Ken Maes

In anemia of multiple myeloma, hepcidin is induced by increased bone morphogenetic protein 2

Hepcidin is the principal iron-regulatory hormone and a pathogenic factor in anemia of inflammation. Patients with multiple myeloma (MM) frequently present with anemia. We showed that MM patients had increased serum hepcidin, which inversely correlated with hemoglobin, suggesting that hepcidin contributes to MM-related anemia. Searching for hepcidin-inducing cytokines in MM, we quantified the stimulation of hepcidin promoter-luciferase activity in HuH7 cells by MM sera. MM sera activated the hepcidin promoter significantly more than did normal sera. We then examined the role of bone morphogenetic proteins (BMPs) and interleukin-6 (IL-6), the major transcriptional regulators of hepcidin. Mutations in both BMP-responsive elements abrogated the activation dramatically, while mutations in the IL-6-responsive signal transducer and activator of transcription 3-binding site (STAT3-BS) had only a minor effect. Cotreatment with anti-BMP-2/4 or noggin-Fc blocked the promoter induction with all MM sera, anti-IL-6 blocked it with a minority of sera, whereas anti-BMP-4, -6, or -9 antibodies had no effect. BMP-2-immunodepleted MM sera had decreased promoter stimulatory capacity, and BMP-2 concentrations in MM sera were significantly higher than in normal sera. Our results demonstrate that BMP-2 is a major mediator of the hepcidin stimulatory activity of MM sera.

Epigenetic Modulating Agents as a New Therapeutic Approach in Multiple Myeloma

Multiple myeloma (MM) is an incurable B-cell malignancy. Therefore, new targets and drugs are urgently needed to improve patient outcome. Epigenetic aberrations play a crucial role in development and progression in cancer, including MM. To target these aberrations, epigenetic modulating agents, such as DNA methyltransferase inhibitors (DNMTi) and histone deacetylase inhibitors (HDACi), are under intense investigation in solid and hematological cancers. A clinical benefit of the use of these agents as single agents and in combination regimens has been suggested based on numerous studies in pre-clinical tumor models, including MM models. The mechanisms of action are not yet fully understood but appear to involve a combination of true epigenetic changes and cytotoxic actions. In addition, the interactions with the BM niche are also affected by epigenetic modulating agents that will further determine the in vivo efficacy and thus patient outcome. A better understanding of the molecular events underlying the anti-tumor activity of the epigenetic drugs will lead to more rational drug combinations. This review focuses on the involvement of epigenetic changes in MM pathogenesis and how the use of DNMTi and HDACi affect the myeloma tumor itself and its interactions with the microenvironment.

The bone marrow microenvironment enhances multiple myeloma progression by exosome-mediated activation of myeloid-derived suppressor cells

Exosomes, extracellular nanovesicles secreted by various cell types, modulate the bone marrow (BM) microenvironment by regulating angiogenesis, cytokine release, immune response, inflammation, and metastasis. Interactions between bone marrow stromal cells (BMSCs) and multiple myeloma (MM) cells play crucial roles in MM development. We previously reported that BMSC-derived exosomes directly promote MM cell growth, whereas the other possible mechanisms for supporting MM progression by these exosomes are still not clear. Here, we investigated the effect of BMSC-derived exosomes on the MM BM cells with specific emphasis on myeloid-derived suppressor cells (MDSCs). BMSC-derived exosomes were able to be taken up by MM MDSCs and induced their expansion in vitro. Moreover, these exosomes directly induced the survival of MDSCs through activating STAT3 and STAT1 pathways and increasing the anti-apoptotic proteins Bcl-xL and Mcl-1. Inhibition of these pathways blocked the enhancement of MDSC survival. Furthermore, these exosomes increased the nitric oxide release from MM MDSCs and enhanced their suppressive activity on T cells. Taken together, our results demonstrate that BMSC-derived exosomes activate MDSCs in the BM through STAT3 and STAT1 pathways, leading to increased immunosuppression which favors MM progression.

Novel strategies to target the ubiquitin proteasome system in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the accumulation of plasma cells in the bone marrow (BM). The success of the proteasome inhibitor bortezomib in the treatment of MM highlights the importance of the ubiquitin proteasome system (UPS) in this particular cancer. Despite the prolonged survival of MM patients, a significant amount of patients relapse or become resistant to therapy. This underlines the importance of the development and investigation of novel targets to improve MM therapy. The UPS plays an important role in different cellular processes by targeted destruction of proteins. The ubiquitination process consists of enzymes that transfer ubiquitin to proteins targeting them for proteasomal degradation. An emerging and promising approach is to target more disease specific components of the UPS to reduce side effects and overcome resistance. In this review, we will focus on different components of the UPS such as the ubiquitin activating enzyme E1, the ubiquitin conjugating enzyme E2, the E3 ubiquitin ligases, the deubiquitinating enzymes (DUBs) and the proteasome. We will discuss their role in MM and the implications in drug discovery for the treatment of MM.

Induction of miR-146a by multiple myeloma cells in mesenchymal stromal cells stimulates their pro-tumoral activity.

Mutual communication between multiple myeloma (MM) cells and mesenchymal stromal cells (MSC) plays a pivotal role in supporting MM progression. In MM, MSC exhibit a different genomic profile and dysregulated cytokine secretion compared to normal MSC, however the mechanisms involved in these changes are not fully understood. Here, we examined the miRNA changes in human MSC after culture with conditioned medium of MM cells and found 19 dysregulated miRNAs, including upregulated miR-146a. Moreover, exosomes derived from MM cells contained miR-146a and could be transferred into MSC. After overexpressing miR-146a in MSC, secretion of several cytokines and chemokines including CXCL1, IL6, IL-8, IP-10, MCP-1, and CCL-5 was elevated, resulting in the enhancement of MM cell viability and migration. DAPT, an inhibitor of the endogenous Notch pathway, was able to abrogate the miR-146a-induced increase of cytokines in MSC, suggesting the involvement of the Notch pathway. Taken together, our results demonstrate a positive feedback loop between MM cells and MSC: MM cells promote the increase of miR146a in MSC which leads to more cytokine secretion, which in turn favors MM cell growth and migration.

Extracellular vesicle cross-talk in the bone marrow microenvironment: implications in multiple myeloma.

The bone marrow (BM) represents a complex microenvironment containing stromal cells, immune cells, osteoclasts, osteoblasts, and hematopoietic cells, which are crucial for the immune response, bone formation, and hematopoiesis. Apart from soluble factors and direct cell-cell contact, extracellular vesicles (EVs), including exosomes, were recently identified as a third mediator for cell communication. Solid evidence has already demonstrated the involvement of various BM-derived cells and soluble factors in the regulation of multiple biological processes whereas the EV-mediated message delivery system from the BM has just been explored in recent decades. These EVs not only perform physiological functions but can also play a role in cancer development, including in Multiple Myeloma (MM) which is a plasma cell malignancy predominantly localized in the BM. This review will therefore focus on the multiple functions of EVs derived from BM cells, the manipulation of the BM by cancer-derived EVs, and the role of BM EVs in MM progression.

The therapeutic potential of cell cycle targeting in multiple myeloma

Proper cell cycle progression through the interphase and mitosis is regulated by coordinated activation of important cell cycle proteins (including cyclin-dependent kinases and mitotic kinases) and several checkpoint pathways. Aberrant activity of these cell cycle proteins and checkpoint pathways results in deregulation of cell cycle progression, which is one of the key hallmarks of cancer. Consequently, intensive research on targeting these cell cycle regulatory proteins identified several candidate small molecule inhibitors that are able to induce cell cycle arrest and even apoptosis in cancer cells. Importantly, several of these cell cycle regulatory proteins have also been proposed as therapeutic targets in the plasma cell malignancy multiple myeloma (MM). Despite the enormous progress in the treatment of MM the past 5 years, MM still remains most often incurable due to the development of drug resistance. Deregulated expression of the cyclins D is observed in virtually all myeloma patients, emphasizing the potential therapeutic interest of cyclin-dependent kinase inhibitors in MM. Furthermore, other targets have also been identified in MM, such as microtubules, kinesin motor proteins, aurora kinases, polo-like kinases and the anaphase promoting complex/cyclosome. This review will provide an overview of the cell cycle proteins and checkpoint pathways deregulated in MM and discuss the therapeutic potential of targeting proteins or protein complexes involved in cell cycle control in MM.Proper cell cycle progression through the interphase and mitosis is regulated by coordinated activation of important cell cycle proteins (including cyclin-dependent kinases and mitotic kinases) and several checkpoint pathways. Aberrant activity of these cell cycle proteins and checkpoint pathways results in deregulation of cell cycle progression, which is one of the key hallmarks of cancer. Consequently, intensive research on targeting these cell cycle regulatory proteins identified several candidate small molecule inhibitors that are able to induce cell cycle arrest and even apoptosis in cancer cells. Importantly, several of these cell cycle regulatory proteins have also been proposed as therapeutic targets in the plasma cell malignancy multiple myeloma (MM). Despite the enormous progress in the treatment of MM the past 5 years, MM still remains most often incurable due to the development of drug resistance. Deregulated expression of the cyclins D is observed in virtually all myeloma patients, emphasizing the potential therapeutic interest of cyclin-dependent kinase inhibitors in MM. Furthermore, other targets have also been identified in MM, such as microtubules, kinesin motor proteins, aurora kinases, polo-like kinases and the anaphase promoting complex/cyclosome. This review will provide an overview of the cell cycle proteins and checkpoint pathways deregulated in MM and discuss the therapeutic potential of targeting proteins or protein complexes involved in cell cycle control in MM.

Leptin receptor antagonism of iNKT cell function : a novel strategy to combat multiple myeloma

A hallmark of bone marrow changes with aging is the increase in adipocyte composition, but how this impacts development of multiple myeloma (MM) is unknown. Here, we report the role of the adipokine leptin as master regulator of anti-myeloma tumor immunity by modulating the invariant natural killer T (iNKT) cell function. A marked increase in serum leptin levels and leptin receptor (LR) expression on iNKT cells in MM patients and the 5T33 murine MM model was observed. MM cells and leptin synergistically counteracted anti-tumor functionality of both murine and human iNKT cells. In vivo blockade of LR signaling combined with iNKT stimulation resulted in superior anti-tumor protection. This was linked to persistent IFN-γ secretion upon repeated iNKT cell stimulation and a restoration of the dynamic antigen-induced motility arrest as observed by intravital microscopy, thereby showing alleviation of iNKT cell anergy. Overall our data reveal the LR axis as novel therapeutic target for checkpoint inhibition to treat MM.

The insulin-like growth factor system in Multiple Myeloma: diagnostic and therapeutic potential.

Multiple myeloma (MM) is a highly heterogeneous plasma cell malignancy. The MM cells reside in the bone marrow (BM), where reciprocal interactions with the BM niche foster MM cell survival, proliferation, and drug resistance. As in most cancers, the insulin-like growth factor (IGF) system has been demonstrated to play a key role in the pathogenesis of MM. The IGF system consists of IGF ligands, IGF receptors, IGF binding proteins (IGFBPs), and IGFBP proteases and contributes not only to the survival, proliferation, and homing of MM cells, but also MM-associated angiogenesis and osteolysis. Furthermore, increased IGF-I receptor (IGF-IR) expression on MM cells correlates with a poor prognosis in MM patients. Despite the prominent role of the IGF system in MM, strategies targeting the IGF-IR using blocking antibodies or small molecule inhibitors have failed to translate into the clinic. However, increasing preclinical evidence indicates that IGF-I is also involved in the development of drug resistance against current standard-of-care agents against MM, including proteasome inhibitors, immunomodulatory agents, and corticoids. IGF-IR targeting has been able to overcome or revert this drug resistance in animal models, enhancing the efficacy of standard-of-care agents. This finding has generated renewed interest in the therapeutic potential of IGF-I targeting in MM. The present review provides an update of the impact of the different IGF system components in MM and discusses the diagnostic and therapeutic potentials.

Inhibiting the anaphase promoting complex/cyclosome induces a metaphase arrest and cell death in multiple myeloma cells

The anaphase promoting complex/cyclosome (APC/C) is an ubiquitin ligase involved in cell cycle. During the metaphase-anaphase transition the APC/C is activated by Cdc20. The aim of this study is to elucidate the importance and therapeutic potential of APC/C and its co-activator Cdc20 in multiple myeloma (MM). Gene expression analysis revealed that Cdc20 was expressed at higher levels in gene expression-based high-risk MM patients. Moreover, high Cdc20 expression correlated with poor prognosis. Treatment of human myeloma cell lines with proTAME, an APC/C inhibitor, resulted in an accumulation of APC/CCdc20 substrate cyclin B1 and an accumulation of cells in metaphase. Moreover we observed a significant dose-dependent decrease in viability and increase in apoptosis in MM cells upon proTAME treatment. The induction of apoptosis was accompanied with caspase 3, 8, 9 and PARP cleavage. A similar metaphase arrest and induction of apoptosis were obtained with specific knockdown of Cdc20. In addition, we demonstrated the accumulation of Bim was partially responsible for the observed cell death. Combining proTAME with another APC/C inhibitor apcin or the alkylating agent melphalan resulted in enhanced anti-MM activity. This study suggests that the APC/C and its co-activator Cdc20 could be a new and promising target especially in high-risk MM patients.