Dual targeting of the proteasome regulates survival and homing in Waldenstrom macroglobulinemia.

Waldenström macroglobulinemia (WM) is an incurable low-grade B-cell lymphoma characterized by high protein turnover. We dissected the biologic role of the proteasome in WM using 2 proteasome inhibitors, NPI-0052 and bortezomib. We found that NPI-0052 inhibited proliferation and induced apoptosis in WM cells, and that the combination of NPI-0052 and bortezomib induced synergistic cytotoxicity in WM cells, leading to inhibition of nuclear translocation of p65NF-kappaB and synergistic induction of caspases-3, -8, and -9 and PARP cleavage. These 2 agents inhibited the canonical and noncanonical NF-kappaB pathways and acted synergistically through their differential effect on Akt activity and on chymotrypsin-like, caspaselike, and trypsinlike activities of the proteasome. We demonstrated that NPI-0052-induced cytotoxicity was completely abrogated in an Akt knockdown cell line, indicating that its major activity is mediated through the Akt pathway. Moreover, we demonstrated that NPI-0052 and bortezomib inhibited migration and adhesion in vitro and homing of WM cells in vivo, and overcame resistance induced by mesenchymal cells or by the addition of interleukin-6 in a coculture in vitro system. Theses studies enhance our understanding of the biologic role of the proteasome pathway in WM, and provide the preclinical basis for clinical trials of combinations of proteasome inhibitors in WM.

Targeting NF-kappaB in Waldenstrom macroglobulinemia.

The nuclear factor-kappaB (NF-kappaB) path-way has been implicated in tumor B-cell survival, growth, and resistance to therapy. Because tumor cells overcome single-agent antitumor activity, we hypothesized that combination of agents that target differentially NF-kappaB pathway will induce significant cytotoxicity. Therapeutic agents that target proteasome and Akt pathways should induce significant activity in B-cell malignancies as both pathways impact NF-kappaB activity. We demonstrated that perifosine and bortezomib both targeted NF-kappaB through its recruitment to the promoter of its target gene IkappaB using chromatin immunoprecipitation assay. This combination led to synergistic cytotoxicity in Waldenstrom macroglobulinemia (WM) cells that was mediated through a combined reduction of the PI3K/Akt and ERK signaling pathways, found to be critical for survival of WM cells. Moreover, a combination of these drugs with the CD20 monoclonal antibody rituximab further increased their cytotoxic activity. Thus, effective WM therapy may require combination regimens targeting the NF-kappaB pathway.

Targeting normal and neoplastic tissues in the rat jejunum and colon with boronated, cationic acrylamide copolymers.

A series of boronated cationic copolymers, composed of different ratios of acrylamide, N-acryloyl-3-aminophenylboronic acid and N-acryloyl-diaminoethane (the cationic moiety), were prepared with the intention of localizing boron neutron capture therapy (BNCT) in experimentally induced polyps on the luminal side of the gut of the rat. The goals of this study were to: (a) test the effect of cationization of the boronated copolymers on their uptake by polyps and normal adjacent epithelium; (b) compare the whole rat body distribution of aminophenylboronic acid (APB) and polymeric APB after local application; (c) measure the effect of micro-environmental parameters such as pH, the presence of mucin and cations on the interaction between the APB-copolymers and the epithelium of the rat intestines. Direct analysis of tissue boron levels showed that polymeric APB-uptake was higher in the colonic polyps than in the surrounding normal tissues. Free APB, however, was found in similar quantities in both. When tested in the normal jejunum and colon of the rat, polymeric APB uptake was directly proportional to the molar content of the cationic monomer in the copolymers. The presence of magnesium ions, free boron cationic monomer and mucin interfered with this uptake in a concentration-dependent manner. The uptake was pH-independent at pH 5, 7 and 10. APB accumulation in the colon polyps was inversely proportional to the cationic monomer content in the copolymers, suggesting an increased amount of mucus around the polyps, which probably impeded the electrostatic attachment of the polymer to the malignant tissue. The use polymeric APB for targeting BNCT in perioperative treatment of colorectal carcinoma is suggested, especially in the cases of microscopic residual disease after curative resection.

Key role of microRNAs in Waldenström's macroglobulinemia pathogenesis.

Epigenetics represent heritable changes in gene expression that are not due to any alteration in the DNA sequence. One of the best-known epigenetic markers is histone acetylation, which has been shown to be deregulated in neoplastic diseases, including B-cell malignancies, such as Waldenström's Macroglobulinemia (WM), a low-grade B-cell lymphoma characterized by the presence of lymphoplasmacytic cells in the bone marrow and a serum monoclonal immunoglobulin M in the circulation. It has been recently demonstrated that microRNAs may be responsible for modulating histone acetylation in WM cells, thus providing the preclinical evidences for using microRNA-based therapeutic strategies in this disease.

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.

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.

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.

Optical techniques for tracking multiple myeloma engraftment, growth, and response to therapy.

Multiple myeloma (MM), the second most common hematological malignancy, initiates from a single site and spreads via circulation to multiple sites in the bone marrow (BM). Methods to track MM cells both in the BM and circulation would be useful for developing new therapeutic strategies to target MM cell spread. We describe the use of complementary optical techniques to track human MM cells expressing both bioluminescent and fluorescent reporters in a mouse xenograft model. Long-term tumor growth and response to therapy are monitored using bioluminescence imaging (BLI), while numbers of circulating tumor cells are detected by in-vivo flow cytometry. Intravital microscopy is used to detect early seeding of MM cells to the BM, as well as residual cancer cells that remain in the BM after the bulk of the tumor is eradicated following drug treatment. Thus, intravital microscopy provides a powerful, albeit invasive, means to study cellular processes in vivo at the very early stage of the disease process and at the very late stage of therapeutic intervention when the tumor burden is too small to be detected by other imaging methods.