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Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms Activation of the PTEN-PI3K-mTORC1 pathway consolidates metabolic programs that sustain cancer cell growth and proliferation,. Here we show that mTORC1 regulates polyamine dynamics, a metabolic route that is essential for oncogenicity. Through the use of integrative metabolomics in a mouse model and human biopsies of prostate cancer, we identified alterations in tumours impacting on the production of decarboxylated S-adenosylmethionine (dcSAM) and polyamine synthesis. Mechanistically, this metabolic rewiring stems from mTORC1-dependent regulation of S-adenosylmethionine decarboxylase 1 (AMD1) stability. This novel molecular regulation was validated in murine and human cancer specimens. AMD1 was upregulated in prostate cancer specimens with activated mTORC1. Conversely, samples from a clinical trial with the mTORC1 inhibitor everolimus exhibited a predominant decrease in AMD1 immunoreactivity that was associated to a decrease in proliferation, in line with the requirement of dcSAM production for oncogenicity. These findings provide fundamental information about the complex regulatory landscape controlled by mTORC1 to integrate and translate growth signals into an oncogenic metabolic program.

Glucocorticoid-induced TNF receptor (GITR) plays a crucial role in modulating immune response and inflammation, however the role of GITR in human cancers is poorly understood. In this study, we demonstrated that GITR is inactivated during tumor progression in Multiple Myeloma (MM) through promoter CpG island methylation, mediating gene silencing in primary MM plasma cells and MM cell lines. Restoration of GITR expression in GITR deficient MM cells led to inhibition of MM proliferation in vitro and in vivo and induction of apoptosis. These findings were supported by the presence of induction of p21 and PUMA, two direct downstream targets of p53, together with modulation of NF-κB in GITR-overexpressing MM cells. Moreover, the unbalanced expression of GITR in clonal plasma cells correlated with MM disease progression, poor prognosis and survival. These findings provide novel insights into the pivotal role of GITR in MM pathogenesis and disease progression.

miR-155 acts as an oncogenic miR in B-cell lymphoproliferative disorders, including Waldenstrom macroglobulinemia (WM) and chronic lymphocytic leukemia, and is therefore a potential target for therapeutic intervention. However, efficient targeting of miRs in tumor cells in vivo remains a significant challenge for the development of miR-155–based therapeutics for the treatment of B-cell malignancies. In the present study, we show that an 8-mer locked nucleic acid anti–miR-155 oligonucleotide targeting the seed region of miR-155 inhibits WM and chronic lymphocytic leukemia cell proliferation in vitro. Moreover, anti–miR-155 delivered systemically showed uptake in the BM CD19+ cells of WM-engrafted mice, resulting in the up-regulation of several miR-155 target mRNAs in these cells, and decreased tumor growth significantly in vivo. We also found miR-155 levels to be elevated in stromal cells from WM patients compared with control samples. Interestingly, stromal cells from miR-155–knockout mice led to significant inhibition of WM tumor growth, indicating that miR-155 may also contribute to WM proliferation through BM microenvironmental cells. The results of the present study highlight the therapeutic potential of anti–miR-155–mediated inhibition of miR-155 in the treatment of WM.

The spread of multiple myeloma (MM) involves (re)circulation into the peripheral blood and (re)entrance or homing of MM cells into new sites of the BM. Hypoxia in solid tumors was shown to promote metastasis through activation of proteins involved in the endothelial to mesenchymal transition (EMT) process. In this study, we hypothesized that MM associated hypoxic conditions activates EMT related proteins and promotes metastasis of MM cells. Hypoxia activated EMT-related machinery in MM cells, decreased expression of E-cadherin and consequently decreased adhesion of MM cells to the BM and enhanced egress of MM cells to the circulation. In parallel, hypoxia increased the expression of CXCR4, and consequently increased the migration and homing of circulating MM cells to new BM niches. Further studies to manipulate hypoxia in order to regulate tumor dissemination as a therapeutic strategy are warranted.

Interactions between multiple myeloma (MM) cells and the BM microenvironment play a critical role in the pathogenesis of MM and in the development of drug resistance by MM cells. Selectins are involved in extravasation and homing of leukocytes to target organs. In the present study, we focused on adhesion dynamics that involve P-selectin glycoprotein ligand-1 (PSGL-1) on MM cells and its interaction with selectins in the BM microenvironment. We show that PSGL-1 is highly expressed on MM cells and regulates the adhesion and homing of MM cells to cells in the BM microenvironment in vitro and in vivo. This interaction involves both endothelial cells and BM stromal cells. Using loss-of-function studies and the small-molecule pan-selectin inhibitor GMI-1070, we show that PSGL-1 regulates the activation of integrins and downstream signaling. We also document that this interaction regulates MM-cell proliferation in coculture with BM microenvironmental cells and the development of drug resistance. Furthermore, inhibiting this interaction with GMI-1070 enhances the sensitization of MM cells to bortezomib in vitro and in vivo. These data highlight the critical contribution of PSGL-1 to the regulation of growth, dissemination, and drug resistance in MM in the context of the BM microenvironment.

Mammalian target of rapamycin (mTOR) is a downstream serine/threonine kinase of the PI3K/Akt pathway that integrates signals from the tumor microenvironment to regulate multiple cellular processes. Rapamycin and its analogs have not shown significant activity in multiple myeloma (MM), likely because of the lack of inhibition of TORC2. In the present study, we investigated the baseline activity of the PI3K/Akt/mTOR pathway TORC1/2 in MM cell lines with different genetic abnormalities. TORC1/2 knock-down led to significant inhibition of the proliferation of MM cells, even in the presence of BM stromal cells. We also tested INK128, a dual TORC1/2 inhibitor, as a new therapeutic agent against these MM cell lines. We showed that dual TORC1/2 inhibition is much more active than TORC1 inhibition alone (rapamycin), even in the presence of cytokines or stromal cells. In vitro and in vivo studies showed that p-4EBP1 and p-Akt inhibition could be predictive markers of TORC2 inhibition in MM cell lines. Dual TORC1/2 inhibition showed better inhibition of adhesion to BM microenvironmental cells and inhibition of homing in vivo. These studies form the basis for further clinical testing of TORC1/2 inhibitors in MM.

Abstract 471 Multiple myeloma (MM) is characterized by widespread dissemination of the MM cells at diagnosis associated with multiple focal bone lesions, implying (re)circulation of MM cells into the peripheral blood and (re)entrance or homing into new sites of the BM. However, the driving force for MM cells to leave the BM, egress, and home to new BM niches is still not well understood. Hypoxia (low oxygen) in solid tumors was shown to promote metastasis in solid tumors through activation of proteins involved in the endothelial to mesenchymal Transition (EMT). In this study, we hypothesized that MM tumor progression induces hypoxic conditions, which in turn activates EMT related proteins and promotes metastasis of MM cells. To test this hypothesis, we examined levels of hypoxia in MM cells at different stages of tumor progression in vivo in two animal models: the first by injecting MM1s cell to SCID mice, and the second by injecting 5T33MM cells to C57BL/KaLwRijHsd mice. Hypoxic markers were examined using flow cytometry and immunohistochemistry. We found that tumor progression induced hypoxia in both the MM cells and the tumor microenvironment. Similarly, hypoxia induced genes (HIF1a, HIF1b, HIF2b, CREBBP, HYOU1, VEGF1, HIF1a-inhibitory protein) were increased in MM patients (n=68) compared to plasma cells from healthy donors (n=14). Using flow cytometry we found that the number of circulating MM cells increased with the progression; however, the correlation was observed in late stages of the progression but not in the early stages. A better direct correlation was achieved with the hypoxic state of the MM cells in the BM. Circulating MM cells were more hypoxic that MM cells in the BM (especially at low tumor burden). Moreover, we found that the level of hypoxia in MM cells in the PB did not correlate with the hypoxia in the BM. Next, we tested the mechanism in which hypoxia induces cell egress. We found that MM cells isolated from MM patients have higher gene expression of EMT inducing proteins (E-cadherin, SNAIL, FOXC2, TGFb1) in parallel to a decrease of expression in E-cadherin, and we confirmed the downregulation of E-cadherin expression in correlation with the increase of hypoxia in MM cell and cells in the BM microenvironment in vivo. Culturing MM cells under hypoxic conditions increased the expression of HIF1a and HIF2a. In parallel, hypoxia induced acquisition of EMT related features including downregulation of E-cadherin, upregulation of SNAIL, and inhibition of GSK3b. In addition, hypoxia decreased the adhesion of MM cells to stromal cells. To complete the metastatic process after egress, MM cells need to home to new sites in the BM. Therefore we investigated the effect of hypoxia on expression of CXCR4, chemotaxis and homing of MM cells to the BM. Using flow cytometry we found a direct correlation between hypoxia and the expression of CXCR4 in MM cells in vivo using the SCID-MM1s model. These results were confirmed in vitro, where hypoxia increased the expression of CXCR4 at protein and mRNA levels in MM cells. Moreover, the expression of CXCR4 in MM cells isolated from the PB was higher than cells isolated from the BM especially at low tumor burden, correlating with higher hypoxic state of the circulating tumor cells. Functionally, hypoxia increased the chemotaxis of MM cells towards SDF1a in vitro and, using in vivo confocal microscopy, it was shown to accelerate the homing of MM cells to the BM in vivo. To demonstrate that the chemotaxis and homing were CXCR4 dependent, we treated the hypoxic MM cells with AMD3100 (a CXCR4 inhibitor) and showed that it inhibited chemotaxis in vitro and homing of MM to the BM in vivo. In conclusion, we demonstrate that tumor progression induces hypoxia in the MM cells and in the BM microenvironment. Hypoxia activates EMT-related machinery in MM cells, decreases expression of E-cadherin and consequently decreased the adhesion of MM cells to the BM, and enhance egress of MM cells to the circulation. In parallel, hypoxia increases the expression of CXCR4, and consequently increased the migration and homing of MM cells in from the peripheral blood to the BM. Further studies to manipulate hypoxia in order to regulate tumor dissemination as a therapeutic strategy are warranted. Disclosures: Roccaro: Roche: . Kung:Novartis Pharmaceuticals: Consultancy, Research Funding. Ghobrial:Novartis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Millennium: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Research Funding; Noxxon: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Waldenstrom macroglobulinemia (WM) is a low-grade B-cell lymphoma characterized by widespread involvement of the bone marrow with lymphoplasmacytic cells. In approximately 20% of patients, the malignant clone also involves the lymph nodes and induces hepatosplenomegaly. The mechanisms by which the tumor cells home to the bone marrow and preferentially reside in the marrow niches are not fully elucidated. In this review, we examine the role of the bone marrow microenvironment in the regulation of cell growth, survival and cell dissemination in WM. We also summarize specific regulators of niche-dependent tumor proliferation in WM. These include chemokines, adhesion molecules, Src/PI3K/Akt/mTOR signaling, NF-kB activation, and micro-RNA regulation in WM. Targeting these pathways in clinical trials could lead to significant responses in this rare disease.

We have previously shown clinical activity of a mammalian target of rapamycin (mTOR) complex 1 inhibitor in Waldenstrom macroglobulinemia (WM). However, 50% of patients did not respond to therapy. We therefore examined mechanisms of activation of the phosphoinositide 3-kinase (PI3K)/Akt/mTOR in WM, and mechanisms of overcoming resistance to therapy. We first demonstrated that primary WM cells show constitutive activation of the PI3K/Akt pathway, supported by decreased expression of phosphate and tensin homolog tumor suppressor gene (PTEN) at the gene and protein levels, together with constitutive activation of Akt and mTOR. We illustrated that dual targeting of the PI3K/mTOR pathway by the novel inhibitor NVP-BEZ235 showed higher cytotoxicity on WM cells compared with inhibition of the PI3K or mTOR pathways alone. In addition, NVP-BEZ235 inhibited both rictor and raptor, thus abrogating the rictor-induced Akt phosphorylation. NVP-BEZ235 also induced significant cytotoxicity in WM cells in a caspase-dependent and -independent manner, through targeting the Forkhead box transcription factors. In addition, NVP-BEZ235 targeted WM cells in the context of bone marrow microenvironment, leading to significant inhibition of migration, adhesion in vitro, and homing in vivo. These studies therefore show that dual targeting of the PI3K/mTOR pathway is a better modality of targeted therapy for tumors that harbor activation of the PI3K/mTOR signaling cascade, such as WM.

Within the past few years, major advances in the preclinical and clinical testing of novel therapeutic agents have occurred in Waldenstrom's macroglobulinemia (WM). These include agents that target the PI3K/Akt/mTOR pathway, PKC pathways, NF-kB signaling pathway, as well as tyrosine kinases and histone deacetylase inhibitors. In this review, we summarize the current understanding of the clinical development of these agents in WM.