Critical roles for immunoglobulin translocations and cyclin D dysregulation in multiple myeloma

The SAGA acetyltransferase module is required for the maintenance of MAF and MYC oncogenic gene expression programs in multiple myeloma

Despite recent advances in therapeutic treatments, multiple myeloma (MM) remains an incurable malignancy. Epigenetic factors contribute to the initiation, progression, relapse, and clonal heterogeneity in MM, but our knowledge on epigenetic mechanisms underlying MM development is far from complete. The SAGA complex serves as a coactivator in transcription and catalyzes acetylation and deubiquitylation. Analyses of datasets in the Cancer Dependency Map Project revealed many SAGA components are selective dependencies in MM. To define SAGA-specific functions, we focused on ADA2B, the only subunit in the lysine acetyltransferase (KAT) module that specifically functions in SAGA. Integration of RNA-seq, ATAC-seq, and CUT&RUN results identified pathways directly regulated by ADA2B include MTORC1 signaling, MYC, E2F, and MM-specific MAF oncogenic programs. We discovered that ADA2B is recruited to MAF and MYC gene targets, and that MAF shares a majority of its targets with MYC in MM cells. Furthermore, we found the SANT domain of ADA2B is required for interaction with both GCN5 and PCAF acetyltransferases, incorporation into SAGA, and ADA2B protein stability. Our findings uncover previously unknown SAGA KAT module-dependent mechanisms controlling MM cell growth, revealing a vulnerability that might be exploited for future development of MM therapy.

MAF functions as a pioneer transcription factor that initiates and sustains myelomagenesis

Deregulated expression of lineage-affiliated transcription factors (TFs) is a major mechanism of oncogenesis. However, how the deregulation of nonlineage affiliated TF affects chromatin to initiate oncogenic transcriptional programs is not well-known. To address this, we studied the chromatin effects imposed by oncogenic MAF as the cancer-initiating driver in the plasma cell cancer multiple myeloma. We found that the ectopically expressed MAF endows myeloma plasma cells with migratory and proliferative transcriptional potential. This potential is regulated by the activation of enhancers and superenhancers, previously inactive in healthy B cells and plasma cells, and the cooperation of MAF with the plasma cell-defining TF IRF4. Forced ectopic MAF expression confirms the de novo ability of oncogenic MAF to convert transcriptionally inert chromatin to active chromatin with the features of superenhancers, leading to the activation of the MAF-specific oncogenic transcriptome and the acquisition of cancer-related cellular phenotypes such as CCR1-dependent cell migration. These findings establish oncogenic MAF as a pioneer transcription factor that can initiate as well as sustain oncogenic transcriptomes and cancer phenotypes. However, despite its pioneer function, myeloma cells remain MAF-dependent, thus validating oncogenic MAF as a therapeutic target that would be able to circumvent the challenges of subsequent genetic diversification driving disease relapse and drug resistance.

Targeting cyclin D1 as a therapeutic approach for papillary thyroid carcinoma

Cyclin D1 functions as a mitogenic sensor that specifically binds to CDK4/6, thereby integrating external mitogenic inputs and cell cycle progression. Cyclin D1 interacts with transcription factors and regulates various important cellular processes, including differentiation, proliferation, apoptosis, and DNA repair. Therefore, its dysregulation contributes to carcinogenesis. Cyclin D1 is highly expressed in papillary thyroid carcinoma (PTC). However, the particular cellular mechanisms through which abnormal cyclin D1 expression causes PTC are poorly understood. Unveiling the regulatory mechanisms of cyclin D1 and its function in PTC may help determine clinically effective strategies, and open up better opportunities for further research, leading to the development of novel PTC regimens that are clinically effective. This review explores the mechanisms underlying cyclin D1 overexpression in PTC. Furthermore, we discuss the role of cyclin D1 in PTC tumorigenesis via its interactions with other regulatory elements. Finally, recent progress in the development of therapeutic options targeting cyclin D1 in PTC is examined and summarized.

Posttranslational modification of Aurora A-NSD2 loop contributes to drug resistance in t(4;14) multiple myeloma

Background

t(4;14)(p16;q32) cytogenetic abnormality renders high level of histone methyltransferase NSD2 in multiple myeloma (MM) patients, and predicts poor clinical prognosis, but mechanisms of NSD2 in promoting chemoresistance have not been well elucidated.

Methods

An epigenetics compound library containing 181 compounds was used to screen inhibitors possessing a prior synergistic effect with bortezomib (BTZ) in vitro. Molecular biology techniques were applied to uncover underlying mechanisms. Transcriptome profile assay was performed by RNA‐seq. NSG mouse‐based xenograft model and intra‐bone model were applied to qualify the synergistic effect in vivo.

Results

We identified an Aurora kinase A inhibitor (MLN8237) possessed a significant synergistic effect with BTZ on t(4;14) positive MM cells. Aurora A protein level positively correlated with NSD2 level, and gain‐ and loss‐of‐functions of Aurora A correspondingly altered NSD2 protein and H3K36me2 levels. Mechanistically, Aurora A phosphorylated NSD2 at S56 residue to protect the protein from cleavage and degradation, thus methylation of Aurora A and phosphorylation of NSD2 bilaterally formed a positive regulating loop. Transcriptome profile assay of MM cells with AURKA depletion identified IL6R, STC2 and TCEA2 as the downstream target genes responsible for BTZ‐resistance (BR). Clinically, higher expressions of these genes correlated with poorer outcomes of MM patients. Combined administration of MLN8237 and BTZ significantly suppressed tumour growth in LP‐1 cells derived xenografts, and remarkably alleviated bone lesion in femurs of NSG mice.

Conclusions

Aurora A phosphorylates NSD2 at S56 residue to enhance NSD2 methyltransferase activity and form a positive regulating loop in promoting MM chemoresistance, thus pharmacologically targeting Aurora A sensitizes t(4;14) positive MM to the proteasome inhibitors treatment. Our study uncovers a previously unknown reason of MM patients with t(4;14) engendering chemoresistance, and provides a theoretical basis for developing new treatment strategy for MM patients with different genomic backgrounds.

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

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

Genetic Predictors of Mortality in Patients with Multiple Myeloma

Multiple myeloma (MM) is a heterogeneous disease featured by clonal plasma cell proliferation and genomic instability. The advent of next-generation sequencing allowed unraveling the complex genomic landscape of the disease. Several recurrent genomic aberrations including immunoglobulin genes translocations, copy number abnormalities, complex chromosomal events, transcriptomic and epigenomic deregulation, and mutations define various molecular subgroups with distinct outcomes. In this review, we describe the recurrent genomic events identified in MM impacting patients’ outcome and survival. These genomic aberrations constitute new markers that could be incorporated into a prognostication model to eventually guide therapy at every stage of the disease.

Molecular Insights into the Potential of Extracellular Vesicles Released from Mesenchymal Stem Cells and Other Cells in the Therapy of Hematologic Malignancies

Hematologic cancer encompasses the heterogeneous group of neoplasms that affect different stages of blood cell linages. Despite the significant improvements made in the new modalities of anticancer therapy, many forms of blood cancer remain untreatable, putting the afflicted patients at high risk of death. Therefore, there has been an urgent need for novel therapy to improve the clinical outcomes of patients with blood cancer. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been reported to possess an anticancer activity. This review discusses (i) the therapeutic potential of MSC-EVs against blood cancer, (ii) the possibility of using EVs from sources other than MSCs as a mean for blood cancer vaccination and drug delivery, and (iii) areas to be optimized for MSC-EV-based clinical application on blood malignancies.

Revealing the impact of structural variants in multiple myeloma

The landscape of structural variants (SVs) in multiple myeloma remains poorly understood. Here, we performed comprehensive analysis of SVs in a large cohort of 752 multiple myeloma patients by low coverage long-insert whole genome sequencing. We identified 68 SV hotspots involving 17 new candidate driver genes, including the therapeutic targets BCMA (TNFRSF17), SLAMF and MCL1. Catastrophic complex rearrangements termed chromothripsis were present in 24% of patients and independently associated with poor clinical outcomes. Templated insertions were the second most frequent complex event (19%), mostly involved in super-enhancer hijacking and activation of oncogenes such as CCND1 and MYC. Importantly, in 31% of patients two or more seemingly independent putative driver events were caused by a single structural event, demonstrating that the complex genomic landscape of multiple myeloma can be acquired through few key events during tumor evolutionary history. Overall, this study reveals the critical role of SVs in multiple myeloma pathogenesis.

The contribution of immune activation and accelerated aging in multiple myeloma occurring in HIV-infected population

: The widespread use of antiretroviral treatment results in a significant improvement in immunological condition of people living with HIV (PLWH) who nevertheless experience a significantly increased risk to develop non-Hodgkin lymphoma compared with the general population. Despite many literature observations regarding multiple myeloma in PLWH, a consensus on its relevance in HIV infection does not exist. A number of large population studies on multiple myeloma in PLWH gave contrasting results, fluctuating from increased standardized incidence ratios to the lack of observed cases of multiple myeloma. Use of antiretroviral treatment, in this context, seems to induce a slight reduction of standardized incidence ratio, although with a partial effect, especially in young patients. However, a high variability in clinical onset has been described in different reports: the only common feature of multiple myeloma in PLWH is an atypical presentation as compared with general population, with a worse prognosis in case of uncontrolled HIV infection. We identified three pathogenetic steps in the complex scenario of multiple myeloma in PLWH: first, antigenic trigger; second, persistent T cell deficiency/dysfunction; third, altered regulation of B cells. All these pathogenetic steps play a role in immunological dysregulation, leading to B cell abnormalities and hyperactivation and, finally, resulting in the development of lymphoid malignancies. HIV has a role in each one of these three steps, due to its ability to trigger and dysregulate immune system. We hypothesize that HIV could be closely implicated in the multiple myeloma development in PLWH by accelerating the carcinogenesis events in a complex and only partially understood early aging process.

MMSET I acts as an oncoprotein and regulates GLO1 expression in t(4;14) multiple myeloma cells

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. T(4;14) MM overexpresses multiple myeloma SET domain-containing protein (MMSET). MMSET has three major isoforms: the full-length form MMSET II and the short isoforms REIIBP and MMSET I. Here we show that the short isoform MMSET I is an oncoprotein that promoted cell survival and tumorigenesis in vitro and in vivo. Gene expression array analysis indicated that MMSET I increased glyoxalase I (GLO1) expression. Chromatin immunoprecipitation (ChIP) coupled with qPCR indicated that MMSET I bound upstream of the GLO1 transcription start site. Ectopic overexpression of MMSET I or its mutants showed MMSET I depended on its C terminus to regulate GLO1 expression. GLO1 knockdown (KD) induced apoptosis and reduced colony formation. MMSET I or GLO1 KD reduced the levels of anti-apoptosis factors such as MCL1 and BCL2. Ectopic overexpression of GLO1 resulted in the significant rescue of KMS11 cells from MMSET I KD-induced apoptosis and glycolysis inhibition. This suggested that GLO1 may be of functional importance target downstream of MMSET I. Cumulatively, our study suggests that MMSET I is an oncoprotein and potential therapeutic target for t(4;14) MM.

Preclinical development of G1T38: A novel, potent and selective inhibitor of cyclin dependent kinases 4/6 for use as an oral antineoplastic in patients with CDK4/6 sensitive tumors

Inhibition of the p16^INK4a/cyclin D/CDK4/6/RB pathway is an effective therapeutic strategy for the treatment of estrogen receptor positive (ER⁺) breast cancer. Although efficacious, current treatment regimens require a dosing holiday due to severe neutropenia potentially leading to an increased risk of infections, as well as tumor regrowth and emergence of drug resistance. Therefore, a next generation CDK4/6 inhibitor that can inhibit proliferation of CDK4/6-dependent tumors while minimizing neutropenia could reduce both the need for treatment holidays and the risk of inducing drug resistance.

Here, we describe the preclinical characterization and development of G1T38; a novel, potent, selective, and orally bioavailable CDK4/6 inhibitor. In vitro, G1T38 decreased RB1 (RB) phosphorylation, caused a precise G1 arrest, and inhibited cell proliferation in a variety of CDK4/6-dependent tumorigenic cell lines including breast, melanoma, leukemia, and lymphoma cells. In vivo, G1T38 treatment led to equivalent or improved tumor efficacy compared to the first-in-class CDK4/6 inhibitor, palbociclib, in an ER⁺ breast cancer xenograft model. Furthermore, G1T38 accumulated in mouse xenograft tumors but not plasma, resulting in less inhibition of mouse myeloid progenitors than after palbociclib treatment. In larger mammals, this difference in pharmacokinetics allowed for 28 day continuous dosing of G1T38 in beagle dogs without producing severe neutropenia. These data demonstrate G1T38 has unique pharmacokinetic and pharmacodynamic properties, which result in high efficacy against CDK4/6 dependent tumors while minimizing the undesirable on-target bone marrow activity, thus potentially allowing G1T38 to be used as a continuous, daily oral antineoplastic agent.

Genetic interrogation of circulating multiple myeloma cells at single-cell resolution

Multiple myeloma (MM) remains an incurable disease, with a treatment-refractory state eventually developing in all patients. Constant clonal evolution and genetic heterogeneity of MM are a likely explanation for the emergence of drug-resistant disease. Monitoring of MM genomic evolution on therapy by serial bone marrow biopsy is unfortunately impractical because it involves an invasive and painful procedure. We describe how noninvasive and highly sensitive isolation and characterization of circulating tumor cells (CTCs) from peripheral blood at single-cell resolution recapitulate MM in the bone marrow. We demonstrate that CTCs provide the same genetic information as bone marrow MM cells and even reveal mutations with greater sensitivity than bone marrow biopsies in some cases. Single CTC RNA sequencing enables classification of MM and quantitative assessment of genes that are relevant for prognosis. We propose that the genomic characterization of CTCs should be included in clinical trials to follow the emergence of resistant subclones after MM therapy.

High glucose concentration induces endothelial cell proliferation by regulating cyclin-D2-related miR-98

Cyclin D2 is involved in the pathology of vascular complications of type 2 diabetes mellitus (T2DM). This study investigated the role of cyclin‐D2‐regulated miRNAs in endothelial cell proliferation of T2DM. Results showed that higher glucose concentration (4.5 g/l) significantly promoted the proliferation of rat aortic endothelial cells (RAOECs), and significantly increased the expression of cyclin D2 and phosphorylation of retinoblastoma 1 (p‐RB1) in RAOECs compared with those under low glucose concentration. The cyclin D2‐3′ untranslated region is targeted by miR‐98, as demonstrated by miRNA analysis software. Western blot also confirmed that cyclin D2 and p‐RB1 expression was regulated by miR‐98. The results indicated that miR‐98 treatment can induce RAOEC apoptosis. The suppression of RAOEC growth by miR‐98 might be related to regulation of Bcl‐2, Bax and Caspase 9 expression. Furthermore, the expression levels of miR‐98 decreased in 4.5 g/l glucose‐treated cells compared with those treated by low glucose concentration. Similarly, the expression of miR‐98 significantly decreased in aortas of established streptozotocin (STZ)‐induced diabetic rat model compared with that in control rats; but cyclin D2 and p‐RB1 levels remarkably increased in aortas of STZ‐induced diabetic rats compared with those in healthy control rats. In conclusion, this study demonstrated that high glucose concentration induces cyclin D2 up‐regulation and miR‐98 down‐regulation in the RAOECs. By regulating cyclin D2, miR‐98 can inhibit human endothelial cell growth, thereby providing novel therapeutic targets for vascular complication of T2DM.

MMSET regulates expression of IRF4 in t(4;14) myeloma and its silencing potentiates the effect of bortezomib

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. In t(4;14) MM, the MM SET domain (MMSET) protein is universally overexpressed and has been suggested to have an important tumorigenic role. However, the exact molecular targets underlying MMSET activity are not well understood. Here, we found in t(4;14) MM cells that MMSET knockdown decreases interferon regulatory factor 4 (IRF4) expression, and ectopic MMSET increases IRF4 expression, suggesting that MMSET is an upstream regulator of IRF4. Further analyses indicated an interaction between MMSET and nuclear factor-κB, which both bind to the IRF4 promoter region. A luciferase reporter assay showed that MMSET is an important functional element for the IRF4 promoter. MMSET knockdown induces apoptosis and potentiates the effects of bortezomib in vitro and in vivo. Importantly, we found that bortezomib could reduce expression of MMSET and IRF4. This might partly explain the additive effect of combining MMSET knockdown and bortezomib treatment. These results identify MMSET as a key regulator involved in the regulatory network of transcription factor IRF4, which is critical for MM cell survival, suggesting that the combination of MMSET inhibition and bortezomib is likely to improve patient outcome in MM.

MMSET: role and therapeutic opportunities in multiple myeloma

Recurrent chromosomal translocations are central to the pathogenesis, diagnosis, and prognosis of hematologic malignancies. The translocation t(4; 14)(p16; q32) is one of the most common translocations in multiple myeloma (MM) and is associated with very poor prognosis. The t(4; 14) translocation leads to the simultaneous overexpression of two genes, FGFR3 (fibroblast growth factor receptor 3) and MMSET (multiple myeloma SET domain), both of which have potential oncogenic activity. However, approximately 30% of t(4; 14) MM patients do not express FGFR3 and have poor prognosis irrespective of FGFR3 expression, whereas MMSET overexpression is universal in t(4; 14) cases. In this review, we provide an overview of recent findings regarding the oncogenic roles of MMSET in MM and its functions on histone methylation. We also highlight some of MMSET partners and its downstream signalling pathways and discuss the potential therapeutics targeting MMSET.

Plasma membrane proteomics identifies biomarkers associated with MMSET overexpression in T(4;14) multiple myeloma

Multiple myeloma (MM) is characterized by recurrent chromosomal translocations. MMSET, identified by its fusion to the IgH locus in t(4;14) MM, is universally overexpressed in t(4;14) MM. In order to identify cell surface biomarkers associated with t(4;14) MM for small molecule or antibody based therapies, we knocked down MMSET expression with shRNA and generated a cell line pair from KMS11, a t(4;14) MM cell line. We used quantitative mass spectrometry to identify plasma membrane proteins associated with MMSET overexpression. Using this approach, 50 cell surface proteins were identified as differentially expressed between KMS11 and KMS11/shMMSET. Western blot and flow cytometry analysis indicated SLAMF7 was over-expressed in t(4;14) MM cell lines and down-regulated by MMSET shRNAs. SLAMF7 expression was also confirmed in primary t(4;14) MM samples by flow cytometry analysis. Quantitative RT-PCR and ChIP analysis indicated MMSET might regulate the transcription level of SLAMF7 and be an important functional element for SLAMF7 promoter activity. Furthermore, SLAMF7 shRNA could induce G1 arrest or apoptosis and reduce clonogenetic capacity in t(4;14) MM cells. Overall, these results illustrated SLAMF7 might be a novel cell surface protein associated with t(4;14) MM. It is potential to develop t(4;14) MM targeted therapy by SLAMF7 antibody mediated drug delivery.

The role of epigenetics in the biology of multiple myeloma

Several recent studies have highlighted the biological complexity of multiple myeloma (MM) that arises as a result of several disrupted cancer pathways. Apart from the central role of genetic abnormalities, epigenetic aberrations have also been shown to be important players in the development of MM, and a lot of research during the past decades has focused on the ways DNA methylation, histone modifications and noncoding RNAs contribute to the pathobiology of MM. This has led to, apart from better understanding of the disease biology, the development of epigenetic drugs, such as histone deacetylase inhibitors that are already used in clinical trials in MM with promising results. This review will present the role of epigenetic abnormalities in MM and how these can affect specific pathways, and focus on the potential of novel 'epidrugs' as future treatment modalities for MM.

Review of molecular diagnostics in multiple myeloma

Multiple myeloma evolves clinically from monoclonal gammopathy of undetermined significance through smoldering disease, active myeloma with end organ damage to a preterminal phase of extramedullary disease and marrow collapse. The molecular equivalents of such clinical observation can now be defined as genetically dormant, genetic crisis and genetic chaos (popularly termed malignant myeloma). Patients may present for the first time in any one of these stages. Not surprisingly, clinical outcomes for multiple myeloma are variable and the prospects for therapeutic responsiveness are defined by the stage at presentation. We describe here a genetically driven definition of high- and low-risk myeloma and offer guidelines for the adoption of routine diagnostic testing. We define high-risk disease as the presence of t(4;14), t(14;16), deletion 17p13 by FISH or the presence of hypodiploidy or deletion of chromosome 13 by conventional cytogenetics. By default, other patients are not considered high risk. Thus, as a minimum, we recommend routine testing for t(4;14) and 17p13 deletion by FISH and conventional cytogenetics. This classification will identify multiple myeloma patients at high genetic risk for early progression after conventional therapies.

Regular aspirin use and risk of multiple myeloma: a prospective analysis in the health professionals follow-up study and nurses' health study

Multiple myeloma is a lethal malignancy with an unknown etiology and no prevention strategy. Aspirin inhibits several pathways mediated by NF-κB, COX-2, or their targets that are important in multiple myeloma pathogenesis. We conducted prospective analyses in the Health Professionals Follow-up Study and Nurses' Health Study cohorts to examine whether regular aspirin use influences multiple myeloma risk. We used biennially updated data to characterize aspirin use from baseline through a cancer diagnosis, death, or 2008. We applied a 4-year lag in exposure classification to diminish the influence of preclinical multiple myeloma on aspirin use habits. We obtained HRs and 95% confidence intervals (CI) from multivariable proportional hazard models to assess the association of aspirin use with multiple myeloma risk. We tested for trend across increasing quantity and duration of use. During 2,395,458 person-years, we confirmed 328 incident multiple myeloma diagnoses, including 265 with prospective information on typical aspirin dose and frequency. Participants with a cumulative average of ≥5 adult strength (325 mg) tablets per week had a 39% lower multiple myeloma risk than nonusers (HR; 95% CI, 0.61, 0.39-0.94; tablets per week, Ptrend = 0.06). Persons with ≥11 years of continuous regular aspirin use also had a lower multiple myeloma risk (HR; 95% CI, 0.63, 0.41-0.95; duration, Ptrend = 0.17). The associations appeared stronger in men than in women, possibly reflecting gender differences in aspirin use patterns. This prospective study of aspirin use and multiple myeloma supports an etiologic role for aspirin-inhibited (i.e., NF-κB- or COX-2 mediated) pathways. The utility of aspirin for multiple myeloma chemoprevention warrants further evaluation.

Emerging pathways as individualized therapeutic target of multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to the growing knowledge of disease pathobiology.

AREAS COVERED

Intrinsic genetic lesions, as well as the bone marrow microenvironment, contribute to the activation of proliferation and survival pathways, impairment of cell death mechanisms and drug resistance. The phosphatidylinositol 3-kinase (PI3K) and the Ras/mitogen-activated protein kinase (MAPK) cascades are the signaling pathways mainly involved in the MM development. In the last decade, several molecules interfering with growth and survival promoting signaling have been developed.

EXPERT OPINION

Despite the availability of novel therapeutics, MM still evolves into a drug-resistant phase and most patients die of progressive disease. Therefore, there is an urgent need of novel therapeutic strategies. Among a plethora of new investigational agents, microRNA (miRNA) represents the basis for the design of novel therapeutic strategies which basically rely on miRNA inhibition or miRNA replacement approaches and take benefit respectively from the use of miRNA inhibitors or synthetic miRNAs as well as from lipid-based nanoparticles as carriers for in vivo delivery.

Plasma cell disorders in HIV-infected patients: epidemiology and molecular mechanisms

Highly active antiretroviral therapy (HAART) has significantly improved the outcome and survival of human immunodeficiency virus (HIV)-infected patients. Subsequently, long-term morbidities including cancer have become of major public health and clinical interest for this patient population. Plasma cell disorders occur at higher incidence in HIV-infected patients; however, the molecular mechanisms driving the plasma cell disease process and the optimal management for these patients remain to be defined. This article provides an up-to-date review of the characteristics and management of HIV-infected patients with plasma cell disorders. We first present 3 cases of plasma cell disorders in HIV-infected patients, ranging from polyclonal hypergammaglobulinemia to symptomatic multiple myeloma. We then discuss the epidemiology, clinical presentation, and management of each of these plasma cell disorders, with an emphasis on the molecular events underlying the progression of plasma cell diseases from monoclonal gammopathy to symptomatic multiple myeloma. We propose a three-step hypothesis for the development of multiple myeloma. Finally, we discuss the use of high dose chemotherapy and autologous hematopoietic stem cell transplantation in the treatment of HIV-infected patients with multiple myeloma. Our review includes the care of HIV-infected patients with plasma cell disorders in the current era of HAART and novel agents available for the treatment of multiple myeloma.

Biological activity of lenalidomide and its underlying therapeutic effects in multiple myeloma

Lenalidomide is a synthetic compound derived by modifying the chemical structure of thalidomide. It belongs to the second generation of immunomodulatory drugs (IMiDs) and possesses pleiotropic properties. Even if lenalidomide has been shown to be active in the treatment of several hematologic malignancies, this review article is mostly focalized on its mode of action in multiple myeloma. The present paper is about the direct and indirect antitumor effects of lenalidomide on malignant plasmacells, bone marrow microenvironment, bone resorption and host's immune response. The molecular mechanisms and targets of lenalidomide remain largely unknown, but recent evidence shows cereblon (CRBN) as a possible mediator of its therapeutical effects.

The genetic architecture of multiple myeloma

Based on the clinical features of myeloma and related malignancies of plasma cells, it has been possible to generate a model system of myeloma progression from a normal plasma cell through smouldering myeloma to myeloma and then plasma cell leukaemia. Using this model system we can study at which points the genetic alterations identified through whole-tumour molecular analyses function in the initiation and progression of myeloma. Further genetic complexity, such as intraclonal heterogeneity, and insights into the molecular evolution and intraclonal dynamics in this model system are crucial to our understandings of tumour progression, treatment resistance and the use of currently available and future treatments.

Report from the European Myeloma Network on interphase FISH in multiple myeloma and related disorders

The European Myeloma Network has organized two workshops on fluorescence in situ hybridization in multiple myeloma. The first aimed to identify specific indications and consensus technical approaches of current practice. A second workshop followed a quality control exercise in which 21 laboratories analyzed diagnostic cases of purified plasma cells for recurrent abnormalities. The summary report was discussed at the EHA Myeloma Scientific Working Group Meeting 2010. During the quality control exercise, there was acceptable agreement on more than 1,000 tests. The conclusions from the exercise were that the primary clinical applications for FISH analysis were for newly diagnosed cases of MM or frank relapse cases. A range of technical recommendations included: 1) material should be part of the first draw of the aspirate; 2) samples should be sent at suitable times to allow for the lengthy processing procedure; 3) most importantly, PCs must be purified or specifically identified; 4) positive cut-off levels should be relatively conservative: 10% for fusion or break-apart probes, 20% for numerical abnormalities; 5) informative probes should be combined to best effect; 6) in specialist laboratories, a single experienced analyst is considered adequate; 7) at least 100 PC should be scored; 8) essential abnormalities to test for are t(4;14), t(14;16) and 17p13 deletions; 9) suitable commercial probes should be available for clinically relevant abnormalities; 10) the clinical report should be expressed clearly and must state the percentage of PC involved and the method used for identification; 11) a retrospective European based FISH data bank linked to clinical data should be generated; and 12) prospective analysis should be centralized for upcoming trials based on the recommendations made. The European Myeloma Network aims to build on these recommendations to establish standards for a common European data base to define subgroups with prognostic significance.

The impact of cyclin D1 mRNA isoforms, morphology and p53 in mantle cell lymphoma: p53 alterations and blastoid morphology are strong predictors of a high proliferation index

BACKGROUND

Mantle cell lymphoma is a clinically heterogeneous disease characterized by overexpression of cyclin D1 protein. Blastoid morphology, high proliferation, and secondary genetic aberrations are markers of aggressive behavior. Expression profiling of mantle cell lymphoma revealed that predominance of the 3'UTR-deficient, short cyclin D1 mRNA isoform was associated with high cyclin D1 levels, a high "proliferation signature" and poor prognosis.

DESIGN AND METHODS

Sixty-two cases of mantle cell lymphoma were analyzed for cyclin D1 mRNA isoforms and total cyclin D1 levels by real-time reverse transcriptase polymerase chain reaction, and TP53 alterations were assessed by immunohistochemistry and molecular analysis. Results were correlated with proliferation index and clinical outcome.

RESULTS

Predominance of the short cyclin D1 mRNA was found in 14 (23%) samples, including four with complete loss of the standard transcript. TP53 alterations were found in 15 (24%) cases. Predominance of 3'UTR-deficient mRNA was significantly associated with high cyclin D1 mRNA levels (P=0.009) and more commonly found in blastoid mantle cell lymphoma (5/11, P=0.060) and cases with a proliferation index of >20% (P=0.026). Both blastoid morphology (11/11, P<0.001) and TP53 alterations (15/15, P<0.001) were significantly correlated with a high proliferation index. A proliferation index of 10% was determined to be a significant threshold for survival in multivariate analysis (P=0.01).

CONCLUSIONS

TP53 alterations are strongly associated with a high proliferation index and aggressive behavior in mantle cell lymphoma. Predominance of the 3'UTR-deficient transcript correlates with higher cyclin D1 levels and may be a secondary contributing factor to high proliferation, but failed to reach prognostic significance in this study.

Measures of association for identifying microRNA-mRNA pairs of biological interest

MicroRNAs are a class of small non-protein coding RNAs that play an important role in the regulation of gene expression. Most studies on the identification of microRNA-mRNA pairs utilize the correlation coefficient as a measure of association. The use of correlation coefficient is appropriate if the expression data are available for several conditions and, for a given condition, both microRNA and mRNA expression profiles are obtained from the same set of individuals. However, there are many instances where one of the requirements is not satisfied. Therefore, there is a need for new measures of association to identify the microRNA-mRNA pairs of interest and we present two such measures. The first measure requires expression data for multiple conditions but, for a given condition, the microRNA and mRNA expression may be obtained from different individuals. The new measure, unlike the correlation coefficient, is suitable for analyzing large data sets which are obtained by combining several independent studies on microRNAs and mRNAs. Our second measure is able to handle expression data that correspond to just two conditions but, for a given condition, the microRNA and mRNA expression must be obtained from the same set of individuals. This measure, unlike the correlation coefficient, is appropriate for analyzing data sets with a small number of conditions. We apply our new measures of association to multiple myeloma data sets, which cannot be analyzed using the correlation coefficient, and identify several microRNA-mRNA pairs involved in apoptosis and cell proliferation.

Targeting bone in myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone are dependent on its interactions with bone elements; thus, targeting these interactions should have anti-myeloma activities. Indeed, both experimental and clinical findings indicate that bone-targeted therapies, not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This chapter summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.

A gene expression-based predictor for myeloma patients at high risk of developing bone disease on bisphosphonate treatment

PURPOSE

Myeloma bone disease impairs quality of life and is associated with impaired survival. Even with effective bisphosphonate treatment, a significant proportion of patients still develop skeletal-related events (SRE). Identifying such patients at presentation would allow treatment modification.

EXPERIMENTAL DESIGN

To investigate the molecular basis of bone disease at presentation and to develop a predictive signature for patients at high risk of developing SREs on bisphosphonates, 261 presenting myeloma samples were analyzed by global gene expression profiling. The derived "SRE gene signature" was complemented by the integration of associated clinical parameters to generate an optimal predictor.

RESULTS

Fifty genes were significantly associated with presenting bone disease, including the WNT signaling antagonist DKK1 and genes involved in growth factor signaling and apoptosis. Higher serum calcium level and the presence of bone disease and hyperdiploidy at presentation were associated with high risk of SRE development. A gene signature derived from the fourteen genes overexpressed in the SRE group was able to identify patients at high risk of developing an SRE on treatment. These genes either belonged to the IFN-induced family or were involved in cell signaling and mitosis. Multivariate logistic model selection yielded an optimal SRE predictor comprising seven genes and calcium level, which was validated as an effective predictor in a further set of patients.

CONCLUSIONS

The simple expression-based SRE predictor can effectively identify individuals at high risk of developing bone disease while being on bisphosphonates. This predictor could assist with developing future trials on novel therapies aimed at reducing myeloma bone disease.

Targeting bone as a therapy for myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis, is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone is dependent on its interactions with bone elements, thus targeting these interactions should have antimyeloma activities. Indeed both experimental and clinical findings indicate that bone-targeted therapies not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This review summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.

Small compound 6-O-angeloylplenolin induces mitotic arrest and exhibits therapeutic potentials in multiple myeloma

Background

Multiple myeloma (MM) is a disease of cell cycle dysregulation while cell cycle modulation can be a target for MM therapy. In this study we investigated the effects and mechanisms of action of a sesquiterpene lactone 6-O-angeloylplenolin (6-OAP) on MM cells.

Methodology/Principal Findings

MM cells were exposed to 6-OAP and cell cycle distribution were analyzed. The role for cyclin B1 to play in 6-OAP-caused mitotic arrest was tested by specific siRNA analyses in U266 cells. MM.1S cells co-incubated with interleukin-6 (IL-6), insulin-like growth factor-I (IGF-I), or bone marrow stromal cells (BMSCs) were treated with 6-OAP. The effects of 6-OAP plus other drugs on MM.1S cells were evaluated. The in vivo therapeutic efficacy and pharmacokinetic features of 6-OAP were tested in nude mice bearing U266 cells and Sprague-Dawley rats, respectively. We found that 6-OAP suppressed the proliferation of dexamethasone-sensitive and dexamethasone-resistant cell lines and primary CD138+ MM cells. 6-OAP caused mitotic arrest, accompanied by activation of spindle assembly checkpoint and blockage of ubiquitiniation and subsequent proteasomal degradation of cyclin B1. Combined use of 6-OAP and bortezomib induced potentiated cytotoxicity with inactivation of ERK1/2 and activation of JNK1/2 and Casp-8/-3. 6-OAP overcame the protective effects of IL-6 and IGF-I on MM cells through inhibition of Jak2/Stat3 and Akt, respectively. 6-OAP inhibited BMSCs-facilitated MM cell expansion and TNF-α-induced NF-κB signal. Moreover, 6-OAP exhibited potent anti-MM activity in nude mice and favorable pharmacokinetics in rats.

Conclusions/Significance

These results indicate that 6-OAP is a new cell cycle inhibitor which shows therapeutic potentials for MM.

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.

The tricyclic antidepressant amitriptyline inhibits D-cyclin transactivation and induces myeloma cell apoptosis by inhibiting histone deacetylases: in vitro and in silico evidence

Amitriptyline is a classic tricyclic antidepressant (TCA) and has been used to treat the depression and anxiety of patients with cancer, but its relevance to cancer cell apoptosis is not known. In the present study, we demonstrated that amitriptyline inhibited cyclin D2 transactivation and displayed potential antimyeloma activity by inhibiting histone deacetylases (HDACs). Amitriptyline markedly decreased cyclin D2 promoter-driven luciferase activity, reduced cyclin D2 expression, and arrested cells at the G(0)/G(1) phase of the cell cycle. Amitriptyline-induced apoptosis was confirmed by Annexin V staining, and cleavage of caspase-3 and poly(ADP-ribose) polymerase-1. D-Cyclin expression is reported to be epigenetically regulated by histone acetylation. Thus, we examined the effects of amitriptyline on histone 3 (H3) acetylation and demonstrated that amitriptyline increased acetylation of H3 and expression of p27 and p21. Further studies indicated that amitriptyline interfered with HDAC function by down-regulation of HDAC3, -6, -7, and -8, but not HDAC2, and by interacting with HDAC7. Molecular docking analysis and molecular dynamics simulations revealed that amitriptyline bound to HDAC7 and formed strong van der Waals interactions with five residues of HDAC7, including Phe162, His192, Phe221, Leu293, and His326, thus inhibiting HDAC activity. Therefore, we found that amitriptyline inhibited cyclin D2 transactivation and HDAC activity and could be a promising treatment for multiple myeloma.

Molecular pathogenesis of multiple myeloma: chromosomal aberrations, changes in gene expression, cytokine networks, and the bone marrow microenvironment

This chapter focuses on two aspects of myeloma pathogenesis: (1) chromosomal aberrations and resulting changes in gene and protein expression with a special focus on growth and survival factors of malignant (and normal) plasma cells and (2) the remodeling of the bone marrow microenvironment induced by accumulating myeloma cells. We begin this chapter with a discussion of normal plasma cell generation, their survival, and a novel class of inhibitory factors. This is crucial for the understanding of multiple myeloma, as several abilities attributed to malignant plasma cells are already present in their normal counterpart, especially the production of survival factors and interaction with the bone marrow microenvironment (niche). The chapter closes with a new model of pathogenesis of myeloma.

Proliferation is a central independent prognostic factor and target for personalized and risk-adapted treatment in multiple myeloma

BACKGROUND

Proliferation of malignant plasma cells is a strong adverse prognostic factor in multiple myeloma and simultaneously targetable by available (e.g. tubulin polymerase inhibitors) and upcoming (e.g. aurora kinase inhibitors) compounds.

DESIGN AND METHODS

We assessed proliferation using gene expression-based indices in 757 samples including independent cohorts of 298 and 345 samples of CD138-purified myeloma cells from previously untreated patients undergoing high-dose chemotherapy, together with clinical prognostic factors, chromosomal aberrations, and gene expression-based high-risk scores.

RESULTS

In the two cohorts, 43.3% and 39.4% of the myeloma cell samples showed a proliferation index above the median plus three standard deviations of normal bone marrow plasma cells. Malignant plasma cells of patients in advanced stages or those harboring disease progression-associated gain of 1q21 or deletion of 13q14.3 showed significantly higher proliferation indices; patients with gain of chromosome 9, 15 or 19 (hyperdiploid samples) had significantly lower proliferation indices. Proliferation correlated with the presence of chromosomal aberrations in metaphase cytogenetics. It was significantly predictive for event-free and overall survival in both cohorts, allowed highly predictive risk stratification (e.g. event-free survival 12.7 versus 26.2 versus 40.6 months, P < 0.001) of patients, and was largely independent of clinical prognostic factors, e.g. serum β₂-microglobulin, International Staging System stage, associated high-risk chromosomal aberrations, e.g. translocation t(4;14), and gene expression-based high-risk scores.

CONCLUSIONS

Proliferation assessed by gene expression profiling, being independent of serum-β₂-microglobulin, International Staging System stage, t(4;14), and gene expression-based risk scores, is a central prognostic factor in multiple myeloma. Surrogating a biological targetable variable, gene expression-based assessment of proliferation allows selection of patients for risk-adapted anti-proliferative treatment on the background of conventional and gene expression-based risk factors.

TG101209, a novel JAK2 inhibitor, has significant in vitro activity in multiple myeloma and displays preferential cytotoxicity for CD45+ myeloma cells

Interaction of myeloma cells with the bone marrow microenvironment is mediated in large part through different cytokines, especially VEGF and IL6. These cytokines, especially IL6, leads to upregulation of the JAK/STAT pathway in myeloma cell, contributing to increased proliferation, decreased apoptosis, and acquired drug resistance. Here, we examined the preclinical activity of a novel JAK2 inhibitor TG101209. TG101209 induced dose- and time-dependent cytotoxicity in a variety of multiple myeloma (MM) cell lines. The induction of cytotoxicity was associated with inhibition of cell cycle progression and induction of apoptosis in myeloma cell lines and patient-derived plasma cells. Evaluation of U266 cell lines and patient cells, which have a mix of CD45 positive and negative cells, demonstrated more profound cytotoxicity and antiproliferative activity of the drug on the CD45+ population relative to the CD45- cells. Exploring the mechanism of action of TG101209 indicated downregulation of pJak2, pStat3, and Bcl-xl levels with upregulation of pErk and pAkt levels indicating cross talk between signaling pathways. TG101209, when used in combination with the PI3K inhibitor LY294002, demonstrated synergistic cytotoxicity against myeloma cells. Our results provide the rationale for clinical evaluation of TG101209 alone or in combination with PI3K/Akt inhibitors in MM.

Immunohistochemical analysis of NOTCH1 and JAGGED1 expression in multiple myeloma and monoclonal gammopathy of undetermined significance

Notch signaling is implicated in the pathogenesis of multiple myeloma expressing high level of active Notch proteins NOTCH1 and JAGGED1 in tumor plasma cells. We investigated expression of NOTCH1 and JAGGED1 in bone marrow trephine biopsies of 80 newly diagnosed multiple myeloma and 20 monoclonal gammopathy of undetermined significance patients using immunohistochemical methods. The number of positive tumor cells was counted per 1000 tumor cells and the intensity of staining was assessed semi quantitatively. Multiple myelomas expressed NOTCH1 in 92.31% (72/78) and JAGGED1 in 92.21% (71/77) cases. NOTCH1 staining was strong in the majority of cases (59.7%), whereas JAGGED1 was predominately weak (67.6% of cases). In contrast, both markers were negative in all monoclonal gammopathy of undetermined significance cases. However, upon progression of disease from monoclonal gammopathy of undetermined significance to multiple myeloma (seen in 4 patients), analysis of the subsequent bone marrow biopsy showed weak expression of both markers in tumorous plasma cells. Immunohistochemistry results were compared with the pattern of bone marrow infiltration, plasma cell differentiation, and the presence of t(11;14)(q13,q32), t(14;16)(q32;q23),and t(4;14)(p16.3;q23) and overall survival in multiple myeloma patients. A significant correlation was found between strong NOTCH1 staining in multiple myeloma plasma cells and the diffuse type of bone marrow infiltration (P = .002) and an immature morphologic type of plasma cells (P = .043). After a median follow-up of 20.3 months, in multiple myeloma patients no difference in overall survival between NOTCH1 (P = .484) and JAGGED1 (P = .822) positive and negative cases were found. In conclusion, our results indicate importance of NOTCH1 and JAGGED1 expression in plasma cell neoplasia and a possible diagnostic value of their immunohistochemical evaluation of bone marrow infiltrates for multiple myeloma.

APRIL promotes cell-cycle progression in primary multiple myeloma cells: influence of D-type cyclin group and translocation status

A proliferation-inducing ligand (APRIL) promotes survival and drug resistance in multiple myeloma (MM) cell lines. We studied the effect of APRIL on cell-cycle behavior in primary MM cells and correlated our findings with D-type cyclin expression by immunohistochemistry and/or Western blotting. In MM cases, expressing cyclin D2 APRIL significantly increased the percentage of CD138(+) cells in S + G(2)/M phase (from 8.4% ± 1.9% to 14.3% ± 2.6%, n = 15, P < .01), whereas a lesser effect was seen in cases expressing cyclin D1 (n = 18). Cell-cycle response to APRIL was most marked for cyclin D2-expressing cases with IgH translocations (P < .01) and was accompanied by increased expression of cyclin D2, CDK4, CDK6, and phospho-retinoblastoma protein. Cell-cycle proteins in cyclin D1(+) cells were not modulated by APRIL. Surface expression of B-cell maturation antigen and transmembrane activator and calcium-modulating cyclophilin ligand interactor was not significantly different between cyclin D1(+) and D2(+) MM cells. We observed activation of nuclear factor-κB and PI3-kinase pathways in response to APRIL in both cyclin D1(+) and D2(+) MM cells. In conclusion, APRIL stimulates G(1)/S progression in cyclin D2(+) MM cells bearing IgH translocations but has minimal effect on cyclin D1(+) cells, suggesting MM cells from different cyclin D/translocation classes rely on different mechanisms for cell-cycle re-entry.

Methylation status of nine tumor suppressor genes in multiple myeloma

Aberrant methylation in promoter-associated CpG islands has been recognized as a major mechanism for tumor suppressor gene silencing in several malignancies. We determined the methylation status of nine tumor suppressor genes in 68 newly diagnosed MM patients by methylation-specific PCR. The frequency of promoter hypermethylation for individual genes was: CDH1, 50%; p16 INK4a, 42.8%; p15 INK4b, 16.2%; SHP1, 14.7%; ER and BNIP3, 13.2%; RAR beta, 11.8%; DAPK 5.9%; and MGMT 0%. Overall, 79% of patients presented at least one hypermethylated gene. By univariate analysis, hypermethylation of DAPK (P < 0.001) and RAR beta (P = 0.01) genes were identified as adverse prognostic features. Median OS of patients with hypermethylation in DAPK (4 months) and RAR beta (34 months) was significantly lower than in patients without hypermethylation (median survival not reached), with values of P < 0.001 and P = 0.01, respectively. Our data suggest that DAPK and RAR beta hypermethylation are adverse prognostic factors in MM. The relevance of these findings as poor prognosis indicators requires confirmation in a larger sample with longer follow-ups.

Therapeutic efficacy of the pan-cdk inhibitor PHA-793887 in vitro and in vivo in engraftment and high-burden leukemia models

OBJECTIVE

The aim of the work was to determine and characterize, in vitro and in vivo, the therapeutic activity of PHA-793887, a new potent pan-cdk inhibitor, in the context of hematopoietic neoplasms.

MATERIALS AND METHODS

Thirteen leukemic cell lines bearing different cytogenetic abnormalities and normal hematopoietic cells were used in cytotoxicity and colony assays. The drug activity at the molecular level was analyzed by Western blotting. PHA-793887 was also tested in vivo in several leukemia xenograft models.

RESULTS

PHA-793887 was cytotoxic for leukemic cell lines in vitro, with IC(50) ranging from 0.3 to 7 microM (mean: 2.9 microM), regardless of any specific chromosomal aberration. At these doses, the drug was not cytotoxic for normal unstimulated peripheral blood mononuclear cells or CD34(+) hematopoietic stem cells. Interestingly, in colony assays PHA-793887 showed very high activity against leukemia cell lines, with an IC(50) <0.1 microM (mean: 0.08 microM), indicating that it has efficient and prolonged antiproliferative activity. PHA-793887 induced cell-cycle arrest, inhibited Rb and nucleophosmin phosphorylation, and modulated cyclin E and cdc6 expression at low doses (0.2-1 microM) and induced apoptosis at the highest dose (5 microM). It was also effective in vivo in both subcutaneous xenograft and primary leukemic disseminated models that better mimic naturally occurring human disease. Interestingly, in one disseminated model derived from a relapsed Philadelphia-positive acute lymphoid leukemia patient, PHA-793887 showed strong therapeutic activity also when treatment was started after establishment of high disease burden.

CONCLUSIONS

We conclude that PHA-793887 has promising therapeutic activity against acute leukemias in vitro and in vivo.

Dihydroorotate dehydrogenase inhibitor A771726 (leflunomide) induces apoptosis and diminishes proliferation of multiple myeloma cells

Multiple myeloma is still an incurable disease; therefore, new therapeutics are urgently needed. A771726 is the active metabolite of the immunosuppressive drug leflunomide, which is currently applied in the treatment of rheumatoid arthritis, BK virus nephropathy, and cytomegaly viremia. Here, we show that dihydroorotate dehydrogenase (DHODH) is commonly expressed in multiple myeloma cell lines and primary multiple myeloma cells. The DHODH inhibitor A771726 inhibits cell growth in common myeloma cell lines at clinically achievable concentrations in a time- and dose-dependent manner. Annexin V-FITC/propidium iodide staining revealed induction of apoptosis of multiple myeloma cell lines and primary multiple myeloma cells. The 5-bromo-2'-deoxyuridine cell proliferation assay showed that inhibition of cell growth was partly due to inhibition of multiple myeloma cell proliferation. A771726 induced G(1) cell cycle arrest via modulation of cyclin D2 and pRb expression. A771726 decreased phosphorylation of protein kinase B (Akt), p70S6K, and eukaryotic translation initiation factor 4E-binding protein-1 as shown by Western blotting experiments. Furthermore, we show that the stimulatory effect of conditioned medium of HS-5 bone marrow stromal cells on multiple myeloma cell growth is completely abrogated by A771726. In addition, synergism studies revealed synergistic and additive activity of A771726 together with the genotoxic agents melphalan, treosulfan, and doxorubicin as well as with dexamethasone and bortezomib. Taken together, we show that inhibition of DHODH by A771726/leflunomide is effective in multiple myeloma. Considering the favorable toxicity profile and the great clinical experience with leflunomide in rheumatoid arthritis, this drug represents a potential new candidate for targeted therapy in multiple myeloma.