inhibition might impact upon the metabolism of cells able to resist apoptosis. Conditional deletion of Mcl1 in FOXP3 Treg cells resulted in a lethal multiorgan autoimmunity due to the depletion of the Treg cell compartment. This striking phenotype was completely rescued by concomitant deletion of the apoptotic effector proteins BAK and BAX, indicating that apoptosis plays a pivotal role in the homeostasis of Treg cells. Notably, MCL-1-deficient Treg cells rescued from apoptosis displayed normal metabolic capacity. Moreover, pharmacological inhibition of MCL-1 in Treg cells resistant to apoptosis did not perturb their metabolic function. We conclude that Treg cells require MCL-1 only to antagonize apoptosis and not for metabolism. Therefore, MCL-1 inhibition could be used to manipulate Treg cell survival for clinical benefit without affecting the metabolic fitness of cells resisting apoptosis.
Pairing MCL-1 inhibition with venetoclax improves therapeutic efficiency of BH3-mimetics in AML.
Hormi Myriam,Birsen Rudy,Belhadj Maya,Huynh Tony,Cantero Aguilar Lilia,Grignano Eric,Haddaoui Lamya,Guillonneau Francois,Mayeux Patrick,Hunault Mathilde,Tamburini Jérôme,Kosmider Olivier,Fontenay Michaela,Bouscary Didier,Chapuis Nicolas
European journal of haematology
OBJECTIVES:Venetoclax combined with hypomethylating agents is a new therapeutic strategy frequently used for treating AML patients who are not eligible for conventional chemotherapy. However, high response rates are heterogeneous due to different mechanisms mediating resistance to venetoclax such as up-regulation of MCL-1 expression. We thus tested the anti-leukemic activity of S63845, a specific MCL-1 inhibitor. METHODS:Apoptosis induces by S63845 with or without venetoclax was evaluated in primary AML samples and in AML cell lines co-cultured or not with bone marrow (BM) mesenchymal stromal cells. Sensitivity of leukemic cells to S63845 was correlated to the expression level of BCL-2, MCL-1, and BCL-XL determined by Western Blot and mass spectrometry-based proteomics. RESULTS:We observed that even if MCL-1 expression is weak compared to BCL-2, S63845 induces apoptosis of AML cells and strongly synergizes with venetoclax. Furthermore, AML cells resistant to venetoclax are highly sensitive to S63845. Interestingly, the synergistic effect of S63845 toward venetoclax-mediated apoptosis of AML cells is still observed in a context of interaction with the BM microenvironment that intrinsically mediates resistance to BCL2 inhibition. CONCLUSION:These results are therefore of great relevance for clinicians as they provide the rational for combining BCL-2 and MCL-1 inhibition in AML.
Mcl-1-mediated mitochondrial fission protects against stress but impairs cardiac adaptation to exercise.
Moyzis Alexandra G,Lally Navraj S,Liang Wenjing,Leon Leonardo J,Najor Rita H,Orogo Amabel M,Gustafsson Åsa B
Journal of molecular and cellular cardiology
Myeloid cell leukemia-1 (Mcl-1) is a structurally and functionally unique anti-apoptotic Bcl-2 protein. While elevated levels of Mcl-1 contribute to tumor cell survival and drug resistance, loss of Mcl-1 in cardiac myocytes leads to rapid mitochondrial dysfunction and heart failure development. Although Mcl-1 is an anti-apoptotic protein, previous studies indicate that its functions extend beyond regulating apoptosis. Mcl-1 is localized to both the mitochondrial outer membrane and matrix. Here, we have identified that Mcl-1 in the outer mitochondrial membrane mediates mitochondrial fission, which is independent of its anti-apoptotic function. We demonstrate that Mcl-1 interacts with Drp1 to promote mitochondrial fission in response to various challenges known to perturb mitochondria morphology. Induction of fission by Mcl-1 reduces nutrient deprivation-induced cell death and the protection is independent of its BH3 domain. Finally, cardiac-specific overexpression of Mcl-1, but not Mcl-1, contributes to a shift in the balance towards fission and leads to reduced exercise capacity, suggesting that a pre-existing fragmented mitochondrial network leads to decreased ability to adapt to an acute increase in workload and energy demand. Overall, these findings highlight the importance of Mcl-1 in maintaining mitochondrial health in cells.
HIF-1α suppresses myeloma progression by targeting Mcl-1.
Wu Feng,Tong Dong-Dong,Ni Lei,Wang Lu-Min,Wang Meng-Chang
International journal of clinical and experimental pathology
HIF-1α is involved in the carcinogenesis and progression of multiple types of cancer. However, the precise role of HIF-1α is unclear in multiple myeloma. Through the qRT-PCR and CCK-8 assays, we demonstrated that silencing the expression of HIF-1α and Mcl-1, MM proliferation can be decreased and apoptosis can be induced. Next, using the GEO database, we found that Mcl-1 was increased in MMs. Mcl-1 overexpression counterbalanced the tumor suppressing effect of siHIF-1α on MM apoptosis. Additionally, HIF-1α acting as a transcription factor, could directly target the promoter region of Mcl-1 to promote Mcl-1 expression. Based on the experimental result, our findings strongly suggest that HIF-1α regulated the progression of MMs by directly targeting the Mcl-1.
Discovery of a Copper-Based Mcl-1 Inhibitor as an Effective Antitumor Agent.
Lu Xing,Liu Yan-Cheng,Orvig Chris,Liang Hong,Chen Zhen-Feng
Journal of medicinal chemistry
Myeloid cell leukemia 1 (Mcl-1), which belongs to the Bcl-2 family of prosurvival proteins, is a key regulator of cancer cell survival. To date, few drug-like Mcl-1 inhibitors have been reported. Herein, we report the preparation of 10 copper complexes with 9-substituted β-carboline ligands that act as metal-based Mcl-1 inhibitors. Complex was identified as a potent and selective Mcl-1 inhibitor with strong antitumor activity. Mechanistic studies demonstrated that complex disrupted Mcl-1-Bax/Bak heterodimerization and induced Bax/Bak-dependent apoptosis. In addition, complex significantly ( < 0.001) inhibited tumor growth , induced tumor necrosis, and extended survival time in an NCI-H460 xenograft model. Furthermore, complex showed no apparent toxicity in mice. Together, these findings indicate that complex is a copper-based Mcl-1 inhibitor with high efficacy and low toxicity that could be developed for the treatment of Mcl-1-related cancers.
Multiscale Model Identifies Improved Schedule for Treatment of Acute Myeloid Leukemia In Vitro With the Mcl-1 Inhibitor AZD5991.
Goliaei Ardeshir,Woods Haley A,Tron Adriana E,Belmonte Matthew A,Secrist J Paul,Ferguson Douglas,Drew Lisa,Fretland Adrian J,Aldridge Bree B,Gibbons Francis D
CPT: pharmacometrics & systems pharmacology
Anticancer efficacy is driven not only by dose but also by frequency and duration of treatment. We describe a multiscale model combining cell cycle, cellular heterogeneity of B-cell lymphoma 2 family proteins, and pharmacology of AZD5991, a potent small-molecule inhibitor of myeloid cell leukemia 1 (Mcl-1). The model was calibrated using in vitro viability data for the MV-4-11 acute myeloid leukemia cell line under continuous incubation for 72 hours at concentrations of 0.03-30 μM. Using a virtual screen, we identified two schedules as having significantly different predicted efficacy and showed experimentally that a "short" schedule (treating cells for 6 of 24 hours) is significantly better able to maintain the rate of cell kill during treatment than a "long" schedule (18 of 24 hours). This work suggests that resistance can be driven by heterogeneity in protein expression of Mcl-1 alone without requiring mutation or resistant subclones and demonstrates the utility of mathematical models in efficiently identifying regimens for experimental exploration.
Downregulation of CDC20 Increases Radiosensitivity through Mcl-1/p-Chk1-Mediated DNA Damage and Apoptosis in Tumor Cells.
International journal of molecular sciences
Radiotherapy is an important modality for the local control of human cancers, but the radioresistance induced by aberrant apoptotic signaling is a hallmark of cancers. Restoring the aberrant apoptotic pathways is an emerging strategy for cancer radiotherapy. In this study, we determined that targeting cell division cycle 20 (CDC20) radiosensitized colorectal cancer (CRC) cells through mitochondrial-dependent apoptotic signaling. CDC20 was overexpressed in CRC cells and upregulated after radiation. Inhibiting CDC20 activities genetically or pharmacologically suppressed the proliferation and increased radiation-induced DNA damage and intrinsic apoptosis in CRC cells. Mechanistically, knockdown of CDC20 suppressed the expression of antiapoptotic protein Mcl-1 but not other Bcl-2 family proteins. The expressions of CDC20 and Mcl-1 respond to radiation simultaneously through direct interaction, as evidenced by immunoprecipitation and glutathione S-transferase (GST) pull-down assays. Subsequently, decreased Mcl-1 expression inhibited the expression level of phosphorylated checkpoint kinase 1 (p-Chk1), thereby resulting in impaired DNA damage repair through downregulating the homologous recombination repair protein Rad51 and finally causing apoptotic signaling. In addition, both CDC20 and Chk1 inhibitors together, through in vivo studies, confirmed the radiosensitizing effect of CDC20 via inhibiting Mcl-1 and p-Chk1 expression. In summary, our results indicate that targeting CDC20 is a promising strategy to improve cancer radiotherapy.
Recent Advances in the Development of Selective Mcl-1 Inhibitors for the Treatment of Cancer (2017-Present).
Fan Ying,Hou Xuben,Fang Hao
Recent patents on anti-cancer drug discovery
BACKGROUND:Myeloid cell leukemia-1 (Mcl-1) protein, as a critical pro-survival member of the B-cell lymphoma 2 (Bcl-2) protein family, plays an important role in apoptosis, carcinogenesis and resistance to chemotherapies. Hence, potently and selectively inhibiting Mcl-1 to induce apoptosis has become a widely accepted anticancer strategy. OBJECTIVE:This review intends to provide a comprehensive overview of patents and primary literature, published from 2017 to present, on small molecule Mcl-1 inhibitors with various scaffolds. By analyzing the modes of compound-protein interactions, the similarities and differences of those structures are discussed, which could provide guidance for future drug design. METHODS:The primary accesses for patent searching are SciFinder and Espacenet®. Besides the data disclosed in patents, some results published in the follow-up research papers will be included in this review. RESULTS:The review covers dozens of patents on Mcl-1 inhibitors in the past three years, and the scaffolds of compounds are mainly divided into indole scaffolds and non-indole scaffolds. The compounds described here are compared with the relevant inhibitors disclosed in previous patents, and representative compounds, especially those launched in clinical trials, are emphasized in this review. CONCLUSION:For most of the compounds in these patents, analyses of the binding affinity to Mcl-1 and studies in multiple cell lines were conducted, wherein some compounds were tested in preclinical cancer models or were included in other biological studies. Some compounds showed promising results and potential for further study.
Peptide and Small Molecule Inhibitors Targeting Myeloid Cell Leukemia 1 (Mcl-1) as Novel Antitumor Agents.
Lu Xing,Liang Hong,Orvig Chris,Chen Zhen-Feng
Current molecular medicine
Myeloid cell leukemia 1 (Mcl-1) is a member of the Bcl-2 family of proteins with anti-apoptotic activity. It plays a key role in the regulation of the intrinsic pathway of apoptosis. Moreover, Mcl-1 is correlated with the progression and drug-resistance of various cancers. The development of inhibitors of Mcl-1 may provide effective cancer therapies. While the inhibitors of other Bcl-2 anti-apoptotic proteins have been well explored, the discovery of Mcl-1inhibitors with high selectivity has been challenging. In this review, we summarize the recent literature on small molecule and peptide inhibitors of Mcl-1, which are divided into different types including peptide inhibitors, gossypol derivatives, marinopyrrole derivatives, S1 derivatives, indole derivatives, quinoline derivatives, S63845, AZD5991, AMG176, etc. Their biological activities are also summarized. Mcl-1 is a valid drug target and inhibition of Mcl-1 with a small molecule inhibitor is a promising strategy for cancer therapy.
Regulation of Platelet Production and Life Span: Role of Bcl-xL and Potential Implications for Human Platelet Diseases.
Josefsson Emma C,Vainchenker William,James Chloe
International journal of molecular sciences
Blood platelets have important roles in haemostasis, where they quickly stop bleeding in response to vascular damage. They have also recognised functions in thrombosis, immunity, antimicrobal defense, cancer growth and metastasis, tumour angiogenesis, lymphangiogenesis, inflammatory diseases, wound healing, liver regeneration and neurodegeneration. Their brief life span in circulation is strictly controlled by intrinsic apoptosis, where the prosurvival Bcl-2 family protein, Bcl-xL, has a major role. Blood platelets are produced by large polyploid precursor cells, megakaryocytes, residing mainly in the bone marrow. Together with Mcl-1, Bcl-xL regulates megakaryocyte survival. This review describes megakaryocyte maturation and survival, platelet production, platelet life span and diseases of abnormal platelet number with a focus on the role of Bcl-xL during these processes.
Mcl-1 and Bok transmembrane domains: Unexpected players in the modulation of apoptosis.
Lucendo Estefanía,Sancho Mónica,Lolicato Fabio,Javanainen Matti,Kulig Waldemar,Leiva Diego,Duart Gerard,Andreu-Fernández Vicente,Mingarro Ismael,Orzáez Mar
Proceedings of the National Academy of Sciences of the United States of America
The Bcl-2 protein family comprises both pro- and antiapoptotic members that control the permeabilization of the mitochondrial outer membrane, a crucial step in the modulation of apoptosis. Recent research has demonstrated that the carboxyl-terminal transmembrane domain (TMD) of some Bcl-2 protein family members can modulate apoptosis; however, the transmembrane interactome of the antiapoptotic protein Mcl-1 remains largely unexplored. Here, we demonstrate that the Mcl-1 TMD forms homooligomers in the mitochondrial membrane, competes with full-length Mcl-1 protein with regards to its antiapoptotic function, and induces cell death in a Bok-dependent manner. While the Bok TMD oligomers locate preferentially to the endoplasmic reticulum (ER), heterooligomerization between the TMDs of Mcl-1 and Bok predominantly takes place at the mitochondrial membrane. Strikingly, the coexpression of Mcl-1 and Bok TMDs produces an increase in ER mitochondrial-associated membranes, suggesting an active role of Mcl-1 in the induced mitochondrial targeting of Bok. Finally, the introduction of Mcl-1 TMD somatic mutations detected in cancer patients alters the TMD interaction pattern to provide the Mcl-1 protein with enhanced antiapoptotic activity, thereby highlighting the clinical relevance of Mcl-1 TMD interactions.
Nutrient Deprivation Promotes MCL-1 Degradation in an Autophagy-Independent Manner.
Pervushin N V,Senichkin V V,Kapusta A A,Gorbunova A S,Kaminskyy V O,Zhivotovsky B,Kopeina G S
The antiapoptotic protein Mcl-1, which is an attractive target for cancer treatment, is degraded under nutrient deprivation conditions in different types of cancer. This process sensitizes cancer cells to chemotherapy. It has been found that nutrient deprivation leads to suppression of Mcl-1 synthesis; however, the mechanisms of Mcl-1 degradation under such conditions remain to be elucidated. In this study, we have investigated the contribution of autophagy and proteasomal degradation to the regulation of the level of Mcl-1 protein under nutrient deprivation conditions. We found that these circumstances cause a decrease in the level of Mcl-1 in cancer cells in a macroautophagy-independent manner via proteasomal degradation.
Inhibition of the anti-apoptotic protein MCL-1 severely suppresses human hematopoiesis
Bohler Sheila,Afreen Sehar,Fernandez-Orth Juncal,Demmerath Eva-Maria,Molnar Christian,Wu Ying,Weiss Julia Miriam,Mittapalli Venugopal Rao,Konstantinidis Lukas,Schmal Hagen,Kunze Mirjam,Erlacher Miriam
BH3-mimetics inhibiting anti-apoptotic BCL-2 proteins represent a novel and promising class of antitumor drugs. While the BCL-2 inhibitor venetoclax is already FDA-approved, BCL-XL and MCL-1 inhibitors are currently in early clinical trials. To predict side effects of therapeutic MCL-1 inhibition on the human hematopoietic system, we used RNAi and the small molecule inhibitor S63845 on cord blood-derived CD34+ cells. Both approaches resulted in almost complete depletion of human hematopoietic stem and progenitor cells. As a consequence, maturation into the different hematopoietic lineages was severely restricted and CD34+ cells expressing MCL-1 shRNA showed a very limited engraftment potential upon xenotransplantation. In contrast, mature blood cells survived normally in the absence of MCL-1. Combined inhibition of MCL-1 and BCL-XL resulted in synergistic effects with relevant loss of colony-forming HSPCs already at inhibitor concentrations of 0.1 μM each, indicating "synthetic lethality" of the two BH3-mimetics in the hematopoietic system.
Interdiction at a protein-protein interface: MCL-1 inhibitors for oncology.
Bioorganic & medicinal chemistry letters
A hallmark of cancer is the evasion of apoptosis. Myeloid cell leukemia-1 (MCL-1) is an anti-apoptotic member of the B-cell lymphoma-2 (BCL-2) family of proteins that regulates the mitochondrial apoptosis pathway. Overexpression of MCL-1 contributes to oncogenesis and confers resistance to cancer treatments. Protein-protein interactions (PPI) are constitutive of the dynamic interplay between the pro- and anti-apoptotic proteins of the BCL-2 family, which is integral to controlling the apoptotic threshold of cells. Therapeutic intervention by small molecule BH3 mimetics to pharmacologically target the PPI and antagonize MCL-1 has made significant progress in recent years in oncology with multiple candidates entering clinical trials. This digest accounts the state-of-art MCL-1 inhibitors with emphasis on their discovery medicinal chemistry, highlighted in structure-based drug design (SBDD) and biological evaluations.
MCL-1 inhibitors, fast-lane development of a new class of anti-cancer agents.
Bolomsky Arnold,Vogler Meike,Köse Murat Cem,Heckman Caroline A,Ehx Grégory,Ludwig Heinz,Caers Jo
Journal of hematology & oncology
Cell death escape is one of the most prominent features of tumor cells and closely linked to the dysregulation of members of the Bcl-2 family of proteins. Among those, the anti-apoptotic family member myeloid cell leukemia-1 (MCL-1) acts as a master regulator of apoptosis in various human malignancies. Irrespective of its unfavorable structure profile, independent research efforts recently led to the generation of highly potent MCL-1 inhibitors that are currently evaluated in clinical trials. This offers new perspectives to target a so far undruggable cancer cell dependency. However, a detailed understanding about the tumor and tissue type specific implications of MCL-1 are a prerequisite for the optimal (i.e., precision medicine guided) use of this novel drug class. In this review, we summarize the major functions of MCL-1 with a special focus on cancer, provide insights into its different roles in solid vs. hematological tumors and give an update about the (pre)clinical development program of state-of-the-art MCL-1 targeting compounds. We aim to raise the awareness about the heterogeneous role of MCL-1 as drug target between, but also within tumor entities and to highlight the importance of rationale treatment decisions on a case by case basis.
Development of Mcl-1 inhibitors for cancer therapy.
Negi Arvind,Murphy Paul V
European journal of medicinal chemistry
The myeloid leukemia cell differentiation protein (Mcl-1) is an anti-apoptotic protein of the B-cell lymphoma 2 (Bcl-2) family, which regulates cellular apoptosis. Mcl-1 expression plays a key role in survival of cancer cells and therefore serves as a promising target in cancer therapy. Besides, its importance as a cancer target, various peptides and small-molecule inhibitors have been successfully designed and synthesized, yet no Mcl-1 inhibitor is approved for clinical use. However, recent development on the understanding of Mcl-1's role in key cellular processes in cancer and an upsurge of reports highlighting its association in various anticancer drug resistance supports the view that Mcl-1 is a key target in various cancers, especially hematological cancers. This review compiles structures of a variety of inhibitors of Mcl-1 reported to date. These include inhibitors based on a diverse range of heterocycles (e.g. indole, imidazole, thiophene, nicotinic acid, piperazine, triazine, thiazole, isoindoline), oligomers (terphenyl, quaterpyridine), polyphenol, phenalene, anthranilic acid, anthraquinone, macrocycles, natural products, and metal-based complexes. In addition, an effort has been made to summarize the structure activity relationships, based on a variety of assays, of some important classes of Mcl-1 inhibitors, giving affinities and selectivities for Mcl-1 compared to other Bcl-2 family members. A focus has been placed on categorizing the inhibitors based on their core frameworks (scaffolds) to appeal to the chemical biologist or medicinal chemist.
Targeting MCL-1 dysregulates cell metabolism and leukemia-stroma interactions and resensitizes acute myeloid leukemia to BCL-2 inhibition.
MCL-1 and BCL-2 are both frequently overexpressed in acute myeloid leukemia and critical for the survival of acute myeloid leukemia cells and acute myeloid leukemia stem cells. MCL-1 is a key factor in venetoclax resistance. Using genetic and pharmacological approaches, we discovered that MCL-1 regulates leukemia cell bioenergetics and carbohydrate metabolisms, including the TCA cycle, glycolysis and pentose phosphate pathway and modulates cell adhesion proteins and leukemia-stromal interactions. Inhibition of MCL-1 sensitizes to BCL-2 inhibition in acute myeloid leukemia cells and acute myeloid leukemia stem/progenitor cells, including those with intrinsic and acquired resistance to venetoclax through cooperative release of pro-apoptotic BIM, BAX, and BAK from binding to anti-apoptotic BCL-2 proteins and inhibition of cell metabolism and key stromal microenvironmental mechanisms. The combined inhibition of MCL-1 by MCL-1 inhibitor AZD5991 or CDK9 inhibitor AZD4573 and BCL-2 by venetoclax greatly extended survival of mice bearing patient-derived xenografts established from an acute myeloid leukemia patient who acquired resistance to venetoclax/decitabine. These results demonstrate that co-targeting MCL-1 and BCL-2 improves the efficacy of and overcomes preexisting and acquired resistance to BCL-2 inhibition. Activation of metabolomic pathways and leukemia-stroma interactions are newly discovered functions of MCL-1 in acute myeloid leukemia, which are independent from canonical regulation of apoptosis by MCL-1. Our data provide new mechanisms of synergy and rationale for co-targeting MCL-1 and BCL-2 clinically in patients with acute myeloid leukemia and potentially other cancers.
Phosphatase PP2A enhances MCL-1 protein half-life in multiple myeloma cells.
Cell death & disease
Multiple myeloma (MM), a treatable but incurable malignancy, is characterized by the growth of clonal plasma cells in protective niches in the bone marrow. MM cells depend on expression of BCL-2 family proteins, in particular MCL-1, for survival. The regulation of MCL-1 is complex and cell type-dependent. Unraveling the exact mechanism by which MCL-1 is overexpressed in MM may provide new therapeutic strategies for inhibition in malignant cells, preferably limiting side effects in healthy cells. In this study, we reveal that one cause of overexpression could be stabilization of the MCL-1 protein. We demonstrate this in a subset of MM and diffuse large B cell lymphoma (DLBCL) cell lines and MM patient samples. We applied a phosphatase siRNA screen to identify phosphatases responsible for MCL-1 stabilization in MM, and revealed PP2A as the MCL-1 stabilizing phosphatase. Using the PP2A inhibitor okadaic acid, we validated that PP2A dephosphorylates MCL-1 at Ser159 and/or Thr163, and thereby stabilizes MCL-1 in MM cells with long MCL-1 half-life, but not in DLBCL cells. Combined kinase and phosphatase inhibition experiments suggest that the MCL-1 half-life in MM is regulated by the counteracting functions of JNK and PP2A. These findings increase the understanding of the mechanisms by which MCL-1 is post-translationally regulated, which may provide novel strategies to inhibit MCL-1 in MM cells.
Stroma-Mediated Resistance to S63845 and Venetoclax through MCL-1 and BCL-2 Expression Changes Induced by miR-193b-3p and miR-21-5p Dysregulation in Multiple Myeloma.
Algarín Esperanza M,Quwaider Dalia,Campos-Laborie Francisco J,Díaz-Tejedor Andrea,Mogollón Pedro,Vuelta Elena,Martín-Sánchez Montserrat,San-Segundo Laura,González-Méndez Lorena,Gutiérrez Norma C,García-Sanz Ramón,Paíno Teresa,De Las Rivas Javier,Ocio Enrique M,Garayoa Mercedes
BH3-mimetics targeting anti-apoptotic proteins such as MCL-1 (S63845) or BCL-2 (venetoclax) are currently being evaluated as effective therapies for the treatment of multiple myeloma (MM). Interleukin 6, produced by mesenchymal stromal cells (MSCs), has been shown to modify the expression of anti-apoptotic proteins and their interaction with the pro-apoptotic BIM protein in MM cells. In this study, we assess the efficacy of S63845 and venetoclax in MM cells in direct co-culture with MSCs derived from MM patients (pMSCs) to identify additional mechanisms involved in the stroma-induced resistance to these agents. MicroRNAs miR-193b-3p and miR-21-5p emerged among the top deregulated miRNAs in myeloma cells when directly co-cultured with pMSCs, and we show their contribution to changes in MCL-1 and BCL-2 protein expression and in the activity of S63845 and venetoclax. Additionally, direct contact with pMSCs under S63845 and/or venetoclax treatment modifies myeloma cell dependence on different BCL-2 family anti-apoptotic proteins in relation to BIM, making myeloma cells more dependent on the non-targeted anti-apoptotic protein or BCL-X. Finally, we show a potent effect of the combination of S63845 and venetoclax even in the presence of pMSCs, which supports this combinatorial approach for the treatment of MM.
Targeting MCL-1 in cancer: current status and perspectives.
Wang Haolan,Guo Ming,Wei Hudie,Chen Yongheng
Journal of hematology & oncology
Myeloid leukemia 1 (MCL-1) is an antiapoptotic protein of the BCL-2 family that prevents apoptosis by binding to the pro-apoptotic BCL-2 proteins. Overexpression of MCL-1 is frequently observed in many tumor types and is closely associated with tumorigenesis, poor prognosis and drug resistance. The central role of MCL-1 in regulating the mitochondrial apoptotic pathway makes it an attractive target for cancer therapy. Significant progress has been made with regard to MCL-1 inhibitors, some of which have entered clinical trials. Here, we discuss the mechanism by which MCL-1 regulates cancer cell apoptosis and review the progress related to MCL-1 small molecule inhibitors and their role in cancer therapy.
Pharmacologic Targeting of Mcl-1 Induces Mitochondrial Dysfunction and Apoptosis in B-Cell Lymphoma Cells in a and Dependent Manner.
Clinical cancer research : an official journal of the American Association for Cancer Research
PURPOSE:Bcl-2 has been effectively targeted in lymphoid malignancies. However, resistance is inevitable, and novel approaches to target mitochondrial apoptosis are necessary. AZD5991, a selective BH3-mimetic in clinical trials, inhibits Mcl-1 with high potency. EXPERIMENTAL DESIGN:We explored the preclinical activity of AZD5991 in diffuse large B-cell lymphoma (DLBCL) and ibrutinib-resistant mantle cell lymphoma (MCL) cell lines, MCL patient samples, and mice bearing DLBCL and MCL xenografts using flow cytometry, immunoblotting, and Seahorse respirometry assay. Cas9 gene editing and functional drug screen assays helped identify mechanisms of resistance to Mcl-1 inhibition. RESULTS:Mcl-1 was expressed in DLBCL and MCL cell lines and primary tumors. Treatment with AZD5991 restricted growth of DLBCL cells independent of cell of origin and overcame ibrutinib resistance in MCL cells. Mcl-1 inhibition led to mitochondrial dysfunction as manifested by mitochondrial membrane depolarization, decreased mitochondrial mass, and induction of mitophagy. This was accompanied by impairment of oxidative phosphorylation. and were essential for sensitivity to Mcl-1, and oxidative phosphorylation was implicated in resistance to Mcl-1 inhibition. Induction of prosurvival proteins (e.g., Bcl-xL) in stromal conditions that mimic the tumor microenvironment rendered protection of primary MCL cells from Mcl-1 inhibition, while BH3-mimetics targeting Bcl-2/xL sensitized lymphoid cells to AZD5991. Treatment with AZD5991 reduced tumor growth in murine lymphoma models and prolonged survival of MCL PDX mice. CONCLUSIONS:Selective targeting Mcl-1 is a promising therapeutic approach in lymphoid malignancies. apoptotic network and metabolic reprogramming underlie susceptibility to Mcl-1 inhibition.
Physiological Functions of Mcl-1: Insights From Genetic Mouse Models.
Chin Hui San,Fu Nai Yang
Frontiers in cell and developmental biology
The ability to regulate the survival and death of a cell is paramount throughout the lifespan of a multicellular organism. Apoptosis, a main physiological form of programmed cell death, is regulated by the Bcl-2 family proteins that are either pro-apoptotic or pro-survival. The functions of distinct Bcl-2 family members are largely unmasked by genetically engineered murine models. is one of the two Bcl-2 like pro-survival genes whose germline deletion causes embryonic lethality in mice. Its requisite for the survival of a broad range of cell types has been further unraveled by using conditional and inducible deletion murine model systems in different tissues or cell lineages and at distinct developmental stages. Moreover, genetic mouse cancer models have also demonstrated that is essential for the survival of multiple tumor types. The locus is commonly amplified across various cancer types in humans. Small molecule inhibitors with high affinity and specificity to human MCL-1 have been developed and explored for the treatment of certain cancers. To facilitate the pre-clinical studies of MCL-1 in cancer and other diseases, transgenic mouse models over-expressing human as well as humanized mouse models have been recently engineered. This review discusses the current advances in understanding the physiological roles of Mcl-1 based on studies using genetic murine models and its critical implications in pathology and treatment of human diseases.
Myeloid cell leukemia 1 (MCL-1): Structural characteristics and application in cancer therapy.
Mittal Pooja,Singh Sujata,Sinha Rajesh,Shrivastava Anju,Singh Archana,Singh Indrakant Kumar
International journal of biological macromolecules
Apoptosis, a major hallmark of cancer cells, regulates cellular fate and homeostasis. BCL-2 (B-cell CLL/Lymphoma 2) protein family is popularly known to mediate the intrinsic mode of apoptosis, of which MCL-1 is a crucial member. Myeloid cell leukemia 1 (MCL-1) is an anti-apoptotic oncoprotein and one of the most investigated members of the BCL-2 family. It is commonly known to be genetically altered, aberrantly overexpressed, and primarily associated with drug resistance in various human cancers. Recent advancements in the development of selective MCL-1 inhibitors and evaluating their effectiveness in cancer treatment establish its popularity as a molecular target. The overall aim is the selective induction of apoptosis in cancer cells by using a single or combination of BCL-2 family inhibitors. Delineating the precise molecular mechanisms associated with MCL-1-mediated cancer progression will certainly improve the efficacy of clinical interventions aimed at MCL-1 and hence patient survival. This review is structured to highlight the structural characteristics of MCL-1, its specific interactions with NOXA, MCL-1-regulatory microRNAs, and at the same time focus on the emerging therapeutic strategies targeting our protein of interest (MCL-1), alone or in combination with other treatments.
Mcl-1 Inhibition: Managing Malignancy in Multiple Myeloma.
Al-Odat Omar,von Suskil Max,Chitren Robert,Elbezanti Weam,Srivastava Sandeep,Budak-Alpddogan Tulin,Jonnalagadda Subash,Aggarwal Bharat,Pandey Manoj
Frontiers in pharmacology
Multiple myeloma (MM) is a plasma cells neoplasm. The overexpression of Bcl-2 family proteins, particularly myeloid cell leukemia 1 (Mcl-1), plays a critical role in the pathogenesis of MM. The overexpression of Mcl-1 is associated with drug resistance and overall poor prognosis of MM. Thus, inhibition of the Mcl-1 protein considered as a therapeutic strategy to kill the myeloma cells. Over the last decade, the development of selective Mcl-1 inhibitors has seen remarkable advancement. This review presents the critical role of Mcl-1 in the progression of MM, the most prominent BH3 mimetic and semi-BH3 mimetic that selectively inhibit Mcl-1, and could be used as single agent or combined with existing therapies.
MCL-1 Inhibition Overcomes Anti-apoptotic Adaptation to Targeted Therapies in B-Cell Precursor Acute Lymphoblastic Leukemia.
Manzano-Muñoz Albert,Alcon Clara,Menéndez Pablo,Ramírez Manuel,Seyfried Felix,Debatin Klaus-Michael,Meyer Lüder H,Samitier Josep,Montero Joan
Frontiers in cell and developmental biology
Multiple targeted therapies are currently explored for pediatric and young adult B-cell precursor acute lymphoblastic leukemia (BCP-ALL) treatment. However, this new armamentarium of therapies faces an old problem: choosing the right treatment for each patient. The lack of predictive biomarkers is particularly worrying for pediatric patients since it impairs the implementation of new treatments in the clinic. In this study, we used the functional assay dynamic BH3 profiling (DBP) to evaluate two new treatments for BCP-ALL that could improve clinical outcome, especially for relapsed patients. We found that the MEK inhibitor trametinib and the multi-target tyrosine kinase inhibitor sunitinib exquisitely increased apoptotic priming in an NRAS-mutant and in a -rearranged cell line presenting a high expression of FLT3, respectively. Following these observations, we sought to study potential adaptations to these treatments. Indeed, we identified with DBP anti-apoptotic changes in the BCL-2 family after treatment, particularly involving MCL-1 - a pro-survival strategy previously observed in adult cancers. To overcome this adaptation, we employed the BH3 mimetic S63845, a specific MCL-1 inhibitor, and evaluated its sequential addition to both kinase inhibitors to overcome resistance. We observed that the metronomic combination of both drugs with S63845 was synergistic and showed an increased efficacy compared to single agents. Similar observations were made in BCP-ALL -rearranged PDX cells in response to sunitinib, showing an analogous DBP profile to the SEM cell line. These findings demonstrate that rational sequences of targeted agents with BH3 mimetics, now extensively explored in clinical trials, may improve treatment effectiveness by overcoming anti-apoptotic adaptations in BCP-ALL.
Cotargeting of Bcl-2 and Mcl-1 shows promising antileukemic activity against AML cells including those with acquired cytarabine resistance.
Liu Fangbing,Zhao Qiushi,Su Yongwei,Lv Jing,Gai Yuqing,Liu Shuang,Lin Hai,Wang Yue,Wang Guan
Acute myeloid leukemia (AML) remains a clinical challenge. Venetoclax is an effective Bcl-2 selective inhibitor approved by the U.S. Food and Drug Administration (FDA) for treatment of AML in patients who are 75 years and older or who have comorbidities. However, resistance to venetoclax limits its clinical efficacy. Mcl-1 has been identified as one determinant of resistance to venetoclax treatment. In this study, we investigate the Mcl-1 inhibitor S63845 in combination with venetoclax in AML cells. We found that S63845 synergizes with venetoclax in AML cell lines and primary patient samples. Bak/Bax double knockdown and treatment with the pan-caspase inhibitor Z-VAD-FMK revealed that the combination induces intrinsic apoptosis in AML cells. Inhibition of Mcl-1 using another Mcl-1 selective inhibitor, AZD5991, also synergistically enhanced apoptosis induced by venetoclax in a caspase-dependent manner. Importantly, S63845 in combination with venetoclax can effectively combat AML cells with acquired resistance to the standard chemotherapy drug cytarabine. In light of these facts, the combined inhibition of Mcl-1 and Bcl-2 shows promise against AML cells, including relapse/refractory AML.
Mcl-1 and Bcl-xL levels predict responsiveness to dual MEK/Bcl-2 inhibition in B-cell malignancies.
Most patients with chronic lymphocytic leukemia (CLL) initially respond to targeted therapies, but eventually relapse and develop resistance. Novel treatment strategies are therefore needed to improve patient outcomes. Here, we performed direct drug testing on primary CLL cells and identified synergy between eight different mitogen-activated protein kinase kinase (MEK) inhibitors and the B-cell lymphoma 2 (Bcl-2) antagonist venetoclax. Drug sensitivity was independent of immunoglobulin heavy-chain gene variable region (IGVH) and tumor protein p53 (TP53) mutational status, and CLL cells from idelalisib-resistant patients remained sensitive to the treatment. This suggests that combined MEK/Bcl-2 inhibition may be an option for high-risk CLL. To test whether sensitivity could be detected in other B-cell malignancies, we performed drug testing on cell line models of CLL (n = 4), multiple myeloma (MM; n = 8), and mantle cell lymphoma (MCL; n = 7). Like CLL, MM cells were sensitive to the MEK inhibitor trametinib, and synergy was observed with venetoclax. In contrast, MCL cells were unresponsive to MEK inhibition. To investigate the underlying mechanisms of the disease-specific drug sensitivities, we performed flow cytometry-based high-throughput profiling of 31 signaling proteins and regulators of apoptosis in the 19 cell lines. We found that high expression of the antiapoptotic proteins myeloid cell leukemia-1 (Mcl-1) or B-cell lymphoma-extra large (Bcl-xL) predicted low sensitivity to trametinib + venetoclax. The low sensitivity could be overcome by combined treatment with an Mcl-1 or Bcl-xL inhibitor. Our findings suggest that MEK/Bcl-2 inhibition has therapeutic potential in leukemia and myeloma, and demonstrate that protein expression levels can serve as predictive biomarkers for treatment sensitivities.
The BCL-2 inhibitor ABT-199/venetoclax synergizes with proteasome inhibition via transactivation of the MCL-1 antagonist NOXA.
Cell death discovery
Enhanced expression of anti-apoptotic B-cell lymphoma 2 (BCL-2) protein is frequent in cancer. Targeting of BCL-2 with the specific inhibitor ABT-199 (Venetoclax) has significant clinical activity in malignant diseases such as chronic lymphocytic leukemia and multiple myeloma. The small molecule drug ABT-199 mimics the pro-apoptotic BCL-2 homology domain 3 of BH3-only proteins and blocks the hydrophobic BC-groove in BCL-2. We have previously shown that ABT-199 synergizes with the proteasome inhibitor (PI) bortezomib in soft tissue sarcoma derived cells and cell lines to induce apoptosis. Synergistic apoptosis induction relies on the pore-forming effector BAX and expression of the pro-apoptotic BH3-only protein NOXA. Bortezomib augments expression of NOXA by blocking its proteasomal degradation. Interestingly, shown here for the first time, expression of NOXA is strongly enhanced by ABT-199 induced integrated stress response (ISR). ISR transcription factors ATF3 & ATF4 mediate transactivation of the BH3-only protein NOXA which specifically inhibits the anti-apoptotic MCL-1. Thus, NOXA potentiates the efficacy of the BCL-2 inhibitor ABT-199 by simultaneous inhibition of MCL-1. Hence, ABT-199 has a double impact by directly blocking anti-apoptotic BCL-2 and inhibiting MCL-1 via transactivated NOXA. By preventing degradation of NOXA PIs synergize with ABT-199. Synergism of ABT-199 and PIs therefore occurs on several, previously unexpected levels. This finding should prompt clinical evaluation of combinatorial regimens in further malignancies.