Understanding the hypoxic niche of multiple myeloma: therapeutic implications and contributions of mouse models

Just scratching the surface: novel treatment approaches for multiple myeloma targeting cell membrane proteins

A better understanding of the roles of the adaptive and innate immune systems in the oncogenesis of cancers including multiple myeloma (MM) has led to the development of novel immune-based therapies. B cell maturation antigen (BCMA), G protein-coupled receptor family C group 5 member D (GPRC5D) and Fc receptor-like protein 5 (FcRL5, also known as FcRH5) are cell-surface transmembrane proteins expressed by plasma cells, and have been identified as prominent immunotherapeutic targets in MM, with promising activity demonstrated in patients with heavily pretreated relapsed and/or refractory disease. Indeed, since 2020, antibody-drug conjugates, bispecific T cell engagers and autologous chimeric antigen receptor T cells targeting BCMA or GPRC5D have been approved for the treatment of relapsed and/or refractory MM. However, responses to these therapies are not universal, and acquired resistance invariably occurs. In this Review, we discuss the various immunotherapeutic approaches targeting BCMA, GPRC5D and FcRL5 that are currently either available or in clinical development for patients with MM. We also review the mechanisms underlying resistance to such therapies, and discuss potential strategies to overcome these mechanisms and improve patient outcomes.

Acidification of intracellular pH in MM tumor cells overcomes resistance to hypoxia-mediated apoptosis in vitro and in vivo

Introduction

Multiple myeloma (MM) is an incurable cancer of malignant plasma cells that engraft in the bone marrow (BM). It is more than likely that the poorly investigated physical parameters of hypoxia and pH in the tumor microenvironment (TME) is critical for MM survival. Here, we explore the effects of a hypoxic environment on pH regulation and its role in MM survival.

Methods

We used in vitro models of MM, in which the culturing medium was modified to specific pH and pO2 levels and then measured the effects on cell survival that was correlated with changes in intracellular (pHi) and extracellular pH (pHe). In a MM xenograft model, we used PET/CT to study hypoxia-mediated effects on tumor growth.

Results

Hypoxia-mediated apoptosis of MM cells is correlated with acidic intracellular pHi (less than < 6.6) that is dependent on HIF activity. Using a polyamide HIF responsive element binding compound, a carbonic anhydrase inhibitor (acetazolamide), and an NHE-1 inhibitor (amiloride) acidified the pHi and lead to cell death. In contrast, treatment of cells with an alkalization agent, Na-lactate, rescued these cells by increasing the pHi (pH > 6.6). Finally, treatment of mice with acetazolamide decreased cell growth in the tumor nodules.

Discussion

Targeting hypoxia and HIF have been proposed as an anti-tumor therapy but the clinical efficacy of such strategies are modest. We propose that targeting the pHi may be more effective at treating cancers within a hypoxic TME.

Metabolic crosstalk between stromal and malignant cells in the bone marrow niche

Bone marrow is the primary site of blood cell production in adults and serves as the source of osteoblasts and osteoclasts that maintain bone homeostasis. The medullary microenvironment is also involved in malignancy, providing a fertile soil for the growth of blood cancers or solid tumors metastasizing to bone. The cellular composition of the bone marrow is highly complex, consisting of hematopoietic stem and progenitor cells, maturing blood cells, skeletal stem cells, osteoblasts, mesenchymal stromal cells, adipocytes, endothelial cells, lymphatic endothelial cells, perivascular cells, and nerve cells. Intercellular communication at different levels is essential to ensure proper skeletal and hematopoietic tissue function, but it is altered when malignant cells colonize the bone marrow niche. While communication often involves soluble factors such as cytokines, chemokines, and growth factors, as well as their respective cell-surface receptors, cells can also communicate by exchanging metabolic information. In this review, we discuss the importance of metabolic crosstalk between different cells in the bone marrow microenvironment, particularly concerning the malignant setting.

Computational modeling of multiple myeloma interactions with resident bone marrow cells

The interaction of multiple myeloma with bone marrow resident cells plays a key role in tumor progression and the development of drug resistance. The tumor cell response involves contact-mediated and paracrine interactions. The heterogeneity of myeloma cells and bone marrow cells makes it difficult to reproduce this environment in in-vitro experiments. The use of in-silico established tools can help to understand these complex problems. In this article, we present a computational model based on the finite element method to define the interactions of multiple myeloma cells with resident bone marrow cells. This model includes cell migration, which is controlled by stress-strain equilibrium, and cell processes such as proliferation, differentiation, and apoptosis. A series of computational experiments were performed to validate the proposed model. Cell proliferation by the growth factor IGF-1 is studied for different concentrations ranging from 0-10 ng/mL. Cell motility is studied for different concentrations of VEGF and fibronectin in the range of 0-100 ng/mL. Finally, cells were simulated under a combination of IGF-1 and VEGF stimuli whose concentrations are considered to be dependent on the cancer-associated fibroblasts in the extracellular matrix. Results show a good agreement with previous in-vitro results. Multiple myeloma growth and migration are shown to correlate linearly to the IGF-1 stimuli. These stimuli are coupled with the mechanical environment, which also improves cell growth. Moreover, cell migration depends on the fiber and VEGF concentration in the extracellular matrix. Finally, our computational model shows myeloma cells trigger mesenchymal stem cells to differentiate into cancer-associated fibroblasts, in a dose-dependent manner.

Diversity in the bone marrow niche: Classic and novel strategies to uncover niche composition

Our view on the role and composition of the bone marrow (BM) has dramatically changed over time from a simple nutrient for the bone to a highly complex multicellular tissue that sustains haematopoiesis. Among these cells, multipotent haematopoietic stem cells (HSCs), which are predominantly quiescent, possess unique self-renewal capacity and multilineage differentiation potential and replenish all blood lineages to maintain lifelong haematopoiesis. Adult HSCs reside in specialised BM niches, which support their functions. Much effort has been put into deciphering HSC niches due to their potential clinical relevance. Multiple cell types have been implicated as HSC-niche components including sinusoidal endothelium, perivascular stromal cells, macrophages, megakaryocytes, osteoblasts and sympathetic nerves. In this review we provide a historical perspective on how technical advances, from genetic mouse models to imaging and high-throughput sequencing techniques, are unveiling the plethora of molecular cues and cellular components that shape the niche and regulate HSC functions.

Drug resistance in multiple myeloma: Soldiers and weapons in the bone marrow niche

Multiple myeloma (MM) is still an incurable disease, despite considerable improvements in treatment strategies, as resistance to most currently available agents is not uncommon. In this study, data on drug resistance in MM were analyzed and led to the following conclusions: resistance occurs via intrinsic and extrinsic mechanisms, including intraclonal heterogeneity, drug efflux pumps, alterations of drug targets, the inhibition of apoptosis, increased DNA repair and interactions with the bone marrow (BM) microenvironment, cell adhesion, and the release of soluble factors. Since MM involves the BM, interactions in the MM-BM microenvironment were examined as well, with a focus on the cross-talk between BM stromal cells (BMSCs), adipocytes, osteoclasts, osteoblasts, endothelial cells, and immune cells. Given the complex mechanisms that drive MM, next-generation treatment strategies that avoid drug resistance must target both the neoplastic clone and its non-malignant environment. Possible approaches based on recent evidence include: (i) proteasome and histone deacetylases inhibitors that not only target MM but also act on BMSCs and osteoclasts; (ii) novel peptide drug conjugates that target both the MM malignant clone and angiogenesis to unleash an effective anti-MM immune response. Finally, the role of cancer stem cells in MM is unknown but given their roles in the development of solid and hematological malignancies, cancer relapse, and drug resistance, their identification and description are of paramount importance for MM management.

Prognostic Value of Association of Copy Number Alterations and Cell-Surface Expression Markers in Newly Diagnosed Multiple Myeloma Patients

Multiple myeloma results from the clonal proliferation of abnormal plasma cells (PCs) in the bone marrow (BM). In this study, the cell surface expression markers (CD) on atypical PCs (detected by multiparametric flow cytometry (MFC)) were correlated with copy number alterations (CNAs) in the genome (detected by multiplex ligation-dependent probe amplification (MLPA)) to assess their impact on prognosis in newly diagnosed MM patients. Statistically significant results were obtained when different stages of PC maturation (classified based on CD19 and CD81 expression) were associated with CD117 expression and identified CNAs. In the intermediately differentiated PC group (CD19(−) CD81(+)), patients who didn’t express CD117 had a lower median progression free survival (PFS) (p = 0.024). Moreover, within this group, patients with less than three adverse CNAs, which harbor CD117, had a better outcome with a PFS of more than 48 months compared with 19 months (p = 0.008). Considering all the results, our study suggested the need to integrate both the CD markers and copy number alterations to evaluate the prognosis of newly diagnosed multiple myeloma patients.

Autophagy and the Bone Marrow Microenvironment: A Review of Protective Factors in the Development and Maintenance of Multiple Myeloma

The role of the unfolded protein response (UPR) in plasma cells (PC) and their malignant multiple myeloma (MM) counterparts is a well described area of research. The importance of autophagy in these cells, as well as the interplay between autophagy and the UPR system, has also been well studied. In this review, we will discuss the relationship between these two cellular responses and how they can be utilized in MM to account for the high levels of monoclonal immunoglobulin (Ig) protein synthesis that is characteristic of this disease. Interactions between MM cells and the bone marrow (BM) microenvironment and how MM cells utilize the UPR/autophagy pathway for their survival. These interacting pathways form the foundation for the mechanism of action for bortezomib, a proteasome inhibitor used to modify the progression of MM, and the eventual drug resistance that MM cells develop. One important resistance pathway implicated in MM progression is caspase 10 which attenuates autophagy to maintain its prosurvival function and avoid cell death. We lay a groundwork for future research including 3D in vitro models for better disease monitoring and personalized treatment. We also highlight pathways involved in MM cell survival and drug resistance that could be used as new targets for effective treatment.

RNA-Sequencing-Based Transcriptomic Score with Prognostic and Theranostic Values in Multiple Myeloma

Multiple myeloma (MM) is the second most frequent hematological cancer and is characterized by the clonal proliferation of malignant plasma cells. Genome-wide expression profiling (GEP) analysis with DNA microarrays has emerged as a powerful tool for biomedical research, generating a huge amount of data. Microarray analyses have improved our understanding of MM disease and have led to important clinical applications. In MM, GEP has been used to stratify patients, define risk, identify therapeutic targets, predict treatment response, and understand drug resistance. In this study, we built a gene risk score for 267 genes using RNA-seq data that demonstrated a prognostic value in two independent cohorts (n = 674 and n = 76) of newly diagnosed MM patients treated with high-dose Melphalan and autologous stem cell transplantation. High-risk patients were associated with the expression of genes involved in several major pathways implicated in MM pathophysiology, including interferon response, cell proliferation, hypoxia, IL-6 signaling pathway, stem cell genes, MYC, and epigenetic deregulation. The RNA-seq-based risk score was correlated with specific MM somatic mutation profiles and responses to targeted treatment including EZH2, MELK, TOPK/PBK, and Aurora kinase inhibitors, outlining potential utility for precision medicine strategies in MM.

An Overview of Organoid and 3-Dimensional Models in Multiple Myeloma

ABSTRACT

Multiple myeloma is a hematological malignancy of differentiated B cells that resides primarily in bone marrow niches. Its interaction with the microenvironment is known to provide a survival advantage and plays an important role in drug resistance. Despite the increased efficacy of new treatment drugs, clinical results oftentimes fall short of in vitro observations, and this disease remains incurable. Conventional 2-dimensional cultures used to perform chemosensitivity assays and the established multiple myeloma cells lines commonly used do not replicate the conditions seen in vivo. This review presents various 3-dimensional culture platforms for myeloma that attempt to overcome this obstacle by incorporating aspects of the tumor microenvironment. The unique features of each model and contributions they have provided in personalized medicine, tumor physiology, and chemosensitivity assays will be summarized.

Can Targeting Hypoxia-Mediated Acidification of the Bone Marrow Microenvironment Kill Myeloma Tumor Cells?

Multiple myeloma (MM) is an incurable cancer arising from malignant plasma cells that engraft in the bone marrow (BM). The physiology of these cancer cells within the BM microenvironment (TME) plays a critical role in MM development. These processes may be similar to what has been observed in the TME of other (non-hematological) solid tumors. It has been long reported that within the BM, vascular endothelial growth factor (VEGF), increased angiogenesis and microvessel density, and activation of hypoxia-induced transcription factors (HIF) are correlated with MM progression but despite a great deal of effort and some modest preclinical success the overall clinical efficacy of using anti-angiogenic and hypoxia-targeting strategies, has been limited. This review will explore the hypothesis that the TME of MM engrafted in the BM is distinctly different from non-hematological-derived solid tumors calling into question how effective these strategies may be against MM. We further identify other hypoxia-mediated effectors, such as hypoxia-mediated acidification of the TME, oxygen-dependent metabolic changes, and the generation of reactive oxygen species (ROS), that may prove to be more effective targets against MM.

Recent Progress of Exosomes in Multiple Myeloma: Pathogenesis, Diagnosis, Prognosis and Therapeutic Strategies

Simple Summary

In the pathogenesis of multiple myeloma (MM), some exosomes act on different cells in the bone marrow microenvironment, which can create an environment conducive to the survival and growth of MM cells. In addition, due to the abnormal expression of cargos in the exosomes of MM patients, exosomes may help with the diagnosis and prognosis of MM. In contrast to traditional nanomaterials, exosomes exhibit very good safety, biocompatibility, stability and biodegradability, which shows their potential for delivering anti-cancer drugs and cancer vaccines. Given the research in recent decades, exosomes are becoming increasingly relevant to MM. Although exosomes have not been applied in the clinic for help with diagnosing, prognosticating or providing therapy for MM, they are very promising for clinical applications concerning MM, which will possibly materialize in the near future. Therefore, this review is worth reading for further understanding of the important roles of exosomes in MM..

Abstract

Multiple myeloma (MM) is a hematological malignancy that is still incurable. The bone marrow microenvironment (BMM), with cellular and non-cellular components, can create a favorable environment for the survival, proliferation and migration of MM cells, which is the main reason for the failure of MM therapies. Many studies have demonstrated that exosomes play an important role in the tumor-supportive BMM. Exosomes are nanoscale vesicles that can be released by various cells. Some exosomes contribute to the pathogenesis and progression of MM. MM-derived exosomes act on different cells in the BMM, thereby creating an environment conducive to the survival and growth of MM cells. Owing to the important roles of exosomes in the BMM, targeting the secretion of exosomes may become an effective therapeutic strategy for MM. In addition, the abnormal expression of “cargos” in the exosomes of MM patients may be used to diagnose MM or used as part of a screen for the early prognoses of MM patients. Exosomes also have good biological properties, including safety, biocompatibility, stability and biodegradability. Therefore, the encapsulation of anti-cancer drugs in exosomes, along with surface modifications of exosomes with targeting molecules, are very promising strategies for cancer therapies—particularly for MM. In addition, DC-derived exosomes (DC-EXs) can express MHC-I, MHC-II and T cell costimulatory molecules. Therefore, DC-EXs may be used as a nanocarrier to deliver cancer vaccines in MM. This review summarizes the recent progress of exosome research regarding the pathogenesis of, diagnosis of, prognosis of and therapeutic strategies for MM.

The "Vesicular Intelligence" Strategy of Blood Cancers

Blood cancers are a heterogeneous group of disorders including leukemia, multiple myeloma, and lymphoma. They may derive from the clonal evolution of the hemopoietic stem cell compartment or from the transformation of progenitors with immune potential. Extracellular vesicles (EVs) are membrane-bound nanovesicles which are released by cells into body fluids with a role in intercellular communication in physiology and pathology, including cancer. EV cargos are enriched in nucleic acids, proteins, and lipids, and these molecules can be delivered to target cells to influence their biological properties and modify surrounding or distant targets. In this review, we will describe the “smart strategy” on how blood cancer-derived EVs modulate tumor cell development and maintenance. Moreover, we will also depict the function of microenvironment-derived EVs in blood cancers and discuss how the interplay between tumor and microenvironment affects blood cancer cell growth and spreading, immune response, angiogenesis, thrombogenicity, and drug resistance. The potential of EVs as non-invasive biomarkers will be also discussed. Lastly, we discuss the clinical application viewpoint of EVs in blood cancers. Overall, blood cancers apply a ‘vesicular intelligence’ strategy to spread signals over their microenvironment, promoting the development and/or maintenance of the malignant clone.

Treatment Strategies Considering Micro-Environment and Clonal Evolution in Multiple Myeloma

Simple Summary

Multiple myeloma is an uncurable hematological malignancy, although the prognosis of myeloma patients is getting better using proteasome inhibitors (PIs), immune modulatory drugs (IMiDs), monoclonal antibodies (MoAbs), and cytotoxic agents. Drug resistance makes myeloma difficult to treat and it can be subdivided into two broad categories: de novo and acquired. De novo drug resistance is associated with the bone marrow microenvironment including bone marrow stromal cells, the vascular niche and endosteal niche. Acquired drug resistance is related to clonal evolution and non-genetic diversity. The initial treatment plays the most important role considering de novo and acquired drug resistance and should contain PIs, IMIDs, MoAbs, and autologous stem cell transplantation because these treatments improve the bone marrow microenvironment and might prevent clonal evolution via sustained deep response including minimal residual disease negativity.

Abstract

Multiple myeloma is an uncurable hematological malignancy because of obtained drug resistance. Microenvironment and clonal evolution induce myeloma cells to develop de novo and acquired drug resistance, respectively. Cell adhesion-mediated drug resistance, which is induced by the interaction between myeloma and bone marrow stromal cells, and soluble factor-mediated drug resistance, which is induced by cytokines and growth factors, are two types of de novo drug resistance. The microenvironment, including conditions such as hypoxia, vascular and endosteal niches, contributes toward de novo drug resistance. Clonal evolution was associated with acquired drug resistance and classified as branching, linear, and neutral evolutions. The branching evolution is dependent on the microenvironment and escape of immunological surveillance while the linear and neutral evolution is independent of the microenvironment and associated with aggressive recurrence and poor prognosis. Proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), monoclonal antibody agents (MoAbs), and autologous stem cell transplantation (ASCT) have improved prognosis of myeloma via improvement of the microenvironment. The initial treatment plays the most important role considering de novo and acquired drug resistance and should contain PIs, IMIDs, MoAb and ASCT. This review summarizes the role of anti-myeloma agents for microenvironment and clonal evolution and treatment strategies to overcome drug resistance.

Current Understanding of Myelomatous Mesenchymal Stromal Cells Extended through Advances in Experimental Methods

Simple Summary

As the amount of information available has grown, now it is known that many types of non-hematopoietic cells, including mesenchymal stem/progenitor cells, mature mesenchymal cells, and endothelial cells, as well as mature hematopoietic cells such as monocytes, macrophages, T-cells, and B-cells, have roles in the pathogenesis of multiple myeloma. This review focuses on the role of mesenchymal cells in the microenvironment of multiple myeloma. We summarize the experimental strategies and current understanding of the biological roles in the pathogenesis of myeloma. Furthermore, we discuss the possible clinical applications targeting mesenchymal cells.

Abstract

Multiple myeloma is an incurable cancer formed by malignant plasma cells. For the proliferation and survival of myeloma cells, as well as the occurrence of the complications, numerous intra- and extra-cellular mechanisms are involved. The interaction of myeloma cells with the microenvironment is known to be one of the most critical mechanisms. A specific microenvironment could affect the progression and growth of tumor cells, as well as drug resistance. Among various microenvironment components, such as hematological and non-hematological cells, and soluble factors (cytokines, chemokines, and extracellular matrix (ECM) proteins), in this review, we focus on the role of mesenchymal cells. We aimed to summarize the experimental strategies used for conducting studies and current understanding of the biological roles in the pathogenesis of myeloma. Furthermore, we discuss the possible clinical applications targeting mesenchymal cells.

JZL184, A Monoacylglycerol Lipase Inhibitor, Induces Bone Loss in a Multiple Myeloma Model of Immunocompetent Mice

Multiple myeloma (MM) patients develop osteolysis characterised by excessive osteoclastic bone destruction and lack of osteoblast bone formation. Pharmacological manipulation of monoacylglycerol lipase (MAGL), an enzyme responsible for the degradation of the endocannabinoid 2-arachidonoyl glycerol (2-AG), reduced skeletal tumour burden and osteolysis associated with osteosarcoma and advanced breast and prostate cancers. MM and hematopoietic, immune and bone marrow cells express high levels of type 2 cannabinoid receptor and osteoblasts secrete 2-AG. However, the effects of MAGL manipulation on MM have not been investigated. Here, we report that treatment of pre-osteoclasts with non-cytotoxic concentrations of JZL184, a verified MAGL inhibitor, enhanced MM- and RANKL-induced osteoclast formation and size in vitro. Exposure of osteoblasts to JZL184 in the presence of MM cell-derived factors reduced osteoblast growth but had no effect on the ability of these cells to mature or form bone nodules. In vivo, administration of JZL184 induced a modest, yet significant, bone loss at both trabecular and cortical compartments of long bones of immunocompetent mice inoculated with the syngeneic 5TGM1-GFP MM cells. Notably, JZL184 failed to inhibit the in vitro growth of a panel of mouse and human MM cell lines, or reduce tumour burden in mice. Thus, MAGL inhibitors such as JZL184 can exacerbate MM-induced bone loss.

Hypoxia Impairs NK Cell Cytotoxicity through SHP-1-Mediated Attenuation of STAT3 and ERK Signaling Pathways

Natural killer (NK) cells are innate immune effectors with potent antitumor activity. However, tumor cells can create an immunosuppressive microenvironment to escape immune surveillance. Although accumulating evidence indicates that microenvironmental hypoxia plays an important role in favoring tumor development and immune evasion, it remains unclear by what means hypoxia directly impairs NK cell antitumor activity. In this study, we confirmed that hypoxic NK cells showed significantly lower cytotoxicity against tumor cells. Consistent with this finding, we found that the reduction in NK cell cytotoxicity resulting from hypoxia correlated to the lower expression of granzyme B, IFN-γ, and degranulation marker CD107a, as well as activating receptors including NKp30, NKp46, and NKG2D expressed on the surface of NK cells. More importantly, we further demonstrated that a reduction in the phosphorylation levels of ERK and STAT3 secondary to hypoxia was strongly associated with the attenuated NK cell cytotoxicity. Focusing on the mechanism responsible for reduced phosphorylation levels of ERK and STAT3, we reveal that the activation of protein tyrosine phosphatase SHP-1 (Src homology region 2 domain-containing phosphatase-1) following hypoxia might play an essential role in this process. By knocking down SHP-1 or blocking its activity using a specific inhibitor TPI-1, we were able to partially restore NK cell cytotoxicity under hypoxia. Taken together, we demonstrate that hypoxia could impair NK cell cytotoxicity by decreasing the phosphorylation levels of ERK and STAT3 in a SHP-1-dependent manner. Therefore, targeting SHP-1 could provide an approach to enhance NK cell-based tumor immunotherapy.

Therapeutic targets in myeloma bone disease

Multiple myeloma (MM) is the second most common haematological malignancy and is characterized by a clonal proliferation of neoplastic plasma cells within the bone marrow. MM is the most frequent cancer involving the skeleton, causing osteolytic lesions, bone pain and pathological fractures that dramatically decrease MM patients' quality of life and survival. MM bone disease (MBD) results from uncoupling of bone remodelling in which excessive bone resorption is not compensated by new bone formation, due to a persistent suppression of osteoblast activity. Current management of MBD includes antiresorptive agents, bisphosphonates and denosumab, that are only partially effective due to their inability to repair the existing lesions. Thus, research into agents that prevent bone destruction and more importantly repair existing lesions by inducing new bone formation is essential. This review discusses the mechanisms regulating the uncoupled bone remodelling in MM and summarizes current advances in the treatment of MBD. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

miR-489 suppresses multiple myeloma cells growth through inhibition of LDHA-mediated aerobic glycolysis

BACKGROUND

Dysregulation of miR-489 in human tumors has been widely reported. Lactate dehydrogenase isoform A (LDHA)-mediated aerobic glycolysis participates in proliferation of multiple myeloma (MM) cells.

OBJECTIVE

To investigate whether miR-489 induced MM growth inhibition via targeting to LDHA-mediated aerobic glycolysis.

METHODS

Expression of miR-489 in representative MM cell lines was determined via qRT-PCR (quantitative real-time polymerase chain reaction). MTT (3-(4, 5-di methyl thiazol-2-yl)-2, 5-di phenyl tetrazolium bromide) and colony formation assays were utilized to detect cell viability and proliferation. Effect of miR-489 on aerobic glycolysis was detected via glucose uptake, lactate and ATP production. Binding ability between miR-489 and LDHA was conducted via luciferase activity assay.

RESULTS

MiR-489 was down-regulated in representative MM cell lines. Gain-of functional assays indicated that over-expression of miR-489 decreased cell viability and inhibited cell proliferation of MM cells. Moreover, miR-489 inhibited aerobic glycolysis via decrease of glucose uptake, lactate and ATP production. LDHA was identified as target of miR-489, suggesting a negative correlation between miR-489 and LDHA in MM cells. Mechanically, the inhibition ability of miR-489 on proliferation of MM cells was through inhibition of LDHA-mediated aerobic glycolysis.

CONCLUSIONS

miR-489 inhibited MM tumor growth via LDHA-mediated glycolytic metabolism, suggesting potential therapeutic target ability of miR-489/LDHA for MM.

SRC3 expressed in bone marrow mesenchymal stem cells promotes the development of multiple myeloma

SRC3 plays critical roles in various biological processes of diseases, including proliferation, apoptosis, migration, and cell cycle arrest. However, the effect of SRC3 expression in mesenchymal stem cells (MSCs) on multiple myeloma (MM) is not clear yet. In our study, MSCs (MSC-SRC3, MSC-SRC3-/-) and MM cells were co-cultured in a direct or indirect way. The proliferation of MM cells was studied by CCK-8 and colony formation assays. The apoptosis and cell cycle of MM cells were detected by flow cytometry. In addition, the expressions of proteins in MM cells were detected by western blot analysis and the secretions of cytokines were measured by ELISA. Our data showed that the expression of SRC3 in bone marrow mesenchymal stem cells (BM-MSCs) could promote cell proliferation and colony formation of MM cells through accelerating the transformation of the G1/S phase, no matter what kind of culture method was adopted. Meanwhile, SRC3 expressed in BM-MSCs could inhibit the apoptosis of MM cells through the caspase apoptosis pathway and mitochondrial apoptosis pathway. Moreover, SRC3 could enhance the adhesion ability of MM cells through up-regulating the expression of adhesion molecules including CXCL4, ICAM1, VLA4, and syndecan-1. SRC3 also played a regulatory role in the progress of MM through the NF-κB and PI-3K/Akt pathways. SRC3 expressed in MSCs was found to promote the growth and survival of MM cells, while SRC3 silencing in MSCs could inhibit the development of MM. These results would be useful for developing a more effective new strategy for MM treatment.

Anticancer activity of a Gold(I) phosphine thioredoxin reductase inhibitor in multiple myeloma

Multiple myeloma (MM), the second most common haematological malignancy, is a clonal plasma B-cell neoplasm that forms within the bone marrow. Despite recent advancements in treatment, MM remains an incurable disease. Auranofin, a linear gold(I) phosphine compound, has previously been shown to exert a significant anti-myeloma activity by inhibiting thioredoxin reductase (TrxR) activity. A bis-chelated tetrahedral gold(I) phosphine complex [Au(d2pype)₂]Cl (where d2pype is 1,2-bis(di-2-pyridylphosphino)ethane) was previously designed to improve the gold(I) compound selectivity towards selenol- and thiol-containing proteins, such as TrxR. In this study, we show that [Au(d2pype)₂]Cl significantly inhibited TrxR activity in both bortezomib-sensitive and resistant myeloma cells, which led to a significant reduction in cell proliferation and induction of apoptosis, both of which were dependent on ROS. In clonogenic assays, treatment with [Au(d2pype)₂]Cl completely abrogated the tumourigenic capacity of MM cells, whereas auranofin was less effective. We also show that [Au(d2pype)₂]Cl exerted a significant anti-myeloma activity in vivo in human RPMI8226 xenograft model in immunocompromised NOD/SCID mice. The MYC oncogene, known to drive myeloma progression, was downregulated in both in vitro and in vivo models when treated with [Au(d2pype)₂]Cl. This study highlights the "proof of concept" that improved gold(I)-based compounds could potentially be used to not only treat MM but as an alternative tool to understand the role of the Trx system in the pathogenesis of this blood disease.

The emerging role of exosomes in multiple myeloma

Multiple myeloma (MM), one of the most prevalent hematological malignancies, accounts for approximately 10% of all blood cancers. In spite of the recent advancements in MM therapy, this malignancy of terminally differentiated plasma cells (PCs) continues to remain a hard-to-cure disease due to the emergence of drug resistance and frequent relapses. It is now well-established that the tumor-supportive involvement of the bone marrow microenvironment (BMM) including the cellular and non-cellular elements are the major causes behind treatment failures of MM as well as its main complications such as osteolytic bone loss. Exosomes (EXs) are membranous structures that carry signaling molecules and have recently received a great deal of attention as important mediators of inter-cellular communication in health and disease. EXs involve in the growth and drug resistance of many tumors via delivering their rich contents of bioactive molecules including miRNAs, growth factors, cytokines, signaling molecules, etc. With regard to MM, many studies have reported that EXs are among the main culprits playing key roles in the vicious network within the BMM of these patients. The main producers of EXs that largely contribute to MM pathogenesis are bone marrow stromal cells (BMSCs) as well as MM cells themselves. These cell types produce large amounts of EXs that affect a variety of target cells including natural killer (NK) cells, osteoclasts (OCs) and osteoblasts (OBs) to the advantage of tumor survival and progression. These EXs contain a different profile of proteins and miRNAs from that of EXs obtained from their counterparts in healthy individuals. MM patients exhibit distinguishable elevations in some of their contents such as miR-21, miR-146a, let-7b and miR-18a, while some molecules like miR-15a are markedly downregulated in EXs of MM patients compared to healthy individuals. These findings make EXs desirable biomarkers for early prediction of disease progression and drug resistance in the context of MM. On the other hand, due to the tumor-supportive role of EXs, targeting these structures in parallel to the conventional therapeutic regimens may be a promising approach to a successful anti-MM therapy. In the present work, an extensive review of the literature has been carried out to highlight the recent advances in the field.

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

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

The Lipid Side of Bone Marrow Adipocytes: How Tumor Cells Adapt and Survive in Bone

PURPOSE OF REVIEW

Bone marrow adipocytes have emerged in recent years as key contributors to metastatic progression in bone. In this review, we focus specifically on their role as the suppliers of lipids and discuss pro-survival pathways that are closely linked to lipid metabolism, affected by the adipocyte-tumor cell interactions, and likely impacting the ability of the tumor cell to thrive in bone marrow space and evade therapy.

RECENT FINDINGS

The combined in silico, pre-clinical, and clinical evidence shows that in adipocyte-rich tissues such as bone marrow, tumor cells rely on exogenous lipids for regulation of cellular energetics and adaptation to harsh metabolic conditions of the metastatic niche. Adipocyte-supplied lipids have a potential to alter the cell's metabolic decisions by regulating glycolysis and respiration, fatty acid oxidation, lipid desaturation, and PPAR signaling. The downstream effects of lipid signaling on mitochondrial homeostasis ultimately control life vs. death decisions, providing a mechanism for gaining survival advantage and reduced sensitivity to treatment. There is a need for future research directed towards identifying the key metabolic and signaling pathways that regulate tumor dependence on exogenous lipids and consequently drive the pro-survival behavior in the bone marrow niche.

Daratumumab induces CD38 internalization and impairs myeloma cell adhesion

Daratumumab (Dara), a human immunoglobulin G1 kappa (IgG1κ) monoclonal anti-CD38 antibody, has been approved by the U.S. Food and Drug Administration for the treatment of relapsed multiple myeloma (MM) as a single agent as well as in combination with immunomodulatory drugs (IMiDs) and proteasome inhibitors (PI). Although the scientific rationale behind the use of Dara in combination with IMiDs has been extensively explored, the molecular mechanisms underlying Dara-PI regimens have not yet been investigated. Here, we demonstrate that CD38 on the surface of MM cells is rapidly internalized after Dara treatment; we also show that Dara treatment impairs MM cell adhesion, an effect that can be rescued by using the endocytosis inhibitor Dynasore. Finally, we show that Dara potentiates bortezomib (BTZ) killing of MM cells in vitro and in vivo, independent of its function as an immune activator. In conclusion, our data show that Dara impairs MM cell adhesion, which results in an increased sensitivity of MM to proteasome inhibition.

New role of hypoxia in pathophysiology of multiple myeloma through miR-210

Bone is one of the most common sites of complication in multiple myeloma (MM) progression and bone remodeling gets definitively perturbed during disease progression. Hypoxia and miR-210 play an important role in hematological malignancies. In an attempt to elucidate the specificity of the pathways of hypoxia and miR-210 in suppression of osteoblastic differentiation in MM patients, we examined the effect of miR-210 and hypoxia on expression of important cytokines and genes of myeloma cells. Differentiation of BM-MSCs towards osteoblastic cells in response to microvesicles (MVs) was also investigated. Finally, we proposed a molecular model on how HIF-1α may promote bone lesions in MM patients. To validate the effect of miR-210 and HIF-1α on targeted genes, the shRNA of HIF-1α and off-hsa-miR-210 were transfected into RPMI-8226 cells. BM-MSCs were cultured in osteoblastic inducer and 50 µg/mL of MVs derived from both hypoxic and normoxic myeloma cells. We designed an in vitro study to establish the effects of HIF-1α and miR-210 on the crosstalk between MM and osteoblasts. We here showed that hypoxia-induced miR-210 increased the mRNA expression of VLA-4, CXCR4, IL-6 and TGF-β in myeloma cells. MiR-210 is mandatory for the hypoxia-increased resistance of MM cells to melphalan. Moreover, MVs derived from hypoxic myeloma cells substantially decreased osteoblast differentiation. Considered comprehensively, our findings explain one of the reasons of bone loss that occurs at the sites of MM and a nascent crosstalk model in MM pathogenesis.

Hierarchical Involvement of Myeloid-Derived Suppressor Cells and Monocytes Expressing Latency-Associated Peptide in Plasma Cell Dyscrasias

Objective:

Plasma cell dyscrasias (PCDs) are disorders of plasma cells having in common the production of a monoclonal M-protein. They include a spectrum of conditions that may represent a natural progression of the same disease from monoclonal gammopathy of unknown significance to asymptomatic and symptomatic multiple myeloma, plasma cell leukemia, and Waldenström’s macroglobulinemia. In PCDs, the immune system is actively suppressed through the secretion of suppressive factors and the recruitment of immune suppressive subpopulations. In this study, we examined the expression of two subpopulations of cells with immunosuppressive activity, monocytic myeloid-derived suppressor cells (MDSCs) and monocytes expressing latency-associated peptide (LAP), in patients with different PCDs and in healthy volunteers.

Materials and Methods:

A total of 27 consecutive patients with PCDs were included in this study. Nineteen healthy volunteers served as controls.

Results:

We observed a hierarchical correlation between disease activity and the presence of monocytes with immunosuppressive activity.

Conclusion:

These results suggest that MDSCs and monocytes expressing LAP have diverging roles in PCDs and may perhaps serve as biomarkers of tumor activity and bulk.

Role of the Bone Microenvironment in the Development of Painful Complications of Skeletal Metastases

Cancer-induced bone pain (CIBP) is the most common and painful complication in patients with bone metastases. It causes a significant reduction in patient quality of life. Available analgesic treatments for CIBP, such as opioids that target the central nervous system, come with severe side effects as well as the risk of abuse and addiction. Therefore, alternative treatments for CIBP are desperately needed. Although the exact mechanisms of CIBP have not been fully elucidated, recent studies using preclinical models have demonstrated the role of the bone marrow microenvironment (e.g., osteoclasts, osteoblasts, macrophages, mast cells, mesenchymal stem cells, and fibroblasts) in CIBP development. Several clinical trials have been performed based on these findings. CIBP is a complex and challenging condition that currently has no standard effective treatments other than opioids. Further studies are clearly warranted to better understand this painful condition and develop more effective and safer targeted therapies.

Daratumumab augments alloreactive natural killer cell cytotoxicity towards CD38+ multiple myeloma cell lines in a biochemical context mimicking tumour microenvironment conditions

Natural killer (NK) cell-based immunotherapy is a promising novel approach to treat cancer. However, NK cell function has been shown to be potentially diminished by factors common in the tumor microenvironment (TME). In this study, we assessed the synergistic potential of antibody-dependent cell-mediated cytotoxicity (ADCC) and killer immunoglobin-like receptor (KIR)-ligand mismatched NK cells to potentiate NK cell antitumor reactivity in multiple myeloma (MM). Hypoxia, lactate, prostaglandin E2 (PGE2) or combinations were selected to mimic the TME. To investigate this, NK cells from healthy donors were isolated and NK cell ADCC capacity in response to MM cells was assessed in flow cytometry-based cytotoxicity and degranulation (CD107a) assays in the presence of TME factors. Hypoxia, lactate and PGE2 reduced cytotoxicity of NK cells against myeloma target cells. The addition of daratumumab (anti-CD38 antibody) augmented NK-cell cytotoxicity against target cells expressing high CD38, but not against CD38 low or negative target cells also in the presence of TME. Co-staining for inhibitory KIRs and NKG2A demonstrated that daratumumab enhanced degranulation of all NK cell subsets. Nevertheless, KIR-ligand mismatched NK cells were slightly better effector cells than KIR-ligand matched NK cells. In summary, our study shows that combination therapy using strategies to maximize activating NK cell signaling by triggering ADCC in combination with an approach to minimize inhibitory signaling through a selection of KIR-ligand mismatched donors, can help to overcome the NK-suppressive TME. This can serve as a platform to improve the clinical efficacy of NK cells.

Granulocyte-like myeloid derived suppressor cells (G-MDSC) are increased in multiple myeloma and are driven by dysfunctional mesenchymal stem cells (MSC)

Granulocytic-Myeloid-derived suppressor cells (G-MDSC) are increased in Multiple Myeloma (MM) patients but the mechanisms of G-MDSC generation are still unknown. There are many evidences of the role of mesenchymal stem cells (MSC) in promoting MM cell growth, survival and drug-resistance. We here used a specific experimental model in vitro to evaluate the ability of MSC to induce G-MDSC. We found that although MSC derived from healthy donors (HD), MGUS and MM were able to generate the same amount of MDSC, only MM-MSC-educated G-MDSC exhibited suppressive ability. In addition, in comparison with MSC derived from HD, MM-MSC produce higher amount of immune-modulatory factors that could be involved in MDSC induction. Compared to G-MDSC obtained from co-culture models with MSC from healthy subjects, both MGUS and MM-MSC-educated G-MDSC showed increase of immune-modulatory factors. However, only MM-MSC educated G-MDSC 1) up-regulated immune-suppressive factors as ARG1 and TNFα, 2) expressed higher levels of PROK2, important in angiogenesis and inflammatory process, and 3) showed ability to digest bone matrix.Our data demonstrate that MM-MSC are functionally different from healthy subjects and MGUS-MSC, supporting an evolving concept regarding the contribution of MM-MSC to tumor development and progression.

Hypoxia promotes IL-32 expression in myeloma cells, and high expression is associated with poor survival and bone loss

Multiple myeloma (MM) is a hematologic cancer characterized by expansion of malignant plasma cells in the bone marrow. Most patients develop an osteolytic bone disease, largely caused by increased osteoclastogenesis. The myeloma bone marrow is hypoxic, and hypoxia may contribute to MM disease progression, including bone loss. Here we identified interleukin-32 (IL-32) as a novel inflammatory cytokine expressed by a subset of primary MM cells and MM cell lines. We found that high IL-32 gene expression in plasma cells correlated with inferior survival in MM and that IL-32 gene expression was higher in patients with bone disease compared with those without. IL-32 was secreted from MM cells in extracellular vesicles (EVs), and those EVs, as well as recombinant human IL-32, promoted osteoclast differentiation both in vitro and in vivo. The osteoclast-promoting activity of the EVs was IL-32 dependent. Hypoxia increased plasma-cell IL-32 messenger RNA and protein levels in a hypoxia-inducible factor 1α-dependent manner, and high expression of IL-32 was associated with a hypoxic signature in patient samples, suggesting that hypoxia may promote expression of IL-32 in MM cells. Taken together, our results indicate that targeting IL-32 might be beneficial in the treatment of MM bone disease in a subset of patients.

Contextual tumor suppressor function of T cell death-associated gene 8 (TDAG8) in hematological malignancies

Background

Extracellular acidosis is a condition found within the tumor microenvironment due to inadequate blood perfusion, hypoxia, and altered tumor cell metabolism. Acidosis has pleiotropic effects on malignant progression; therefore it is essential to understand how acidosis exerts its diverse effects. TDAG8 is a proton-sensing G-protein-coupled receptor that can be activated by extracellular acidosis.

Methods

TDAG8 gene expression was analyzed by bioinformatic analyses and quantitative RT-PCR in human hematological malignancies. Retroviral transduction was used to restore TDAG8 expression in U937, Ramos and other blood cancer cells. Multiple in vitro and in vivo tumorigenesis and metastasis assays were employed to evaluate the effects of TDAG8 expression on blood cancer progression. Western blotting, immunohistochemistry and biochemical approaches were applied to elucidate the underlying mechanisms associated with the TDAG8 receptor pathway.

Results

TDAG8 expression is significantly reduced in human blood cancers in comparison to normal blood cells. Severe acidosis, pH 6.4, inhibited U937 cancer cell proliferation while mild acidosis, pH 6.9, stimulated its proliferation. However, restoring TDAG8 gene expression modulated the U937 cell response to mild extracellular acidosis and physiological pH by reducing cell proliferation. Tumor xenograft experiments further revealed that restoring TDAG8 expression in U937 and Ramos cancer cells reduced tumor growth. It was also shown U937 cells with restored TDAG8 expression attached less to Matrigel, migrated slower toward a chemoattractant, and metastasized less in severe combined immunodeficient mice. These effects correlated with a reduction in c-myc oncogene expression. The mechanistic investigation indicated that Gα13/Rho signaling arbitrated the TDAG8-mediated c-myc oncogene repression in response to acidosis.

Conclusions

This study provides data to support the concept that TDAG8 functions as a contextual tumor suppressor down-regulated in hematological malignancies and potentiation of the TDAG8 receptor pathway may be explored as a potential anti-tumorigenic approach in blood cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1305-6) contains supplementary material, which is available to authorized users.

Multiple myeloma

Multiple myeloma is a malignancy of terminally differentiated plasma cells, and patients typically present with bone marrow infiltration of clonal plasma cells and monoclonal protein in the serum and/or urine. The diagnosis of multiple myeloma is made when clear end-organ damage attributable to the plasma cell proliferative disorder or when findings that suggest a high likelihood of their development are present. Distinguishing symptomatic multiple myeloma that requires treatment from the precursor stages of monoclonal gammopathy of undetermined significance and smouldering multiple myeloma is important, as observation is the standard for those conditions. Much progress has been made over the past decade in the understanding of disease biology and individualized treatment approaches. Several new classes of drugs, such as proteasome inhibitors and immunomodulatory drugs, have joined the traditional armamentarium (corticosteroids, alkylating agents and anthracyclines) and, along with high-dose therapy and autologous haemopoietic stem cell transplantation, have led to deeper and durable clinical responses. Indeed, an increasing proportion of patients are achieving lasting remissions, raising the possibility of cure for this disease. Success will probably depend on using combinations of effective agents and treating patients in the early stages of disease, such as patients with smouldering multiple myeloma.

Pharmacokinetic study of bortezomib administered intravenously in Taiwanese patients with multiple myeloma

This phase 4, single-arm, non-randomized, open-label, post approval commitment study evaluated the pharmacokinetics and safety of bortezomib in Taiwanese patients with multiple myeloma. Patients (≥20 years) with measurable secretory multiple myeloma (serum monoclonal IgG ≥10, IgA/IgE ≥5, IgD ≥0.5 g/L, IgM present [regardless of level], and urine M protein of ≥200 mg/24 h) received intravenous bortezomib 1.3 mg/m² , twice weekly for 2 weeks, followed by a 10-day resting phase (days 12 to 21). Pharmacokinetics and safety were assessed at pre-specified time points. All enrolled patients (n = 18, men: 11; women: 7) completed the study. Mean (SD) C_max (maximum observed plasma concentration) on day 11 was 266 (77.5) ng/mL, approximately 60% higher compared with non-Asian patients receiving a similar bortezomib regimen but with overlapping ranges. Because of the protracted terminal phase, half-life (t_1/2 ), area under the plasma concentration-time curve from time 0 to infinity (AUC_∞ ), volume of distribution (V_z ), and systemic clearance were not assessable. All patients experienced treatment-emergent adverse events (TEAEs); 78% were drug-related. Most commonly reported TEAEs were thrombocytopenia (n = 11 [61%]), neutropenia (n = 9 [50%]), leukopenia (n = 6 [33%]), and diarrhoea (n = 6 [33%]); the most common serious adverse event was pneumonia (n = 2 [11%]). One patient had a dose reduction due to a TEAE of thrombocytopenia. Overall, bortezomib exposure (AUC) in Taiwanese patients (AUC_last [SD]: 230 [147] ng·h/mL) with twice weekly intravenous administration was comparable with non-Asian population (AUC_last [SD]: 241 [82] ng·h/mL). Bortezomib treatment was associated with manageable toxicity profile and did not limit the continuity of therapy.

Exosomes promote bone marrow angiogenesis in hematologic neoplasia: the role of hypoxia

PURPOSE OF REVIEW

To review the data on angiogenesis related to exosomes secreted by tumor cells in hematologic neoplasia and to elucidate the role of exosomes and exosomal miRNA in the bone marrow microenvironment, especially under hypoxic conditions.

RECENT FINDINGS

Cross-talk between bone marrow tumor cells and surrounding cells, including endothelial cells, is important for tumor growth in hematologic neoplasia. In addition to conventional signaling pathways, exosomes, which are small endosome-derived vesicles containing miRNAs, can help to modulate the microenvironment without directly contacting nontumorous cells. The human myeloid leukemia cell line K562 secretes exosomes containing a large amount of miR-92a that enhances angiogenesis under normoxic and hypoxic conditions. With chronic hypoxia, exosomes secreted by multiple myeloma cells also enhance angiogenesis by targeting factor-inhibiting hypoxia-inducible factor-1 via miR-135b.

SUMMARY

Intercellular communication between tumor cells and a heterogeneous population of bone marrow stromal cells is mediated by exosomes containing various functional proteins, mRNA, and miRNA. Hypoxia is a major regulator of exosomal content and affects angiogenesis in various types of hematologic neoplasia. Functional analysis of exosomes and exosome-mediated cell-cell interactions not only clarifies molecular pathogenesis but also suggests new treatment strategies for hematologic neoplasia through targeting exosomes.

A novel hypoxia-selective epigenetic agent RRx-001 triggers apoptosis and overcomes drug resistance in multiple myeloma cells

The hypoxic bone-marrow (BM) microenvironment confers growth/survival and drug-resistance in multiple myeloma (MM) cells. Novel therapies targeting the MM cell in its hypoxic-BM milieu may overcome drug resistance. Recent studies led to the development of a novel molecule RRx-001 with hypoxia-selective epigenetic and Nitric Oxide-donating properties. Here we demonstrate that RRx-001 decreases the viability of MM cell lines and primary patient cells, as well as overcomes drug-resistance. RRx-001 inhibits MM cell growth in the presence of BM stromal cells. RRx-001 induced apoptosis is associated with: 1) activation of caspases; 2) release of ROS and nitrogen-species; 3) induction of DNA damage via ATM/γ-H2AX; and 4) decrease in DNA methytransferase (DNMT) and global methylation. RNA interference study shows a predominant role of DNMT1 in MM cell survival versus DNMT3a or DNMT3b. Deubiquitylating enzyme USP7 stimulates DNMT1 activity; and conversely, USP7-siRNA reduced DNMT1 activity and decreased MM cell viability. RRx-001 plus USP7 inhibitor P5091 triggered synergistic anti-MM activity. MM xenograft studies show that RRx-001 is well tolerated, inhibits tumor growth, and enhances survival. Combining RRx-001 with pomalidomide, bortezomib or SAHA induces synergistic anti-MM activity. Our results provide the rationale for translation of RRx-001, either alone or in combination, to clinical evaluation in MM.

Chetomin, targeting HIF-1α/p300 complex, exhibits antitumour activity in multiple myeloma

Background:

Multiple myeloma (MM) is an incurable clonal plasma cell malignancy. The constitutive expression of HIF-1α in MM suggests that inhibition of HIF-1α-mediated transcription represents an interesting target in MM.

Methods:

As p300 is a crucial co-activator of hypoxia-inducible transcription, disrupting the complex HIF-1α/p300 to target HIF activity appears to be an attractive strategy.

Results:

We reported that chetomin, an inhibitor of HIF-1α/p300 interaction, exhibits antitumour activity in human myeloma cell lines and primary MM cells from patients.

Conclusions:

Our data suggest that chetomin may be of clinical value in MM and especially for patients characterised by a high EP300/HIF-1α expression and a poor prognosis.

Signaling Interplay between Bone Marrow Adipose Tissue and Multiple Myeloma cells

In the year 2000, Hanahan and Weinberg (1) defined the six Hallmarks of Cancer as: self-sufficiency in growth signals, evasion of apoptosis, insensitivity to antigrowth mechanisms, tissue invasion and metastasis, limitless replicative potential, and sustained angiogenesis. Eleven years later, two new Hallmarks were added to the list (avoiding immune destruction and reprograming energy metabolism) and two new tumor characteristics (tumor-promoting inflammation and genome instability and mutation) (2). In multiple myeloma (MM), a destructive cancer of the plasma cell that grows predominantly in the bone marrow (BM), it is clear that all these hallmarks and characteristics are in play, contributing to tumor initiation, drug resistance, disease progression, and relapse. Bone marrow adipose tissue (BMAT) is a newly recognized contributor to MM oncogenesis and disease progression, potentially affecting MM cell metabolism, immune action, inflammation, and influences on angiogenesis. In this review, we discuss the confirmed and hypothetical contributions of BMAT to MM development and disease progression. BMAT has been understudied due to technical challenges and a previous lack of appreciation for the endocrine function of this tissue. In this review, we define the dynamic, responsive, metabolically active BM adipocyte. We then describe how BMAT influences MM in terms of: lipids/metabolism, hypoxia/angiogenesis, paracrine or endocrine signaling, and bone disease. We then discuss the connection between BMAT and systemic inflammation and potential treatments to inhibit the feedback loops between BM adipocytes and MM cells that support MM progression. We aim for researchers to use this review to guide and help prioritize their experiments to develop better treatments or a cure for cancers, such as MM, that associate with and may depend on BMAT.

Systemic modeling myeloma-osteoclast interactions under normoxic/hypoxic condition using a novel computational approach

Interaction of myeloma cells with osteoclasts (OC) can enhance tumor cell expansion through activation of complex signaling transduction networks. Both cells reside in the bone marrow, a hypoxic niche. How OC-myeloma interaction in a hypoxic environment affects myeloma cell growth and their response to drug treatment is poorly understood. In this study, we i) cultured myeloma cells in the presence/absence of OCs under normoxia and hypoxia conditions and did protein profiling analysis using reverse phase protein array; ii) computationally developed an Integer Linear Programming approach to infer OC-mediated myeloma cell-specific signaling pathways under normoxic and hypoxic conditions. Our modeling analysis indicated that in the presence OCs, (1) cell growth-associated signaling pathways, PI3K/AKT and MEK/ERK, were activated and apoptotic regulatory proteins, BAX and BIM, down-regulated under normoxic condition; (2) β1 Integrin/FAK signaling pathway was activated in myeloma cells under hypoxic condition. Simulation of drug treatment effects by perturbing the inferred cell-specific pathways showed that targeting myeloma cells with the combination of PI3K and integrin inhibitors potentially (1) inhibited cell proliferation by reducing the expression/activation of NF-κB, S6, c-Myc, and c-Jun under normoxic condition; (2) blocked myeloma cell migration and invasion by reducing the expression of FAK and PKC under hypoxic condition.

Concise review: Defining and targeting myeloma stem cell-like cells

Multiple myeloma (MM) remains incurable despite recent advances in the treatment of MM. Although the idea of MM cancer stem cells (CSCs) has been proposed for the drug resistance in MM, MM CSCs have not been properly defined yet. Besides clonotypic B cells, phenotypically distinct MM plasma cell fractions have been demonstrated to possess a clonogenic capacity, leading to long-lasting controversies regarding the cells of origin in MM or MM-initiating cells. However, MM CSCs may not be a static population and survive as phenotypically and functionally different cell types via the transition between stem-like and non-stem-like states in local microenvironments, as observed in other types of cancers. Targeting MM CSCs is clinically relevant, and different approaches have been suggested to target molecular, metabolic and epigenetic signatures, and the self-renewal signaling characteristic of MM CSC-like cells.

Exosomal miR-135b shed from hypoxic multiple myeloma cells enhances angiogenesis by targeting factor-inhibiting HIF-1

Exosomes are small endosome-derived vesicles containing a wide range of functional proteins, mRNA, and miRNA. Exosomal miRNA from cancer cells helps modulate the microenvironment. In multiple myeloma (MM), the massive proliferation of malignant plasma cells causes hypoxia. To date, the majority of in vitro hypoxia studies of cancer cells have used acute hypoxic exposure (3-24 hours). Thus, we attempted to clarify the role of MM-derived exosomes in hypoxic bone marrow by using MM cells grown continuously in vitro under chronic hypoxia (hypoxia-resistant MM [HR-MM] cells). The HR-MM cells produced more exosomes than the parental cells under normoxia or acute hypoxia conditions, and miR-135b was significantly upregulated in exosomes from HR-MM cells. Exosomal miR-135b directly suppressed its target factor-inhibiting hypoxia-inducible factor 1 (FIH-1) in endothelial cells. Finally, exosomal miR-135b from HR-MM cells enhanced endothelial tube formation under hypoxia via the HIF-FIH signaling pathway. This in vitro HR myeloma cell model will be useful for investigating MM cell-endothelial cell interactions under hypoxic conditions, which may mimic the in vivo bone marrow microenvironment. Although tumor angiogenesis is regulated by various factors, exosomal miR-135b may be a target for controlling MM angiogenesis.

Cancer associated fibroblasts and tumor growth: focus on multiple myeloma

Cancer associated fibroblasts (CAFs) comprise a heterogeneous population that resides within the tumor microenvironment. They actively participate in tumor growth and metastasis by production of cytokines and chemokines, and the release of pro-inflammatory and pro-angiogenic factors, creating a more supportive microenvironment. The aim of the current review is to summarize the origin and characteristics of CAFs, and to describe the role of CAFs in tumor progression and metastasis. Furthermore, we focus on the presence of CAFs in hypoxic conditions in relation to multiple myeloma disease.

Immunological dysregulation in multiple myeloma microenvironment

Multiple Myeloma (MM) is a systemic hematologic disease due to uncontrolled proliferation of monoclonal plasma cells (PC) in bone marrow (BM). Emerging in other solid and liquid cancers, the host immune system and the microenvironment have a pivotal role for PC growth, proliferation, survival, migration, and resistance to drugs and are responsible for some clinical manifestations of MM. In MM, microenvironment is represented by the cellular component of a normal bone marrow together with extracellular matrix proteins, adhesion molecules, cytokines, and growth factors produced by both stromal cells and PC themselves. All these components are able to protect PC from cytotoxic effect of chemo- and radiotherapy. This review is focused on the role of immunome to sustain MM progression, the emerging role of myeloid derived suppressor cells, and their potential clinical implications as novel therapeutic target.

Plasma cell formation, secretion, and persistence: the short and the long of it

B cells can be activated by cognate antigen, anti-B-cell receptor antibody, complement receptors, or polyclonal stimulators like lipopolysaccharide; the overall result is a large shift in RNA processing to the secretory-specific form of immunoglobulin (Ig) heavy chain mRNA and an upregulation of Igh mRNA amounts. Associated with this shift is the large-scale induction of Ig protein synthesis and the unfolded protein response to accommodate the massive quantity of secretory Ig that results. Stimulation to secretion also produces major structural accommodations and stress, with extensive generation of endoplasmic reticulum and Golgi as part of the cellular architecture. Reactive oxygen species can lead to either activation or apoptosis based on context and the high or low oxygen tension surrounding the cells. Transcription elongation factor ELL2 plays an important role in the induction of Ig secretory mRNA production, the unfolded protein response, and gene expression during hypoxia. After antigen stimulation, activated B cells from either the marginal zones or follicles can produce short-lived antibody secreting cells; it is not clear whether cells from both locations can become long-lived plasma cells. Autophagy is necessary for plasma cell long-term survival through the elimination of some of the accumulated damage to the ER from producing so much protein. Survival signals from the bone marrow stromal cells also contribute to plasma cell longevity, with BCMA serving a potentially unique survival role. Integrating the various information pathways converging on the plasma cell is crucial to the development of their long-lived, productive immune response.

Synergistic induction of apoptosis in multiple myeloma cells by bortezomib and hypoxia-activated prodrug TH-302, in vivo and in vitro

Recently, we showed that hypoxia is a critical microenvironmental factor in multiple myeloma, and that the hypoxia-activated prodrug TH-302 selectively targets hypoxic multiple myeloma cells and improves multiple disease parameters in vivo. To explore approaches for sensitizing multiple myeloma cells to TH-302, we evaluated in this study the antitumor effect of TH-302 in combination with the clinically used proteasome inhibitor bortezomib. First, we show that TH-302 and bortezomib synergistically induce apoptosis in multiple myeloma cell lines in vitro. Second, we confirm that this synergism is related to the activation of caspase cascades and is mediated by changes of Bcl-2 family proteins. The combination treatment induces enhanced cleavage of caspase-3/8/9 and PARP, and therefore triggers apoptosis and enhances the cleavage of proapoptotic BH3-only protein BAD and BID as well as the antiapoptotic protein Mcl-1. In particular, TH-302 can abrogate the accumulation of antiapoptotic Mcl-1 induced by bortezomib, and decreases the expression of the prosurvival proteins Bcl-2 and Bcl-xL. Furthermore, we found that the induction of the proapoptotic BH3-only proteins PUMA (p53-upregulated modulator of apoptosis) and NOXA is associated with this synergism. In response to the genotoxic and endoplasmic reticulum stresses by TH-302 and bortezomib, the expression of PUMA and NOXA were upregulated in p53-dependent and -independent manners. Finally, in the murine 5T33MMvv model, we showed that the combination of TH-302 and bortezomib can improve multiple disease parameters and significantly prolong the survival of diseased mice. In conclusion, our studies provide a rationale for clinical evaluation of the combination of TH-302 and bortezomib in patients with multiple myeloma.