A review of current murine models of multiple myeloma used to assess the efficacy of therapeutic agents on tumour growth and bone disease

Delivery of Therapeutic RNA to the Bone Marrow in Multiple Myeloma Using CD38-Targeted Lipid Nanoparticles

Multiple myeloma (MM) is a cancer of differentiated plasma cells that occurs in the bone marrow (BM). Despite the recent advancements in drug development, most patients with MM eventually relapse and the disease remains incurable. RNA therapy delivered via lipid nanoparticles (LNPs) has the potential to be a promising cancer treatment, however, its clinical implementation is limited due to inefficient delivery to non-hepatic tissues. Here, targeted (t)LNPs designed for delivery of RNA payload to MM cells are presented. The tLNPs consist of a novel ionizable lipid and are coated with an anti-CD38 antibody (αCD38-tLNPs). To explore their therapeutic potential, it is demonstrated that LNPs encapsulating small interference RNA (siRNA) against cytoskeleton-associated protein 5 (CKAP5) lead to a ≈90% decrease in cell viability of MM cells in vitro. Next, a new xenograft MM mouse model is employed, which clinically resembles the human disease and demonstrates efficient homing of MM cells to the BM. Specific delivery of αCD38-tLNPs to BM-residing and disseminated MM cells and the improvement in therapeutic outcome of MM-bearing mice treated with αCD38-tLNPs-siRNA-CKAP5 are shown. These results underscore the potential of RNA therapeutics for treatment of MM and the importance of developing effective targeted delivery systems and reliable preclinical models.

HSV1716 Prevents Myeloma Cell Regrowth When Combined with Bortezomib In Vitro and Significantly Reduces Systemic Tumor Growth in Mouse Models

Multiple myeloma remains largely incurable due to refractory disease; therefore, novel treatment strategies that are safe and well-tolerated are required. Here, we studied the modified herpes simplex virus HSV1716 (SEPREHVIR®), which only replicates in transformed cells. Myeloma cell lines and primary patient cells were infected with HSV1716 and assessed for cell death using propidium iodide (PI) and Annexin-V staining and markers of apoptosis and autophagy by qPCR. Myeloma cell death was associated with dual PI and Annexin-V positivity and increased expression of apoptotic genes, including CASP1, CASP8, CASP9, BAX, BID, and FASL. The combination of HSV1716 and bortezomib treatments prevented myeloma cell regrowth for up to 25 days compared to only transient cell growth suppression with bortezomib treatment. The viral efficacy was tested in a xenograft (JJN-3 cells in NSG mice) and syngeneic (murine 5TGM1 cells in C57BL/KaLwRijHsd mice) systemic models of myeloma. After 6 or 7 days, the post-tumor implantation mice were treated intravenously with the vehicle or HSV1716 (1 × 107 plaque forming units/1 or 2 times per week). Both murine models treated with HSV1716 had significantly lower tumor burden rates compared to the controls. In conclusion, HSV1716 has potent anti-myeloma effects and may represent a novel therapy for multiple myeloma.

Interleukin-32γ promotes macrophage-mediated chemoresistance by inducing CSF1-dependent M2 macrophage polarization in multiple myeloma

Macrophages (MΦs) are an abundant component in the multiple myeloma (MM) environment and contribute to MM drug resistance. We previously showed that interleukin-32 (IL-32) is highly expressed in MM patients and induces the immunosuppressive function of MΦs. The present study was designed to explore the role of IL-32 in MΦ-mediated MM drug resistance and the underlying mechanism. Our analysis revealed that IL-32 expression was upregulated in relapsed MM patients and associated with CD206⁺ M2 MΦ infiltration. Subsequently, we found that the most active isoform, IL-32γ, promoted MΦs to protect MM cells from drug-induced apoptosis both in vitro and in vivo. Furthermore, by evaluating many parameters, including surface markers, cytokines, metabolic enzymes and characteristic molecules, IL-32γ was verified to induce the polarization of M2 MΦs, a function that was partly dependent on increasing the expression of colony-stimulating factor 1 (CSF1). Taken together, the results of our study indicate that IL-32γ promotes MΦ-mediated MM drug resistance and modifies MΦs toward the M2 phenotype, providing a crucial theoretical basis for targeted MΦ immunotherapy.

[Establishment and comparison of three human multiple myeloma cell line transplantation models in mice]

Objective: To establish three types of xenotransplantation models using human myeloma cell lines ARP1, MM.1S, and NCI-H929 and to compare the proliferation, tumor load, and biological characteristics of the three types of cells after transplantation. Methods: Suspensions of human myeloma cell lines ARP1, MM.1S, and NCI-H929 were implanted into NOD/SCID mice by subcutaneous injection or tail vein injection. The survival of the mice was observed weekly, and the tumor load was measured. Flow cytometry was used to detect the proportion of CD138(+) cells in tumor tissue or the mouse bone marrow. CD138(+) cells and light chains were detected by immunofluorescence. Light chains in bone marow and peipheral blood were measured by ELISA, and bone disease was assessed by micro-CT. Results: Mice injected with ARP1, MM.1S, and NCI-H929 cells all formed tumors subcutaneously in about 2 weeks. Immunofluorescence detection supported plasma cell tumors. Kappa light chains were detected in the peripheral blood of ARP1 mice on day 20 after tail vein transplantation (8.2±1.0 ng/ml) . After 6 weeks of tail vein transplantation, mice in the ARP1 group showed signs of weight loss, mental depression, and dragging legs, and human CD138(+)CD38(+) cells were detected in the bone marrow (BM) . Furthermore, bortezomib (BTZ) treatment given once the tumor was established significantly reduced the tumor burden[ (5.7±0.2) % vs (21.3±2.1) %, P<0.01]. Human CD138(+)CD38(+) cells were not detected in the BM of the MM.1S or NCI-H929 groups. Conclusion: The results of this study suggest that the mouse models constructed by the three cell lines (ARP1, MM.1S, and NCI-H929) can be used as models for the pathogenesis and clinical research of MM.

Tissue biodistribution and tumor targeting of near-infrared labelled anti-CD38 antibody-drug conjugate in preclinical multiple myeloma

Daratumumab (DARA) is an FDA-approved high-affinity monoclonal antibody targeting CD38 that has shown promising therapeutic efficacy in double refractory multiple myeloma (MM) patients. Despite the well-established clinical efficacy of DARA, not all heavily pretreated patients respond to single-agent DARA, and the majority of patients who initially respond eventually progress. Antibody-drug conjugates (ADCs) combine the highly targeted tumor antigen recognition of antibodies with the cell killing properties of chemotherapy for effective internalization and processing of the drug. In this study, we evaluated the anti-tumor efficacy of DARA conjugated to the maytansine derivative, mertansine (DM1), linked via a non-cleavable bifunctional linker. The ADC was labelled with the near-infrared (NIR) fluorophore IRDye800 (DARA-DM1-IR) to evaluate its stability, biodistribution and pharmacokinetics in vitro and in vivo. We demonstrated the conjugation of: 1) DM1 enhanced tumor-killing efficacy of the native DARA and 2) IRDye800 allowed for visualization of uptake and tumor targeting ability of the ADC. With the advent of other classes of immunoconjugates for use in MM, we reasoned that such imaging techniques can be utilized to evaluate other promising conjugates in preclinical MM models on a whole-body and cellular level.

Laboratory Mice - A Driving Force in Immunopathology and Immunotherapy Studies of Human Multiple Myeloma

Mouse models of human cancer provide an important research tool for elucidating the natural history of neoplastic growth and developing new treatment and prevention approaches. This is particularly true for multiple myeloma (MM), a common and largely incurable neoplasm of post-germinal center, immunoglobulin-producing B lymphocytes, called plasma cells, that reside in the hematopoietic bone marrow (BM) and cause osteolytic lesions and kidney failure among other forms of end-organ damage. The most widely used mouse models used to aid drug and immunotherapy development rely on in vivo propagation of human myeloma cells in immunodeficient hosts (xenografting) or myeloma-like mouse plasma cells in immunocompetent hosts (autografting). Both strategies have made and continue to make valuable contributions to preclinical myeloma, including immune research, yet are ill-suited for studies on tumor development (oncogenesis). Genetically engineered mouse models (GEMMs), such as the widely known Vκ*MYC, may overcome this shortcoming because plasma cell tumors (PCTs) develop de novo (spontaneously) in a highly predictable fashion and accurately recapitulate many hallmarks of human myeloma. Moreover, PCTs arise in an intact organism able to mount a complete innate and adaptive immune response and tumor development reproduces the natural course of human myelomagenesis, beginning with monoclonal gammopathy of undetermined significance (MGUS), progressing to smoldering myeloma (SMM), and eventually transitioning to frank neoplasia. Here we review the utility of transplantation-based and transgenic mouse models of human MM for research on immunopathology and -therapy of plasma cell malignancies, discuss strengths and weaknesses of different experimental approaches, and outline opportunities for closing knowledge gaps, improving the outcome of patients with myeloma, and working towards a cure.

Bisphosphonates for delivering drugs to bone

Advances in the design of potential bone-selective drugs for the treatment of various bone-related diseases are creating exciting new directions for multiple unmet medical needs. For bone-related cancers, off-target/non-bone toxicities with current drugs represent a significant barrier to the quality of life of affected patients. For bone infections and osteomyelitis, bacterial biofilms on infected bones limit the efficacy of antibiotics because it is hard to access the bacteria with current approaches. Promising new experimental approaches to therapy, based on bone-targeting of drugs, have been used in animal models of these conditions and demonstrate improved efficacy and safety. The success of these drug-design strategies bodes well for the development of therapies with improved efficacy for the treatment of diseases affecting the skeleton. 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.

Reovirus-induced cell-mediated immunity for the treatment of multiple myeloma within the resistant bone marrow niche

BACKGROUND

Multiple myeloma (MM) remains an incurable disease and oncolytic viruses offer a well-tolerated addition to the therapeutic arsenal. Oncolytic reovirus has progressed to phase I clinical trials and its direct lytic potential has been extensively studied. However, to date, the role for reovirus-induced immunotherapy against MM, and the impact of the bone marrow (BM) niche, have not been reported.

METHODS

This study used human peripheral blood mononuclear cells from healthy donors and in vitro co-culture of MM cells and BM stromal cells to recapitulate the resistant BM niche. Additionally, the 5TGM1-Kalw/RijHSD immunocompetent in vivo model was used to examine reovirus efficacy and characterize reovirus-induced immune responses in the BM and spleen following intravenous administration. Collectively, these in vitro and in vivo models were used to characterize the development of innate and adaptive antimyeloma immunity following reovirus treatment.

RESULTS

Using the 5TGM1-Kalw/RijHSD immunocompetent in vivo model we have demonstrated that reovirus reduces both MM tumor burden and myeloma-induced bone disease. Furthermore, detailed immune characterization revealed that reovirus: (i) increased natural killer (NK) cell and CD8+ T cell numbers; (ii) activated NK cells and CD8+ T cells and (iii) upregulated effector-memory CD8+ T cells. Moreover, increased effector-memory CD8+ T cells correlated with decreased tumor burden. Next, we explored the potential for reovirus-induced immunotherapy using human co-culture models to mimic the myeloma-supportive BM niche. MM cells co-cultured with BM stromal cells displayed resistance to reovirus-induced oncolysis and bystander cytokine-killing but remained susceptible to killing by reovirus-activated NK cells and MM-specific cytotoxic T lymphocytes.

CONCLUSION

These data highlight the importance of reovirus-induced immunotherapy for targeting MM cells within the BM niche and suggest that combination with agents which boost antitumor immune responses should be a priority.

Targeting the Endothelin-1 Receptors Curtails Tumor Growth and Angiogenesis in Multiple Myeloma

The endothelin-1 (ET-1) receptors were recently found to mediate pro-survival functions in multiple myeloma (MM) cells in response to autocrine ET-1. This study investigated the effectiveness of macitentan, a dual ET-1 receptor antagonist, in MM treatment, and the mechanisms underlying its activities. Macitentan affected significantly MM cell (RPMI-8226, U266, KMS-12-PE) survival and pro-angiogenic cytokine release by down-modulating ET-1-activated MAPK/ERK and HIF-1α pathways, respectively. HIF-1α silencing abrogated the ET-1 mediated induction of genes encoding for pro-angiogenic cytokines such as VEGF-A, IL-8, Adrenomedullin, and ET-1 itself. Upon exposure to macitentan, MM cells cultured in the presence of the hypoxia-mimetic agent CoCl₂, exogenous ET-1, or CoCl₂ plus ET-1, down-regulated HIF-1α and the transcription and release of downstream pro-angiogenic cytokines. Consistently, macitentan limited significantly the basal pro-angiogenic activity of RPMI-8226 cells in chorioallantoic membrane assay. In xenograft mouse models, established by injecting NOG mice either via intra-caudal vein with U266 or subcutaneously with RPMI-8226 cells, macitentan reduced effectively the number of MM cells infiltrating bone marrow, and the size and microvascular density of subcutaneous MM tumors. ET-1 receptors targeting by macitentan represents an effective anti-proliferative and anti-angiogenic therapeutic approach in preclinical settings of MM.

Multiple myeloma-A painful disease of the bone marrow

Multiple myeloma is a bone marrow neoplasia with an incidence of 6/100,000/year in Europe. While the disease remains incurable, the development of novel treatments such as autologous stem cell transplantation, proteasome inhibitors and monoclonal antibodies has led to an increasing subset of patients living with long-term myeloma. However, more than two thirds of patients suffer from bone pain, often described as severe, and knowledge on the pain mechanisms and its effect on their health-related quality of life (HRQoL) is limited. In this review, we discuss the mechanisms of myeloma bone disease, the currently available anti-myeloma treatments and the lessons learnt from clinical studies regarding HRQoL in myeloma patients. Moreover, we discuss the mechanisms of cancer-induced bone pain and the knowledge that animal models of myeloma-induced bone pain can provide to identify novel analgesic targets. To date, information regarding bone pain and HRQoL in myeloma patients is still scarce and an effort should be made to use standardised questionnaires to assess patient-reported outcomes that allow inter-study comparisons of the available clinical data.

Preclinical Development of Near-Infrared-Labeled CD38-Targeted Daratumumab for Optical Imaging of CD38 in Multiple Myeloma

PURPOSE

Cluster of differentiation 38 (CD38) is a promising therapeutic target in multiple myeloma (MM) patients and has resulted in the development of several CD38 immunotherapies. Current methods to evaluate CD38 expression in the preclinical setting include ex vivo flow cytometry and immunohistochemistry, which can be cumbersome and do not give whole-body information. In vivo imaging technologies such as positron emission tomography rely on decay of radioisotopes, limiting the number of molecular interactions observed at any given time point. Here, we demonstrate the use of near-infrared (NIR) fluorescence imaging for spatiotemporal monitoring of CD38 expression in preclinical MM using the anti-CD38 daratumumab (DARA) conjugated to the NIR fluorophore IRDye800CW (DARA-IRDye800).

PROCEDURES

Stability studies with human serum and binding assays with human myeloma cells were performed with DARA-IRDye800. Immunocompromised mice with intra- and extramedullary tumors (n = 5/group) were administered with DARA-IRDye800 for in vivo imaging up to 7 days after injection. Ex vivo biodistribution and flow cytometry studies were performed to validate in vivo imaging results. A separate therapy study was performed in mice with intramedullary tumors that were treated and not treated with DARA at a therapeutic dose (n = 7/group). DARA-IRDye800 was administered for subsequent in vivo and ex vivo imaging in both cohorts of mice.

RESULTS

DARA-IRDye800 maintained stability and had high affinity for CD38 (K_D = 3.5 ± 0.05 nM). DARA-IRDye800 demonstrated a 5- and 18-fold increase in contrast in tumor-bearing regions of mice with extra- and intramedullary MM. Finally, mice treated with therapeutic doses of DARA and imaged with DARA-IRDye800 showed an 11-fold decrease in fluorescence intensities in vivo compared with untreated controls.

CONCLUSIONS

Our studies establish DARA-IRDye800 as a promising contrast agent for preclinical evaluation of CD38 expression and for further investigating myeloma engraftment and kinetics in relation to anti-CD38 therapies.

ImmunoPET in Multiple Myeloma-What? So What? Now What?

Despite constant progress over the past three decades, multiple myeloma (MM) is still an incurable disease, and the identification of new biomarkers to better select patients and adapt therapy is more relevant than ever. Recently, the introduction of therapeutic monoclonal antibodies (mAbs) (including direct-targeting mAbs and immune checkpoint inhibitors) appears to have changed the paradigm of MM management, emphasizing the opportunity to cure MM patients through an immunotherapeutic approach. In this context, immuno-positron emission tomography (immunoPET), combining the high sensitivity and resolution of a PET camera with the specificity of a radiolabelled mAb, holds the capability to cement this new treatment paradigm for MM patients. It has the potential to non-invasively monitor the distribution of therapeutic antibodies or directly monitor biomarkers on MM cells, and to allow direct observation of potential changes over time and in response to various therapeutic interventions. Tumor response could, in the future, be anticipated more effectively to provide individualized treatment plans tailored to patients according to their unique imaging signatures. This work explores the important role played by immunotherapeutics in the management of MM, and focuses on some of the challenges for this drug class and the significant interest of companion imaging agents such as immunoPET.

Twist-1 is upregulated by NSD2 and contributes to tumour dissemination and an epithelial-mesenchymal transition-like gene expression signature in t(4;14)-positive multiple myeloma

Approximately 15% of patients with multiple myeloma (MM) harbour the t(4;14) chromosomal translocation, leading to the overexpression of the histone methyltransferase NSD2. Patients with this translocation display increased tumour dissemination, accelerated disease progression and rapid relapse. Using publicly available gene expression profile data from NSD2^high (n = 135) and NSD2^low (n = 878) MM patients, we identified 39 epithelial-mesenchymal transition (EMT)-associated genes which are overexpressed in NSD2^high MM plasma cells. In addition, our analyses identified Twist-1 as a key transcription factor upregulated in NSD2^high MM patients and t(4;14)-positive cell lines. Overexpression and knockdown studies confirmed that Twist-1 is involved in driving the expression of EMT-associated genes in the human MM cell line KMS11 and promoted the migration of myeloma cell lines in vitro. Notably, Twist-1 overexpression in the mouse MM cell line 5TGM1 significantly increased tumour dissemination in an intratibial tumour model. These findings demonstrate that Twist-1, downstream of NSD2, contributes to the induction of an EMT-like signature in t(4;14)-positive MM and enhances the dissemination of MM plasma cells in vivo, which may, in part, explain the aggressive disease features associated with t(4;14)-positive MM.

Differential Pain-Related Behaviors and Bone Disease in Immunocompetent Mouse Models of Myeloma

Bone pain is a serious and debilitating symptom of multiple myeloma (MM) that impairs the quality of life of patients. The underlying mechanisms of the pain are unknown and understudied, and there is a need for immunocompetent preclinical models of myeloma-induced bone pain. The aim of this study was to provide the first in-depth behavioral characterization of an immunocompetent mouse model of MM presenting the clinical disease features: osteolytic bone disease and bone pain. We hypothesized that a widely used syngeneic model of MM, established by systemic inoculation of green fluorescent protein-tagged myeloma cells (5TGM1-GFP) in immunocompetent C57Bl/KaLwRijHsd (BKAL) mice, would present pain-related behaviors. Disease phenotype was confirmed by splenomegaly, high serum paraprotein, and tumor infiltration in the bone marrow of the hind limbs; however, myeloma-bearing mice did not present pain-related behaviors or substantial bone disease. Thus, we investigated an alternative model in which 5TGM1-GFP cells were directly inoculated into the intrafemoral medullary cavity. This localized myeloma model presented the hallmarks of the disease, including high serum paraprotein, tumor growth, and osteolytic bone lesions. Compared with control mice, myeloma-bearing mice presented myeloma-induced pain-related behaviors, a phenotype that was reversed by systemic morphine treatment. Micro-computed tomography analyses of the myeloma-inoculated femurs showed bone disease in cortical and trabecular bone. Repeated systemic bisphosphonate treatment induced an amelioration of the nociceptive phenotype, but did not completely reverse it. Furthermore, intrafemorally injected mice presented a profound denervation of the myeloma-bearing bones, a previously unknown feature of the disease. This study reports the intrafemoral inoculation of 5TGM1-GFP cells as a robust immunocompetent model of myeloma-induced bone pain, with consistent bone loss. Moreover, the data suggest that myeloma-induced bone pain is caused by a combinatorial mechanism including osteolysis and bone marrow denervation. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

T Lymphocytes Attenuate Dermal Scarring by Regulating Inflammation, Neovascularization, and Extracellular Matrix Remodeling

Objective: While tissue injury and repair are known to involve adaptive immunity, the profile of lymphocytes involved and their contribution to dermal scarring remain unclear. We hypothesized that restoration of T cell deficiency attenuates dermal scarring. Approach: We assessed the temporal-spatial distribution of T lymphocytes and their subtypes during the physiological dermal wound repair process in mice. Also, we compared the scarring outcomes between wild-type (WT) and severe combined immunodeficient (SCID) mice, which are lymphocyte deficient. Complementary gain-of-function experiments were performed by adoptively transferring lymphocyte subsets to validate their contribution to tissue repair in wounded SCID mice. Results: CD4⁺ T lymphocytes were present within dermal wounds of WT mice beginning on day 1 and remained through day 30. Wounds of SCID mice exhibited accelerated closure, increased inflammation, limited neovascularization, and exacerbated scarring compared with WT mice. Conversely, transfer of either mixed B and T lymphocytes or CD4⁺ lymphocytes alone into SCID mice resulted in moderated healing with less inflammation, collagen deposition, and scarring than control SCID wounds. In contrast, transfer of other lymphocyte subsets, including helper T lymphocytes (CD3⁺CD4⁺CD25^-), CD8⁺ T cells and B cells, or regulatory T lymphocytes (CD4⁺CD25⁺CD127^low), did not reduce scar. Innovation: The finding that lymphocytes delay wound healing but reduce scar is novel and provides new insights into how dermal scarring is regulated. Conclusion: Our data support a suppressive role for CD4⁺ T cells against inflammation and collagen deposition, with protective effects in early-stage dermal wound healing. These data implicate adaptive immunity in the regulation of scarring phenotypes.

The Use of Murine Models for Studying Mechanistic Insights of Genomic Instability in Multiple Myeloma

Multiple myeloma (MM) is a B-cell malignancy characterized by the accumulation of clonal plasma cells in the bone marrow. In normal plasma cell development, cells undergo programmed DNA breaks and translocations, a process necessary for generation of a wide repertoire of antigen-specific antibodies. This process also makes them vulnerable for the acquisition of chromosomal defects. Well-known examples of these aberrations, already seen at time of MM diagnosis, are hyperdiploidy or the translocations involving the immunoglobulin heavy chain. Over the recent years, however, novel aspects concerning genomic instability and its role in tumor development, disease progression and nascence of refractory disease were identified. As such, genomic instability is becoming a very relevant research topic with the potential identification of novel disease pathways. In this review, we aim to describe recent studies involving murine MM models focusing on the deregulation of processes implicated in genomic instability and their clinical impact. More specifically, we will discuss chromosomal instability, DNA damage and repair responses, development of drug resistance, and recent insights into the study of clonal hierarchy using different murine MM models. Lastly, we will discuss the importance and the use of murine MM models in the pre-clinical evaluation of promising novel therapeutic agents.

Activated gp130 signaling selectively targets B cell differentiation to induce mature lymphoma and plasmacytoma

Aberrant activity of the glycoprotein 130 130/JAK/STAT3 (gp130/JAK/STAT3) signaling axis is a recurrent event in inflammation and cancer. In particular, it is associated with a wide range of hematological malignancies, including multiple myeloma and leukemia. Novel targeted therapies have only been successful for some subtypes of these malignancies, underlining the need for developing robust mouse models to better dissect the role of this pathway in specific tumorigenic processes. Here, we investigated the role of selective gp130/JAK/STAT3 activation by generating a conditional mouse model. This model targeted constitutively active, cell-autonomous gp130 activity to B cells, as well as to the entire hematopoietic system. We found that regardless of the timing of activation in B cells, constitutively active gp130 signaling resulted in the formation specifically of mature B cell lymphomas and plasma cell disorders with full penetrance, only with different latencies, where infiltrating CD138+ cells were a dominant feature in every tumor. Furthermore, constitutively active gp130 signaling in all adult hematopoietic cells also led to the development specifically of largely mature, aggressive B cell cancers, again with a high penetrance of CD138+ tumors. Importantly, gp130 activity abrogated the differentiation block induced by a B cell-targeted Myc transgene and resulted in a complete penetrance of the gp130-associated, CD138+, mature B cell lymphoma phenotype. Thus, gp130 signaling selectively provides a strong growth and differentiation advantage for mature B cells and directs lymphomagenesis specifically toward terminally differentiated B cell cancers.

Preventing and Repairing Myeloma Bone Disease by Combining Conventional Antiresorptive Treatment With a Bone Anabolic Agent in Murine Models

Multiple myeloma is a plasma cell malignancy, which develops in the bone marrow and frequently leads to severe bone destruction. Current antiresorptive therapies to treat the bone disease do little to repair damaged bone; therefore, new treatment strategies incorporating bone anabolic therapies are urgently required. We hypothesized that combination therapy using the standard of care antiresorptive zoledronic acid (Zol) with a bone anabolic (anti-TGFβ/1D11) would be more effective at treating myeloma-induced bone disease than Zol therapy alone. JJN3 myeloma-bearing mice (n = 8/group) treated with combined Zol and 1D11 resulted in a 48% increase (p ≤ 0.001) in trabecular bone volume (BV/TV) compared with Zol alone and a 65% increase (p ≤ 0.0001) compared with 1D11 alone. Our most significant finding was the substantial repair of U266-induced osteolytic bone lesions with combination therapy (n = 8/group), which resulted in a significant reduction in lesion area compared with vehicle (p ≤ 0.01) or Zol alone (p ≤ 0.01). These results demonstrate that combined antiresorptive and bone anabolic therapy is significantly more effective at preventing myeloma-induced bone disease than Zol alone. Furthermore, we demonstrate that combined therapy is able to repair established myelomatous bone lesions. This is a highly translational strategy that could significantly improve bone outcomes and quality of life for patients with myeloma. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Immunotherapeutics in Multiple Myeloma: How Can Translational Mouse Models Help?

Multiple myeloma (MM) is usually diagnosed in older adults at the time of immunosenescence, a collection of age-related changes in the immune system that contribute to increased susceptibility to infection and cancer. The MM tumor microenvironment and cumulative chemotherapies also add to defects in immunity over the course of disease. In this review we discuss how mouse models have furthered our understanding of the immune defects caused by MM and enabled immunotherapeutics to progress to clinical trials, but also question the validity of using immunodeficient models for these purposes. Immunocompetent models, in particular the 5T series and Vk^⁎MYC models, are increasingly being utilized in preclinical studies and are adding to our knowledge of not only the adaptive immune system but also how the innate system might be enhanced in anti-MM activity. Finally we discuss the concept of immune profiling to target patients who might benefit the most from immunotherapeutics, and the use of humanized mice and 3D culture systems for personalized medicine.

Animal Models of Multiple Myeloma

Multiple myeloma (MM) is a plasma cell neoplasm which is defined by strong interactions with the bone marrow microenvironment, a compartment with high cellular heterogeneity and unique structural and extracellular components. This necessitates the use of in vivo models for research to fully recapitulate MM growth conditions. The selection of appropriate model system is crucial, as each has advantages and shortcomings. Here, we describe the murine models available for studying MM, and focus on the methods for inoculating mice with MM cells via intravenous, intratibial or subcutaneous delivery, as well as monitoring of disease and organ processing for further analysis. The interaction and destruction of bone is a hallmark symptom of MM, and therefore many other complementary techniques used in calcified tissue research can be used, such as microCT, histomorphometry, and biomechanical testing.

Therapeutic effects of the novel subtype-selective histone deacetylase inhibitor chidamide on myeloma-associated bone disease

Histone deacetylases are promising therapeutic targets in hematological malignancies. In the work herein, we investigated the effect of chidamide, a new subtype-selective histone deacetylase inhibitor that was independently produced in China, on multiple myeloma and its associated bone diseases using different models. The cytotoxicity of chidamide toward myeloma is due to its induction of cell apoptosis and cell cycle arrest by increasing the levels of caspase family proteins p21 and p27, among others. Furthermore, chidamide exhibited significant cytotoxicity against myeloma cells co-cultured with bone mesenchymal stromal cells and chidamide-pretreated osteoclasts. Importantly, chidamide suppressed osteoclast differentiation and resorption in vitro by dephosphorylating p-ERK, p-p38, p-AKT and p-JNK and inhibiting the expression of Cathepsin K, NFATc1 and c-fos. Finally, chidamide not only prevented tumor-associated bone loss in a disseminated murine model by partially decreasing the tumor burden but also prevented rapid receptor activator of nuclear factor κ-β ligand (RANKL)-induced bone loss in a non-tumor-bearing mouse model. Based on our results, chidamide exerted dual anti-myeloma and bone-protective effects in vitro and in vivo. These findings strongly support the potential clinical use of this drug as a treatment for multiple myeloma in the near future.

Mouse models of multiple myeloma: technologic platforms and perspectives

Murine models of human multiple myeloma (MM) are key tools for the study of disease biology as well as for investigation and selection of novel candidate therapeutics for clinical translation. In the last years, a variety of pre-clinical models have been generated to recapitulate a wide spectrum of biological features of MM. These systems range from spontaneous or transgenic models of murine MM, to subcutaneous or orthothopic xenografts of human MM cell lines in immune compromised animals, to platform allowing the engraftment of primary/bone marrow-dependent MM cells within a human bone marrow milieu to fully recapitulate human disease. Selecting the right model for specific pre-clinical research is essential for the successful completion of investigation. We here review recent and most known pre-clinical murine, transgenic and humanized models of MM, focusing on major advantages and/or weaknesses in the light of different research aims.

Efficacy and Mechanism of Antitumor Activity of an Antibody Targeting Transferrin Receptor 1 in Mouse Models of Human Multiple Myeloma

The transferrin receptor 1 (TfR1) is an attractive target for Ab-mediated cancer therapy. We previously developed a mouse/human chimeric IgG3 Ab (ch128.1) targeting human TfR1, which exhibits direct in vitro cytotoxicity against certain human malignant B cells through TfR1 degradation and iron deprivation. ch128.1 also demonstrates exceptional antitumor activity against the B cell malignancy multiple myeloma (MM) in xenograft models of SCID-Beige mice bearing either disseminated ARH-77 or KMS-11 cells in an early disease setting. Interestingly, this activity is observed even against KMS-11 cells, which show no sensitivity to the direct cytotoxic activity of ch128.1 in vitro. To understand the contributions of the Fc fragment, we generated a ch128.1 mutant with impaired binding to FcγRs and to the complement component C1q, which retains binding to the neonatal Fc receptor. We now report that this mutant Ab does not show antitumor activity in these two MM models, indicating a crucial role of the Fc fragment in the antitumor activity of ch128.1, which can be attributed to effector functions (Ab-dependent cell-mediated cytotoxicity, Ab-dependent cell-mediated phagocytosis, and/or complement-dependent cytotoxicity). Interestingly, in the KMS-11 model, complement depletion does not affect protection, whereas macrophage depletion does. Consistent with this observation, we found that ch128.1 induces Ab-dependent cell-mediated cytotoxicity and Ab-dependent cell-mediated phagocytosis against KMS-11 cells in the presence of murine bone marrow-derived macrophages. Finally, we found that ch128.1 therapy effectively increases survival in a late MM disease setting. Our results suggest that macrophages play a major role in ch128.1-mediated antitumor protection in our models and that ch128.1 can be effective against human B cell malignancies such as MM.

Surgical thyroparathyroidectomy prevents progression of 5TGM1 murine multiple myeloma in vivo

The 5TGM1 multiple myeloma transplanted C57BL6/KaLwRij model recapitulates many disease features including monoclonal paraprotein production as well as the development of osteolytic bone lesions. Since a significant association between serum parathyroid hormone PTH variations, bone anabolism and myeloma progression in patients receiving proteasome inhibitors exists, this study investigated the effect of the PTH axis on murine myeloma development in vivo. C57BL6/KaLwRij myeloma-bearing mice underwent thyroparathyroidectomy (TPTX) before and after 5TGM1 cell transplantation. TPTX significantly and permanently inhibited 5TGM1 myeloma cell engraftment and prevented multiple myeloma growth and progression. These data support the hypothesis that the PTH axis is an important mediator of myeloma bone disease.

Human platelets repurposed as vehicles for in vivo imaging of myeloma xenotransplants

Human platelets were identified in tumors by Trousseau in 1865, although their roles in tumor microenvironments have only recently attracted the attention of cancer researchers. In this study we exploit and enhance platelet interactions in tumor microenvironments by introducing tumor-targeting and imaging functions. The first step in repurposing human platelets as vehicles for tumor-targeting was to inhibit platelet-aggregation by cytoplasmic-loading of kabiramide (KabC), a potent inhibitor of actin polymerization and membrane protrusion. KabC-Platelets can accumulate high levels of other membrane-permeable cytoxins and probes, including epidoxorubicin, carboxyfluorescein di-ester and chlorin-e6. Finally, mild reaction conditions were developed to couple tumor-targeting proteins and antibodies to KabC-platelets. Fluorescence microscopy studies showed KabC-platelets, surface-coupled with transferrin and Cy5, bind specifically to RPMI8226 and K562 cells, both of which over-express the transferrin receptor. Repurposed platelets circulate for upto 9-days a feature that increases their chance of interacting with target cells. KabC-platelets, surface-coupled with transferrin and Cy7, or chlorin-e6, and injected in immuno-compromised mice were shown to accumulate specifically in sub-cutaneous and intra-cranial myeloma xenotransplants. The high-contrast, in vivo fluorescence images recorded from repurposed platelets within early-stage myeloma is a consequence in part of their large size (φ∼2μm), which allows them to transport 100 to 1000-times more targeting-protein and probe molecules respectively. Human platelets can be configured with a plurality of therapeutic and targeting antibodies to help stage tumor environments for an immunotherapy, or with combinations of therapeutic antibodies and therapeutic agents to target and treat cardiovascular and neurologic diseases.

Altered bone microarchitecture and gene expression profile due to calcium deficiency in a mouse model of myeloma

It is not clear why patients with an indolent form of multiple myeloma (MM) develop into an aggressive form with poor prognostic. We investigated the effect of a dietary calcium deficiency on tumor growth, osteolysis and gene expression in the 5T2MM murine model. Two groups of C57BL/KaLwRij mice received 5T2MM cells and started a diet with normal (0.8%; "normal-Ca-MM") or low calcium content (0.05%; "low-Ca-MM"). Two control groups (without 5T2MM cells) received either a normal or low calcium diet (normal-Ca and low-Ca groups). Tumor growth, osteolysis and marrow gene expression of the Wnt pathway, RANKL and MIP-1α were monitored at 6, 8 and 10 weeks (w) after cell injection. In low-Ca mice, serum level of PTH was higher after 10w; microCT showed trabecular bone loss and decrease of cortical thickness at the tibia. A higher M-protein level was evidenced at 10w and 4 mice developed paraplegia at 8/9w in low-Ca-MM group only. Numerous cortical perforations of the tibia were observed in MM groups with a marked decrease in cortical thickness in low-Ca-MM. At 6w, osteoclast number from the endosteum was significantly higher in low-Ca-MM compared to normal-Ca MM. This observation was not found at 8 and 10w. MicroCT of the lumbar vertebrae showed dramatic bone destruction in the low-Ca-MM group. qPCR revealed no difference in RANKL expression whereas differences were obtained in the expression of Lrp5/Lrp6 and MIP-1α from 6w. A low calcium diet induced higher bone destruction in the tibia and vertebra associated with an earlier decrease in bone formation level and a higher increase in bone resorption level at early time in the MM development.

Evaluating Acetate Metabolism for Imaging and Targeting in Multiple Myeloma

PURPOSE

We hypothesized that in multiple myeloma cells (MMC), high membrane biosynthesis will induce acetate uptake in vitro and in vivo Here, we studied acetate metabolism and targeting in MMC in vitro and tested the efficacy of ¹¹C-acetate-positron emission tomography (PET) to detect and quantitatively image myeloma treatment response in vivo EXPERIMENTAL DESIGN: Acetate fate tracking using ¹³C-edited-¹H NMR (nuclear magnetic resonance) was performed to study in vitro acetate uptake and metabolism in MMC. Effects of pharmacological modulation of acetate transport or acetate incorporation into lipids on MMC cell survival and viability were assessed. Preclinical mouse MM models of subcutaneous and bone tumors were evaluated using ¹¹C-acetate-PET/CT imaging and tissue biodistribution.

RESULTS

In vitro, NMR showed significant uptake of acetate by MMC and acetate incorporation into intracellular metabolites and membrane lipids. Inhibition of lipid synthesis and acetate transport was toxic to MMC, while sparing resident bone cells or normal B cells. In vivo, ¹¹C-acetate uptake by PET imaging was significantly enhanced in subcutaneous and bone MMC tumors compared with unaffected bone or muscle tissue. Likewise, ¹¹C-acetate uptake was significantly reduced in MM tumors after treatment.

CONCLUSIONS

Uptake of acetate from the extracellular environment was enhanced in MMC and was critical to cellular viability. ¹¹C-Acetate-PET detected the presence of myeloma cells in vivo, including uptake in intramedullary bone disease. ¹¹C-Acetate-PET also detected response to therapy in vivo Our data suggested that acetate metabolism and incorporation into lipids was crucial to MM cell biology and that ¹¹C-acetate-PET is a promising imaging modality for MM. Clin Cancer Res; 23(2); 416-29. ©2016 AACR.

Preclinical animal models of multiple myeloma

Multiple myeloma is an incurable plasma-cell malignancy characterized by osteolytic bone disease and immunosuppression. Murine models of multiple myeloma and myeloma bone disease are critical tools for an improved understanding of the pathogenesis of the disease and the development of novel therapeutic strategies. This review will cover commonly used immunocompetent and xenograft models of myeloma, describing the advantages and disadvantages of each model system. In addition, this review provides detailed protocols for establishing systemic and local models of myeloma using both murine and human myeloma cell lines.

Navigating the bone marrow niche: translational insights and cancer-driven dysfunction

The bone marrow niche consists of stem and progenitor cells destined to become mature cells such as haematopoietic elements, osteoblasts or adipocytes. Marrow cells, influenced by endocrine, paracrine and autocrine factors, ultimately function as a unit to regulate bone remodelling and haematopoiesis. Current evidence highlights that the bone marrow niche is not merely an anatomic compartment; rather, it integrates the physiology of two distinct organ systems, the skeleton and the marrow. The niche has a hypoxic microenvironment that maintains quiescent haematopoietic stem cells (HSCs) and supports glycolytic metabolism. In response to biochemical cues and under the influence of neural, hormonal, and biochemical factors, marrow stromal elements, such as mesenchymal stromal cells (MSCs), differentiate into mature, functioning cells. However, disruption of the niche can affect cellular differentiation, resulting in disorders ranging from osteoporosis to malignancy. In this Review, we propose that the niche reflects the vitality of two tissues - bone and blood - by providing a unique environment for stem and stromal cells to flourish while simultaneously preventing disproportionate proliferation, malignant transformation or loss of the multipotent progenitors required for healing, functional immunity and growth throughout an organism's lifetime. Through a fuller understanding of the complexity of the niche in physiologic and pathologic states, the successful development of more-effective therapeutic approaches to target the niche and its cellular components for the treatment of rheumatic, endocrine, neoplastic and metabolic diseases becomes achievable.

The Nuclear Factor (Erythroid-derived 2)-like 2 and Proteasome Maturation Protein Axis Mediate Bortezomib Resistance in Multiple Myeloma

Resistance to the proteasome inhibitor bortezomib is an emerging clinical problem whose mechanisms have not been fully elucidated. We considered the possibility that this could be associated with enhanced proteasome activity in part through the action of the proteasome maturation protein (POMP). Bortezomib-resistant myeloma models were used to examine the correlation between POMP expression and bortezomib sensitivity. POMP expression was then modulated using genetic and pharmacologic approaches to determine the effects on proteasome inhibitor sensitivity in cell lines and in vivo models. Resistant cell lines were found to overexpress POMP, and while its suppression in cell lines enhanced bortezomib sensitivity, POMP overexpression in drug-naive cells conferred resistance. Overexpression of POMP was associated with increased levels of nuclear factor (erythroid-derived 2)-like (NRF2), and NRF2 was found to bind to and activate the POMP promoter. Knockdown of NRF2 in bortezomib-resistant cells reduced POMP levels and proteasome activity, whereas its overexpression in drug-naive cells increased POMP and proteasome activity. The NRF2 inhibitor all-trans-retinoic acid reduced cellular NRF2 levels and increased the anti-proliferative and pro-apoptotic activities of bortezomib in resistant cells, while decreasing proteasome capacity. Finally, the combination of all-trans-retinoic acid with bortezomib showed enhanced activity against primary patient samples and in a murine model of bortezomib-resistant myeloma. Taken together, these studies validate a role for the NRF2/POMP axis in bortezomib resistance and identify NRF2 and POMP as potentially attractive targets for chemosensitization to this proteasome inhibitor.