Clinical significance of sCD105 in angiogenesis and disease activity in multiple myeloma

High concentrations of soluble endoglin can inhibit BMP9 signaling in non-endothelial cells

Endoglin (ENG) is a single-pass transmembrane protein highly expressed on vascular endothelial cells, although low expression levels can be detected in many other cell types. Its extracellular domain can be found in circulation known as soluble endoglin (sENG). Levels of sENG are elevated in many pathological conditions, in particular preeclampsia. We have shown that while loss of cell surface ENG decreases BMP9 signaling in endothelial cells, knocking down ENG in blood cancer cells enhances BMP9 signaling. Despite sENG binding to BMP9 with high affinity and blocking the type II receptor binding site on BMP9, sENG did not inhibit BMP9 signaling in vascular endothelial cells, but the dimeric form of sENG inhibited BMP9 signaling in blood cancer cells. Here we report that in non-endothelial cells such as human multiple myeloma cell lines and the mouse myoblast cell line C2C12, both monomeric and dimeric forms of sENG inhibit BMP9 signaling when present at high concentrations. Such inhibition can be alleviated by the overexpression of ENG and ACVRL1 (encoding ALK1) in the non-endothelial cells. Our findings suggest that the effects of sENG on BMP9 signaling is cell-type specific. This is an important consideration when developing therapies targeting the ENG and ALK1 pathway.

Mesenchymal stromal cell senescence in haematological malignancies

Acute myeloid leukaemia (AML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM) are age-related haematological malignancies with defined precursor states termed myelodysplastic syndrome (MDS), monoclonal B-cell lymphocytosis (MBL), and monoclonal gammopathy of undetermined significance (MGUS), respectively. While the progression from asymptomatic precursor states to malignancy is widely considered to be mediated by the accumulation of genetic mutations in neoplastic haematopoietic cell clones, recent studies suggest that intrinsic genetic changes, alone, may be insufficient to drive the progression to overt malignancy. Notably, studies suggest that extrinsic, microenvironmental changes in the bone marrow (BM) may also promote the transition from these precursor states to active disease. There is now enhanced focus on extrinsic, age-related changes in the BM microenvironment that accompany the development of AML, CLL, and MM. One of the most prominent changes associated with ageing is the accumulation of senescent mesenchymal stromal cells within tissues and organs. In comparison with proliferating cells, senescent cells display an altered profile of secreted factors (secretome), termed the senescence-associated-secretory phenotype (SASP), comprising proteases, inflammatory cytokines, and growth factors that may render the local microenvironment favourable for cancer growth. It is well established that BM mesenchymal stromal cells (BM-MSCs) are key regulators of haematopoietic stem cell maintenance and fate determination. Moreover, there is emerging evidence that BM-MSC senescence may contribute to age-related haematopoietic decline and cancer development. This review explores the association between BM-MSC senescence and the development of haematological malignancies, and the functional role of senescent BM-MSCs in the development of these cancers.

Soluble Endoglin (sCD105) as a Novel Biomarker for Detecting Aggressive Prostate Cancer

BACKGROUND/AIM

We have previously found elevated levels of endoglin (CD105) in the prostate cancer (PC) tissue of men with poor prognosis, compared to men with indolent disease. Herein, we examined whether plasma levels of the soluble form of CD105 (sCD105) differ according to the PC grade at diagnosis.

PATIENTS AND METHODS

We measured sCD105 in 73 subjects with biopsy-confirmed PC at the Durham, North Carolina, Veteran Affairs Health System. The association between sCD105 and intermediate/high-grade PC risk [Gleason Group (GG) 2-5 vs. 1] was examined using regression models.

RESULTS

Of 73 men, 27 had low-grade PC and 46 high-grade PC. Higher GG was linked to lower sCD105 (GG1: 6938 pg/ml, GG2-3: 6150 pg/ml, GG4-5: 5554 pg/ml; p=0.012). On multivariable analysis, lower sCD105 was associated with increased high-grade PC risk (OR_{per 1000 units}=1.33, p=0.028).

CONCLUSION

Lower sCD105 levels were associated with intermediate and high-risk PC. Further investigation is warranted in a larger PC cohort.

Prognostic Biomarkers in the Progression From MGUS to Multiple Myeloma: A Systematic Review

Multiple myeloma (MM), characterized by malignant plasma cells in the bone marrow, is consistently preceded by asymptomatic premalignant stage monoclonal gammopathy of undetermined significance (MGUS). These MGUS patients have an annual risk of 1% to progress to MM. Clinical, imaging, and genomic (genetic and epigenetic) factors were identified, whose presence increased the risk of progression from MGUS to MM. In this systematic review we summarize the currently identified clinical, imaging, and genomic biomarkers suggested to increase the progression risk or shown to be differentially expressed/present between both cohorts of patients. Despite the wide range of proposed markers, there are still no reliable biomarkers to individually predict which MGUS patient will progress to MM and which will not. Research on biomarkers in the progression from MGUS to MM will give more insight in the unknown pathogenesis of this hematological malignancy. This would improve research by elucidating new pathways and potential therapeutic targets as well as clinical management by closer follow-up and earlier treatment of high-risk MGUS patients.

The role of bone morphogenetic proteins in myeloma cell survival

Multiple myeloma is characterized by slowly growing clones of malignant plasma cells in the bone marrow. The malignant state is frequently accompanied by osteolytic bone disease due to a disturbed balance between osteoblasts and osteoclasts. Bone morphogenetic proteins (BMPs) are present in the bone marrow and are important for several aspects of myeloma pathogenesis including growth and survival of tumor cells, bone homeostasis, and anemia. Among cancer cells, myeloma cells are particularly sensitive to growth inhibition and apoptosis induced by BMPs and therefore represent good models to study BMP receptor usage and signaling. Our review highlights and discusses the current knowledge on BMP signaling in myeloma.

Bone morphogenetic protein-9 suppresses growth of myeloma cells by signaling through ALK2 but is inhibited by endoglin

Multiple myeloma is a malignancy of plasma cells predominantly located in the bone marrow. A number of bone morphogenetic proteins (BMPs) induce apoptosis in myeloma cells in vitro, and with this study we add BMP-9 to the list. BMP-9 has been found in human serum at concentrations that inhibit cancer cell growth in vitro. We here show that the level of BMP-9 in serum was elevated in myeloma patients (median 176 pg/ml, range 8–809) compared with healthy controls (median 110 pg/ml, range 8–359). BMP-9 was also present in the bone marrow and was able to induce apoptosis in 4 out of 11 primary myeloma cell samples by signaling through ALK2. BMP-9-induced apoptosis in myeloma cells was associated with c-MYC downregulation. The effects of BMP-9 were counteracted by membrane-bound (CD105) or soluble endoglin present in the bone marrow microenvironment, suggesting a mechanism for how myeloma cells can evade the tumor suppressing activity of BMP-9 in multiple myeloma.

Myeloma in scar tissue--an underreported phenomenon or an emerging entity in the novel agents' era? A single center series

Tumor relapse in scar tissue is uncommon in cancer patients. Likewise, extramedullary plasmacytoma (EMP) relapse in scar tissue in the setting of multiple myeloma (MM) has been rarely reported. We report a series of 3 patients whose disease progressed as EMP at the site of a wound from previous invasive procedures. All 3 patients were treated for the relapsed disease with different treatment modalities, but failed to respond adequately and died several months after relapse. At original MM diagnosis, all had advanced-stage disease. They were treated with novel agents with or without autologous hematopoietic stem cell transplantation and achieved either a complete or very good partial response. We suggest that these treatments, which have become the standard of care in MM, may permit a predominance of myeloma subclones which are independent of the bone marrow microenvironment. These myeloma subclones then gain a survival advantage in the active scar-tissue niche, allowing for their uncontrolled proliferation. This case series might represent an underreported phenomenon and therefore may indicate an emerging and difficult-to-treat disease in the era of targeted therapies in MM. Physicians treating MM should be aware of this phenomenon, especially when referring their patients for invasive procedures.

Antibody-directed coupling of endoglin and MMP-14 is a key mechanism for endoglin shedding and deregulation of TGF-β signaling

Endoglin is a transforming growth factor β (TGF-β) coreceptor that serves as a prognostic, diagnostic and therapeutic vascular target in human cancer. A number of endoglin ectodomain-targeting antibodies (Abs) can effectively suppress both normal and tumor-associated angiogenesis, but their molecular actions remain poorly characterized. Here we define a key mechanism for TRACON105 (TRC105), a humanized monoclonal Ab in clinical trials for treatment of advanced or metastatic tumors. TRC105, along with several other endoglin Abs tested, enhance endoglin shedding through direct coupling of endoglin and the membrane-type 1 matrix metalloproteinase (MMP)-14 at the cell surface to release the antiangiogenic factor, soluble endoglin (sEng). In addition to this coupling process, endoglin shedding is further amplified by increased MMP-14 expression that requires TRC105 concentration-dependent c-Jun N-terminal kinase (JNK) activation. There were also notable counterbalancing effects on canonical Smad signaling in which TRC105 abrogated both the steady-state and TGF-β-induced Smad1/5/8 activation while augmenting Smad2/3 activation. Interestingly, TRC105-induced sEng and aberrant Smad signaling resulted in an excessive migratory response through enhanced stress fiber formation and disruption of endothelial cell–cell junctions. Collectively, our study defines endoglin shedding and deregulated TGF-β signaling during migration as major mechanisms by which TRC105 inhibits angiogenesis.

Potential therapeutic biomarkers in plasma cell myeloma: a flow cytometry study

OBJECTIVE

To investigate the expression profile of potential therapeutic biomarkers in plasma cell myeloma (PCM) by multicolor flow cytometry analysis.

METHODS

Bone marrow (BM) specimens were collected consecutively and analyzed using a routine PCM panel (CD38/CD138/CD45/CD19/CD20/CD28/CD56/CD117, cyto-kappa/lambda). The specimens were further assessed for CD30, CD44, CD49d, CD70, CD105, and CD184 expression in cases containing a substantial number of neoplastic plasma cells.

RESULTS

Totally, 101 patient BM samples were assessed, including 58 men and 43 women, with a median age of 64 years (34-89). Twenty-nine patients had newly diagnosed/untreated PCM, 40 had persistent/residual disease undergoing various therapies and 32 had relapsed disease. CD49d was expressed brightly and uniformly in all 45 patients tested. Expression of CD44 and CD184 was more variable with a median percentage of 77% (1-100) and 65% (5-100) respectively. Using an arbitrary 20% cutoff, CD44 was positive in 74 (73%) and CD184 in 92 (91%) cases with a mean fluorescence intensity ratio of 42.8 and 21.4. A higher CD44 expression was observed in patients with recurrent/persistent disease (P = 0.028). Additionally, both CD44 (P = 0.002) and CD184 (P = 0.026) showed higher expressions in CD117-positive cases, but there was no correlation with cytogenetic groups. The CD30, CD70, and CD105 were expressed very infrequently in PCM, with a median expression of 0.2%, 0.2%, and 0.4% respectively.

CONCLUSIONS

CD49d, CD44, and CD184, are highly expressed in PCM. CD49d expression is bright and uniform, whereas CD44 and CD184 are more heterogeneous. In contrast, surface CD30, CD70, and CD105 are infrequent. These data provide useful preclinical information for the design of potential novel targeted therapies in PCM patients.

Emerging roles of endoglin/CD105 and angiogenic cytokines for disease development and progression in multiple myeloma patients

Angiogenesis is an essential process for the expansion of multiple myeloma (MM), in which many angiogenic factors participate. Endoglin (CD105) is a transforming growth factor-β co-receptor, being mainly expressed in angiogenic endothelial cells and has been used as a marker of tumor angiogenesis, having prognostic potential. The aim of the study was to evaluate serum levels of soluble CD105 (sCD105) in MM patients, both during diagnosis and after effective conventional chemotherapy, in the plateau phase, and to correlate them with the clinical stage of the disease, as well as with the known angiogenic factors vascular endothelial growth factor, angiogenin and interleukin-18 (IL-18). Serum levels of the aforementioned factors were measured, by enzyme-linked immunosorbent assay, in 56 newly diagnosed MM patients, in 35 of them who entered plateau phase and in 24 healthy controls. Bone marrow aspirations were also performed in all patients to determine plasma cell infiltration. All measured cytokines were higher in MM patients compared with controls and with advancing disease stage (p < 0.001 for all cases). Furthermore, the values of all factors decreased significantly in the plateau phase (p < 0.001 for all cases). Serum levels of sCD105 correlated with the other angiogenic cytokines, whereas only serum levels of angiogenin had prognostic value for the survival. In conclusion, CD105 and the angiogenic cytokines vascular endothelial growth factor, angiogenin and IL-18, seem to have emerging roles both in angiogenesis and tumor growth in MM.

The relationship between soluble receptor of interleukin-6 with angiogenic cytokines and proliferation markers in multiple myeloma

Soluble interleukin-6 receptor (sIL-6R) is part of IL-6 receptor that may stimulate cells that do not express the whole molecule. It may enhance myeloma cell proliferation and furthermore angiogenesis. The aim of the study was to evaluate the clinical significance and the relationship between serum levels of sIL-6R, with various stimulators of angiogenesis, such as hepatocyte growth factor (HGF) and interleukin-18 (IL-18) and with markers of proliferation, such as beta-2 microglobulin (B2M) levels and plasma cell Ki-67 proliferation index in the bone marrow, in patients with multiple myeloma (MM). We studied 45 newly diagnosed MM patients. Serum levels of sIL-6R, HGF, IL-18, and B2M and Ki-67 proliferation index (Ki-67 PI) in bone marrow's plasma cells were determined. The mean concentrations of sIL-6R, HGF, IL-18, and B2M and the value of Ki-67 were significantly higher in the patients compared to controls and with increasing disease stage. sIL-6R was strongly positively correlated with HGF, IL-18, B2M, and Ki-67 PI. There is a positive correlation between plasma cell growth, as determined by Ki-67 PI, and different angiogenic cytokines, such as HGF and IL-18, with sIL-6R. This relationship suggests the significant role of these cytokines in the proliferation and disease activity in MM patients.