Growth factors and antiapoptotic signaling pathways in multiple myeloma

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

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

AT-101 Enhances the Antitumor Activity of Lenalidomide in Patients with Multiple Myeloma

Bcl-2 and Mcl-1 proteins play a role in multiple myeloma (MM) cell survival, for which targeted inhibitors are being developed. AT-101 is an oral drug, which disrupts Bcl-2 and Mcl-1 function, impedes mitochondrial bioenergetic processes and induces apoptosis in MM cells. When combined with lenalidomide and dexamethasone (Rd), AT-101 significantly reduced tumor burden in an in vivo xenograft model of MM. These data provided rationale for a phase I/II study to establish the effective dose of AT-101 in combination with Rd (ARd regimen) in relapsed/refractory MM. A total of 10 patients were enrolled, most with high-risk cytogenetics (80%) and prior stem cell transplant (70%). Three patients were lenalidomide-refractory, 2 were bortezomib-refractory and 3 were daratumumab-refractory. The ARd combination was well tolerated with most common grade 3/4 adverse events being cytopenia's. The overall response rate was 40% and clinical benefit rate was 90%. The median progression free survival was 14.9 months (95% CI 7.1-NE). Patients responsive to ARd showed a decrease in Bcl-2:Bim or Mcl-1:Noxa protein complexes, increased CD8+ T and NK cells and depletion of T and B-regulatory cells. The ARd regimen demonstrated an acceptable safety profile and promising efficacy in patients with relapsed/refractory MM prompting further investigation in additional patients.

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.

Growth inhibition and apoptosis of human multiple myeloma cells induced by 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid derivatives

Multiple myeloma is a blood cell cancer and can cause symptoms such as bone loss and fatigue. Recent studies have shown that the bone marrow microenvironment may mediate tumor proliferation, drug resistance, and migration of the multiple myeloma cells. Synthetic triterpenoids have been used for the treatment of cancer due to their antiproliferative and anti-inflammatory effects. The objective of this study is to examine the effect of 2-cyano-3, 12 dioxoolean-1,9-dien-28-oic acid (CDDO) derivatives on human multiple myeloma cells. Three CDDO derivatives, such as CDDO-methyl ester, CDDO-trifluroethyl amide, and CDDO-imidazolide (Im), were tested on the growth of human multiple myeloma cells. Our results show that all CDDO derivatives decrease the viability of multiple myeloma cells in a dose- and time-dependent manner, with CDDO-Im being the most potent. CDDO-Im was selected to investigate whether its inhibitory effect on multiple myeloma cell growth is due to cell cycle arrest and induction of apoptosis. The results suggest that CDDO-Im may inhibit cell cycle progression in the G0/G1 phase and induce the intrinsic apoptotic pathway. The effect of CDDO-Im on multiple myeloma cells was evaluated in a Transwell model using myeloma cells co-culturing with human HS-5 stromal cells to simulate the bone marrow microenvironment in vitro. The results showed that CDDO-Im induced multiple myeloma cell apoptosis in the presence of HS-5 cells, albeit to a lower extent than in multiple myeloma cells cultured alone. In conclusion, our data suggest that CDDO-Im inhibits the growth of multiple myeloma cells, either cultured alone or co-cultured with bone marrow stromal cells, through the induction of apoptosis.

Ruxolitinib Regulates the Autophagy Machinery in Multiple Myeloma Cells

BACKGROUND

Ruxolitinib is a selective JAK1/2 inhibitor approved by the FDA for myelofibrosis in 2014 and nowadays, comprehensive investigations on the potential of the agent as a targeted therapy for haematological malignancies are on the rise. In multiple myeloma which is a cancer of plasma cells, the Interleukin- 6/JAK/STAT pathway is emerging as a therapeutic target since the overactivation of the pathway is associated with poor prognosis.

OBJECTIVE

In this study, our purpose was to discover the potential anticancer effects of ruxolitinib in ARH-77 multiple myeloma cell line compared to NCI-BL 2171 human healthy B lymphocyte cell line.

METHODS

Cytotoxic effects of ruxolitinib in ARH-77 and NCI-BL 2171 cells were determined via WST-1 assay. The autophagy mechanism induced by ruxolitinib measured by detecting autophagosome formation was investigated. Apoptotic effects of ruxolitinib were analyzed with Annexin V-FITC Detection Kit and flow cytometry. We performed RT-qPCR to demonstrate the expression changes of the genes in the IL-6/JAK/STAT pathway in ARH-77 and NCI-BL 2171 cells treated with ruxolitinib.

RESULTS

We identified the IC50 values of ruxolitinib for ARH-77 and NCI-BL 2171 as 20.03 and 33.9μM at the 72nd hour, respectively. We showed that ruxolitinib induced autophagosome accumulation by 3.45 and 1.70 folds in ARH-77 and NCI-BL 2171 cells compared to the control group, respectively. Treatment with ruxolitinib decreased the expressions of IL-6, IL-18, JAK2, TYK2, and AKT genes, which play significant roles in MM pathogenesis.

CONCLUSION

All in all, ruxolitinib is a promising agent for the regulation of the IL-6/JAK/STAT pathway and interferes with the autophagy mechanism in MM.

MAP-kinase and JAK-STAT pathways dysregulation in plasmablastic lymphoma

Plasmablastic lymphoma (PBL) is an aggressive B-cell lymphoma with an immunoblastic/large cell morphology and plasmacytic differentiation. The differential diagnosis with Burkitt lymphoma (BL), plasma cell myeloma (PCM) and some variants of diffuse large B-cell lymphoma (DLBCL) may be challenging due to the overlapping morphological, genetic and immunophenotypic features. Furthermore, the genomic landscape in PBL is not well known. To characterize the genetic and molecular heterogeneity of these tumors, we investigated thirty-four PBL using an integrated approach, including fluorescence in situ hybridization, targeted sequencing of 94 B-cell lymphoma related genes, and copy-number arrays. PBL were characterized by high genetic complexity including MYC translocations (87%), gains of 1q21.1-q44, trisomy 7, 8q23.2-q24.21, 11p13-p11.2, 11q14.2-q25, 12p and 19p13.3-p13.13, losses of 1p33, 1p31.1-p22.3, 13q and 17p13.3-p11.2, and recurrent mutations of STAT3 (37%), NRAS and TP53 (33%), MYC and EP300 (19%) and CARD11, SOCS1 and TET2 (11%). Pathway enrichment analysis suggested a cooperative action between MYC alterations and MAPK (49%) and JAK-STAT (40%) signaling pathways. Of note, EBVnegative PBL cases had higher mutational and copy-number load and more frequent TP53, CARD11 and MYC mutations, whereas EBV-positive PBL tended to have more mutations affecting the JAK-STAT pathway. In conclusion, these findings further unravel the distinctive molecular heterogeneity of PBL identifying novel molecular targets and the different genetic profile of these tumors related to EBV infection.

Cytokine-Mediated Dysregulation of Signaling Pathways in the Pathogenesis of Multiple Myeloma

Multiple myeloma (MM) is a hematologic disorder of B lymphocytes characterized by the accumulation of malignant plasma cells (PCs) in the bone marrow. The altered plasma cells overproduce abnormal monoclonal immunoglobulins and also stimulate osteoclasts. The host’s immune system and microenvironment are of paramount importance in the growth of PCs and, thus, in the pathogenesis of the disease. The interaction of MM cells with the bone marrow (BM) microenvironment through soluble factors and cell adhesion molecules causes pathogenesis of the disease through activation of multiple signaling pathways, including NF-κβ, PI3K/AKT and JAK/STAT. These activated pathways play a critical role in the inhibition of apoptosis, sustained proliferation, survival and migration of MM cells. Besides, these pathways also participate in developing resistance against the chemotherapeutic drugs in MM. The imbalance between inflammatory and anti-inflammatory cytokines in MM leads to an increased level of pro-inflammatory cytokines, which in turn play a significant role in dysregulation of signaling pathways and proliferation of MM cells; however, the association appears to be inadequate and needs more research. In this review, we are highlighting the recent findings on the roles of various cytokines and growth factors in the pathogenesis of MM and the potential therapeutic utility of aberrantly activated signaling pathways to manage the MM disease.

FGF Trapping Inhibits Multiple Myeloma Growth through c-Myc Degradation-Induced Mitochondrial Oxidative Stress

Multiple myeloma, the second most common hematologic malignancy, frequently relapses because of chemotherapeutic resistance. Fibroblast growth factors (FGF) act as proangiogenic and mitogenic cytokines in multiple myeloma. Here, we demonstrate that the autocrine FGF/FGFR axis is essential for multiple myeloma cell survival and progression by protecting multiple myeloma cells from oxidative stress-induced apoptosis. In keeping with the hypothesis that the intracellular redox status can be a target for cancer therapy, FGF/FGFR blockade by FGF trapping or tyrosine kinase inhibitor impaired the growth and dissemination of multiple myeloma cells by inducing mitochondrial oxidative stress, DNA damage, and apoptotic cell death that were prevented by the antioxidant vitamin E or mitochondrial catalase overexpression. In addition, mitochondrial oxidative stress occurred as a consequence of proteasomal degradation of the c-Myc oncoprotein that led to glutathione depletion. Accordingly, expression of a proteasome-nondegradable c-Myc protein mutant was sufficient to avoid glutathione depletion and rescue the proapoptotic effects due to FGF blockade. These findings were confirmed on bortezomib-resistant multiple myeloma cells as well as on bone marrow-derived primary multiple myeloma cells from newly diagnosed and relapsed/refractory patients, including plasma cells bearing the t(4;14) translocation obtained from patients with high-risk multiple myeloma. Altogether, these findings dissect the mechanism by which the FGF/FGFR system plays a nonredundant role in multiple myeloma cell survival and disease progression, and indicate that FGF targeting may represent a therapeutic approach for patients with multiple myeloma with poor prognosis and advanced disease stage. SIGNIFICANCE: This study provides new insights into the mechanisms by which FGF antagonists promote multiple myeloma cell death. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/11/2340/F1.large.jpg.

SLAMF3-Mediated Signaling via ERK Pathway Activation Promotes Aggressive Phenotypic Behaviors in Multiple Myeloma

The signaling lymphocytic activation molecule family 3 (SLAMF3) is a member of the immunoglobulin superfamily expressed on T, B, and natural killer cells and modulates the activation and cytotoxicity of these cells. SLAMF3 is also expressed on plasma cells from patients with multiple myeloma (MM), although its role in MM pathogenesis remains unclear. This study found that SLAMF3 is highly and constitutively expressed on MM cells regardless of disease stage and that SLAMF3 knockdown/knockout suppresses proliferative potential and increases drug-induced apoptosis with decreased levels of phosphorylated ERK protein in MM cells. SLAMF3-overexpressing MM cells promote aggressive myeloma behavior in comparison with cytoplasmic domain-truncated SLAMF3 (ΔSLAMF3) cells. SLAMF3 interacts directly with adaptor proteins SH2 domain-containing phosphatase 2 (SHP2) and growth factor receptor bound 2 (GRB2), which also interact with each other. SLAMF3 knockdown, knockout, ΔSLAMF3, and SHP2 inhibitor-treated MM cells decreased phosphorylated ERK protein levels. Finally, serum soluble SLAMF3 (sSLAMF3) levels were markedly increased in advanced MM. Patients with high levels of sSLAMF3 progressed to the advanced stage significantly more often and had shorter progression-free survival times than those with low levels. This study revealed that SLAMF3 molecules consistently expressed on MM cells transmit MAPK/ERK signals mediated via the complex of SHP2 and GRB2 by self-ligand interaction between MM cells and induce a high malignant potential in MM. Furthermore, high levels of serum sSLAMF3 may reflect MM disease progression and be a useful prognostic factor. IMPLICATIONS: SLAMF3 may be a new therapeutic target for immunotherapy and novel agents such as small-molecule inhibitors.

Monoclonal Antibodies for the Treatment of Multiple Myeloma: An Update

The past two decades have seen a revolution in multiple myeloma (MM) therapy with the introduction of several small molecules, mostly orally effective, whose mechanisms are based on proteasome inhibition, histone deacetylase (HDAC) blockade, and immunomodulation. Immunotherapeutic approaches to MM treatment using monoclonal antibodies (mAbs), while long in development, began to reap success with the identification of CD38 and SLAMF7 as suitable targets for development, culminating in the 2015 Food and Drug Administration (FDA) approval of daratumumab and elotuzumab, respectively. This review highlights additional mAbs now in the developmental pipeline. Isatuximab, another anti-CD38 mAb, currently is under study in four phase III trials and may offer certain advantages over daratumumab. Several antibody-drug conjugates (ADCs) in the early stages of development are described, including JNJ-63723283, which has attained FDA breakthrough status for MM. Other mAbs described in this review include denosumab, recently approved for myeloma-associated bone loss, and checkpoint inhibitors, although the future status of the latter combined with immunomodulators has been clouded by unacceptably high death rates that caused the FDA to issue clinical holds on several of these trials. Also highlighted are the therapies based on the B Cell Maturation Antigen (BCMA), another very promising target for anti-myeloma development.

Celastrol Attenuates the Invasion and Migration and Augments the Anticancer Effects of Bortezomib in a Xenograft Mouse Model of Multiple Myeloma

Several lines of evidence have demonstrated that deregulated activation of NF-κB plays a pivotal role in the initiation and progression of a variety of cancers including multiple myeloma (MM). Therefore, novel molecules that can effectively suppress deregulated NF-κB upregulation can potentially reduce MM growth. In this study, the effect of celastrol (CSL) on patient derived CD138+ MM cell proliferation, apoptosis, cell invasion, and migration was investigated. In addition, we studied whether CSL can potentiate the apoptotic effect of bortezomib, a proteasome inhibitor in MM cells and in a xenograft mouse model. We found that CSL significantly reduced cell proliferation and enhanced apoptosis when used in combination with bortezomib and upregulated caspase-3 in these cells. CSL also inhibited invasion and migration of MM cells through the suppression of constitutive NF-κB activation and expression of downstream gene products such as CXCR4 and MMP-9. Moreover, CSL when administered either alone or in combination with bortezomib inhibited MM tumor growth and decreased serum IL-6 and TNF-α levels. Overall, our results suggest that CSL can abrogate MM growth both in vitro and in vivo and may serve as a useful pharmacological agent for the treatment of myeloma and other hematological malignancies.

Oscillating expression of interleukin-16 in multiple myeloma is associated with proliferation, clonogenic growth, and PI3K/NFKB/MAPK activation

Multiple myeloma (MM) is an incurable hematologic malignancy emerging from a plasma cell clone located in the bone marrow and is characterized by a high rate of fatal relapses after initially effective treatment. We have previously identified Interleukin-16 (IL-16) as an important factor promoting the proliferation of MM cells. We demonstrate here an upregulated, periodic expression, and secretion of IL-16 by MM cells leading to high extracellular IL-16 levels. The level of IL-16 released from a given MM cell line correlated with its proliferative activity. Establishing an inducible knockdown system and performing gene expression arrays we observed an association between IL-16 expression and activation of PI3, NFκB and MAP kinase pathways and, specifically, genes involved in tumor cell proliferation. Functional assays showed that IL-16 knockdown reduced the proliferative activity with a significant delay in cell cycle progression to G2 phase of conventional MM cells and completely suppressed the growth of clonogenic MM cells, which are suspected to be responsible for the high relapse rates in MM. Overall, our results demonstrate that tumor-regenerating MM cells may be particularly susceptible to IL-16 neutralization, suggesting an important role of anti-IL-16 therapies in the treatment of MM, particularly in combination with existing strategies targeting the bulk of myeloma cells.

Mature adipocytes in bone marrow protect myeloma cells against chemotherapy through autophagy activation

A major problem in patients with multiple myeloma is chemotherapy resistance, which develops in myeloma cells upon interaction with bone marrow stromal cells. However, few studies have determined the role of bone marrow adipocytes, a major component of stromal cells in the bone marrow, in myeloma chemotherapy resistance. We reveal that mature human adipocytes activate autophagy and upregulate the expression of autophagic proteins, thereby suppressing chemotherapy-induced caspase cleavage and apoptosis in myeloma cells. We found that adipocytes secreted known and novel adipokines, such as leptin and adipsin. The addition of these adipokines enhanced the expression of autophagic proteins and reduced apoptosis in myeloma cells. In vivo studies further demonstrated the importance of bone marrow-derived adipocytes in the reduced response of myeloma cells to chemotherapy. Our findings suggest that adipocytes, adipocyte-secreted adipokines, and adipocyte-activated autophagy are novel targets for combatting chemotherapy resistance and enhancing treatment efficacy in myeloma patients.

CD38 Monoclonal Antibody Therapies for Multiple Myeloma

The goal of this review is to provide historical, recent preclinical, and current clinical summaries of efforts to understand the CD38 molecule and to develop monoclonal antibodies that target it. We focus particularly on efforts involving multiple myeloma, a malignancy of terminally differentiated B cells that remains incurable despite many advances. An era of anti-CD38 monoclonal antibody therapy for myeloma is approaching, one that, we hope, will enable patients to live longer and better lives.

The proportion of CD16(+)CD14(dim) monocytes increases with tumor cell load in bone marrow of patients with multiple myeloma

Multiple myeloma is an incurable cancer with expansion of malignant plasma cells in the bone marrow. Previous studies have shown that monocytes and macrophages in the bone marrow milieu are important for tumor growth and may play a role in the drug response. We therefore characterized monocytes in bone marrow aspirates by flow cytometry. We found that there was significant correlation between the proportion of CX₃CR₁⁺, CD16⁺CD14^dim non classical monocytes, and percent plasma cells (PC) in the bone marrow of myeloma patients. The bone marrow monocytes could be stimulated by TLR ligands to produce cytokines which promote myeloma cell growth. The proportion of the non-classical monocytes increased with the tumor load, particularly in patients with tumor loads in the range of 10–30% bone marrow PC.

RNA interference screening identifies lenalidomide sensitizers in multiple myeloma, including RSK2

To identify molecular targets that modify sensitivity to lenalidomide, we measured proliferation in multiple myeloma (MM) cells transfected with 27 968 small interfering RNAs in the presence of increasing concentrations of drug and identified 63 genes that enhance activity of lenalidomide upon silencing. Ribosomal protein S6 kinase (RPS6KA3 or RSK2) was the most potent sensitizer. Other notable gene targets included 5 RAB family members, 3 potassium channel proteins, and 2 peroxisome family members. Single genes of interest included I-κ-B kinase-α (CHUK), and a phosphorylation dependent transcription factor (CREB1), which associate with RSK2 to regulate several signaling pathways. RSK2 knockdown induced cytotoxicity across a panel of MM cell lines and consistently increased sensitivity to lenalidomide. Accordingly, 3 small molecular inhibitors of RSK2 demonstrated synergy with lenalidomide cytotoxicity in MM cells even in the presence of stromal contact. Both RSK2 knockdown and small molecule inhibition downregulate interferon regulatory factor 4 and MYC, and provides an explanation for the synergy between lenalidomide and RSK2 inhibition. Interestingly, RSK2 inhibition also sensitized MM cells to bortezomib, melphalan, and dexamethasone, but did not downregulate Ikaros or influence lenalidomide-mediated downregulation of tumor necrosis factor-α or increase lenalidomide-induced IL-2 upregulation. In summary, inhibition of RSK2 may prove a broadly useful adjunct to MM therapy.

A novel selective small-molecule PI3K inhibitor is effective against human multiple myeloma in vitro and in vivo

Developing effective therapies against multiple myeloma (MM) is an unresolved challenge. Phosphatidylinositol-3-kinase (PI3K) activation may be associated with tumor progression and drug resistance, and inhibiting PI3K can induce apoptosis in MM cells. Thus, targeting of PI3K is predicted to increase the susceptibility of MM to anticancer therapy. The lead compound of a novel class of PI3K inhibitors, BAY80-6946 (IC50=0.5 nM against PI3K-α), was highly efficacious in four different MM cell lines, where it induced significant antitumoral effects in a dose-dependent manner. The compound inhibited cell cycle progression and increased apoptosis (P<0.001 compared with controls). Moreover, it abrogated the stimulation conferred by insulin-like growth-factor-1, a mechanism relevant for MM progression. These cellular effects were paralleled by decreased Akt phosphorylation, the main downstream target of PI3K. Likewise, profound antitumoral activity was observed ex vivo, as BAY80-6946 significantly inhibited proliferation of freshly isolated myeloma cells from three patients (P<0.001 compared with vehicle). In addition, BAY80-6946 showed convincing in vivo activity against the human AMO-1 and MOLP-8 myeloma cell lines in a preclinical murine xenograft model, where treatment with 6 mg/kg every other day for 2 weeks reduced the cell numbers by 87.0% and 69.3%, respectively (P<0.001 compared with vehicle), without overt toxicity in treated animals.

Small-molecule multi-targeted kinase inhibitor RGB-286638 triggers P53-dependent and -independent anti-multiple myeloma activity through inhibition of transcriptional CDKs

Small molecule multi-targeted CDK inhibitors (CDKIs) are of particular interest due to their potent antitumor activity independent of p53 gene alterations. P53 deletion is associated with a very poor prognosis in multiple myeloma (MM). In this regard, we tested the anti-MM activity of RGB-286638, an indenopyrazole-derived CDKI with Ki-nanomolar activity against transcriptional CDKs. We examined RGB-286638’s mode-of-action in MM cell lines with wild type (wt)-p53 and those expressing mutant p53. RGB-286638 treatment resulted in MM cytotoxicity in vitro associated with inhibition of MM tumor growth and prolonged survival in vivo. RGB-286638 displayed caspase-dependent apoptosis in both wt-p53 and mutant-p53 cells that was closely associated with the downregulation of RNA polymerase II phosphorylation and inhibition of transcription. RGB-286638-triggered p53 accumulation via nucleolar stress and loss of Mdm2, accompanied by induction of p53 DNA binding activity. Additionally, RGB-286638 mediated p53-independent activity, which was confirmed by cytotoxicity in p53-knockdown and p53-mutant cells. We also demonstrated downregulation of oncogenic miR-19, miR-92a-1, and miR-21. Our data provide the rationale for the development of transcriptional CDK inhibitors as therapeutic agents, which activate p53 in competent cells, while circumventing p53 deficiency through alternative p53-independent cell death mechanisms in p53-mutant/deleted cells.

Platelet factor 4 induces cell apoptosis by inhibition of STAT3 via up-regulation of SOCS3 expression in multiple myeloma

Platelet factor 4 (PF4) is an angiostatic chemokine that suppresses tumor growth and metastasis. We previously revealed frequent transcriptional silencing of PF4 in multiple myeloma, but the functional roles of this chemokine are still unknown. We studied the apoptotic effects of PF4 on myeloma cell lines and primary myeloma in vitro, and investigated the involved signaling pathway. The in vivo effects were also studied using a mouse model. PF4 not only suppressed myeloma-associated angiogenesis, but also inhibited growth and induced apoptosis in myeloma cells. We found that PF4 negatively regulated STAT3 and concordantly inhibited constitutive and interleukin-6-induced phosphorylation of STAT3, and down-regulated the expression of STAT3 target genes (Mcl-1, survivin and VEGF). Overexpression of constitutively activated STAT3 could rescue PF4-induced apoptotic effects. Furthermore, we found that PF4 induced the expression of SOCS3, a STAT3 inhibitor, and gene silencing of SOCS3 abolished its ability to inhibit STAT3 activation, suggesting a critical role of SOCS3 in PF4-induced STAT3 inhibition. Knockdown of LRP1, a putative PF4 receptor, could also abolish PF4-induced apoptosis and STAT3 inhibition. Finally, the tumor growth inhibitory effect of PF4 was confirmed by in vivo mouse models. Immunostaining of rabbit bone xenografts from PF4-treated mice showed induction of apoptosis of myeloma cells and inhibition of angiogenesis, which was associated with suppression of STAT3 activity. Together, our preclinical data indicate that PF4 may be a potential new targeting agent for the treatment of myeloma.

A novel molecular mechanism involved in multiple myeloma development revealed by targeting MafB to haematopoietic progenitors

Transgenic expression of the MafB oncogene in haematopoietic stem/progenitor cells induces plasma cell neoplasia reminiscent of human multiple myeloma and suggests DNA methylation as cause of malignant transformation.

Understanding the cellular origin of cancer can help to improve disease prevention and therapeutics. Human plasma cell neoplasias are thought to develop from either differentiated B cells or plasma cells. However, when the expression of Maf oncogenes (associated to human plasma cell neoplasias) is targeted to mouse B cells, the resulting animals fail to reproduce the human disease. Here, to explore early cellular changes that might take place in the development of plasma cell neoplasias, we engineered transgenic mice to express MafB in haematopoietic stem/progenitor cells (HS/PCs). Unexpectedly, we show that plasma cell neoplasias arise in the MafB-transgenic mice. Beyond their clinical resemblance to human disease, these neoplasias highly express genes that are known to be upregulated in human multiple myeloma. Moreover, gene expression profiling revealed that MafB-expressing HS/PCs were more similar to B cells and tumour plasma cells than to any other subset, including wild-type HS/PCs. Consistent with this, genome-scale DNA methylation profiling revealed that MafB imposes an epigenetic program in HS/PCs, and that this program is preserved in mature B cells of MafB-transgenic mice, demonstrating a novel molecular mechanism involved in tumour initiation. Our findings suggest that, mechanistically, the haematopoietic progenitor population can be the target for transformation in MafB-associated plasma cell neoplasias.

Targeting the IGF-1R signaling and mechanisms for epigenetic gene silencing in human multiple myeloma

Multiple myeloma (MM) is a B cell malignancy characterized by the expansion of clonal plasmablast/plasma cells within the bone-marrow. It is well established that the bone-marrow microenvironment has a pivotal role in providing critical cytokines and cell-cell interactions to support the growth and survival of the MM tumor clone. The pathogenesis of MM is, however, only fragmentarily understood. Detailed genomic analysis reveals a heterogeneous and complex pattern of structural and numerical chromosomal aberrations. In this review we will discuss some of the recent results on the functional role and potential clinical use of the IGF-1R, one of the major mediators of growth and survival for MM. We will also describe some of our results on epigenetic gene silencing in MM, as it may indeed constitute a novel basis for the understanding of tumor initiation and maintenance in MM and thus may change the current view on treatment strategies for MM.

Monoclonal antibody-based therapy as a new treatment strategy in multiple myeloma

The introduction of autologous stem cell transplantation combined with the introduction of immunomodulatory drugs (IMiDs) and proteasome inhibitors has significantly improved survival of multiple myeloma patients. However, ultimately the majority of patients will develop refractory disease, indicating the need for new treatment modalities. In preclinical and clinical studies, promising results have been obtained with several monoclonal antibodies (mAbs) targeting the myeloma tumor cell or the bone marrow microenvironment. The mechanisms underlying the therapeutic efficacy of these mAbs include direct induction of tumor cell apoptosis via inhibition or activation of target molecules, complement-dependent cytotoxicity and antibody-dependent cell-mediated cytotoxicity (ADCC). The capability of IMiDs to enhance ADCC and the modulation of various important signaling cascades in myeloma cells by both bortezomib and IMiDs forms the rationale to combine these novel agents with mAbs as new treatment strategies for myeloma patients. In this review, we will give an overview of various mAbs directly targeting myeloma tumor cells or indirectly via effects on the bone marrow microenvironment. Special focus will be on the combination of these mAbs with IMiDs or bortezomib.

Environmental-mediated drug resistance: a target for multiple myeloma therapy

Multiple myeloma is an incurable malignancy of mature clonal B cells. The refractory nature of this disease has long been attributed to the acquisition of drug resistance. Traditionally, mechanisms of drug resistance have been defined by genetic, acquired changes in the expression or function of specific genes products. However, over the past 10 years a large body of evidence has emerged demonstrating that in addition to mechanisms of drug resistance intrinsic to the cancer cell, there exist dynamic, de novo mechanisms coordinated by the tumor microenvironment resulting in a environmental-mediated drug resistance (EM-DR). Within this review we will provide an overview of some of these mechanisms of drug resistance and how they contribute to minimal residual disease and subsequent treatment failure. By understanding mechanisms of EM-DR, therapeutic targets can be identified and interventions designed to reduce minimal residual disease and improve clinical outcomes.

Drug inhibition profile prediction for NFκB pathway in multiple myeloma

Nuclear factor κB (NFκB) activation plays a crucial role in anti-apoptotic responses in response to the apoptotic signaling during tumor necrosis factor (TNFα) stimulation in Multiple Myeloma (MM). Although several drugs have been found effective for the treatment of MM by mainly inhibiting NFκB pathway, there are not any quantitative or qualitative results of comparison assessment on inhibition effect between different drugs either used alone or in combinations. Computational modeling is becoming increasingly indispensable for applied biological research mainly because it can provide strong quantitative predicting power. In this study, a novel computational pathway modeling approach is employed to comparably assess the inhibition effects of specific drugs used alone or in combinations on the NFκB pathway in MM and to predict the potential synergistic drug combinations.

CXCR4 antagonist 4F-benzoyl-TN14003 inhibits leukemia and multiple myeloma tumor growth

OBJECTIVE

The chemokine receptor CXCR4 and its ligand CXCL12 are involved in the progression and dissemination of a diverse number of solid and hematological malignancies. Binding CXCL12 to CXCR4 activates a variety of intracellular signal transduction pathways that regulate cell chemotaxis, adhesion, survival, proliferation, and apoptosis.

MATERIALS AND METHODS

Here, we demonstrate that the CXCR4 antagonist, 4F-benzoyl-TN14003 (BKT140), but not AMD3100, exhibits a CXCR4-dependent preferential cytotoxicity toward malignant cells of hematopoietic origin. BKT140 significantly and preferentially stimulated multiple myeloma apoptotic cell death. BKT140 treatment induced morphological changes, phosphatidylserine externalization, decreased mitochondrial membrane potential, caspase-3 activation, sub-G1 arrest, and DNA double-stranded breaks.

RESULTS

In vivo, subcutaneous injections of BKT140 significantly reduced, in a dose-dependent manner, the growth of human acute myeloid leukemia and multiple myeloma xenografts. Tumors from animals treated with BKT140 were smaller in size and weights, had larger necrotic areas and high apoptotic scores.

CONCLUSIONS

Taken together, these results suggest a potential therapeutic use for BKT140 in multiple myeloma and leukemia patients.

Pasteurella multocida toxin-stimulated osteoclast differentiation is B cell dependent

Pasteurella multocida is a Gram-negative bacillus that infects a number of wild and domestic animals, causing respiratory diseases. Toxigenic Pasteurella multocida strains produce a protein toxin (PMT) that leads to atrophic rhinitis in swine due to enhanced osteoclastogenesis and the inhibition of osteoblast function. We show that PMT-induced osteoclastogenesis is promoted by an as-yet-uncharacterized B-cell population. The toxin, however, is not acting at the level of hematopoietic stem cells, since purified CD117(+) cells from murine hematopoietic progenitor cells cultivated with PMT did not mature into osteoclasts. The early macrophages contained within this cell population (CD117(+)/CD11b(+)) did not further differentiate into osteoclasts but survived and were able to phagocytose. Within the CD117(-) population, however, we detected PMT-induced generation of a B220(+)/CD19(+) and B220(+)/IgM(+) B-cell population that was able to take up fluorescently labeled PMT. Using purified B-cell and macrophage populations, we show that these B cells are needed to efficiently generate osteoclasts from macrophages. Cells of the immune system are thought to affect osteoclast formation and function by secreting cytokines and growth factors. We show here that PMT-stimulated B cells produce elevated levels of the osteoclastogenic factors interleukin-1β (IL-1β), IL-6, tumor necrosis factor alpha, and receptor activator of nuclear factor receptor ligand (RANKL) compared to B cells generated through incubation with IL-7. These results suggest that the osteoclastic properties characteristic for PMT may result from a cross talk between bone cells and lymphoid cells and that B cells might be an important target of Pasteurella multocida.

Bone morphogenetic proteins and receptors are over-expressed in bone-marrow cells of multiple myeloma patients and support myeloma cells by inducing ID genes

We assessed the expression pattern and clinical relevance of BMPs and related molecules in multiple myeloma (MM). MM bone-marrow samples (n=32) had increased BMP4, BMP6, ACVR1 and ACVR2A, and decreased NOG expression compared with controls (n=15), with BMP6 having the highest sensitivity/specificity. Within MM bone-marrow, the source of BMPs was mainly CD138(+) plasma-cell population, and BMP6 and ACVR1 expression correlated with plasma-cell percentage. Using myeloma cell lines NCI H929 and Thiel we showed that BMPs induced ID1, ID2 and IL6, and suppressed CDKN1A and BAX gene expression, and BAX protein expression. Finally, BMPs partially protected myeloma cells from bortezomib- and TRAIL-induced apoptosis. We concluded that BMPs may be involved in MM pathophysiology and serve as myeloma cell biomarkers.

Control of apoptosis in human multiple myeloma by insulin-like growth factor I (IGF-I)

Human multiple myeloma (MM) is characterized by the expansion of neoplastic plasmablasts/plasma cells with complex genetic aberrations and high dependence for survival and growth on cytokines produced in the bone marrow microenvironment. As tools in the study of MM about 80 authentic MM cell lines and a few relevant in vivo mouse models are available. The dependence on insulin-like growth factor receptor (IGF-IR) signaling in the development and maintenance of the malignant phenotype in a variety of cancers is a rationale for attempts to improve tumor treatment by selectively inhibiting the IGF-IR in malignant cells by neutralizing antibodies, dominant negative IGF-IR, and IGF-IR siRNA. Testing the hypothesis that abrogating IGF-IR-mediated signaling of survival should make MM cells more susceptible to apoptosis, our studies have so far provided proof-of-principle by the demonstration that inhibition of a signaling pathway stimulating survival renders cells susceptible to drug-induced apoptosis when the drug (dexamethasone) and inhibitor (rapamycin) converge on the same target, that is p70(S6K). The recent publication of the three-dimensional structure of the IGF-IR kinase domain has facilitated the development of IGF-IR inhibitors of the cyclolignan family, that is picropodophyllin, with capacity to distinguish also in vivo between the IGF-IR and the insulin receptor. Studies in vitro and in vivo with picropodophyllin show promising effects, that is apoptosis induction and growth arrest, and have made it possible to evaluate the biological and therapeutic effects of inhibition of the IGF-IR signaling in MM.

The small GTPase RhoA is crucial for MC3T3-E1 osteoblastic cell survival

Prolongation of cell survival through prevention of apoptosis is considered to be a significant factor leading to anabolic responses in bone. The current studies were carried out to determine the role of the small GTPase, RhoA, in osteoblast apoptosis, since RhoA has been found to be critical for cell survival in other tissues. We investigated the effects of inhibitors and activators of RhoA signaling on osteoblast apoptosis. In addition, we assessed the relationship of this pathway to parathyroid hormone (PTH) effects on apoptotic signaling and cell survival. RhoA is activated by geranylgeranylation, which promotes its membrane anchoring. In serum-starved MC3T3-E1 osteoblastic cells, inhibition of geranylgeranylation with geranylgeranyl transferase I inhibitors increased activity of caspase-3, a component step in the apoptosis cascade, and increased cell death. Dominant negative RhoA and Y27632, an inhibitor of the RhoA effector Rho kinase, also increased caspase-3 activity. A geranylgeranyl group donor, geranylgeraniol, antagonized the effect of the geranylgeranyl transferase I inhibitor GGTI-2166, but could not overcome the effect of the Rho kinase inhibitor. PTH 1-34, a potent anti-apoptotic agent, completely antagonized the stimulatory effects of GGTI-2166, dominant negative RhoA, and Y27632, on caspase-3 activity. The results suggest that RhoA signaling is essential for osteoblastic cell survival but that the survival effects of PTH 1-34 are independent of this pathway.

Concomitant downregulation of proliferation/survival pathways dependent on FGF-R3, JAK2 and BCMA in human multiple myeloma cells by multi-kinase targeting

The identification of proliferation/survival pathways constitutively activated by genetic alterations in multiple myeloma (MM), or sustained by the bone marrow (BM) microenvironment, provides novel opportunities for the development of targeted therapies. The deregulated function of protein tyrosine kinases plays a critical role in driving MM malignant phenotype. We investigated the effects of the multi-target tyrosine kinase inhibitor RPI-1 in a panel of human MM cell lines, including t(4;14) positive cell lines expressing the TK receptor FGF-R3. Cells harboring FGF-R3 activating mutations (KMS11 and OPM2) displayed the highest sensitivity to RPI-1 antiproliferative effect. The stimulating effect of the aFGF ligand was abrogated in cells harboring a non-constitutively active receptor. Drug treatment inhibited activation and expression of the FGF-R3(Y373C) mutant as well as aFGF-dependent signaling involving AKT and ERKs. Inhibition of JAK2, an additional RPI-1 target, resulted in STAT3 inactivation. Blockade of these proliferation/survival pathways was associated with caspase-dependent apoptosis. Moreover, drug treatment abrogated proliferative and pro-invasive stimuli provided by conditioned medium from mesenchymal stromal cells. Gene expression profile of KMS11 cells showed 22 upregulated and 52 downregulated genes upon RPI-1 treatment, with an early modulation of genes implicated in MM pathobiology such as SAT-1, MYC, MIP-1alpha/beta, FGF-R3, and the growth factor receptor B-cell maturation antigen (BCMA). Thus, concomitant blockade of FGF-R3 and JAK2 results in inhibition of several MM-promoting pathways, including BCMA-regulated signaling, and downregulation of disease-associated proteins. These data may have therapeutic implications in the design of treatment strategies resulting in the concomitant inhibition of FGF-R3 and JAK2 signaling pathways in t(4;14) MM.

The role of the insulin-like growth factor 1 receptor axis in multiple myeloma

Multiple myeloma remains a fatal B cell malignancy with severe clinical features such as anaemia and bone fractures, caused by the predominant localization of the myeloma cells in the bone marrow (BM). The MM cells first migrate towards the BM, followed by their clonal expansion and induction of angiogenesis and osteolysis. Insulin-like growth factor 1 or IGF-1 is a cytokine which plays a role in myeloma development. Besides serving as a growth and survival factor, it attracts the cells towards the BM, and is involved in the angiogenesis process. This makes the IGF-1R an interesting target for therapeutical interventions. Apart from mediating aspects of the malignant phenotype, it also appears not to be an absolute requirement for normal cell homeostasis. Various strategies targeting the IGF-1R have emerged with the two main strategies being blocking antibodies and small molecule inhibitors. After encouraging preclinical results both strategies are now in clinical trials.

The oral protein-kinase C beta inhibitor enzastaurin (LY317615) suppresses signalling through the AKT pathway, inhibits proliferation and induces apoptosis in multiple myeloma cell lines

Deregulation of the protein kinase C (PKC) signalling pathway has been implicated in tumor progression. Here we investigated the PKC inhibitor enzastaurin for its activity against multiple myeloma (MM) cells. Enzastaurin suppresses cell proliferation in a large panel of human myeloma cell lines (HMCLs), with IC50 values ranging from 1.3 to 12.5 microM and induces apoptosis, which is prevented by the ZVAD-fmk broad caspase inhibitor. These results are consistent with decreased phosphorylation of AKT and GSK3-beta, a downstream target of the AKT pathway and a pharmacodynamic marker for enzastaurin. Furthermore, enzastaurin cytotoxicity is retained when HMCLs were cocultured with multipotent mesenchymal stromal cells. Enzastaurin has additive or synergistic cytotoxic effects with bortezomib or thalidomide. Considering the strong anti-myeloma activity of enzastaurin in vitro and in animal models and its safe toxicity profile, phase II studies in MM patients of enzastaurin alone or in combination with other drugs are warranted.

KD5170, a novel mercaptoketone-based histone deacetylase inhibitor, exerts antimyeloma effects by DNA damage and mitochondrial signaling

Histone deacetylase inhibitors have emerged as promising anticancer drugs. Using an unbiased ultrahigh throughput screening system, a novel mercaptoketone-based histone deacetylase inhibitor series was identified that was optimized to the lead compound, KD5170. KD5170 inhibited the proliferation of myeloma cell lines and the viability of CD138(+) primary myeloma cells by induction of apoptosis, accompanied by an increase of acetylation of histones and activation of caspase-3, caspase-8, and caspase-9. Treatment with KD5170 caused a loss of mitochondrial membrane potential resulting in release of apoptogenic factors such as cytochrome c, Smac, and apoptosis-inducing factor. Furthermore, KD5170 induced oxidative stress and oxidative DNA damage in myeloma cells as evidenced by the up-regulation of heme oxygenase-1 and H2A.X phosphorylation. Combination of KD5170 with proteasome inhibitor bortezomib or tumor necrosis factor-related apoptosis-inducing ligand synergistically enhanced the antimyeloma activity. We further found that resistance of myeloma cells to KD5170 was associated with activation of the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway under treatment with KD5170. Pretreatment with the mitogen-activated protein kinase inhibitor U0126 restored sensitivity to KD5170, suggesting that the combination of KD5170 with U0126 could overcome drug resistance. Growth of myeloma tumor xenografts in KD5170-treated nude mice was significantly inhibited and survival was prolonged. Histone acetylation was increased in spleen and tumor tissues of animals treated with KD5170. Our data indicate that KD5170 has potent antimyeloma activity in vitro and in vivo, which is mediated by DNA damage and mitochondrial signaling and subsequent induction of apoptosis.

Membrane expression of DR4, DR5 and caspase-8 levels, but not Mcl-1, determine sensitivity of human myeloma cells to Apo2L/TRAIL

The improved recombinant form of the death ligand Apo2L/TRAIL (Apo2L/TRAIL.0) is not cytotoxic for normal human cells and is a good candidate for the therapy of multiple myeloma (MM), a B-cell neoplasia that remains incurable. We have analyzed the molecular determinants of myeloma sensitivity to Apo2L/TRAIL.0 in a number of MM cell lines, the mechanisms of resistance and a possible way of overcoming it. Expression of one death receptor for Apo2L/TRAIL (DR4 or DR5) is sufficient to transduce death signals, though DR5 was more efficient when both receptors were present. Membrane expression of decoy receptors (DcR1, DcR2) and intracellular levels of c-FLIP(L), XIAP and Mcl-1 were not predictive of resistance to Apo2L/TRAIL. Inhibition of Mcl-1 degradation did not prevent Apo2L/TRAIL-induced apoptosis. In IM-9 cells, resistance was associated to a reduced caspase-8 expression. U266 cells, though expressing significant levels of DR4 and caspase-8, were nevertheless resistant to Apo2L/TRAIL. This resistance could be overcome by co-treatment with valproic acid (VPA), a histone deacetylase inhibitor. VPA caused the redistribution of DR4 to plasma membrane lipid rafts and restored DR4 signaling. Overexpression of Mcl-1 in U266 cells did not prevent Apo2L/TRAIL cytotoxicity in VPA-sensitized cells. These results, taken together, support the possible use of Apo2L/TRAIL.0 in the treatment of MM.

Plasma cells from multiple myeloma patients express B7-H1 (PD-L1) and increase expression after stimulation with IFN-γ and TLR ligands via a MyD88-, TRAF6-, and MEK-dependent pathway

Multiple myeloma (MM) cells inhibit certain T-cell functions. We examined the expression of B7-H1 (PD-L1), a B7-related protein that inhibits T-cell responses, in CD138-purified plasma cells isolated from MM patients, monoclonal gammopathy of undetermined significance patients, and healthy donors. We observed that B7-H1 was expressed in most MM plasma cells, but not cells isolated from monoclonal gammopathy of undetermined significance or healthy donors. This expression was increased or induced by IFN-γ and Toll-like receptor (TLR) ligands in isolated MM plasma cells. Blocking the MEK/ERK pathway inhibited IFN-γ–mediated and TLR-mediated expression of B7-H1. Inhibition of the MyD88 and TRAF6 adaptor proteins of the TLR pathway blocked not only B7-H1 expression induced by TLR ligands but also that mediated by IFN-γ. IFN-γ–induced STAT1 activation, via MEK/ERK and MyD88/TRAF6, and inhibition of STAT1 reduced B7-H1 expression. MM plasma cells stimulated with IFN-γ or TLR ligands inhibited cytotoxic T lymphocytes (CTLs) generation and this immunosuppressive effect was inhibited by preincubation with an anti-B7-H1 antibody, the UO126 MEK inhibitor, or by transfection of a dominant-negative mutant of MyD88. Thus, B7-H1 expression by MM cells represents a possible immune escape mechanism that could be targeted therapeutically through inhibition of MyD88/TRAF6 and MEK/ERK/STAT1.

Monoclonal gammopathy of undetermined significance and smoldering multiple myeloma

Monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM) are asymptomatic disorders characterized by monoclonal plasma cell proliferation in the bone marrow in the absence of end-organ damage. Updated diagnostic criteria for these disorders, risk-stratification models to determine prognosis, and the current management of these two entities are discussed in this review.

Monoclonal gammopathy of undetermined significance, Waldenström macroglobulinemia, AL amyloidosis, and related plasma cell disorders: diagnosis and treatment

The spectrum of plasma cell disorders is broad. Monoclonal gammopathy of undetermined significance and smoldering multiple myeloma are asymptomatic disorders characterized by monoclonal plasma cell proliferation in the bone marrow in the absence of end-organ damage. Waldenström macroglobulinemia typically involves an ontogenically less mature lymphoplasmacytic bone marrow cell and is characterized by secretion of a monoclonal IgM protein. Solitary plasmacytoma is the only known potentially curable plasma cell disorder. Finally, AL (immunoglobulin light chain) amyloidosis and POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome are disorders characterized by low tumor burden but profound multisystemic disease. Updated diagnostic criteria for these disorders, risk stratification models to determine prognosis, and the current management of these diverse entitles are discussed in this review.