Hai Ngo

LNA-mediated anti–miR-155 silencing in low-grade B-cell lymphomas

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.

Combination Mammalian Target of Rapamycin Inhibitor Rapamycin and HSP90 Inhibitor 17-Allylamino-17-Demethoxygeldanamycin Has Synergistic Activity in Multiple Myeloma

Purpose: The phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (mTOR) pathway and the heat shock protein family are up-regulated in multiple myeloma and are both regulators of the cyclin D/retinoblastoma pathway, a critical pathway in multiple myeloma. Inhibitors of mTOR and HSP90 protein have showed in vitro and in vivo single-agent activity in multiple myeloma. Our objective was to determine the effects of the mTOR inhibitor rapamycin and the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) on multiple myeloma cells. Experimental Design: Multiple myeloma cell lines were incubated with rapamycin (0.1-100 nmol/L) and 17-AAG (100-600 nmol/L) alone and in combination. Results: In this study, we showed that the combination of rapamycin and 17-AAG synergistically inhibited proliferation, induced apoptosis and cell cycle arrest, induced cleavage of poly(ADP-ribose) polymerase and caspase-8/caspase-9, and dysregulated signaling in the phosphatidylinositol 3-kinase/AKT/mTOR and cyclin D1/retinoblastoma pathways. In addition, we showed that both 17-AAG and rapamycin inhibited angiogenesis and osteoclast formation, indicating that these agents target not only multiple myeloma cells but also the bone marrow microenvironment. Conclusions: These studies provide the basis for potential clinical evaluation of this combination for multiple myeloma patients.

Proteomic Analysis of Waldenstrom Macroglobulinemia

To better understand the molecular changes that occur in Waldenstrom macroglobulinemia (WM), we employed antibody-based protein microarrays to compare patterns of protein expression between untreated WM and normal bone marrow controls. Protein expression was defined as a >2-fold or 1.3-fold change in at least 67% of the tumor samples. Proteins up-regulated by >2-fold included Ras family proteins, such as Rab-4 and p62DOK, and Rho family proteins, such as CDC42GAP and ROKalpha. Other proteins up-regulated by >1.3-fold included cyclin-dependent kinases, apoptosis regulators, and histone deacetylases (HDAC). We then compared the samples of patients with symptomatic and asymptomatic WM and showed similar protein expression signatures, indicating that the dysregulation of signaling pathways occurs early in the disease course. Three proteins were different by >2-fold in symptomatic versus asymptomatic, including the heat shock protein HSP90. Elevated protein expression was confirmed by immunohistochemistry and immunoblotting. Functional significance was validated by the induction of apoptosis and inhibition of proliferation using specific HDAC and HSP90 inhibitors. This study, therefore, identifies, for the first time, multiple novel proteins that are dysregulated in WM, which both enhance our understanding of disease pathogenesis and represent targets of novel therapeutics.

Novel Tumor Suppressor Function of Glucocorticoid-Induced TNF Receptor GITR in Multiple Myeloma

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.

Targeting the bone marrow in Waldenstrom Macroglobulinemia

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.

Novel therapeutic agents in Waldenstrom's macroglobulinemia.

Within the past few years, major advances in the preclinical and clinical testing of novel therapeutic agents have occurred in Waldenströms 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.

The bone marrow microenvironment in Waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) is a low-grade B-cell lymphoproliferative disorder characterized primarily by specific homing and growth of tumor cells within the bone marrow niches. The progressive growth of tumor cells throughout the bone marrow indicates that the tumor cells are capable of homing and adhering to specific niches that allow growth, survival and drug resistance. In this review we highlight the interaction of the tumor cells in WM and the bone marrow microenvironment including bone marrow stromal cells, endothelial cells and mast cells. Migration, adhesion and downstream activation of signaling pathways leads to cell trafficking and cell dissemination in WM. Future therapeutic agents need to target not only the tumor clone, but also its close interaction with the bone marrow microenvironment.

The Bone Marrow Niche in Waldenström's Macroglobulinemia

The widespread involvement of the bone marrow with tumor cells indicates that there is continuous cell trafficking of WM cells in and out of the bone marrow leading to cell dissemination in the bone marrow and in the lymph nodes in many patients with WM. The interaction of the WM cells with the bone marrow is critical for the regulation of cell proliferation, cell cycle, drug resistance as well as cell dissemination and trafficking. Advances in understanding the interaction of the tumor clone with the BM microenvironment have led to the development of therapeutic agents that not only target the tumor clone but also regulate the bone marrow microenvironment. Here, we review the role of the cellular and liquid bone marrow compartments in the regulation of cell proliferation and dissemination in WM.