The role of the bone microenvironment in the pathophysiology and therapeutic management of multiple myeloma: interplay of growth factors, their receptors and stromal interactions

TGF-β: an active participant in the immune and metabolic microenvironment of multiple myeloma : TGF-β in the microenvironment of multiple myeloma

Although substantial quantities of potent therapies for multiple myeloma (MM) have been established, MM remains an incurable disease. In recent years, our understanding of the initiation, development, and metastasis of cancers has made a qualitative leap. Cancers attain the abilities to maintain proliferation signals, escape growth inhibitors, resist cell death, induce angiogenesis, and more importantly, escape anti-tumor immunity and reprogram metabolism, which are the hallmarks of cancers. Besides, different cancers have different tumor microenvironments (TME), thus, we pay more attention to the TME in the pathogenesis of MM. Many researchers have identified that myeloma cells interact with the components of TME, which is beneficial for their survival, ultimately causing the formation of immunosuppressive and high-metabolism TME. In the process, transforming growth factor-β (TGF-β), as a pivotal cytokine in the TME, controls various cells' fates and influences numerous metabolic pathways, including inhibiting immune cells to infiltrate the tumors, suppressing the activation of anti-tumor immune cells, facilitating more immunosuppressive cells, enhancing glucose and glutamine metabolism, dysregulating bone metabolism and so on. Thus, we consider TGF-β as the tumor promoter. However, in healthy cells and the early stage of tumors, it functions as a tumor suppressor. Due to the effect of context dependence, TGF-β has dual roles in TME, which attracts us to further explore whether targeting it can overcome obstacles in the treatment of MM by regulating the progression of myeloma, molecular mechanisms of drug resistance, and various signaling pathways in the immune and metabolic microenvironment. In this review, we predominantly discuss that TGF-β promotes the development of MM by influencing immunity and metabolism.

Association of Thrombocytopenia With Disease Burden, High-Risk Cytogenetics, and Survival in Newly Diagnosed Multiple Myeloma Patients Treated With Novel Therapies

BACKGROUND

The effect of thrombocytopenia has not been studied in the era of novel treatments in multiple myeloma (MM).

OBJECTIVE

To evaluate the clinical characteristics and outcomes in MM patients presenting with thrombocytopenia.

MATERIALS

Newly diagnosed MM patients between 2008 and 2018 who received at least 2 novel agents at induction. Thrombocytopenia was defined as a platelet count of less than < 150,000/mm3.

RESULTS

A total of 648 patients were identified. Thrombocytopenia was found in 120 patients (18.5%). Baseline disease characteristics associated with higher rates of thrombocytopenia at baseline included IgA myeloma, P < .01, ISS 3 versus 1 or 2, P < .01, R-ISS 3 versus 1 or 2, P < .01, renal failure (CrCl < 30 mL/min), P < .01, hypercalcemia (Ca > 11.5 mg/dL), P < .01, elevated LDH, P < .03, anemia (Hb < 10 g/dL), P < .01, higher serum monoclonal protein, P < .02, and > 60% plasma cells in the bone marrow, P < .01. Thrombocytopenia was more prevalent across patients with t(4;14) and t(14;16), but was not associated with an overall high-risk fluorescence in situ hybridization (FISH) classification. Median OS was significantly lower among patients with thrombocytopenia (64.4 vs. 145.0 months, P < .01). In multivariable Cox regression, thrombocytopenia was associated with mortality (HR = 2.45, 95% CI, 1.7-3.6) independently of age, sex, high-risk FISH, ISS stage, response at induction, percentage of plasma cells in the BM, and anemia.

CONCLUSION

We found that thrombocytopenia was seen among one-fifth of MM patients and was more common in patients with (t[4; 14] and t[14; 16]). Thrombocytopenia had an independent association with worse survival.

Inhibition of VCP modulates NF-κB signaling pathway to suppress multiple myeloma cell proliferation and osteoclast differentiation

Multiple myeloma (MM) is the second most common hematological malignancy, in which the dysfunction of the ubiquitin-proteasome pathway is associated with the pathogenesis. The valosin containing protein (VCP)/p97, a member of the AAA+ ATPase family, possesses multiple functions to regulate the protein quality control including ubiquitin-proteasome system and molecular chaperone. VCP is involved in the occurrence and development of various tumors while still elusive in MM. VCP inhibitors have gradually shown great potential for cancer treatment. This study aims to identify if VCP is a therapeutic target in MM and confirm the effect of a novel inhibitor of VCP (VCP20) on MM. We found that VCP was elevated in MM patients and correlated with shorter survival in clinical TT2 cohort. Silencing VCP using siRNA resulted in decreased MM cell proliferation via NF-κB signaling pathway. VCP20 evidently inhibited MM cell proliferation and osteoclast differentiation. Moreover, exosomes containing VCP derived from MM cells partially alleviated the inhibitory effect of VCP20 on cell proliferation and osteoclast differentiation. Mechanism study revealed that VCP20 inactivated the NF-κB signaling pathway by inhibiting ubiquitination degradation of IκBα. Furthermore, VCP20 suppressed MM cell proliferation, prolonged the survival of MM model mice and improved bone destruction in vivo. Collectively, our findings suggest that VCP is a novel target in MM progression. Targeting VCP with VCP20 suppresses malignancy progression of MM via inhibition of NF-κB signaling pathway.

Past, Present, and a Glance into the Future of Multiple Myeloma Treatment

Multiple myeloma (MM) is a challenging hematological cancer which typically grows in bone marrow. MM accounts for 10% of hematological malignancies and 1.8% of cancers. The recent treatment strategies have significantly improved progression-free survival for MM patients in the last decade; however, a relapse for most MM patients is inevitable. In this review we discuss current treatment, important pathways for proliferation, survival, immune suppression, and resistance that could be targeted for future treatments.

Metabolic cross-talk within the bone marrow milieu: focus on multiple myeloma

Cancer cells are well-known for their capacity to adapt their metabolism to their increasing energy demands which is necessary for tumor progression. This is no different for Multiple Myeloma (MM), a hematological cancer which develops in the bone marrow (BM), whereby the malignant plasma cells accumulate and impair normal BM functions. It has become clear that the hypoxic BM environment contributes to metabolic rewiring of the MM cells, including changes in metabolite levels, increased/decreased activity of metabolic enzymes and metabolic shifts. These adaptations will lead to a pro-tumoral environment stimulating MM growth and drug resistance In this review, we discuss the identified metabolic changes in MM and the BM microenvironment and summarize how these identified changes have been targeted (by inhibitors, genetic approaches or deprivation studies) in order to block MM progression and survival.

Nucleic Acid Biomarkers in Waldenström Macroglobulinemia and IgM-MGUS: Current Insights and Clinical Relevance

Waldenström Macroglobulinemia (WM) is an indolent lymphoplasmacytic lymphoma, characterized by the production of excess immunoglobulin M monoclonal protein. WM belongs to the spectrum of IgM gammopathies, ranging from asymptomatic IgM monoclonal gammopathy of undetermined significance (IgM-MGUS), through IgM-related disorders and asymptomatic WM to symptomatic WM. In recent years, its complex genomic and transcriptomic landscape has been extensively explored, hereby elucidating the biological mechanisms underlying disease onset, progression and therapy response. An increasing number of mutations, cytogenetic abnormalities, and molecular signatures have been described that have diagnostic, phenotype defining or prognostic implications. Moreover, cell-free nucleic acid biomarkers are increasingly being investigated, benefiting the patient in a minimally invasive way. This review aims to provide an extensive overview of molecular biomarkers in WM and IgM-MGUS, considering current shortcomings, as well as potential future applications in a precision medicine approach.

Deciphering mechanisms of immune escape to inform immunotherapeutic strategies in multiple myeloma

Multiple myeloma is an incurable cancer characterized by the uncontrolled growth of malignant plasma cells nurtured within a permissive bone marrow microenvironment. While patients mount numerous adaptive immune responses directed against their disease, emerging data demonstrate that tumor intrinsic and extrinsic mechanisms allow myeloma cells to subvert host immunosurveillance and resist current therapeutic strategies. Myeloma downregulates antigens recognized by cellular immunity and modulates the bone marrow microenvironment to promote uncontrolled tumor proliferation, apoptotic resistance, and further hamper anti-tumor immunity. Additional resistance often develops after an initial clinical response to small molecules, immune-targeting antibodies, immune checkpoint blockade or cellular immunotherapy. Profound quantitative and qualitative dysfunction of numerous immune effector cell types that confer anti-myeloma immunity further supports myelomagenesis, disease progression and the emergence of drug resistance. Identification of tumor intrinsic and extrinsic resistance mechanisms may direct the design of rationally-designed drug combinations that prevent or overcome drug resistance to improve patient survival. Here, we summarize various mechanisms of immune escape as a means to inform novel strategies that may restore and improve host anti-myeloma immunity.

Involvement of Alarmins in the Pathogenesis and Progression of Multiple Myeloma

OBJECTIVE

Multiple Myeloma (MM) is a haematological disease resulting from the neoplastic transformation of plasma cells. The uncontrolled growth of plasma cells in the bone marrow and the delivery of several cytokines causes bone erosion that often does not regress, even in the event of disease remission. MM is characterised by a multi-step evolutionary path, which starts with an early asymptomatic stage defined as monoclonal gammopathy of undetermined significance (MGUS) evolving to overt disease.

DATA SOURCES AND STUDY SELECTION

We have selected scientific publications on the specific topics "alarmis, MGUS, and MM", drawing from PubMed. The keywords we used were alarmines, MGUS, MM, and immune system.

RESULTS

The analysis confirms the pivotal role of molecules such as high-mobility group box-1, heat shock proteins, and S100 proteins in the induction of neoangiogenesis, which represents a milestone in the negative evolution of MM as well as other haematological and non-haematological tumours.

CONCLUSIONS

Modulation of the host immune system and the inhibition of neoangiogenesis may represent the therapeutic target for the treatment of MM that is capable of promoting better survival and reducing the risk of RRMM.

Extracellular Matrices and Cancer-Associated Fibroblasts: Targets for Cancer Diagnosis and Therapy?

Solid cancer progression is dictated by neoplastic cell features and pro-tumoral crosstalks with their microenvironment. Stroma modifications, such as fibroblast activation into cancer-associated fibroblasts (CAFs) and extracellular matrix (ECM) remodeling, are now recognized as critical events for cancer progression and as potential therapeutic or diagnostic targets. The recent appreciation of the key, complex and multiple roles of the ECM in cancer and of the CAF diversity, has revolutionized the field and raised innovative but challenging questions. Here, we rapidly present CAF heterogeneity in link with their specific ECM remodeling features observed in cancer, before developing each of the impacts of such ECM modifications on tumor progression (survival, angiogenesis, pre-metastatic niche, chemoresistance, etc.), and on patient prognosis. Finally, based on preclinical studies and recent results obtained from clinical trials, we highlight key mechanisms or proteins that are, or may be, used as potential therapeutic or diagnostic targets, and we report and discuss benefits, disappointments, or even failures, of recently reported stroma-targeting strategies.

The Role of Marrow Microenvironment in the Growth and Development of Malignant Plasma Cells in Multiple Myeloma

The development and effectiveness of novel therapies in multiple myeloma have been established in large clinical trials. However, multiple myeloma remains an incurable malignancy despite significant therapeutic advances. Accumulating data have elucidated our understanding of the genetic background of the malignant plasma cells along with the role of the bone marrow microenvironment. Currently, the interaction among myeloma cells and the components of the microenvironment are considered crucial in multiple myeloma pathogenesis. Adhesion molecules, cytokines and the extracellular matrix play a critical role in the interplay among genetically transformed clonal plasma cells and stromal cells, leading to the proliferation, progression and survival of myeloma cells. In this review, we provide an overview of the multifaceted role of the bone marrow microenvironment in the growth and development of malignant plasma cells in multiple myeloma.

Tumor Microenvironment Proteomics: Lessons From Multiple Myeloma

Although the "seed and soil" hypothesis was proposed by Stephen Paget at the end of the 19th century, where he postulated that tumor cells (seeds) need a propitious medium (soil) to be able to establish metastases, only recently the tumor microenvironment started to be more studied in the field of Oncology. Multiple myeloma (MM), a malignancy of plasma cells, can be considered one of the types of cancers where there is more evidence in the literature of the central role that the bone marrow (BM) microenvironment plays, contributing to proliferation, survival, migration, and drug resistance of tumor cells. Despite all advances in the therapeutic arsenal for MM treatment in the last years, the disease remains incurable. Thus, studies aiming a better understanding of the pathophysiology of the disease, as well as searching for new therapeutic targets are necessary and welcome. Therefore, the present study aimed to evaluate the protein expression profiling of mononuclear cells derived from BM of MM patients in comparison with these same cell types derived from healthy individuals, in order to fill this gap in MM treatment. Proteomic analysis was performed using the mass spectrometry technique and further analyses were done using bioinformatics tools, to identify dysregulated biological pathways and/or processes in the BM microenvironment of patients with MM as a result of the disease. Among the pathways identified in this study, we can highlight an upregulation of proteins related to protein biosynthesis, especially chaperone proteins, in patients with MM. Additionally, we also found an upregulation of several proteins involved in energy metabolism, which is one of the cancer hallmarks. Finally, with regard to the downregulated proteins, we can highlight mainly those involved in different pathways of the immune response, corroborating the data that has demonstrated that the immune system of MM is impaired and, therefore, the immunotherapies that have been studied recently for the treatment of the disease are extremely necessary in the search for a control and a cure for these patients who live with the disease.

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.

Targeted Disruption of Bone Marrow Stromal Cell-Derived Gremlin1 Limits Multiple Myeloma Disease Progression In Vivo

In most instances, multiple myeloma (MM) plasma cells (PCs) are reliant on factors made by cells of the bone marrow (BM) stroma for their survival and growth. To date, the nature and cellular composition of the BM tumor microenvironment and the critical factors which drive tumor progression remain imprecisely defined. Our studies show that Gremlin1 (Grem1), a highly conserved protein, which is abundantly secreted by a subset of BM mesenchymal stromal cells, plays a critical role in MM disease development. Analysis of human and mouse BM stromal samples by quantitative PCR showed that GREM1/Grem1 expression was significantly higher in the MM tumor-bearing cohorts compared to healthy controls (p < 0.05, Mann–Whitney test). Additionally, BM-stromal cells cultured with 5TGM1 MM PC line expressed significantly higher levels of Grem1, compared to stromal cells alone (p < 0.01, t-test), suggesting that MM PCs promote increased Grem1 expression in stromal cells. Furthermore, the proliferation of 5TGM1 MM PCs was found to be significantly increased when co-cultured with Grem1-overexpressing stromal cells (p < 0.01, t-test). To examine the role of Grem1 in MM disease in vivo, we utilized the 5TGM1/KaLwRij mouse model of MM. Our studies showed that, compared to immunoglobulin G (IgG) control antibody-treated mice, mice treated with an anti-Grem1 neutralizing antibody had a decrease in MM tumor burden of up to 81.2% (p < 0.05, two-way ANOVA). The studies presented here demonstrate, for the first time, a novel positive feedback loop between MM PCs and BM stroma, and that inhibiting this vicious cycle with a neutralizing antibody can dramatically reduce tumor burden in a preclinical mouse model of MM.

Transmembrane Activator and CAML Interactor (TACI): Another Potential Target for Immunotherapy of Multiple Myeloma?

Multiple myeloma (MM) has emerged as the next most likely oncological or hematological disease indication amenable for cellular immunotherapy. Much of the attention has been focused on B cell maturation antigen (BCMA) as a unique cell surface protein on myeloma cells that is available for monoclonal antibodies, antibody drug conjugates (ADCs), T-cell redirecting bispecific molecules, and chimeric antigen receptor (CAR) T cell targeting. BCMA is a member of the tumor necrosis factor receptor (TNFR) superfamily that binds two ligands B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) and mediates the growth and survival of plasma and MM cells. Interestingly, transmembrane activator and CAML interactor (TACI), another TNFR superfamily member, also binds the same ligands and plays largely overlapping roles as BCMA in normal plasma and malignant MM cells. In this article, we review the biology of TACI, focusing on its role in normal B and plasma cells and malignant MM cells, and also discuss various ways to incorporate TACI as a potential target for immunotherapies against MM.

Bone Marrow Stromal Cell-Derived IL-8 Upregulates PVR Expression on Multiple Myeloma Cells via NF-kB Transcription Factor

Bone marrow stromal cells (BMSCs) strongly contribute to multiple myeloma (MM) progression, promoting the survival and growth of malignant plasma cells (PCs). However, the possible impact of these cells on the immune-mediated recognition of MM cells remains largely unknown. DNAM-1 activating receptor plays a prominent role in NK cell anti-MM response engaging the ligands poliovirus receptor (PVR) and nectin-2 on malignant PCs. Here, we analysed the role of MM patient-derived BMSCs in the regulation of PVR expression. We found that BMSCs enhance PVR surface expression on MM cells and promote their NK cell-mediated recognition. PVR upregulation occurs at transcriptional level and involves NF-kB transcription factor activation by BMSC-derived soluble factors. Indeed, overexpression of a dominant-negative mutant of IKBα blocked PVR upregulation. IL-8 plays a prominent role in these mechanisms since blockade of CXCR1/2 receptors as well as depletion of the cytokine via RNA interference prevents the enhancement of PVR expression by BMSC-derived conditioned medium. Interestingly, IL-8 is associated with stromal microvesicles which are also required for PVR upregulation via CXCR1/CXCR2 signaling activation. Our findings identify BMSCs as regulators of NK cell anti-MM response and contribute to define novel molecular pathways involved in the regulation of PVR expression in cancer cells.

Bone Marrow-Derived Mesenchymal Stromal Cells: A Novel Target to Optimize Hematopoietic Stem Cell Transplantation Protocols in Hematological Malignancies and Rare Genetic Disorders

: Mesenchymal stromal cells (MSCs) are crucial elements in the bone marrow (BM) niche where they provide physical support and secrete soluble factors to control and maintain hematopoietic stem progenitor cells (HSPCs). Given their role in the BM niche and HSPC support, MSCs have been employed in the clinical setting to expand ex-vivo HSPCs, as well as to facilitate HSPC engraftment in vivo. Specific alterations in the mesenchymal compartment have been described in hematological malignancies, as well as in rare genetic disorders, diseases that are amenable to allogeneic hematopoietic stem cell transplantation (HSCT), and ex-vivo HSPC-gene therapy (HSC-GT). Dissecting the in vivo function of human MSCs and studying their biological and functional properties in these diseases is a critical requirement to optimize transplantation outcomes. In this review, the role of MSCs in the orchestration of the BM niche will be revised, and alterations in the mesenchymal compartment in specific disorders will be discussed, focusing on the need to correct and restore a proper microenvironment to ameliorate transplantation procedures, and more in general disease outcomes.

A review on tumor heterogeneity and evolution in multiple myeloma: pathological, radiological, molecular genetics, and clinical integration

Recent research has dramatically advanced our understanding of the genetic basis of multiple myeloma (MM). MM displays enormous inter- and intratumoral heterogeneity, and underlies a clonal evolutionary process driven and shaped by diverse factors such as clonal competition, tumor microenvironment, host immunity, and therapy. Two main cytogenetic groups are distinguished: MM with recurrent translocations involving the immunoglobulin heavy chain locus and MM with hyperdiploidy involving the odd chromosomes. The disease virtually always starts with a preneoplastic prodromal phase-monoclonal gammopathy of undetermined significance-that variably progresses to symptomatic MM within a few months or many years. Tumor heterogeneity and its evolution in space and time have important consequences for the clinical management and outcome of MM patients. At diagnosis, spatial intratumoral heterogeneity poses a challenge for classification and risk stratification. During maintenance therapy, clonal evolution may complicate disease monitoring and promote drug resistance. Upon progression or transformation, identifying the dominant disease-driving neoplastic clones and elucidating their properties are key to tailor personalized therapy. In this review, we discuss tumor heterogeneity and clonal evolution in MM, integrating pathological, radiological, molecular genetics, and clinical data. Current and prospective classification schemes and prognostic parameters, incorporating new genetic and proteomic discoveries and advances in imaging, are highlighted. In addition, the roles of the tumor microenvironment, host immunity, and resistance mutations, and their effects on therapy, are discussed. An improved understanding of high-risk disease, tumor heterogeneity, and clonal evolution will guide future therapies and may ultimately lead towards a cure 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.

The role of CD24 in multiple myeloma tumorigenicity and effects of the microenvironment on its expression

Multiple myeloma (MM) is an incurable neoplasm characterized by infiltration of malignant plasma cells (PCs). Recently, the tumor microenvironment has become of great interest in MM as it known to be involved in progression and metastasis of the disease. CD24, is an adhesion molecule expressed during B cell maturation, is down regulated through the cells differentiation into PCs. Though the role of CD24 in solid cancers is well defined, its role in MM remains unknown. We aimed to understand the involvement of CD24 in MM by up-regulating its expression on MM cell lines by co-culturing the cells with bone marrow stromal cell (BMSCs). We then studied the differences between CD24+ and CD24− MM cells and found that CD24+ MM cells presented a less tumorigenic phenotype by impaired capability to migrate and to create colonies as compared with CD24− MM cells. Furthermore, there were significantly more apoptotic cells in the CD24+ fraction. Additionally, the CD24+ cells also upregulated CXCR4 expression. The decrease tumorigenicity correlated with a “more normal” PC immunophenotype in patients with MM and correlated with CD45 expression and a stronger expression of CXCR4. In summary, we found the expression of CD24 on PCs to correlate with attenuated tumorigenicity.

Longitudinal preclinical magnetic resonance imaging of diffuse tumor burden in intramedullary myeloma following bortezomib therapy

Multiple myeloma (MM) is a largely incurable, debilitating hematologic malignancy of terminally differentiated plasma cells in the bone marrow (BM). Identification of therapeutic response is critical for improving outcomes and minimizing costs and off-target toxicities. To assess changes in BM environmental factors and therapy efficacy, there is a need for noninvasive, nonionizing, longitudinal, preclinical methods. Here, we demonstrate the feasibility of preclinical magnetic resonance imaging (MRI) for longitudinal imaging of diffuse tumor burden in a syngeneic, immunocompetent model of intramedullary MM. C57Bl/KaLwRij mice were implanted intravenously with 5TGM1-GFP tumors and treated with a proteasome inhibitor, bortezomib, or vehicle control. MRI was performed weekly with a Helmholtz radiofrequency coil placed on the hind leg. Mean normalized T1-weighted signal intensities and T2 relaxation times were quantified for each animal following manual delineation of BM regions in the femur and tibia. Finally, tumor burden was quantified for each tissue using hematoxylin and eosin staining. Changes in T2 relaxation times correlated strongly to cell density and overall tumor burden in the BM. Median T2 relaxation times and regional T1-weighted contrast uptake were shown to be most relevant in identifying posttherapy disease stage in this model of intramedullary MM. In summary, our results highlighted potential preclinical MRI markers for assessing tumor burden and BM heterogeneity following bortezomib therapy, and demonstrated the application of longitudinal imaging with preclinical MRI in an immunocompetent, intramedullary setting.

Monoclonal antibodies against RANKL and sclerostin for myeloma-related bone disease: can they change the standard of care?

Introduction: Over 80% of the patients with multiple myeloma (MM) develop myeloma bone disease (MBD) during the disease course. The clinical consequences include serious skeletal-related events (SRE) that impact survival and quality of life. Bisphosphonates are the mainstay in the treatment of MBD. Currently, new therapeutic strategies are being introduced and broaden the therapeutic options in MBD. Areas covered: The purpose of this review is to summarize the current clinical management of MBD and present novel data regarding monoclonal antibodies against the receptor activator of NF-kappa B ligand (RANKL) and sclerostin that may change the clinical practice. Expert opinion: Our better understanding of the pathophysiology of MBD has identified several factors as potential therapeutic targets. Recent data have shown that the RANKL inhibitor denosumab constitutes a new promising option. The non-inferiority compared with bisphosphonates in terms of SRE prevention, the potential survival benefit, the convenience of subcutaneous administration, and the favorable toxicity profile makes denosumab a valuable alternative for physicians in the current treatment of MBD. Anti-sclerostin antibodies are currently under clinical development. Further investigations are needed to address open questions in the field including the value of anabolic agents combined with anti-resorptive and anti-MM drugs in MBD.

Emerging Role of Mesenchymal Stromal Cell-Derived Extracellular Vesicles in Pathogenesis of Haematological Malignancies

Homoeostasis of bone marrow microenvironment depends on a precise balance between cell proliferation and death, which is supported by the cellular-extracellular matrix crosstalk. Multipotent mesenchymal stromal cells (MSC) are the key elements to provide the specialized bone marrow microenvironment by supporting, maintaining, and regulating the functions and fate of haematopoietic stem cells. Despite the great potential of MSC for cell therapy in several diseases due to their regenerative, immunomodulatory, and anti-inflammatory properties, they can also contribute to modulate tumor microenvironment. The extracellular vesicles that comprise exosomes and microvesicles are important mediators of intercellular communication due to their ability to change phenotype and physiology of different cell types. These vesicles may interact not only with neighbouring cells but also with cells from distant tissues to either maintain tissue homoeostasis or participate in disease pathogenesis. This review focuses on the current knowledge about the physiological role of MSC-extracellular vesicles, as well as their deregulation in haematological malignancies and their potential applications as biomarkers for diagnosis, progression, and treatment monitoring of such diseases.

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.

Effects of triptolide on bone marrow-derived mesenchymal stem cells from patients with multiple myeloma

Triptolide (TPL), an extract of the Chinese herb Tripterygium wilfordii Hook F, is a potent anti-inflammatory agent that further possesses anticancer activity. Its antiproliferative effects are well established. Only few studies have focused on TPL as a potential treatment in multiple myeloma (MM). In the current study, bone marrow-derived mesenchymal stem cells (BMMSCs) from patients with MM were isolated and treated with TPL at varying concentrations. Thalidomide is currently used as a positive control drug in the treatment of MM. Cell Counting kit-8 assays were performed to assess proliferation activity and flow cytometry with Annexin V-fluorescein/propidium iodide was used to detect cell apoptosis of TPL-treated BMMSCs. Reverse transcription-quantitative polymerase chain reaction assays were applied to measure interleukin (IL)-6, IL-1β and stem cell factor (SCF or Kit ligand) mRNA expression and western blot assays were performed to analyze transcription factor p65 (P65) expression in TPL-treated BMMSCs. ELISA was applied to measure vascular endothelial growth factor (VEGF) levels in the supernatant of the cultured and treated BMMSCs. TPL treatment significantly inhibited BMMSC proliferation compared with the untreated control (P<0.05). At 48 h following TPL treatment, a Cell Counting kit-8 study was performed and the IC₅₀ value was determined at 101.55±2.45 ng/ml. Apoptotic rates were observed to increase with increasing concentrations of TPL (P<0.001), and IL-6, IL-1β and SCF mRNA expression was significantly decreased with increasing TPL (P<0.001). P65 expression following TPL treatment was significantly decreased compared with the untreated control (P<0.05). VEGF levels were significantly reduced in the presence of increasing amounts of TPL (P<0.05). These findings suggest that TPL inhibited BMMSC growth and improved the bone marrow hematopoietic microenvironment by decreasing IL-6, IL-1β and SCF mRNA expression, subsequently inhibiting the proliferation of MM cells. Therefore, TPL may be used in the future to treat patients with MM.

Transcriptome Analysis of Mesenchymal Stem Cells from Multiple Myeloma Patients Reveals Downregulation of Genes Involved in Cell Cycle Progression, Immune Response, and Bone Metabolism

A growing body of evidence suggests a key role of tumor microenvironment, especially for bone marrow mesenchymal stem cells (MSC), in the maintenance and progression of multiple myeloma (MM), through direct and indirect interactions with tumor plasma cells. Thus, this study aimed to investigate the gene expression and functional alterations of MSC from MM patients (MM-MSC) in comparison with their normal counterparts from normal donors (ND-MSC). Gene expression analysis (Affymetrix) was performed in MM-MSC and ND-MSC after in vitro expansion. To validate these findings, some genes were selected to be evaluated by quantitative real time PCR (RT-qPCR), and also functional in vitro analyses were performed. We demonstrated that MM-MSC have a distinct gene expression profile than ND-MSC, with 485 differentially expressed genes (DEG) - 280 upregulated and 205 downregulated. Bioinformatics analyses revealed that the main enriched functions among downregulated DEG were related to cell cycle progression, immune response activation and bone metabolism. Four genes were validated by qPCR - ZNF521 and SEMA3A, which are involved in bone metabolism, and HLA-DRA and CHIRL1, which are implicated in the activation of immune response. Taken together, our results suggest that MM-MSC have constitutive abnormalities that remain present even in the absence of tumors cells. The alterations found in cell cycle progression, immune system activation, and osteoblastogenesis suggest, respectively, that MM-MSC are permanently dependent of tumor cells, might contribute to immune evasion and play an essential role in bone lesions frequently found in MM patients.

Liposomal dexamethasone inhibits tumor growth in an advanced human-mouse hybrid model of multiple myeloma

Glucocorticoids are the cornerstone in the clinic for treatment of hematological malignancies, including multiple myeloma. Nevertheless, poor pharmacokinetic properties of glucocorticoids require high and frequent dosing with the off-target adverse effects defining the maximum dose. Recently, nanomedicine formulations of glucocorticoids have been developed that improve the pharmacokinetic profile, limit adverse effects and improve solid tumor accumulation. Multiple myeloma is a hematological malignancy characterized by uncontrolled growth of plasma cells. These tumors initiate increased angiogenesis and microvessel density in the bone marrow, which might be exploited using nanomedicines, such as liposomes. Nano-sized particles can accumulate as a result of the increased vascular leakiness at the bone marrow tumor lesions. Pre-clinical screening of novel anti-myeloma therapeutics in vivo requires a suitable animal model that represents key features of the disease. In this study, we show that fluorescently labeled long circulating liposomes were found in plasma up to 24 h after injection in an advanced human-mouse hybrid model of multiple myeloma. Besides the organs involved in clearance, liposomes were also found to accumulate in tumor bearing human-bone scaffolds. The therapeutic efficacy of liposomal dexamethasone phosphate was evaluated in this model showing strong tumor growth inhibition while free drug being ineffective at an equivalent dose (4 mg/kg) regimen. The liposomal formulation slightly reduced total body weight of myeloma-bearing mice during the course of treatment, which appeared reversible when treatment was stopped. Liposomal dexamethasone could be further developed as monotherapy or could fit in with existing therapy regimens to improve therapeutic outcomes for multiple myeloma.

Liposomal drug delivery in an in vitro 3D bone marrow model for multiple myeloma

Purpose

Liposomal drug delivery can improve the therapeutic index of treatments for multiple myeloma. However, an appropriate 3D model for the in vitro evaluation of liposomal drug delivery is lacking. In this study, we applied a previously developed 3D bone marrow (BM) myeloma model to examine liposomal drug therapy.

Material and methods

Liposomes of different sizes (~75-200 nm) were tested in a 3D BM myeloma model, based on multipotent mesenchymal stromal cells, endothelial progenitor cells, and myeloma cells cocultured in hydrogel. The behavior and efficacy of liposomal drug therapy was investigated, evaluating the feasibility of testing liposomal drug delivery in 3D in vitro. Intracellular uptake of untargeted and integrin α₄β₁ (very late antigen-4) targeted liposomes was compared in myeloma and supporting cells, as well as the effectivity of free and liposome-encapsulated chemotherapy (bortezomib, doxorubicin). Either cocultured myeloma cell lines or primary CD138⁺ myeloma cells received the treatments.

Results

Liposomes (~75-110 nm) passively diffused throughout the heterogeneously porous (~80-850 nm) 3D hydrogel model after insertion. Cellular uptake of liposomes was observed and was increased by targeting very late antigen-4. Liposomal bortezomib and doxorubicin showed increased cytotoxic effects toward myeloma cells compared with the free drugs, using either a cell line or primary myeloma cells. Cytotoxicity toward supporting BM cells was reduced using liposomes.

Conclusion

The 3D model allows the study of liposome-encapsulated molecules on multiple myeloma and supporting BM cells, looking at cellular targeting, and general efficacy of the given therapy. The advantages of liposomal drug delivery were demonstrated in a primary myeloma model, enabling the study of patient-to-patient responses to potential drugs and treatment regimes.

Chemoresistance of Cancer Cells: Requirements of Tumor Microenvironment-mimicking In Vitro Models in Anti-Cancer Drug Development

For decades, scientists have been using two-dimensional cell culture platforms for high-throughput drug screening of anticancer drugs. Growing evidence indicates that the results of anti-cancer drug screening vary with the cell culture microenvironment, and this variation has been proposed as a reason for the high failure rate of clinical trials. Since the culture condition-dependent drug sensitivity of anti-cancer drugs may negatively impact the identification of clinically effective drug candidates, more reliable in vitro cancer platforms are urgently needed. In this review article, we provide an overview of how cell culture conditions can alter drug efficacy and highlight the importance of developing more reliable cancer drug testing platforms for use in the drug discovery process. The environmental factors that can alter drug delivery and efficacy are reviewed. Based on these observations of chemoresistant tumor physiology, we summarize the recent advances in the fabrication of in vitro cancer models and the model-dependent cytotoxicity of anti-cancer drugs, with a particular focus on engineered environmental factors in these platforms. It is believed that more physiologically relevant cancer models can revolutionize the drug discovery process.

Subclonal evolution in disease progression from MGUS/SMM to multiple myeloma is characterised by clonal stability

Multiple myeloma (MM) is a largely incurable haematological malignancy defined by the clonal proliferation of malignant plasma cells (PCs) within the bone marrow. Clonal heterogeneity has recently been established as a feature in MM, however, the subclonal evolution associated with disease progression has not been described. Here, we performed whole-exome sequencing of serial samples from 10 patients, providing new insights into the progression from monoclonal gammopathy of undetermined significance (MGUS) and smouldering MM (SMM), to symptomatic MM. We confirm that intraclonal genetic heterogeneity is a common feature at diagnosis and that the driving events involved in disease progression are more subtle than previously reported. We reveal that MM evolution is mainly characterised by the phenomenon of clonal stability, where the transformed subclonal PC populations identified at MM are already present in the asymptomatic MGUS/SMM stages. Our findings highlight the possibility that PC extrinsic factors may play a role in subclonal evolution and MGUS/SMM to MM progression.

How I treat the young patient with multiple myeloma

The treatment landscape for multiple myeloma has been transformed by the introduction of novel agents, including immunomodulatory drugs, proteasome inhibitors, and monoclonal antibodies. These have been shown to be more effective and generally better tolerated than conventional chemotherapy, with their introduction into clinical practice leading to improved survival. Furthermore, a better understanding of disease biology, improved diagnostic criteria, and the development of sensitive and specific tools for disease prognostication have contributed to better outcome. Treatment in the younger patient can now be individualized based on host and disease features with enhanced monitoring of response and use of high-sensitivity techniques for evaluating residual disease. The current standard of care has been significantly enhanced by novel agents with a paradigm shift toward optional or delayed autologous stem cell transplant as a reasonable choice in selected patients. Conversely, extended treatment with induction of remission followed by maintenance strategies is now a standard of care, conferring prolonged disease control with more manageable toxicities in both the short and long term, as well as improved quality of life.

Evaluation of in vitro effects of various targeted drugs on plasma cells and putative neoplastic stem cells in patients with multiple myeloma

Multiple myeloma (MM) is a malignancy characterized by monoclonal paraproteinemia and tissue plasmocytosis. In advanced MM cytopenia and osteopathy may occur. Although several effective treatment strategies have been developed in recent years, there is still a need to identify new drug targets and to develop more effective therapies for patients with advanced MM. We examined the effects of 15 targeted drugs on growth and survival of primary MM cells and 5 MM cell lines (MM.1S, NCI-H929, OPM-2, RPMI-8226, U-266). The PI3-kinase blocker BEZ235, the pan-BCL-2 inhibitor obatoclax, the Hsp90-targeting drug 17AAG, and the Polo-like kinase-1 inhibitor BI2536, were found to exert major growth-inhibitory effects in all 5 MM cell lines tested. Moreover, these drugs suppressed the in vitro proliferation of primary bone marrow-derived MM cells and induced apoptosis at pharmacologic drug concentrations. Apoptosis-inducing effects were not only seen in the bulk of MM cells but also in MM stem cell-containing CD138⁻/CD20⁺/CD27⁺ memory B-cell fractions. Synergistic growth-inhibitory effects were observed in MM cell lines using various drug combinations, including 17AAG+BI2536 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+BEZ235 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+obatoclax in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+BEZ235 in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+obatoclax in MM.1S, OPM-2 and RPMI-8226 cells, and BEZ235+obatoclax in MM.1S and RPMI-8226 cells. Together, our data show that various targeted drugs induce profound and often synergistic anti-neoplastic effects in MM cells which may have clinical implications and may contribute to the development of novel treatment strategies in advanced MM.

Biology and treatment of myeloma related bone disease

Myeloma bone disease (MBD) is the most common complication of multiple myeloma (MM), resulting in skeleton-related events (SREs) such as severe bone pain, pathologic fractures, vertebral collapse, hypercalcemia, and spinal cord compression that cause significant morbidity and mortality. It is due to an increased activity of osteoclasts coupled to the suppressed bone formation by osteoblasts. Novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition have recently been described, including the receptor activator of nuclear factor-kB ligand/osteoprotegerin pathway, activin-A and the wingless-type signaling inhibitors, dickkopf-1 (DKK-1) and sclerostin. These molecules interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma but also for the treatment of MM itself. Currently, bisphosphonates are the mainstay of the treatment of myeloma bone disease although several novel agents such as denosumab and sotatercept appear promising. This review focuses on recent advances in MBD pathophysiology and treatment, in addition to the established therapeutic guidelines.

Bone Marrow Stroma and Vascular Contributions to Myeloma Bone Homing

PURPOSE OF THE REVIEW

Herein we dissect mechanisms behind the dissemination of cancer cells from primary tumor site to the bone marrow, which are necessary for metastasis development, with a specific focus on multiple myeloma.

RECENT FINDINGS

The ability of tumor cells to invade vessels and reach the systemic circulation is a fundamental process for metastasis development; however, the interaction between clonal cells and the surrounding microenvironment is equally important for supporting colonization, survival, and growth in the secondary sites of dissemination. The intrinsic propensity of tumor cells to recognize a favorable milieu where to establish secondary growth is the basis of the "seed and soil" theory. This theory assumes that certain tumor cells (the "seeds") have a specific affinity for the milieu of certain organs (the "soil"). Recent literature has highlighted the important contributions of the vascular niche to the hospitable "soil" within the bone marrow. In this review, we discuss the crucial role of stromal cells and endothelial cells in supporting primary growth, homing, and metastasis to the bone marrow, in the context of multiple myeloma, a plasma cell malignancy with the unique propensity to primarily grow and metastasize to the bone marrow.

Mechanisms of bone destruction in multiple myeloma

Osteolytic bone disease is a frequent complication of multiple myeloma, resulting in skeletal complications that are a significant cause of morbidity and mortality. It is the result of an increased activity of osteoclasts, which is not followed by reactive bone formation by osteoblasts. Recent studies have revealed novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition. Among them, the most important include the receptor activator of nuclear factor-kappa B ligand/osteoprotegerin pathway, the macrophage inflammatory proteins and the activin-A that play a crucial role in osteoclast stimulation in myeloma, while the wingless-type (Wnt) signalling inhibitors (sclerostin and dickkopf-1) along with the growth factor independence-1 are considered the most important factors for the osteoblast dysfunction of myeloma patients. Finally, the role of osteocytes, which is the key cell for normal bone remodelling, has also revealed during the last years through their interaction with myeloma cells that leads to their apoptosis and the release of RANKL and sclerostin maintaining bone loss in these patients. This review focuses on the latest available data for the mechanisms of bone destruction in multiple myeloma.

Cutting edge genomics reveal new insights into tumour development, disease progression and therapeutic impacts in multiple myeloma

Multiple Myeloma (MM) is a haematological malignancy characterised by the clonal expansion of plasma cells (PCs) within the bone marrow. Despite advances in therapy, MM remains a largely incurable disease with a median survival of 6 years. In almost all cases, the development of MM is preceded by the benign PC condition Monoclonal Gammopathy of Undetermined Significance (MGUS). Recent studies show that the transformation of MGUS to MM is associated with complex genetic changes. Understanding how these changes contribute to evolution will present targets for clinical intervention. We discuss three models of MM evolution; the linear, the expansionist and the intraclonal heterogeneity models. Of particular interest is the intraclonal heterogeneity model. Here, distinct populations of MM PCs carry differing combinations of genetic mutations. Acquisition of additional mutations can contribute to subclonal lineages where "driver" mutations may influence selective pressure and dominance, and "passenger" mutations are neutral in their effects. Furthermore, studies show that clinical intervention introduces additional selective pressure on tumour cells and can influence subclone survival, leading to therapy resistance. This review discusses how Next Generation Sequencing approaches are revealing critical insights into the genetics of MM development, disease progression and treatment. MM disease progression will illuminate possible mechanisms underlying the tumour.

Abnormal repression of SHP-1, SHP-2 and SOCS-1 transcription sustains the activation of the JAK/STAT3 pathway and the progression of the disease in multiple myeloma

Sustained activation of JAK/STAT3 signaling pathway is classically described in Multiple Myeloma (MM). One explanation could be the silencing of the JAK/STAT suppressor genes, through the hypermethylation of SHP-1 and SOCS-1, previously demonstrated in MM cell lines or in whole bone marrow aspirates. The link between such suppressor gene silencing and the degree of bone marrow invasion or the treatment response has not been evaluated in depth. Using real-time RT-PCR, we studied the expression profile of three JAK/STAT suppressor genes: SHP-1, SHP-2 and SOCS-1 in plasma cells freshly isolated from the bone marrows of MM patients and healthy controls. Our data demonstrated an abnormal repression of such genes in malignant plasma cells and revealed a significant correlation between such defects and the sustained activation of the JAK/STAT3 pathway during MM. The repressed expression of SHP-1 and SHP-2 correlated significantly with a high initial degree of bone marrow infiltration but was, unexpectedly, associated with a better response to the induction therapy. Collectively, our data provide new evidences that substantiate the contribution of JAK/STAT suppressor genes in the pathogenesis of MM. They also highlight the possibility that the decreased gene expression of SHP-1 and SHP-2 could be of interest as a new predictive factor of a favorable treatment response, and suggest new potential mechanisms of action of the therapeutic molecules. Whether such defect helps the progression of the disease from monoclonal gammopathy of unknown significance to MM remains, however, to be determined.

Two diagnoses from bone marrow biopsy: multiple myeloma and Paget's disease of bone

Multiple myeloma and Paget's disease of bone show certain similarities such as increased osteoclastic activity and predilection to the axial skeleton. However, pathological and radiological changes of the bones are distinctive between multiple myeloma and Paget's disease of bone. This case report describes a patient who had a concomitant diagnosis of multiple myeloma and Paget's disease evidenced from bone marrow biopsy. Such a co-existence is rare, with only a few cases reported so far.

Cyclophilin A as a downstream effector of PI3K/Akt signalling pathway in multiple myeloma cells

Cyclophilin A (Cyp A), a member of the peptidyl-prolyl isomerase (PPI) family, may function as a molecular signalling switch. Comparative proteomic studies have identified Cyp A as a potential downstream target of protein kinase B (Akt). This study confirmed that Cyp A is a downstream effector of the phosphatidylinositide 3-kinase (PI3K)/Akt signalling pathway. Cyp A was highly phosphorylated in response to interleukin-6 treatment, which was consistent with the accumulation of phosphorylated Akt, suggesting that Cyp A is a phosphorylation target of Akt and downstream effector of the PI3K/Akt pathway. Cyclosporine A (CsA), a PPI inhibitor, inhibited the growth of multiple myeloma (MM) U266 cells. Moreover, CsA treatment inhibited the activation of the signal transducer and activator of transcription 3 (STAT3) in MM U266 cells. Several Cyp A mutants were generated. Mutants with mutated AKT phosphorylation sites increased the G1 phase arrest in MM U266 cells. The other mutants that mimicked the phosphorylated state of Cyp A decreased the percentage of G1 phase. These results demonstrated that the states of phosphorylation of Cyp A by Akt can influence the progress of the cell cycle in MM U266 cells and that this effect is probably mediated through the Janus-activated kinase 2/STAT3 signalling pathway.

In vitro cancer cell-ECM interactions inform in vivo cancer treatment

The general progression of cancer drug development involves in vitro testing followed by safety and efficacy evaluation in clinical trials. Due to the expense of bringing candidate drugs to trials, in vitro models of cancer cells and tumor biology are required to screen drugs. There are many examples of drugs exhibiting cytotoxic behavior in cancer cells in vitro but losing efficacy in vivo, and in many cases, this is the result of poorly understood chemoresistant effects conferred by the cancer microenvironment. To address this, improved methods for culturing cancer cells in biomimetic scaffolds have been developed; along the way, a great deal about the nature of cancer cell-extracellular matrix (ECM) interactions has been discovered. These discoveries will continue to be leveraged both in the development of novel drugs targeting these interactions and in the fabrication of biomimetic substrates for efficient cancer drug screening in vitro.

Multiple myeloma cell lines and primary tumors proteoma: protein biosynthesis and immune system as potential therapeutic targets

Despite great advance in multiple myeloma (MM) treatment since 2000s, it is still an incurable disease and novel therapies are welcome. Therefore, the purpose of this study was to explore MM plasma cells' (MM-PC) proteome, in comparison with their normal counterparts (derived from palatine tonsils of normal donors, ND-PC), in order to find potential therapeutic targets expressed on the surface of these cells. We also aimed to evaluate the proteome of MM cell lines with different genetic alterations, to confirm findings obtained with primary tumor cells. Bone marrow (BM) samples from eight new cases of MM and palatine tonsils from seven unmatched controls were submitted to PC separation and, in addition to two MM cell lines (U266, RPMI-8226), were submitted to protein extraction for mass spectrometry analyses. A total of 81 proteins were differentially expressed between MM-PC and ND-PC - 72 upregulated and nine downregulated; U266 vs. RPMI 8226 cell lines presented 61 differentially expressed proteins - 51 upregulated and 10 downregulated. On primary tumors, bioinformatics analyses highlighted upregulation of protein biosynthesis machinery, as well as downregulation of immune response components, such as MHC class I and II, and complement receptors. We also provided comprehensive information about U266 and RPMI-8226 cell lines' proteome and could confirm some patients' findings.

Targeting the Bone Marrow Microenvironment

Unprecedented advances in multiple myeloma (MM) therapy during the last 15 years are predominantly based on our increasing understanding of the pathophysiologic role of the bone marrow (BM) microenvironment. Indeed, new treatment paradigms, which incorporate thalidomide, immunomodulatory drugs (IMiDs), and proteasome inhibitors, target the tumor cell as well as its BM microenvironment. Ongoing translational research aims to understand in more detail how disordered BM-niche functions contribute to MM pathogenesis and to identify additional derived targeting agents. One of the most exciting advances in the field of MM treatment is the emergence of immune therapies including elotuzumab, daratumumab, the immune checkpoint inhibitors, Bispecific T-cell engagers (BiTes), and Chimeric antigen receptor (CAR)-T cells. This chapter will review our knowledge on the pathophysiology of the BM microenvironment and discuss derived novel agents that hold promise to further improve outcome in MM.

Epigenetics in Multiple Myeloma

Multiple myeloma is characterized by clonal proliferation of plasma cells within the bone marrow resulting in anemia, lytic bone lesions, hypercalcemia, and renal impairment. Despite advanced in our understanding of this complex disease in recent years, it is still considered an incurable malignancy. This is, in part, due to the highly heterogenous genomic and phenotypic nature of the disease, which is to date incompletely understood. It is clear that a deeper level of knowledge of the biological events underlying the development of these diseases is needed to identify new targets and generate effective novel therapies. MicroRNAs (miRNAs), which are single strand, 20-nucleotide, noncoding RNA's, are key regulators of gene expression and have been reported to exert transcriptional control in multiple myeloma. miRNAs are now recognized to play a role in many key areas such as cellular proliferation, differentiation, apoptosis and stress response. Substantial advances have been made in recent years in terms of our understanding of the biological role of miRNAs in a diverse range of hematological and solid malignancues, In multiple myeloma these advances have yielded new information of prognostic and diagnostic relevance which have helped to shed light on epigenetic regulation in this disease.

Blocking the ZZ domain of sequestosome1/p62 suppresses myeloma growth and osteoclast formation in vitro and induces dramatic bone formation in myeloma-bearing bones in vivo

We reported that p62 (sequestosome 1) serves as a signaling hub in bone marrow stromal cells (BMSC) for the formation of signaling complexes, including NFκB, p38MAPK, and JNK, that are involved in the increased osteoclastogenesis and multiple myeloma (MM) cell growth induced by BMSC that are key contributors to myeloma bone disease (MMBD), and demonstrated that the ZZ-domain of p62 (p62-ZZ) is required for BMSC enhancement of MMBD. We recently identified a novel p62-ZZ inhibitor, XRK3F2, that inhibits MM cell growth and BMSC growth enhancement of human MM cells. In the current study we evaluate the relative specificity of XRK3F2 for p62-ZZ, characterize XRK3F2’s capacity to inhibit growth of primary MM cells and human MM cell lines, and test the in vivo effects of XRK3F2 in the immunocompetent 5TGM1 MM model. We found that XRK3F2 induces dramatic cortical bone formation that is restricted to MM containing bones and blocked the effects and upregulation of TNFα, an OBL differentiation inhibitor that is increased in the MM bone marrow microenvironment and utilizes signaling complexes formed on p62-ZZ, in BMSC. Interestingly, XRK3F2 had no effect on non-MM bearing bone. These results demonstrate that targeting p62 in MM models has profound effects on MMBD.

The Cyclophilin A-CD147 complex promotes the proliferation and homing of multiple myeloma cells

B cell malignancies frequently colonize the bone marrow. The mechanisms responsible for this preferential homing are incompletely understood. Here we studied multiple myeloma (MM) as a model of a terminally differentiated B cell malignancy that selectively colonizes the bone marrow. We found that extracellular CyPA (eCyPA), secreted by bone marrow endothelial cells (BMECs), promoted the colonization and proliferation of MM cells in an in vivo scaffold system via binding to its receptor, CD147, on MM cells. The expression and secretion of eCyPA by BMECs was enhanced by BCL9, a Wnt-β-catenin transcriptional coactivator that is selectively expressed by these cells. eCyPA levels were higher in bone marrow serum than in peripheral blood in individuals with MM, and eCyPA-CD147 blockade suppressed MM colonization and tumor growth in the in vivo scaffold system. eCyPA also promoted the migration of chronic lymphocytic leukemia and lymphoplasmacytic lymphoma cells, two other B cell malignancies that colonize the bone marrow and express CD147. These findings suggest that eCyPA-CD147 signaling promotes the bone marrow homing of B cell malignancies and offer a compelling rationale for exploring this axis as a therapeutic target for these malignancies.

Revealing Genomic Profile That Underlies Tropism of Myeloma Cells Using Whole Exome Sequencing

Background. Previously we established two cell lines (SNU_MM1393_BM and SNU_MM1393_SC) from different tissues (bone marrow and subcutis) of mice which were injected with single patient's myeloma sample. We tried to define genetic changes specific for each cell line using whole exome sequencing (WES). Materials and Methods. We extracted DNA from SNU_MM1393_BM and SNU_MM1393_SC and performed WES. For single nucleotide variants (SNV) calling, we used Varscan2. Annotation of mutation was performed using ANNOVAR. Results. When calling of somatic mutations was performed, 68 genes were nonsynonymously mutated only in SNU_MM1393_SC, while 136 genes were nonsynonymously mutated only in SNU_MM1393_BM. KIAA1199, FRY, AP3B2, and OPTC were representative genes specifically mutated in SNU_MM1393_SC. When comparison analysis was performed using TCGA data, mutational pattern of SNU_MM1393_SC resembled that of melanoma mostly. Pathway analysis using KEGG database showed that mutated genes specific of SNU_MM1393_BM were related to differentiation, while those of SNU_MM1393_SC were related to tumorigenesis. Conclusion. We found out genetic changes that underlie tropism of myeloma cells using WES. Genetic signature of cutaneous plasmacytoma shares that of melanoma implying common mechanism for skin tropism. KIAA1199, FRY, AP3B2, and OPTC are candidate genes for skin tropism of cancers.

Ex Vivo Maintenance of Primary Human Multiple Myeloma Cells through the Optimization of the Osteoblastic Niche

We previously reported a new approach for culturing difficult-to-preserve primary patient-derived multiple myeloma cells (MMC) using an osteoblast (OSB)-derived 3D tissue scaffold constructed in a perfused microfluidic environment and a culture medium supplemented with patient plasma. In the current study, we used this biomimetic model to show, for the first time, that the long-term survival of OSB is the most critical factor in maintaining the ex vivo viability and proliferative capacity of MMC. We found that the adhesion and retention of MMC to the tissue scaffold was meditated by osteoblastic N-cadherin, as one of potential mechanisms that regulate MMC-OSB interactions. However, in the presence of MMC and patient plasma, the viability and osteogenic activity of OSB became gradually compromised, and consequently MMC could not remain viable over 3 weeks. We demonstrated that the long-term survival of both OSB and MMC could be enhanced by: (1) optimizing perfusion flow rate and patient-derived plasma composition in the culture medium and (2) replenishing OSB during culture as a practical means of prolonging MMC's viability beyond several weeks. These findings were obtained using a high-throughput well plate-based perfusion device from the perspective of optimizing the ex vivo preservation of patient-derived MM biospecimens for downstream use in biological studies and chemosensitivity analyses.

Relationship between circulating syndecan-1 levels (CD138s) and serum free light chains in monoclonal gammopathies

Background

Monoclonal gammopathies encompass a wide range of diseases characterized by the monoclonal expansion of a B-cell clone. Despite emerging therapeutic strategies, chances of survival of patients who are affected are still scarce, which implies that new tools are necessary not only for the diagnosis but also for the follow-up of patients affected by such diseases. In this context, the use of free light chains (FLCs) has been incorporated into many guidelines.

Likewise, tumor microenvironment is consistently gaining importance as role player in tumor pathogenesis. Specifically, Syndecan-1 (CD138), a heparan-sulfate proteoglycan is attracting interests as it is highly expressed and shed by myeloma plasma-cells.

The aim of our study was to analyze CD138 levels in the serum of patients affected by multiple myeloma or light chain only disease, and to compare the values obtained with free light chain (FLC) kappa, lambda and FLC ratio in both groups of patients.

Methods

84 patients affected by Multiple Myeloma and Light Chain Myeloma were recruited for this study. Serum CD138 was assessed by ELISA (Diaclone Research, France) and FLC values were quantified by nephelometry (Freelite TM Human Kappa and Lambda Free Kits, The Binding Site, UK). Data was analyzed by GraphPad Prism software and Statgraph.

Results

We observed higher CD138 mean values in myeloma patients compared to the light chain only myeloma group. A positive linear regression of CD138 and FLC was observed in the light chain only cohort as opposed to myeloma patients which show an inverse trend.

Conclusions

The study highlighted an existing relationship between FLCs and CD138 and wishes to seek also a correlation in order to rapidly and efficiently perform diagnosis and different diagnostic schemes.