A Transgenic Mouse Model of Plasma Cell Malignancy Shows Phenotypic, Cytogenetic, and Gene Expression Heterogeneity Similar to Human Multiple Myeloma

An Improved Animal Model of Multiple Myeloma Bone Disease

Multiple myeloma (MM) is a plasma cell malignancy that causes an accumulation of terminally differentiated monoclonal plasma cells in the bone marrow, accompanied by multiple myeloma bone disease (MMBD). MM animal models have been developed and enable to interrogate the mechanism of MM tumorigenesis. However, these models demonstrate little or no evidence of MMBD. We try to establish the MMBD model with severe bone lesions and easily accessible MM progression. 1 × 106 luciferase-expressing 5TGM1 cells were injected into 8-12 week-old NOD SCID gamma mouse (NSG) and C57BL/KaLwRij mouse via the tail vein. Myeloma progression was assessed weekly via in vivo bioluminescence (BL) imaging using IVIS-200. The spine and femur/tibia were extracted and scanned by the micro-computer tomography for bone histo-morphometric analyses at the postmortem. The median survivals were 56 days in NSG while 44.5 days in C57BL/KaLwRij agreed with the BL imaging results. Histomorphic and DEXA analyses demonstrated that NSG mice have severe bone resorption that occurred at the lumbar spine but no significance at the femur compared to C57BL/KaLwRij mice. Based on these, we conclude that the systemic 5TGM1 injected NSG mouse slowly progresses myeloma and develops more severe MMBD than the C57BL/KaLwRij model.

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.

Generation of a lenalidomide-sensitive syngeneic murine in vivo multiple myeloma model by expression of CrbnI391V

The immunomodulatory drugs (IMiDs) thalidomide, lenalidomide, and pomalidomide are approved drugs for the treatment of multiple myeloma. IMiDs induce cereblon (CRBN) E3 ubiquitin ligase-mediated ubiquitination and degradation of Ikaros transcription factors Ikaros (IKZF1) and Aiolos (IKZF3), which are essential for multiple myeloma. However, because of a single amino acid substitution of valine to isoleucine in mouse CRBN at position 391, mice are not susceptible to IMiD-induced degradation of neosubstrates. Here, we report that expression of human CRBN or the Crbn^I391V mutant enables IMiD-induced degradation of IKZF1 and IKZF3 in murine MOPC.315.BM.Luc.eGFP and 5T33MM multiple myeloma cells. Accordingly, lenalidomide and pomalidomide decreased cell viability in a dose-dependent fashion in murine multiple myeloma cells expressing Crbn^I391V in vitro. The sensitivity of murine cells expressing Crbn^I391V to IMiDs highly correlated with their dependence on IKZF1. After transplantation, MOPC.315.BM.Luc.eGFP cells expressing murine Crbn^I391V induced multiple myeloma in mice, and treatment with lenalidomide and pomalidomide significantly delayed tumor growth. This straightforward model provides a proof-of-concept for studying the effects of IMiDs in multiple myeloma in mice, which allows for in vivo testing of IMiDs and other CRBN E3 ligase modulators.

Multiple myeloma immunoglobulin lambda translocations portend poor prognosis

Multiple myeloma is a malignancy of antibody-secreting plasma cells. Most patients benefit from current therapies, however, 20% of patients relapse or die within two years and are deemed high risk. Here we analyze structural variants from 795 newly-diagnosed patients as part of the CoMMpass study. We report translocations involving the immunoglobulin lambda (IgL) locus are present in 10% of patients, and indicative of poor prognosis. This is particularly true for IgL-MYC translocations, which coincide with focal amplifications of enhancers at both loci. Importantly, 78% of IgL-MYC translocations co-occur with hyperdiploid disease, a marker of standard risk, suggesting that IgL-MYC-translocated myeloma is being misclassified. Patients with IgL-translocations fail to benefit from IMiDs, which target IKZF1, a transcription factor that binds the IgL enhancer at some of the highest levels in the myeloma epigenome. These data implicate IgL translocation as a driver of poor prognosis which may be due to IMiD resistance.

Multiple myeloma is frequently characterised by translocation of genes next to the immunoglobulin heavy chain locus. In this study, the authors sequence a large cohort of high risk myeloma samples and find translocations of cMyc to the immunoglobulin heavy chain locus and this is associated with poor prognosis.

Discovery platform for inhibitors of IgH gene enhancer activity

Immunoglobulin heavy chain (IgH) translocations are common and early oncogenic events in B cell and plasma cell malignancies including B cell non-Hodgkin's lymphoma (NHL) and multiple myeloma (MM). IgH translocations bring oncogenes into close proximity with potent enhancer elements within the IgH locus, leading to oncogene up-regulation. As IgH enhancer activity is tightly controlled by B cell lineage-specific signaling and transcriptional networks, we hypothesized that IgH enhancers are potentially druggable targets/elements. To test this, we developed a molecular imaging-based high-throughput screening platform for discovering inhibitors of IgH enhancer-driven transcriptional activity. As proof of concept, we identified a low micromolar potency molecule (compound 30666) that inhibited immunoglobulin production by MM cells and blocked expression of an array of IgH translocation-induced oncogenes (CCND1, FGFR3/MMSET, and MYC) in MM and NHL cell lines. Prolonged exposure to 30666 significantly reduced the viability of IgH translocation-positive NHL and MM cells, but was less effective against cells lacking IgH translocations. Compound 30666 exhibited suitable pharmacological properties, including metabolic stability in liver microsomes and oral bioavailability in mice, and demonstrated preclinical anti-MM activity in a plasmacytoma mouse model. Our work suggests that IgH enhancers are attractive and potentially druggable targets for IgH translocation driven malignancies.

Deficiency of the Endocytic Protein Hip1 Leads to Decreased Gdpd3 Expression, Low Phosphocholine, and Kypholordosis

Deficiency of huntingtin-interacting protein 1 (Hip1) results in degenerative phenotypes. Here we generated a Hip1 deficiency allele where a floxed transcriptional stop cassette and a human HIP1 cDNA were knocked into intron 1 of the mouse Hip1 locus. CMV-Cre-mediated germ line excision of the stop cassette resulted in expression of HIP1 and rescue of the Hip1 knockout phenotype. Mx1-Cre-mediated excision led to HIP1 expression in spleen, kidney and liver, and also rescued the phenotype. In contrast, hGFAP-Cre-mediated, brain-specific HIP1 expression did not rescue the phenotype. Metabolomics and microarrays of several Hip1 knockout tissues identified low phosphocholine (PC) levels and low glycerophosphodiester phosphodiesterase domain containing 3 (Gdpd3) gene expression. Since Gdpd3 has lysophospholipase D activity that results in the formation of choline, a precursor of PC, Gdpd3 downregulation could lead to the low PC levels. To test whether Gdpd3 contributes to the Hip1 deficiency phenotype, we generated Gdpd3 knockout mice. Double knockout of Gdpd3 and Hip1 worsened the Hip1 phenotype. This suggests that Gdpd3 compensates for Hip1 loss. More-detailed knowledge of how Hip1 deficiency leads to low PC will improve our understanding of HIP1 in choline metabolism in normal and disease states.

Germline Lysine-Specific Demethylase 1 (LSD1/KDM1A) Mutations Confer Susceptibility to Multiple Myeloma

Given the frequent and largely incurable occurrence of multiple myeloma, identification of germline genetic mutations that predispose cells to multiple myeloma may provide insight into disease etiology and the developmental mechanisms of its cell of origin, the plasma cell (PC). Here, we identified familial and early-onset multiple myeloma kindreds with truncating mutations in lysine-specific demethylase 1 (LSD1/KDM1A), an epigenetic transcriptional repressor that primarily demethylates histone H3 on lysine 4 and regulates hematopoietic stem cell self-renewal. In addition, we found higher rates of germline truncating and predicted deleterious missense KDM1A mutations in patients with multiple myeloma unselected for family history compared with controls. Both monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma cells have significantly lower KDM1A transcript levels compared with normal PCs. Transcriptome analysis of multiple myeloma cells from KDM1A mutation carriers shows enrichment of pathways and MYC target genes previously associated with myeloma pathogenesis. In mice, antigen challenge followed by pharmacologic inhibition of KDM1A promoted PC expansion, enhanced secondary immune response, elicited appearance of serum paraprotein, and mediated upregulation of MYC transcriptional targets. These changes are consistent with the development of MGUS. Collectively, our findings show that KDM1A is the first autosomal-dominant multiple myeloma germline predisposition gene providing new insights into its mechanistic roles as a tumor suppressor during post-germinal center B-cell differentiation.Significance: KDM1A is the first germline autosomal dominant predisposition gene identified in multiple myeloma and provides new insights into multiple myeloma etiology and the mechanistic role of KDM1A as a tumor suppressor during post-germinal center B-cell differentiation. Cancer Res; 78(10); 2747-59. ©2018 AACR.

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.

[Pharmacological characteristics and clinical study results of the oral proteasome inhibitor ixazomib (NINLARO® capsules; 2.3 mg, 3 mg, and 4 mg)]

Ixazomib (Ninlaro^® capsule) is an oral small molecule 20S proteasome inhibitor created by Millennium Pharmaceuticals, Inc (Takeda Oncology Company). Ubiquitin proteasome system is a major regulatory system for maintaining protein homeostasis, and an important mechanism for degrading proteins, such as those involved in proliferation regulation, cell cycle regulation and apoptosis, in cells. Ixazomib selectively and reversibly binds to the β5 subunit of the 20S proteasome, inhibits its chymotrypsin-like activity, and thereby accumulates ubiquitinated proteins. It induces ER stress and apoptosis of myeloma cells. The phase 3, randomized, double-blind, multicenter global study (TOURMALINE-MM1) in patients with relapsed and/or refractory multiple myeloma, who have received 1 to 3 prior lines of therapy, showed that addition of ixazomib to lenalidomide-dexamethasone (ixazomib-Rd) demonstrated significant improvement in progression-free survival (hazard ratio = 0.742, P = 0.012) versus placebo-Rd (20.6 vs. 14.7 months in the median) (data cut-off as of October 30, 2014). Ixazomib has been approved by the United States Food and Drug Administration in November 2015, and the European Medicines Agency in November 2016 for the treatment of multiple myeloma (MM) patients who have received at least one prior therapy. In Japan, ixazomib was approved for the treatment of relapsed and/or refractory MM in March, 2017. It is expected to demonstrate that the oral proteasome inhibitor ixazomib is an effective and convenient treatment option in clinical practice.

BCL-B (BCL2L10) is overexpressed in patients suffering from multiple myeloma (MM) and drives an MM-like disease in transgenic mice

Luciano et al. generate transgenic mice expressing the Bcl-B gene under the control of the VH promoter and Eµ enhancer and show that these mice recapitulate the characteristic features of human MM.

Multiple myeloma (MM) evolves from a premalignant condition known as monoclonal gammopathy of undetermined significance (MGUS). However, the factors underlying the malignant transformation of plasmocytes in MM are not fully characterized. We report here that Eµ-directed expression of the antiapoptotic Bcl-B protein in mice drives an MM phenotype that reproduces accurately the human disease. Indeed, with age, Eµ-bcl-b transgenic mice develop the characteristic features of human MM, including bone malignant plasma cell infiltration, a monoclonal immunoglobulin peak, immunoglobulin deposit in renal tubules, and highly characteristic bone lytic lesions. In addition, the tumors are serially transplantable in irradiated wild-type mice, underlying the tumoral origin of the disease. Eµ-bcl-b plasmocytes show increased expression of a panel of genes known to be dysregulated in human MM pathogenesis. Treatment of Eµ-bcl-b mice with drugs currently used to treat patients such as melphalan and VELCADE efficiently kills malignant plasmocytes in vivo. Finally, we find that Bcl-B is overexpressed in plasmocytes from MM patients but neither in MGUS patients nor in healthy individuals, suggesting that Bcl-B may drive MM. These findings suggest that Bcl-B could be an important factor in MM disease and pinpoint Eµ-bcl-b mice as a pertinent model to validate new therapies in MM.

An oncogenic Ezh2 mutation induces tumors through global redistribution of histone 3 lysine 27 trimethylation

B cell lymphoma and melanoma harbor recurrent mutations in the gene encoding the EZH2 histone methyltransferase (EZH2), but the carcinogenic role of these mutations is unclear. Here we describe a mouse model in which the most common somatic Ezh2 gain-of-function mutation (EZH2(Y646F) in human; Ezh2(Y641F) in mouse) is conditionally expressed. Expression of Ezh2(Y641F) in mouse B cells or melanocytes caused high-penetrance lymphoma or melanoma, respectively. Overexpression of the anti-apoptotic protein Bcl2, but not the oncoprotein Myc, or loss of the tumor suppressor protein p53 (encoded by Trp53 in mice) further accelerated lymphoma progression. Expression of the mutant Braf but not the mutant Nras oncoprotein further accelerated melanoma progression. Although expression of Ezh2(Y641F) globally increased the abundance of trimethylated Lys27 of histone H3 (H3K27me3), it also caused a widespread redistribution of this repressive mark, including a loss of H3K27me3 that was associated with increased transcription at many loci. These results suggest that Ezh2(Y641F) induces lymphoma and melanoma through a vast reorganization of chromatin structure, inducing both repression and activation of polycomb-regulated loci.

PIAS1 Promotes Lymphomagenesis through MYC Upregulation

The MYC proto-oncogene is a transcription factor implicated in a broad range of cancers. MYC is regulated by several post-translational modifications including SUMOylation, but the functional impact of this post-translational modification is still unclear. Here, we report that the SUMO E3 ligase PIAS1 SUMOylates MYC. We demonstrate that PIAS1 promotes, in a SUMOylation-dependent manner, MYC phosphorylation at serine 62 and dephosphorylation at threonine 58. These events reduce the MYC turnover, leading to increased transcriptional activity. Furthermore, we find that MYC is SUMOylated in primary B cell lymphomas and that PIAS1 is required for the viability of MYC-dependent B cell lymphoma cells as well as several cancer cell lines of epithelial origin. Finally, Pias1-null mice display endothelial defects reminiscent of Myc-null mice. Taken together, these results indicate that PIAS1 is a positive regulator of MYC.

Plasmacytomagenesis in Eμ-v-abl transgenic mice is accelerated when apoptosis is restrained

Mice susceptible to plasma cell tumors provide a useful model for human multiple myeloma. We previously showed that mice expressing an Eµ-v-abl oncogene solely develop plasmacytomas. Here we show that loss of the proapoptotic BH3-only protein Bim or, to a lesser extent, overexpression of antiapoptotic Bcl-2 or Mcl-1, significantly accelerated the development of plasmacytomas and increased their incidence. Disease was preceded by an increased abundance of plasma cells, presumably reflecting their enhanced survival capacity in vivo. Plasmacytomas of each genotype expressed high levels of v-abl and frequently harbored a rearranged c-myc gene, probably as a result of chromosome translocation. As in human multiple myelomas, elevated expression of cyclin D genes was common, and p53 deregulation was rare. Our results for plasmacytomas highlight the significance of antiapoptotic changes in multiple myeloma, which include elevated expression of Mcl-1 and, less frequently, Bcl-2, and suggest that closer attention to defects in Bim expression is warranted.

(18)F-FDG-PET/CT imaging in an IL-6- and MYC-driven mouse model of human multiple myeloma affords objective evaluation of plasma cell tumor progression and therapeutic response to the proteasome inhibitor ixazomib

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and computed tomography (CT) are useful imaging modalities for evaluating tumor progression and treatment responses in genetically engineered mouse models of solid human cancers, but the potential of integrated FDG-PET/CT for assessing tumor development and new interventions in transgenic mouse models of human blood cancers such as multiple myeloma (MM) has not been demonstrated. Here we use BALB/c mice that contain the newly developed iMyc(ΔEμ) gene insertion and the widely expressed H2-L(d)-IL6 transgene to demonstrate that FDG-PET/CT affords an excellent research tool for assessing interleukin-6- and MYC-driven plasma cell tumor (PCT) development in a serial, reproducible and stage- and lesion-specific manner. We also show that FDG-PET/CT permits determination of objective drug responses in PCT-bearing mice treated with the investigational proteasome inhibitor ixazomib (MLN2238), the biologically active form of ixazomib citrate (MLN9708), that is currently in phase 3 clinical trials in MM. Overall survival of 5 of 6 ixazomib-treated mice doubled compared with mice left untreated. One outlier mouse presented with primary refractory disease. Our findings demonstrate the utility of FDG-PET/CT for preclinical MM research and suggest that this method will play an important role in the design and testing of new approaches to treat myeloma.

Bortezomib resistance can be reversed by induced expression of plasma cell maturation markers in a mouse in vitro model of multiple myeloma

Multiple myeloma (MM), the second most common hematopoietic malignancy, remains an incurable plasma cell (PC) neoplasm. While the proteasome inhibitor, bortezomib (Bz) has increased patient survival, resistance represents a major treatment obstacle as most patients ultimately relapse becoming refractory to additional Bz therapy. Current tests fail to detect emerging resistance; by the time patients acquire resistance, their prognosis is often poor. To establish immunophenotypic signatures that predict Bz sensitivity, we utilized Bz-sensitive and -resistant cell lines derived from tumors of the Bcl-X_L/Myc mouse model of PC malignancy. We identified significantly reduced expression of two markers (CD93, CD69) in “acquired” (Bz-selected) resistant cells. Using this phenotypic signature, we isolated a subpopulation of cells from a drug-naïve, Bz-sensitive culture that displayed “innate” resistance to Bz. Although these genes were identified as biomarkers, they may indicate a mechanism for Bz-resistance through the loss of PC maturation which may be induced and/or selected by Bz. Significantly, induction of PC maturation in both “acquired” and “innate” resistant cells restored Bz sensitivity suggesting a novel therapeutic approach for reversing Bz resistance in refractory MM.

Germinal centre protein HGAL promotes lymphoid hyperplasia and amyloidosis via BCR-mediated Syk activation

The human germinal centre associated lymphoma (HGAL) gene is specifically expressed in germinal centre B-lymphocytes and germinal centre-derived B-cell lymphomas, but its function is largely unknown. Here we demonstrate that HGAL directly binds Syk in B-cells, increases its kinase activity upon B-cell receptor stimulation and leads to enhanced activation of Syk downstream effectors. To further investigate these findings in vivo, HGAL transgenic mice were generated. Starting from 12 months of age these mice developed polyclonal B-cell lymphoid hyperplasia, hypergammaglobulinemia and systemic reactive AA amyloidosis, leading to shortened survival. The lymphoid hyperplasia in the HGAL transgenic mice are likely attributable to enhanced B-cell receptor signalling as shown by increased Syk phosphorylation, ex vivo B-cell proliferation and increased RhoA activation. Overall, our study shows for the first time that the germinal centre protein HGAL regulates B-cell receptor signalling in B-lymphocytes which, without appropriate control, may lead to B-cell lymphoproliferation.

Profiling bortezomib resistance identifies secondary therapies in a mouse myeloma model

Multiple myeloma is a hematologic malignancy characterized by the proliferation of neoplastic plasma cells in the bone marrow. Although the first-to-market proteasome inhibitor bortezomib (Velcade) has been successfully used to treat patients with myeloma, drug resistance remains an emerging problem. In this study, we identify signatures of bortezomib sensitivity and resistance by gene expression profiling (GEP) using pairs of bortezomib-sensitive (BzS) and bortezomib-resistant (BzR) cell lines created from the Bcl-XL/Myc double-transgenic mouse model of multiple myeloma. Notably, these BzR cell lines show cross-resistance to the next-generation proteasome inhibitors, MLN2238 and carfilzomib (Kyprolis) but not to other antimyeloma drugs. We further characterized the response to bortezomib using the Connectivity Map database, revealing a differential response between these cell lines to histone deacetylase (HDAC) inhibitors. Furthermore, in vivo experiments using the HDAC inhibitor panobinostat confirmed that the predicted responder showed increased sensitivity to HDAC inhibitors in the BzR line. These findings show that GEP may be used to document bortezomib resistance in myeloma cells and predict individual sensitivity to other drug classes. Finally, these data reveal complex heterogeneity within multiple myeloma and suggest that resistance to one drug class reprograms resistant clones for increased sensitivity to a distinct class of drugs. This study represents an important next step in translating pharmacogenomic profiling and may be useful for understanding personalized pharmacotherapy for patients with multiple myeloma.

Mouse models as a translational platform for the development of new therapeutic agents in multiple myeloma

Mouse models of multiple myeloma (MM) are basic tools for translational research and play a fundamental role in the development of new therapeutics against plasma cell malignancies. All available models, including transplantable murine tumors in syngenic mice, xenografts of established human cell lines in immunocompromised mice and transgenic models that mirror specific steps of MM pathogenesis, have demonstrated some weaknesses in predicting clinical results, particularly for new drugs targeting the human bone marrow microenvironment (huBMM). The recent interest to models recapitulating the in vivo growth of primary MM cells in a human (SCID-hu) or humanized (SCID-synth-hu) host recipient has provided powerful platforms for the investigation of new compounds targeting MM and/or its huBMM. Here, we review and discuss strengths and weaknesses of the key in vivo models that are currently utilized in the MM preclinical investigation.

Myeloid-derived suppressor cells regulate growth of multiple myeloma by inhibiting T cells in bone marrow

Myeloid-derived suppressor cells (MDSC) are one of the major factors limiting the immune response in cancer. However, their role in bone marrow (BM), the site of primary localization of multiple myeloma (MM), is poorly understood. In this study, we found a significant accumulation of CD11b(+)CD14(-)CD33(+) immunosuppressive MDSC in BM of patients with newly diagnosed MM. To assess the possible role of MDSC in MM, we used immunocompetent mouse models. Immunosuppressive MDSC accumulated in BM of mice as early as 1 wk after tumor inoculation. S100A9 knockout (KO) mice, which are deficient in their ability to accumulate MDSC in tumor-bearing hosts, demonstrated reduced MDSC accumulation in BM after injection of MM cells compared with wild-type mice. Growth of the immunogenic MM cells was significantly reduced in S100A9KO mice. This effect was associated with the accumulation of Ag-specific CD8(+) T cells in BM and spleens of S100A9KO mice, but not wild-type mice, and was abrogated by the administration of anti-CD8 Ab or adoptive transfer of MDSC. Thus, the accumulation of MDSC at early stages of MM plays a critical role in MM progression and suggests that MDSC can be considered a possible therapeutic target in this disease.

Characterization of a novel mouse model of multiple myeloma and its use in preclinical therapeutic assessment

To aid preclinical development of novel therapeutics for myeloma, an in vivo model which recapitulates the human condition is required. An important feature of such a model is the interaction of myeloma cells with the bone marrow microenvironment, as this interaction modulates tumour activity and protects against drug-induced apoptosis. Therefore NOD/SCIDγc(null) mice were injected intra-tibially with luciferase-tagged myeloma cells. Disease progression was monitored by weekly bioluminescent imaging (BLI) and measurement of paraprotein levels. Results were compared with magnetic resonance imaging (MRI) and histology. Assessment of model suitability for preclinical drug testing was investigated using bortezomib, melphalan and two novel agents. Cells engrafted at week 3, with a significant increase in BLI radiance occurring between weeks 5 and 7. This was accompanied by an increase in paraprotein secretion, MRI-derived tumour volume and CD138 positive cells within the bone marrow. Treatment with known anti-myeloma agents or novel agents significantly attenuated the increase in all disease markers. In addition, intra-tibial implantation of primary patient plasma cells resulted in development of myeloma within bone marrow. In conclusion, using both myeloma cell lines and primary patient cells, we have developed a model which recapitulates human myeloma by ensuring the key interaction of tumour cells with the microenvironment.

Antitumor activity of the investigational proteasome inhibitor MLN9708 in mouse models of B-cell and plasma cell malignancies

PURPOSE

The clinical success of the first-in-class proteasome inhibitor bortezomib (VELCADE) has validated the proteasome as a therapeutic target for treating human cancers. MLN9708 is an investigational proteasome inhibitor that, compared with bortezomib, has improved pharmacokinetics, pharmacodynamics, and antitumor activity in preclinical studies. Here, we focused on evaluating the in vivo activity of MLN2238 (the biologically active form of MLN9708) in a variety of mouse models of hematologic malignancies, including tumor xenograft models derived from a human lymphoma cell line and primary human lymphoma tissue, and genetically engineered mouse (GEM) models of plasma cell malignancies (PCM).

EXPERIMENTAL DESIGN

Both cell line-derived OCI-Ly10 and primary human lymphoma-derived PHTX22L xenograft models of diffuse large B-cell lymphoma were used to evaluate the pharmacodynamics and antitumor effects of MLN2238 and bortezomib. The iMyc(Cα)/Bcl-X(L) GEM model was used to assess their effects on de novo PCM and overall survival. The newly developed DP54-Luc-disseminated model of iMyc(Cα)/Bcl-X(L) was used to determine antitumor activity and effects on osteolytic bone disease.

RESULTS

MLN2238 has an improved pharmacodynamic profile and antitumor activity compared with bortezomib in both OCI-Ly10 and PHTX22L models. Although both MLN2238 and bortezomib prolonged overall survival, reduced splenomegaly, and attenuated IgG2a levels in the iMyc(Cα)/Bcl-X(L) GEM model, only MLN2238 alleviated osteolytic bone disease in the DP54-Luc model.

CONCLUSIONS

Our results clearly showed the antitumor activity of MLN2238 in a variety of mouse models of B-cell lymphoma and PCM, supporting its clinical development. MLN9708 is being evaluated in multiple phase I and I/II trials.

Deciphering the rules of programmed cell death to improve therapy of cancer and other diseases

Apoptosis, the major form of programmed cell death in metazoan organisms, plays critical roles in normal development, tissue homeostasis and immunity, and its disturbed regulation contributes to many pathological states, including cancer, autoimmunity, infection and degenerative disorders. In vertebrates, it can be triggered either by engagement of 'death receptors' of the tumour necrosis factor receptor family on the cell surface or by diverse intracellular signals that act upon the Bcl-2 protein family, which controls the integrity of the mitochondrial outer membrane through the complex interactions of family members. Both pathways lead to cellular demolition by dedicated proteases termed caspases. This review discusses the groundbreaking experiments from many laboratories that have clarified cell death regulation and galvanised efforts to translate this knowledge into novel therapeutic strategies for the treatment of malignant and perhaps certain autoimmune and infectious diseases.

MAGED1: molecular insights and clinical implications

The melanoma antigen (MAGE) protein family contains more than 25 members that share a conserved MAGE homology domain (MHD). Type I MAGE genes exhibit cancer/testis-specific expression patterns and antigenic properties which render them ideal candidates for cancer immunotherapies. Maged1, a type II MAGE gene, is ubiquitously expressed and has been previously shown to play an important role in neuronal apoptosis during development. Recent studies have expanded the functional tissues and processes in which Maged1 activity is important and uncovered interacting partners of MAGED1 protein, adding novel layers to Maged1 functions. Maged1 plays a role in anti-tumorigenesis in a variety of cell types, and the down-regulation of MAGED1 has been observed in tumor cells. Moreover, MAGED1 can interact with a specific group of nuclear members and regulate circadian clock functions. These newly identified functions will enrich the molecular and clinical studies of the MAGE family of proteins.

Pathogenesis of myeloma

Multiple myeloma (MM) is a neoplasm of post-germinal center, terminally differentiated B cells. It is characterized by a multifocal proliferation of clonal, long-lived plasma cells within the bone marrow (BM) and associated skeletal destruction, serum monoclonal gammopathy, immune suppression, and end-organ sequelae. MM is preceded by an age-progressive premalignant condition termed monoclonal gammopathy of undetermined significance. Unlike the genomes of most hematological malignancies, and similar to those of solid-tissue neoplasms, MM genomes are typified by numerous structural and numerical chromosomal aberrations as well as mutations in a number of oncogenes and tumor-suppressor genes, some of which have been linked to disease pathogenesis and clinical behavior. Recent studies have also defined the importance of interactions between the MM cells and their BM microenvironment, dysregulation in signaling pathways and in a specialized subpopulation of cells within the tumor (termed myeloma cancer stem cells) for tumor cell growth and survival, and the development of resistance to therapy.

Anaplastic plasmacytoma of mouse--establishing parallels between subtypes of mouse and human plasma cell neoplasia

Mouse models may provide an important tool for basic and applied research on human diseases. An ideal tumour model should replicate the phenotypic and molecular characteristics of human malignancy as well as the typical physiological effects and dissemination patterns. The histopathological and molecular genetic characterization of anaplastic plasmacytoma (APCT) in strain NSF.V(+) mice provides an example to achieve this goal for a specific lymphoma subtype. Firstly, it demonstrates that, like plasma-cell neoplasms in humans, those in mice occur as distinct subtypes. Secondly, it shows that mouse APCT exhibits striking parallels to possible human tumour counterparts for which good mouse models of de novo tumour development are sorely needed: IgM(+) multiple myeloma and Waldenström's macroglobulinaemia. Thirdly, it strongly suggests that insertional somatic mutagenesis, by either a murine leukaemia virus or an oncogenic transposon, would be an effective experimental approach to accelerating malignant transformation of mature B cells and plasma cells in mice and, thereby, tagging and uncovering cancer driver genes that may be of great relevance for the tumour initiation and progression in lymphoma.

Anaplastic plasmacytomas: relationships to normal memory B cells and plasma cell neoplasms of immunodeficient and autoimmune mice

Anaplastic plasmacytomas (APCTs) from NFS.V(+) congenic mice and pristane-induced plasmacytic PCTs from BALB/c mice were previously shown to be histologically and molecularly distinct subsets of plasma cell neoplasms (PCNs). Here we extended these comparisons, contrasting primary APCTs and PCTs by gene expression profiling in relation to the expression profiles of normal naïve, germinal centre, and memory B cells and plasma cells. We also sequenced immunoglobulin genes from APCT and APCT-derived cell lines and defined surface phenotypes and chromosomal features of the cell lines by flow cytometry and by spectral karyotyping and fluorescence in situ hybridization. The results indicate that APCTs share many features with normal memory cells and the plasma cell-related neoplasms (PLs) of FASL-deficient mice, suggesting that APCTs and PLs are related and that both derive from memory B cells. Published in 2010 by John Wiley & Sons, Ltd.

Cancer stem cells: controversies in multiple myeloma

Increasing data suggest that the initiation, relapse, and progression of human cancers are driven by specific cell populations within an individual tumor. However, inconsistencies have emerged in precisely defining phenotypic markers that can reliably identify these "cancer stem cells" in nearly every human malignancy studied to date. Multiple myeloma, one of the first tumors postulated to be driven by a rare population of cancer stem cells, is no exception. Similar to other diseases, controversy surrounds the exact phenotype and biology of multiple myeloma cells with the capacity for clonogenic growth. Here, we review the studies that have led to these controversies and discuss potential reasons for these disparate findings. Moreover, we speculate how these inconsistencies may be resolved through studies by integrating advancements in both myeloma and stem cell biology.

NOTCH is part of the transcriptional network regulating cell growth and survival in mouse plasmacytomas

Aside from Myc-activating translocations characteristic of plasmacytomas (PCT), little is known about genetic factors and signaling pathways responsible for the development of spontaneous B-cell lineage lymphomas of mice. Here, we characterized the transcriptional profiles of PCT, centroblastic diffuse large B-cell lymphomas (CBL), and high-grade splenic marginal zone B-cell lymphoma (MZL++) using high-throughput quantitative reverse transcription-PCR. Expression profiles of CBL and MZL++ were strikingly similar and quite unlike that of PCT. Among the genes expressed at significantly higher levels by PCT were a number involved in NOTCH signaling, a finding supported by gene set enrichment analyses of microarray data. To investigate the importance of this pathway, NOTCH signaling was blocked in PCT cell lines by treatment with a gamma-secretase inhibitor (GSI) or transduction of a dominant-negative mutant of MAML1. These treatments resulted in reduced expression of NOTCH transcriptional targets in association with impaired proliferation and increased apoptosis. GSI treatment of transformed plasma cells in a primary PCT also induced apoptosis. These results integrate NOTCH activation with oncogenic signaling pathways downstream of translocated Myc in the pathogenesis of mouse PCT, two signaling pathways also implicated in development of human multiple myeloma and T-cell lymphoblastic lymphoma.

NF-kappaB in the pathogenesis and treatment of multiple myeloma

PURPOSE OF REVIEW

This review aims to summarize recent advances in the mechanisms through which the activation of the transcription factor NF-kappaB contributes to the pathogenesis of multiple myeloma.

RECENT FINDINGS

This transcription factor regulates expression of numerous genes involved in multiple myeloma pathogenesis, including growth, survival, immortalization, angiogenesis and metastasis. Recently, mutations of NF-kappaB signaling molecules have been identified in multiple myeloma cells. In addition, interactions between multiple myeloma cells and the bone marrow environment play critical roles in NF-kappaB activation as well as in multiple myeloma pathogenesis. Moreover, several drugs that are effective against multiple myeloma, including bortezomib, thalidomide, lenalidomide and arsenic trioxide, have been found to block activation of NF-kappaB. The combination of conventional chemotherapeutic drugs and those that block NF-kappaB activation has now proven to be effective in the treatment of multiple myeloma.

SUMMARY

Recent studies further underscore the critical role of NF-kappaB in multiple myeloma pathogenesis and have provided the rationale for multiple myeloma therapy with NF-kappaB-specific inhibitors combined with conventional chemotherapeutic drugs.

Multiple myeloma cancer stem cells

Multiple myeloma is characterized by the clonal expansion of neoplastic plasma cells within the bone marrow, elevated serum immunoglobulin, and osteolytic bone disease. The disease is highly responsive to a wide variety of anticancer treatments including conventional cytotoxic chemotherapy, corticosteroids, radiation therapy, and a growing number of agents with novel mechanisms of action. However, few if any patients are cured with these modalities and relapse remains a critical issue. A better understanding of clonogenic multiple myeloma cells is essential to ultimately improving long-term outcomes, but the nature of the cells responsible for myeloma regrowth and disease relapse is unclear. We review evidence that functional heterogeneity exists in multiple myeloma and discuss potential strategies and clinical implications of the stem-cell model of cancer in this disease.