Multiple Myeloma Bone Marrow Niche Research Articles

Preliminary Results of the Oral CD73 Inhibitor, Oric-533, in Relapsed/Refractory Multiple Myeloma (RRMM)

Background: Although recently available immune-based approaches in multiple myeloma produce high response rates, curative outcomes have not yet been achieved, which highlights the need for new agents that further activate the immune system without increasing toxicity. ORIC-533 is a highly potent and selective, orally bioavailable, small molecule inhibitor of CD73, an enzyme expressed by various cell types, including immune cells and which catalyzes the generation of adenosine from adenosine monophosphate (AMP) (Allard 2019). Adenosine itself is highly immunosuppressive, diminishing activity of a range of immune cell types, including T, NK, and dendritic cells (Young 2014). By blocking adenosine production from AMP via inhibition of CD73, ORIC-533 has demonstrated the ability to restore and enhance immune function. Multiple myeloma (MM) patient bone marrow (BM) contains multiple cell types that also express CD73, including immune cells, cancer-associated fibroblasts, mesenchymal stem cells, and endothelial cells (Allard 2019). Moreover, elevated adenosine levels in the MM BM niche correlate with disease progression (Horenstein 2016; Yang 2020). We have previously observed that CD73-mediated adenosine activity suppresses the cytolytic antitumor immune function in the MM BM milieu (Ray 2022). ORIC-533 treatment reduced adenosine production, overcame this immune suppression with evidence of restored DC-mediated priming and activated cytotoxic CD8 + T-cell function, and significantly enhanced immune cell cytolytic behavior against RRMM tumor cells in autologous patient ex vivo experiments (Junttila 2022), making ORIC-533 a potential immunotherapy for patients with MM. Methods: ORIC-533-01 (NCT05227144) is an ongoing i3+3 Phase 1b dose escalation study in patients with RRMM. The primary objectives are to determine single agent safety/tolerability and pharmacokinetics (PK) of ORIC-533 to select the RP2D. Pharmacodynamic assessments include measurement of CD73 functional activity in serum and BM, as well as enumeration of immune cell subsets and activation state in blood and BM. Patients are also evaluated for clinical efficacy using IMWG criteria. Results: As of 23 June 2023, 17 patients received ORIC-533 once daily across 4 dose levels (400 mg to 1600 mg). All patients were triple-class refractory, 88% were penta-refractory, and 59% also received prior anti-BCMA/CD3 bispecific therapy or anti-BCMA CAR-T therapy. Overall, ORIC-533 was very well tolerated, with 5 patients experiencing a total of 10 treatment-related adverse events (TRAEs). Fatigue was the only G3 AE and the only TRAE seen in more than 1 patient (1 event each of G3 and G2); all other events seen in 1 patient each, were G1 or G2 in severity, and of no specific system organ class. No dose limiting toxicities, no Grade ≥4 TRAEs, and no treatment-related serious adverse events have been observed. PK showed increased exposure with dose with a plasma half-life of ~24 hrs. Soluble CD73 enzymatic activity was nearly completely inhibited by C1D15 in serum of all patients across all dose levels, while the largest relative suppression in surface CD73 activity in BM cells was observed at the highest dose level. There was also evidence for increases in the abundance of circulating NK and CD8+ T cells after 1 treatment cycle, with preliminary evidence of enhanced CD8+ T-cell activation at the highest dose levels tested in both peripheral blood and BM. In addition, early evidence of single agent clinical activity was observed. Conclusions: ORIC-533 has demonstrated an acceptable safety profile and preliminary evidence of immune activation in a heavily pretreated RRMM patient population. Enrollment is ongoing and updated data will be presented.

CXCL10 Recruitment of γδ T Cells into the Hypoxic Bone Marrow Environment Leads to IL17 Expression and Multiple Myeloma Progression.

In multiple myeloma (MM), bone marrow stromal cells (BMSC) shape a unique niche within the bone marrow, promoting T-cell dysfunction and driving MM progression; however, the precise underlying mechanisms remain elusive. Here, we show that BMSC-mediated reprogramming of MM cells led to heightened production of CXCL10. CXCL10 orchestrated the recruitment of γδ T cells into the bone marrow, and this was observed in both the Vk*MYC and 5TGM1 mouse models of MM, as well as in patients experiencing refractory or relapsed MM. Furthermore, the dysfunctional γδ T cells in the MM bone marrow niche exhibited increased PD-1 expression and IL17 production. In the Vk*MYC mouse model, MM-associated bone lesions and mortality were markedly alleviated in Tcrd-/- mice, and MM disease progression could be rescued in these mice upon transplantation of γδ T cells expanded from wild-type mice, but not from Il17-/- mice. Mechanistically, the hypoxic microenvironment prevailing in the MM bone marrow niche stimulated the expression of steroid receptor coactivator 3 (SRC-3) in γδ T cells, which in turn interacted with the transcriptional factor RORγt, promoting Il17 transcription. Pharmacologic inhibition of SRC-3 utilizing SI-2 effectively suppressed Il17A expression in γδ T cells, leading to alleviation of MM progression in the murine models and enhancing the anti-multiple myeloma efficacy of bortezomib. Our results illuminated the bone marrow microenvironment's involvement in provoking γδ T-cell dysfunction throughout MM progression and suggest SRC-3 inhibition as a promising strategy to enhance the effectiveness of immunotherapies targeting γδ T cells.

Armored BCMA CAR T Cells Eliminate Multiple Myeloma and Are Resistant to the Suppressive Effects of TGF-β.

CAR T-cell therapies targeting the B-cell maturation antigen eliminate tumors in relapsed/refractory multiple myeloma patients, however durable remissions remain difficult to attain. Transforming growth factor beta (TGF-β) is a multifunctional cytokine abundantly expressed in the multiple myeloma bone marrow niche, where it promotes an immunosuppressive tumor microenvironment. We hypothesized that BCMA CAR T-cells armored to resist the suppressive effects of TGF-β will provide an advantage in treating multiple myeloma. The armored B2ARM CAR T cells, co-expressing BCMA targeting CAR with TGF-β dominant-negative receptor II, were generated by lentiviral transduction of primary human CD4+ and CD8+ T cells. The B2ARM CAR T cells eliminated MM.1S multiple myeloma targets in long-term cytotoxicity assays, even under TGF-β-high conditions, whereas cytotoxic function of the non-armored B2 CAR -T cells was inhibited by TGF-β. Concordantly, after long-term exposure to targets in the presence of TGF-β, the B2ARM CAR T cells were enriched for Granzyme B, CD107a, Ki67 and polyfunctional cells T-cells (double or triple-positive for IFN-γ, IL-2 and/or TNF-α), as determined by flow cytometry. In addition, the B2ARM CAR T-cells, but not the conventional B2 CAR T-cells, resisted the TGF-β-mediated suppression of activation (CD25), exhaustion (PD-1, LAG3), and differentiation to T effectors (CD45RA+ CD45RO-CD62L-). In NSG mice bearing RPMI-8226 tumors overexpressing TGF-β, the B2ARM CAR mediated 100% tumor rejection and survival, superior infiltration of tumors on day 7 post CAR T treatment (%CD3+CAR+), and greater expression of IFN-γ, TNF-α, Ki67, Granzyme B, and PD-1, as compared to tumor-infiltrating non-armored B2 CAR T-cells. In NSG RPMI-8226 xenograft model in which tumors were additionally supplemented with TGF-β injections on days -1 through 11 of CAR T treatment, the B2ARM CAR T cells rejected tumors faster than the non-armored B2 CARs, and showed greater numbers of CD3+ and CD3+CAR+, central memory (CD45RO+CD62L+) and effector memory (CD45RO+CD62L-) T cells in the peripheral blood 18 days after treatment. In summary, the armored B2ARM CAR T cells mediate superior persistence, proliferation, multi-functionality, effector differentiation and anti-tumor function in pre-clinical models of multiple myeloma, while abrogating TGF-β-mediated suppression.

CD73 Inhibition Overcomes Immunosuppression and Triggers Autologous T-Cell Mediated Multiple Myeloma Cell Lysis in the Bone Marrow Milieu

CD73 Inhibition Overcomes Immunosuppression and Triggers Autologous T-Cell Mediated Multiple Myeloma Cell Lysis in the Bone Marrow Milieu

Large-Scale Mass Cytometry Reveals Significant Activation of Innate and Adaptive Immunity in Bone Marrow Tumor Microenvironment of Iberdomide-Treated Myeloma Patients

Background: Iberdomide (IBER) is a potent cereblon E3 ligase modulator (CELMoD agent) with direct anti-tumor and immunomodulatory activities in multiple myeloma (MM). An ongoing phase 1b/2a multicenter, open-label, dose-escalation study has reported favorable efficacy and safety of IBER plus low-dose dexamethasone (DEX) in heavily pretreated patients with relapsed/refractory MM (RRMM). While previous studies focused on IMiD/CELMoD agent immune effects in peripheral blood (Amatangelo, ASH 2019), a large-scale characterization of pharmacodynamics in the bone marrow (BM) tumor microenvironment (TME) has not been reported. Here, we present data on BM aspirates (BMAs) of 99 individuals pre-/post-treatment with IBER in the largest study of TME immune dynamics of RRMM patients to date.Methods: A mass cytometry (CyTOF) panel was designed/validated to capture deep and comprehensive immunophenotyping of T, B, and NK cell subpopulations. In all, staining with 37 metal-tagged Abs characterized 110 supervised cell phenotypes. Paired longitudinal assessment was conducted for viably preserved BMAs of IBER±DEX treated patients in dose-escalation of the CC220-MM-001 Ph 1b/2a study pre (SCREEN) and post treatment (cycle 2 day 15, C2D15). For a subset of patients (n=12), samples were available at disease progression (PD) . A training set analysis (n=64, data reported here) collected in North America, was validated against an independent test set (n=35) recruited in Europe. An R-based computational workflow and manual hierarchical gating identified subpopulations of B, T, NK and myeloid cells. In total, more than 5M immune cells were captured (approx. 40K per specimen). Cell populations are expressed as percentage of non-tumor bone marrow mononuclear cells (BMMC, i.e. CD45+CD66b-). P values are by Mann-Whitney U test for unpaired and Wilcoxon test for paired analyses.Results: IBER treatment resulted in profound immune shifts in the TME. B cells decreased (median SCREEN 3.3% vs C2D15 0.7%, p=0.001), with significant reduction of naïve (p=0.001) and regulatory B cells (p<0.001). Decrease occurred in CD4+ T cells (median 15.3% vs 8.9%, p<0.001), whereas CD8+ T cells increased (median 14.9% vs 17.4%). T cell subtypes showed a shift towards cytotoxic effector-memory phenotype (CCR7-CD45RA) (median 67.6% vs 80.9% of CD4+ T cells, p<0.001 and median 78.2% vs 89.2% of CD8+ T cells, p<0.001) with concurrent reduction of naive (CD45RA+CCR7+), central-memory (CD45RA-CCR7+) and EMRA (CD45RA+CCR7-) T cells. The shift towards a cytotoxic TME is confirmed by significant increases of GZMB+, HLA-DR+, ICOS+, Ki-67+, CXCR3+ and CD38+ activated CD8+ T cells (p≤0.001, paired). Conversely, CD8+ T cells expressing inhibitory checkpoints TIGIT and KLRG1 decreased significantly (p≤0.001, paired). Similar changes (with minor deviations) were noted in the CD4+ T cell compartment.NK cells increased (median 4.2% vs 8.7%, p=0.003), with increase of both CD56hi cytokine-producing (median 1.9% vs 4.5%, p<0.001) and CD16+ cytolytic (median 1.8% vs 2.6%, p=0.06) subsets. NKG2A+ and NKG2D+ subsets were increased (p<0.001, paired), as well as subsets expressing markers of activation: GZMB, ICOS, CD38 and PD-1 (p<0.05, paired). TIGIT+ NK cells decreased significantly. NKT cells were also significantly increased (median 1.4% vs 2.2%, p<0.001). Increase of NK and NKT cells expressing the activating receptor NKG2D was limited to patients achieving best response of PR or better. Additional analyses correlating immune phenotypes at baseline/post-treatment with outcomes are ongoing and will be reported at the meeting, as will data on how prior treatment (e.g. with CD38-mAb) shapes the TME at baseline and affects response.Conclusion: Our analysis on a large cohort of RRMM patients provides unique insights into the heterogeneity of the immune TME of heavily pretreated MM patients and how it changes upon treatment with IBER±DEX. We found significant increases of effector T and NK cells in paired analysis, demonstrating innate and adaptive immune enhancement in the MM bone marrow niche as an important mechanism of action. Importantly, these changes were observed throughout dose escalation and in patients previously refractory to lenalidomide/pomalidomide. The presented platform of large-scale immune profiling demonstrates a strategy to design and study rational combinations with (other) immune-enhancing therapies in MM. [Display omitted] DisclosuresAmatangelo: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Gooding: Bristol Myers Squibb: Research Funding. Jagannath: Legend Biotech: Consultancy; Bristol Myers Squibb: Consultancy; Karyopharm Therapeutics: Consultancy; Janssen Pharmaceuticals: Consultancy; Takeda: Consultancy; Sanofi: Consultancy. Pierceall: BMS: Current Employment, Current equity holder in publicly-traded company. Parekh: Foundation Medicine Inc: Consultancy; Amgen: Research Funding; PFIZER: Research Funding; CELGENE: Research Funding; Karyopharm Inv: Research Funding. Thakurta: Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company.

Myeloma cells self-promote migration by regulating TAB1-driven TIMP-1 expression in mesenchymal stem cells

Multiple myeloma (MM) is an intractable hematological malignancy characterized by abnormal plasma cells in the bone marrow (BM) and increased osteolytic lesions. Within the BM niche, mesenchymal stem cells (MSCs) have been proposed to contribute to functionally important MM-MSC interactions. However, despite various studies on MM pathology, the impact of MM on MSCs during the early stages of malignancy has not been adequately addressed. We previously identified tissue inhibitor of matrix metalloproteinase 1 (TIMP-1) as a cytokine that is modulated in vivo within the MM BM niche, and highlighted its potential relevance in MM. Given the role of TIMP-1 in preventing migration of breast cancer cells, this study aimed to investigate the relationship between MSC-secreted TIMP-1 and MM progression. Here, we examined the effect of MSC-derived TIMP-1 on MM cell migration, and found that TIMP-1 secreted by human MSCs play a role in preventing migration of MM cells by reducing the levels of MM cell-derived MMP-9. We also investigated how MM cells regulate expression of TIMP-1 in MSCs. Using a knockdown approach in MSCs, we implicated TGF-B activated kinase 1 binding protein 1 (TAB1) as an upstream effector of TIMP-1 that was downregulated in the presence of MM cells, which resulted in reduced TIMP-1 secretion. Overall, our findings uncover how MSCs in the MM BM niche are modulated to promote MM progression, and unravel a previously unreported role of the TAB1-TIMP-1 axis in the context of the MM BM niche.

Single Cell Transcriptomic Analysis of the Multiple Myeloma Bone Marrow Identifies a Unique Inflammatory Stromal Cell Population Associated with TNF Signaling

Background: In multiple myeloma, tumor cell survival, disease progression and therapy response are influenced by signals derived from the non-malignant bone marrow niche. This notwithstanding, a detailed in-vivo definition of the cells that define the multiple myeloma niche is lacking. Mesenchymal stromal cells are important niche constituents. Recent progress made with single cell transciptomics suggests that mesenchymal stromal cells are a dynamic population of cells that can exist as several subsets with functionally distinct activation and differentiation profiles. Aim: To identify mesenchymal stromal cell subsets specific for the multiple myeloma bone marrow niche, by comparing stromal cells from myeloma patients to non-cancer controls. Methods: The non-hematopoietic bone marrow niche was isolated from viably frozen bone marrow aspirates from 10 newly diagnosed multiple myeloma patients (6 hyperdiploid, 3 t(11;14) and 1 with deletion of 17p) and 2 non-cancer controls using high speed cell sorting. The purified cells were analyzed by 10X Genomics single cell sequencing directly post-thawing, without prior cell culture. From 10 multiple myeloma patients we generated single cell transcriptomes with an average read-depth of 20,000 reads per cell of in total 12,000 niche cells and from the 2 non-cancer controls a total of 3,500 niche cells. Transcriptomes were pooled and subjected to clustering analyses using the Seurat package for R to identify genetically distinct clusters of niche cells and changes in these clusters associated specifically with multiple myeloma. Results: The bioinformatical analyses generated 10 distinct clusters of niche cells, all of which were present in both non-cancer and multiple myeloma bone marrow. One of these clusters contained CDH5+ endothelial cells while the remaining 9 clusters were subsets of CXCL12+LEPR+ mesenchymal stromal cells. Because samples were taken from the central marrow by aspiration, peripheral endosteal or neuronal lineage cells were not represented in these clusters. Gene Set Enrichment Analysis (GSEA) of the stromal cell clusters from myeloma versus non-cancer controls revealed two significantly altered pathways: TNF signaling via NF-kB and Inflammatory response. Detailed analyses of the individual stromal cell clusters identified two clusters that were responsible for the inflammatory changes identified by GSEA. Both clusters were present in all myeloma patients, constituted on average 20% of total stromal cells and were defined by transcription of the inflammatory chemokines CXCL2, CXCL3 and CXCL8 the cytokine IL6. All these transcripts were absent from the equivalent clusters in control bone marrow. The presence of inflammatory stroma in the multiple myeloma niche indicates either the appearance of a novel stromal cell subset, or activation of pre-existing stromal cells. GSEA analyses suggested inflammatory signaling, and to functionally confirm this, we tested whether activation of stromal cells would induce the inflammatory stromal phenotype. Stimulation of primary human stromal cells in vitro with recombinant TNF was sufficient to induce transcription of CXCL2, CXCL3 and CXCL8, recapitulating the inflammatory transcriptome. Moreover, manual removal of these TNF target genes from the in-silico clustering analyses led to a merging of the inflammatory clusters with non-inflammatory clusters. This indicates that the major distinguishing feature of the myeloma-specific stromal cells are genes induced upon stromal cell activation. Conclusion: Through single cell transcriptomic analyses we have identified the presence of activated inflammatory stromal cells associated with TNF signaling in the multiple myeloma stromal niche. These inflammatory stromal cells are reminiscent of pathogenic cancer-associated fibroblasts found in solid tumors, where these cells create a pro-tumorigenic niche that favors tumor survival and proliferation while simultaneously inhibiting anti-cancer immunity. These findings represent the first description of myeloma-specific stromal cell subsets, and provide novel cellular targets for interventions aimed at disrupting the pro-tumorigenic microenvironment in multiple myeloma. Disclosures Broyl: Celgene, amgen, Janssen,Takeda: Honoraria. Sonneveld:Amgen: Honoraria, Research Funding; BMS: Honoraria; Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; SkylineDx: Research Funding; Takeda: Honoraria, Research Funding; Karyopharm: Honoraria, Research Funding.

A novel 3D mesenchymal stem cell model of the multiple myeloma bone marrow niche: biologic and clinical applications.

Specific niches within the tumor bone marrow (BM) microenvironment afford a sanctuary for multiple myeloma (MM) clones due to stromal cell-tumor cell interactions, which confer survival advantage and drug resistance. Defining the sequelae of tumor cell interactions within the MM niches on an individualized basis may provide the rationale for personalized therapies. To mimic the MM niche, we here describe a new 3D co-culture ex-vivo model in which primary MM patient BM cells are co-cultured with mesenchymal stem cells (MSC) in a hydrogel 3D system. In the 3D model, MSC with conserved phenotype (CD73+CD90+CD105+) formed compact clusters with active fibrous connections, and retained lineage differentiation capacity. Extracellular matrix molecules, integrins, and niche related molecules including N-cadherin and CXCL12 are expressed in 3D MSC model. Furthermore, activation of osteogenesis (MMP13, SPP1, ADAMTS4, and MGP genes) and osteoblastogenic differentiation was confirmed in 3D MSC model. Co-culture of patient-derived BM mononuclear cells with either autologous or allogeneic MSC in 3D model increased proliferation of MM cells, CXCR4 expression, and SP cells. We carried out immune profiling to show that distribution of immune cell subsets was similar in 3D and 2D MSC model systems. Importantly, resistance to novel agents (IMiDs, bortezomib, carfilzomib) and conventional agents (doxorubicin, dexamethasone, melphalan) was observed in 3D MSC system, reflective of clinical resistance. This 3D MSC model may therefore allow for studies of MM pathogenesis and drug resistance within the BM niche. Importantly, ongoing prospective trials are evaluating its utility to inform personalized targeted and immune therapy in MM.

Mimicking Myeloma Niche Ex Vivo

Introduction: Recent studies have elucidated the importance of using 3-dimensional rather than 2-dimensional models in order to create an experimental system recapitulating the specialized properties of the bone marrow microenvironment. Since the neoplastic bone marrow (BM) milieu plays important roles in multiple myeloma (MM) pathogenesis, novel models to study the MM cell in its neoplastic microenvironment are needed.Methods: To mimic the neoplastic BM microenvironment of MM patients, we have established a special hydrogel-based 3-dimensional (3-D) model by ex-vivo culturing MM patient-derived mesenchymal stem cells (MM-MSCs), the predominant cellular component of the marrow niche, which promotes greater mineralization and differentiation than a 2-dimensional (2-D) system.Results: To characterize MM-MSCs in different stages of MM, we utilized an 11 multi-color flow cytometry panel. The percentage of MSCs (CD73+CD90+CD105+lin-CD45-CD34-HLA-DR-) population in BM aspirate samples of 50 MM patients (MGUS, smoldering MM, newly diagnosed MM, and relapsed or relapsed/refractory MM) was evaluated, and correlated with the distribution of (CD38+ CD138+) plasma cells. MSCs were less frequent (10x) than plasma cells, and increased with disease progression to relapsed/refractory MM. We seeded MM-MSCs (N=34) which had been expanded by adhesion methods in 2-D versus 3-D models in order to create an ex-vivo MM niche-like structure. In the hydrogel-based 3-D model, MM-MSCs formed compact clusters with active fibrous connections and meshwork-like structures at day 3 to 7. Moreover, calcium mineralization of clusters was observed, associated with the capacity for differentiation towards the osteoblastogenic or adipogenic lineage when cultured with differentiation media. Furthermore, the production of osteopontin (OPN) and angiopoietin-2 (Ang-2) was significantly higher in 3-D vs. 2-D MM-MSCs, assessed by multiplex luminex technology. Phenotypic profiling of 3-D MM-MSCs clusters revealed high expression of CD73+CD90+CD105+ and lack of expression of CD45, CD34 and HLA-DR, as in to 2-D MM-MSCs. MSC-specific markers including CD166 and HLA-ABC did not reveal any significant changes in 3-D vs. 2-D MM-MSCs; however, 3-D MM-MSCs had significantly decreased expression of CD271 and CD146 compared to 2-D cultures. We also observed significantly higher expression of extracellular matrix (ECM) molecules including fibronectin, laminin, collagen I, and collagen IV (p<0.001) in 3-D vs. 2-D MM-MSCs. Similarly, activation of integrins including VLA-2, VLA-4 and VLA-5 on the MSCs surface was also increased in 3-D MM-MSCs, as determined by confocal microscopy and flow cytometry analysis. Importantly, MM-MSCs cultured in 3-D vs. 2-D model have higher expression of N-cadherin and CXCL12 and decreased expression of nestin, reflecting the MM BM niche. Gene expression analyses of 3-D MM-MSCs revealed upregulation of BMP-2, MGP, PTGIS, COL14A1 and other genes and down-regulation of DKK1, ADAM9, OPCML genes and others compared to 2-D MM-MSCs. We also measured significantly higher production of IL-6 (p=0.002), IL-8, MCP-1(MCAF), RANTES, VEGF and HGF (p<0.001) in 3-D vs. 2-D MM-MSCs, by multiplex luminex analysis. Next, we co-cultured tumor cells from MM patients (12 MM patients) with either autologous or allogeneic MM-MSCs in 3-D vs. 2-D model. Plasma (CD38/CD138+) cells in 3-D co-culture were increased in 8/12 MM patients and equivalent to 2-D in 4/12 patients. By co-culturing MM cell lines (OPM1, RPMI-S, OCIMY5 and KMS11) labeled with CFSE fluorescent dye with various MSCs, we evaluated expression of side population (SP) cells, identified by Hoechst staining, and gating on CFSE positive MM cells, as low Hoechst stained cells. Our results showed that the SP fraction was significantly lower in 3-D compared to 2-D in co-cultures of various MM-MSCs with all 4 MM cell lines. Finally, we validated drug resistance to melphalan, bortezomib, lenalidomide, and carfilzomib in 3-D co-cultures of CFSE labeled primary tumor cells with various MM-MSCs.Conclusions: This 3-D co-culture system closely mimics the myeloma BM niche, and therefore may be useful to identify and validate novel targeted therapies. DisclosuresNo relevant conflicts of interest to declare.

Myeloma Patient-Derived Mesenchymal Stem Cells Grown In 3-D Culture Induce Primary Myeloma Cell Proliferation and Resistance To Therapy

IntroductionThe neoplastic bone marrow (BM) milieu or so-called myeloma niche plays an essential role in initiation, development, and progression of multiple myeloma (MM). It is known that regulatory signaling molecules and cell-cell crosstalk interactions involved in the normal hematopoietic stem cell niche have also been implicated in MM. Defining phenotypic features and molecular signatures of the neoplastic BM niche in MM will provide the framework for future development of new treatment strategies targeting MM cells and their BM niche. Methods and ResultsTo investigate the neoplastic BM microenvironment of MM patients, we compared a special gel-based 3-dimensional (3-D) model with a 2-dimensional (2-D) system for culturing MM patient-derived mesenchymal stem cells (MM-MSCs) ex-vivo. In the gel-based 3-D model, MM-MSCs formed compact clusters with active fibrous connections between clusters to create a MM niche-like structure. Phenotypic profiling of 3-D MM-MSCs clusters revealed high expression of MSC-specific markers including CD73, CD90, CD105, CD166, and HLA-ABC. On the other hand, 3-D MM-MSCs clusters lacked expression of CD45, CD34 and HLA-DR. In order to confirm differentiation potential of 3-D MM-MSC, we cultured them with differentiation media towards either osteogenic or adipogenic lineages. The lineage differentiation capacity of the 3-D system was comparable to the 2-D MM-MSCs, with stronger calcium mineralization of clusters associated with differentiation towards the osteoblastogenic lineage. Moreover, the production of osteopontin and angiopoietin-2 was evident in 3-D MM-MSCs. In these models of the neoplastic BM microenvironment in MM, significantly higher production of IL-6 (p=0.002), IL-8, MCP-1(MCAF), RANTES, VEGF and HGF (p<0.001) was observed in 3-D vs. 2-D MM-MSCs.To define the functional myeloma niche, key hematopoietic and/or neoplastic niche molecules were investigated by analyzing 30 MM-MSCs and 5 healthy volunteers MSCs. MM-MSCs cultured in 3-D vs. 2-D model have higher expression of N-cadherin and CXCL12 and decreased expression of nestin by flow cytometry analysis, reflecting the MM BM niche. Higher pattern of cytokine production of leptin, SCF and sTie-2 was evident in 3-D MM-MSCs compared to 2-D system, as well as cancer biomarkes like IGFBP-1, sEGFR and sHER2neu performed by multiplex luminex technology. Next, we observed statistically significant higher expression of extracellular matrix (ECM) molecules including fibronectin, laminin, collagen I, and collagen IV (p<0.001) at 7 days MM-MSC culture in 3-D compared to 2-D, as determined by confocal microscopy and flow cytometry analysis. Furthermore, the activation of integrins such as VLA-2, VLA-4 and VLA-5, on the MSCs surface was also increased in 3-D MM-MSCs, as confirmed by flow cytometry analysis.To investigate the pathogenesis of MM in neoplastic BM niche, we co-cultured BM aspirates of MM cells (N=30) with MM-MSCs in vitro. Co-culturing BM aspirates with (autologous) MM-MSCs increased MM cells (CD38+/CD138+/CD19-) as well as stimulated their proliferation (determined by CFSE proliferation dye) in 3-D vs. 2-D system. MM cells in 3-D MM-MSCs were 4-fold more resistant to bortezomib and pomalidomide as well as melphalan, compared to 2-D. Finally, MM cells expressing CXCR4, as well as MM side population with “stem-like” features, were significantly increased in 3-D MM-MSCs vs. 2-D MM-MSCs cultures. ConclusionsOur 3-D MM-MSCs model mimics the neoplastic BM microenvironment and myeloma niche in vitro, and may be useful to identify novel targets, validate targeted therapies and determine mechanisms of drug resistance in MM. Disclosures:Hideshima:Acetylon Pharmaceuticals: Consultancy. Richardson:Millennium: Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Anderson:celgene: Consultancy; onyx: Consultancy; gilead: Consultancy; sanofi aventis: Consultancy; oncopep: Equity Ownership; acetylon: Equity Ownership.

Formation of the Functional Niche in Vitro by Mimicking the Pathophysiological Features of the Bone Marrow Microenvironment in Multiple Myeloma

Abstract 1812The neoplastic bone marrow (BM) milieu plays important roles in the development of multiple myeloma (MM). Specifically, cell-cell crosstalk interactions and regulatory signaling molecules involved in the normal hematopoietic stem cell niche have also been implicated in initiation, development, and progression of MM. Moreover, this “myeloma niche” serves as a sanctuary site for MM stem cells. The increasing knowledge of interactions between complex of MM cells and other normal hematopoietic cells and also non-hematopoietic mesenchymal stem cells and their progeny may enhance our understanding of MM cell biology and pathogenesis as well as provide the basis for novel therapeutic strategies.In order to develop an experimental system mimicking the specialized properties of the neoplastic BM microenvironment, we used hydrogel based 3-dimensional (3-D) versus 2-dimensional (2-D) models together with MM-derived mesenchymal stem cells (MM-MSCs) to create MM niche-like structures in vitro. In this 3-D model, MM-MSCs grew with the matrix fibers and at day 7 formed stable compact clusters, with fibrous meshwork-like structure among them. Furthermore, we showed tri-lineage differentiation capacity of 3-D comparable to 2D MM-MSCs towards osteogenic, adipogenic, and chondrogenic lineages. Our 3-D MM-MSCs model also showed calcium mineralization of clusters associated with differentiation towards the osteoblastogenic lineage. The phenotypic profile of MM-MSCs grown in the 2-D vs. 3-D model using MSC-specific markers (such as CD166, HLA-ABC, CD73, CD105, and CD90) did not reveal any significant changes, however CD271 was more highly expressed in the 3-D model, while CD146 was overexpressed in 2-D cultures.Because the stem cell niche is enriched with extracellular matrix (ECM) molecules resulting in an overexpansion of the stem cell pool, we studied whether expression of these molecules was conserved in the 3-D model. Analyzing 30 MM-MSCs vs. 5 normal donor MSCs, we observed that the 3-D MM-MSCs expressed significantly high level of ECM molecules including laminin, fibronectin, collagen I, collagen IV and vitronectin (p<0.001) after 7 days of culture compared to the 2-D model, as determined by flow cytometry and confocal microscopy analysis. Furthermore, the formation of dimeric active integrins (α2β1, α4β1 and α5β1) on the MSCs surface when engaged by these ECM molecules, inducing MM proliferation and survival, was also increased in the 3-D model, associated with transcriptional up-regulation of integrin subunits as confirmed by qRT-PCR. We also investigated the key molecules that play an important role in the MM niche including N-cadherin and nestin, as well as the interactions of MM cells with MSCs in the niche via CXCL12/CXCR4 axis. MM-MSCs cultured in the 3-D vs. 2-D model have higher expression of N-cadherin and CXCL12 and decreased expression of nestin, reflecting the MM BM niche.To mimic the functional marrow niche of MM in our model, we cultured the tumor cells from MM patients (N=30) with their autologous MM-MSCs in vitro. MM plasma cells (identified as CD38/CD138+ cells) were increased in percentage and proliferation after 14 days in the 3-D vs. 2-D model. Finally, MM cells expressing CXCR4, as well as MM side population with “stem-like” features (Jakubikova J et al., Blood 2011) were also significantly increased in 3-D MM-MSCs vs. 2-D MM-MSCs cultures. Our study shows that hydrogel based 3-D MM-MSCs model forms a functional niche in vitro, and may be useful to identify novel targets and validate therapies directed at MM stem cells in the MM BM niche. Disclosures:Munshi:Celgene: Membership on an entity’s Board of Directors or advisory committees; Millenium: Membership on an entity’s Board of Directors or advisory committees; Onyx: Membership on an entity’s Board of Directors or advisory committees; Merck: Consultancy; Oncopep: Patents & Royalties. Richardson:Novartis: Membership on an entity’s Board of Directors or advisory committees; Celgene: Membership on an entity’s Board of Directors or advisory committees; Millennium: Membership on an entity’s Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity’s Board of Directors or advisory committees. Anderson:Onyx: Membership on an entity’s Board of Directors or advisory committees; BMS: Membership on an entity’s Board of Directors or advisory committees; Millennium: Membership on an entity’s Board of Directors or advisory committees; Celgene Corp: Membership on an entity’s Board of Directors or advisory committees.

Multiple Myeloma Bone Marrow Niche

"Niche" is defined as a specialized regulatory microenvironment, consisting of components which control the fate specification of stem and progenitor cells, as well as maintaining their development by supplying the requisite factors. Bone marrow (BM) niche has a well-organized architecture and is composed of osteoblasts, osteoclasts, bone marrow endothelial cells, stromal cells, adipocytes and extracellular matrix proteins (ECM). These elements play an essential role in the survival, growth and differentiation of diverse lineages of blood cells, but also provide optimal growth environment for multiple hematological malignancies including multiple myeloma (MM). MM is a neoplastic plasma cell disorder which not only resides in BM but also converts it into specialized neoplastic niche. This niche aids the growth and spreading of tumor cells by a complex interplay of cytokines, chemokines, proteolytic enzymes and adhesion molecules. Moreover, the MM BM microenvironment was shown to confer survival and chemoresistance of MM cells to current therapies. However, our knowledge in this field is still in infancy and many details are unknown. Therefore, there is a strong need to further dissect the MM BM niche and understand the process of how the complex interactions with BM milieu influence MM growth, survival and development of resistance to chemotherapy. A better and more detailed understanding of neoplastic MM niche will provide a guiding model for identifying and validating novel targeted therapies directed against MM. Therefore, in the present review, we have focused principally on the basic features, physical structures, and functions of the BM niche and have highlighted its interaction with MM cells.