Myeloma Cell Survival Research Articles

The deubiquitinase USP7 stabilizes Maf proteins to promote myeloma cell survival

The Maf proteins, including c-Maf, MafA, and MafB, are critical transcription factors in myelomagenesis. Previous studies demonstrated that Maf proteins are processed by the ubiquitin-proteasome pathway, but the mechanisms remain elusive. This study applied MS to identify MafB ubiquitination-associated proteins and found that the ubiquitin-specific protease USP7 was present in the MafB interactome. Moreover, USP7 also interacted with c-Maf and MafA and blocked their polyubiquitination and degradation. Consistently, knockdown of USP7 resulted in Maf protein degradation along with increased polyubiquitination levels. The action of USP7 thus promoted Maf transcriptional activity as evidenced by luciferase assays and by the up-regulation of the expression of Maf-modulated genes. Furthermore, USP7 was up-regulated in myeloma cells, and it was negatively associated with the survival of myeloma patients. USP7 promoted myeloma cell survival, and when it was inhibited by its specific inhibitor P5091, myeloma cell lines underwent apoptosis. These results therefore demonstrated that USP7 is a deubiquitinase of Maf proteins and promotes MM cell survival in association with Maf stability. Given the significance of USP7 and Maf proteins in myeloma genesis, targeting the USP7/Maf axle is a potential strategy to the precision therapy of MM.

Deep profiling of apoptotic pathways with mass cytometry identifies a synergistic drug combination for killing myeloma cells.

Multiple myeloma is an incurable and fatal cancer of immunoglobulin-secreting plasma cells. Most conventional therapies aim to induce apoptosis in myeloma cells but resistance to these drugs often arises and drives relapse. In this study, we sought to identify the best adjunct targets to kill myeloma cells resistant to conventional therapies using deep profiling by mass cytometry (CyTOF). We validated probes to simultaneously detect 26 regulators of cell death, mitosis, cell signaling, and cancer-related pathways at the single-cell level following treatment of myeloma cells with dexamethasone or bortezomib. Time-resolved visualization algorithms and machine learning random forest models (RFMs) delineated putative cell death trajectories and a hierarchy of parameters that specified myeloma cell survival versus apoptosis following treatment. Among these parameters, increased amounts of phosphorylated cAMP response element-binding protein (CREB) and the pro-survival protein, MCL-1, were defining features of cells surviving drug treatment. Importantly, the RFM prediction that the combination of an MCL-1 inhibitor with dexamethasone would elicit potent, synergistic killing of myeloma cells was validated in other cell lines, in vivo preclinical models and primary myeloma samples from patients. Furthermore, CyTOF analysis of patient bone marrow cells clearly identified myeloma cells and their key cell survival features. This study demonstrates the utility of CyTOF profiling at the single-cell level to identify clinically relevant drug combinations and tracking of patient responses for future clinical trials.

Multiple myeloma and integrins

Integrins play an important role in the homing, survival, proliferation, and drug resistance of multiple myeloma (MM) cells in the bone marrow. Among the many integrin families, the integrins α4β1 (VLA-4) and α4β7 have been reported to have important functions in MM cells. Previous studies have also reported that the three-dimensional structure of an integrin changes depending on its activation state; however, the conformations of integrins expressed in MM cells have not been studied so far. We recently observed that integrin α4β7 constitutively adopts an active conformation in MM cells, and chimeric antigen receptor (CAR) T cell therapy that targets the activated conformation of integrin β7 is a promising new treatment for MM. We are now clarifying the mechanism for the constitutive activation of integrin β7 in MM and its relationship with the pathology of MM.

Clinical prognostic implications of EPB41L4A expression in multiple myeloma.

Background: Multiple myeloma (MM) is one of the most common incurable malignancies in malignant plasma cell disease. EPB41L4A is a target gene for the Wnt/β-catenin pathway, which is closely related to the survival of multiple myeloma cells. However, there is currently no research report on the prognostic significance of the EPB41L4A gene in MM.Methods: We studied the biological significance and prognostic significance of EPB41L4A expression in MM by integrating 1956 MM samples from 7 datasets, and explored the relationship between EPB41L4A expression and MM ISS stage, molecular type, therapeutic response and survival.Results: We found that the expression level of EPB41L4A is inversely proportional to the copy number of 1q21 (P = 3.4e-13). EPB41L4A was low expressed in MAF, MMSET and proliferating molecular typing patients (P <= 0.001). High expression of EPB41L4A can predict good survival in MM (EFS: P < 0.0001; OS: P < 0.0001). We found that patients with relapsed MM had lower expression levels of EPB41L4A than those without recurrence (P = 0.0039). We also found that EPB41L4A can predict the prognosis of MM patients may be related to DNA replication. These results indicate that the initial expression level of EPB41L4A can predict the prognosis of MM patients.Conclusions: We found that the high expression of EPB41L4A predicts good survival level in MM.

Selective Antisense Oligonucleotide Inhibition of Human IRF4 Prevents Malignant Myeloma Regeneration Via Cell Cycle Disruption

In multiple myeloma, pro-inflammatory factors such as interleukin-6 signaling and downstream anti-viral response pathway activation have been correlated with disease progression, symptom severity, and cancer stem cell generation. However, the role of interferon-response factors in the maintenance of malignant progenitors has not been explored. We hypothesized that the key B-cell progenitor fate determinant, interferon-response factor-4 (IRF4), governs regeneration of drug-resistant malignant progenitors in multiple myeloma. Using diverse pre-clinical models, including a humanized in vivo model that recapitulates IRF4 pathway activation detected by RNA-sequencing in primary high-risk samples, we tested whether direct targeting of human IRF4 using state-of-the-art antisense oligonucleotide (ASO) agents could impair myeloma regeneration. While human IRF4 overexpression expanded a putative progenitor population in vitro, IRF4 ASO treatment impaired myeloma cell survival commensurate with reduced IRF4 and MYC gene and protein expression. In addition to impeding subcutaneous tumor formation and myeloma dissemination in xenograft immunocompromised mouse models, human IRF4-targeted ASO monotherapy significantly improved overall animal survival. Moreover, in a patient-derived mouse model of high-risk myeloma, treatment with a lead IRF4 ASO that will advance to a Phase 1 trial (NCT04398485) eradicated CD138-negative MM progenitors and their malignant plasma cell progeny at doses that spared normal human hematopoietic stem cells and B cell development. Complementary mechanistic studies uncovered a role for IRF4 inhibition in disrupting microenvironment-responsive cell cycle progression, down-regulating stem cell regulatory and cell adhesion transcript expression including MYC and CXCR4, and promoting sensitivity to standard-of-care therapeutic agents. These comprehensive therapeutic index and proof-of-concept studies will enable rapid clinical development of IRF4 inhibition to prevent myeloma relapse driven by retention of dormant, drug-resistant progenitors in inflammatory microenvironments.

Myeloma Cells Down-Regulate Adiponectin in Bone Marrow Adipocytes Via TNF-Alpha.

ABSTRACTMultiple myeloma is caused by abnormal plasma cells that accumulate in the bone marrow and interact with resident cells of the bone microenvironment to drive disease progression and development of an osteolytic bone disease. Bone marrow adipocytes (BMAds) are emerging as having important endocrine functions that can support myeloma cell growth and survival. However, how BMAds respond to infiltrating tumor cells remains poorly understood. Using the C57BL/KaLwRij murine model of myeloma, bone marrow adiposity was found to be increased in early stage myeloma with BMAds localizing along the tumor‐bone interface at later stages of disease. Myeloma cells were found to uptake BMAd‐derived lipids in vitro and in vivo, although lipid uptake was not associated with the ability of BMAds to promote myeloma cell growth and survival. However, BMAd‐derived factors were found to increase myeloma cell migration, viability, and the evasion of apoptosis. BMAds are a major source of adiponectin, which is known to be myeloma‐suppressive. Myeloma cells were found to downregulate adiponectin specifically in a model of BMAds but not in white adipocytes. The ability of myeloma cells to downregulate adiponectin was dependent at least in part on TNF‐α. Collectively our data support the link between increased bone marrow adiposity and myeloma progression. By demonstrating how TNF‐α downregulates BMAd‐derived adiponectin, we reveal a new mechanism by which myeloma cells alter the bone microenvironment to support disease progression. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Abstract C052: FGF trapping impairs multiple myeloma growth through c-Myc degradation-induced mitochondrial oxidative stress

Abstract Multiple myeloma (MM) remains incurable because of chemotherapeutic resistance. Fibroblast growth factors (FGF) play a pivotal role in MM by acting as an autocrine/paracrine mitogen on plasma cells, bone marrow-derived endothelial cells and fibroblasts. Also, a recurrent chromosomal translocation t(4;14) is associated with FGFR3 upregulation in MM patients. Thus, agents able to hamper FGF signaling may represent a novel approach for MM treatment. Recently we have identified the PTX3-derived small molecule NSC12 as the first orally active antitumor pan-FGF trap. Here, the role of FGF/FGFR system in MM cell survival and the therapeutic potential of NSC12 were investigated. In vitro effects of NSC12 were tested on four human MM cell lines harboring (KMS-11 and OPM-2 cells) or not (U-266 and RPMI8226 cells) the t(4:14) translocation and on patient-derived MM cells (N = 26). In vivo effects of FGF blockade were investigated using subcutaneous (KMS-11 and RPMI8226 cells) and systemic (MM-1S cells) xenografts grown in NOD/SCID mice. In addition, gene expression profiling (GEP) and gene set enrichment analyses (GSEA) were performed in NSC12-treated MM cells. NSC12 blocked the proliferation of all human MM cell lines tested, causing inhibition of FGFR signaling, downregulation of the anti-apoptotic protein mcl-1 and caspase 3 activation. Cytofluorimetric analysis revealed a significant increase of apoptotic cells as early as 6 hrs after NSC12 treatment, with 100% of cell death after 24 hrs even when MM cells were co-cultured with patient-derived bone marrow stromal cells. In vivo, NSC12 blocked FGFR activation and reduced the growth of subcutaneous xenografts and MM cell dissemination in the BM. GEP and GSEA analyses of NSC12-treated cells revealed the upregulation of oxidative stress-induced genes and the downmodulation of c-Myc targets. Accordingly, NSC12 caused the rapid proteasomal degradation of c-Myc paralleled by GSH depletion, mitochondrial ROS production and depolarization, DNA damage and finally apoptosis in KMS-11 cells but not in KMS-11 cells expressing the undegradable mutated (T58A) form of c-Myc. Interestingly, these findings were confirmed on Bortezomib-resistant MM cells as well as on bone marrow-derived primary MM cells from newly diagnosed and relapsed/refractory patients, including plasma cells bearing the t(4;14) translocation obtained from high-risk MM patients. Our data reveal that FGF blockade triggers MM mitochondrial oxidative stress, DNA damage and apoptotic cell death via the proteasomal degradation of the c-Myc oncoprotein. Altogether, our findings dissect for the first time the mechanism by which the FGF/FGFR system plays a non-redundant role in MM cell survival and disease progression, and indicate that FGF targeting may represent a therapeutic approach for MM patients with poor prognosis and advanced disease stage. Citation Format: Roberto Ronca, Gaia Cristina Ghedini, Federica Maccarinelli, Antonio Sacco, Silvia Laura Locatelli, Eleonora Foglio, Sara Taranto, Elisabetta Grillo, Sara Matarazzo, Riccardo Castelli, Vanessa Desantis, Nadia Cattane, Annamaria Cattaneo, Marco Mor, Carmelo Carlo-Stella, Aldo Maria Roccaro, Marco Presta, Arianna Giacomini. FGF trapping impairs multiple myeloma growth through c-Myc degradation-induced mitochondrial oxidative stress [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C052. doi:10.1158/1535-7163.TARG-19-C052

ATR addiction in multiple myeloma: synthetic lethal approaches exploiting established therapies.

Therapeutic strategies designed to interfere with cancer cell DNA damage response have led to the widespread use of PARP inhibitors for BRCA1/2-mutated cancers. In the haematological cancer multiple myeloma, we sought to identify analogous synthetic lethality mechanisms that could be exploited in established cancer treatments. The combination of ATR inhibition using the compound VX-970 with a drug eliciting interstrand cross-links, melphalan, was tested in in vitro, ex vivo, and most notably in in vivo models. Cell proliferation, induction of apoptosis, tumor growth and animal survival were assessed. The combination of ATM inhibition with a drug triggering double strand breaks, doxorucibin, was also analyzed. We found that ATR inhibition is strongly synergistic with melphalan, even in resistant cells. The combination was dramatically effective in targeting myeloma primary patient cells and cell lines by reducing cell proliferation and inducing apoptosis. The combination therapy significantly reduced tumor burden and prolonged survival in animal models. Conversely, ATM inhibition only marginally impacted on myeloma cell survival, even in combination with doxorucibin at high doses. These results indicate that myeloma cells extensively rely on ATR, but not on ATM, for DNA repair. Our findings postulate that adding an ATR inhibitor such as VX-970 to established therapeutic regimens may provide a remarkably broad benefit to myeloma patients.

GFI1-Dependent SGPP1 Repression Promotes Growth and Survival of Myeloma Cells

Multiple myeloma (MM) remains incurable for the vast majority of patients due to emergence of drug resistant clones and mutations inducing drug resistant relapses. This is despite the fact that new therapies have greatly improved progression-free and overall survival for patients with standard risk myeloma. We recently found that the transcriptional repressor GFI1 is increased in bone marrow stromal cells of MM patients (MM-BMSC) where it causes prolonged suppression of osteoblast differentiation, and in CD138+ cells from MM patients, where GFI1 levels significantly correlate with disease progression. We also found that GFI1 overexpression (o/e) enhances MM cell growth and partially confers resistance to proteasome inhibitors in vitro as well as enhances tumor growth and osteoclastogenesis in vivo. Although the mechanisms responsible for these GFI1 effects in p53wt MM cells were p53-dependent, we found that GFI1 is also essential for MM cell survival regardless of their p53 status. The p53-independent mechanisms responsible for Gfi1 effects on MM cells growth and survival of are unknown. Sphingolipids are bioactive lipids that can control MM cell growth and survival. The balance between the levels of Sphingosine-1-phosphate (S1P) and its metabolic precursors ceramide (Cer) and sphingosine (SPH) form a rheostat that determines whether a cell proliferates or dies. We hypothesized that GFI1 represses SGPP1, the enzyme responsible for degrading S1P via salvage and recycling of sphingosine into long-chain ceramides. This repression changes the intracellular sphingolipid profile (Cer/S1P/SPH ratio) to maintain c-Myc upregulation in a protein phosphatase 2 (PP2A)-dependent manner, thus promoting growth and survival of MM cells. To test this hypothesis we measured S1P, SPH and Cer levels by mass spectrometry (LC-MS/MS). LC-MS/MS evaluation showed that bone marrow plasma of MM patients has significant higher levels of S1P when compared to normal donors. Moreover, intracellular S1P levels of MM.1S GFI1 o/e cells were also significantly higher as compared to those of MM.1S empty vector controls. Knock-down (KD) of Gfi1 in MM.1S cells strikingly increased SGPP1 and decreased SphK1 (the enzyme which catalyzes S1P production) mRNA levels, while GFI1 o/e cells had the opposite effect. We found that CD138+ cells isolated from MM patients expressed elevated levels of SphK1 mRNA compared to MGUS patients, and that SphK1 protein levels directly correlate with GFI1 levels in MM patient CD138+ cells and cell lines (r= 0.527). We also detected an indirect correlation (r= -0.961) between GFI1 and SGPP1 mRNA levels in five different MM cell lines. These results indicate a GFI1-dependent imbalance of the enzymes regulating S1P production. Further, KD GFI1 and SphK1 inhibition (5 μM SK1I) had a profound inhibitory effect on c-Myc protein levels and induced caspase 3 activation as detected by Western blotting, while GFI1 o/e cells had significant higher levels of c-Myc and were more resistant to SK1I treatment. Exogenous ceramide (10 μM Cer 16:0) treatment or SphK1 inhibition (5 μM SK1I), both treatments known to trigger intracellular ceramide production, significantly inhibited MM cell viability (measured by AlamarBlue), regardless of their p53 status (MM1.S p53 +/+ and KMS-11 p53 -/-). This inhibition of MM viability was GFI1-dependent, as GFI1 o/e cells were significantly more resistant to ceramide-induced cell death, which was PP2A dependent, as PP2A inhibition with okadaic acid (OA) restored it. MM.1S cells with KD of GFI1 exhibited significantly higher PP2A activity then control cells, supporting our observation that c-Myc modulation by GFI1 is PP2A-dependent. c-Myc protein levels were significantly decreased in MM.1S control cells treated with ceramide and rescued by OA pre-treatment; thus mimicking the effects of changing GFI1 levels and I2PP2A (the PP2A endogenous inhibitor) and confirms that PP2A mediates the effects of GFI1 on c-Myc. Taken together, our results show that GFI1 acts as a key regulator of MM growth and survival, at least partially through modulation of SGPP1. Therefore, targeting lipid metabolism to modulate the levels of specific bioactive lipid components that can modify cancer cell fate may provide a new and attractive therapeutic approach for MM. Disclosures Roodman: Amgen: Membership on an entity's Board of Directors or advisory committees.

A High-Throughput Drug Screen Reveals a Novel Compound Class That Significantly Depletes IRF4 Expression in Multiple Myeloma

Introduction Multiple myeloma (MM) is an incurable hematological malignancy characterized by the clonal expansion of malignant plasma cells (PCs) within the bone marrow. MM is genetically heterogeneous with aberrations including hyperdiploidy and chromosomal translocations commonly involving the immunoglobulin heavy chain (IgH) region. Many transcription factors can revoke their normal processes and act as oncogenes when they are brought under the control of IgH regulatory regions by a chromosomal translocation. Interferon Regulatory Factor 4 (IRF4) is a transcription factor which controls plasma cell differentiation and possesses many regulatory roles including interferon response, immune cell response, cell proliferation, apoptosis, and metabolism. IRF4 has proven to be a genetic vulnerability in MM as silencing studies in a large panel of MM cell lines with various genetic etiologies have demonstrated IRF4 expression is essential for MM cell survival. Standard of care treatments that indirectly suppress IRF4 including Proteasome inhibitors and Cereblon modulators have provided the greatest clinical outcomes for patients. However, like many other transcription factors, IRF4 has been notoriously difficult to target due to the protein's lack of amenable binding pockets favored for small molecule inhibitor development. Thus, identifying novel mechanisms and compounds to target IRF4 (directly or indirectly) can provide significant clinical impacts for MM patients. Methods To discover compounds capable of depleting IRF4 levels, we performed a high-throughput drug screen utilizing the Selleckchem Drug Repurposing Library on a widely accepted IRF4-dependent cell line. This library consists of over 2,000 diverse compounds that have well validated mechanisms of actions and have additionally passed clinical phase 1 safety trials for accelerated translational use. MM.1S cells were treated for 48 hours in duplicate (n = 2) with 10 μM compound. Following treatment, the cells were fixed, permeabilized, and stained for viability and IRF4 levels. IRF4 expression and viability was acquired by using flow cytometry, with high dose lenalidomide and shRNA for IRF4 as positive controls. Compounds that reduced IRF4 levels and cell viability across both experimental runs were ranked and selected with a cutoff of 40% as promising candidate compounds for further validation. Results Our drug screen results revealed 20 compounds (undisclosed) which met our cutoff of a decrease of IRF4 levels by 40% or greater. Ten hits were selected as having greater or equal to IRF4 depleting properties of lenalidomide and moved forward to be validated by western blot. Six drugs were shown to deplete IRF4 by western blot in MM.1S and KMS-18 cells at 10 μM doses. Interestingly, 4 out of the 10 hits all belong to same compound class that selectively bind to the same target receptor (undisclosed). Additional experiments confirmed these class of compounds deplete IRF4 levels in a dose dependent manner (EC50 = 1 μM). A time course revealed that IRF4 levels decrease shortly after the binding of these drugs to their widely reported target receptor, suggesting this is a selective drug/target receptor-mediated mechanism directly altering levels of IRF4. In vitro studies demonstrated the ability to both halt cell growth and decrease the viability of a panel of 8 MM cell lines, with IC50's ranging from 1.6 - 8.5 μM. Synergy studies with Lenolidomide and Bortezomib are underway to determine any synergistic combinations with standard of care therapies. In vivo studies and RNA-sequencing are also currently underway to determine the impact of these compounds on MM tumor growth and overall survival, as well as better define the mechanism of action driving this novel class of IRF4 targeting compounds. Conclusions Despite knowledge that IRF4 is a biologically potent target in MM there have been no extensive studies highlighting drugs capable of targeting this transcription factor and its oncogenic signaling network. This screen has revealed novel compounds, some of which are clinically used, that are capable of depleting a highly dependent gene in MM. Notably, these compounds are able to deplete IRF4 in a novel mechanism which is capable of affecting survival of MM cell lines that represent the heterogeneity of myeloma, and thus holds potential for significant clinical impact. Disclosures Ghobrial: Amgen: Consultancy; Janssen: Consultancy; Celgene: Consultancy; Takeda: Consultancy; Sanofi: Consultancy; BMS: Consultancy.

T(11;14) and High BCL2 Expression Are Predictive Biomarkers of Response to Venetoclax in Combination with Bortezomib and Dexamethasone in Patients with Relapsed/Refractory Multiple Myeloma: Biomarker Analyses from the Phase 3 Bellini Study

T(11;14) and High BCL2 Expression Are Predictive Biomarkers of Response to Venetoclax in Combination with Bortezomib and Dexamethasone in Patients with Relapsed/Refractory Multiple Myeloma: Biomarker Analyses from the Phase 3 Bellini Study

Novel ZBP1-IRF3 Dependency in Multiple Myeloma Mediated By IRF3-Driven Regulation of Cell Cycle Genes

ZBP1 is an inducible nucleic acid (NA) sensor that is activated when pathogen NA bind to its Zα and Zβ domains. ZBP1 is required for TBK1-dependent phosphorylation of the transcription factor IRF3 (pIRF3) followed by its direct activation of type I interferon genes. However, the role, if any, of ZBP1 in tumour biology is not known. By searching for genes selectively expressed in multiple myeloma (MM) we identified ZBP1 mRNA expressed in 29 MM cell lines (MMCL) but not in &gt;1000 other cancer cell lines (CCLE dataset); ZBP1 was expressed in all 766 patient myeloma PC (CoMMpass dataset) but not in normal blood cells (Blueprint) or 53 healthy tissues (GTex). We confirmed expression of ZBP1 mRNA and/or protein in MMCL, primary human and murine germinal centre B (GCB) and plasma cells (PC) as well as in myeloma PC. By inducing T cell-dependent humoral immune responses after ip alum-NP-KLH immunisation, we explored the role of selective and constitutive expression of Zbp1 in GCB to PC transition. We found no differences in the frequency of splenic GCB cells and PC between control WT and Zbp1-/- mice and in GCB cell frequency between immunised WT and Zbp1-/- mice. However, compared to WT, the increase in PC frequency in immunised Zbp1-/- mice was 50% lower (n=10/group, p&lt;0.0001) commensurate with a 40% (n=6/group, p&lt;0.01), lower increase in NP-KLH-specific IgG but not IgM levels in Zbp1-/- mice. These findings suggest that although Zbp1 is not required for GCB cell and PC development it is required for optimal, T cell-dependent humoral immune responses. To explore the function of ZBP1 in MM we depleted by 2 lentiviral shRNAs either isoform 1 (contains both Zα and Zβ domains; shRNA1) or both isoform 1 and isoform 2 (latter lacks Zα domain; shRNA2). Both shRNAs were toxic to all 5 MMCL tested suggesting that isoform 1 but not isoform 2 is essential for myeloma cell survival. This effect was specific because survival of K562 cells, which lack expression of ZBP1, was not affected by either shRNA and exogenous ZBP1 cDNA rescued cell death of ZBP1-depleted myeloma cells. Dox-induced ZBP1 depletion was toxic to MMCL in vitro and significantly inhibited myeloma cell growth in a subcutaneous NSG model of the MMCL H929 and MM.1S. Together, these findings reveal a novel myeloma cell-specific ZBP1 dependency. Transcriptome analysis of ZBP1-depleted H929 and MM.1S cells showed amongst the significantly downregulated genes enrichment for the cell cycle control and DNA repair pathways consistent with a critical role of ZBP1 in promoting myeloma cell proliferation. Flow-cytometric analysis of ZBP1-depleted MMCL as well as of patient-derived myeloma PC revealed cell cycle arrest at the G0/1 phase and increasing apoptosis. Exploring potential links with IRF3, we first observed that unlike in non-malignant cells, IRF3 was constitutively phosphorylated in MMCL. Using protein-co-immunoprecipitation we found that endogenous ZBP1 interacts with IRF3 and TBK1 while upon co-transfection with different ZBP1 deletion mutants, ZBP1-IRF3 interaction required primarily the ZBP1, RHIM domain-containing, C-terminus. Further, while in ZBP1-depleted myeloma cells total IRF3 and TBK1 levels were not altered, pIRF3 and pTBK1 levels decreased thus showing a post-translational dependency of constitutive pIRF3 and pTBK1 on ZBP1. Finally, pharmacological inhibition of TBK1 resulted in decrease of pIRF3 without affecting total IRF3. Importantly, shRNA-mediated IRF3 depletion resulted in cell cycle arrest and death of MMCL. By integrating histone mark and in-house IRF3 ChiP-seq with transcriptome of IRF3-depleted MM.1S cells we identified 770 down- and 330 up-regulated genes predicted to be directly regulated by IRF3. Pathway enrichment analysis confirmed cell cycle as the most highly regulated by IRF3. Notably, we observed no direct or indirect regulation of the interferon genes (e.g., IFNA1, IFNB1) by IRF3. As well as the IRF3 motif, IRF3 cistrome analysis revealed significant enrichment for the distinct IRF4 motif. Integration of the IRF3/IRF4 cistromes identified &gt;80% IRF3 binding regions are co-occupied by IRF4 and co-regulation of cell cycle genes. Further we validated IRF3-IRF4 interaction at the IRF4 super-enhancer by ChIP-re-ChIP. These data show a novel dependency in MM comprising constitutive activation of the ZBP1-IRF3 pathway and regulation of cell cycle and proliferation by IRF3 thus providing opportunities for therapeutic targeting. Disclosures Caputo: GSK: Research Funding. Auner:Amgen: Other: Consultancy and Research Funding; Takeda: Consultancy; Karyopharm: Consultancy. Karadimitris:GSK: Research Funding.

Targeting Glycolysis in Multiple Myeloma: Novel Strategies in the Treatment of Proteasome Inhibitor Resistant in Hypoxic Conditions

Introduction: Multiple myeloma (MM) is one of the hematological malignancy and characterized by the clonal expansion of plasma cells in the bone marrow. The treatment of MM patients has been dramatically changed by new agents such as proteasome inhibitors and immunomodulatory drugs, however, many patients will relapse even if new agents provide therapeutic advantages. Therefore, a new strategy is still needed to increase MM patient survival. Hypoxia is an important component of the bone marrow microenvironment. Hypoxia may increase myeloma cell survival. Because cells shift primarily to a glycolytic mode for generation of energy in hypoxic conditions, glycolytic activities can be targeted therapeutically in MM patients. The 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB) is responsible for maintaining the cellular levels of fructose-2,6-bisphosphate which is a regulator of glycolysis. Materials and Methods: In this study, we investigated whether PFKFB was involved in myeloma cells in hypoxia condition. We also investigated whether PFKFB inhibitors could suppress myeloma cells and enhance the sensitivity of myeloma cells to proteasome inhibition. Results: We first investigated the expression of PFKBP in the myeloma cell lines in hypoxia condition. PFKFB family contains four tissue-specific isoenzymes encoded by four different genes. We found expression of PFKBP3 and PFKBP4 were increased in hypoxia condition. We found gene expression of PFKBP3 and PFKBP4 were involved in myeloma cell lines and myeloma patient samples in hypoxia condition from the public microarray datasets (GSE80140 and GSE80545). In hypoxia condition, expression of hypoxia-inducible factor 1α (HIF1α) was increased and phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) was activated in myeloma cell lines. Expression of PFKBP3 and PFKBP4 were inhibited by HIF1α inhibitor and p38 MAPK inhibitor treatment. In the hypoxia condition, activity of proteasome inhibitors were reduced compared to normoxia condition. We next investigated whether PFKBP3 inhibitor, PFK158 and PFKBP4 inhibitor, 5MPN could inhibit the proliferation of myeloma cells. We found PFK158 and 5MPN treatment inhibited the growth of myeloma cells in a dose dependent manner in hypoxia condition. Combined treatment of myeloma cells with carfilzomib and PFK158 or 5MPN caused more cytotoxicity than each drug alone. Caspase 3/7 activity and cellular cytotoxicity was also increased. We found proteasomal activity was also reduced by carfilzomib and PFK158 or 5MPN treatment. Adenosine triphosphate (ATP) is the most important source of energy for intracellular reactions. Intracellular ATP levels drastically decreased after carfilzomib and PFK158 or 5MPN treatment. Because mitochondria generate ATP and participate in signal transduction and cellular pathology and cell death. The quantitative analysis of JC-1 stained cells changed mitochondrial membrane potential in cell death, which were induced by carfilzomib and PFK158 or 5MPN on myeloma cells. In the hypoxia condition and inhibitor treatment, glycolytic activities (e.g. glucose and lactate) were changed in myeloma cells. Conclusion: The PFKBP3 and PFKBP4 are enhanced in hypoxia condition and involved in proteasome inhibitor sensitivity. Our data also suggested that administration of PFKBP3 and PFKBP4 inhibitors may be a powerful strategy against myeloma cells and enhance cytotoxic effects of proteasome inhibitors in hypoxia condition. Disclosures No relevant conflicts of interest to declare.

The Role of Proteasome Activator PA28α in Multiple Myeloma

Multiple myeloma (MM) is a commonly occurring hematologic malignancy in the United States with poor prognosis. Among all treatments, proteasome inhibitor (PI) based regimens have been a major breakthrough for patients' outcomes. Available PIs all target 20S proteasome core complex, and the duration of response is limited by toxicity and resistance development. Until now, the underlying mechanism of drug resistance remains unclear. The proteasome is the major proteolytic machinery in protein homeostasis which is pivotal for myeloma cell survival. A functional proteasome consists of 20S proteasome core particle with regulatory particle on one or both ends. There are 3 types of proteasome regulators that could activate a 20S proteasome, PA700 (19S), 11S REG (PA28) and PA200. The 11S REG (PA28) protein family consists of three members, α, β, and γ. PA28 α/β are IFN-γ inducible and with higher expression in antigen presenting cells. Currently, the function of 11S subunit remains largely unknown. Our analysis of plasma cells from MM patients and healthy donors has demonstrated that expression of 11S proteasome is higher in myeloma cells than normal plasma cells and progressively upregulated with disease progression. To further identify the function of 11S proteasome especially PA28α in MM, we generate PA28α knockdown stable MM cell lines. We have found that knockdown of PA28α inhibits MM cell growth and proliferation, also induces myeloma cell resistance to PIs. The mechanism of PI resistance is different from knocking down of 19S or 20S proteasome subunits. Silencing of PA28α inhibits proteasome activity and decreases proteasome work load concurrently, resulting in a favorable proteasome load vs capacity ratio. Altogether, in this report, we describe the function of PA28α in MM cells, also provide novel insights into regulating PIs sensitivity through modulation of the 11S proteasome subunit PA28α. Disclosures Hofmeister: Nektar: Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Imbrium: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Membership on an entity's Board of Directors or advisory committees. Kaufman:Karyopharm: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria; Amgen: Consultancy; Bristol-Myers Squibb: Consultancy; Incyte: Consultancy; Celgene: Consultancy; Winship Cancer Institute of Emory University: Employment; AbbVie: Consultancy; Takeda: Consultancy; TG Therapeutics: Consultancy. Nooka:Amgen: Honoraria, Other: advisory board participation; GSK: Honoraria, Other: advisory board participation; Celgene: Honoraria, Other: advisory board participation; Takeda: Honoraria, Other: advisory board participation; Spectrum pharmaceuticals: Honoraria, Other: advisory board participation; BMS: Honoraria, Other: advisory board participation; Janssen: Honoraria, Other: advisory board participation; Adaptive technologies: Honoraria, Other: advisory board participation. Boise:Genentech Inc.: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Honoraria, Research Funding. Lonial:Takeda: Consultancy, Research Funding; Amgen: Consultancy; BMS: Consultancy; Janssen: Consultancy, Research Funding; GSK: Consultancy; Karyopharm: Consultancy; Genentech: Consultancy; Celgene Corporation: Consultancy, Research Funding.

CC-92480 Is a Novel Cereblon E3 Ligase Modulator with Enhanced Tumoricidal and Immunomodulatory Activity Against Sensitive and Resistant Multiple Myeloma Cells

Lenalidomide- and pomalidomide-based therapies are effective drugs in the treatment of patients with multiple myeloma (MM), however most patients with MM eventually relapse or become resistant. CC-92480, a novel cereblon (CRBN) E3 ligase modulator (CELMoD) with multiple activities including potent immunomodulation and single-agent antiproliferative effects, is being investigated in a phase 1 clinical trial (CC-92480-MM-001; NCT03374085) for patients with relapsed/refractory MM (RRMM). The present study investigates the preclinical data and mechanism of action of CC-92480 in MM models. CELMoD agents bound to CRBN confer differentiated substrate-degradation specificity on the CRL4CRBN E3 ubiquitin ligase. CRBN-modulator agents mediate destruction of Ikaros and Aiolos, transcription factors that contribute to myeloma cell survival. CC-92480 was found to produce rapid, deep, and sustained degradation of Ikaros and Aiolos, with superior antimyeloma activity. Accordingly, in a CRBN protein competitive binding assay, CC-92480 displaced a Cy-5-labeled CELMoD analog from CRBN with a 50% inhibitory concentration (IC50) value of 0.03 μM, whereas lenalidomide competed with an IC50 value of 1.27 μM in the same assay, demonstrating a higher binding affinity of CC-92480 for CRBN. Additionally, CC-92480 promoted the recruitment of Ikaros to the CRBN E3 ligase complex more effectively than pomalidomide in 2 orthogonal CRBN/Ikaros binding assays; it also triggered a more extensive cellular ubiquitination of Ikaros, and a faster, more efficient depletion of cellular Ikaros and Aiolos than pomalidomide. In various MM cell lines, including those with acquired resistance to lenalidomide or pomalidomide and low levels of CRBN, CC-92480 produced robust degradation of Ikaros and Aiolos followed by strong reduction of 2 additional and highly critical transcription factors, c-Myc and interferon regulatory factor 4, which are linked to the induction of apoptosis as measured by cleaved caspase-3. The tumoricidal activity of CC-92480 was shown to be CRBN dependent, since the effect was prevented by complete loss of CRBN or by the stabilization of Ikaros and Aiolos. CC-92480 displayed broad and potent antiproliferative activity across a panel of 20 MM cell lines that are either sensitive, have acquired resistance, or are refractory to lenalidomide or pomalidomide; the cell lines also contained diverse chromosomal translocations and oncogenic drivers typically found in MM patients. Approximately half of the MM cell lines evaluated were highly sensitive to CC-92480, with IC50 values for antiproliferative activity ranging from 0.04 to 5 nM; only 2 cell lines had IC50 values &gt; 100 nM. CC-92480 inhibits cell proliferation and induces apoptosis in MM cell lines that are not sensitive to lenalidomide or pomalidomide. This panel of cell lines includes both refractory cell lines and resistant cell lines generated through continuous exposure to lenalidomide and pomalidomide that acquired low levels of CRBN protein or mutations in the CRBN gene. CC-92480 also induced deep destruction of Ikaros and Aiolos in cultures of peripheral blood mononuclear cells (PBMCs), which led to the activation of T cells and increased production of the cytokines interleukin-2 and interferon gamma. These responses occurred at the range of CC-92480 concentrations that show potent tumoricidal effect against MM cells. The T cell activation and enhanced cytokine production by CC-92480 led to the potent and effective immune-mediated killing of MM cells in co-cultures with PBMCs. CC-92480 is a potent antiproliferative and proapoptotic novel CELMoD with enhanced autonomous cell-killing activity in MM cells that are either sensitive, resistant, or have acquired resistance to lenalidomide and pomalidomide. CC-92480 has a unique and rapid degradation profile stemming from the enhanced efficiency to drive the formation of a protein-protein interaction between Ikaros and Aiolos and CRBN, inducing cytotoxic effects in a CRL4CRBN-dependent fashion that leads ultimately to the induction of apoptosis, even in the context of low or mutated CRBN protein. Additionally, similar to lenalidomide, CC-92480 conserves immunomodulatory activity against MM cells. These data support the clinical investigation of CC-92480 in patients with RRMM. Disclosures Lopez-Girona: Celgene Corporation: Employment. Havens:Pfizer: Employment, Equity Ownership; Celgene: Equity Ownership. Lu:Celgene Corporation: Employment, Equity Ownership. Rychak:Celgene Corporation: Employment, Equity Ownership. Mendy:Celgene Corporation: Employment. Gaffney:Celgene: Employment. Surka:Celgene: Employment, Equity Ownership. Lu:Celgene Corporation: Employment, Equity Ownership. Matyskiela:Celgene corporation: Employment. Khambatta:Celgene: Employment. Wong:Celgene Corporation: Employment, Equity Ownership. Hansen:Celgene Corporation: Employment. Pierce:Celgene Corporation: Employment, Equity Ownership. Cathers:Global Blood Therapeutics (GBT): Employment; Celgene Corporation: Equity Ownership. Carmichael:Celgene plc: Employment, Equity Ownership.

Activity of TAS4464, a novel NEDD8 activating enzyme E1 inhibitor, against multiple myeloma via inactivation of nuclear factor κB pathways.

The ubiquitin proteasome pathway is essential for the proliferation and survival of multiple myeloma (MM) cells. TAS4464, a novel highly potent inhibitor of NEDD8 activating enzyme, selectively inactivates cullin‐RING ubiquitin E3 ligases, resulting in accumulation of their substrates. Here, we examined 14 MM cell lines treated with TAS4464. TAS4464 induced growth arrest and cell death in the MM cell lines even in the presence of bone marrow stromal cells. It also induced the accumulation of phospho‐inhibitor of κBα and phospho‐p100, impaired the activities of nuclear factor κB (NF‐κB) transcription factors p65 and RelB, and decreased the expression of NF‐κB target genes, suggesting that TAS4464 inhibits both the canonical and non–canonical NF‐κB pathways. TAS4464 had similar effects in an in vivo human‐MM xenograft mouse model in which it was also observed to have strong antitumor effects. TAS4464 synergistically enhanced the antitumor activities of the standard MM chemotherapies bortezomib, lenalidomide/dexamethasone, daratumumab and elotuzumab. Together, these results suggest that the anti–MM activity of TAS4464 occurs via inhibition of the NF‐κB pathways, and that treatment with TAS4464 is a potential approach for treating MM by single and combination therapies.

RNF6 promotes myeloma cell proliferation and survival by inducing glucocorticoid receptor polyubiquitination.

RNF6, a RING-type ubiquitin ligase, has been identified as an oncogene in various cancers but its role in multiple myeloma (MM) remains elusive. In the present study we first showed that the expression levels of RNF6 in MM were significantly elevated compared with the bone marrow cells of healthy donors. Overexpression of RNF6 in LP1 and PRMI-8266 MM cell lines promoted cell proliferation, whereas knockdown of RNF6 led to apoptosis of MM cells. Furthermore, we revealed that RNF6, as a ubiquitin ligase, interacted with glucocorticoid receptor (GR) and induced its K63-linked polyubiquitination. Different from current knowledge, RNF6 increased GR stability at both endogenous and exogenous contexts. Such an action greatly promoted GR transcriptional activity, which was confirmed by luciferase assays and by the increased expression levels of prosurvival genes including Bcl-xL and Mcl-1, two typical downstream genes of the GR pathway. Consistent with these findings, ectopic expression of RNF6 in MM cells conferred resistance to dexamethasone, a typical anti-myeloma agent. In conclusion, we demonstrate that RNF6 promotes MM cell proliferation and survival by inducing atypical polyubiquitination to GR, and RNF6 could be a promising therapeutic target for the treatment of MM.

The Covalent CDK7 Inhibitor THZ1 Potently Induces Apoptosis in Multiple Myeloma Cells In Vitro and In Vivo.

The goal of this study was to characterize the activity of the covalent CDK7 inhibitor THZ1 in multiple myeloma models. Multiple myeloma lines were exposed to varying THZ1 concentrations alone or with carfilzomib or ABT-199, after which apoptosis was monitored by flow cytometry, protein expression by Western blot analysis, mRNA by RT-PCR. Analogous studies were performed in cells ectopically expressing c-MYC, MCL-1, or BCL-XL, or CRISPER-Cas CDK7 sgRNA knockout. Primary multiple myeloma cells were exposed to THZ1 ± carfilzomib or ABT-199. In vivo effects of THZ1 were examined in a systemic U266 xenograft model. THZ1 markedly diminished multiple myeloma cell proliferation and survival despite bortezomib or stromal cell resistance in association with G2-M arrest, inactivation of CTD RNA Pol II, dephosphorylation of CDKs 7 as well as 1, 2, and 9, and MCL-1, BCL-xL, and c-MYC mRNA or protein downregulation. Ectopic MCL-1, c-MYC, or BCL-XL expression significantly protected cells from THZ1 lethality. Both THZ1 and CRISPR-Cas CDK7 knockout sharply diminished multiple myeloma cell proliferation and significantly increased carfilzomib and ABT-199 lethality. Parallel effects and interactions were observed in primary CD138+ (N = 22) or primitive multiple myeloma cells (CD138-/CD19+/CD20+/CD27+; N = 16). THZ1 administration [10 mg/kg i.p. twice daily (BID), 5 days/week] significantly improved survival in a systemic multiple myeloma xenograft model with minimal toxicity and induced similar events observed in vitro, for example, MCL-1 and c-MYC downregulation. THZ1 potently reduces multiple myeloma cell proliferation through transcriptional downregulation of MCL-1, BCL-XL, and c-MYC in vitro and in vivo. It warrants further attention as a therapeutic agent in multiple myeloma.

RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

Oncogenic RAS provides crucial survival signaling for up to half of multiple myeloma (MM) cases, but has so far remained a clinically undruggable target. RAS-like protein (RAL) is a member of the RAS superfamily of small GTPases and is considered to be a potential mediator of oncogenic RAS signaling. In primary MM, we found RAL to be overexpressed in the vast majority of samples when compared with pre-malignant monoclonal gammopathy of undetermined significance or normal plasma cells. We analyzed the functional effects of RAL abrogation in myeloma cell lines and found that RAL is a critical mediator of survival. RNAi-mediated knockdown of RAL resulted in rapid induction of tumor cell death, an effect which was independent from signaling via mitogen-activated protein kinase, but appears to be partially dependent on Akt activity. Notably, RAL activation was not correlated with the presence of activating RAS mutations and remained unaffected by knockdown of oncogenic RAS. Furthermore, transcriptome analysis yielded distinct RNA expression signatures after knockdown of either RAS or RAL. Combining RAL depletion with clinically relevant anti-myeloma agents led to enhanced rates of cell death. Our data demonstrate that RAL promotes MM cell survival independently of oncogenic RAS and, thus, this pathway represents a potential therapeutic target in its own right.

ATR addiction in Multiple Myeloma: synthetic lethal approaches exploiting established therapies

Therapeutic strategies designed to tinker with cancer cell DNA damage response have led to the widespread use of PARP inhibitors for BRCA1/2-mutated cancers. In the hematological cancer multiple myeloma, we sought to identify analogous synthetic lethality mechanisms that could be leveraged upon established cancer treatments. The combination of ATR inhibition with a drug eliciting interstrand cross-links, melphalan, was tested in in vitro, ex vivo, and most notably in vivo models. Cell proliferation, induction of apoptosis, tumor growth and animal survival were assessed. The combination of ATM inhibition with a drug triggering double strand breaks, doxorucibin, was also probed. We found that ATR inhibition is strongly synergistic with melphalan, even in resistant cells. The combination was dramatically effective in targeting myeloma primary patient cells and cell lines reducing cell proliferation and inducing apoptosis. The combination therapy significantly reduced tumor burden and prolonged survival in animal models. Conversely, ATM inhibition only marginally impacted on myeloma cell survival, even in combination with doxorucibin at high doses. These results indicate that myeloma cells extensively rely on ATR, but not on ATM, for DNA repair. Our findings posit that adding ATR inhibitors to established therapeutic regimens provides a remarkably broad benefit to myeloma patients.