Primary Multiple Myeloma Cells Research Articles

PF561 DUAL‐TARGETING OF PROMOTER AND ENHANCER DRIVEN PROCESSES SUPPRESSES MYELOMA CELL GROWTH AND VIABILITY VIA PERTURBATION OF THE MYELOMA PROLIFERATIVE PROGRAM

Background:Cancer cells are characterized by perturbed transcriptional profiles. These dysregulated programs create dependencies on transcriptional regulators not predicted by genetic changes. Tumor cells, including multiple myeloma cells, tend to develop striking dependencies on super‐enhancer regulatory elements. In addition to super‐enhancers, promoter proximal transcription factors such as E2F1 and SP1 play a prominent role in myeloma cell biology via their control of proliferative and survival genes. Importantly, our genome‐wide profiling of the MM epigenome landscape revealed that promoter‐ and enhancer‐associated factors govern distinct biological functions providing a non‐overlapping control of the myeloma transcriptome.Aims:The goal of this study is to improve our understanding of global gene regulation in MM, with the aim of deploying novel therapeutics to target uncontrolled MM cell proliferation.Methods:We performed integrated genomic analysis using a combination of ChIP‐seq, ATAC‐seq, and RNA‐seq technologies as well as loss of function screening in MM cell lines and primary MM cells.Results:Global chromatin analysis of MM cells revealed two distinct regulatory axes, with SP1, DP1, E2F and MYC predominantly localized to promoters of growth/proliferation genes and CDK9, BETs and other factors disproportionately enriched at enhancer‐regulated tissue‐specific genes. This divergent enhancer and promoter axes is also observed in diffuse large B‐cell lymphoma, suggesting a broader transcriptome control process. Importantly, we have observed that dual inhibition of promoter and enhancer axes using RNA interference shows a superior inhibition of MM cell growth and viability both in vitro and in vivo compared to single perturbation alone, providing an important molecular mechanism for combination therapy. We have further gone on to target TFs SP1 with a small molecule inhibitor Terameprocol which inhibits its DNA binding activity and a cell‐permeable peptide to disrupt the heterodimerization of E2F1 with its partner DP1 responsible for the E2F transcriptional activity. These strategies have been successful in inhibiting MM cell growth and viability, and the effect was augmented in the presence of inhibitors of enhancers, such as the small molecule BRD4 inhibitor JQ1.We have further investigated inhibitors of upstream regulators of the pRB‐E2F axis such as CDK4/6 to impact E2F1 activity. CDK4–6 complexes can phosphorylate RB, releasing the E2F and modulating the expression of E2F target genes. Therefore, we investigated the combination of CDK4/6 inhibitor Palbociclib with low doses of JQ1 and observed a profound effects on E2F promoter driven transcriptional activity, and a highly synergistic effect on growth and survival in a large panel of cell lines and primary MM cells from newly diagnosed and relapsed patients. Cell cycle analysis revealed complete G1 arrest after treatment. Importantly, the combination regimen had no significant effect on healthy donor PBMCs activated with PHA, suggesting a favorable therapeutic index.Summary/Conclusion:These data implicate the existence of a sequestered cellular function by promoter and enhancer driven processes providing non‐overlapping vulnerabilities. Simultaneous targeting of these processes using clinically applicable agents can synergistically impair the myeloma proliferative program, with potential for development of a promising therapeutic strategy.

Metabolic, Anti-apoptotic and Immune Evasion Strategies of Primary Human Myeloma Cells Indicate Adaptations to Hypoxia*

Multiple Myeloma (MM) is an incurable plasma cell malignancy primarily localized within the bone marrow (BM). It develops from a premalignant stage, monoclonal gammopathy of undetermined significance (MGUS), often via an intermediate stage, smoldering MM (SMM). The mechanisms of MM progression have not yet been fully understood, all the more because patients with MGUS and SMM already carry similar initial mutations as found in MM cells. Over the last years, increased importance has been attributed to the tumor microenvironment and its role in the pathophysiology of the disease. Adaptations of MM cells to hypoxic conditions in the BM have been shown to contribute significantly to MM progression, independently from the genetic predispositions of the tumor cells. Searching for consequences of hypoxia-induced adaptations in primary human MM cells, CD138-positive plasma cells freshly isolated from BM of patients with different disease stages, comprising MGUS, SMM, and MM, were analyzed by proteome profiling, which resulted in the identification of 6218 proteins. Results have been made fully accessible via ProteomeXchange with identifier PXD010600. Data previously obtained from normal primary B cells were included for comparative purposes. A principle component analysis revealed three clusters, differentiating B cells as well as MM cells corresponding to less and more advanced disease stages. Comparing these three clusters pointed to the alteration of pathways indicating adaptations to hypoxic stress in MM cells on disease progression. Protein regulations indicating immune evasion strategies of MM cells were determined, supported by immunohistochemical staining, as well as transcription factors involved in MM development and progression. Protein regulatory networks related to metabolic adaptations of the cells became apparent. Results were strengthened by targeted analyses of a selected panel of metabolites in MM cells and MM-associated fibroblasts. Based on our data, new opportunities may arise for developing therapeutic strategies targeting myeloma disease progression.

Antioxidant Defenses Confer Resistance to High Dose Melphalan in Multiple Myeloma Cells

Background: Multiple myeloma (MM) is the second most common hematological cancer after lymphoma. It is characterized by the accumulation of clonal malignant plasma cells within the bone marrow. The development of drug resistance remains a major problem for effective treatment of MM. Understand the mechanisms underlying drug resistance in MM is a focal point to improve MM treatment. Methods: In the current study, we analyzed further the role of redox imbalance induction in melphalan-induced toxicity both in human myeloma cell lines (HMCLs) and primary myeloma cells from patients. Results: We developed an in-vitro model of short-term resistance to high-dose melphalan and identified that pretreatment with physiological concentration of GSH protects HMCLs from melphalan-induced cell cycle arrest and cytotoxicity. We validated these results using primary MM cells from patients co-cultured with their bone marrow microenvironment. GSH did not affect the ability of melphalan to induce DNA damages in MM cells. Interestingly, melphalan induced reactive oxygen species, a significant decrease in GSH concentration, protein and lipd oxydation together with NRF2 (NF-E2-related factor 2) pathway activation. Conclusions: Our data demonstrate that antioxidant defenses confers resistance to high dose melphalan in MM cells, supporting that redox status in MM cells could be determinant for patients’ response to melphalan.

Trabectedin triggers direct and NK-mediated cytotoxicity in multiple myeloma

BackgroundGenomic instability is a feature of multiple myeloma (MM), and impairment in DNA damaging response (DDR) has an established role in disease pathobiology. Indeed, a deregulation of DNA repair pathways may contribute to genomic instability, to the establishment of drug resistance to genotoxic agents, and to the escape from immune surveillance. On these bases, we evaluated the role of different DDR pathways in MM and investigated, for the first time, the direct and immune-mediated anti-MM activity of the nucleotide excision repair (NER)-dependent agent trabectedin.MethodsGene-expression profiling (GEP) was carried out with HTA2.0 Affymetrix array. Evaluation of apoptosis, cell cycle, and changes in cytokine production and release have been performed in 2D and 3D Matrigel-spheroid models through flow cytometry on MM cell lines and patients-derived primary MM cells exposed to increasing nanomolar concentrations of trabectedin. DNA-damage response has been evaluated through Western blot, immunofluorescence, and DNA fragmentation assay. Trabectedin-induced activation of NK has been assessed by CD107a degranulation. miRNAs quantification has been done through RT-PCR.ResultsBy comparing GEP meta-analysis of normal and MM plasma cells (PCs), we observed an enrichment in DNA NER genes in poor prognosis MM. Trabectedin triggered apoptosis in primary MM cells and MM cell lines in both 2D and 3D in vitro assays. Moreover, trabectedin induced DDR activation, cellular stress with ROS production, and cell cycle arrest. Additionally, a significant reduction of MCP1 cytokine and VEGF-A in U266-monocytes co-cultures was observed, confirming the impairment of MM-promoting milieu. Drug-induced cell stress in MM cells led to upregulation of NK activating receptors ligands (i.e., NKG2D), which translated into increased NK activation and degranulation. Mechanistically, this effect was linked to trabectedin-induced inhibition of NKG2D-ligands negative regulators IRF4 and IKZF1, as well as to miR-17 family downregulation in MM cells.ConclusionsTaken together, our findings indicate a pleiotropic activity of NER-targeting agent trabectedin, which appears a promising candidate for novel anti-MM therapeutic strategies.

The IAP antagonist birinapant potentiates bortezomib anti-myeloma activity in vitro and in vivo

BackgroundMechanisms by which Smac mimetics (SMs) interact with proteasome inhibitors (e.g., bortezomib) are largely unknown, particularly in multiple myeloma (MM), a disease in which bortezomib represents a mainstay of therapy.MethodsInteractions between the clinically relevant IAP (inhibitor of apoptosis protein) antagonist birinapant (TL32711) and the proteasome inhibitor bortezomib were investigated in multiple myeloma (MM) cell lines and primary cells, as well as in vivo models. Induction of apoptosis and changes in gene and protein expression were monitored using MM cell lines and confirmed in primary MM cell populations. Genetically modified cells (e.g., exhibiting shRNA knockdown or ectopic expression) were employed to evaluate the functional significance of birinapant/bortezomib-induced changes in protein levels. A MM xenograft model was used to evaluate the in vivo activity of the birinapant/bortezomib regimen.ResultsBirinapant and bortezomib synergistically induced apoptosis in diverse cell lines, including bortezomib-resistant cells (PS-R). The regimen robustly downregulated cIAP1/2 but not the canonical NF-κB pathway, reflected by p65 phosphorylation and nuclear accumulation. In contrast, the bortezomib/birinapant regimen upregulated TRAF3, downregulated TRAF2, and diminished p52 processing and BCL-XL expression, consistent with disruption of the non-canonical NF-κB pathway. TRAF3 knockdown, ectopic TRAF2, or BCL-XL expression significantly diminished birinapant/bortezomib toxicity. The regimen sharply increased extrinsic apoptotic pathway activation, and cells expressing dominant-negative FADD or caspase-8 displayed markedly reduced birinapant/bortezomib sensitivity. Primary CD138+ (n = 43) and primitive MM populations (CD138−/19+/20+/27+; n = 31) but not normal CD34+ cells exhibited significantly enhanced toxicity with combined treatment (P < 0.0001). The regimen was also fully active in the presence of HS-5 stromal cells or growth factors (e.g., IL-6 and VEGF). Finally, the regimen was well tolerated and significantly increased survival (P < 0.05 and P < 0.001) compared to single agents in a MM xenograft model. Combined treatment also downregulated cIAP1/2 and p52 while increasing PARP cleavage in MM cells in vivo.ConclusionsOur data suggest that birinapant and bortezomib interact synergistically in MM cells, including those resistant to bortezomib, through inactivation of the non-canonical NF-κB and activation of the extrinsic apoptotic pathway both in vitro and in vivo. They also argue that a strategy combining cIAP antagonists and proteasome inhibitors warrants attention in MM.

Replacement of miR-155 Elicits Tumor Suppressive Activity and Antagonizes Bortezomib Resistance in Multiple Myeloma.

Aberrant expression of microRNAs (miRNAs) has been associated to the pathogenesis of multiple myeloma (MM). While miR-155 is considered a therapeutic target in several malignancies, its role in MM is still unclear. The analysis of miR-155 expression indicates its down-regulation in MM patient-derived as compared to healthy plasma cells, thus pointing to a tumor suppressor role in this malignancy. On this finding, we investigated miR-155 replacement as a potential anti-tumor strategy in MM. The miR-155 enforced expression triggered anti-proliferative and pro-apoptotic effects in vitro. Given the lower miR-155 levels in bortezomib-resistant as compared to sensitive MM cells, we analyzed the possible involvement of miR-155 in bortezomib resistance. Importantly, miR-155 replacement enhanced bortezomib anti-tumor activity both in vitro and in vivo in a xenograft model of human MM. In primary MM cells, we observed an inverse correlation between miR-155 and the mRNA encoding the proteasome subunit gene PSMβ5, whose dysregulation has been largely implicated in bortezomib resistance, and we validated PSMβ5 3′UTR mRNA targeting, along with reduced proteasome activity, by miR-155. Collectively, our findings demonstrate that miR-155 elicits anti-MM activity, likely via proteasome inhibition, providing the framework for miR-155-based anti-MM therapeutic strategies.

Neutrophil-Derived MRP14 Supports Plasma Cell Commitment and Protects Myeloma Cells from Apoptosis.

Neutrophils have recently been proposed as cells with high functional plasticity and are involved in the pathogenesis of infections, malignancy, and autoimmune diseases. However, less is known about the role of neutrophil in humoral response. In this study, we examined the importance of neutrophils and the neutrophil-derived DAMP protein, MRP14, in antibody production. Splenic neutrophils and MRP14 that are present in the splenic peri-MZ region have a close contact with MZ B cells and promote their differentiation into plasma cells. Using neutrophil-depleting mice and an MRP14-blocking compound, we showed that the presence of neutrophil and MRP14 is required for class switch, plasma cell maintenance, and antibody production in the spleen. We found that MRP14 could also be produced by neutrophils in the bone marrow and support the maintenance of bone marrow plasma cells. MRP14 binding could enhance the effect of the BAFF signal and protect primary multiple myeloma cells from doxorubicin-induced apoptosis. Our data demonstrate the effects of neutrophils on neighboring B cells and plasma cells, which provides new insights into the connection between neutrophil and humoral responses.

The anti-myeloma effects of the selective JAK1 inhibitor (INCB052793) alone and in combination in vitro and in vivo.

The Janus kinase (JAK) pathway has been shown to play key roles in the growth and resistance to drugs that develop in multiple myeloma (MM) patients. The anti-MM effects of the selective JAK1 inhibitor INCB052793 (INCB) alone and in combination with anti-MM agents were evaluated in vitro and in vivo. Significant inhibition of cell viability of primary MM cells obtained fresh from MM patients, and the MM cell lines RPMI8226 and U266, was observed with single agent INCB and was enhanced in combination with other anti-MM agents including proteasome inhibitors and glucocorticosteroids. Single-agent INCB resulted in decrease in tumor growth of the MM xenograft LAGκ-1A growing in severe combined immunodeficient mice. Mice dosed with INCB (30mg/kg) showed significant reductions in tumor volume on days 28, 35, 42, 49, 56, and 63. Similarly, INCB at 10mg/kg showed anti-tumor effects on days 56 and 63. Tumor-bearing mice receiving combinations of INCB with carfilzomib, bortezomib, dexamethasone, or lenalidomide showed significantly smaller tumors when compared to vehicle control and mice treated with single agents. These results provide further support for the clinical evaluation of INCB052793 alone and in combination treatment for MM patients.

Proliferation and Molecular Risk Score of Low Risk Myeloma Cells Are Increased in High Risk Microenvironment Via Augmented Bioavailability of Growth Factors

Introduction:Multiple myeloma (MM) cells from patients with smoldering MM (SMM) and low-risk (LR) MM harbor genetic alterations typically seen in patients with high-risk (HR) disease. To test whether the bone marrow (BM) microenvironment plays a role in controlling growth of LR MM cells, we established an experimental model that mimics a HR microenvironment by co-culturing normal mesenchymal stem cells (MSCs) with HR MM cells. We previously have shown that MSC conditioned media (CM) promotes growth of MM cells more effectively than cell-cell contact, as adhesion to MSCs often promotes survival at the expense of proliferation. Therefore, we utilized CM andhypothesized that MSC CM is enriched with bioactive growth factors that facilitate proliferation of LR MM cells.The aim of the study was to test the effect of CM from unprimed and primed MSCs on the survival, growth, and molecular properties of LR MM cells, and identify molecular pathways that mediate these effects.Methods:Primed MSCs were prepared by co-culturing normal MSCs with BM-dependent MM lines for 5 days. MSCs were trypsinized, replated for 40 min followed by serial washing to remove MM cells.Molecularly classified CD138-selected LR MM cells from 8 newly diagnosed patients were treated with 50% primed CM or unprimed CM, or growth media (CONT) for 5 days. Growth and survival of primary MM cells was assessed by MTT assay and detection of annexin V/PI and KI67 by flow cytometry.Microarrays were performed on primed and unprimed MSCs (n=7) and on primary LR MM cells treated with primed and unprimed MSCs CM (n=3). Pathways were analyzed using Ingenuity. Ultra low depth WGS was performed to assess copy number variation. Protein arrays were performed to test levels of secreted factors in CM (n=7).Results:Growth of primary LR MM cells (n=8) was increased by primed CM 5.1±0.05 (p<0.0001) and 7.0±0.6 (p<0.0001) folds compared to unprimed CM or CONT, respectively. In contrast, unprimed MSC CM increased growth in these cells by 1.3 fold. Flow cytometry analyses revealed no differences in proportion of annexin V/PI+ cells. However, the proportion of KI67+ cells was increased from 0.95±0.1% in unprimed CM group to 4.6±1.5% in primed CM group (p<0.04).Primed MSC CM caused MM cell GEP70 score to increase resulting in change from LR to HR in 2 experiments and from an ultra LR score to an intermediate score in another. Pathway analyses on genes differentially expressed between primed CM- and unprimed CM-treated MM cells identified oxidative phosphorylation with mitochondrial dysfunction, cell cycle, mitosis and p53 as the most significantly altered pathways. Top transcription regulators included FOXO3, TP53, E2F4, MYC and E2F1, whereas mir-16-5p and let-7 were the top microRNAs. Top significantly upregulated genes (>2 fold) by primed MSC CM included proliferation-related factors (MKI67, TOP2A, CCNB1, BIRC5 and RRM2), whereas underexpressed genes (< 2 fold) involved regulators of cell dormancy including BCL2 (survival), RICTOR (mTOR), HEY1 (NOTCH), JUN (AP-1) and CXCR4 (adhesion). Four genes we reported to powerfully predict progression of SMM to MM (Khan et al., Haematologica 2015) were highly upregulated in MM cells by primed MSC CM.WGS revealed similar copy number variation in MM cells treated with unprimed and primed CM, suggesting other mechanisms produced the observed gene expression changes.IGF1 is a central MM growth factor and IGF binding proteins (IGFBPs) control its bioavailability. We recently reported that mesenchymal cells are the main source of IGFBPs in BM, with IGFBP2 being the most downregulated gene in MM bone (Schinke et al., CCR 2018). Expression and secretion of IGFBPs (particularly IGFBP2) by MSCs were significantly reduced by priming these cells with MM cells, whereas IGF1 levels remained unchanged. IGFBP2 markedly blocked IGF1-induced MM cell growth (p<0.0003). Addition of IGF1R inhibitor significantly blocked primed CM-induced MM cell growth (p<0.02).Conclusions:MSCs primed by HR MM cells mimic a HR microenvironment, reflected by reduced level of factors that restrain bioavailability of MM growth factors such as IGF1, resulting in shutdown of master regulators of cell dormancy, which then enable a MM cells to proliferate. Such a scenario is particularly applicable in SMM and LR disease where MM cells exhibit a low proliferative index and their expansion is accelerated in distinct HR BM microenvironmental niches such as focal lesions. DisclosuresEpstein:University of Arkansas for Medical Sciences: Employment. Davies:Abbvie: Consultancy; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; ASH: Honoraria; MMRF: Honoraria; Janssen: Consultancy, Honoraria; TRM Oncology: Honoraria. Morgan:Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Janssen: Research Funding.

Functional Role of Linc-RNAs in Multiple Myeloma: Linc-MIR17HG Affects Fatty Acid Biosynthesis Via transcriptional Regulation of ACC1 with Potential Therapeutic Implications

Besides the well described function of RNA to produce proteins, a large volume of transcribed product has non-coding function. A recent analysis of RNA repertoire has identified a family of non-coding transcripts with sequence longer than 200 nucleotides, the long intergenic non-coding RNAs (lincRNAs). Although lincRNAs have been considered to provide regulatory functions, their precise role in cellular biology remains unclear. Using our RNA-seq data from 360 newly-diagnosed patients and 18 normal plasma cells, we have recently described the landscape of lincRNAs in multiple myeloma (MM) and reported their role as independent risk predictors for survival outcome.We have now studied the functional role of a lincRNA, the miR-17-92 primary precursor linc-MIR17HG, present in our lincRNA profile and highly correlated with overall survival in MM. We observe that inhibition of linc-MIR17HG by antisense LNA GapmeRs (n=2) leads to apoptosis in 12 genotypically distinct MM cell lines as well as in 13 primary patient MM cells. These effects are not fully rescued by expression of miR-17-92 microRNAs, suggesting a distinct biological function for linc-MIR17HG in MM. We therefore performed gene expression profile in 2 MM cell lines (AMO1 and NCI-H929) and in 2 primary patient MM cells after short-term suppression of linc-MIR17HG; and, at these early time points (18-36h), we found significant downregulation of a subset of genes (FC>2; p<0.05) including ACC1, EXT1, EPT1, ANO6, CCDC91 and KIA1109, but not miR-17-92 microRNAs. These transcriptional changes were validated by qRT-PCR in MM cell lines and primary MM cells exposed to different LNA GapmeRs targeting linc-MIR17HG with a non-overlapping spectrum of off-target effects. Importantly, our RNA-seq analysis of 360 newly-diagnosed MM patients from IFM/DFCI 2009 clinical study showed that expression of linc-MIR17HG strongly correlated with the expression of each of these genes (R2>0.4; p<0.01) in MM patients, further suggesting a regulatory function by linc-MIR17HG at transcriptional level. Using CRISPR interference (CRISPRi), we have also identified that the linc-MIR17HG with transcriptional regulatory functions is not produced from the canonical transcript isoforms MIR17HG-201/-203; these isoforms, rather, appear to be involved in production of microRNAs, leaving an alternative transcription start site usage as possible source for the transcriptional regulator isoform(s).We next investigated whether regulation of these early targets may contribute to the activity of linc-MIR17HG. We performed a RNAi-based screening in 2 MM cells lines (AMO1 and NCI-H929) by silencing each of the linc-MIR17HG downstream target genes with at least 2 different highly-specific siRNAs. This approach revealed that silencing of acetyl-CoA carboxylase 1 (ACC1, also known as ACACA), a gene encoding the limiting enzyme in the biosynthesis of fatty acids, significantly affects MM cell growth and viability. These results were validated using stable knock-down via shRNAs, confirming ACC1 as a novel vulnerability in MM. These results provide a molecular basis for reported role of fatty acid metabolism in MM cell growth and survival. We have now evaluated two orally available inhibitors of ACC1 activity, ND-630 and ND-646, in a panel of 10 MM cell lines, an report a potent time- and dose-dependent anti-proliferative effect. The activity of these inhibitors and linc-MIR17HG on fatty acid biosynthesis in MM cells is under investigation and will be presented.We have also begun to investigate molecular pathway used by linc-MIR17HG to modulate ACC1 function. Our preliminary data suggest that linc-MIR17HG may function as a scaffold between MYC and the E-box motifs present on ACC1 intronic sequences, facilitating MYC binding and its transcriptional activity.In conclusion, we highlight a transcriptional regulatory activity of a lincRNA in MM with significant functional impact that can be therapeutically translated. DisclosuresAnderson:Bristol Myers Squibb: Consultancy; Millennium Takeda: Consultancy; Gilead: Membership on an entity's Board of Directors or advisory committees; OncoPep: Equity Ownership, Other: Scientific founder; C4 Therapeutics: Equity Ownership, Other: Scientific founder; Celgene: Consultancy. Munshi:OncoPep: Other: Board of director.

CD38low Natural Killer Cells Transiently Expressing CD16F158V m-RNA Potentiates the Therapeutic Activity of Daratumumab Against Multiple Myeloma with Minimal Effector NK Cell Fratricide

Introduction: Multiple Myeloma (MM) is a clonal plasma cell malignancy typically associated with the high and uniform expression of CD38 transmembrane glycoprotein. Daratumumab is a humanized IgG1κ CD38 monoclonal antibody (moAb) which has demonstrated impressive single agent activity even in relapsed refractory MM patients as well as strong synergy with other anti-MM drugs. Natural Killer (NK) cells are cytotoxic immune effector cells mediating tumour immunosurveillance in vivo. NK cells also play an important role during moAb therapy by inducing antibody dependent cellular cytotoxicity (ADCC) via their Fcγ RIII (CD16) receptor. Furthermore, 15% of the population express a naturally occurring high affinity variant of CD16 harbouring a single point polymorphism (F158V), and this variant has been linked to improved ADCC. However, the contribution of NK cells to the efficacy of Daratumumab remains debatable as clinical data clearly indicate rapid depletion of CD38high peripheral blood NK cells in patients upon Daratumumab administration. Therefore, we hypothesize that transiently expressing the CD16F158V receptor using a “safe” mRNA electroporation-based approach, on CD38low NK cells could significantly enhance therapeutic efficacy of Daratumumab in MM patients. In the present study, we investigate the optimal NK cell platform for generating CD38low CD16F158V NK cells which can be administered as an “off-the-shelf”cell therapy product to target both CD38high and CD38low expressing MM patients in combination with Daratumumab.Methods: MM cell lines (n=5) (MM.1S, RPMI-8226, JJN3, H929, and U266) and NK cells (n=3) (primary expanded, NK-92, and KHYG1) were immunophenotyped for CD38 expression. CD16F158V coding m-RNA transcripts were synthesized using in-vitro transcription (IVT). CD16F158V expression was determined by flow cytometry over a period of 120 hours (n=5). 24-hours post electroporation, CD16F158V expressing KHYG1 cells were co-cultured with MM cell lines (n=4; RPMI-8226, JJN3, H929, and U266) either alone or in combination with Daratumumab in a 14-hour assay. Daratumumab induced NK cell fratricide and cytokine production (IFN-γ and TNF-α) were investigated at an E:T ratio of 1:1 in a 14-hour assay (n=3). CD38+CD138+ primary MM cells from newly diagnosed or relapsed-refractory MM patients were isolated by positive selection (n=5), and co-cultured with mock electroporated or CD16F158V m-RNA electroporated KHYG1 cells. CD16F158V KHYG1 were also co-cultured with primary MM cells from Daratumumab relapsed-refractory (RR) patients.Results: MM cell lines were classified as CD38hi (RPMI-8226, H929), and CD38lo (JJN3, U266) based on immunophenotyping (n=4). KHYG1 NK cell line had significantly lower CD38 expression as compared to primary expanded NK cells and NK-92 cell line (Figure 1a). KHYG1 electroporated with CD16F158V m-RNA expressed CD16 over a period of 120-hours post-transfection (n=5) (Figure 1b). CD16F158V KHYG1 in-combination with Daratumumab were significantly more cytotoxic towards both CD38hi and CD38lo MM cell lines as compared to CD16F158V KHYG1 alone at multiple E:T ratios (n=4) (Figure 1c, 1d). More importantly, Daratumumab had no significant effect on the viability of CD38low CD16F158V KHYG1. Moreover, CD16F158V KHYG1 in combination with Daratumumab produced significantly higher levels of IFN-γ (p=0.01) upon co-culture with CD38hi H929 cell line as compared to co-culture with mock KHYG1 and Daratumumab. The combination of CD16F158V KHYG1 with Daratumumab was also significantly more cytotoxic to primary MM cell ex vivo as compared to mock KHYG1 with Daratumumab at E:T ratio of 0.5:1 (p=0.01), 1:1 (p=0.005), 2.5:1 (p=0.003) and 5:1 (p=0.004) (Figure 1e). Preliminary data (n=2) also suggests that CD16F158V expressing KHYG1 can eliminate 15-17% of primary MM cells from Daratumumab RR patients ex vivo. Analysis of more Daratumumab RR samples are currently ongoing.Conclusions: Our study provides the proof-of-concept for combination therapy of Daratumumab with “off-the-shelf” CD38low NK cells transiently expressing CD16F158V for treatment of MM. Notably, this approach was effective against MM cell lines even with low CD38 expression (JJN3) and primary MM cells cultured ex vivo. Moreover, the enhanced cytokine production by CD16F158V KHYG1 cells has the potential to improve immunosurveillance and stimulate adaptive immune responses in vivo. [Display omitted] DisclosuresSarkar:Onkimmune: Research Funding. Chauhan:Onkimmune: Research Funding. Stikvoort:Onkimmune: Research Funding. Mutis:Genmab: Research Funding; OnkImmune: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Gilead: Research Funding; Celgene: Research Funding; Novartis: Research Funding. O'Dwyer:Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; BMS: Research Funding; Glycomimetics: Research Funding; Onkimmune: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding.

CD38 Specific Chimeric Antigen Receptor KHYG-1 Natural Killer Cells: A Potential “Off the Shelf” Therapy for Multiple Myeloma

Chimeric Antigen Receptors (CARs) are engineered transmembrane proteins consisting of an antibody-derived antigen recognition domain linked to intracellular cell signaling domains. CAR engineered autologous T cells have been successful in the treatment of a variety of hematologic malignancies. However, several major caveats, including lack of universal donors, long manufacturing times, and absence of a donor in immunologically frail patients, have limited the successful translation of CAR-T cell based therapy to a larger pool of patients. A universal, easy to manufacture, “off the shelf” CAR-based product could potentially address these limitations and result in a lower cost of goods.Towards developing an “off the shelf” CAR-based therapy for Multiple Myeloma (MM), we explored the feasibility and preclinical efficacy of expressing CD38 CARs in KHYG-1 cells, a natural killer (NK) cell line, first established by Yagita et al from a patient with aggressive NK leukemia (Leukemia, 2000). To this end, we effectively transduced KHYG-1 cells with high-affinity CD38 CARs as well as our recently reported affinity-optimized CD38 CARs, which can readily target MM cells with high CD38 expression, while ignoring non-malignant cells with intermediate, low or no CD38 expression when brought to expression on T cells (Drent et al, Molecular Therapy 2017). Moreover, we assessed performance of first and second generation CARs, with co-stimulatory domains CD28 and 4-1BB, and found the combination of CD28/CD3ζ to lead to the best results. After expanding the CAR transduced KHYG-1 cells, we analyzed their phenotype and efficacy in MM by analyzing their cytotoxic activity against CD38+ and CD38- MM and AML cell lines (UM9/THP-1 and U266/HL60, respectively), and against primary MM cells. The CD38-CAR transduced KHYG-1 cells showed no phenotypic alterations, and at effector to target ratios as low as 1:1, induced a high cytotoxicity towards CD38+ cell lines as compared to mock or non-transduced KHYG-1, demonstrating the important contribution of the CD38 CAR on the KHYG-1 NK cell surface. CD38- cell lines were unaffected by both CD38-CAR transduced KHYG-1 cells and mock or non-transduced KHYG-1 cells, indicating the specificity towards CD38 of the CAR and thus the potential safety of the CD38-CAR KHYG-1 cell. Similarly, ex vivo assays using primary MM cells revealed superior cytotoxic activity of CD38-CAR KHYG-1 cells as compared to mock or non-transduced KHYG-1 cells (median 86,5% vs 14% at 1:1 E:T ratio, n=2, Figure 1A). Confirming our previous results we identified an affinity-optimized CD38-CAR which mediated strong primary MM cell cytotoxicity with little or no “off tumor” effect. Normal immune cells (B, T, monocytes), which were either CD38 negative or only intermediate positive, were unaffected (Figure 1B-D), suggesting the potential safety of the CAR-NK cell therapy for clinical applications. As clinical administration would require irradiation of CD38-CAR KHYG-1 cells, we tested the effect of irradiation on their proliferative and cytotoxicity potential. Irradiation with 10Gy, while drastically inhibiting proliferative activity and viability (50% survival after 3 days), did not affect cytotoxicity, suggesting that repeated administrations of irradiated, CD38-CAR transduced KYHG-1 cells may exert effective in vivo anti-tumor activity, which is currently being evaluated in appropriate in vivo models, specifically the humanized bone scaffold in vivo model published by Groen et al (Blood, 2012).In conclusion, we demonstrate that the incorporation of CAR technology into the immortal NK cell line KHYG-1 has enormous potential to become a safe and effective “off the shelf” therapy for MM. [Display omitted] DisclosuresStikvoort:Onkimmune: Research Funding. Sarkar:Onkimmune: Research Funding. van de Donk:Amgen: Research Funding; Janssen Pharmceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Research Funding; Bristol-Myers Squibb: Research Funding; Celgene: Research Funding. Zweegman:Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corp.: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding. O'Dwyer:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Onkimmune: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Research Funding; Celgene: Research Funding; Glycomimetics: Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees. Mutis:Gilead: Research Funding; Celgene: Research Funding; Novartis: Research Funding; OnkImmune: Research Funding; Genmab: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Respective Place of Venetoclax and MCL1 BH3 Mimetics in Multiple Myeloma Treatment

Targeting anti-apoptotic proteins of the BCL2 family by BH3 mimetics is a new promising therapeutic approach in multiple myeloma (MM). The specific BH3 mimetic targeting BCL2, BCLXL or MCL1 trigger apoptosis and exploit the dependency on these different anti-apoptotic proteins to kill tumor cells. Because MM is mostly considered as dependent on MCL1, the recent clinical availability of MCL1 BH3 mimetics underlines an urgent need to better define patients that would benefit from a MCL1 targeted therapy. In the present study, we used a BH3 mimetic toolkit that includes venetoclax, A1155463 and A1210477, which target BCL2, BCLXL and MCL1 respectively to define dependencies/co-dependencies in a large cohort of 60 myeloma patients (21 at diagnosis and 39 at relapse). Alternatively, MCL1 dependency was confirmed using the S63845 MCL1 inhibitor in MM patient samples. Mononuclear bone marrow/blood cells were treated overnight with the respective BH3 mimetic and cell death was specifically measured in the tumor cell population. Primary MM cells dependencies were stratified using PCA analysis in three groups as highly dependent, intermediately dependent or not dependent. Our study demonstrated that half of patients at diagnosis were BCL2 dependent while only 10% were BCLXL dependent. The dependence on BCL2 or BCLXL was not significantly different between samples at diagnosis and relapse. Strikingly, we found that the MCL1 dependency was 33% at diagnosis while it was 69% at relapse, suggesting a significant increase in MCL1 dependency during the disease progression (p=0.01). Besides, 36% of overall patients showed co-dependencies on BCL2/MCL1. We also identified primary MM cells that did not depend on any of the three pro-survival molecules, both at diagnosis and relapse.Among this cohort of MM patients, 47 samples were further analyzed for the presence of recurrent translocations (t(11;14), t(6;14), t(4;14) and t(14;16)) allowing the analysis of dependencies in the different subgroups; these recurrent translocations lead to the overexpression of CCND1, CCND3, MMSET and MAF oncogenes, respectively. We found that BCL2 dependency was significantly higher in CCND1 subgroup (83%) compared to all other subgroups (20%, p=0.008). We also confirmed the BCL2/BCLXL mRNA ratio as a valuable biomarker to define BCL2 dependence (p=0.0001). At diagnosis, MCL1 dependency was absent in patients not harboring the common recurrent translocations while at relapse 6 out 9 patients not harboring the recurrent translocations were MCL1 dependent, indicating an increase of MCL1 dependency at relapse in this subgroup (p=0.03).Mechanistically, we demonstrated that BAK is crucial for cell death induced by MCL1 mimetic A1210477, according to the protection of cell death observed by BAK knock-down and the complete disruption of MCL1/BAK complexes upon A1210477 treatment, observed in MM cell lines and also in a patient sample. Interestingly, this complex was also dissociated in A1210477 resistant cells but free BAK was simultaneously recaptured by BCLXL, supporting the role of BCLXL in A1210477 resistance. Thus, BCLXL may act as a sink to bind freed pro-apoptotic proteins from MCL1 and limits MM cell death triggered by the specific targeting of MCL1.In conclusion, our study highlights the potential clinical use of BH3 mimetics in MM treatment guided by the practical ex-vivo testing of myeloma cell dependencies using the BH3 toolkit. This strategy could be used to identify the respective and tailored use of venetoclax, MCL1 BH3 mimetics or their combination in myeloma treatment. DisclosuresMoreau:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Analysis of the Multiple Myeloma HLA Peptidome Identifies a Naturally Presented Bcma-Derived Peptide As an Immunogenic T-Cell Epitope for Immunotherapeutic Approaches

The B-cell maturation antigen (BCMA) is selectively expressed by cells of the B-lineage, including multiple myeloma (MM) cells, and constitutes a promising target for immunotherapeutic approaches. At present, BCMA is being evaluated as target for immunotherapeutic approaches, such as CAR T cells and bispecific antibodies, which have demonstrated promising results in phase I clinical trials. The utilization of cytotoxic T cells bearing T-cell receptors against BCMA constitutes an alternative promising approach to target MM cells. Therefore, the identification of BCMA-derived peptides that are naturally presented by human leukocyte antigens (HLA) and thus can serve as target structures for CD8+ T cells, is indispensable.In a previous study, we characterized the immunopeptidomic landscape of MM by mass spectrometry-based analysis of naturally presented HLA ligands from primary MM samples and MM cell lines (Walz et al., Blood, 2015). Comparative HLA peptidome profiling of the MM-derived HLA ligands versus the immunopeptidome of numerous benign samples from different tissues identified several strictly MM-associated antigens. Here, we evaluated this dataset for the presence of BCMA-derived MM-exclusive antigens and identified two HLA class I-restricted, BCMA-derived peptides in the immunopeptidome of our cohort comprising 15 primary MM samples and MM cell lines. Notably, one of these peptides showes strictly MM-associated presentation and was never detected on any benign tissues according to our extensive immunopeptidome database (135,354 HLA ligands originating from 16,626 source proteins detected in 337 samples from various benign tissues including blood, bone marrow, lung, kidney, liver, and spleen). This HLA-B*18-restricted ligand P(BCMA)B*18 is represented in 20% (3/15) of the analyzed MM immunopeptidomes.For immunological characterization of the P(BCMA)B*18 peptide, we performed in vitro artificial antigen-presenting cell-based priming experiments engaging naïve CD8+ T cells obtained from healthy volunteers (HV). Induction of tetramer-positive T-cell populations with frequencies ranging from 0.1-2.9% of viable CD8+ T cells was observed for all analyzed healthy whole blood donors, which demonstrates the immunogenicity of P(BCMA)B*18. Subsequently, we functionally characterized the induced P(BCMA)B*18-specific CD8+ T cells using intracellular cytokine staining. Upon stimulation with P(BCMA)B*18, we observed an increased IFNγ and TNF production specifically in the peptide-specific CD8+ T cells. In addition, the degranulation marker CD107a was found to be upregulated in the analyzed tetramer-positive T cells, confirming the activity of CD8+ T cells upon peptide-stimulation. Priming experiments using naïve CD8+ T cells obtained from MM patients as well as in vitro cytotoxicity assays with polyclonal peptide-specific effector T cells are presently ongoing in order to assess the capacity of P(BCMA)B*18-specific CD8+ T cells to induce antigen-specific cell lysis.Taken together, we identified a naturally presented and MM-associated, BCMA-derived peptide, which constitutes a promising target for tailored T cell-based immunotherapeutic approaches. DisclosuresSalih:Several patent applications: Patents & Royalties: e.g. EP3064507A1. Kowalewski:Immatics Biotechnologies GmbH: Employment. Weisel:Amgen, BMS, Celgene, Janssen, and Takeda: Honoraria; Amgen, BMS, Celgene, Janssen, Juno, Sanofi, and Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen, Celgene, Janssen, and Sanofi: Research Funding.

Aryl Hydrocarbon Receptor (AHR) Antagonism As a Transformative, Dual-Mechanism Novel Therapy for Multiple Myeloma

BACKGROUNDThe aryl hydrocarbon receptor (AHR) is a transcription factor that regulates xenobiotic-metabolizing enzymes in response to exogenous polycyclic aromatic hydrocarbons. However, we have described a critical role for AHR in normal lymphocyte development and identified the functional expression of AHR in multiple myeloma (MM). Interest is growing in AHR as a novel anti-cancer therapeutic target in solid tumors, but very little comparatively is known about AHR in hematologic malignancies. Epidemiologic data suggest that exposure to the AHR agonists 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), benzene and dioxin may be linked to increased rates of MGUS and MM in Vietnam-era veterans as well as firefighters at the World Trade Center attacks in September, 2001. Whereas we have shown that AHR antagonism facilitates normal, healthy natural killer (NK) cell lymphocyte development and acquisition of cytolytic potential, herein, we show that AHR antagonism impairs MM cell viability. In addition, we characterize the direct effects of AHR antagonism on MM cells as well as complementary mechanisms by which the NK cell versus MM effect is augmented, further strengthening ongoing interest in targeting AHR as a novel anti-MM therapy. METHODSThe MM cell lines MM.1S, MM.1R, OPM-2, and U266 were obtained from ATCC. Primary cells from healthy donors and patients with MM were procured under IRB-approved protocols. AHR expression was studied by Western blot, flow cytometry and real time PCR. AHR function was assessed by expression of the downstream target CYP1A1 by real time PCR. Clinical MM outcomes were determined with data obtained from a publically available database. Cell proliferation and viability were studied by light microscopy (trypan blue exclusion) and Sytox. Immunophenotyping was conducted by flow cytometry. Cytotoxicity was measured by 51Cr release assay. The AHR antagonists CH233191 and CB7993113 and the high affinity AHR agonist 5,11-dihydroindolol[3,2-b]carbazole-6-carboxaldehyde (FICZ) were utilized to study the in vitro effects of AHR modulation. RESULTSAHR transcript and protein are expressed in human NK cells, plasma cells and B cells, as well as MM cell lines and primary MM samples. AHR agonism increases transcription of CYP1A1 in MM cells whereas AHR antagonism suppresses CYP1A1; these observations confirm that AHR is functionally active in MM. AHR is abundantly expressed from the CD38brightCD27(+) MM stem cell compartment to primary plasma cell leukemia samples. MM cases with high AHR expression are associated with inferior survival as compared to MM cases with low AHR expression (median OS = 50 months versus not reached at 70 months, p = 0.00002). AHR stimulation reduces expression of CD38, CD56, and CD138 and upregulates CD10, CD11a, CD13, CD19, CD20, CD27, CD40, CD45, and CD117 consistent with MM clonogenic progenitor cells previously described as “stem-like” and drug resistant. AHR antagonism suppresses MM cell line and primary MM cell viability, including cytogenetically high-risk, plasma cell leukemia primary samples. These effects are preserved in 7- and 14-day washout experiments. AHR antagonism increases expression of CD38 (2.1-fold) and SLAMF7 (CS1, 1.54-fold) among other antigens. AHR antagonism enhances NK cell cytolytic potential by promoting expression of CD94, TRAIL, perforin and granzyme B, whereas in MM cells, AHR antagonism upregulates surface expression of NK cell activating ligands: CD112, CD54, ULBP1, ULBP2, ULBP3, ULBP4, CD155, MICA/B, and DR4 and DR5. Pretreatment of MM cell targets with an AHR antagonist enhances susceptibility to NK-cell cytotoxicity (p < 0.005) and augments NK-cell mediated ADCC in combination with daratumumab (p = 0.001) and elotuzumab (p = 0.001) versus controls. CONCLUSIONSThese data confirm functional expression of AHR in MM and may provide insight to growing epidemiologic data indicting a link between environmental exposure to aromatic hydrocarbons and subsequent risk of MM. In addition, as opposed to the direct, deleterious effects of AHR antagonism on MM cell viability, AHR antagonism promotes NK cell development, surveillance of MM, and direct as well as ADCC-mediated cytotoxicity against MM targets. Taken together, these data strongly support the concept of targeting AHR as a novel direct anti-MM therapy and anti-MM immunotherapeutic strategy. DisclosuresNo relevant conflicts of interest to declare.

MCL-1 Inhibition Is Highly Effective Against Multiple Myeloma Cells from Poor Prognosis Patients

Introduction: Despite recent advances in treatment, multiple myeloma (MM) is still considered incurable. Several novel therapies with different mechanisms of action are currently being studied for use in MM. These include targeted therapies such as pathway inhibitors and BCL-2 homology domain 3 (BH3) mimetics. BH3-mimetics overcome apoptosis resistance by binding and inhibiting select pro-survival BCL-2 family proteins. In MM, overexpression of MCL-1 leads to apoptosis resistance and is associated with shorter patient survival. In addition to MCL-1, overexpression of BCL-2 and/or BCL-XL has been observed in MM, suggesting that these three pro-survival proteins are promising targets for therapy. Finding tumor characteristics that can predict responses to MCL-1, BCL-2 or BCL-XL inhibitors is essential for finding optimal therapy combinations for each patient. Besides MM patient age, fitness and disease characteristics, several genetic aberrations are associated with treatment response and patient survival. This study aims at finding predictors of BH3-mimetic inhibitors in MM.Methods: Using primary MM (n=42) and monoclonal gammopathy of undetermined significance (MGUS) (n=10) bone marrow aspirates and a collection of human myeloma cell lines (HMCL), we determine dependence on MCL-1, BCL-2, and BCL-XL, and investigate whether this correlates to protein expression, disease stage, tumor cytogenetics, and patient characteristics. We use potent and specific BH3-mimetics S63845 (MCL-1), ABT-199/Venetoclax (BCL-2), and A-1155463 (BCL-XL) to assess pro-survival protein dependence. In addition, combinations of these BH3-mimetics are used to determine whether they act in synergy.Results: In HMCL, sensitivity to BCL-2 family inhibitors depends to a large extent on expression of BCL-2 and BCL-XL, as was shown previously. Inhibition of MCL-1 efficiently induces apoptosis in HMCL and acts in synergy with BCL-XL inhibition. For primary MM cells, we observed that MCL-1 and BCL-2 inhibitor sensitivity varies greatly between patients. In contrast, MM plasma cells (PC) are generally insensitive to BCL-XL inhibitors as single treatment. As observed with HMCL, combining BCL-2 family inhibitors further increased the level of apoptosis in these cultures. The t(11;14) translocation was previously linked to increased sensitivity towards Venetoclax in MM patients. Our experimental setup and data confirms this correlation (fold difference = 2.3, P=0.009 at 100 nM). Interestingly, we found an even greater difference in Venetoclax sensitivity when comparing patient samples with high versus low BCL-2 protein expression in MM PC (fold difference = 3.0, P=0.0002 at 100 nM). MGUS PC were generally insensitive to BCL-2 and BCL-XL inhibition, and sensitivity to MCL-1 inhibition was limited. These data reveal that MM PC are more dependent on BCL-2 family proteins for survival than PC from premalignant MGUS patients. Next, we investigated whether known poor prognostic characteristics correlate to inhibitor sensitivity and found that MM cells from patients with advanced disease stage (i.e. ISS 3), renal failure, or poor cytogenetics were markedly more sensitive to MCL-1 inhibition (ISS 3: P=0.029, β2M: P=0.020, renal failure: P=0.045, 1q+/17p+/t(4;14)+/t(14;16)+: P=0.039, and HD-/t(11;14)-: P=0.005).Conclusions: We observed for the first time that cells from MM patients with poor prognosis disease are more sensitive to inhibition of MCL-1. Combining BH3-mimetic inhibitors synergistically increased apoptosis compared to the single inhibitors. In addition, including flow cytometric determination of BCL-2 protein expression in MM cells at diagnosis may aid in predicting patient sensitivity to Venetoclax. Combined, our data indicate that BCL-2 protein expression, in combination with disease characteristics and cytogenetic testing, may predict sensitivity to BCL-2 and MCL-1 inhibitors in subsets of MM patients. [Display omitted] DisclosuresSonneveld:Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Minnema:Amgen: Consultancy; Celgene: Consultancy, Research Funding; Takeda: Consultancy; Janssen: Consultancy; Servier: Consultancy.

TBK1/Ikkε Inhibitor Amlx Blocks Multiple Myeloma Cell Growth in Vitro and In Vivo

Multiple myeloma (MM) is the most frequent cancer to involve the skeleton and remains incurable for most patients, thus novel therapies are needed. MM bone disease is characterized by osteolytic lesions that contribute significantly to patient morbidity and mortality. We showed that TBK1 signaling is a novel pathway that increases osteoclast (OCL) formation in Paget's disease, an inflammatory bone disease. Therefore, we hypothesized that TBK1 plays a similar role in MM induction of OCL. We found that MM conditioned media (MM-CM) dose-dependently increased bone marrow monocyte (BMM) expression of activated TBK1 protein and enhanced RANKL-driven OCL formation. TBK1 knockdown by shRNA transduction into BMM significantly attenuated the ability of MM-CM to increase OCL differentiation without altering OCL differentiation in control media. We found that the TBK1/IKKε inhibitor Amlexanox (Amlx) blocked normal and MM-enhanced OCL formation. Importantly, TBK1 mRNA expression in CD138+ plasma cells (PC) isolated from MM or PC leukemia patients is significantly higher as compared to PC from Monoclonal Gammopathy of Undetermined Significance (MGUS) patients.Therefore, we tested whether targeting the TBK1/ IKKε signaling pathways would also affect MM cells. We found that Amlx strongly decreased the viability of several MM cell lines and primary MM cells via induction of apoptosis. Amlx treatment of MM cell lines also induced a G1/S blockade, decreased activated ERK1/2, and increased translation of the dominant-negative C/EBPb-LIP isoform in several MM cell lines. The positive-acting C/EBPb-LAP isoform was previously shown to be a critical transcription factor for MM viability. Importantly, Amlx also enhanced the effectiveness of the proteasome inhibitors bortezomib and carfilzomib to kill MM cells in culture. Further, Amlx sensitized MM1.S cells to the induction of apoptosis by the autophagic inhibitor Bafilomycin A. Amlx dose-dependently inhibited tumor growth in a syngeneic MM mouse model in which 5TGM1 MM cells expressing secreted GLuc were injected subcutaneously into immunocompetent C57Bl/KaLwRij. Tumor growth was assessed by measuring tumor volumes and by the levels of secreted GLuc in the blood. Further, OCL formation ex vivo from bone marrow monocytes obtained from AMLX-treated mice versus controls was decreased. Amlx did not affect the viability of primary BMM, bone marrow stromal cells (BMSC), or splenocytes. Further, Amlx treatment of primary BMSC from MM patients or normal donors decreased expression of TNFα, IL-6 and RANKL, thereby decreasing BMSC support of MM survival and OCL differentiation. Amlx pretreatment of BMSC and murine pre-osteoblast MC4 cells also decreased VCAM1 expression and reduced MM cell adhesion, another mechanism for Amlx reduction of bone microenvironmental MM support.These data suggest that targeting TBK1/IKKε signaling may decrease MM bone disease by slowing MM growth, directly and indirectly, and preventing MM-induced osteolysis. DisclosuresGiuliani:Janssen Pharmaceutica: Other: Avisory Board, Research Funding; Celgene Italy: Other: Avisory Board, Research Funding; Takeda Pharmaceutical Co: Research Funding. Roodman:Amgen Denosumab: Membership on an entity's Board of Directors or advisory committees.

3D-Tissue Engineered Bone Marrow (3DTEBM) Culture Retrospectively Predicts Treatment Clinical Outcomes of Multiple Myeloma Patients

Background:Multiple Myeloma (MM) is the second most common hematological malignancy, and continues to be a fatal disease even with the development of novel therapies. Despite promising preclinical data in standard tissue culture models, most drugs fail in clinical trials and show lower efficacy in patients. This highlights the discrepancy between the current in vitro models, the pathophysiology of the disease in the patients, and the urgent need for better in vitro models for drug development and improved prediction of efficacy in patients. We have previously developed a patient-derived 3D-Tissue Engineered Bone Marrow (3DTEBM) culture model, which showed superior properties for proliferation of primary MM cells ex vivo, and better recapitulated drug resistance. The long-term goal of this study is to use the 3DTEBM model as a tool to perform drug screens on BM aspirates of MM patients and prospectively predict the efficacy of different therapies in individual patients, and help treatment providers develop personalized treatment plans for each individual patient. In the current study, we used the 3DTEBM model to, retrospectively, predict clinical responses of MM patients to therapy, as a proof of concept.Methods:We used whole-BM, viably frozen tissue banked samples from 20 MM patients with clear clinical response patterns of complete remission, and either very good partial response (sensitive) or progressive disease (non-sensitive). The BM aspirates were used to develop a 3DTEBM that represents each individual patient. The patient-derived 3DTEBM cultures were treated ex vivo with the same therapeutic regimen that the patient received in the clinic for 3 days. The treatment ex vivo was based on combinations at different concentrations which mimic the steady state concentrations (Css) of each drug. The efficacy of the treatment ex vivo was evaluated by digestion of the 3DTEBM matrix, extraction of the cells, and analysis for prevalence of MM cells in the treatment groups compared to the non-treated controls. Patients were defined “sensitive” if the effect reached 50% killing in the range of 10xCss. The ex vivo sensitivity data was then correlated with the clinical response outcomes.Results:We found that the 3DTEBM was predictive in approximately 80% of the cases (in about 85% of the combination therapy cases, and in about 70% of the single therapy cases). Broken down by individual drug, it was predictive in 80% of the cases treated with Bortezomib, 78% Lenalidomide, 84% Dexamethasone, 100% Daratumumab, 50% Carfilzomib, 50% Pomalidomide, and 100% Doxorubicin.Conclusions:The 3DTEBM is a more pathophysiologically relevant model which predicts clinical efficacy of drugs in multiple myeloma patients, retrospectively. This data provides the bases for future studies which will examine the ability of the 3DTEBM model to predict treatment efficacy, prospectively, for development of personalized treatment plans in individual multiple myeloma patients. DisclosuresJeske:Cellatrix LLC: Employment. Azab:Cellatrix LLC: Employment. De La Puente:Cellatrix LLC: Other: Co-founder. Vij:Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharma: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Jansson: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Azab:Ach Oncology: Research Funding; Cellatrix LLC: Equity Ownership, Other: Founder and owner; Glycomimetics: Research Funding; Targeted Therapeutics LLC: Equity Ownership, Other: Founder and owner.

The Critical Role of HDAC1-IRF4-Pim-2 Axis in Myeloma Cell Growth and Survival: Therapeutic Impacts of Targeting the HDAC1-IRF4-Pim-2 Axis

Multiple myeloma (MM) is a heterogeneous clonal plasma cell proliferative disorder with CRAB features. Although survival of MM patients has been greatly prolonged by recent implementation of various combinatory treatments with novel anti-MM agents, MM still remains incurable. MM cells preferentially grow and expand in the bone marrow to elicit the alteration of gene expression and thereby drug resistance. To improve the therapeutic efficacy, we urgently need to develop novel treatment strategies targeting the BM microenvironment-mediated drug resistance. The serine/threonine kinase Pim-2 is constitutively over-expressed and acts as a pro-survival mediator in MM cells. We have reported that cocultures with bone marrow stromal cells (BMSCs) or osteoclasts (OCs) further up-regulate Pim-2 expression in MM cells to confer drug resistance (Leukemia 2011, 2015). Therefore, Pim-2 appears to be an important therapeutic target to impair the BM microenvironment-mediated drug resistance in MM.Histone deacetylases (HDACs) are generally accepted to be therapeutic targets for MM treatment. However, clinical application of currently available pan-HDAC inhibitors is limited with their adverse effects induced by a non-selective HDAC inhibition. To develop safe and effective HDAC inhibitor-based treatment, the therapeutic roles of HDAC isoform-specific inhibition should be elucidated. In this regard, we have recently reported therapeutic impacts on MM cells of inhibition of class-I HDACs, especially HDAC1 and HDAC3. HDAC3-selective inhibitor BG45 induces anti-MM activity in combination with DNA methyltransferase (DNMT) inhibitor azacytidine (Leukemia 2017). In the present study, we aimed to clarify the underlying mechanisms for impairment of MM cell growth and survival by HDAC1 inhibition.We first referenced the expression of class-I HDACs using a publicly available GSE6691 data set. Among class-I HDACs, HDAC1 and HDAC3 were highly expressed in MM cells. We then knockdowned HDAC1 gene using lentiviral shRNA system in MM cell lines. The HDAC1 gene silencing induced MM cell death with caspase-3 activation, indicating the critical role of HDAC1 in MM cell growth and survival. To determine target molecules of HDAC1, we carried out RNA-sequencing with and without the HDAC1 gene silencing in RPMI 8226 cells. Among genes whose expression significantly changed by the HDAC1 knockdown (adjusted P values < 0.05, log fold change > 0.5), we focused on IRF4 together with PIM2, because MM cell has been demonstrated to addict to aberrant IRF4-c-Myc regulatory network (Nature 2008). Downregulation of IRF4 and Pim-2 by the HDAC1 knockdown was further confirmed by quantitative PCR (Q-PCR) and immunoblotting in RPMI 8226 and MM.1S cells. Treatment with the class I HDAC-selective inhibitor MS-275 (entinostat) also induced MM cell death along with reduction of IRF4 and Pim-2 expression.Since previous study has shown that IRF4 binds to PIM2 promoter in MM cells (Nature 2008), we examined whether IRF4 regulates PIM2 expression. We found that IRF4 binds to the PIM2 promoter region by analyzing ChIP-Seq data in KMS-12 cells (GSE22901). We further confirmed the binding of IRF4 on PIM2 promoter by ChIP-Q-PCR. Indeed, the IRF4 knockdown downregulated Pim-2 expression in RPMI 8226 cells. These results suggest that HDAC1 inhibition downregulates IRF4 expression, thereby transcriptionally reducing PIM2 expression in MM cells.Pim-2 expression can also be augmented by multiple signaling pathways, including HIF-1a, JAK-STAT and NF-kB-mediated ones in MM cells through the interaction with BM microenvironment. Interestingly, the Pim inhibitor SMI-16a and MS-275 cooperatively induced apoptotic cell death in MM cell lines and CD138-positive primary MM cells even in the presence of BMSCs.Taken together, our results demonstrate the critical role of the HDAC1-IRF4-Pim-2 axis in MM cell growth and survival, and provoke the novel treatment strategy targeting the HDAC1-IRF4-Pim-2 axis in MM cells. DisclosuresAnderson:Takeda Millennium: Consultancy; Gilead: Membership on an entity's Board of Directors or advisory committees; Oncopep: Equity Ownership; C4 Therapeutics: Equity Ownership; Celgene: Consultancy; Bristol Myers Squibb: Consultancy.

The JAK Inhibitor Blocks PD-L1, PD-L2 and CD44 Expression in Multiple Myeloma (MM) and Sensitizes MM Cells to Lenalidomide and Steroids

Introduction: Ruxolitinib (RUX) is an inhibitor of the Janus kinase family of protein tyrosine kinases (JAKs) that is effective for the treatment of myeloproliferative diseases. Immunomodulatory drugs including lenalidomide (LEN) and corticosteroids (dexamethasone [DEX]) have shown efficacy in the treatment of multiple myeloma (MM). We have demonstrated that the combination of the RUX, LEN and steroids shows both preclinical and clinical efficacy for the treatment of patients with relapsed and refractory MM. The immune inhibitory proteins PD-L1 and PD-L2 and CD44 are highly expressed in MM; moreover, increased expression of these proteins is associated with resistance to treatment in MM. In this study, we investigated the effects of RUX on expression of PD-L1, PD-L2 and CD44 in MM, and the effect of RUX in combination with LEN and DEX on growth of human MM in vivo.Methods: Bone marrow mononuclear cells (BMMCs) were purified from aspirates from MM patients with progressive disease (PD) or in complete remission (CR) before and after treatment with RUX in combination with LEN and methylprednisolone (MP). The cells were stained with antibodies directed against human PD-L1, PD-L2 and CD44 and flow cytometric analysis (FCA) was performed. MM biopsies or BMMCs were analyzed using immunofluorescent analysis (IFA). Total RNA was extracted from monocytes. Quantitative PCR (qPCR) was measured for gene expression of PD-L1, PD-L2 and CD44 and the housekeeping gene HPRT1 with TaqMan technology following standard qPCR protocol. The human MM xenograft LAGκ-2 was surgically implanted into the left superficial gluteal muscle of anaesthetized naive SCID mice. LEN was administered via oral gavage daily (15 mg/kg) and DEX was administered intraperitoneally daily (1 mg/kg). RUX was given via intraperitoneal (IP) injection twice daily (1.5 mg/kg). Seven days following tumor implantation, mice were treated with vehicle alone, single agent RUX, LEN or DEX or using combination treatments.Results: We examined PD-L1 gene expression in MM patients with PD or in CR and those with monoclonal gammopathy of undetermined significance (MGUS). The results showed that PD-L1 gene expression was markedly increased in BMMCs from MM patients with PD compared with those patients in CR or with MGUS. We determined the effects of RUX on expression of PD-L1 and CD44. The FCA data showed the percentage of PD-L1+ BMMCs was markedly reduced in MM patients treated with RUX, LEN and MP compared to those before starting treatment whereas there were decreased CD44+ cells in the MM patients after this treatment compared to those before treatment with this combination. IFA further confirmed that PD-L1+ and CD44+ BMMCs staining was markedly deceased in MM patients treated with this three drug combination compared to those without treatment. We further investigated the in vitro effects of RUX on gene expression of PD-L1, PD-L2 and CD44 in MM cell lines and primary MM cells co-cultured with THP1 monocytes. MM cells showed marked upregulation of these genes following co-culture with THP1 cells. RUX treatment markedly reduced PD-L1, PD-L2 and CD44 gene expression in the MM tumor cells co-cultured with monocytes compared with cells not treated with the JAK1/2 inhibitor. To evaluate these drugs in vivo, the human MM xenograft LAGκ-2 model was used. The mice were then treated with RUX, LEN or DEX alone, doublets or the combination of all three drugs. RUX alone produced minimal anti-MM effects whereas the doublets showed more anti-MM effects than any single agent, and the combination of all three drugs showed the most marked anti-MM effects.Conclusion: The PD-L1/PD-1 pathway delivers inhibitory signals that regulate both peripheral and central tolerance and inhibit anti-tumor immune-mediated responses. This study demonstrated that the JAK inhibitor RUX downregulated expression of PD-L1, PD-L2 and CD44 in MM tumor cells which should help overcome the immune resistance generated by these proteins for patients with this B-cell malignancy. We also demonstrated the combination of RUX with LEN and DEX showed enhanced anti-MM efficacy in vivo. These results also suggest that JAK inhibitors may be effective for treating MM patients through their ability to reduce expression of checkpoint proteins involved in the development of immune resistance that frequently occurs in MM patients. DisclosuresChen:OncoTracker: Equity Ownership. Li:OncoTracker: Equity Ownership. Sanchez:OncoTracker: Equity Ownership. Wang:OncoTracker: Equity Ownership. Berenson:Janssen: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria; Daiichi: Speakers Bureau; Takeda: Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau.