Vascular endothelial growth factor and its receptors in multiple myeloma

Inhibition of Ephrin B2 Reverse Signaling Abolishes Multiple Myeloma Pathogenesis

Bone marrow vascular endothelial cells (BM EC) regulate multiple myeloma pathogenesis. Identification of the mechanisms underlying this interaction could lead to the development of improved strategies for treating multiple myeloma. Here, we performed a transcriptomic analysis of human ECs with high capacity to promote multiple myeloma growth, revealing overexpression of the receptor tyrosine kinases, EPHB1 and EPHB4, in multiple myeloma-supportive ECs. Expression of ephrin B2 (EFNB2), the binding partner for EPHB1 and EPHB4, was significantly increased in multiple myeloma cells. Silencing EPHB1 or EPHB4 in ECs suppressed multiple myeloma growth in coculture. Similarly, loss of EFNB2 in multiple myeloma cells blocked multiple myeloma proliferation and survival in vitro, abrogated multiple myeloma engraftment in immune-deficient mice, and increased multiple myeloma sensitivity to chemotherapy. Administration of an EFNB2-targeted single-chain variable fragment also suppressed multiple myeloma growth in vivo. In contrast, overexpression of EFNB2 in multiple myeloma cells increased STAT5 activation, increased multiple myeloma cell survival and proliferation, and decreased multiple myeloma sensitivity to chemotherapy. Conversely, expression of mutant EFNB2 lacking reverse signaling capacity in multiple myeloma cells increased multiple myeloma cell death and sensitivity to chemotherapy and abolished multiple myeloma growth in vivo. Complementary analysis of multiple myeloma patient data revealed that increased EFNB2 expression is associated with adverse-risk disease and decreased survival. This study suggests that EFNB2 reverse signaling controls multiple myeloma pathogenesis and can be therapeutically targeted to improve multiple myeloma outcomes.

SIGNIFICANCE

Ephrin B2 reverse signaling mediated by endothelial cells directly regulates multiple myeloma progression and treatment resistance, which can be overcome through targeted inhibition of ephrin B2 to abolish myeloma.

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

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

Multiple myeloma and malignant lesions: a potential risk factor for local anesthetic systemic toxicity

BACKGROUND

Multiple myeloma is a cancer of plasma cells that often leads to complications including osteolytic bone lesions, nephropathy and neuropathy. Multiple myeloma is only one etiology of many cancer pain conditions that may necessitate interventional pain treatment when refractory to multimodal medications. Notably, local anesthetic systemic toxicity is a rare but life-threatening complication of local anesthetic administered for these interventions.

CASE PRESENTATION

A 50-60-year-old woman presented with multiple myeloma complicated by chronic bone pain and in an acute pain crisis. A fluoroscopic-guided L4-5 epidural catheter was placed with clinical doses of bupivacaine for comfort to undergo MRI of the spine. Soon after, she became tachycardic, tachypneic and hypoxic requiring non-invasive positive pressure airway support. As this respiratory distress was attributed to a large pleural effusion, a pigtail catheter was inserted in the intensive care unit with submaximally dosed lidocaine infiltration. She then developed a left bundle branch block followed by cardiovascular collapse minimally responsive to high-dose inotrope and vasopressor support. Lipid emulsion was started with dramatic therapeutic response and recovery to baseline. A CT of the thoracolumbar spine showed worsening extensive lytic lesions throughout all vertebral bodies and ribs from diffuse myeloma.

CONCLUSIONS

Patients with oncologic lesions focal to the thoracolumbar spine may be at higher risk for local anesthetic systemic toxicity from palliative epidurals due to increased cancer-related angiogenesis. Likewise, local anesthetic infiltration for procedures near any malignant sites could have a similar risk and may require lower initial fractionated dosages with increased vigilance.

The multifunctional role of Notch signaling in multiple myeloma

Multiple myeloma (MM) is a hematologic cancer characterized by uncontrolled growth of malignant plasma cells in the bone marrow and currently is incurable. The bone marrow microenvironment plays a critical role in MM. MM cells reside in specialized niches where they interact with multiple marrow cell types, transforming the bone/bone marrow compartment into an ideal microenvironment for the migration, proliferation, and survival of MM cells. In addition, MM cells interact with bone cells to stimulate bone destruction and promote the development of bone lesions that rarely heal. In this review, we discuss how Notch signals facilitate the communication between adjacent MM cells and between MM cells and bone/bone marrow cells and shape the microenvironment to favor MM progression and bone disease. We also address the potential and therapeutic approaches used to target Notch signaling in MM.

Anti-VEGF Drugs in the Treatment of Multiple Myeloma Patients

The interaction between the bone marrow microenvironment and plasma cells plays an essential role in multiple myeloma progression and drug resistance. The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway in vascular endothelial cells activates and promotes angiogenesis. Moreover, VEGF activates and promotes vasculogenesis and vasculogenic mimicry when it interacts with VEGF receptors expressed in precursor cells and inflammatory cells, respectively. In myeloma bone marrow, VEGF and VEGF receptor expression are upregulated and hyperactive in the stromal and tumor cells. It has been demonstrated that several antiangiogenic agents can effectively target VEGF-related pathways in the preclinical phase. However, they are not successful in treating multiple myeloma, probably due to the vicarious action of other cytokines and signaling pathways. Thus, the simultaneous blocking of multiple cytokine pathways, including the VEGF/VEGFR pathway, may represent a valid strategy to treat multiple myeloma. This review aims to summarize recent advances in understanding the role of the VEGF/VEGFR pathway in multiple myeloma, and mainly focuses on the transcription pathway and on strategies that target this pathway.

Maintaining therapeutic progress in multiple myeloma by integrating genetic and biological advances into the clinic

INTRODUCTION

Utilizing advances in genetic and immunologic analysis to segment and direct treatment is potentially a way of maintaining therapeutic progress toward cure in multiple myeloma (MM). This approach works well using clinical segments but can be optimized using recent genetic and immunologic technologies, which have opened the possibility of enhancing risk stratification and disease subclassification. Areas covered: This position paper discusses strategies to segment myeloma into subgroups with distinct risk profiles and distinct targetable lesions are presented. Expert commentary: Risk stratified treatment of MM is already a clinical reality that can be enhanced by the developmental of unified segmentation and testing approaches. Mutation-targeted treatment has proven to be effective against the RAS pathway, but is compromised by intra-clonal and spatiotemporal heterogeneity. Identifying new disease segments based on tumor biology or immunological content of the microenvironment offers an exciting new way to control and even eradicate myeloma clones. Going forward, risk and biologically stratified therapy for myeloma is a promising way of maintaining therapeutic progress, as is precision immunotherapy directed by the cellular context of the bone marrow.

Nonmyelomatous Ascites Resulting from the Increased Secretion of Vascular Endothelial Growth Factor in Multiple Myeloma

Ascites is a rare complication of multiple myeloma (MM); in most cases, the direct invasion of myeloma cells to the peritoneal cavity has been assumed to be the etiology because the effusion is usually exudative and contains a high proportion of myeloma cells. We herein report a case of MM with massive ascites containing only a small amount of myeloma cells. Instead, high levels of serum and ascitic vascular endothelial growth factor were detected. This was suggested to be a potential mechanism underlying the development of ascites.

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.

Role of Galectins in Multiple Myeloma

Galectins are a family of lectins that bind β-galactose-containing glycoconjugates and are characterized by carbohydrate-recognition domains (CRDs). Galectins exploit several biological functions, including angiogenesis, regulation of immune cell activities and cell adhesion, in both physiological and pathological processes, as tumor progression. Multiple myeloma (MM) is a plasma cell (PC) malignancy characterized by the tight adhesion between tumoral PCs and bone marrow (BM) microenvironment, leading to the increase of PC survival and drug resistance, MM-induced neo-angiogenesis, immunosuppression and osteolytic bone lesions. In this review, we explore the expression profiles and the roles of galectin-1, galectin-3, galectin-8 and galectin-9 in the pathophysiology of MM. We focus on the role of these lectins in the interplay between MM and BM microenvironment cells showing their involvement in MM progression mainly through the regulation of PC survival and MM-induced angiogenesis and osteoclastogenesis. The translational impact of these pre-clinical pieces of evidence is supported by recent data that indicate galectins could be new attractive targets to block MM cell growth in vivo and by the evidence that the expression levels of LGALS1 and LGALS8, genes encoding for galectin-1 and galectin-8 respectively, correlate to MM patients’ survival.

Integration of Genomics Into Treatment: Are We There Yet?

Using advances in genetic analysis to segment and direct treatment of multiple myeloma (MM) represents a way of maintaining therapeutic progress. Recent genetic analyses have opened the possibility of enhancing risk stratification approaches and of using different risk and biologic strata as part of clinical trials. The Myeloma Genome Project is a collaborative project that has compiled the largest set of cases with sequencing and have outcome data that are available for stratification purposes. Mutation-targeted treatment of the Ras pathway has been shown to be active in MM, but is compromised by the presence of the subclonal genetic variation typical of myeloma. Going forward, risk and biologically stratified therapy for MM looks to be a promising way of maintaining therapeutic progress, as does precision immunotherapy directed by the cellular context of the bone marrow.

Heparanase-induced shedding of syndecan-1/CD138 in myeloma and endothelial cells activates VEGFR2 and an invasive phenotype: prevention by novel synstatins

Multiple myeloma arises when malignant plasma cells invade and form multiple tumors in the bone marrow. High levels of heparanase (HPSE) correlate with poor prognosis in myeloma patients. A likely target of the enzyme is the heparan sulfate (HS) proteoglycan syndecan-1 (Sdc1, CD138), which is highly expressed on myeloma cells and contributes to poor prognosis in this disease. We find that HPSE promotes an invasive phenotype mediated by the very late antigen-4 (VLA-4, or α4β1 integrin) in myeloma cells plated on either fibronectin (FN) or vascular endothelial cell adhesion molecule-1 (VCAM-1), ligands that are prevalent in the bone marrow. The phenotype depends on vascular endothelial cell growth factor receptor-2 (VEGFR2), which is aberrantly expressed in myeloma, and is characterized by a highly protrusive lamellipodium and cell invasion. HPSE-mediated trimming of the HS on Sdc1 and subsequent matrix metalloproteinase-9-mediated shedding of the syndecan exposes a juxtamembrane site in Sdc1 that binds VEGFR2 and VLA-4, thereby coupling VEGFR2 to the integrin. Shed Sdc1 can be mimicked by recombinant Sdc1 ectodomain or by a peptide based on its binding motif, which causes VLA-4 to re-orient from the lagging edge (uropod) to the leading edge of migrating cells, couple with and activate VEGFR2. Peptides (called 'synstatins') containing only the VLA-4 or VEGFR2 binding sites competitively inhibit invasion, as they block coupling of the receptors. This mechanism is also utilized by vascular endothelial cells, in which it is also activated by HPSE, during endothelial cell tube formation. Collectively, our findings reveal for the first time the mechanism through which HPSE modulates Sdc1 function to promote both tumor cell invasion and angiogenesis, thereby driving multiple myeloma progression. The inhibitory synstatins, or inhibitors of HPSE enzyme activity, are likely to show promise as therapeutics against myeloma extravasation and spread.

The Emerging Regulation of VEGFR-2 in Triple-Negative Breast Cancer

Vascular endothelial growth factor-A (VEGF) signals vascular development and angiogenesis mainly by binding to VEGF receptor family member 2 (VEGFR-2). Adaptor proteins mediate many VEGFR-2's functions in the development of blood vessels. Cancer cells secrete VEGF to activate VEGFR-2 pathway in their neighboring endothelial cells in the process of cancer-related angiogenesis. Interestingly, activation of VEGFR-2 signaling is found in breast cancer cells, but its role and regulation are not clear. We highlighted research advances of VEGFR-2, with a focus on VEGFR-2's regulation by mutant p53 in breast cancer. In addition, we reviewed recent Food and Drug Administration-approved tyrosine kinase inhibitor drugs that can inhibit the function of VEGFR-2. Ongoing preclinical and clinical studies might prove that pharmaceutically targeting VEGFR-2 could be an effective therapeutic strategy in treating triple-negative breast cancer.

Associations of VEGF and VEGFR2 polymorphisms with increased risk and aggressiveness of multiple myeloma

Angiogenesis has been highlighted as a critical component in the progression of multiple myeloma (MM), and vascular endothelial growth factor (VEGF) as well as its type 2 receptor (VEGFR2) are thought to play a major role in the process. Single nucleotide polymorphisms (SNPs) have been described in VEGF and VEGFR2 genes, with quantitative or qualitative changes in encoded VEGF and VEGFR2. The roles of VEGF -2578C/A, -1154G/A, and -634G/C as well as VEGFR2 -604T/C and +1192G/A SNPs in the risk and manifestations of MM are still unknown; therefore, this study aimed to clarify this issue. DNA from 192 patients and 209 controls were analyzed by real-time polymerase chain reaction for identification of genotypes. The frequencies of VEGF -2578CC, VEGF -2578CC plus VEGF -634GG, and VEGF -2578CC plus VEGF -1154GG plus VEGF -634GG genotypes were higher in patients than in controls. Carriers of the respective genotypes had a 1.89-, a 5.52-, and a 4.91-fold increased risk for MM than others. VEGF -2578CC plus VEGFR2 +1192GG, VEGF -2578CC plus VEGF -634GG plus VEGFR2 +1192GG, and VEGF -1154GG plus VEGF -634GG plus VEGFR2 -604TT combined genotypes were more common in patients than in controls. Carriers of the respective genotypes had a 2.56-, a 10.97-, and a 14.10-fold increased risk for MM than others. An excess of VEGFR2 -604TT genotype was also seen in patients with stage II or III tumors when compared with those with stage I tumors. Our data suggest, for the first time, that inherited abnormalities in VEGF and VEGFR2 pathways influence the risk and aggressiveness of MM.

The evaluation of angiogenesis and matrix metalloproteinase-2 secretion in bone marrow of multiple myeloma patients before and after the treatment

PURPOSE

Angiogenesis appears to be a prominent feature of many hematological disorders, particularly in multiple myeloma (MM). Progression in MM also involves secretion of the metaloproteinases (MMPs). In this study, the expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and its receptor, in bone marrow trephine biopsy (TB) of thirty six MM patients before and after the treatment or during progression was examined. The MMP-2 secretion was assessed from the same patients.

MATERIAL/METHODS

Immunohistochemical staining of bone marrow specimens for angiogenic factors and microvessel density (MVD) and bone marrow aspirates for Western blot analysis of MMP-2 expression was performed.

RESULTS

In active, untreated MM patients, we found statistically significant differences in the expression of angiogenic factors according to the patients after the anti-angiogenic treatment. We found statistical differences of the expression of angiogenic factors between the group of patients with a response after the treatment and the patients who had progression during the treatment. The data showed statistically significant decreased MVD after the treatment. The results showed statistically significant differences between initial secretion of MMP-2 in active, untreated MM patients and patients with a response after the treatment and patients with progression during the treatment.

CONCLUSIONS

We showed that not only decreased expression of angiogenic cytokines is present after the anti-angiogenic treatment but also activity of MMP-2 in MM patients who responded to the treatment. Combination therapy with the inhibition of the activity of MMPs could represent an interesting therapeutical approach in MM.

Angiogenic cytokines profile in smoldering multiple myeloma: no difference compared to MGUS but altered compared to symptomatic myeloma

Background

Symptomatic multiple myeloma (MM) evolves from an asymptomatic precursor state termed monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM). Angiogenesis plays a key role in the pathogenesis of MM but there are very limited data for angiogenesis in SMM.

Material/Methods

We measured the circulating levels of angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), vascular endothelial growth factor (VEGF), and angiogenin in 54 patients with SMM. The results were compared with those of 27 MGUS patients, 55 MM patients, and 22 healthy controls. The expression of VEGF-A gene was also evaluated in 10 patients with SMM, 10 with symptomatic MM, and 10 with MGUS.

Results

The ratio of circulating Ang-1/Ang-2 was reduced in MM patients with symptomatic disease due to a dramatic increase of Ang-2 (p<0.001), but not in patients with SMM or MGUS, in whom it did not differ compared to controls. VEGF and angiogenin were increased in all patients compared to controls. However, circulating VEGF was higher in symptomatic MM compared to SMM and MGUS, while angiogenin was reduced. There were no differences in the expression of VEGF-A among the 3 patients categories.

Conclusions

SMM has a circulating angiogenic cytokine profile similar to that of MGUS, but has altered profile compared to symptomatic MM. Thus, in the progression of MGUS to SMM, circulating angiogenic cytokines seem to be the same. On the contrary, in symptomatic myeloma, the alterations of angiopoietins along with VEGF contribute to myeloma cell growth, supporting the target of these molecules for the development of novel anti-myeloma agents.

miR-15a and miR-16 affect the angiogenesis of multiple myeloma by targeting VEGF

Deregulated microRNAs (miRNAs) and their roles in cancer development have attracted much attention. Two miRNAs, miR-15a and miR-16, which act as putative tumor suppressor by targeting the oncogene BCL2, have been implicated in cell cycle, apoptosis and proliferation. In this study, we investigated the possible role of miR-15a/16 in the angiogenesis of multiple myeloma (MM). Using a stem-loop quantitative reverse transcription-PCR, we analyzed miR-15a/16 expressions in bone marrow samples from newly diagnosed MM patients and a panel of MM cell lines. miRNA transfection, western blotting analysis and assay of luciferase activity were used to examine whether vascular endothelial growth factor (VEGF) is the target of miR-15a/16. The functional roles of miR-15a/16 on tumorigenesis and angiogenesis were examined by in vitro angiogenesis models and in vivo tumor xenograft model. We showed that miR-15a and miR-16 were significantly underexpressed in primary MM cells as well as in MM cell lines. The aberrant expression of miR-15a/16 was detected especially in advanced stage MM. In human MM cell lines and normal plasma cells, expression of miR-15a/16 inversely correlated with the expression of VEGF-A. Western blotting combined with the luciferase reporter assay demonstrated that VEGF-A was a direct target of miR-15a/16. Ectopic overexpression of miR-15a/16 led to decreased pro-angiogenic activity of MM cells. Finally, infection of lentivirus-miR-15a or lentivirus-miR-16 resulted in significant inhibition of tumor growth and angiogenesis in nude mice. This study suggest that miR-15a/16 could play a role in the tumorigenesis of MM at least in part by modulation of angiogenesis through targeting VEGF-A.

Curative one-shot systemic virotherapy in murine myeloma

Current therapy for multiple myeloma is complex and prolonged. Antimyeloma drugs are combined in induction, consolidation and/or maintenance protocols to destroy bulky disease, then suppress or eradicate residual disease. Oncolytic viruses have the potential to mediate both tumor debulking and residual disease elimination, but this curative paradigm remains unproven. Here we engineered an oncolytic vesicular stomatitis virus to minimize its neurotoxicity, enhance induction of antimyeloma immunity, and facilitate noninvasive monitoring of its intratumoral spread. Using high resolution imaging, autoradiography and immunohistochemistry, we demonstrate that the intravenously administered virus extravasates from tumor blood vessels in immunocompetent myeloma-bearing mice, nucleating multiple intratumoral infectious centers which expand rapidly and necrose at their centers, ultimately coalescing to cause extensive tumor destruction. This oncolytic tumor debulking phase lasts only for 72 hours after virus administration, and is completed before antiviral antibodies become detectable in the bloodstream. Anti-myeloma T cells, cross-primed as the virus-infected cells provoke an antiviral immune response, then eliminate residual uninfected myeloma cells. The study establishes a curative oncolytic paradigm for multiple myeloma where direct tumor debulking and immune eradication of minimal disease are mediated by a single intravenous dose of a single therapeutic agent. Clinical translation is underway.

Angiogenesis and multiple myeloma

The bone marrow microenvironment in multiple myeloma is characterized by an increased microvessel density. The production of pro-angiogenic molecules is increased and the production of angiogenic inhibitors is suppressed, leading to an "angiogenic switch". Here we present an overview of the role of angiogenesis in multiple myeloma, the pro-angiogenic factors produced by myeloma cells and the microenvironment, and the mechanisms involved in the myeloma-induced angiogenic switch. Current data suggest that the increased bone marrow angiogenesis in multiple myeloma is due to the aberrant expression of angiogenic factors by myeloma cells, the subsequent increase in pro-angiogenic activity of normal plasma cells as a result of myeloma cell angiogenic activity, and the increased number of plasma cells overall. Hypoxia also contributes to the angiogenic properties of the myeloma marrow microenvironment. The transcription factor hypoxia-inducible factor-1α is overexpressed by myeloma cells and affects their transcriptional and angiogenic profiles. In addition, potential roles of the tumor suppressor gene inhibitor of growth family member 4 and homeobox B7 have also been recently highlighted as repressors of angiogenesis and pro-angiogenic related genes, respectively. This complex pathogenetic model of myeloma-induced angiogenesis suggests that several pro-angiogenic molecules and related genes in myeloma cells and the microenvironment are potential therapeutic targets.

Association of clinicopathologic parameters with the expression of inducible nitric oxide synthase and vascular endothelial growth factor in mucoepidermoid carcinoma

BACKGROUND

The roles that inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF) play in tumorigenesis have been given special attention. In many tumors, their expression is upregulated. In addition, iNOS can stimulate the expression of VEGF. This study was carried out to investigate the expression of iNOS and VEGF as well as their relationship with angiogenesis and the clinicopathological characteristics of mucoepidermoid carcinoma (MEC).

METHOD

The expression of iNOS and VEGF was detected by Streptavidin-peroxidase immunohistochemistry, and microvessel density (MVD) was determined by anti-CD34 antibody staining in 70 MEC cases and 40 normal salivary gland tissues (NSG). Follow-up was performed on the 70 patients with MEC. Non-parametric tests were performed for the comparison of iNOS and VEGF expression.

RESULTS

The positive expression rates of iNOS and VEGF were successively enhanced in NSG, well-differentiated and poorly differentiated MEC (P < 0.05). MVD counts were positively correlated with the expression levels of iNOS and VEGF in MEC (P < 0.05). The expression of iNOS was positively correlated with the expression of VEGF (P < 0.05). iNOS and VEGF expression were significantly associated with tumor differentiation, size metastasis, and relapse (P < 0.05) but were not correlated lymph node metastasis and metastasis.

CONCLUSION

Inducible nitric oxide synthase can stimulate the expression of VEGF, and their expression status may help assess tumor malignancy and patient prognosis.

Targeting the microenvironment

The microenvironment in which cancer arises plays a critical role in tumorigenesis. Although previously regarded as an innocent bystander, evidence has accumulated over the past 10 years that the microenvironment contributes to tumor growth and progression by providing nutrients and survival signals, and protecting the tumor from normal immune responses and anticancer drugs. Exactly how normal stromal cells, whose function should be to suppress malignant growth, become co-opted into facilitating tumor development is only just beginning to be understood, but a complex story is emerging wherein tumor and stromal cells appear to co-evolve. A better understanding of tumor-stromal interactions and the molecular alterations that result in stromal dysfunction may help to identify patients who will benefit from either more aggressive or risk-adapted therapy regimens, and/or novel compounds that disrupt the tumor microenvironment and re-establishing normal control mechanisms.

Biological impact of vascular endothelial growth factor on vessel density and survival in multiple myeloma and plasmacytoma

We compared the differences in a number of angiogenesis-related immunohistochemical parameters, including microvascular density (MVD) and tumor cell activity, between multiple myeloma (MM) and solitary plasmacytoma (SP). Tissue sections from tumors of MM and SP were immunohistochemically stained and analyzed using ImageJ image analysis software for the expression of vascular endothelial growth factor (VEGF), VEGF receptors (Flt-1 and Flk-1), inducible nitric oxide (iNOS), and anti-apoptotic (Bcl-2) protein. Tumor tissues were cytologically graded as high-, intermediate-, or low-grade. Two pathologists determined the MVD of each section independently by recording the average number of CD34+ blood vessels in 500 unit fields. The arithmetic means for MVD were statistically analyzed using the Student's t-test and the significance level was calculated at P-value <0.001. The results indicate a direct correlation between upregulation of iNOS/VEGF in high-grade tumors. For MM, an increase in MVD is also correlated with a high-grade. Tumor survival signaling by Bcl-2 in both SP and MM emphasizes the fact that VEGF has a bimodal role that is mainly angiogenic in MM and tumorigenic, promoting tumor cell survival in SP.

Vascular endothelial growth factor (VEGF)-A: role on cardiac angiogenesis following myocardial infarction

The current study is to determine the regulatory role of VEGF-A in cardiac angiogenesis following myocardial infarction (MI). Cardiac angiogenic response and temporal/spatial expression of VEGF-A/VEGF receptors (VEGFR) were examined at 1, 2, 6, 12 h and 1, 2, 3, 4, 7, 14, and 28 days postMI. We found that following MI, newly formed vessels first appeared at the border zone between noninfarcted and infarcted myocardium as early as day 3 and subsequently in the infarcted myocardium. Vascular density in the infarcted myocardium peaked at day 7 and then gradually declined. VEGF-A mRNA started to increase at the border zone at 2 h postMI, reached peak at 12 h, declined at day 1, and returned to normal levels at day 2 and thereafter. VEGF-A protein levels at the border zone were only increased during day 1 postMI. VEGF-A within the infarcted myocardium levels, however, was persistently suppressed postMI. VEGFR expression was significantly increased only at the border zone at day 1, but not in the later stages. The expression of VEGF-A/VEGFR remained unchanged in the noninfarcted myocardium. Thus, the early rise of VEGF-A/VEGFR at the border zone suggests that VEGF-A initiates the cardiac angiogenic response postMI, but short-lived VEGF-A/VEGFR activation at the border zone and consistently suppressed VEGF-A within the infarcted myocardium suggests that VEGF-A may not be crucial to the later stages of angiogenesis.

Lysophosphatidic acid receptor expression in chronic lymphocytic leukemia leads to cell survival mediated though vascular endothelial growth factor expression

Lysophosphatidic acid (LPA) protects chronic lymphocytic leukemia (CLL) cells from apoptosis. Vascular endothelial growth factor (VEGF) also protects CLL cells against apoptosis. The mechanism for LPA protection against apoptosis in CLL cells is unknown. Herein, we show CLL cells express LPA receptors LPA(1-5) but in normal B cells, LPA(1) was rarely expressed and LPA(3,) LPA(4,) and LPA(6) were undetectable whereas the other LPA receptors were expressed. LPA plasma levels are similar in patients with CLL compared to healthy controls. In contrast, plasma levels of VEGF are elevated in patients with CLL compared to healthy controls and LPA treatment induced VEGF secretion in CLL cells. CLL cells also express VEGF receptors and LPA protection against Flu induced apoptosis is blocked by inhibition of VEGF receptor activation. These results indicate that LPA protects CLL cells from apoptosis through higher expression of LPA receptors and autocrine production of VEGF.

Reduction of serum IGF-I levels in patients affected with Monoclonal Gammopathies of undetermined significance or Multiple Myeloma. Comparison with bFGF, VEGF and K-ras gene mutation

Background

Serum levels of IGF-I in patients affected with multiple myeloma (MM) have been scarcely studied. The present study is aimed to explore this point comparing 55 healthy subjects, 71 monoclonal gammopaties of uncertain significance (MGUS) and 77 overt MM patients. In the same subjects, basic FGF and VEGF, have been detected. All three mediators were analyzed in function of K-ras mutation and melphalan response. Concerning IGF-I, two representative monitoring examples have also been added.

Methods

Cytokine determinations were performed by commercially available ELISA kits, while K12-ras mutation was investigated on genomic DNA isolated from bone marrow cell specimens by RFLP-PCR assay.

Results

Significant reductions of IGF-I levels were observed in MGUS and MM as compared with healthy controls. In addition, MM subjects showed significantly decreased serum IGF-I levels than MGUS. Conversely, increasing levels were observed for bFGF and VEGF, molecules significantly correlated. A multivariate analysis corrected for age and gender confirmed the significant difference only for IGF-I values (P = 0.01). K12-ras mutation was significantly associated with malignancy, response to therapy and with significantly increased serum bFGF levels.

Conclusion

IGF-I reduction in the transition: Controls→MGUS→MM and changes observed over time suggest that IGF-I should be furtherly studied in future clinical trials as a possible monitoring marker for MM.

Validation of PDGFRbeta and c-Src tyrosine kinases as tumor/vessel targets in patients with multiple myeloma: preclinical efficacy of the novel, orally available inhibitor dasatinib

Inhibition of multiple myeloma (MM) plasma cells in their permissive bone marrow microenvironment represents an attractive strategy for blocking the tumor/vessel growth associated with the disease progression. However, target specificity is an essential aim of this approach. Here, we identified platelet-derived growth factor (PDGF)-receptor beta (PDGFRbeta) and pp60c-Src as shared constitutively activated tyrosine-kinases (TKs) in plasma cells and endothelial cells (ECs) isolated from MM patients (MMECs). Our cellular and molecular dissection showed that the PDGF-BB/PDGFRbeta kinase axis promoted MM tumor growth and vessel sprouting by activating ERK1/2, AKT, and the transcription of MMEC-released proangiogenic factors, such as vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8). Interestingly, pp60c-Src TK-activity was selectively induced by VEGF in MM tumor and ECs, and the use of small-interfering (si)RNAs validated pp60c-Src as a key signaling effector of VEGF loop required for MMEC survival, migration, and angiogenesis. We also assessed the antitumor/vessel activity of dasatinib, a novel orally bioactive PDGFRbeta/Src TK-inhibitor that significantly delayed MM tumor growth and angiogenesis in vivo, showing a synergistic cytotoxicity with conventional and novel antimyeloma drugs (ie, melphalan, prednisone, bor-tezomib, and thalidomide). Overall data highlight the biologic and therapeutic relevance of the combined targeting of PDGFRbeta/c-Src TKs in MM, providing a framework for future clinical trials.

Constitutive expression of IL-12R beta 2 on human multiple myeloma cells delineates a novel therapeutic target

The interleukin-12 (IL-12) receptor (R) B2 gene acts as tumor suppressor in human acute and chronic B-cell leukemias/lymphomas and IL-12rb2-deficient mice develop spontaneously localized plasmacytomas. With this background, we investigated the role of IL-12R beta 2 in multiple myeloma (MM) pathogenesis. Here we show the following: (1) IL-12R beta 2 was expressed in primary MM cells but down-regulated compared with normal polyclonal plasmablastic cells and plasma cells (PCs). IL-6 dampened IL-12R beta 2 expression on polyclonal plasmablastic cells and MM cells. (2) IL-12 reduced the proangiogenic activity of primary MM cells in vitro and decreased significantly (P = .001) the tumorigenicity of the NCI-H929 cell line in SCID/NOD mice by inhibiting cell proliferation and angiogenesis. The latter phenomenon was found to depend on abolished expression of a wide panel of proangiogenic genes and up-regulated expression of the antiangiogenic genes IFN-gamma, IFN-alpha, platelet factor-4, and TIMP-2. Inhibition of the angiogenic potential of primary MM cells was related to down-regulated expression of the proangiogenic genes CCL11, vascular endothelial-cadherin, CD13, and AKT and to up-regulation of an IFN-gamma-related antiangiogenic pathway. Thus, IL-12R beta 2 directly restrains MM cell growth, and targeting of IL-12 to tumor cells holds promise as new therapeutic strategy.

Lysophosphatidic acid (LPA) induces the expression of VEGF leading to protection against apoptosis in B-cell derived malignancies

Vascular endothelial growth factor (VEGF) is a survival and angiogenesis factor that is a target for therapy in a variety of cancers. In many hematological malignancies, VEGF production is increased leading to cell survival responses. Herein, we demonstrate that lysophosphatidic acid (LPA) induces mRNA expression of VEGF in the multiple myeloma cell line, U266, the Burkitt's lymphoma cell line, BJAB, and the chronic lymphocytic leukemia (CLL)-like cell line, I-83. This increase in mRNA levels of VEGF corresponded with increased luciferase activity of the VEGF promoter in BJAB and I-83 cells and increased protein levels in I-83 cells. Secretion of VEGF was also increased in these cells following LPA treatment. LPA treatment also caused the activation of both VEGFR1 and VEGFR2. The increase in VEGF expression by LPA is mediated by the activation of c-Jun N-terminal Kinase (JNK) and transcription factor NFkappaB since blocking JNK or NFkappaB activation inhibited LPA induced VEGF expression. Furthermore, we have demonstrated that LPA protects cells from apoptosis and blocking activation of both VEGFR1 and VEGFR2 using a VEGF receptor kinase inhibitor prevented LPA survival responses. Knocking down expression of VEGFR1 and inhibiting activation of NFkappaB and JNK also blocked LPA induced protection against apoptosis. Taken together, this indicates that LPA contributes to VEGF production in B cell malignancies leading to cell survival.

Bone marrow angiogenesis and angiogenic factors in multiple myeloma treated with novel agents

INTRODUCTION

An increased bone marrow (BM) angiogenesis is associated with poor outcome in multiple myeloma (MM).

OBJECTIVE

Angiogenesis study in MM treated with novel antimyeloma agents: thalidomide, lenalidomide, bortezomib, and with dexamethasone.

PATIENTS AND METHODS

Forty-four patients with MM (14 newly diagnosed, 30 refractory/relapsed) were treated with novel agents at our institution. A BM biopsy was obtained before the initiation of therapy in 19. Angiogenesis was assessed by microvessel density (MVD) estimation in BM biopsies stained with the monoclonal anti-CD34 antibody, and by serum levels of angiogenic factors (VEGF, bFGF, and HGF) and cytokines (IL-6 and TNF-alpha).

RESULTS

A positive correlation was found between BM plasma cell involvement and MVD estimation (p=0.01). However, MVD was not significantly correlated with either disease phase (p=0.065) or response to therapy (p=0.79). Neither baseline serum levels of angiogenic cytokines correlated to response to treatment. No significant correlation was found between BM MVD and serum levels of angiogenic cytokines. Serum levels of angiogenic cytokines before and after therapy showed a significant increase of bFGF (p=0.008).

CONCLUSION

There is no relationship between MVD estimation and baseline serum levels of angiogenic cytokines, neither between each of them and response to therapy.

Targeting the vascular endothelial growth factor pathway in the treatment of multiple myeloma

Multiple myeloma is a clonal plasma cell malignancy within the bone marrow associated with bone loss, renal disease and immunodeficiency. Despite new insights into the pathogenesis of multiple myeloma and novel targeted therapies, the median survival remains 3-5 years. It is now well established that the intimate relation between the tumor cells and components of the microenvironment plays a key role in multiple myeloma pathogenesis. Specifically, tumor cells impact the bone marrow and thereby cause immune suppression and lytic bone lesions; conversely, components of the bone marrow provide signals that influence the behavior of multiple myeloma cells, including tumor cell growth, survival, migration and drug resistance. Important contributing effectors are tumor cell-stroma cell and cell-extracellular matrix contacts, the bone marrow vasculature, and a variety of cytokines and growth factors in the bone marrow milieu.

Reduction of intracellular pH inhibits the expression of VEGF in K562 cells after targeted inhibition of the Na+/H+ exchanger

To explore the effect of inhibition of Na(+)/H(+) exchanger isoform 1 (NHE1) on the expression of vascular endothelial growth factor (VEGF) mRNA and protein in human myeloid K562 cells. The expression of VEGFmRNA was detected by RT-PCR technique. The levels of VEGF protein were measured by Western blotting and immunocytochemistry assay. pHi values were measured with fluorescence spectrophotometer. The three RT-PCR products detected were VEGF121, VEGF165, and VEGF189, respectively. Treatment of K562 cells either with amiloride (an inhibitor of NHE1) or with 5-(N-ethyl-N-isopropyl)-amiloride (EIPA, a selective inhibitor of NHE1) resulted in significant decrease of VEGF mRNA and VEGF protein levels. Either amiloride or EIPA decreased intracellular pH (pHi) values in K562 cells. These data strongly suggested that the expression of VEGF mRNA and protein in K562 cells was inhibited accompanying its reduction in pHi value after targeted inhibition of NHE1.

Antibody targeting of the insulin-like growth factor I receptor enhances the anti-tumor response of multiple myeloma to chemotherapy through inhibition of tumor proliferation and angiogenesis

Although many multiple myeloma (MM) patients initially respond to cytotoxic therapy, most eventually relapse. Novel therapeutic strategies employing a combination of chemotherapy with targeted biologics may significantly enhance the response of tumor cells to treatment. We tested a fully human anti-IGF-IR antibody (A12) against MM, and showed specific inhibition of IGF-I or serum-induced IGF-IR signaling in MM cells in vitro. The A12 as a single agent was demonstrated to exert modest to significant inhibition of tumor growth in vivo in various subcutaneous xenograft MM models. The A12 was also evaluated in a disseminated xenograft MM.1S NOD/SCID model as monotherapy or in combination with other drugs (bortezomib, melphalan) currently in clinical use. The tumor burden, as determined by luciferase bioimaging, was sharply decreased, and overall survival significantly prolonged when the therapies were combined. Immunohistochemical analysis demonstrated that the A12 treated tumors had significantly decreased vascularization compared to control tumors. Furthermore, most MM lines constitutively secreted significant quantities of VEGF, and this was enhanced following IGF-I treatment. Inhibition of IGF-IR by the A12 in vitro suppressed both constitutive and IGF-I-induced secretion of VEGF, indicating that a putative anti-angiogenic mechanism associated with the A12 treatment may contribute to its anti-tumor effect.

Dihydroartemisinin inhibits angiogenesis induced by multiple myeloma RPMI8226 cells under hypoxic conditions via downregulation of vascular endothelial growth factor expression and suppression of vascular endothelial growth factor secretion

Multiple myeloma remains incurable to date; therefore, new biologically target-based therapies are urgently needed. Our previous studies have showed that the antimalarial dihydroartemisinin possessed antiangiogenic activity in solid tumors. The present study evaluated the effect of dihydroartemisinin on human multiple myeloma-induced angiogenesis under hypoxia and elucidated its mechanism of action. An in-vivo chicken chorioallantoic membrane model was used to examine the effect of dihydroartemisinin on multiple myeloma-induced angiogenesis. Compared with conditioned medium of control, conditioned medium from human multiple myeloma RPMI8226 cells pretreated with 3 micromol/l dihydroartemisinin in hypoxia was observed to reduce microvessel growth on chicken chorioallantoic membranes by approximately 28.6% (P<0.05). The level of vascular endothelial growth factor in conditioned medium was determined by enzyme-linked immunosorbent assay. The results confirmed that 3 micromol/l dihydroartemisinin could significantly decrease vascular endothelial growth factor secretion by RPMI8226 cells (P<0.05), which correlated well with the reduction of multiple myeloma-induced angiogenesis on chicken chorioallantoic membranes. Western blot and reverse transcription-polymerase chain reaction results revealed that dihydroartemisinin downregulated the expression of vascular endothelial growth factor in RPMI8226 cells in hypoxia. In addition, we demonstrated that dihydroartemisinin reduced extracellular signal-regulated kinase 1/2 activation and inhibited growth of RPMI8226 cells under hypoxic conditions. Therefore, we concluded that dihydroartemisinin, which is already used to treat malaria and is well tolerated, possesses potential as an antiangiogenic drug in multiple myeloma therapy and thereby may improve patient outcome.

Angiogenesis in multiple myeloma

Multiple myeloma (MM) was the first haematological malignancy in which a prognostic relevance of bone marrow microvessel density (MVD) was shown. Myeloma-induced angiogenesis involves either the direct production of angiogenic molecules by myeloma cells or their induction in bone marrow stromal cells or endothelial cells (EC). Recent data demonstrate an increased angiogenic potential and a paracrine stimulatory effect of bone marrow EC on plasma cells (PC) in MM. Soluble angiogenic factors are elevated in bone marrow (BM) and in peripheral blood samples from myeloma patients. Furthermore, correlation with disease stage and prognosis was shown for serum levels of the angiogenic factors basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF). In this review we summarize recent data which give strong evidence for an increased angiogenic activity in bone marrow microenvironment and support the hypothesis that angiogenesis is not only an epiphenomenon of tumour growth but may also promote PC growth in MM.

Tissue factor as an effector of angiogenesis and tumor progression in hematological malignancies

In the last few years, it has become clear that the processes of tumor angiogenesis, metastasis and invasiveness are highly dependent on components of the blood coagulation cascade. One of the key proteins in coagulation is tissue factor (TF). In addition, TF is also known as a mediator of intracellular signaling events that can alter gene expression patterns and cell behavior. TF significantly participates in tumor-associated angiogenesis and its expression levels have been correlated with the metastatic potential of many types of hematological malignancies. Signaling pathways initiated by both, tissue factor-activated factor VII (TF-FVIIa) protease activation of protein-activated receptors (PARs), and phosphorylation of the TF-cytoplasmic domain, appear to regulate these tumoral functions. Advances in antiangiogenic therapies and preclinical studies with TF-targeted therapeutics are hopeful in the control of tumor growth and metastasis, but continued studies on the regulation of TF are still needed. In the last few years, the use of approaches of functional genomics and proteomics has allowed the discovery of new proteins involved in the origin of the neoplasia and their participation in the development of the disease. This review attempts to establish a cellular and molecular causal link between cancer coagulopathy, angiogenesis and tumor progression in hematological malignancies.

Importance of the bone marrow microenvironment in inducing the angiogenic response in multiple myeloma

Tumor microenvironment is essential for tumor cell proliferation, angiogenesis, invasion and metastasis through its provision of survival signals, secretion of growth and pro-angiogenic factors, and direct adhesion molecule interactions. This review examines its importance in the induction of an angiogenic response in multiple myeloma (MM). The encouraging results of preclinical and clinical trials in which MM has been treated by targeting the tumor microenvironment are also discussed.

ARK5 is transcriptionally regulated by the Large-MAF family and mediates IGF-1-induced cell invasion in multiple myeloma: ARK5 as a new molecular determinant of malignant multiple myeloma

ARK5, AMP-activated protein kinase (AMPK)-related protein kinase mediating Akt signals, is closely involved in tumor progression, and its stage-associated expression was observed in colorectal cancer. In this study, we found ARK5 expression in multiple myeloma cell lines expressing c-MAF and MAFB. In addition, gene expression profiling of 351 clinical specimens revealed ARK5 expression in primary myelomas expressing c-MAF and MAFB, suggesting that ARK5 may be a transcriptional target of the Large-MAF family. Sequence analysis of the ARK5 gene promoter revealed that it contains two putative MAF-recognition element (MARE) sequences. In support of this hypothesis, ARK5 was induced when an MAFB or c-MAF expression vector was introduced into non-ARK5-expressing colon cancer cells. Furthermore, ARK5 promoter activity was dramatically decreased by mutation or deletion of MARE sequences. Chromatin immunoprecipitation assays revealed an interaction between the Large-MAF family proteins and MARE sequences in the ARK5 promoter. Moreover, in ARK5 mRNA-expressing multiple myeloma lines, but not in ARK5-negative lines, insulin-like growth factor (IGF)-1 increased invasion activity. IGF-1-induced invasion was reproduced when ARK5 was overexpressed in Burkitt's lymphoma and plasmacytoma lines. Based on results, we conclude that ARK5 is a transcriptional target of the Large-MAF family through MARE sequence and that ARK5 may in part mediate the aggressive phenotype associated with c-MAF- and MAFB-expressing myelomas.

Targeting receptor kinases by a novel indolinone derivative in multiple myeloma: abrogation of stroma-derived interleukin-6 secretion and induction of apoptosis in cytogenetically defined subgroups

In multiple myeloma (MM), both vascular endothelial (VEGF) and basic fibroblast growth factor (bFGF) promote tumor growth and survival. We have used the novel indolinone BIBF 1000 to study effects of simultaneous inhibition of VEGF, FGF and transforming growth factor-beta on MM cells and their interactions with bone marrow stroma cells (BMSCs). Both, in the absence and presence of myeloma-stroma cell contacts, BIBF 1000 abrogated BMSC-derived secretion of interleukin-6 (IL-6). In addition, BIBF 1000 directly induced apoptosis in t(4;14)-positive cell lines as well as in CD138+ marrow cells from patients with t(4;14) myeloma. To a similar extent, BIBF 1000 induced apoptosis in MM.1S and MM.1R cells carrying the translocation t(14;16). In case of MM.1S and other dexamethasone-sensitive t(14;16) cell lines, BIBF 1000 and dexamethasone had additive proapoptotic effects. Induction of apoptosis by BIBF 1000 was associated with inhibition of the mitogen-activated protein kinases (MAPK) pathway in t(4;14) and inhibition of the phosphatidyl-inositol-3 kinase/AKT pathway in t(14;16) cells. Apoptotic effects did not occur in t(4;14)-or t(14;16)-positive MM cells carrying n- or k-Ras mutations. The data provide the rationale for clinical evaluation of this class of targeted kinase inhibitors in MM with focus on defined cytogenetic subgroups.

Accelerated lymphangiogenesis in malignant lymphoma: possible role of VEGF-A and VEGF-C

There is little information regarding the lymphangiogenesis of malignant lymphoma. In this study, we evaluated the lymphangiogenesis and angiogenesis in 44 lymph nodes of 39 malignant lymphomas and five non-reactive normal lymph nodes, based on the lymphatic vessel density (LVD) and microvessel density (MVD) calculated by the computer-assisted assessment of vessel density. The LVD of malignant lymphomas was significantly higher than that of non-reactive normal lymph nodes, irrespective of subtypes (P = 0.00077). On the contrary, there was no difference in MVD between malignant lymphomas and non-reactive normal lymph nodes, except for diffuse large B cell lymphomas, which had a significantly low value of MVD, in comparison with non-reactive normal lymph nodes (P = 0.009). We further examined the expression of vascular endothelial growth factor (VEGF)-C and VEGF-A, which function on lymphangiogenesis in lymph node samples. VEGF-C was expressed in 36 of 39 malignant lymphomas. All 39 of the malignant lymphoma samples expressed VEGF-A. Furthermore, the level of LVD and VEGF-A or VEGF-C was positively correlated. These findings suggest that lymphangiogenesis is actively developed in lymph nodes of malignant lymphomas and it may be induced by both VEGF-A and VEGF-C secreted from lymphoma cells.

Angiogenic switch in multiple myeloma

Angiogenesis is the hallmark of cancer. Growing evidence indicates that an imbalance between pro- and anti-angiogenic molecules triggers the angiogenic switch during tumor progression. Several molecules, able to affect vascular formation and function, are now beginning to be elucidated. Recent data indicate that angiogenesis also occurs in hematological malignancies. In multiple myeloma it has been demonstrated that patients with active disease have an increase in bone marrow angiogenesis correlated with the progression of disease and an adverse prognosis. The pathophysiology of myeloma-induced angiogenesis is complex and involves either the direct production of angiogenic molecules by myeloma cells or their induction in the microenvironment. In this review we have focalized our attention on the main factors involved in the angiogenic switch that occurs in MM patients.

VEGF induces Mcl-1 up-regulation and protects multiple myeloma cells against apoptosis

Interleukin-6 (IL-6) triggers multiple myeloma (MM) cell proliferation and protects against apoptosis by up-regulating myeloid cell leukemia 1 (Mcl-1). Vascular endothelial growth factor (VEGF) induces modest proliferation of MM cells and induces IL-6 secretion in a paracrine loop involving MM cells and bone marrow stromal cells. Using murine embryonic fibroblast cell lines as a model (Mcl-1wt/wt and Mcl-1Δ/null MEFs), we here demonstrate that deletion of Mcl-1 reduces fetal bovine serum (FBS)-, VEGF-, and IL-6-induced proliferation. We also show that VEGF up-regulates Mcl-1 expression in a time- and dose-dependent manner in 3 human MM cell lines and MM patient cells. Importantly, we demonstrate that the pan-VEGF inhibitor, GW654652, inhibits VEGF-induced up-regulation of Mcl-1 and, as with Mcl-1 siRNA, is associated with decreased proliferation and induction of apoptosis. Finally, we show that VEGF protects MM patient cells against FBS starvation-induced apoptosis. Our studies therefore demonstrate that VEGF-induced MM cell proliferation and survival are mediated via Mcl-1, providing the preclinical framework for novel therapeutics targeting Mcl-1 and/or VEGF to improve patient outcome in MM.