Multiple Myeloma Bone Marrow Samples Research Articles

Multiple Myeloma B Cells and Pre-Plasma Cells Are Important Reservoirs for Myeloma Relapse Following Plasma Cell-Directed Therapy and Prevent Cure with Standard Therapies

Multiple Myeloma (MM) is a B cell neoplasm characterized by the accumulation of mature plasma cells (PCs) within the bone marrow (BM). Despite treatment advances, MM remains incurable in the vast majority of patients. Disease relapse typically occurs regardless of treatment with proteasome inhibitors (such as bortezomib and carfilzomib), immunomodulatory drugs (such as lenalidomide and pomalidomide), anti-CD38 monoclonal antibodies (such as daratumumab and isatuximab) or myeloablative melphalan and autologous stem cell transplantation, and also occurs following treatment with immunotherapeutics such as bispecific antibodies and/or CAR-T cells (targeting BCMA, FcRH5 or GPRC5D). This failure to achieve reliable cure in MM, despite the routine attainment of deep treatment responses against PCs, indicates the existence of important intra-tumor heterogeneity and the presence of rare drug-resistant MM cells with full tumorigenic capacity. To identify intra-clonal MM cell subpopulations, we examined BM samples from MM patients using a combination of FACS, single cell resolved immunoflourescence-FISH (IF-FISH), whole exome sequencing (WES), custom-capture targeted deep sequencing (CC-Seq) and single cell RNA sequencing (scRNAseq). We sought to characterize the genomic landscape and to track the dynamic interconnectedness of these intra-clonal subpopulations in patients over time. Using sequential FACS-IF-FISH studies of MM BM samples (n=140) we identified MM clone cellular subpopulations within the BM of MM patients that recapitulate the normal maturation stages between non-malignant post germinal centre B cells and mature PCs. These subpopulations include rare MM cells that resemble CD20 +CD38 -CD138 -Bcma -Irf4 - Xbp1s - B cells, CD20 -CD38 -CD138 - Bcma -Irf4 -Xbp1s - pre-plasmablasts and CD38 +CD138 -Bcma -/lowIrf4 -/+Xbp1s + pre-plasma cells, as well as predominating tumor-bulk CD38 +CD138 +Irf4 +Bcma +Xbp1s + plasma cells. Importantly, MM progenitor cells were typically found to possess all of the chromosomal translocations and copy number variations (CNV) present in MM PCs including whole chromosome ploidy changes, translocations such as t(11;14), t(4;14) and t(14;16), and secondary aberrations such as gain(1q), del(1p) and del(17p). To examine if MM progenitor cells also possess the single nucleotide variations (SNV) present within MM PCs, and are thus fully malignant, and to track MM progenitor subpopulations and their inter-relatedness within patients over time, we performed WES (n=60) plus targeted deep CC-Seq (n=210) on purified cell subpopulations from 17 patients, including 5 patients whom we sampled serially over >3 years. A median of 5 cellular subpopulations were isolated from each BM sample, enriched by factors of up to 1000-fold or more, and each subpopulation was then sequenced to a depth of 4,000-20,000x. Significantly, SNVs that were present in tumor-bulk MM PCs were also regularly detected in MM progenitor cells, although the low frequency of the clonal progenitor cells often prevented capture of complete SNV profiles. At the same time, analyses of serial BM samples from repeat donor patients taken pre- and post-treatment demonstrated that relapsing MM PCs typically did not appear to derive linearly from pre-treatment PCs, as the relapsing PCs commonly lacked a number of SNVs that had been present in pre-treatment PCs. Importantly, we instead observed that relapsed MM plasma cells appeared to consistently derive from MM progenitor cell populations, frequently B cells, as emergent relapse-specific SNVs that were exclusively detected in relapsing post-treatment PCs (but in not pre-treatment PCs) could often also be detected within pre-treatment CD138- CD38- progenitor cells isolated from BM samples that had been collected up to 3 years prior to relapse. We conclude that MM B cells and pre-plasma cell progenitors possess all of the clonal genomic aberrations required for full malignant potential. Tracking of these cells in vivo in patients over time by their SNV profile implicates them as the cellular origin of PC relapse and recurrent MM disease. We propose that cure of MM requires eradication of MM progenitor cells alongside plasma cells. We are currently conducting scRNA-seq and CITE-seq studies of primary MM samples to further characterize MM progenitor cells for gene and protein expression in order to define their optimal therapeutic targets.

Mitochondrial Fitness and Immune Function of Natural Killer Cells Are Impaired By the Multiple Myeloma (MM) Tumor Cells: The Role of MM Microenvironment Interactions

The immune system including Natural Killer (NK) activity was shown to be impaired in active MM. We and others have previously demonstrated the important role of the bone marrow (BM) microenvironment in MM pathophysiology, however, data on its effects on NK activity in MM is limited. We first assessed the phenotype of the BM-derived NK cells. BM-NK from MM pts (n=10) showed an exhausted phenotypic signature with significantly reduced expression of CD16 (p<0.01), and increased expression of exhaustion markers CD39 (p<0.001) and CD57 (p<0.001) compared to BM-NK cells from healthy controls (n=8). Furthermore, MM-BM NK cells demonstrated reduced mitochondrial membrane potential, suggesting impaired mitochondrial fitness. The dysfunction of the mitochondria led to deficiency of ATP synthesis; mitochondrial ATP levels were reduced in NK cells from MM BM samples in comparison to the normal BMs (p<0.001). Next, the functional response of BM NK cells to the stimulation with IL-2 (2000 IU/ml for 7 and 14 days) was evaluated in vitro. NK cells from MM BM demonstrated reduced proliferation capacity, increased CD39, reduced expression of activating receptors NKp44 and NKp30, and reduced mitochondrial membrane potential upon the activation with IL-2. The impaired mitochondrial fitness correlated with reduced levels of NKp44, indicating a potential link between the decreased mitochondrial activity and the reduced functionality of NK cells. Indeed, in vitro, the cytotoxic activity of IL-2-stimulated MM-BM NK cells against MM cell lines was significantly diminished compared to healthy IL-2-activated BM-NK cells. Glucose and fatty acids (FA) are key substrates of the mitochondrial bioenergetic pathways and essential for NK cell activation. Of note, glucose uptake was increased comparably upon IL-2 stimulation in NK cells from both MM patients and healthy donors. In contrast, MM-BM NK cells demonstrated reduced FA uptake in response to IL-2 stimulation compared to BM NK cells from healthy donors. These data indicate impaired mitochondrial and NK cell properties in the BM MM niche. Next, we established an in vitro model to interrogate the relationship between NK cell mitochondrial and immune dysfunction within the MM BM microenvironment. Specifically, we cultured MM cell lines (n=5) with the NK92 cell line or primary IL-2-activated or not activated blood-derived NK cells, and assessed NK cell mitochondrial fitness, metabolic activity, and immune functional properties. Co-culture with MM cells significantly impaired mitochondrial mass and mitochondrial membrane potential in NK cells, decreased mitochondrial ATP levels, while upregulating MM mitochondrial ROS in NK cells, indicating that MM cells induce mitochondrial damage and impair ATP synthesis in NK cells. Mitochondrial fitness and energy production are pivotal for NK cell persistence and cytotoxicity. In accordance, direct interaction with MM cells suppressed NK cell proliferation in vitro, inducing G0/G1 cell cycle arrest. Moreover, MM-induced mitochondrial impairment in NK cells correlated with reduced responsiveness of MM cells to NK-induced killing, while short-term exposure to MM cells significantly diminished the anti-myeloma cytotoxic activity of NK cells. Accordingly, CD39 expression was upregulated, while NKp44 levels significantly decreased in NK cells upon interaction with MM cells. To further characterize the molecular mechanisms associated with MM-mediated NK cell mitochondrial impairment, we assessed the gene expression profile of MM-exposed sorted NK92 cells versus unexposed cells. A distinct metabolic signature characterized by reduced expression of genes involved in the mitochondrial activity was detected in MM-exposed NK cells. Thus, genes involved in respiratory activity and mitochondrial dynamics were downregulated post-MM exposure. Furthermore, a profound increase in fructose-1,6-biphosphatase 1 (FBP1) expression was detected in MM-exposed NK cells. FBP1 is the rate-limiting enzyme for gluconeogenesis that simultaneously inhibits glycolysis, possibly interfering with NK cell metabolic activity and immune function. Altogether, our data suggest that MM BM microenvironment and direct interactions with malignant plasma cells impair NK mitochondrial fitness, diminishing energy production, increasing oxidative stress, and driving exhaustion with reduced anti-tumor capacity in NK cells.

Hsa_Circ_0134426 Attenuates the Malignant Biological Behaviors of Multiple Myeloma by Suppressing miR-146b-3p to Upregulate NDNF.

We focused on hsa_circ_0134426 (circ_0134426) to determine its functional effects and targets in multiple myeloma (MM) development. The relative expression of circ_0134426, miR-146b-3p, and neuron-derived neurotrophic factor (NDNF) in the MM samples was confirmed by quantitative real-time PCR (qPCR) or western blotting. The protein levels of epithelial-to-mesenchymal transition (EMT)-linked markers were identified using western blotting. Xenograft models in nude mice were used for in vivo functional analysis of circ_0134426. The binding of miR-146b-3p to circ_0134426 or NDNF was confirmed by dual-luciferase and RIP assays. Poor levels of circ_0134426 and NDNF and high levels of miR-146b-3p were observed in MM bone marrow samples and cell lines. Circ_0134426 overexpression blocked MM cell growth, colony formation, and migration and impeded tumor development in xenograft models. circRNA_0134426 decoys miR-146b-3p to repress its expression. Overexpression of miR-146b-3p restored MM cell activities that were blocked by circ_0134426 overexpression. NDNF is a functional molecule targeted by miR-146b-3p, and miR-146b-3p sequesters NDNF expression. The inhibitory effects of NDNF upregulation on MM cell growth, colony formation, and migration were partially abolished by miR-146b-3p overexpression. Circ_0134426 regulates the miR-146b-3p/NDNF network to restrain the development of MM, to some extent, suggesting that the development of MM therapeutic strategies might focus on circ_0134426 regulatory networks.

Abstract 1729: Single-cell transcriptome profiling of multiple myeloma bone marrow samples suggests that disease progression interplays with tumor and tumor microenvironment in The MMRF CoMMpass Study

Abstract Multiple Myeloma (MM) is a hematologic malignancy marked by uncontrolled clonal expansion of plasma cells. Previous research has examined single-cell transcriptome profiles of Monoclonal gammopathy of undetermined significance (MGUS) and MM tumor microenvironment (TME) and found that natural killer (NK) cell abundance is elevated in the early stages and correlated with altered chemokine receptor expression. This study suggested the critical role of immune cells on myeloma progression from asymptomatic MGUS to symptomatic MM. Up to date, however, there are no published studies comprehensively comparing tumor and immune populations differences between MM NON-progressors (NPs) and FAST-progressors (FPs) and investigating how clonal plasma cells affect disease progression in a large cohort. Therefore, understanding how tumor and immune cells influence disease progression within symptomatic MM is of great interest.Here, we subjected CD138-negative Bone Marrow Mononuclear cells (BMMC) samples from 418 MM patients to scRNA-seq. From MMRF CoMMpass study (NCT01454297), we also have whole exome sequencing (WES) and bulk RNA-seq from CD138-positive fraction of BMMC samples. Based on time to progressive disease (TTPD), we classified patients into 2 categories. Patients with TTPD less than 18 months were classified as FAST-progressors (FPs), whereas patients with TTPD more than 5 years were classified as NON-progressors (NPs). By analyzing patient genomic alterations and its association with progression, we found that there was a significant association of slow MM progression with t(11;14) (p = 0.048), consistent with previous study. In our preliminary analysis, we profiled 83 CD138-sorted MM bone marrow samples using scRNA-seq. Interestingly, we found plasma cells from samples with the same genetic alterations tend to cluster together, highlighting the important role of genetic drivers in transcriptome profiles of plasma cells. Moreover, integrated analysis of bone marrow samples from 83 MM patients and 4 healthy donors revealed an atypical naïve-B cell subset with enrichment of cells from fast-progressors and partial expression of MS4A1. Differentially expressed genes for this naïve-B cell subset includes KLF9, BCL2L11, JOSD1, and IRS2, etc. Overall, as part of MMRF immune profiling research, this study will help to interrogate how genetic alterations and disease progression interplay MM tumor and TME and provide a sufficiently broad and valuable dataset for systematically characterizing MM at single-cell resolution. Hopefully, this study could identify novel targets for MM immunotherapies, and ultimately identify patients with high risk of fast progression for early intervention in the clinic. Citation Format: Lijun Yao, Tianjiao Wang, Kazuhiro Sato, Reyka Jayasinghe, I-Ling Chiang, Darwin D'souza, William Pilcher, Edgar Gonzalez-Kozlova, Yered Pita-Juarez, Taxiarchis Kourelis, Deon Bryant Doxie, Beena Thomas, Brian Lee, Swati Sharma Bhasin, Upadhyaya Bhaskar, Mark Fiala, Julie Fortier, Travis Dawson, John Leech, Shaji Kumar, Hearn Cho, Seunghee Kim-Schulze, Bee Raj, Stephen Oh, the MMRF Immune Profiling Research Team, John Dipersio, Ravi Vij, Adeeb Rahman, Ionnis Vlachos, Shaadi Mehr, Mark Hamilton, Daniel Auclair, Surendra Dasari, David Avigan, Madhav Dhodapkar, Sacha Gnjatic, Manoj Bhasin, Li Ding. Single-cell transcriptome profiling of multiple myeloma bone marrow samples suggests that disease progression interplays with tumor and tumor microenvironment in The MMRF CoMMpass Study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1729.

Preclinical Evaluation of MEDI2228, a BCMA-Targeting Pyrrolobenzodiazepine-Linked Antibody Drug Conjugate for the Treatment of Multiple Myeloma

Despite remarkable progress in treatment over the past two decades, multiple myeloma (MM) remains an incurable disease. B-cell maturation antigen (BCMA, TNFRSF17) is a suitable therapeutic target for the treatment of MM due to its restricted expression on normal plasma cells and universal expression in myeloma cells. Targeting BCMA with an antibody-drug conjugate (ADC) is an attractive therapeutic option, combining the specificity of a monoclonal antibody with a potent cytotoxic drug to preferentially eliminate antigen-positive cells for the treatment of cancer.Here we describe MEDI2228, a novel ADC that targets BCMA. MEDI2228 is composed of a fully human antibody site-specifically conjugated to a DNA cross-linking pyrrolobenzodiazepine (PBD) dimer via a protease-cleavable linker. Flow cytometry studies show that MEDI2228 is rapidly internalized and trafficked to lysosomes. Upon release, the warhead binds to the minor-groove and cross-links DNA, leading to DNA damage and apoptotic cell death.The anti-tumor activity of MEDI2228 was assessed in vitro in 10 MM and plasma cell leukemia (PCL) cell lines encompassing several cytogenetic subtypes. MEDI2228 was highly active in 8 of 10 MM cell lines tested (IC50 range 6 to 210 ng/mL) including cell lines with high (~19,000 receptors/cell) or low (~930 receptors/cell) expression of BCMA. In addition, MEDI2228 is active in the presence of bone marrow stromal cells, which have been shown to play a role in chemotherapy resistance, and in cell models resistant to Lenalidomide. In vivo antitumor activity was evaluated in 4 separate MM and PCL subcutaneous xenograft models and 2 PCL disseminated xenograft models, where a single injection of MEDI2228 induced tumor regression at doses as low as 0.1 mg/kg.A soluble form of BCMA (sBCMA) has been detected in the serum of MM patients (Sanchez et. al. Br J Haematol 2012) and is comprised of the entire extracellular domain of the molecule (Laurent et. al. Nat Commun 2015). Therefore, sBCMA could diminish the effects of antibody-based therapies. We found that levels of sBCMA are elevated in the sera of MM patients compared with healthy donor controls, with levels ranging from 23 ng/mL to 728 ng/mL. The functional features of sBCMA and recombinant monomeric human BCMA are similar (Laurent et. al. Nat Commun 2015). Therefore, to mitigate the potential effects of sBCMA on the efficacy of our drug, the antibody component of MEDI2228 was selected because it possessed weak binding to recombinant monomeric human BCMA and strong binding to membrane-bound BCMA. The in vitro cytotoxicity of MEDI2228 in the presence of clinically-relevant levels of sBCMA was evaluated using NCI-H929 and MM.1S cells. MEDI2228 was cytotoxic to both MM.1S and NCI-H929 in vitro, killing an average of 95% of tumor cells in the presence of sBCMA at levels up to 720 ng/mL with little impact on IC50. ADCs developed from antibodies that possessed a similar affinity between monomeric BCMA and membrane-bound BCMA exhibited a sBCMA-dose dependent drop in potency, with a 20-fold shift in IC50 in the presence of 720 ng/mL sBCMA.MM is a clonally heterogeneous disease, and previously it has been reported that a small population of CD19+CD138- clonogenic cells can be identified in the bone marrow (BM) of MM patients (Matsui et. al. Blood 2004). We used flow cytometric sorting of CD19 and CD138 populations and outgrowth in methocult to confirm that CD19+CD138- cells are the clonogenic cells in MM BM samples. Furthermore, we found that this population contains the same light chain restriction, genetic translocation, and aberrant phenotype as the MM plasma cells. These cells express BCMA and can be killed by MEDI2228 in methocult outgrowth assays.These data demonstrate that MEDI2228 exhibits potent antitumor activity in preclinical models of MM. Importantly, in vitro experiments suggest that this activity is maintained in the presence of sBCMA. MEDI2228, bearing a potent PBD payload, may effectively target both the bulk myeloma plasma cells as well as the more quiescent, CD19+CD138- clonogenic cells, which may offer an opportunity for more durable clinical response in this genetically heterogeneous disease. DisclosuresKinneer:MedImmune: Employment. Meekin:MedImmune: Employment. Varkey:MedImmune: Employment. Xiao:MedImmune: Employment; Bristol-Myers Squibb: Employment. Zhong:MedImmune: Employment. Breen:MedImmune: Employment. Hurt:MedImmune: Employment. Thomas:MedImmune: Employment. Flynn:MedImmune: Employment. Hynes:MedImmune: Employment. Bezabeh:Salubris Biotherapeutics Inc: Employment; MedImmune: Employment. Chen:MedImmune: Employment. Wetzel:MedImmune: Employment. Chen:MedImmune: Employment. Anderson:Gilead Sciences: Membership on an entity's Board of Directors or advisory committees; MedImmune: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Oncopep: Other: scientific founder; C4 Therapeutics: Other: scientific founder; Millenium Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Herbst:MedImmune: Employment. Tice:MedImmune: Employment.

PIM Kinase Inhibition Decreases the Proangiogenic Properties of Multiple Myeloma Cells and Affects the Metabolic State of the Vascular Endothelium

The development and progression of multiple myeloma (MM) depend on the formation and perpetual evolution of an immunosuppressive and hypervascular bone marrow microenvironment. MM undergoes an angiogenic switch during its early progression stages and initiates the secretion of proangiogenic proteins, such as VEGFA and Galectin-1. Following their engagement with the VEGF receptor 2 on the surface of the endothelium, quiescent endothelial cells (ECs) rapidly switch to an activated state, thus gaining the ability to create sprouts, migrate and proliferate. However, chronic angiogenic stimulation results in the formation of a dense and leaky network of pathological vessels, which in the case of MM also serves as a major source of prosurvival paracrine signals. Since PIM kinases are known modulators of cytokine signaling, owing to their ability to activate NFκB, JAK/STAT and mTOR pathways, we analyzed the expression pattern of PIM1, PIM2 and PIM3 in multiple myeloma bone marrow samples using immunohistochemistry. We found that both MM cells as well as myeloma-associated ECs exhibit a significantly higher PIM3 expression than their normal bone marrow counterparts. Since the role of PIM kinases in the vascular compartment of the tumor microenvironment is currently unknown, we decided to explore the proangiogenic functions of PIM kinases using in vitro MM and EC model cell lines. 3 MM cell lines (RPMI 8226, MM1.s, U266), immortalized bone marrow ECs (HBMEC-60) and human umbilical vein ECs (HUVECs) were used for the experiments. Primary MM cells were obtained from MACS-separated bone marrow aspirates. Chemical blockade of PIM kinase activity was achieved using the pan-PIM inhibitor SEL24/MEN1703. The compound decreased the viability of MM cell lines with IC50 in the submicromolar range, induced G2 cell cycle arrest and apoptosis. Moreover, SEL24/MEN1703 induced apoptosis in primary MM cells, even when cocultured with the CD138- bone marrow fraction. PIM inhibitor treatment inhibited the phosphorylation of mTOR substrates S6 and 4EBP1, STAT3/5, as well as RelA/p65. Consequently, we observed markedly decreased VEGFA and Gal-1 levels in SEL24/MEN1703-treated MM cells. When cultured together, separated by a permeable transwell membrane, both RPMI 8226 cells, as well as ECs, exhibited a 2-fold increase in proliferation rate. This effect was completely blocked by a 2-day treatment with a PIM inhibitor. Exposure of ECs to recombinant VEGFA (10ng/ul) or MM supernatant resulted in an increase in VEGFR2 Y1175 phosphorylation level and induction of PIM3 expression. Increased MYC activity is a hallmark of VEGF-dependent endothelial activation and is necessary to support the creation of new vessels. Since the PIM3 promoter region contains putative MYC-binding sites (E-boxes), we checked if PIM3 induction depends on MYC in ECs. MYC silencing using siRNA resulted in an 88% lower PIM3 expression than the non-targeting siRNA. One of MYC's main tasks during angiogenesis is the stimulation of cellular ATP synthesis to meet the energy demands created by the dynamic remodeling of the actin cytoskeleton. Surprisingly, PIM inhibition decreased the total ATP content in ECs by 25%, thus disrupting the energetic homeostasis, as evidenced by a 9.6-fold increase in phosphorylated AMPK T172 levels. Furthermore, SEL24/MEN1703-treated ECs were depleted of higher-order actin structures necessary for efficient angiogenesis, such as actin stress fibers, membrane ruffles and lamellipodia. In consequence, PIM kinase inhibition decreased proliferation, migration and formation of new vessel-like structures in Matrigel by ECs. Collectively, our data demonstrate that PIM inhibition induces MM cell death and abolishes important tumor cell-ECs interactions. In addition, we show that PIM3 is overexpressed in MM tumor endothelial cells and PIM inhibition disrupts the activation state in in vitro cultured ECs. Hence, targeting PIM kinases may represent an efficient approach to induce tumor cell death and to block angiogenesis in MM. RNA-sequencing studies on the downstream effectors of PIM3 are currently ongoing in order to unravel the molecular mechanism behind the observed effects. Figure Disclosures Brzózka: Ryvu Therapeutics: Current Employment. Rzymski:Ryvu Therapeutics: Current Employment. Tomirotti:Menarini Ricerche: Current Employment. Lech-Marańda:Roche, Novartis, Takeda, Janssen-Cilag, Amgen, Gilead, AbbVie, Sanofi: Consultancy; Roche, Amgen, Gilead: Speakers Bureau. Juszczynski:Ryvu Therapeutics: Other: member of advisory board.

PB2166 SUPERIOR AUTOMATED MAGNETIC ISOLATION OF PLASMA CELLS FROM MYELOMA BONE MARROW YIELDING HIGH‐QUALITY CELLS FOR DOWNSTREAM PROCESSING

Background:Multiple Myeloma is the 2nd most common blood cancer in the western world that forms in terminally differentiated, clonal plasma cells (PCs). These malignant PC accumulate in the bone marrow, which is typically accompanied by secretion of monoclonal immunoglobulins detectable in the serum or urine, thereby skewing the adaptive immune system. Despite remarkable improvements in diagnosis and treatment over the last decade, multiple myeloma remains incurable with a median 5‐year survival rate of just 49%. Hence, there is a strong need for sensitive diagnostics as early therapeutic intervention benefits treatment outcome, particularly when combined with long term monitoring. Therefore, the isolation and pre‐enrichment of PC from patient samples, especially when at low abundance, facilitates subsequent diagnostics and their functional analysis by for instance cytogenetic methods such as FISH or molecular methods as NGS.Aims:To optimize our MACS™ technology‐based automated isolation of PC from myeloma patients’ bone marrow in regards to PC yield and purity as well as their performance in downstream applications.MethodsBone marrow from multiple myeloma patients or a cell line‐based model system were used as source to isolate CD138+ Plasma cells with MACSprep™ Multiple myeloma CD138 MicroBeads, human in an automated manner using the autoMACS® Pro Separator (aMP). For subsequent analysis and performance assessment the cells were measured by flow cytometry using an in‐house developed panel of antibody‐conjugates.Results:The optimization of our workflow strongly improved the PC isolation performance from both, primary multiple myeloma bone marrow samples as well as a cell line‐based model system. This model system is based on a plasma cell line, whose CD138 expression can be set to mimic that of primary PC more closely. Additionally, our workflow isolated CD138+ PCs to considerably higher purity than another separation technology using column‐free magnetic isolation, particularly at lower starting PC frequencies.Noteworthy, the aMP workflow yielded significantly higher cell recoveries over a range of starting PC frequencies. Interestingly, plasma cells isolated with the aMP displayed the expected normal PC morphology as analyzed by flow cytometry, phase contrast microscopy and Pappenheimer staining, whilst those from the other separation technology looked in part abnormal, not uniform and somehow distorted. This, in addition with the large aggregates that were formed during this other separation technology, resulted in clustered cells and hybridization artefacts in downstream FISH analysis, rendering the dispersed normal PC isolated with the aMP much easier to analyze. Furthermore, cells isolated with this other separation technology were contaminated with erythrocytes as examined by flow cytometry and microscopy, despite their obligatory use of a red blood cell lysis reagent. An advantage of the optimized aMP workflow is that it does not require sample preparation or red blood lysis resulting in virtually no hands‐on time.Summary/Conclusion:The fast and virtually no hands‐on aMP workflow significantly improves the performance in regard to obtained cell purity and cell yield when isolating PC from myeloma patient material. Noteworthy, it performs superior to another tested separation technology in regards to downstream analyses, thus facilitating the unambiguous analysis and study of myeloma plasma cells in research as well as routine analysis settings.

SLC46A3 as a Potential Predictive Biomarker for Antibody-Drug Conjugates Bearing Noncleavable Linked Maytansinoid and Pyrrolobenzodiazepine Warheads.

Antibody-drug conjugates (ADC) utilizing noncleavable linker drugs have been approved for clinical use, and several are in development targeting solid and hematologic malignancies including multiple myeloma. Currently, there are no reliable biomarkers of activity for these ADCs other than presence of the targeted antigen. We observed that certain cell lines are innately resistant to such ADCs, and sought to uncover the underlying mechanism of resistance. The expression of 43 lysosomal membrane target genes was evaluated in cell lines resistant to ADCs bearing the noncleavable linker, pyrrolobenzodiazepine payload SG3376, in vitro. The functional relevance of SLC46A3, a lysosomal transporter of noncleavable ADC catabolites whose expression uniquely correlated with SG3376 resistance, was assessed using EPHA2-, HER2-, and BCMA-targeted ADCs and isogenic cells overexpressing or genetically inactivated for SLC46A3. SLC46A3 expression was also examined in patient-derived xenograft and in vitro models of acquired T-DM1 resistance and multiple myeloma bone marrow samples by RT-PCR. Loss of SLC46A3 expression was found to be a mechanism of innate and acquired resistance to ADCs bearing DM1 and SG3376. Sensitivity was restored in refractory lines upon introduction of SLC46A3, suggesting that expression of SLC46A3 may be more predictive of activity than target antigen levels alone. Interrogation of primary multiple myeloma samples indicated a range of SLC46A3 expression, including samples with undetectable levels like multiple myeloma cell lines resistant to BCMA-targeting DM1 and SG3376 ADCs. Our findings support SLC46A3 as a potential patient selection biomarker with immediate relevance to clinical trials involving these ADCs.

Ex Vivo Evaluation of VLA-4 Expression in Primary Human Multiple Myeloma Bone Marrow Samples and In Vivo Mobilization of Murine Multiple Myeloma Cells with Small Molecule VLA-4 Inhibitors

Background: The interaction of multiple myeloma (MM) cells with their microenvironment in the bone marrow (BM) affects disease progression and provides resistance to therapeutic agents. Very-late-antigen 4 (VLA-4, α4β1 integrin, CD49d/CD29) is a noncovalent, heterodimeric transmembrane receptor that is strongly implicated in the pathogenesis of MM via altering cell trafficking, proliferation and drug resistance. LLP2A is a high-affinity peptidomimetic ligand for activated VLA-4. We recently reported (Soodgupta et al. J. Nucl. Med 2016) the sensitive and specific molecular imaging of activated VLA-4 in mouse MM tumors using 64Cu-LLP2A and LLP2A-Cy5. Here we extended these studies by further characterizing VLA-4 expression in primary human MM samples and malignant plasma cells in mouse models of MM.Methods: We evaluated VLA-4 expression in 5 human MM cell lines (U266, OPM2, H929, RPMI-8226 and MM1.S), one mouse MM cell line (5TGM1) and seventeen primary human MM bone marrow samples by flow cytometry using LLP2A-Cy5, soluble VCAM-1/Fc recombinant protein and CD49d (α4) and CD29 (β1) antibodies. The relative mean fluorescence intensity (RMFI) of LLP2A-Cy5 binding was calculated by dividing the MFI of LLP2A-Cy5 binding in the absence of BIO5192 (small molecule VLA-4 inhibitor) by the MFI of LLP2A-Cy5 binding in the presence of excess BIO5192. The 5TGM1/KaLwRij immunocompetent mouse model of MM was used for in vivo study.Results: The expression of activated VLA-4 on MM cell lines as measured by LLP2A-Cy5+ mean fluorescent intensity (MFI) varied 10-fold as follows (LLP2A-Cy5 MFI in parentheses): 5TGM1 (23.7) > U266 (16.1) > OPM2 (4.6) > H929 (3.4) > RPMI-8226 (3.2) > MM1.S (2.1). We observed similar variable expression of LLP2A-Cy5 binding to primary human CD138+CD38+ MM plasma cells (PCs), with 76.47% (13/17) of MM patients exhibiting greater than 20% LLP2A-Cy5+ PCs. expressing VLA-4 on CD138+CD38+ cells. Overall, the mean percentage of positive cells and LLP2A-Cy5 relative MFI (RMFI) on malignant CD138+ PCs from these 13 patients were 78.2% (43.8-98.3%) and 4.3 (1.7-10.8), respectively. Other hematopoietic cells within the BM samples expressed less VLA-4 in descending order as follows; monocytes (58.2%, RMFI 3.0), T-lymphocytes (34.4%, RMFI 2.1) and B-lymphocytes (21.6%, RMFI 1.6). These levels of VLA-4 expression on normal cell subsets within MM patients were comparable to normal blood donors. In general, there was good correlation between LLP2A-Cy5 binding and expression of CD49d and CD29 on CD138+ PCs in MM patients. To our surprise, the four MM patients with <20% LLP2A-Cy5 binding demonstrated high expression of CD49d (92.1%) but very low percentages of CD29 positive cells (17.3%). Using BIO5192 (VLA-4 inhibitor), we found that the LLP2A-Cy5 reagent allowed more accurate detection of activated VLA-4 than the soluble VCAM-1 binding assay as determined by the magnitude of inhibition of binding in the presence of inhibitor. We next evaluated targeting VLA-4 molecule in murine MM model. Preliminary mouse mobilization studies demonstrated that VLA-4 inhibitors effectively and rapidly mobilized murine 5TGM1 MM cells from the bone marrow to the blood (2.49-fold increase in circulating GFP+CD138+ cells) within 1 hour of injection.Summary:This study is the first demonstration that activated VLA4 can be detected on primary human MM cells using LLP2A. These data support the continued development of LLP2A as a molecular diagnostic imaging reagent for MM and as a potential therapeutic target of VLA-4 in MM. Ongoing studies are testing whether small molecule VLA-4 inhibitors can sensitize MM cells to cytotoxic therapy in vivo. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A Dual Color Immunohistochemistry Assay for Measurement of Cereblon in Multiple Myeloma Patient Samples.

Clinical interest in the measurement of Cereblon (CRBN), the primary target of the IMiDs immunomodulatory drugs lenalidomide and pomalidomide, has been fueled by its essential requirement for antitumor or immunomodulatory activity of both drugs in multiple myeloma (MM). However, limited analyses of clinical samples for CRBN gene expression or protein levels have utilized unvalidated reagents and assays, raising uncertainty about the interpretation of these results. We previously described a highly specific rabbit monoclonal antibody CRBN65 against 65-76 AA of human Cereblon. Here we describe a validated dual color bright-field Cereblon/CD138 immunohistochemical (IHC) assay utilizing CRBN65 and a commercial mouse monoclonal CD138 antibody. Sensitivity and specificity of the assay was determined and assay precision was shown for both cytoplasmic and nuclear Cereblon in MM bone marrow samples with coefficient of variation values of 5% and 2%, respectively. The dual IHC assay was effective for detecting a continuous range of Cereblon levels in 22 MM patient bone marrow core biopsies and aspirate clots, as shown by average cytoplasmic H-scores ranging from 63 to 267 and nuclear H-scores ranging from 17 to 250. Interpathologist comparison of MM sample H-scores by 3 pathologists demonstrated good concordance (R=0.73). This dual assay demonstrated superior Cereblon IHC measurement in MM samples compared with the single IHC assay using a published commercial rabbit polyclonal Cereblon antibody and could be used to explore the potential utility of Cereblon as a biomarker in the clinic.

Expression Profile of CD38 and Related Ectoenzymes in Myeloma Bone Niche: A Rational Basis for the Use of Daratumumab to Inhibit Osteoclast Formation and Activity

The relationship between multiple myeloma (MM) cells and osteoblast (OB)s and osteoclast (OCL)s into the bone marrow (BM) niche has a critical role in the pathophysiology of MM and in the development of bone disease in MM patients.Recently, Daratumumab (DARA), a human anti-CD38 monoclonal antibody has been developed with broad-spectrum killing activity including complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and, at least in part, modulation of CD38 enzymatic activity. In pre-clinical studies, DARA has been shown to effectively kill MM cells and clinical trials are ongoing. However, the effects of DARA in the context of the MM bone niche and on MM-induced bone remodeling alterations are unknown.In this study, we have firstly evaluated the expression profile of CD38 and its related ectoenzymes by bone niche cells and, thereafter, we investigated the effect of DARA on OCL and OB formation and bone remodeling. The study design included immunohistochemistry for CD38, CD73, CD39, CD203a (PC-1), CD157 and CD31 on bone biopsies in a cohort of 38 patients with newly diagnosed MM and 14 patients with monoclonal gammopathy of uncertain significance (MGUS). Moreover, the expression profile of these antigens was performed by flow cytometry on primary BM CD138+ cells (sample number=16), mesenchymal stromal cells, OBs, monocytes and OCLs and on the related human cell lines.As expected, we found that CD38 was highly expressed by MM cells that were also positive for CD203a and for CD39 and CD31 at variable level but not for CD157 and CD73. CD38 was also expressed by BM monocytes but not by OBs, OCLs and BM stromal cells. Interestingly, we found that OBs expressed CD73 and CD203a. Any significant difference was not observed in the expression of CD38 and related ectoenzymes between MM and MGUS patients. In line with CD38 expression profile by MM cells and the niche, we further demonstrated that DARA binds both MM cells and monocytes, but not OBs and OCLs. Consistently, we lack to find any significant effect of DARA on OB formation from BM stromal cells or OBs proliferation and survival. Thus, we investigated the effect of DARA (1-25 ug/ml) as compared to human IgG isotype control on OCL formation and activity in the presence of RANKL and M-CSF, using either CD138- cell fraction or purified CD14+ cells from MM BM samples. OCLs were evaluated by both TRAP staining and a fluorimetric osteolysis assay. We found that DARA, between 10 and 25 ug/ml, with a dose dependent effect, significantly inhibited OCL formation and activity from BM mononuclear cells and from the CD138- cell fraction, but not from purified CD14+ cells. The inhibitory effect on OCL formation by DARA was observed when the antibody was present for all the culture period (21-28 days). On the other hand DARA did not show any effect on late OCL progenitors and mature OCLs. Accordingly CD38 expression by monocytes cultured in a pro-osteoclastogenic medium disappeared after 7 days.In conclusion, our data indicate that DARA inhibit osteoclastogenesis, likely mediated by ADCC, targeting monocytes and early OCL progenitors. This evidence supports the use of an anti-CD38 based approach as a treatment for MM bone disease. DisclosuresMalavasi:Janssen: Honoraria, Research Funding. Giuliani:Celgene Italy: Other: Research Grant; Janssen Pharamceutical: Other: Research Grant.

Application of BIOMED- 2 standardized Ig gene rearrangement system in multiple myeloma

目的探讨BIOMED-2标准化Ig基因重排技术在多发性骨髓瘤（MM）诊治中的应用以及采用PCR片段分析毛细管电泳法（简称毛细管电泳法）进行克隆性检测的意义。方法选取2009年至2013年167例MM患者骨髓标本，以20例反应性浆细胞增多症患者骨髓标本作为对照，采用BIOMED-2系统引物，进行多重PCR扩增并采用毛细管电泳法进行Ig基因重排的克隆性分析。结果①167例MM患者中IgH VH-JH重排阳性者107例，阴性者60例，两组患者中IgH DH-JH重排发生率差异有统计学意义（14.0％对30.0%，P=0.013）；121例（72.4%）患者存在IgK重排。IgH VH-JH、IgH DH-JH、IgK联合检查，阳性检出率为94.6%。对照组Ig基因重排检测结果均为阴性。②琼脂糖电泳法结果示167例MM患者中9例（5.4%）患者IgH重排基因克隆性阳性，而毛细管电泳法结果则示为多克隆重排。③53例MM患者同时进行Ig基因重排检测和染色体荧光原位杂交IgH检测，两种方法的IgH阳性检出率差异有统计学意义（67.9％对49.1%，P=0.049）。结论IgH VH-JH、IgH DH-JH、IgK联合检测可大大提高MM患者Ig基因重排克隆性的检出率，尤其对于IgH VH-JH重排阴性者IgH DH-JH重排的补充检测尤为重要。基因重排检测采用毛细管电泳法可有效地区分单克隆、多克隆和寡克隆。Ig基因重排检测较染色体荧光原位杂交技术的IgH阳性检出率高。应用BIOMED-2标准化Ig基因重排技术检测对于MM的诊断有指导意义。

S1P Modulator FTY720 Targets Multiple Myeloma Cell Proliferation and Stromal Interactions Via CXCR4/CXCL12 and mTOR Pathways

Introduction: Multiple myeloma (MM) is an incurable hematological malignancy characterized by proliferation of malignant plasma cells in the bone marrow (BM). Interactions between MM cells and BM milieu facilitate disease progression and therapy resistance. Chemokine receptor CXCR4 and its cognate ligand CXCL12 are implicated in these processes and are associated with poor prognosis. Sphingosine-1-phosphate (S1P) pathway is involved in cancer progression, including oncogenesis, cell survival and cell migration, therefore representing an attractive target for anti-cancer therapy. FTY720 (fingolimod) is a modulator of S1P signaling system that exhibit immunosuppressive and anti-cancer properties. The role of S1P system and FTY720 modulator in MM is less defined. The aim of this study was to explore the functional consequences of possible cross-talk between the CXCR4/CXCL12 and the S1P axes in MM cells and to evaluate the effect of S1P targeting with FTY720 as potential anti-MM therapeutic strategy.Results: The partners of the S1P pathway (S1P receptor 1 and sphingosine kinase 1 (SPHK1)) and CXCL12 chemokine were found to be co-expressed in MM cell lines and primary BM samples from MM patients. Increased mRNA levels of SPHK1 and CXCL12 were detected in MM BM samples (n=24) comparing to BM from healthy donors (n=7) (p<0.01). In vitro treatment of MM cell lines (n=6) with FTY720 modulator resulted in time- and dose-dependent cell death (IC50 2.8 – 5.3 µM). Further characterization of cell death mechanisms revealed that FTY720 treatment induced MM cell apoptosis with mitochondrial involvement, cytochrome C release and caspase 3 activation.Interestingly, suppressive potential of FTY720 negatively correlated with CXCR4 expression on MM cells. Enforced expression of CXCR4 reduced the sensitivity to FTY720, whereas silencing of endogenous CXCL12 increased the sensitivity of MM cells to FTY720-mediated cell death. These results suggested the CXCR4 axis to be directly regulated by S1P pathway. In support, we have found that FTY720 treatment significantly reduced CXCR4-dependent MM cell adhesion to fibronectin and abrogated MM migration toward CXCL12. Activation of signaling pathways, such as MAPK and Akt, in response to CXCL12 stimulation was also fully blocked by FTY720 pre-treatment. In addition to functional suppression, FTY720 directly and profoundly reduced CXCR4 cell-surface levels in a dose-dependent manner. Importantly, none of the suppressive effects of FTY720 (neither apoptosis, nor migration or adhesion inhibition) were dependent on protein phosphatase 2A (PP2A) activation, suggesting alternative mechanism of action.To further investigate down-stream molecular machinery involved in FTY720-mediated CXCR4 targeting in MM cells, the intra-cellular levels of different signaling mediators were evaluated. We identified the mTOR pathway to be regulated by CXCR4 and targeted by FTY720. FTY720 treatment suppressed mTOR signaling in MM cells, as demonstrated by de-phosphorylation of p70S6K and S6. Forced expression of CXCR4 and interaction with BM stromal cells antagonized with FTY720-mediated apoptosis and prevented FTY720-induced S6 de-phosphorylation. While, combination of FTY720 with mTOR inhibitor RAD001 resulted in significantly increased cell death, effectively abrogating CXCR4- and stroma-dependent resistance to FTY720 and suppressing mTOR signaling in MM cells.Finally, in a recently developed novel xenograft model of CXCR4-dependent systemic MM with BM involvement, in vivo FTY720 effectively reduced tumor burden in two third of the treated mice, decreasing both the levels of M protein in blood and the number of MM cells in BM.Conclusions: Taken together, our findings demonstrate cross talk between S1P and CXCR4/CXCL12 signaling pathways that may be of importance for MM cell survival and localization of the MM cells in CXCL12-expressing protective niches in the BM. Moreover, this is, to our knowledge, the first evidence that CXCR4 can be directly targeted with FTY720 modulator, thus restricting the tumor-promoting activities of S1P and CXCR4/CXCL12 axes. In addition, mTOR pathway was recognized as down-stream molecular partner being involved in FTY720-mediated anti-myeloma activities. Combining FTY720 with mTOR inhibitors may thus serve as promising novel therapeutic strategy in MM. DisclosuresPeled:BioLineRx: Research Funding.

Evaluation of Immune Profile in Patients with Multiple Myeloma Using Cytof Technology

Introduction: CyTOF (time-of-flight mass cytometry) is a novel high-dimensional technology which permits immunophenotyping and analysis of signaling in single cells. This approach enables simultaneous evaluation of up to 40 parameters using antibodies tagged with distinct elemental isotopes, by combining flow cytometry with atomic mass spectrometry. Since multiple myeloma (MM) is characterized by immune dysfunction, we used CyTOF technology to define the complex immune profile in MM patient bone marrow (BM) samples.Methods: We used 40 different markers to define various B, T, natural killer (NK) subsets, as well as cells of monocytic, granulocytic, erythroid and platelet lineages. Our preliminary data are results from 10 patients with MGUS/ smoldering MM (SMM); 10 newly diagnosed MM; 20 relapsed/refractory MM; and 15 WM patients (5 newly diagnosed and 10 receiving treatment) in comparison with age-matched healthy donors’ BM (HD). A significantly larger cohort of MM (N=150) and WM (N=50) patients is being similarly analyzed and will be presented. To evaluate phenotypic abnormalities in various B cell subsets, we used B lineage markers CD10, CD19, CD20, CD22, CD27, CD34, CD38, CD45, IgA, IgD, IgG and IgM to define B cells maturation stages from hematopoietic stem cells (HSC) to naïve to mature B lymphocytes (pro-B; pre-B-I; pre-B-II; immature B; and mature (naïve) B cells), as well as memory non-switched and memory switched B cells, plasmablasts, normal (CD138+CD38+CD19+CD45+) and clonal plasma cells (CD138+CD38+CD19-CD45-/low), which reside in the specific BM niche. Furthermore, natural killer (NK) subsets (such as NK and NKT cells) and T cells (such as memory CD4T, naive CD4T, memory CD8T, naive CD8T, T regulatory cells and Tg/d cells) were examined. High-dimensional data was obtained using CyTOF technology and analyzed by SPADE and viSNE software.Results: Our data showed significantly decreased HSC in patients with newly diagnosed and relapsed/refractory MM compared to HD (P<0.025). A significant increase in pre-B-I cells was detected in relapsed/refractory MM vs. MGUS/SMM (P<0.028), but the opposite trend was observed in the pre-B-II subpopulation (P<0.005). No differences in immature B cell populations were observed in different stages of MM. However, a significantly higher percentage of immature B cells was present in relapsed/refractory MM compared to HD (P=0.008), and transitional B cells were significantly decreased in newly diagnosed MM compared to HD (P<0.001). Moreover, memory B cells were significant decreased in all MM stages compared to HD (P<0.003). Non-switched memory B cells were significantly increased in MGUS and SMM compared to newly diagnosed MM, while a significant increase of switched memory B cells was present in newly diagnosed MM compared to relapsed/refractory MM. A significant increase in plasmablasts was seen in relapsed/refractory MM in comparison with other MM stages (P<0.011) by CyTOF analyses. Malignant plasma cells (PC) were defined as CD19-, CD38++, CD45-/dim, CD138+ and either cyk or cyl positive. Importantly, a significant increase in clonal PC was found in all MM stages vs. HD, as well as in newly diagnosed MM compared to relapsed/refractory MM (P<0.01). The percentage of PC from CyTOF analyses correlated with % of PC obtained using flow cytometry by Bland-Altman method comparison. We also observed significant differences in T cell subsets including naïve, central memory, effector, and effector memory CD4+ and CD8+T populations between MGUS and newly diagnosed MM, but no significant changes in T regulatory and Tg/d cells. Furthermore, plasmacytoid dendritic (pDC) cells were significantly increased in newly diagnosed MM, and PD-1 expressed on pDC was significantly decreased in newly diagnosed MM compared to MGUS (P=0.007). Interestingly, PD-1 and its ligand PD-L1 were variably expressed on B cells (2-9% and 3-27%) and PC (0.5-46% and 3-41%) from MM BM samples. Other surface molecules including CD269 (4-32%), CD289 (1-8%), CD362 (0.5-1%) and CD329 (1-4%), were variably expressed in PC.Conclusion: A better understanding of the neoplastic BM milieu will provide the framework for identifying and validating novel targeted therapies directed against MM. CyTOF technology represents a novel diagnostic tool to assess the status not only of MM, but also of host immunity, and may allow for the development of rational personalized therapies. DisclosuresNo relevant conflicts of interest to declare.

Novel Ex Vivo Assay Measures Drug-Induced Depletion of Hematopoietic Progenitors As an Estimate of Hematotoxicity

Background and Objectives: Recently, knowledge of the specific genetic markers responsible for cancer malignancies and their associated signaling pathways have generated many new targets that promise to increase drug efficacy while reducing side effects such as hematotoxicity. Although hematotoxicity is widely assumed to be the result of depleting hematopoietic progenitors, in particular myeloid progenitors, there are no assays to test new compounds in bone marrow samples to investigate this effect. Because these effects are patient-specific, an assay that identifies those patients risk of severe hematotoxicity by certain treatments could help personalizing patient treatment. Here, we show the ability of our flow cytometry-based automated Exvitech© platform to measure depletion analysis of different subsets of CD34+ progenitors and other cell subsets to potentially establish a new assay to screen drug candidates and combinations for hematotoxicity, as well as personalizing therapy to the individual sensitive patient at risk. So that in multiple myeloma (MM) we can identify at the same time CD34+ cells and pathological plasma cells; we could actually measure depletion of both malignant cells and progenitor cells on the same patient sample.Patients and methods: 16 normal bone marrow (NBM) and 4 MM samples were studied. For a proof of concept to test the hypothesis, we have selected two known cytotoxic drugs (cytarabine and clofarabine: N=10NBM) and two novel drugs with low expected cytotoxicity (ruxolotinib and volasertib: N=6NBM). The whole sample was plated into 96-well assay plates containing 8 concentrations of each drug and incubated for 48-hours for NBM and 12h with Bortezomib for MM samples. A multiple staining (CD45v450/Anexin-FITC/CD117-PE/CD34PerCP/CD38APC/CD19APCya7) was used to distinguish between both populations. Drug response was evaluated as a depletion survival index of each cell population relative to the average of 6 control wells in each plate.Results: As expected, nucleoside induces hematotoxicity in most of the studied NBM samples, but not all. Results reflect that cytarabine has similar activity than clofarabine in terms of efficacy (Ymax: 30% vs 23%) but with less potency (EC50: 6µM vs 0.2µM) in the immature population (N=10; Figure 1). This reflects a lower hematological toxicity which is consistent with clinical practice. Interestingly, for both drugs there is a large range of inter-patient variability inside this population in terms of efficacy (cytarabine, range Ymax: 4%-75% and clofarabine, range Ymax: 10%-37%) and potency (cytarabine, range EC50: 1µM-14µM and clofarabine, range EC50: 0.01µM-2µM) suggesting that in a subsets of vulnerable patients, drug doses could be tailored. By contrast, ruxolitinib and volasertib had little effect (Ymax: 80% vs 73%) in the immature population with minimal interpatient variability confirming the low toxicity expected for these novel drugs even at very high concentrations never achieve in vivo (Figure 1).Figure 2 shows bortezomib activity in MM bone marrow samples measuring both the dose response on malignant and myeloid progenitor cells. For Patient 1 the drug depletes myeloid precursor at lower doses than malignant cells, suggestive of severe hematotoxicity before therapeutic benefit can be achieved. Patient 2 shows the opposite case, where bortezomib depletes malignant cells completely without depleting myeloid precursors, suggestive of a good therapeutic index for this individual patient.Conclusions: These preliminary results show that Vivia Exvitech© platform is able to measure hematopoietic progenitors depletion in addition to other cell populations for novel drugs or before patientxs treatment that could contribute to a more selective drug development or a better clinical management of patients. This approach enables screening for hematotoxicty potential new discovery compounds, new drug candidates, and their synergistic combinations, thus supporting drug discovery and development. This assay could be helpful to both hematological and solid tumor drugs. The platform can measure both malignant and progenitor cells in bone marrow samples of MM and Non Hodgkin’s Lymphoma. This simultaneous analysis shown for bortezomib could help guiding the clinical response and possible hematological toxicities associated to drug treatments. [Display omitted] [Display omitted] DisclosuresPrimo:Vivia Biotech: Employment. Ballesteros:Vivia Biotech: Employment. Robles:Vivia Biotech: Employment. Gorrochategui:Vivia Biotech: Employment. Garcia:Vivia Biotech: Employment. Hernandez:Vivia Biotech: Employment. Martinez:Vivia Biotech: Membership on an entity’s Board of Directors or advisory committees.

Cereblon expression in multiple myeloma: not ready for prime time – Response to Lodé et al

We have read with interest the comments provided by Lodé et al (2013) regarding our findings of a correlation of cereblon (CRBN) expression and response in multiple myeloma (MM) patients treated with lenalidomide and dexamethasone (Heintel et al, 2013). We agree that the prime time has not yet arrived for the routine use of CRBN expression as treatment guidance. Lodé et al (2013) raise three important issues that should be evaluated before drawing final conclusions and we wish to add the following: In relation to the first point raised, we suggest that CRBN should be analysed in both the CD138+ and CD138− fraction of MM bone marrow samples in future studies. It is well recognized that at least some of the effect of immunomodulatory drugs (IMiDs) is mediated through the microenvironment by induction of proliferation of T-cells and other effector cells, of expression of co-stimulatory molecules and modification of cytokine signalling (Görgün et al, 2010), resulting in an anti-myeloma immune response. Lopez-Girona et al (2012) showed that CRBN not only mediates the anti-proliferative effects of lenalidomide and pomalidomide in myeloma cells, but also lenalidomide- and pomalidomide -induced cytokine production in T-cells. In our paper we provided data showing that, although median CRBN expression is lower in the CD138− than CD138+ fraction, expression levels of CRBN vary in the MM bone marrow environment and can be considerably higher than in normal bone marrow (Heintel et al, 2013). Thus we speculate that variable levels of CRBN in immune cells in the bone marrow might have contributed to the association with response in our study. We fully agree with the second point raised, that CRBN physiology needs to be studied in detail and the function of the different isoforms elucidated. Lenalidomide treatment was shown to induce 2-fold expression changes in approximately 1200 genes, and the vast majority of these changes seem to be mediated via CRBN (Zhu et al, 2011). Lodé et al (2013) provide important data showing the frequent occurrence of alternative transcripts, accounting in some patients for >50% of total CRBN in some patients. It has been reported that CRBN downregulation mediates resistance to IMiD-based treatment (Zhu et al, 2011; Heintel et al, 2013). As preferential expression of transcripts lacking a functional IMiD binding domain would be anticipated to have a similar effect, we propose studying the expression of alternative transcripts of CRBN with regard to primary resistance and acquisition of resistance to IMiD based treatment. Gandhi et al (2012) reported on an antibody (CRBN65) capable of discriminating the different isoforms by Western blot, and such a tool should be helpful in these studies. In contrast, truncating mutations in CRBN seem to be a rare mechanism of acquisition of resistance (Egan et al, 2013). Once the correlation between CRBN expression and clinical response can be corroborated, antibodies binding to CRBN or its isoforms might provide the basis for developing a reliable routine test for CRBN expression. Developing a flow cytometric technique for detection might provide further insight into intra-tumour heterogeneity of CRBN expression. It should be noted that three other groups have already reported a correlation between CRBN expression and outcome under IMiD therapy, one using tissue microarrays and fluorescence immunohistochemistry to quantify CRBN expression (Klimowicz et al, 2012), the two other groups using gene expression profiling (Broyl et al, 2013; Schuster et al, 2012). The in-silico analysis performed by Lodé et al (2013) provides important insights with regard to CRBN expression in the different molecular MM subgroups. While median CRBN expression is higher in the hyperdiploid subgroup, there seems to be great variability of expression within all subgroups. In our preliminary analysis we could not find a correlation between CRBN expression and fluorescent in situ hybridization-defined high-risk or standard risk disease. We did not study chromosome 3 trisomy in our series of patients but agree that cytogenetic data should be evaluated in relation to CRBN expression. We think that the outcome defined by response is less biased by a possible overweight of hyperdiploid disease, as the main impact of the molecular signature is on survival parameters, not initial response to therapy. A very rapid and deep response to therapy, with regard to serum free-light chain levels, might even identify a subgroup of patients with inferior survival. It should be noted that the groups who have reported a correlation between CRBN expression and outcome with IMiD-based treatment defined by survival have included a bortezomib-treated control group, where this association was lacking (Broyl et al, 2013; Klimowicz et al, 2012), thus making a bias related to a possible prognostic significance of CRBN expression itself less likely.

Detection of Multiple Myeloma Cells in Peripheral Blood Using High-Throughput Sequencing Assay

AbstractAbstract 321 Background:Multiple myeloma (MM) is characterized by the presence of monoclonal protein (M-protein) in serum and/or urine, clonal plasma cell accumulation in bone marrow (BM), and related organ or tissue impairment. MM patients are monitored during therapy and posttherapy using immunoglobulin, M-protein and free light chain assays. Assessing pathological myeloma cells using flow cytometry and RT-PCR has been shown to have superior prognostic value. However, the sensitivity of these techniques has generally limited their use to assessment of BM. In order to determine whether myeloma minimal residual disease could be detected in peripheral blood (PB), we assessed a cohort of MM patients using a sequencing based platform, LymphoSIGHT, with a sensitivity of 1 cancer cell per million leukocytes. Methods:We obtained from 4 sources (UCSF, NYU, Washington Univ, commercial source) pairs of BM and PB samples from 60 MM patients at different points of disease. BM samples were used to identify the clonal MM sequence and detection of that sequence in the PB was assessed. For some patients BM/PB sample pairs were obtained from >1 time point resulting in a total of 78 pairs. In addition blood and bone marrow plasma samples were available for 44 and 6 patients, respectively, to assess presence of the myeloma clonotype in cell free DNA. Altogether there were 206 samples. BM samples were either available as BM mononuclear cells (BMMC) or bead enriched CD138+ cells. Using universal primer sets, we amplified IgH@ variable (V), diversity (D), and joining (J) gene segments from genomic DNA and/or RNA samples, the incomplete IgH rearrangement (DJ), and IgK from genomic DNA. Amplified products were sequenced to obtain >1 million reads and analyzed using standardized algorithms for clonotype determination. Myeloma-specific IgH, IgK, and DJ clonotypes were identified for each patient based on their high frequency in BM samples. The presence of the myeloma clonotype was then assessed in all PBMC (DNA and RNA), BM plasma (DNA), and PB plasma (DNA) samples using the same IgH and in some samples using the IgK sequencing assays. A quantitative and standardized measure of clone level among all leukocytes in each PB or BM sample was determined using internal reference DNA. Here we describe data on 46/60 patients; data from all 60 patients will be presented. Results:In BM samples, we detected the myeloma clonal rearrangement of at least one receptor (“calibrating receptor”) in 34/46 (74%) of MM patients (Table 1). The calibration rate varied by receptor, with 30/46 (65%) patients calibrating with IgH, 14/43 (33%) with IgH DJ, and 22/43 (51%) with IgK (Table 1). Identification of myeloma-specific clonal rearrangement is based on presence at high frequency and may not occur in samples from patients with low disease load (e.g., post-treatment). Of the 12 non-calibrating patients, only 3 had high disease load. The myeloma clonotype that was identified in the BM was also detected in PBMC in 22/30 (73%) and 28/30 (93%) patients with the DNA and RNA IgH analysis, respectively (Table 2). IgK DNA analysis showed the presence of the myeloma clonotype in 9/10 PBMC samples, all of which were concordant with IgH results. The myeloma clonotype that was identified in the BM was also detected in the cell-free BM and PB samples in 5/5 and 7/11 patients, respectively, using the IgH DNA assay. The evaluation of blood plasma and PBMC were at times complementary in detecting the myeloma. Conclusions:Results from the application of a high-throughput sequencing method for detection of myeloma-specific clonotypes in 46 MM patients are shown. A clonal rearrangement was detected in 74% of MM BM samples. Importantly, 93% of peripheral blood samples from 30 patients showed evidence of circulating myeloma in PBMC. Analysis of BM and PB samples from 14 additional MM patients as well as association of the level of myeloma in PBMC and BM with clinical measures is ongoing.Table 1Calibration rates for IgH and IgK receptors in MM patients.Sample sourceIgH (complete)IgKIgH (incomplete)Any receptorUCSF8/126/123/129/12NYU15/2113/2110/2117/21Commercial source7/133/101/108/13Total30/4622/4314/4334/46Table 2Detection of circulating myeloma material in MM patients.Sample sourceIgH clone present in blood DNAIgH clone present in blood RNAIgK clone present in blood DNAUCSF4/87/82/3NYU13/1515/157/7Commercial source5/76/7N/ATotal22/3028/309/10 Disclosures:Faham:Sequenta, Inc.: Employment, Equity Ownership, Research Funding. Klinger:Sequenta, Inc.: Employment, Equity Ownership, Research Funding.

TRAF6 Dominant Negative Peptides Block Intracellular Signaling Resulting in Anti-Myeloma and Anti-Bone Resorptive Effects in Multiple Myeloma

Abstract 2919Tumor necrosis factor receptor-associated factor 6 (TRAF6) has been implicated in regulating the NF-kB and JNK signal transduction pathways; and, thus, is likely to promote tumor cell proliferation and osteoclast formation. We have previously reported inhibition of cell proliferation and increase of apoptosis in multiple myeloma (MM) cells through regulation of these intracellular pathways through silencing of TRAF6 C-domain mRNA. To determine TRAF6 protein expression in fresh MM tumor cells, we performed an immunofluorescence assay (IFA). The results showed that expression of this factor in tumor cells from bone marrow (BM) from MM patients with progressive disease is higher than in cells from patients with monoclonal gammopathies without disease progression or normal controls. We further examined the effects of TRAF6 negative dominant peptides on intracellular signaling pathways. Briefly, cells from the RPMI8226 or MM1s MM cell lines or primary MM BM samples were treated with or without TRAF6 inhibition peptide for 24 hours and then stimulated with either IGF1 (30ng/ml) or IL1 β (20ng/ml) for 30 minutes. The cells were lysed and Western blot analysis performed to determine protein phosphorylation and RT-PCR for gene expression. TRAF6 has been found to be an E3 ligase for Akt ubiquitination. We found that IGF1 increased the phosphorylation of AKT and treatment with TRAF6 inhibition peptide markedly decreased its phosphorylation compared to treatment with a control peptide in RPMI8226 and primary MM tumor cells. Downstream of AKT, C-Raf phosphorylation was also significantly reduced with treatment with TRAF6 inhibition peptide. Notably, cyclin D gene expression in MM tumor cells treated with TRAF6 inhibition peptide was reduced as determined with an RT-PCR. In contrast, the gene expression of mTOR was increased in RPMI8226 cells treated with TRAF6 inhibition peptide whereas there was no change in its expression in MM1s and primary MM tumor cells. It is quite possible that the increase in mTOR expression in RPMI8226 cells may act as a negative feedback which results from blockage of the ubiquitination of TRAF6. We further examined the effect of the TRAF6 inhibition peptide on NF-kB and JNK signaling as determined through evaluation of JUN kinase kinase (JNKK), which activates the MAP kinase homologues SAPK and JNK in response to IL-1 receptor stimulation. Phospho-NF-kB protein was reduced and phosphorylation of JNKK was clearly decreased with exposure to the TRAF6 inhibition peptide. We examined c-Jun, a component of the transcription factor complex AP-1, which binds and activates transcription at TRE/AP-1 elements. Total endogenous c-Jun is reduced following exposure of RPMI8226 cells to the TRAF6 inhibition peptide. Consistent with our past findings, TRAF6 inhibition peptide significantly inhibited osteoclast formation from CD14+ induced by RANKL and M-CSF with in a concentration dependent fashion whereas control peptides showed no effects on osteoclast formation. In addition, inhibition of the TRAF6 signaling blocked not only myeloma cell proliferation induced by AKT and NF-kB activation but also osteoclast cell formation mediated through transcription at TRE/AP-1 elements. The study has been extended to our SCID-hu murine model of human myeloma. Disclosures:No relevant conflicts of interest to declare.

Overexpression of CTLA-4 in the Bone Marrow of Patients with Multiple Myeloma As a Sign of Local Accumulation of Immunosuppressive Tregs – Perspectives for Novel Treatment Strategies

Abstract 1829 Introduction:Multiple myeloma (MM) development involves a series of genetic alterations and changes in the bone marrow (BM) microenvironment, favoring the growth of the tumor and failure of local immune control. T regulatory (Treg) cells play an important role in the maintenance of self-tolerance and modulation of overall immune responses against infections and tumor cells. T-helper-17 (Th17) cells, on the other hand, have a critical function in eradicating extracellular pathogens and tumor cells. The balance between Treg and Th17 cells may be essential for maintaining homeostasis of anti-tumor immunity. The aim of our study was to characterize the expression of Treg- (FOXP3 and CTLA-4) and Th17-related (RORγt) genes in total MM bone marrow samples to assess the local immune milieu as a potential therapeutic target in this still incurable disease. Material and Methods: Expression of FOXP3, CTLA-4 and RORγt was determined by quantitative real-time PCR (qPCR) in BM aspirates of 55 MM patients, 4 patients with monoclonal gammopathy of undetermined significance (MGUS), and 5 healthy BM donors. Genes were considered overexpressed when their expression was at least two times higher in myeloma BM than in normal samples. Results:RORγt showed a non-significant overexpression in MM patients compared to controls. FOXP3, on the other hand, showed a 3.6-fold higher expression in MM patients compared to controls but the difference was not significant and was overexpressed in 63% of MM cases. CTLA-4 expression was 14.6-fold higher in MM patients compared to controls (p=0.03, Mann-Whitney test) and was overexpressed in 70% of MM cases. Importantly the CTLA-4/RORyt ratio was significantly higher in MM samples compared to controls (p = 0.009) while this difference was not significant when controls were compared to MGUS patients, suggesting that the immunological imbalance worsens with the progression of disease. Conclusions: CTLA-4 (cytotoxic T-lymphocyte antigen-4), an intracellular and membrane inhibitory protein expressed on Treg cells, modulates T-cell activation and is critical in maintaining immune tolerance to self-antigens. Monoclonal antibodies targeting CTLA-4 have improved the survival of patients with metastatic melanoma in clinical trials. The myeloma-related overexperssion of CTLA-4 and the increased CTLA-4/RORyt ratio suggest an accumulation of immunosuppressive Tregs in the tumor microenvironment and/or an immediate involvement of this gene in the development and progression of myeloma. If protein expression confirms gene expression imbalance between Treg and Th17 subpopulations, therapeutic approaches that specifically target CTLA-4-expressing Treg myeloma cases may provide a new treatment strategy for this disease. (Supported by CNPq, Brazil). Disclosures:No relevant conflicts of interest to declare.

Multiple Myeloma (MM) Highly Expresses CGEN-928 and the Anti-CGEN-928 TM21 Antibody Markedly Inhibits the Growth of MM Cells and Enhances the Anti-Myeloma Effects of Dexamethasone, Melphalan and Bortezomib

AbstractAbstract 4067Although patients with multiple myeloma (MM) initially respond to current treatment modalities, it remains an incurable disease. Many new therapeutic options have become available during the past several years but nearly all patients develop resistance to currently available therapeutic options. In addition, there is no tumor marker that is uniformly expressed in all MM cells although CD138 is considered to be present on the surface of tumor cells in most cases of MM but generally is only present in a subset of the patients' tumor population and may be absent in the most resistant part of the tumor clone. In order to address these unmet clinical needs, we queried Compugen's MED Platform, an expression database which covers over 40,000 microarray experiments, for genes overexpressed in B cell-derived malignancies including MM and that exhibit low expression levels in normal cells and tissues. One of the most prominent candidates was CGEN-928, which was validated as over-expressed in MM at the mRNA level using an independent panel of both hematological malignancies and normal tissues. In this study, we first investigated whether the previously unidentified membrane antigen CGEN-928 is expressed in cells from human MM cell lines, human MM xenografts and fresh bone marrow (BM) aspirates derived from MM patients using flow cytometric analysis and immunohistochemical staining with the anti-CGEN-928 TM21 polyclonal antibody (Compugen Ltd, Tel Aviv, Israel). Using this antibody, we found that CGEN-928 was highly expressed in cells from the MM1s, U266 and RPMI8226 MM cell lines. Next, we examined CGEN-928 antigen expression in fresh tumor cells from BM aspirates from 17 MM patients and also showed high expression of CGEN-928. Notably, expression of this antigen was not only found on CD138+ MM cells but also on MM tumor cells lacking CD138 expression. We also examined the expression of CGEN-928 using our human MM xenograft models LAGκ-1A (bortezomib-sensitive), LAGκ-1B (bortezomib-resistant) and LAGλ-1 (melphalan-resistant). The bortezomib-sensitive MM tumor LAGκ-1A expresses CD138 whereas the bortezomib-resistant version LAGκ-1B developed from the same patient after the patient developed bortezomib reisistance does not express CD138. Cells from all three tumor types showed high levels of reactivity with the TM21 antibody. Similar to the fresh MM BM samples, CGEN-928 expression was not only found on CD138+ MM cells but also on CD138- tumor cells derived from these human MM xenografts. Because this molecule is highly expressed on MM cells, we hypothesized that the anti-CGEN-928 antibody may show anti-MM effects and enhance the anti-MM effects of other anti-MM drugs. To evaluate this, we examined the effect of the TM21 antibody alone and in combination with dexamethasone, melphalan and bortezomib in vitro using cell proliferation MTT assays. Anti-TM21 polyclonal antibody (100 mg/ml) decreased MM tumor cell proliferation and increased apoptosis in cells from the MM1s, RPMI8226 and U266 cell lines. Next, we determined the effects of combining the anti-CGEN-928 antibody with bortezomib, melphalan or dexamethasone on MM1s cells. Cell proliferation assays demonstrated marked enhanced anti-proliferative effects when CGEN-928 antibody at concentrations of 5, 10, 50 and 100 mg/ml was combined with bortezomib, melphalan or dexamethasone. Further investigations are defining the mechanisms and signal transduction pathways that produce the anti-MM effects of CGEN-928. These preliminary studies suggest that the CGEN-928 antigen is highly expressed in MM and treatment with an anti-CGEN-928 polyclonal antibody produces anti-MM effects alone and in combination with other anti-MM agents; and thus, this antigen may be a target for the treatment of multiple myeloma. Currently, a monoclonal anti-CGEN-928 antibody is in development that will be used by our group to evaluate its anti-MM effects both in vitro and in vivo using our SCID-hu models of human MM. Disclosures:Levy:Compugen Ltd.: Employment. Dassa:Compugen Ltd.: Employment. Cojocaru:Compugen Ltd.: Employment. Berenson:Compugen Ltd.: Research Funding. Levine:Compugen Ltd.: Employment.