The 5T mouse multiple myeloma model: absence of c-myc oncogene rearrangement in early transplant generations

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: the (r)evolution of current therapy and a glance into future

Over the past 20 years, the regulatory approval of several novel agents to treat multiple myeloma (MM) has prolonged median patient survival from 3 to 8-10 years. Increased understanding of MM biology has translated to advances in diagnosis, prognosis, and response assessment, as well as informed the development of targeted and immune agents. Here we provide an overview of the recent progress in MM, and highlight research areas of greatest promise to further improve patient outcome in the future.

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.

Tracking human multiple myeloma xenografts in NOD-Rag-1/IL-2 receptor gamma chain-null mice with the novel biomarker AKAP-4

BACKGROUND

Multiple myeloma (MM) is a fatal malignancy ranking second in prevalence among hematological tumors. Continuous efforts are being made to develop innovative and more effective treatments. The preclinical evaluation of new therapies relies on the use of murine models of the disease.

METHODS

Here we describe a new MM animal model in NOD-Rag1null IL2rgnull (NRG) mice that supports the engraftment of cell lines and primary MM cells that can be tracked with the tumor antigen, AKAP-4.

RESULTS

Human MM cell lines, U266 and H929, and primary MM cells were successfully engrafted in NRG mice after intravenous administration, and were found in the bone marrow, blood and spleen of tumor-challenged animals. The AKAP-4 expression pattern was similar to that of known MM markers, such as paraproteins, CD38 and CD45.

CONCLUSIONS

We developed for the first time a murine model allowing for the growth of both MM cell lines and primary cells in multifocal sites, thus mimicking the disease seen in patients. Additionally, we validated the use of AKAP-4 antigen to track tumor growth in vivo and to specifically identify MM cells in mouse tissues. We expect that our model will significantly improve the pre-clinical evaluation of new anti-myeloma therapies.

Mouse models of human myeloma

Multiple myeloma (MM) remains incurable despite high-dose chemotherapy with stem cell support. There is need, therefore, for continuous efforts directed toward the development of novel rational-based therapeutics for MM, which requires a detailed knowledge of the mutations driving this malignancy. In improving the success rate of effective drug development, it is equally imperative that biologic systems be developed to better validate these target genes. Here we review the recent developments in the generation of mouse models of MM and their impact as preclinical models for designing and assessing target-based therapeutic approaches.

Multiple myeloma: a prototypic disease model for the characterization and therapeutic targeting of interactions between tumor cells and their local microenvironment

The interaction between tumor cells and the local milieu where are homing has recently become the focus of extensive research in a broad range of malignancies. Among them, multiple myeloma (MM) is now recognized as a prototypical tumor model for the characterization of these interactions. This is due not only to the propensity of MM cells to target the skeleton and form lytic bone lesions, but because interactions of MM cells with normal cells of the bone milieu can attenuate the anti-tumor activity of conventional therapies, such as glucocorticoids and standard cytotoxic agents, including alkylators. Herein, we highlight the recent advances in our understanding of cellular and molecular mechanisms of interactions between MM cells and their milieu. Particular emphasis is placed on the interface between MM cells and normal cell compartments of the BM, especially bone marrow stromal cells (BMSCs), and on the development of a series of new classes of therapeutic agents, including the proteasome inhibitor bortezomib, thalidomide and lenalidomide, which counteract specific aspects of those MM-BM interactions. The significant clinical activity of these novel therapies has not only led to a new era in the therapeutic management of this disease, but also underscored the importance of comprehensively characterizing the role of the local microenvironment in the pathophysiology of human neoplasias.

Visualization of 5T33 myeloma cells in the C57BL/KaLwRij mouse: establishment of a new syngeneic murine model of multiple myeloma

OBJECTIVE

Lack of good models for in vivo detection of multiple myeloma (MM) cells hampers our understanding of the disease. Our objective was to establish a murine model for MM, allowing sensitive and labor-free tracing and quantification of MM cells in an immunocompetent host.

METHODS

5T33MM cells were retrovirally transduced, expressing enhanced green fluorescent protein (eGFP) and/or herpes simplex virus thymidine kinase (HSV-tk) as a control. Flow cytometric eGFP detection accuracy and sensitivity were assessed. Functional characteristics of transduced cells, including growth rate and production of IgG2b paraprotein and interleukin-6, were compared to those of nontransduced cells in vitro. For induction of MM, C57BL/KaLwRij mice were injected intravenously with transduced and nontransduced cells. Survival kinetics and distribution of eGFP cells in tissues were evaluated.

RESULTS

Flow cytometric eGFP detection was accurate at 1:1000 transduced/nontransduced cell ratio. Transduced and nontransduced 5T33MM cells exhibited similar growth rates, producing comparable IgG2b and interleukin-6 levels. Intravenous injection of both nontransduced and eGFP-transduced MM cells to C57BL/KaLwRij mice resulted in paraplegia. At the time of paraplegia, eGFP-transduced MM cells were detected substantially in the bone marrow, spleen, and liver, less in lymph nodes, but not in the thymus. The bone marrow of paraplegic mice contained higher eGFP-transduced MM cells compared to that of nonparaplegic animals.

CONCLUSIONS

In the established eGFP-5T33 MM model, MM cells are easily traced in an immunocompetent host. This model simplifies the analysis of homing pattern studies, the evaluation of therapeutic effects of various treatment approaches and contributes towards better understanding of MM.

Animal models of bone metastasis

Animal models will continue to be indispensable to investigate the pathogenesis of bone metastasis in vivo, conduct preclinical chemotherapeutic, chemoprevention and genetic therapy studies, test gene delivery mechanisms, and identify metastasis suppressor and inducer genes. It is likely that the bone marrow microenvironment, such as the endothelial cells, stromal cells, hematopoietic cells, bone cells, and the intercellular matrix play important roles in the localization and clonal growth of cancer cells in bone. Given the complexity of bone metastasis, many genes are expected to be involved in the pathogenesis and few are likely indispensable. The use of genomic and proteomic approaches to study these animal models will identify key targets for therapeutic intervention. As we further refine these models and use imaging for real-time evaluation of cells, and eventually target genes, these models will more closely mirror human disease and will hopefully become more predictive of the human response to therapy.

Neoplastic development in plasma cells

An increasing number of model systems of plasma cell tumor (PCT) formation have been and are being developed. Discussed here are six models in mice and multiple myeloma (MM) in humans. Each model illustrates a unique set of biological factors. There are two general types of model systems: those that depend upon naturally arising mutagenic changes (pristane-induced PCTs, 5TMM, and MM) and those that are associated with oncogenes (Emu-v-abl), growth factors [interleukin-6 (IL-6)], and anti-apoptotic factors (Bcl-xL/Bcl-2). PCTs develop in several special tissue microenvironments that provide essential cytokines (IL-6) and cell-cell interactions. In mice, the activation and deregulation of c-myc by chromosomal translocations is a major feature in many of the models. This mechanism is much less a factor in MM and the 5T model in mice. Genetically determined susceptibility is involved in many of the mouse models, but only a few genes have been implicated thus far.

Multiple myeloma: evolving genetic events and host interactions

Multiple myeloma is a neoplasm of terminally differentiated B cells (plasma cells) in which chromosome translocations frequently place oncogenes under the control of immunoglobulin enhancers. Unlike most haematopoietic cancers, multiple myeloma often has complex chromosomal abnormalities that are reminiscent of epithelial tumours. What causes full-blown myeloma? And can our molecular understanding of this common haematological malignancy be used to develop effective preventive and treatment strategies?

Rearrangements of the c-myc oncogene are present in 15% of primary human multiple myeloma tumors

Rearrangements of the c-myc oncogene have been found in most plasmacytomas induced in mice and human myeloma cell lines (HMCLs) analyzed so far. However, neither induced mouse plasmacytomas nor HMCLs represent relevant models for human multiple myeloma (MM). To evaluate the incidence of c-myc rearrangements in human plasma cell dyscrasias, sets of probes were generated to allow direct assessment of c-myc translocations on interphase plasma cells by using fluorescence in situ hybridization. After validation of these probes, a large cohort of patients with either newly diagnosed MM (n = 529), relapsed MM (n = 58), primary plasma cell leukemia (PCL; n = 23), monoclonal gammopathy of undetermined significance (n = 65), or smoldering MM (n = 24) were analyzed. C-myc rearrangements were identified in 15% of patients with MM or primary PCL, independently of the stage of the disease (ie, diagnosis or relapse and MM or primary PCL). Analysis of the 2 main translocations observed on karyotyping, ie, t(8;14) and t(8;22), revealed that these specific translocations represented only 25% (23 of 91) of c-myc rearrangements. c-myc rearrangements were then correlated with several other patients' characteristics: illegitimate IgH recombinations, chromosome 13 deletions, and serum beta2-microglobulin levels. The only significant correlation was with a high beta2-microglobulin level (P =.002), although a trend for association with t(4;14) was observed (P =.08). Thus, c-myc rearrangement analysis in patients with MM revealed a strikingly lower incidence than that in HMCLs and plasmacytomas induced in mice, indicating that data obtained with these models cannot be directly extrapolated to human MM.

Spontaneous development of plasmacytoid tumors in mice with defective Fas-Fas ligand interactions

B cell malignancies arise with increased frequency in aging individuals and in patients with genetic or acquired immunodeficiency (e.g., AIDS) or autoimmune diseases. The mechanisms of lymphomagenesis in these individuals are poorly understood. In this report we investigated the possibility that mutations at the Fas (lpr) and Fasl (gld) loci, which prevent Fas-mediated apoptosis and cause an early onset benign lymphoid hyperplasia and autoimmunity, also predispose mice to malignant lymphomas later in life. Up to 6 mo of age, hyperplasia in lpr and gld mice results from the predominant accumulation of polyclonal T cell subsets and smaller numbers of polyclonal B cells and plasma cells. Here, we examined C3H-lpr, C3H-gld, and BALB-gld mice 6-15 mo of age for the emergence of clonal T and B cell populations and found that a significant proportion of aging mice exclusively developed B cell malignancies with many of the hallmarks of immunodeficiency-associated B lymphomas. By 1 yr of age, approximately 60% of BALB-gld and 30% of C3H-gld mice had monoclonal B cell populations that grew and metastasized in scid recipients but in most cases were rejected by immunocompetent mice. The tumors developed in a milieu greatly enriched for plasma cells, CD23- B cells and immunodeficient memory T cells and variably depleted of B220+ DN T cells. Growth factor-independent cell lines were established from five of the tumors. The majority of the tumors were CD23- and IgH isotype switched and a high proportion was CD5+ and dull Mac-1+. Considering their Ig secretion and morphology in vivo, most tumors were classified as malignant plasmacytoid lymphomas. The delayed development of the gld tumors indicated that genetic defects in addition to the Fas/Fasl mutations were necessary for malignant transformation. Interestingly, none of the tumors showed changes in the genomic organization of c-Myc but many had one or more somatically-acquired MuLV proviral integrations that were transmitted in scid passages and cell lines. Therefore, insertional mutagenesis may be a mechanism for transformation in gld B cells. Our panel of in vivo passaged and in vitro adapted gld lymphomas will be a valuable tool for the future identification of genetic abnormalities associated with B cell transformation in aging and autoimmune mice.

Characterization of C57BL/6 plasmacytomas lacking a c-myc translocation

BALB/c peritoneal plasmacytomas induced by a variety of agents are invariably associated with a c-myc translocation. In contrast, naturally arising bone marrow plasma cell tumors in C57BL/KaLwRij mice lack this translocation. This difference has led to the suggestion that these are 2 fundamentally different plasma cell diseases. Herein, we have analyzed 2 rare C57BL/6 peritoneal plasmacytomas in terms of characteristics associated with the bone marrow-derived lines. Like the bone marrow lines, these peritoneal plasmacytomas do not exhibit c-myc translocations, indicating that c-myc translocation is not an obligatory event in the development of all murine extramedullary plasmacytomas. However, myc is dysregulated at the mRNA level, indicating that myc overexpression may be fundamental to most plasma cell diseases but that dysregulation can occur by alternative mechanisms possibly reflecting different genetic backgrounds.

Cytogenetic findings in mouse multiple myeloma and Waldenström's macroglobulinemia

Multiple myeloma (MM) and Waldenstrom's macroglobulinemia-like lymphoma (MW) appear spontaneously in C57BL/KaLwRij mice at a frequency of 0.5% and 0.2%, respectively. They can readily be propagated by intravenous transfer of mainly bone marrow or spleen cells into syngeneic recipients. Previous studies demonstrated that these mouse malignant monoclonal gammopathies (MMG) show clinical and biologic features that closely resemble those of the corresponding human diseases and thus could be used as experimental models. We report on cytogenetic analysis of two mouse MW and five MM in vivo cell lines of the 5TMM series propagated in syngeneic mice. These studies demonstrated clonal abnormalities in all cell lines, hyperdiploid karyotype in both MW and one MM lines, and hypotriploidy, hypertriploidy, or hypotetraploidy in the other lines. Structural abnormalities of chromosome 15 were observed in all MM lines. In five MM lines, frequent rearrangements were also found for chromosome numbers 1, 2, 5, and 12. A single chromosomal abnormality, as found in induced mouse plasmacytomas and resembling Burkitt lymphoma, was not found in mouse MM and MW. It was concluded that spontaneously originating C57BL MM of the 5T series is a better model for human MM than pristane-induced BALB/c or NZB plasmacytoma.

Age-related monoclonal gammapathies: clinical lessons from the aging C57BL mouse

In this article the long-held notion that benign monoclonal gammapathy (BMG) is a premalignant stage in the development of multiple myeloma (MM) is attacked. Jiri Radl argues that clinical and experimental observations indicate that they are separate entities which may be distinguished in the laboratory and which should be managed in radically different ways.