Significance of VLA-4-VCAM-1 interaction and CD44 for transendothelial invasion in a bone marrow metastatic myeloma model

Extracellular nicotinamide phosphoribosyltransferase (eNAMPT) drives abnormal pericyte-rich vasculature in triple-negative breast cancer

Tumour angiogenesis supports malignant cells with oxygen and nutrients to promote invasion and metastasis. A number of cytokines released in situ participate in the recruitment of endothelial cells and pericytes to trigger the formation of novel blood vessels, which are often abnormal, leaky, and disorganized. Nicotinamide phosphoribosyltransferase is a key intracellular enzyme involved in NAD metabolism and is up regulated in many cancers to meet bioenergetic demands. Yet, the same protein is also secreted extracellularly (eNAMPT), where it acts as a pro-inflammatory cytokine. High plasma eNAMPT levels have been reported in breast cancer patients and correlate with aggressiveness and prognosis. We now report that in a triple-negative breast cancer model, enriching the tumour microenvironment with eNAMPT leads to abundant angiogenesis and increased metastatization. Atypically, the eNAMPT-mediated pro-angiogenic effect is mainly directed to NG2+ pericytes. Indeed, eNAMPT acts as chemoattractant for pericytes and coordinates vessel-like tube formation, in synergism with the classical factor PDGF-BB. Stimulation of pericytes by eNAMPT leads to a pro-inflammatory activation, characterized by the overexpression of key chemokines (CXCL8, CXCL1, CCL2) and VCAM1, via NF-κB signalling. All these effects were ablated by the use of C269, an anti-eNAMPT neutralizing antibody, suggesting that this might represent a novel anti-angiogenic pharmacological approach for triple-negative breast cancer.

The Evolving Role of Checkpoint Inhibitors in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by production of abnormal levels of a monoclonal immunoglobulin or plasma cell deposition that leads to end organ destruction. The disease remains incurable despite advances in combination treatments with classes of medications that include proteosome inhibitors, immunomodulating agents, monoclonal antibodies, small molecule inhibitors, alkylating agents, T-cell-based immunotherapies, and others. Checkpoint inhibitors (CKP-I), though showing robust efficacy in solid tumor and lymphoma, have had limited success as single agents in the treatment of MM. Furthermore, early FDA holds on trials involving CKP-I in myeloma led to diminished enrollment and data on its potential use. Nevertheless, clearer understanding of the mechanisms of immune dysregulation and unique bone marrow biology in the pathophysiology of MM have opened the opportunity for future uses of CKP-I in multiple myeloma. Herein we provide a comprehensive review of the immunologic basis of multiple myeloma, preclinical and published data from trials utilizing CKP-I in MM patients, and future targets in CKP-I development that may provide promising opportunities in the treatment of MM.

Molecular and immunological mechanisms of clonal evolution in multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy characterized by the proliferation of clonal plasma cells in the bone marrow (BM). It is known that early genetic mutations in post-germinal center B/plasma cells are the cause of myelomagenesis. The acquisition of additional chromosomal abnormalities and distinct mutations further promote the outgrowth of malignant plasma cell populations that are resistant to conventional treatments, finally resulting in relapsed and therapy-refractory terminal stages of MM. In addition, myeloma cells are supported by autocrine signaling pathways and the tumor microenvironment (TME), which consists of diverse cell types such as stromal cells, immune cells, and components of the extracellular matrix. The TME provides essential signals and stimuli that induce proliferation and/or prevent apoptosis. In particular, the molecular pathways by which MM cells interact with the TME are crucial for the development of MM. To generate successful therapies and prevent MM recurrence, a thorough understanding of the molecular mechanisms that drive MM progression and therapy resistance is essential. In this review, we summarize key mechanisms that promote myelomagenesis and drive the clonal expansion in the course of MM progression such as autocrine signaling cascades, as well as direct and indirect interactions between the TME and malignant plasma cells. In addition, we highlight drug-resistance mechanisms and emerging therapies that are currently tested in clinical trials to overcome therapy-refractory MM stages.

Periplocin Overcomes Bortezomib Resistance by Suppressing the Growth and Down-Regulation of Cell Adhesion Molecules in Multiple Myeloma

Multiple myeloma (MM) is an incurable hematological malignant disorder of bone marrow. Patients with MM receive multiple lines of chemotherapeutic treatments which often develop bortezomib (BTZ) resistance and relapse. Therefore, it is crucial to identify an anti-MM agent to overcome the BTZ resistance of MM. In this study, we screened a library of 2370 compounds against MM wild-type (ARP1) and BTZ-resistant type (ARP1-BR) cell lines and found that periplocin (PP) was the most significant anti-MM natural compound. We further investigated the anti-MM effect of PP by using annexin V assay, clonogenic assays, aldefluor assay, and transwell assay. Furthermore, RNA sequencing (RNA-seq) was performed to predict the molecular effects of PP in MM followed by verification through qRT-PCR and Western blot analysis. Moreover, ARP1 and ARP1-BR xenograft mice models of MM were established to confirm the anti-MM effects of PP invivo. The results showed that PP significantly induced apoptosis, inhibited proliferation, suppressed stemness, and reduced the cell migration of MM. The expression of cell adhesion molecules (CAMs) was suppressed upon PP treatment in vitro and in vivo. Overall, our data recommend PP as an anti-MM natural compound with the potential to overcome BTZ resistance and downregulate CAMs in MM.

E-Selectin Targeted Gold Nanoshells to Inhibit Breast Cancer Cell Binding to Lung Endothelial Cells

Extravasation of circulating tumor cells (CTCs) from the vasculature is a key step in cancer metastasis. CTCs bind to cell adhesion molecules (CAMs) expressed by endothelial cells (ECs) for flow arrest prior to extravasation. While a number of EC-expressed CAMs have been implicated in facilitating CTC binding, this work investigated the efficacy of inhibiting cancer cell binding to human lung microvascular ECs via antibody blocking of E-selectin using antibody-functionalized gold nanoshells (NS). The antibody-functionalized gold NS were synthesized using both directional and non-directional antibody conjugation techniques with variations in synthesis parameters (linker length, amount of passivating agents, and ratio of antibodies to NS) to gain a better understanding of these properties on the resultant hydrodynamic diameter, zeta potential, and antibody loading density. We quantified the ability of E-selectin antibody-functionalized NS to bind human lung microvascular endothelial cells (HMVEC-Ls) under non-inflamed and inflamed (TNF-α) conditions to inhibit binding of triple-negative MDA-MB-231s. E-selectin-targeted NS prepared using non-directional conjugation had higher antibody loading than those prepared via directional conjugation, resulting in the conjugates having similar overall binding to HMVEC-Ls at a given antibody concentration. E-selectin-targeted NS reduced MDA-MB-231 binding to HMVEC-Ls by up to 41% as determined using an in vitro binding assay. These results provide useful insights into the characteristics of antibody-functionalized NS prepared under different conditions while also demonstrating proof of concept that these conjugates hold potential to inhibit CTC binding to ECs, a critical step in extravasation during metastasis.

Bone marrow-targetable Green Tea Catechin-Based Micellar Nanocomplex for synergistic therapy of Acute myeloid leukemia

Background

Currently available anti-leukemia drugs have shown limited success in the treatment of acute myeloid leukemia (AML) due to their poor access to bone marrow niche supporting leukemic cell proliferation.

Results

Herein, we report a bone marrow-targetable green tea catechin-based micellar nanocomplex for synergistic AML therapy. The nanocomplex was found to synergistically amplify the anti-leukemic potency of sorafenib via selective disruption of pro-survival mTOR signaling. In vivo biodistribution study demonstrated about 11-fold greater bone marrow accumulation of the nanocomplex compared to free sorafenib. In AML patient-derived xenograft (AML-PDX) mouse model, administration of the nanocomplex effectively eradicated bone marrow-residing leukemic blasts and improved survival rates without noticeable off-target toxicity.

Conclusion

This study may provide insights into the rational design of nanomedicine platforms enabling bone marrow-targeted delivery of therapeutic agents for the treatment of AML and other bone marrow diseases.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01683-4.

Targeting CAM-DR and Mitochondrial Transfer for the Treatment of Multiple Myeloma

The prognosis of patients with multiple myeloma (MM) has improved dramatically with the introduction of new therapeutic drugs, but the disease eventually becomes drug-resistant, following an intractable and incurable course. A myeloma niche (MM niche) develops in the bone marrow microenvironment and plays an important role in the drug resistance mechanism of MM. In particular, adhesion between MM cells and bone marrow stromal cells mediated by adhesion molecules induces cell adhesion-mediated drug resistance (CAM-DR). Analyses of the role of mitochondria in cancer cells, including MM cells, has revealed that the mechanism leading to drug resistance involves exchange of mitochondria between cells (mitochondrial transfer) via tunneling nanotubes (TNTs) within the MM niche. Here, we describe the discovery of these drug resistance mechanisms and the identification of promising therapeutic agents primarily targeting CAM-DR, mitochondrial transfer, and TNTs.

Novel microgel culture system as semi-solid three-dimensional in vitro model for the study of multiple myeloma proliferation and drug resistance

Multiple myeloma (MM) is a hematological malignancy in which the patient's drug resistance is one of the main clinical problems. As 2D cultures do not recapitulate the cellular microenvironment, which has a key role in drug resistance, there is an urgent need for better biomimetic models. Here, a novel 3D platform is used to model MM. The semi-solid culture consists of a dynamic suspension of microspheres and MM cells, termed as microgel. Microspheres are synthesized with acrylic polymers of different sizes, compositions, and functionalities (fibronectin or hyaluronic acid). Optimal conditions for the platform in terms of agitation speed and microsphere size have been determined. With these parameters the system allows good proliferation of the MM cell lines RPMI8226, U226, and MM1.S. Interestingly, when used for drug resistance studies, culture of the three MM cell lines in microgels showed close agreement in revealing the role of acrylic acid in resistance to anti-MM drugs such as dexamethasone and bortezomib. This work presents a unique platform for the in vitro modeling of non-solid tumors since it allows keeping non-adherent cells in suspension conditions but in a 3D context that can be easily tuned with different functionalizations.

Desmoglein-2 expression is an independent predictor of poor prognosis patients with multiple myeloma

Multiple myeloma (MM) is the second most common haematological malignancy and is an incurable disease of neoplastic plasma cells (PC). Newly diagnosed MM patients currently undergo lengthy genetic testing to match chromosomal mutations with the most potent drug/s to decelerate disease progression. With only 17% of MM patients surviving 10‐years postdiagnosis, faster detection and earlier intervention would unequivocally improve outcomes. Here, we show that the cell surface protein desmoglein‐2 (DSG2) is overexpressed in ~ 20% of bone marrow biopsies from newly diagnosed MM patients. Importantly, DSG2 expression was strongly predictive of poor clinical outcome, with patients expressing DSG2 above the 70^th percentile exhibiting an almost 3‐fold increased risk of death. As a prognostic factor, DSG2 is independent of genetic subtype as well as the routinely measured biomarkers of MM activity (e.g. paraprotein). Functional studies revealed a nonredundant role for DSG2 in adhesion of MM PC to endothelial cells. Together, our studies suggest DSG2 to be a potential cell surface biomarker that can be readily detected by flow cytometry to rapidly predict disease trajectory at the time of diagnosis.

Tumour Dissemination in Multiple Myeloma Disease Progression and Relapse: A Potential Therapeutic Target in High-Risk Myeloma

Simple Summary

Like in solid cancers, the process of dissemination is a critical feature of disease progression in the blood cancer multiple myeloma. At diagnosis, myeloma patients have cancer that has spread throughout the bone marrow, with patients with more disseminatory myeloma having worse outcomes for their disease. In this review, we discuss the current understanding of the mechanisms that underpin the dissemination process in multiple myeloma. Furthermore, we discuss the potential for the use of therapies that target the dissemination process as a novel means of improving outcomes for multiple myeloma patients.

Abstract

Multiple myeloma (MM) is a plasma cell (PC) malignancy characterised by the presence of MM PCs at multiple sites throughout the bone marrow. Increased numbers of peripheral blood MM PCs are associated with rapid disease progression, shorter time to relapse and are a feature of advanced disease. In this review, the current understanding of the process of MM PC dissemination and the extrinsic and intrinsic factors potentially driving it are addressed through analysis of patient-derived MM PCs and MM cell lines as well as mouse models of homing and dissemination. In addition, we discuss how patient cytogenetic subgroups that present with highly disseminated disease, such as t(4;14), t(14;16) and t(14;20), suggest that intrinsic properties of MM PC influence their ability to disseminate. Finally, we discuss the possibility of using therapeutic targeting of tumour dissemination to slow disease progression and prevent overt relapse.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Cerebrovascular inflammation promotes the formation of brain metastases

Brain metastases are the most prevalent intracranial malignancy. Patient outcome is poor and treatment options are limited. Hence, new avenues must be explored to identify potential therapeutic targets. Inflammation is a known critical component of cancer progression. Intratumoral inflammation drives progression and leads to the release of circulating tumor cells (CTCs). Inflammation at distant sites promotes adhesion of CTCs to the activated endothelium and then initiates the formation of metastases. These interactions mostly involve cell adhesion molecules expressed by activated endothelial cells. For example, the vascular cell adhesion molecule-1 (VCAM-1) is known to promote transendothelial migration of cancer cells in different organs. However, it is unclear whether a similar mechanism occurs within the specialized environment of the brain. Our objective was therefore to use molecular imaging to assess the potential role of VCAM-1 in promoting the entry of CTCs into the brain. First, magnetic resonance imaging (MRI) and histological analyses revealed that cerebrovascular inflammation induced by intracranial injection of lipopolysaccharide significantly increased the expression of VCAM-1 in the Balb/c mouse brain. Next, intracardiac injection of 4T1 mammary carcinoma cancer cells in animals with cerebrovascular inflammation yielded a higher brain metastasis burden than in the control animals. Finally, blocking VCAM-1 prior to 4T1 cells injection prevented this increased metastatic burden. Here, we demonstrated that by contributing to CTCs adhesion to the activated cerebrovascular endothelium, VCAM-1 improves the capacity of CTCs to form metastatic foci in the brain.

Targeted Approaches to Inhibit Sialylation of Multiple Myeloma in the Bone Marrow Microenvironment

Aberrant glycosylation modulates different aspects of tumor biology, and it has long been recognized as a hallmark of cancer. Among the different forms of glycosylation, sialylation, the addition of sialic acid to underlying oligosaccharides, is often dysregulated in cancer. Increased expression of sialylated glycans has been observed in many types of cancer, including multiple myeloma, and often correlates with aggressive metastatic behavior. Myeloma, a cancer of plasma cells, develops in the bone marrow, and colonizes multiple sites of the skeleton including the skull. In myeloma, the bone marrow represents an essential niche where the malignant cells are nurtured by the microenvironment and protected from chemotherapy. Here, we discuss the role of hypersialylation in the metastatic process focusing on multiple myeloma. In particular, we examine how increased sialylation modulates homing of malignant plasma cells into the bone marrow by regulating the activity of molecules important in bone marrow cellular trafficking including selectins and integrins. We also propose that inhibiting sialylation may represent a new therapeutic strategy to overcome bone marrow-mediated chemotherapy resistance and describe different targeted approaches to specifically deliver sialylation inhibitors to the bone marrow microenvironment.

High-Risk Multiple Myeloma: Integrated Clinical and Omics Approach Dissects the Neoplastic Clone and the Tumor Microenvironment

Multiple myeloma (MM) is a genetically heterogeneous disease that includes a subgroup of 10–15% of patients facing dismal survival despite the most intensive treatment. Despite improvements in biological knowledge, MM is still an incurable neoplasia, and therapeutic options able to overcome the relapsing/refractory behavior represent an unmet clinical need. The aim of this review is to provide an integrated clinical and biological overview of high-risk MM, discussing novel therapeutic perspectives, targeting the neoplastic clone and its microenvironment. The dissection of the molecular determinants of the aggressive phenotypes and drug-resistance can foster a better tailored clinical management of the high-risk profile and therapy-refractoriness. Among the current clinical difficulties in MM, patients’ management by manipulating the tumor niche represents a major challenge. The angiogenesis and the stromal infiltrate constitute pivotal mechanisms of a mutual collaboration between MM and the non-tumoral counterpart. Immuno-modulatory and anti-angiogenic therapy hold great efficacy, but variable and unpredictable responses in high-risk MM. The comprehensive understanding of the genetic heterogeneity and MM high-risk ecosystem enforce a systematic bench-to-bedside approach. Here, we provide a broad outlook of novel druggable targets. We also summarize the existing multi-omics-based risk profiling tools, in order to better select candidates for dual immune/vasculogenesis targeting.

Microenvironment drug resistance in multiple myeloma: emerging new players

Multiple myeloma (MM) drug resistance (DR) is a multistep transformation process based on a powerful interplay between bone marrow stromal cells and MM cells that allows the latter to escape anti-myeloma therapies. Here we present an overview of the role of the bone marrow microenvironment in both soluble factors-mediated drug resistance (SFM-DR) and cell adhesion-mediated drug resistance (CAM-DR), focusing on the role of new players, namely miRNAs, exosomes and cancer-associated fibroblasts.

Clinical Relevance of Multicolour Flow Cytometry in Plasma Cell Disorders

Multicolor flow cytometric (MFC) immunophenotyping is one of the basic test that is needed in the evaluation of hematolymphoid malignancies. Previously, there has been some reluctance in the use of MFC in plasma cell disorders (PCD). It was mainly due tolack of standardization, inadequate experience and detection of the lower number of plasma cells by MFC as compared to morphology. However, MFC has gone through many technological advancements in the last few years and a wide variety of reagents are now commercially available which worldwide allowed the establishment of standardized sensitive MFC-based immunophenotypic assay for PCD. Various studies have proven that MFC has a high clinical relevance in the diagnosis and risk stratification of multiple myeloma, its precursor conditions and other PCDs. Moreover, recent studies have shown that MFC is a highly sensitive and reliable technique for the monitoring of clinical response in the era of novel therapies. In this review, we have discussed the various applications of MFC in the management of PCD and their clinical relevance.

A Human Antibody That Binds to the Sixth Ig-Like Domain of VCAM-1 Blocks Lung Cancer Cell Migration In Vitro

Vascular cell adhesion molecule-1 (VCAM-1) is closely associated with tumor progression and metastasis. However, the relevance and role of VCAM-1 in lung cancer have not been clearly elucidated. In this study, we found that VCAM-1 was highly overexpressed in lung cancer tissue compared with that of normal lung tissue, and high VCAM-1 expression correlated with poor survival in lung cancer patients. VCAM-1 knockdown reduced migration of A549 human lung cancer cells into Matrigel, and competitive blocking experiments targeting the Ig-like domain 6 of VCAM-1 (VCAM-1-D6) demonstrated that the VCAM-1-D6 domain was critical for VCAM-1 mediated A549 cell migration into Matrigel. Next, we developed a human monoclonal antibody specific to human and mouse VCAM-1-D6 (VCAM-1-D6 huMab), which was isolated from a human synthetic antibody library using phage display technology. Finally, we showed that VCAM-1-D6 huMab had a nanomolar affinity for VCAM-1-D6 and that it potently suppressed the migration of A549 and NCI-H1299 lung cancer cell lines into Matrigel. Taken together, these results suggest that VCAM-1-D6 is a key domain for regulating VCAM-1-mediated lung cancer invasion and that our newly developed VCAM-1-D6 huMab will be a useful tool for inhibiting VCAM-1-expressing lung cancer cell invasion.

Expression of Cadherin-17 Promotes Metastasis in a Highly Bone Marrow Metastatic Murine Breast Cancer Model

We previously established 4T1E/M3 highly bone marrow metastatic mouse breast cancer cells through in vivo selection of 4T1 cells. But while the incidence of bone marrow metastasis of 4T1E/M3 cells was high (~80%) when injected intravenously to mice, it was rather low (~20%) when injected subcutaneously. Therefore, using 4T1E/M3 cells, we carried out further in vitro and in vivo selection steps to establish FP10SC2 cells, which show a very high incidence of metastasis to lungs (100%) and spines (85%) after subcutaneous injection into mice. qRT-PCR and western bolt analysis revealed that cadherin-17 gene and protein expression were higher in FP10SC2 cells than in parental 4T1E/M3 cells. In addition, immunostaining revealed the presence of cadherin-17 at sites of bone marrow and lung metastasis after subcutaneous injection of FP10SC2 cells into mice. Suppressing cadherin-17 expression in FP10SC2 cells using RNAi dramatically decreased the cells' anchorage-independent growth and migration in vitro and their metastasis to lung and bone marrow in vivo. These findings suggest that cadherin-17 plays a crucial role in mediating breast cancer metastasis to bone marrow.

Targeting Intrinsic and Extrinsic Vulnerabilities for the Treatment of Multiple Myeloma

Multiple myeloma (MM) is a malignant plasma cell disorder, clinically characterized by osteolytic lesions, immunodeficiency, and renal disease. Over the past decade, MM therapy is significantly improved by the introduction of novel therapeutics such as immunomodulatory agents (thalidomide, lenalidomide, and pomalidomide), proteasome inhibitors (bortezomib, carfilzomib, and ixazomib), monoclonal antibodies (daratumumab and elotuzumab), histone deacetylase (HDAC) inhibitors (Panobinostat). The clinical success of these agents has clearly identified vulnerabilities intrinsic to the MM cell, as well as targets that emanate from the tumor microenvironment. Despite these significant improvements, MM remains incurable due to the development of drug resistance. This perspective will discuss more recent strategies which take advantage of multiple targets within the proteome recycling pathway, chromatin remodeling, and disruption of nuclear export. In addition, we will review the development of strategies designed to block opportunistic survival signaling that occurs between the MM cell and the tumor microenvironment including strategies for inhibiting myeloma-induced immune suppression. It has become clear that MM tumors continue to evolve on therapy leading to drug resistance. It will be important to understand the emerging drug resistant mechanisms and additional vulnerabilities that occur due to the development of clinical resistance. J. Cell. Biochem. 118: 15-25, 2017. © 2016 Wiley Periodicals, Inc.

Increased circulating VCAM-1 correlates with advanced disease and poor survival in patients with multiple myeloma: reduction by post-bortezomib and lenalidomide treatment

Circulating vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1) and selectins were prospectively measured in 145 newly-diagnosed patients with symptomatic myeloma (NDMM), 61 patients with asymptomatic/smoldering myeloma (SMM), 47 with monoclonal gammopathy of undetermined significance (MGUS) and 87 multiple myeloma (MM) patients at first relapse who received lenalidomide- or bortezomib-based treatment (RD, n=47; or VD, n=40). Patients with NDMM had increased VCAM-1 and ICAM-1 compared with MGUS and SMM patients. Elevated VCAM-1 correlated with ISS-3 and was independently associated with inferior overall survival (OS) (45 months for patients with VCAM-1 >median vs 75 months, P=0.001). MM patients at first relapse had increased levels of ICAM-1 and L-selectin, even compared with NDMM patients and had increased levels of VCAM-1 compared with MGUS and SMM. Both VD and RD reduced dramatically serum VCAM-1 after four cycles of therapy, but only VD reduced serum ICAM-1, irrespective of response to therapy. The reduction of VCAM-1 was more pronounced after RD than after VD. Our study provides evidence for the prognostic value of VCAM-1 in myeloma patients, suggesting that VCAM-1 could be a suitable target for the development of anti-myeloma therapies. Furthermore, the reduction of VCAM-1 and ICAM-1 by RD and VD supports the inhibitory effect of these drugs on the adhesion of MM cells to stromal cells.

Blocking the ZZ domain of sequestosome1/p62 suppresses myeloma growth and osteoclast formation in vitro and induces dramatic bone formation in myeloma-bearing bones in vivo

We reported that p62 (sequestosome 1) serves as a signaling hub in bone marrow stromal cells (BMSC) for the formation of signaling complexes, including NFκB, p38MAPK, and JNK, that are involved in the increased osteoclastogenesis and multiple myeloma (MM) cell growth induced by BMSC that are key contributors to myeloma bone disease (MMBD), and demonstrated that the ZZ-domain of p62 (p62-ZZ) is required for BMSC enhancement of MMBD. We recently identified a novel p62-ZZ inhibitor, XRK3F2, that inhibits MM cell growth and BMSC growth enhancement of human MM cells. In the current study we evaluate the relative specificity of XRK3F2 for p62-ZZ, characterize XRK3F2’s capacity to inhibit growth of primary MM cells and human MM cell lines, and test the in vivo effects of XRK3F2 in the immunocompetent 5TGM1 MM model. We found that XRK3F2 induces dramatic cortical bone formation that is restricted to MM containing bones and blocked the effects and upregulation of TNFα, an OBL differentiation inhibitor that is increased in the MM bone marrow microenvironment and utilizes signaling complexes formed on p62-ZZ, in BMSC. Interestingly, XRK3F2 had no effect on non-MM bearing bone. These results demonstrate that targeting p62 in MM models has profound effects on MMBD.

Therapeutic targeting of N-cadherin is an effective treatment for multiple myeloma

Elevated expression of the cell adhesion molecule N-cadherin (cadherin 2, type 1, N-cadherin (neuronal); CDH2) is associated with poor prognosis in newly-diagnosed multiple myeloma (MM) patients. In this study, we investigated whether targeting of N-cadherin represents a potential treatment for the ~50% of MM patients with elevated N-cadherin. Initially, we stably knocked-down N-cadherin in the mouse MM plasma cell (PC) line 5TGM1 to assess the functional role of N-cadherin in MM pathogenesis. When compared with 5TGM1-scramble-shRNA cells, 5TGM1-Cdh2-shRNA cells had significantly reduced adhesion to bone marrow endothelial cells. However, N-cadherin knock-down did not affect 5TGM1 cell proliferation or adhesion to bone marrow stromal cells. In the C57BL/KaLwRij murine MM model, mice intravenously inoculated with 5TGM1-Cdh2-shRNA cells showed significantly decreased tumour burden after 4 weeks, compared with animals bearing 5TGM1-scramble-shRNA cells. Finally, the N-cadherin antagonist ADH-1 had no effect on tumour burden in the established disease setting, whereas up-front ADH-1 treatment resulted in significantly reduced tumour burden after 4 weeks. Our findings demonstrate that N-cadherin may play a key role in the extravasation of circulating MM PCs promoting bone marrow homing. Moreover, these studies suggest that N-cadherin may represent a viable therapeutic target to prevent the dissemination of MM PCs and delay MM disease progression.

Non-invasive imaging provides spatiotemporal information on disease progression and response to therapy in a murine model of multiple myeloma

BACKGROUND

Multiple myeloma (MM) is a B-cell malignancy, where malignant plasma cells clonally expand in the bone marrow of older people, causing significant morbidity and mortality. Typical clinical symptoms include increased serum calcium levels, renal insufficiency, anemia, and bone lesions. With standard therapies, MM remains incurable; therefore, the development of new drugs or immune cell-based therapies is desirable. To advance the goal of finding a more effective treatment for MM, we aimed to develop a reliable preclinical MM mouse model applying sensitive and reproducible methods for monitoring of tumor growth and metastasis in response to therapy.

MATERIAL AND METHODS

A mouse model was created by intravenously injecting bone marrow-homing mouse myeloma cells (MOPC-315.BM) that expressed luciferase into BALB/c wild type mice. The luciferase in the myeloma cells allowed in vivo tracking before and after melphalan treatment with bioluminescence imaging (BLI). Homing of MOPC-315.BM luciferase+ myeloma cells to specific tissues was examined by flow cytometry. Idiotype-specific myeloma protein serum levels were measured by ELISA. In vivo measurements were validated with histopathology.

RESULTS

Strong bone marrow tropism and subsequent dissemination of MOPC-315.BM luciferase(+) cells in vivo closely mimicked the human disease. In vivo BLI and later histopathological analysis revealed that 12 days of melphalan treatment slowed tumor progression and reduced MM dissemination compared to untreated controls. MOPC-315.BM luciferase(+) cells expressed CXCR4 and high levels of CD44 and α4β1 in vitro which could explain the strong bone marrow tropism. The results showed that MOPC-315.BM cells dynamically regulated homing receptor expression and depended on interactions with surrounding cells.

CONCLUSIONS

This study described a novel MM mouse model that facilitated convenient, reliable, and sensitive tracking of myeloma cells with whole body BLI in living animals. This model is highly suitable for monitoring the effects of different treatment regimens.

The biology of CD44 and HCELL in hematopoiesis: the 'step 2-bypass pathway' and other emerging perspectives

PURPOSE OF REVIEW

The homing and egress of hematopoietic stem and progenitor cells (HSPCs) to and from marrow, respectively, and the proliferation and differentiation of HSPCs within marrow are complex processes critically regulated by the ordered expression and function of adhesion molecules that direct key cell-cell and cell-matrix interactions. The integral membrane molecule CD44, known primarily for its role in binding hyaluronic acid, is characteristically expressed on HSPCs. Conspicuously, human HSPCs uniquely display a specialized glycoform of CD44 known as hematopoietic cell E-/L-selectin ligand (HCELL), which is the most potent ligand for both E-selectin and L-selectin expressed on human cells. This review focuses on recent advances in our understanding of the biology of CD44 and HCELL in hematopoiesis.

RECENT FINDINGS

New data indicate that CD44-mediated events in hematopoiesis are more complex than previously imagined. Ex-vivo glycan engineering has established that HCELL serves as a 'bone marrow homing receptor'. Moreover, biochemical studies now show that CD44 forms bimolecular complexes with a variety of membrane proteins, one of which is VLA-4. Engagement of CD44 or of HCELL directly induces VLA-4 activation via G-protein-dependent signaling, triggering a 'step 2-bypass pathway' of cell migration, and extravascular lodgment, in absence of chemokine receptor engagement.

SUMMARY

Recent studies have further clarified the roles of CD44 and its glycoform HCELL in hematopoietic processes, providing key insights on how targeting these molecules may be beneficial in promoting hematopoiesis and in treating hematologic malignancies.

Flow cytometric immunophenotypic characteristics of 36 cases of plasma cell leukemia

Prospective flow cytometric analysis of antigens expression on bone marrow and peripheral blood plasma cells of 36 plasma cell leukemia (PCL) patients enabled to establish the following immunophenotype of leukemic plasma cell: CD38(++), CD138(+), CD54(+), CD49d(+), CD29(+), CD44(+), CD126(+), CD19(-), CD45(-). In one-third of patients PCL cells express CD56, CD71 and CD117. Expression of CD54 on plasma cells was higher as compared to expression of adhesion molecules CD11a, CD18 and CD11b (p<0.01). Expression of CD18, CD11a, CD11b was lower on bone marrow and higher on peripheral blood cells. In conclusion, impaired expression of adhesion molecules such as CD11a/CD18 or CD56 may explain hematogenic dissemination characterizing PCL.

Increased signaling through p62 in the marrow microenvironment increases myeloma cell growth and osteoclast formation

Adhesive interactions between multiple myeloma (MM) cells and marrow stromal cells activate multiple signaling pathways including nuclear factor kappaB (NF-kappaB), p38 mitogen-activated protein kinase (MAPK), and Jun N-terminal kinase (JNK) in stromal cells, which promote tumor growth and bone destruction. Sequestosome-1 (p62), an adapter protein that has no intrinsic enzymatic activity, serves as a platform to facilitate formation of signaling complexes for these pathways. Therefore, we determined if targeting only p62 would inhibit multiple signaling pathways activated in the MM microenvironment and thereby decrease MM cell growth and osteoclast formation. Signaling through NF-kappaB and p38 MAPK was increased in primary stromal cells from MM patients. Increased interleukin-6 (IL-6) production by MM stromal cells was p38 MAPK-dependent while increased vascular cell adhesion molecule-1 (VCAM-1) expression was NF-kappaB-dependent. Knocking-down p62 in patient-derived stromal cells significantly decreased protein kinase Czeta (PKCzeta), VCAM-1, and IL-6 levels as well as decreased stromal cell support of MM cell growth. Similarly, marrow stromal cells from p62(-/-) mice produced much lower levels of IL-6, tumor necrosis factor-alpha (TNF-alpha), and receptor activator of NF-kappaB ligand (RANKL) and supported MM cell growth and osteoclast formation to a much lower extent than normal cells. Thus, p62 is an attractive therapeutic target for MM.

Extravasation and homing mechanisms in multiple myeloma

Multiple myeloma (MM) is a malignant B-cell disorder characterized by a monoclonal expansion of plasma cells (PC) in the bone marrow (BM). During the main course of disease evolution, MM cells depend on the BM microenvironment for their growth and survival. Reciprocal interactions between MM cells and the BM mediate not only MM cell growth, but also protect them against apoptosis and cause bone disease and angiogenesis. A striking feature of MM represents the predominant localization and retention of MM cells in the BM. Although BM PC indeed represent the main neoplastic cell type, small numbers of MM cells can also be detected in the peripheral blood circulation. It can be assumed that these circulating cells represent the tumour-spreading component of the disease. This implicates that MM cells have the capacity to (re)circulate, to extravasate and to migrate to the BM (homing). In analogy to the migration and homing of normal leucocytes, the BM homing of MM cells is mediated by a multistep process of extravasation with adhesion to the endothelium, invasion of the subendothelial basement membrane, followed by further migration within the stroma, mediated by chemotactic factors. At the end stage of disease, MM cells are thought to develop autocrine growth supporting loops that enable them to survive and proliferate in the absence of the BM microenvironment and to become stroma-independent. In this stage, the number of circulating cells increases and growth at extramedullary sites can occur, associated with alteration in adhesion molecule and chemokine receptor expression. This review summarizes the recent progress in the study of the extravasation and homing mechanisms of MM cells.

Thymoglobulin targets multiple plasma cell antigens and has in vitro and in vivo activity in multiple myeloma

Multiple myeloma is characterized by the proliferation of clonal plasma cells that have a heterogeneous expression of various cell surface markers, precluding successful use of monoclonal antibodies for therapeutic targeting of the tumor cell. Thymoglobulin (rabbit-derived polyclonal anti-thymocyte globulin), by virtue of its method of preparation, contains antibodies against several B-cell and plasma cell antigens and offers an attractive option for immunotherapy of myeloma. Here, we demonstrate potent anti-myeloma activity of the rabbit anti-thymocyte globulin preparation Thymoglobulin in vitro and in vivo in an animal model of myeloma. Thymoglobulin was able to induce dose- and time-dependent apoptosis of several myeloma cell lines, including those resistant to conventional anti-myeloma agents. Importantly, the anti-myeloma activity was preserved even when myeloma cells were grown with different cytokines demonstrating the ability to overcome microenvironment-mediated resistance. Thymoglobulin induced apoptosis of freshly isolated primary myeloma cells from patients. Using a competitive flow cytometric analysis, we were able to identify the potential antigen targets for Thymoglobulin preparation. Finally, in a plasmacytoma mouse model of myeloma, Thymoglobulin delayed the tumor growth in a dose-dependent manner providing convincing evidence for continued evaluation of this agent in the clinic in patients with myeloma, either alone or in combination with other agents.

Pathogenesis of bone metastasis: a review

BACKGROUND

Metastasic deposits from malignancies frequently lodge in the skeleton, including the jaw bones.

METHOD

A review of the literature was performed in order to provide a coherent overview on the pathogenesis of bone metastasis.

RESULTS

Bone metastasis follows complex molecular interactions that enable tumor cells to detach from the primary site, invade the extracellular matrix, intra-vasate, extra-vasate, and proliferate within bone. They induce local bone changes that could manifest radiologically as either osteolytic or radiodense. In addition to the direct bone changes, malignancies can elaborate mediators that are released in circulation, leading to generalized osteopenia.

CONCLUSIONS

The spread of malignant neoplasms to bone is not a random process but rather a cascade of specific molecular events orchestrated through complex interactions between neoplastic cells and their environment.

CD44 potentiates the adherence of metastatic prostate and breast cancer cells to bone marrow endothelial cells

The aim of this current study was to examine the significance of CD44 expression in mediating cancer cell adhesion to human bone marrow endothelial cell(s) (hBMEC). Differential CD44 expression on two metastatic prostate cancer cell lines, PC3 (CD44 +ve) and DU145 (CD44 -ve) and four breast cancer cell lines was confirmed by immunoblotting and immunocytochemistry. In cell adhesion assays, PC3 but not DU145 cells demonstrated a rapid adhesion to hBMECs. Treatment of PC3 cells with a neutralizing antibody against CD44 standard (CD44s) and CD44 splice variants decreased PC3 cell adhesion to hBMECs. Similarly, depletion of CD44 expression using RNA interference decreased the ability of PC3 cells and two CD44 +ve breast cancer cell lines (MDA-MB-231 and MDA-MB-157) to bind FITC-conjugated hyaluronan (FITC-HA) and to adhere to hBMECs. In contrast, transfection of DU145 cells or the T47D and MCF-7 breast cancer cell lines to express CD44s increased cell surface binding of FITC-HA and cell adherence to hBMECs. Treatment of PC3 and MDA-MD-231 cells but not hBMECs with hyaluronidase attenuated cell adhesion, suggesting that cell surface expression of CD44 on prostate and breast cancer cells may promote the retention of a HA coat that facilitates their initial arrest on bone marrow endothelium.

Homing and mobilization of hematopoietic stem cells and hematopoietic cancer cells are mirror image processes, utilizing similar signaling pathways and occurring concurrently: circulating cancer cells constitute an ideal target for concurrent treatment with chemotherapy and antilineage-specific antibodies

Adhesion molecules and stromal cell-derived factor-1 (SDF-1)/CXCR4 signaling play key role in homing and mobilization of hematopoietic progenitor (HPC) and hematopoietic cancer clonogenic cells (HCC). High expression of VLA-4 is required for homing of HPC and HCC, whereas downregulation of these molecules is required for successful mobilization of HPC and HCC. Upregulation and activation of the SDF-1/CXCR4 signaling is required for homing of HPC and HCC, whereas disruption of the SDF-1 signaling is required for mobilization of HPC and HCC. Hence, mobilizations of HPC and HCC occur concurrently. It is proposed that drug resistance evolves as a result of repeated cycles of chemotherapy. Following each cycle of chemotherapy, HCC lose adhesion molecules and SDF-1 signaling. Surviving cells, released from tumor sites, circulate until re-expression of adhesion molecules and CXCR4 occurs, then homing to stroma of distal tissues occurs. Cytokines secreted by cells in the new microenvironment induce proliferation and drug resistance of HCC. This process is amplified in each cycle of chemotherapy resulting in disease progression. A novel model for treatment is proposed in which circulating HCC are the target for clinical intervention, and concurrent treatment with chemotherapy and antilineage-specific antibodies will result in abrogation of the 'vicious cycle' of conventional anticancer therapy.

Mobilization of Myeloma Cells Involves SDF-1/CXCR4 Signaling and Downregulation of VLA-4

Adhesion molecules and stromal cell-derived factor-1 (SDF-1)/CXCR4 signaling play key roles in homing and mobilization of hematopoietic stem cells (HSC). Active signaling through SDF-1/CXCR4 and upregulation of adhesion molecules are required for homing, whereas downregulation of adhesion molecules and disruption of SDF-1/CXCR4 signaling are required for mobilization of HSC. We studied the surface expression of CXCR4 very late activation antigen (VLA)-4 and VLA-5 on myeloma cells mobilized with cyclophosphamide and GM-CSF in 12 multiple myeloma patients undergoing HSC mobilization for autologous transplantation. We also studied the plasma levels of SDF-1 in apheresis collection of these patients. We observed a statistically significant decrease in the levels of SDF-1 and surface expression of CXCR4 on myeloma cells in four consecutive apheresis collections compared with premobilization bone marrow specimens. We also observed a statistically significant decrease in surface expression of VLA-4 in myeloma cells in the apheresis collections compared with premobilization bone marrow samples. Furthermore, myeloma cells derived from apheresis collections had decreased adhesion and trans-stromal migration in response to SDF-1, which could be reversed by short incubation with interleukin-6. Hence, mobilization of myeloma cells involves SDF-1/CXCR4 signaling and downregulation of VLA-4.

Bone marrow metastatic myeloma cells promote osteoclastogenesis through RANKL on endothelial cells

We have been using the B9/BM1 murine bone marrow metastasis model to study the function of adhesion molecules in the cell-cell interactions and transendothelial migration, necessary for tumor metastasis. The cell surface phenotype of these cells, which colonize vertebral and femoral marrow after intravenous injection, shows great similarity to that of human myeloma cells. In the present study, we investigated the interaction between B9/BM1 cells and osteoclasts, which likely support tumor metastasis in bone marrow. We found that co-culturing B9/BM1 cells and bone marrow-derived endothelial cells (BMECs) in the presence of vitamin D3 and M-CSF promoted differentiation of primary osteoclast progenitors to osteoclasts (detected by TRAP staining), and that this effect was blocked when BMECs were separated from the other cells by a porous polycarbonate membrane. Flow cytometry analysis showed that BMECs expressed RANKL (receptor activator of NF-kappaB ligand) protein on their surface, and that this expression was up-regulated by co-culture with B9/BM1 cells. Accordingly, RT-PCR showed expression of RANKL mRNA also to be up-regulated in BMECs co-cultured with B9/BM1 cells. Addition of OPG (osteoprotegerin, a decoy RANKL receptor) to the co-culture system completely blocked osteoclast induction, as did addition of anti-CD44 antibody. Furthermore, intravenous injection of B9/BM1 cells substantially increased the numbers of TRAP-positive osteoclasts detected in mice in vivo. Taken together, these findings suggest that B9/BM1 myeloma cells act via CD44 to stimulate RANKL expression on BMECs, which in turn physically interact with osteoclast progenitors to promote their differentiation to osteoclasts and metastasis in bone marrow.

The molecular basis of skeletal metastases

Metastasis is the culmination of numerous highly regulated sequences of steps that results in the proliferation and migration of cells from the primary site to a distant location. The biologic consequence of skeletal metastasis is focal bone sclerosis or osteolysis that leads to pain, pathologic fracture, and biochemical derangement. The difficulty in determining a point of control for clinical application has been because of the numerous systems, substrates, ligands, receptors, factors, and pathways that exist. These may be grouped into functional mechanisms identifiable by their relevance to the metastatic process. These include cell-cell or cell-matrix adhesion, invasion and migration, interactions with endothelial cells, growth factor regulation, proteolysis, and stimulation of differentiated osteoblast and osteoclast function. The challenge for cancer therapy will be to identify means to prevent metastasis or reduce its effect once it occurred. This review examines recent advances in the study of molecular processes of metastasis, which have identified potential sites and substrates for targeting with novel therapies and agents.

Expression of cell adhesion molecules, their ligands and tumour necrosis factor alpha in the liver of patients with metastatic gastrointestinal carcinomas

The expression of the following cell adhesion molecules, their beta1 and beta2 integrin ligands and the cytokine tumour necrosis factor-alpha (TNF-alpha) was investigated by light and electron microscope immunohistochemistry in the liver tissue in 20 patients with colorectal and gastric cancer also presenting with liver metastases: intercellular adhesion molecule-1 (ICAM-1), vascular endothelial adhesion molecule-1 (VCAM-1), E-selectin, leucocyte function-associated antigen-1 (LFA-1), macrophage antigen-1 (Mac-1), and very late antigen-4 (VLA-4). We have found a parallel enhancement of the adhesion molecules and of TNF-alpha in liver sinusoids surrounding metastases. The expression of ICAM-1 was enhanced on sinusoidal cells in all zones of the acinus. VCAM-1 immune reactivity was diffuse but less intensive in the lobule. E-selectin expression was observed in sinusoidal cells attached to metastases. In tumour metastases the expression of ICAM-1, VCAM-1, and E-selectin was visible on the tumour vascular endothelium. Tumour infiltrating host cells sowing positive immunoreactivity for ICAM-1, VCAM-1, LFA-1, Mac-1, and VLA-4 were located mainly at the boundary between liver parenchyma and the metastasis. At the ultrastructural level, ICAM-1-positive immune deposits were observed on the cellular membrane and in some transport vesicles of gastric metastatic cells. Further, the expression of all adhesion molecules was confirmed to sinusoidal endothelial cells and tumour vessels. It is concluded that the enhanced expression of adhesion molecules in liver sinusoids could be a marker for the assessment of the ability of sinusoidal endothelial cells to control the recruitment of leukocytes and monocytes to the metastatic site. They could also direct the adhesion of new circulating tumour cells to sinusoidal endothelium.

Differentiation therapy of human cancer: basic science and clinical applications

Current cancer therapies are highly toxic and often nonspecific. A potentially less toxic approach to treating this prevalent disease employs agents that modify cancer cell differentiation, termed 'differentiation therapy.' This approach is based on the tacit assumption that many neoplastic cell types exhibit reversible defects in differentiation, which upon appropriate treatment, results in tumor reprogramming and a concomitant loss in proliferative capacity and induction of terminal differentiation or apoptosis (programmed cell death). Laboratory studies that focus on elucidating mechanisms of action are demonstrating the effectiveness of 'differentiation therapy,' which is now beginning to show translational promise in the clinical setting.

Conditional vascular cell adhesion molecule 1 deletion in mice: impaired lymphocyte migration to bone marrow

We generated vascular cell adhesion molecule (VCAM)-1 "knock-in" mice and Cre recombinase transgenic mice to delete the VCAM-1 gene (vcam-1) in whole mice, thereby overcoming the embryonic lethality seen with conventional vcam-1-deficient mice. vcam-1 knock-in mice expressed normal levels of VCAM-1 but showed loss of VCAM-1 on endothelial and hematopoietic cells when interbred with a "TIE2Cre" transgene. Analysis of peripheral blood from conditional vcam-1-deficient mice revealed mild leukocytosis, including elevated immature B cell numbers. Conversely, the bone marrow (BM) had reduced immature B cell numbers, but normal numbers of pro-B cells. vcam-1-deficient mice also had reduced mature IgD+ B and T cells in BM and a greatly reduced capacity to support short-term migration of transferred B cells, CD4+ T cells, CD8+ T cells, and preactivated CD4+ T cells to the BM. Thus, we report an until now unappreciated dominant role for VCAM-1 in lymphocyte homing to BM.