CXCR4 Regulates Extra-Medullary Myeloma through Epithelial-Mesenchymal-Transition-like Transcriptional Activation

Highly Expressed Integrin-α8 Induces Epithelial to Mesenchymal Transition-Like Features in Multiple Myeloma with Early Relapse

Despite recent groundbreaking advances in multiple myeloma (MM) treatment, most MM patients ultimately experience relapse, and the relapse biology is not entirely understood. To define altered gene expression in MM relapse, gene expression profiles were examined and compared among 16 MM patients grouped by 12 months progression-free survival (PFS) after autologous stem cell transplantation. To maximize the difference between prognostic groups, patients at each end of the PFS spectrum (the four with the shortest PFS and four with the longest PFS) were chosen for additional analyses. We discovered that integrin-α8 (ITGA8) is highly expressed in MM patients with early relapse. The integrin family is well known to be involved in MM progression; however, the role of integrin-α8 is largely unknown. We functionally overexpressed integrin-α8 in MM cell lines, and surprisingly, stemness features including HIF1α, VEGF, OCT4, and Nanog, as well as epithelial mesenchymal transition (EMT)-related phenotypes, including N-cadherin, Slug, Snail and CXCR4, were induced. These, consequently, enhanced migration and invasion abilities, which are crucial to MM pathogenesis. Moreover, the gain of integrin-α8 expression mediated drug resistance against melphalan and bortezomib, which are the main therapeutic agents in MM. The cBioPortal genomic database revealed that ITGA8 have significant tendency to co-occur with PDGFRA and PDGFRB and their mRNA expression were up-regulated in ITGA8 overexpressed MM cells. In summary, integrin-α8, which was up-regulated in MM of early relapse, mediates EMT-like phenotype, enhancing migration and invasion; therefore, it could serve as a potential marker of MM relapse and be a new therapeutic target.

High-risk multiple myeloma: a multifaceted entity, multiple therapeutic challenges

The term high-risk multiple myeloma is aimed to identify a heterogeneous group of patients who are more likely to progress and die early of their disease. Therefore, recognition of these patients is crucial. With the increase in the number of treatment options, the outcome for high-risk patients has probably improved, although the true extent of this improvement remains unknown, due to both the heterogeneous components of high-risk disease and its under-representation in clinical trials. In this article, we review the definitions of high-risk disease, emphasizing the fact that no single definition can represent the entire high-risk population. In the second part, we review the treatment options available for the management of high-risk myeloma as well as our general approach for high-risk disease. In light of the poor prognosis associated with high-risk myeloma, even in the current era, new approaches for the management of this subset of patients are needed.

MGUS to myeloma: a mysterious gammopathy of underexplored significance

All cases of multiple myeloma (MM) are preceded by precursor states termed monoclonal gammopathy of undetermined significance (MGUS) or smoldering myeloma (SMM). Genetic analyses of MGUS cells have provided evidence that it is a genetically advanced lesion, wherein tumor cells carry many of the genetic changes found in MM cells. Intraclonal heterogeneity is also established early during the MGUS phase. Although the genetic features of MGUS or SMM cells at baseline may predict disease risk, transition to MM involves altered growth of preexisting clones. Recent advances in mouse modeling of MGUS suggest that the clinical dormancy of the clone may be regulated in part by growth controls extrinsic to the tumor cells. Interactions of MGUS cells with immune cells, bone cells, and others in the bone marrow niche may be key regulators of malignant transformation. These interactions involve a bidirectional crosstalk leading to both growth-supporting and inhibitory signals. Because MGUS is already a genetically complex lesion, application of new tools for earlier detection should allow delineation of earlier stages, which we term as pre-MGUS Analyses of populations at increased risk of MGUS also suggest the possible existence of a polyclonal phase preceding the development of MGUS. Monoclonal gammopathy in several patients may have potential clinical significance in spite of low risk of malignancy. Understanding the entire spectrum of these disorders may have broader implications beyond prevention of clinical malignancy.

New approaches to targeting the bone marrow microenvironment in multiple myeloma

Multiple myeloma is a tumour with a remarkably destructive effect on its host organ, the bone marrow. Through expression or secretion of adhesion molecules, growth factors, exosomes, miRNAs, chemokines and inhibitors, the tumour substantially alters its microenvironment, promoting both tumour survival and osteolytic bone disease. This altered niche is ideally suited to the sustenance of its proliferating compartment and the protection and immune evasion of its dormant, drug resistant fraction. The possibility of deepening response to a drug treatment regime, maintaining remission or even eradicating resistant stem cells by pharmacologically manipulating the tumour's interactions with this niche is a major driving force in current myeloma research. Examples of promising therapies include CXCR4 antagonists, RANKL inhibitors, HIF1α pathway inhibitors, and inhibitors of Notch, Wnt and TGFβ family pathways.

How I treat extramedullary myeloma

Extramedullary myeloma (EMM) is defined by the presence of plasma cells (PCs) outside the bone marrow in a patient with multiple myeloma (MM). Using sensitive imaging techniques including magnetic resonance imaging and positron emission tomography/computed tomography, EMM may be found in up to 30% of MM patients across the overall disease course. The molecular mechanisms underlying the hematogenous spread of PCs outside the bone marrow are only partially known and involve hypoxia and an altered expression of adhesion molecules. Extramedullary disease is associated with adverse prognostic factors (ie, high lactate dehydrogenase level, 17p deletion, and high-risk gene expression profile). The prognosis of EMM is poor, and the median overall survival of patients who experience an extramedullary relapse is <6 months. The adverse prognosis is less pronounced in patients with bone-related plasmacytomas than in those with hematogenous EMM. EMM patients should be considered as having high-risk myeloma and treated accordingly. However, EMM clinical situations are extraordinarily heterogeneous, and their management is particularly challenging. In the present review, a case-and-comment format is used to describe our approach to the management of EMM.

Multiple myeloma in the marrow: pathogenesis and treatments

Multiple myeloma (MM) is a B cell malignancy resulting in osteolytic lesions and fractures. In the disease state, bone healing is limited owing to increased osteoclastic and decreased osteoblastic activity, as well as an MM-induced forward-feedback cycle where bone-embedded growth factors further enhance tumor progression as bone is resorbed. Recent work on somatic mutation in MM tumors has provided insight into cytogenetic changes associated with this disease; the initiating driver mutations causing MM are diverse because of the complexity and multitude of mutations inherent in MM tumor cells. This manuscript provides an overview of MM pathogenesis by summarizing cytogenic changes related to oncogenes and tumor suppressors associated with MM, reviewing risk factors, and describing the disease progression from monoclonal gammopathy of undetermined significance to overt MM. It also highlights the importance of the bone marrow microenvironment (BMM) in the establishment and progression of MM, as well as associated MM-induced bone disease, and the relationship of the bone marrow to current and future therapeutics. This review highlights why understanding the basic biology of the healthy and diseased BMM is crucial in the quest for better treatments and work toward a cure for genetically diverse diseases such as MM.

Navigating the bone marrow niche: translational insights and cancer-driven dysfunction

The bone marrow niche consists of stem and progenitor cells destined to become mature cells such as haematopoietic elements, osteoblasts or adipocytes. Marrow cells, influenced by endocrine, paracrine and autocrine factors, ultimately function as a unit to regulate bone remodelling and haematopoiesis. Current evidence highlights that the bone marrow niche is not merely an anatomic compartment; rather, it integrates the physiology of two distinct organ systems, the skeleton and the marrow. The niche has a hypoxic microenvironment that maintains quiescent haematopoietic stem cells (HSCs) and supports glycolytic metabolism. In response to biochemical cues and under the influence of neural, hormonal, and biochemical factors, marrow stromal elements, such as mesenchymal stromal cells (MSCs), differentiate into mature, functioning cells. However, disruption of the niche can affect cellular differentiation, resulting in disorders ranging from osteoporosis to malignancy. In this Review, we propose that the niche reflects the vitality of two tissues - bone and blood - by providing a unique environment for stem and stromal cells to flourish while simultaneously preventing disproportionate proliferation, malignant transformation or loss of the multipotent progenitors required for healing, functional immunity and growth throughout an organism's lifetime. Through a fuller understanding of the complexity of the niche in physiologic and pathologic states, the successful development of more-effective therapeutic approaches to target the niche and its cellular components for the treatment of rheumatic, endocrine, neoplastic and metabolic diseases becomes achievable.