Increased Mcl-1 Expression Research Articles

Abstract 7194: Targeting AXL and MCL-1 to eradicate lazertinib tolerance in EGFR-mutated NSCLC cells

Abstract Lazertinib, a novel third-generation EGFR-tyrosine kinase inhibitor, has shown marked efficacy in patients with EGFR-mutant lung cancer. However, after various periods of therapeutic intervention, most patients eventually acquire resistance to lazertinib. A potential therapeutic approach to address this clinical issue is to overcome the initial drug resistance mechanism. To determine the underlying adaptive lazertinib resistance mechanisms, we evaluated signal transduction, cell apoptosis, and drug sensitivity in mutant EGFR-expressing non-small cell lung cancer (NSCLC) cells treated with lazertinib. The siRNA screening assay demonstrated that AXL knockdown significantly inhibited cell viability in the presence of lazertinib, indicating that AXL activation contributes to lazertinib resistance. However, long-term culture with a combination of lazertinib and AXL inhibitors eventually led to the proliferation of residual cells and increased MCL-1 expression, which was mediated by the nuclear translocation of the transcription factor YAP. Cell-based assays showed that triple therapy with an MCL-1 or YAP inhibitor, in combination with EGFR-TKI lazertinib, an AXL inhibitor, significantly reduced cell viability and increased apoptosis. These results demonstrate that AXL and YAP/MCL-1 signals contribute to the adaptive lazertinib resistance in EGFR-mutant NSCLC cells, suggesting that the initial dual inhibition of AXL and YAP/MCL-1 might be highly effective in eliminating lazertinib-resistant cells. Citation Format: Tadaaki Yamada, Yohei Matsui, Koichi Takayama. Targeting AXL and MCL-1 to eradicate lazertinib tolerance in EGFR-mutated NSCLC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7194.

Abstract 2533: MAPK-driven MCL1 expression promotes osteosarcoma survival in the metastatic niche

Abstract We sought to identify dependencies of slow growing, chemo-resistant osteosarcoma cells that anchor in the metastatic niche. These dependencies yield insight into what allows early cells to survive in the hostile lung environment, as well as potential therapeutic targets. In our studies of metastatic colonization, we identified two distinct populations of osteosarcoma cells. The first, dubbed “anchor cells”, are prevalent in the early metastatic niche where they are hypo-proliferative and hyper-secretory. The second subpopulation, “growth cells”, proliferate rapidly and predominate as lesions begin to grow rapidly. To identify genes and pathways that differentiate anchor cells, we performed scRNAseq on early and late metastases and confirmed these findings with tissue staining of time-matched metastases. To identify ligands that might facilitate survival of anchor cells in the lung microenvironment and their source, we performed scRNAseq on normal and metastasis-bearing lungs at different stages of metastasis. To confirm osteosarcoma cells express receptors for the identified lung growth factors, we used an immunoassay to evaluate tyrosine kinase receptor expression at baseline and in response to lung epithelial cell-conditioned medium. To confirm the growth factors increased MAPK activity in osteosarcoma cells, we used live cell imaging on fluorescent pERK reporter cells, followed by immunofluorescence to determine if increased MAPK activity was necessary for increased MCL1 expression. To determine if MCL1 is a viable therapeutic target and selective for anchor cells, we treated tumor-on-lung anchor cell-rich spheroid models with a MCL1-selective BH3 mimetic, AZD5991, and quantified cell death. To optimize dosing and determine tolerance in vivo, we treated metastasis-bearing mice with different doses of AZD5991 +/- cyclophosphamide. We found anchor cells have upregulated ERK activity and MCL1 expression compared to growth cells. This activity is associated with production of several growth factors in the metastatic niche that can activate receptors expressed by osteosarcoma cells. Growth-factor induced ERK activity is necessary for increased MCL1 expression in osteosarcoma cells. We found expression of many growth factors produced by niche cells becomes augmented as osteosarcoma cells colonize the lung. Additionally, host cells within the niche express comparatively more growth factors early in the metastatic process, with macrophages representing a predominant source of growth factors. We found cells expressing higher levels of MCL1 are vulnerable to its inhibition in vitro. Metastatic burden decreased as the number of AZD5991 doses increased in vivo. Our data suggest growth factors in the lung activate ERK in the early metastatic niche, and ERK-dependent MCL1 expression is required for survival of anchor cells. MCL1-targeting agents may have utility in disrupting colonization of the lungs. Citation Format: Camille A. McAloney, Rawan Makkawi, Matthew V. Cannon, Amy C. Gross, Maren Cam, Emily Franz, Tatyana A. Vetter, Alexander E. Davies, Ryan D. Roberts. MAPK-driven MCL1 expression promotes osteosarcoma survival in the metastatic niche [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2533.

Abstract 4067: Combination venetoclax and selinexor effective in relapsed refractory multiple myeloma with translocation t(11;14)

Abstract Translocation t(11;14) positive multiple myeloma (MM) is sensitive to venetoclax, yet the drug lacks FDA approval in MM. Selinexor is an inhibitor of nuclear exporter XPO1 and is approved in relapsed refractory MM. We recently analyzed RNA-seq from 859 MM patient samples (MMRF CoMMpass study) and compared them to healthy bone marrow samples (GSE114922). After correcting for batch effects, differential gene expression analysis found apoptosis and cell cycle regulation amongst the top upregulated gene pathways in MM. We therefore hypothesized that MM would be sensitive to the combination of the pro-apoptotic drug, venetoclax, and selinexor, which causes cell cycle arrest. Using a panel of 8 MM cell lines (U266-B1, KMS12BM, SKMM2, RPMI-8226, LP1, OPM2, KMS12PE, and NCIH929), we performed cell viability assays in increasing concentrations of selinexor, venetoclax, and a combination of the two drugs at 72 hours. Overall, the combination showed synergy in MM cell lines but strikingly, cell lines that possessed t(11;14) were more sensitive to the drug combination and showed enhanced synergy compared to the non-t(11;14). Average Bliss model synergy score were 0.5 in non-t(11;14) and 10.2 in t(11;14) MM cells (>10 indicates synergistic effects and <-10 indicates antagonistic drug effects). To better understand molecular mechanisms underlying the observed synergistic effect in t(11;14), we performed western blot analysis in these cell lines treated with selinexor, venetoclax, the combination, or DMSO control for 24 hours. We measured protein levels of Cyclin D1, which is overexpressed in t(11;14) and a cargo of XPO1. We confirmed Cyclin D1 overexpression in t(11;14) cells lines but not in non-t(11;14) cells. Cyclin D1 levels decreased with selinexor, and the reduction was enhanced by adding venetoclax. Additionally, we measured levels of XPO1, p53, MCL-1, and p65, which we have previously shown to be altered by selinexor treatment. While venetoclax monotherapy caused increased MCL-1 expression, this was abrogated by combining with selinexor and the effects were statistically more significant in t(11;14) cell lines. Concurrently, two patients with relapsed, refractory t(11;14) MM and disease progression after multiple lines of therapy were treated with venetoclax; however, after initial response, they developed resistance and progressive disease. Based off our preclinical results, selinexor was added to venetoclax and recaptured responses (VGPR and MR, respectively) suggesting a beneficial effect of the combination over single agent venetoclax. To our knowledge, this is the first report of patients with MM treated with the combination of selinexor and venetoclax. Further clinical evaluation of this combination in t(11;14) MM is planned and samples will be collected to better understand the mechanistic correlation between XPO1, BCL2/MCL-1, and Cyclin D1 levels and response. Citation Format: Sana Chaudhry, Nina Nguyen, Rimpi Khurana, Tulasigeri M. Totiger, Skye Montoya, Jumana Afaghani, Terrence Bradley, Francesco Maura, Dickran Kazandjian, Jennifer Chapman, Stephan Schürer, Ola Landgren, James Hoffman, Justin Taylor. Combination venetoclax and selinexor effective in relapsed refractory multiple myeloma with translocation t(11;14) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4067.

CircRNA-DOPEY2 enhances the chemosensitivity of esophageal cancer cells by inhibiting CPEB4-mediated Mcl-1 translation

BackgroundCisplatin-based chemotherapy is a mainstay systematic therapy for advanced esophageal squamous cell carcinoma (ESCC), and cisplatin resistance, which is not uncommon, is the major barrier to improving patient outcomes. Circular RNAs (circRNAs) are novel noncoding RNAs that are implicated in cancer progression, but their involvement in modulating cisplatin responsiveness in ESCC remains unknown.MethodsBioinformatics analysis was used to profile and identify the circRNAs involved in cisplatin responsiveness in ESCC. The chemosensitive role of cDOPEY2 was confirmed both in vitro and in vivo. The molecular mechanism of cDOPEY2 was investigated by mass spectrometry, immunoprecipitation, and ubiquitination analyses.ResultsWe report that a novel circRNA (cDOPYE2, hsa_circ_0008078) was markedly downregulated in cisplatin-resistant ESCC cells (ESCC-CR) compared with parental chemosensitive cells. Re-expression of cDOPEY2 substantially enhanced the cell-killing ability of cisplatin by augmenting the apoptotic process in ESCC-CR cells, which was achieved by decreasing the abundance of the antiapoptotic protein Mcl-1. Mechanistically, we showed that cDOPEY2 acted as a protein scaffold to enhance the interaction between the cytoplasmic polyadenylation element binding protein (CPEB4) and the E3 ligase TRIM25, which in turn facilitated the ubiquitination and degradation of CPEB4. The increased Mcl-1 expression in ESCC-CR cells was dependent on the binding of CPEB4 to its untranslated mRNA, and depletion of CPEB4 mediated by cDOPEY2 reversed this effect. Rescue experiments confirmed that the critical role of cDOPEY2 in maintaining cisplatin sensitivity was dependent on the depletion of CEPB4 and its downstream target Mcl-1. Clinical and in vivo data further corroborated the significant relevance of cDOPEY2 to cisplatin responsiveness in ESCC.ConclusionsWe provide evidence that cDOPEY2 inhibits CPEB4-mediated Mcl-1 translation by promoting the ubiquitination and degradation of CPEB4 to alleviate cisplatin resistance, indicating that cDOPEY2 may serve as a valuable biomarker and potential therapeutic target in ESCC.

Arsenic trioxide-induced p38 MAPK and Akt mediated MCL1 downregulation causes apoptosis of BCR-ABL1-positive leukemia cells

In this study, we investigated the mechanisms underlying arsenic trioxide (ATO)-induced death of human BCR-ABL1-positive K562 and MEG-01 cells. ATO-induced apoptotic death in K562 cells was characterized by ROS-mediated mitochondrial depolarization, MCL1 downregulation, p38 MAPK activation, and Akt inactivation. ATO-induced BCR-ABL1 downregulation caused Akt inactivation but not p38 MAPK activation. Akt inactivation increased GSK3β-mediated MCL1 degradation, while p38 MAPK-mediated NFκB activation coordinated with HDAC1 suppressed MCL1 transcription. Inhibition of p38 MAPK activation or overexpression of constitutively active Akt increased MCL1 expression and promoted the survival of ATO-treated cells. Overexpression of MCL1 alleviated mitochondrial depolarization and cell death induced by ATO. The same pathway was found to be involved in ATO-induced death in MEG-01 cells. Remarkably, YM155 synergistically enhanced the cytotoxicity of ATO on K562 and MEG-01 cells through suppression of MCL1 and survivin. Collectively, our data indicate that ATO-induced p38 MAPK- and Akt-mediated MCL1 downregulation triggers apoptosis in K562 and MEG-01 cells, and that p38 MAPK activation is independent of ATO-induced BCR-ABL1 suppression.

DYRK1A suppression restrains Mcl-1 expression and sensitizes NSCLC cells to Bcl-2 inhibitors.

Objective: Mcl-1 overexpression confers acquired resistance to Bcl-2 inhibitors in non-small cell lung cancer (NSCLC), but no direct Mcl-1 inhibitor is currently available for clinical use. Thus, novel therapeutic strategies are urgently needed to target Mcl-1 and sensitize the anti-NSCLC activity of Bcl-2 inhibitors.Methods: Cell proliferation was measured using sulforhodamine B and colony formation assays, and apoptosis was detected with Annexin V-FITC staining. Gene expression was manipulated using siRNAs and plasmids. Real-time PCR and Western blot were used to measure mRNA and protein levels. Immunoprecipitation and immunofluorescence were used to analyze co-localization of dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) and Mcl-1.Results: Suppression of DYRK1A resulted in reduced Mcl-1 expression in NSCLC cells, whereas overexpression of DYRK1A significantly increased Mcl-1 expression. Suppression of DYRK1A did not alter Mcl-1 mRNA levels, but did result in an accelerated degradation of Mcl-1 protein in NSCLC cells. Furthermore, DYRK1A mediated proteasome-dependent degradation of Mcl-1 in NSCLC cells, and DYRK1A co-localized with Mcl-1 in NSCLC cells and was co-expressed with Mcl-1 in tumor samples from lung cancer patients, suggesting that Mcl-1 may be a novel DYRK1A substrate. We showed that combined therapy with harmine and Bcl-2 antagonists significantly inhibited cell proliferation and induced apoptosis in NSCLC cell lines as well as primary NSCLC cells.Conclusions: Mcl-1 is a novel DYRK1A substrate, and the role of DYRK1A in promoting Mcl-1 stability makes it an attractive target for decreasing Bcl-2 inhibitor resistance.

MCL1 Inhibitors in Multiple Myeloma

Apoptosis plays a key role, not only in normal homeostasis but also in protection against genomic instability. Protection against apoptosis is a hallmark of cancer and is mainly regulated by the overexpression of anti-apoptotic proteins such as Bcl-2, Bcl-Xl or Mcl-1. This results in increased survival of the tumor cells and resistance to therapy. This presentation will focus on MCL-1 (myeloid cell leukemia 1), its expression and its role as potential target in multiple myeloma (MM). MCL1 gene regions are one the most amplified gene regions in several human cancers and Mcl-1 activity is often associated with therapy resistance and relapse. Mcl-1 binds to and sequesters the pro-apoptotic BH3 proteins, thereby preventing apoptosis. Mcl-1 is overexpressed on MM cells from newly diagnosed patients compared to normal plasma cells and in MM cells at relapse. This overexpression is furthermore associated with a shorter survival of these patients. Increased Mcl-1 expression can result either from genetic lesions or by induction through interaction with the bone marrow microenvironment. Its expression is correlated with the molecular heterogeneity of the myeloma patients; while the CCDN1 group has high BCL2 and low MCL-1 expression; the MMSET and MAF group has high MCL-1 and low BCL2 expression. Unlike Bcl-2 and Bcl-Xl, Mcl-1 has a large unstructured aminoterminus and its activity is mainly dependent on posttranslational modifications. The bone marrow microenvironment, by producing high levels of interleukin 6, also induces the upregulation of Mcl-1. Furthermore, our group recently demonstrated that not only stromal cells in the bone marrow microenvironment, but also MDSC (myeloid derived suppressor cells) induce survival of MM cells by increasing Mcl-1 levels through the AMPK pathway. As such, these data suggest the potential therapeutic benefit of targeting Mcl-1 in MM patients. Developing the first-generation inhibitors appeared to be challenging, especially in view of the occurrence of unwanted off target effects. Recent preclinical data with new, selective Mcl-1 inhibitors show promising anti-tumor effects both in vitro and in in vivo myeloma models, either alone or in combination with the Bcl-2 selective inhibitor, venetoclax, especially as it was demonstrated that high levels of MCL-1 are associated with venetoclax resistance in MM. In addition, it was also shown that proteasome inhibition can trigger Mcl-1 accumulation, further pointing to the importance of Mcl-1 inhibition. Induction of NOXA, as an inhibitor of Mcl-1, is also suggested as a therapeutic option, especially in combinations with other drugs. Clinically, following preclinical results, several new Mcl-1 inhibitors have entered phase I trials. Most of them are still recruiting patients, and as such too early to have results. Disclosures No relevant conflicts of interest to declare.

MCL-1 and PKA/AMPK Axis Fuel Venetoclax Resistance in Lymphoid Cancers

MCL-1 and PKA/AMPK Axis Fuel Venetoclax Resistance in Lymphoid Cancers

Genome and Exome-Wide Studies Reveal Potential Predictive Efficacy Markers for Venetoclax and Rituximab (VenR) in Relapsed/Refractory Chronic Lymphocytic Leukemia (R/R CLL): Subgroup Analyses of the Murano Trial

Genome and Exome-Wide Studies Reveal Potential Predictive Efficacy Markers for Venetoclax and Rituximab (VenR) in Relapsed/Refractory Chronic Lymphocytic Leukemia (R/R CLL): Subgroup Analyses of the Murano Trial

ABT-737 and erufosine combination against castration-resistant prostate cancer: a promising but cell-type specific response associated with the modulation of anti-apoptotic signaling.

A deeper understanding of the molecular basis of castration-resistant prostate cancer (CRPC) paved the way for the rational design and development of targeted therapies, which yielded promising preclinical results. However, translation of these potentially promising agents into clinics has usually failed, partly because of tumor heterogeneity. In this study, anticancer activities of the Bcl-2 inhibitor ABT-737 and the Akt-inhibitor erufosine (ErPC3) alone and in combination were compared between CRPC (PC-3 and DU-145) and healthy (PNT-1A) cell lines. The combination of ABT-737 and ErPC3 showed synergistic antiproliferative, antimigratory, and apoptotic effects in PC-3 cells. In DU-145 cells, ErPC3 showed a resistant profile, with half-maximal inhibitory concentration (IC50) values more than two-fold of PC-3, and combining ErPC3 with ABT-737 yielded no added benefit for all the incubation periods compared with ErPC3 alone. In PNT-1A cells, ABT-737 and ErPC3 alone and in combination reduced cell survival slightly and only at the highest concentrations. Apoptosis analysis showed that ABT-737 induced increased Akt expression and ErPC3 induced increased Mcl-1 expression in DU-145 cells. In conclusion, the ABT-737 and ErPC3 combination seems to be promising against CRPC, with a favorable safety profile in healthy cells. However, CRPC cell-type-specific resistance may be induced by enhancement of antiapoptotic signaling.

The Oral CDK9 Inhibitor, TP-1287, Is Active in Non-Clinical Models of Multiple Myeloma

BackgroundWith 31,000 new cases expected in 2018 (US), and a 50% five-year overall survival rate, there is yet a significant unmet need in the treatment of patients with multiple myeloma (MM). The proteasomal inhibitor bortezomib is approved for the treatment of patients with multiple myeloma. Bortezomib inhibits the degradation of many proteins, including the pro-apoptotic protein NOXA. However, low basal levels of NOXA and/or high levels of the anti-apoptotic protein MCL-1 have been implicated in bortezomib resistance and negative patient outcomes. NOXA functions to sequester MCL-1 and prevent its interaction with the apoptosis inducing proteins, BAK or BAX. The BCL-2 inhibitor, venetoclax, has also been investigated in clinical trials for the treatment of multiple myeloma. Increased MCL-1 expression has been shown to be key in the resistance to venetoclax. Considering the central role of MCL-1 to survival and treatment efficacy in myeloma, we investigated the ability of an MCL-1-lowering agent, namely the CDK9 inhibitor, TP-1287, to suppress tumor growth in non-clinical models of multiple myeloma. TP-1287 is an oral form of the CDK9 inhibitor, alvocidib, and suppresses MCL-1 expression via CDK9-mediated regulation of RNA polymerase II. Alvocidib is currently under clinical investigation in patients with acute myeloid leukemia (AML), in both the frontline and relapse/refractory settings.HypothesisWe hypothesized that TP-1287 would suppress tumor growth in models of multiple myeloma and would be active in combinations with bortezomib or venetoclax.MethodsCelltiter-Glo and Caspase-Glo assays were used to evaluate the in vitro anti-tumor activity of TP-1287, bortezomib, and venetoclax. We utilized real time PCR to measure gene expression changes in treated cells. We also measured protein expression changes following treatment, using standard gel electrophoresis and immunoblotting technique. In order to assess the anti-tumor activity of these compounds in vivo, we initiated xenograft studies in the RPMI-8226 model for multiple myeloma.ResultsIn cell viability assays, we observed IC50s ranging from 0.1 nM to over 1000 nM with alvocidib or venetoclax treatment. The addition of up to 100 nM venetoclax resulted in a 2.8-fold reduction in the IC50 of alvocidib in the cultured OPM-2 cell line. Venetoclax activity was potentiated with the addition of alvocidib, resulting in a more than 500-fold decrease in IC50 in the relatively venetoclax-resistant OPM-2 cells. The cleaved form of TP-1287, or alvocidib, was able to reduce MCL-1 protein and mRNA expression in several multiple myeloma cell lines, in a time-dependent fashion. In the RPMI-8226 xenograft model for multiple myeloma, TP-1287 treatment frequency and dose level were explored, with administration of doses up to 15 mg/kg. As a single agent, TP-1287 achieved tumor growth inhibition (%TGI) of 56.0, 76.6, and 93.9% at doses of 2.5, 7.5, and 15 mg/kg, respectively. Additional studies are currently underway to investigate the efficacy of alvocidib and venetoclax in the context of bortezomib resistance where low NOXA may contribute to enhanced cell survival via MCL-1.ConclusionsTaken together, our data suggest that the combination of alvocidib with venetoclax may constitute a novel therapeutic regimen in the treatment of MM. Further, it suggests that CDK9-mediated targeting of MCL-1 may offer a route to addressing intrinsic resistance in multiple myeloma patients. DisclosuresTyagi:Tolero Pharmaceuticals, Inc: Employment. Whatcott:Tolero Pharmaceuticals, Inc: Employment. Foulks:Tolero Pharmaceuticals, Inc: Employment. Siddiqui-Jain:Tolero Pharmaceuticals, Inc: Employment. Bearss:Tolero Pharmaceuticals, Inc: Employment. Warner:Tolero Pharmaceuticals: Employment.

Venetoclax in Combination with FLAG-IDA Chemotherapy (FLAG-V-I) for Fit, Relapsed/Refractory AML Patients: Interim Results of a Phase 1b/2 Dose Escalation and Expansion Study

Venetoclax in Combination with FLAG-IDA Chemotherapy (FLAG-V-I) for Fit, Relapsed/Refractory AML Patients: Interim Results of a Phase 1b/2 Dose Escalation and Expansion Study

Antimyeloma Effect of the Simultaneous Inhibition of MCL-1 (with S63845) and BCL-2 (with Venetoclax) in the Presence of the Microenvironment

Antimyeloma Effect of the Simultaneous Inhibition of MCL-1 (with S63845) and BCL-2 (with Venetoclax) in the Presence of the Microenvironment

Targeting of BMI-1 expression by the novel small molecule PTC596 in mantle cell lymphoma.

Despite the development of the novel Bruton tyrosine kinase inhibitor ibrutinib, mantle cell lymphoma (MCL) remains an incurable B-cell non-Hodgkin lymphoma. BMI-1 is required for the self-renewal and maintenance of MCL-initiating stem cells. Upregulation of BMI-1 has been reported in MCL patients, especially in those with refractory/relapsed disease. We studied the effects of a novel small-molecule selective inhibitor of BMI1 expression, PTC596, in MCL cells. Eight MCL cell lines and patient-derived samples were exposed to PTC596. PTC596 induced mitochondrial apoptosis, as evidenced by loss of mitochondrial membrane potential, caspase-3 cleavage, BAX activation, and phosphatidylserine externalization. There was a positive correlation between baseline BMI-1 protein levels and PTC596-induced apoptosis. p53 status did not affect sensitivity to PTC596. PTC596 effectively decreased BMI-1-expressing and tumor-initiating side population MCL cells (IC50: 138 nM) compared with ibrutinib, which modestly decreased side population cells. Interestingly, PTC596, reported to target cancer stem cells, decreased MCL-1 expression levels and antagonized ibrutinib-induced increase in MCL-1 expression, leading to synergistic apoptosis induction in MCL cells. There are currently no drugs that specifically target cancer stem cell fractions, and a reduction in BMI-1 protein by PTC596 may offer a novel therapeutic strategy for MCL.

Abstract 1106: Alvocidib potentiates the activity of venetoclax in preclinical models of multiple myeloma

Abstract The proteasome inhibitor bortezomib is widely used in the treatment of patients with multiple myeloma (MM). The expression levels of many proteins increase as a result of bortezomib treatment, including the pro-apoptotic protein NOXA. NOXA functions to sequester the anti-apoptotic BCL-2 family member, MCL-1. High levels of MCL-1 and/or low levels of NOXA have been implicated in bortezomib resistance and negative patient outcomes, including short duration of treatment response. The BCL-2-specific BH3 mimetic venetoclax (ABT-199) has also been explored in multiple hematological malignancies, including the treatment of MM. Venetoclax induces apoptosis in a BCL-2 specific manner by directly inhibiting BCL-2 function. However, intrinsic resistance to venetoclax treatment observed in MM patient samples has been attributed to a low BCL-2-to-MCL-1 gene expression ratio, suggesting a central role for MCL-1 in cell survival in this context as well. Increased MCL-1 expression is a known resistance mechanism to venetoclax treatment in a variety of cell types including chronic lymphocytic leukemia and lymphomas. Considering the central role of MCL-1 to treatment efficacy in MM, we investigated the ability of an MCL-1-lowering agent, namely the CDK9 inhibitor alvocidib, to potentiate the activity of venetoclax in MM. Alvocidib suppresses MCL-1 expression via CDK9-mediated regulation of RNA polymerase II. Alvocidib has achieved robust improvements in the clinical response rates of high-risk, newly diagnosed acute myeloid leukemia (AML) patients as part of the time-sequential ACM regimen (alvocidib + cytarabine + mitoxantrone). We therefore hypothesized that alvocidib would potentiate the activity of venetoclax in MM through an MCL-1-dependent mechanism. In this report, we demonstrate that alvocidib inhibits the protein expression of MCL-1 in MM cells in a time-dependent fashion, up to 96 hours. In cell viability assays, the addition of up to 100 nM venetoclax resulted in a 2.8-fold reduction in the IC50 of alvocidib in the cultured OPM-2 cell line. Conversely, the potentiation of venetoclax activity with the addition of alvocidib resulted in a more than 500-fold decrease in IC50 in the relatively venetoclax-resistant OPM-2 cells. Additional studies are currently underway to investigate the efficacy of alvocidib and venetoclax in the context of bortezomib resistance where low NOXA may contribute to enhanced cell survival via MCL-1. Taken together, our data suggest that the combination of alvocidib with venetoclax may constitute a novel therapeutic regimen in the treatment of MM. Further, it suggests that CDK9-mediated targeting of MCL-1 may offer a clinical route to addressing intrinsic resistance in MM patients. Citation Format: Mark Livingston, Wontak Kim, Hillary Haws, Peter Peterson, Clifford J. Whatcott, Adam Siddiqui-Jain, Steven Weitman, David J. Bearss, Steven L. Warner. Alvocidib potentiates the activity of venetoclax in preclinical models of multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1106. doi:10.1158/1538-7445.AM2017-1106

Abstract 5829: Targeting TSLP-induce upregulation of Mcl-1 for the treatment of Ph-like ALL with CRLF2 alterations

Abstract B cell precursor acute lymphoblastic leukemia (B-ALL) is the most common childhood cancer. The subset of pediatric B-ALL patients at greatest risk for relapse and death have a gene expression profile similar to Philadelphia chromosome positive ALL. Approximately half of these Ph-like B-ALL are defined by genetic alterations that result in overexpression of the cytokine receptor, CRLF2. Stimulation of the CRLF2 receptor by the cytokine, TSLP, causes downstream activation of the JAK/STAT5 and PI3/AKT/MTOR pathways. Activation of these pathways has been associated with oncogenesis and chemoresistance. A gene target of activated STAT5 in B cell precursors is Mcl-1, a Bcl2 family pro-survival molecule. Further, Mcl-1 protein levels are increased through post-transcriptional mechanisms induced by activation of the mTOR pathway. We hypothesized that circulating TSLP cytokine contributes to chemoresistance by increasing CRLF2 activation leading to increased Mcl-1 expression and that targeting Mcl-1 could be an effective strategy for treating Ph-like B-ALL with overexpression of CRLF2 (CRLF2 B-ALL). To test this hypothesis we cultured human CRLF2 B-ALL cell lines (MUTZ5 and CALL4) with and without TSLP for 3 days and evaluated expression of Mcl-1 by flow cytometry. We found that TSLP induced significant increases in Mcl-1 proteins in both cell lines. To determine if these results are reflective of what happens in patients, primary CRLF2 B-ALL cells from pediatric patients were cultured with physiological levels of TSLP (~20 pg/ml) and similarly evaluated. Physiological TSLP significantly increased Mcl-1 protein in primary CRLF2 B-ALL cells, including those with activating JAK mutations. Our next question was whether TSLP-induced increases in Mcl-1 could be effectively targeted with Mcl-1 inhibitors (MIM-1 or Maritcolax). CRLF2 B-ALL cells were incubated with and without TSLP and treated with increasing doses of Mcl-1 inhibitor. Dose responses were evaluated by flow cytometry after 2 or 3 days. Mcl-1 inhibitors induced dose-dependent decreases in cell count and increases in caspase-3 activation and apoptosis (Annexin V/7-AAD). These corresponded with dose-dependent decreases in Mcl-1 protein, suggesting that both inhibitors target Mcl-1 for degradation. MIM-1 and Maritoclax showed efficacy against both CRLF2 B-ALL cell lines and primary patient samples, including those with activating JAK mutations, although cells cultured with TSLP typically required twice the dose of Mcl-1 inhibitor to achieve the same effect observed without TSLP. These data provide evidence that TSLP can contribute to leukemia cell survival and identify Mcl-1 inhibitor as a candidate therapy for CRLF2 B-ALL. Ongoing studies are evaluating the efficacy of the Mcl-1 inhibitor, Maritoclax, in novel patient-derived xenograft models of CRLF2 B-ALL that provide physiological levels of human TSLP. Citation Format: Cornelia Stoian, Nathaniel George Mambo, Pierce McCarthy, Veriah Vidales, Jacqueline S. Coats, Ineavely Baez, Sinisa Dovat, Shadi Farzin Gohar, Dhimant Desai, Muhammad Kamal, Kimberly J. Payne. Targeting TSLP-induce upregulation of Mcl-1 for the treatment of Ph-like ALL with CRLF2 alterations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5829. doi:10.1158/1538-7445.AM2017-5829

MACC1 regulates Fas mediated apoptosis through STAT1/3 – Mcl-1 signaling in solid cancers

MACC1 was identified as a novel player in cancer progression and metastasis, but its role in death receptor-mediated apoptosis is still unexplored. We show that MACC1 knockdown sensitizes cancer cells to death receptor-mediated apoptosis. For the first time, we provide evidence for STAT signaling as a MACC1 target. MACC1 knockdown drastically reduced STAT1/3 activating phosphorylation, thereby regulating the expression of its apoptosis targets Mcl-1 and Fas. STAT signaling inhibition by the JAK1/2 inhibitor ruxolitinib mimicked MACC1 knockdown-mediated molecular signatures and apoptosis sensitization to Fas activation. Despite the increased Fas expression, the reduced Mcl-1 expression was instrumental in apoptosis sensitization. This reduced Mcl-1-mediated apoptosis sensitization was Bax and Bak dependent. MACC1 knockdown also increased TRAIL-induced apoptosis. MACC1 overexpression enhanced STAT1/3 phosphorylation and increased Mcl-1 expression, which was abrogated by ruxolitinib. The central role of Mcl-1 was strengthened by the resistance of Mcl-1 overexpressing cells to apoptosis induction. The clinical relevance of Mcl-1 regulation by MACC1 was supported by their positive expression correlation in patient-derived tumors. Altogether, we reveal a novel death receptor-mediated apoptosis regulatory mechanism by MACC1 in solid cancers through modulation of the STAT1/3-Mcl-1 axis.

STK11 Loss Stabilizes MCL1 and Confers Targetable Drug Resistance in KRAS Mutant NSCLC

The combined KRAS/STK11 (serine‐threonine kinase 11, LKB1) mutated genotype is prevalent and predictive of poor clinical outcome in NSCLC as tumors are drug resistant. Here, we demonstrate that the bromodomain and extraterminal inhibitor (BETi) JQ1 can induce apoptosis in KRASm NSCLC by targeting the pro‐apoptotic BIM anti‐apoptotic BCL2/BCL‐XL axis, but not in KRASm/STK11m due to additional elevated MCL1. Specifically, loss of STK11 stabilizes anti‐apoptotic MCL1 protein via activation of the PI3K‐mTOR signaling axis. In NSCLC cell line models, we have demonstrated that overexpressing myristoylated‐PI3K increased MCL1 expression whereas the PI3K/mTOR inhibitor BEZ235 reduced MCL1 in a dose, time, and proteasome‐dependent, yet relatively GSK3β‐independent, manner. Furthermore, MCL1 stability also attenuates the antitumor efficacy of the direct BCL2/BCL‐XL inhibitor, ABT‐263 (Navitoclax) in KRASm/STK11m cells. However, combination of BETi or ABT‐263 with MCL1 protein reduction by siRNA or BEZ235, or direct MCL1 inhibition by the BH3 mimetic, A1210477, could sensitize resistant cells to apoptosis while no monotherapy was effective. Therefore, STK11 mutation or aberrant PI3K/mTOR pathway activations emerge as biomarkers of BET‐ or BCL2/BCL‐XL inhibitor resistance, suggesting patient selection for combined MCL1 inhibition.Support or Funding InformationThis work is supported by research Scholar grant RSG‐14‐229‐01 from the American Cancer Society and United Against Lung Cancer Legacy Program (Lung Cancer Research Foundation). This work is also supported by research fellowship from Sumitomo life social welfare services foundation (E.K), MINECO (SAF2010‐21769), ISCIII (RD12/0036/0045) and Generalitat Valenciana (ACOMP/2013/156 and ACIF/2013/239) (J.C.), and National Institutes of Health grants CA140594, CA122794, CA163896, CA166480 (K.K.W)

Abstract B46: A novel patient-derived xenograft model for evaluating therapies that target the CRLF2 signaling pathway to reduce health disparities for Hispanic children with leukemia

Abstract The purpose of the studies described here was to identify drug targets and develop a preclinical model for testing therapies that can reduce health disparities for Hispanic children with high-risk acute lymphoblastic leukemia (ALL). Hispanic children are 1.24 times more likely to develop ALL than non-Hispanic whites and that number rises to 2.09 by adolescence and early adulthood. A major contributor to this health disparity is a type high-risk B-cell ALL called CRLF2 B-ALL. CRLF2 B-ALL occurs 5 times more often in Hispanic children than others, is prevalent in adolescents and young adults, and is associated with a high relapse rate and poor prognosis. CRLF2 B-ALL is caused by genetic alterations that result in over expression of the cytokine receptor, CRLF2. The CRLF2 receptor is activated by the cytokine, TSLP, causing downstream activation of the JAK/STAT5 and PI3/AKT/MTOR pathways. A gene target of activated STAT5 in B cell precursors is Mcl-1, a Bcl2 family pro-survival molecule. In addition, Mcl-1 protein levels are known to be increased through post-transcriptional mechanisms by activation of the mTOR pathway. We hypothesized that the normal level of circulating TSLP cytokine could induce CRLF2 activation leading to increased Mcl-1 expression in CRLF2 B-ALL cells. Our data show that TSLP increases phosphorylation of STAT5, as well as AKT and S6 (downstream of mTOR) in primary CRLF2 B-ALL cells from Hispanic pediatric patients, even when activating JAK mutations are present. When CRLF2 B-ALL cells from Hispanic pediatric patients were cultured for 3 days with and without physiological levels of TSLP, flow cytometry showed that expression of the Mcl-1 protein was significantly increased in cultures with TSLP as compared to cultures without TSLP. CRLF2 B-ALL cells treated in vitro with Mcl-1 inhibitor showed dose-dependent increases in caspase 3 activation and apoptosis as indicated by flow cytometry. These data provide evidence that TSLP can contribute to leukemia cell survival and identify Mcl-1 inhibitor as a candidate therapy for CRLF2 B-ALL. Our next step was to develop a preclinical model for testing therapies that target genes, such as Mcl-1, that are regulated by TSLP-induced CRLF2 signals in this disease. Patient-derived xenograft (PDX) models produced by transplanting leukemia cells from patients into immune deficient mice provide an in vivo model of disease that includes contributions of the background genetic landscape that can influence disease progression or treatment outcome in health disparities diseases. PDX models are possible because most cytokines produced in the mouse are active on human cells, however mouse TSLP is species-specific. Thus classic PDX models do not provide TSLP that can activate the CRLF2 receptor that is overexpressed in CRLF2 B-ALL. To address this issue we engineered PDX mice to express physiological levels of human TSLP (+T PDX mice) and control -T mice that lacked human TSLP. In vivo TSLP activity was validated and +T PDX were successfully generated using leukemia cells from two Hispanic pediatric patients with CRLF2 B-ALL. To determine whether +T PDX mice provide a preclinical model of B-ALL that more closely mirrors patients than -T PDX mice, we compared RNAseq gene expression profiles of leukemia cells isolated from +T PDX and -T PDX mice to that from the original patient sample. The gene expression pattern in leukemia cells from +T mice was significantly closer to primary patient sample than that from -T mice. The +T PDX mice described here provide a novel in vivo preclinical model for evaluating efficacy of drugs, such as Mcl-1 inhibitor, in context of the background genetic landscape and physiological human TSLP present in patients. Citation Format: Kimberly J. Payne, Cornelia Stoian, Jacqueline S. Coats, Olivia Francis, Terry-Ann M. Milford, Ineavely Baez, Pierce J. McCarthy, George Mambo, Anna V.C. White, Mariah M.Z. Jackson, Juliette M. Personius, Veriah Vidales, Muhammad Omair Kamal, Shadi Farzin Gohar, Sinisa Dovat. A novel patient-derived xenograft model for evaluating therapies that target the CRLF2 signaling pathway to reduce health disparities for Hispanic children with leukemia. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B46.

PS2 - 194 Bcl-2 Family Member Mcl-1 Expression is Reduced Under Hypoxia by the E3 Ligase FBW7 Contributing to BNIP3 Induced Cell Death In Glioma Cells

Mcl-1 is an anti-apoptotic Bcl-2 family member that is often over-expressed in the malignant brain tumour glioblastoma (GBM). It has been previously shown that epidermal growth factor receptors (EGFR) up-regulate Mcl-1 expression contributing to a cell survival response. Hypoxia is a poor prognostic marker in glioblastoma despite the fact that hypoxic regions have areas of necrosis. Hypoxic regions of GBM also highly express the pro-cell death Bcl-2 family member BNIP3, yet when BNIP3 is over-expressed in glioma cells, it induces cell death. The reasons for this discrepancy are unclear. METHODS: Using malignant glioma cell lines +/- hypoxia, gain and/or loss of function assays of BNIP3 or Mcl-1 were performed. BNIP3 and MCL-1 expression was assessed in GBM tumours from adult patients and human gliomas grown as xenografts in immunocompromised mice. RESULTS: Mcl-1 expression is reduced under hypoxia due to degradation by the E3 ligase FBW7 leading to increased hypoxia-induced cell death. This cell death is augmented by EGFR activation leading to increased Mcl-1 expression under hypoxia. Conversely, BNIP3 is over-expressed in hypoxia at times when Mcl-1 expression is decreased. Knocking down BNIP3 expression reduces hypoxia cell death and Mcl-1 expression effectively blocks BNIP3-induced cell death. Of significance, BNIP3 and Mcl-1 are co-localized under hypoxia in glioma cells, GBM tumours and in xenograft glioma tumours expressing mutant EGFR (EGFRvIII). CONCLUSION: These results support that Mcl-1 can block the ability of BNIP3 to induce cell death under hypoxia in GBM tumours