We discovered that monoclonal antibodies (mAbs) specific to human beta(2)-microglobulin (beta(2)M) induce apoptosis in vitro and were therapeutic in mouse models of myeloma and other hematological tumor cells. Cell death occurred rapidly, without the need for exogenous immunological effector mechanisms. The mAbs induced cell death via recruiting MHC class I molecules to lipid rafts and activating Lyn and PLCgamma2, leading to activated JNK and inhibited PI3K/Akt and ERK, compromised mitochondrial integrity, and caspase-9-dependent cascade activation. Although the expression of beta(2)M on normal hematopoietic cells is a potential safety concern, the mAbs were selective to tumor-transformed cells and did not induce apoptosis of normal cells. Therefore, such mAbs offer the potential for a therapeutic approach to hematological malignancies.

Elevated levels of C-reactive protein (CRP) are present in many disease situations including malignancies and may contribute to the pathogenesis of cardiovascular disorders. This study was undertaken in a myeloma setting to determine whether CRP affects tumor cell growth and survival. We show that CRP enhanced myeloma cell proliferation under stressed conditions and protected myeloma cells from chemotherapy drug-induced apoptosis in vitro and in vivo. CRP binds activating Fcgamma receptors; activates PI3K/Akt, ERK, and NF-kappaB pathways; and inhibits caspase cascade activation induced by chemotherapy drugs. CRP also enhanced myeloma cell secretion of IL-6 and synergized with IL-6 to protect myeloma cells from chemotherapy drug-induced apoptosis. Thus, our results implicate CRP as a potential target for cancer treatment.

The multidrug resistance protein MRP4, a member of the ATP-binding cassette superfamily, confers resistance to purine-based antiretroviral agents. However, the antiviral agent ganciclovir (GCV) has not been shown to be a substrate of MRP4. GCV is important not only in antiviral therapy, but also in the selective killing of tumor cells modified to express herpes simplex virus thymidine kinase (HSV-TK). We therefore tested the effect of MRP4 on the cytotoxicity of GCV, on the ability of GCV to kill cells genetically modified to express HSV-TK, and on the bystander effect in which unmodified target cells are killed by GCV. Cells overexpressing MRP4 had markedly increased resistance to the cytotoxicity of GCV. Although, expression of recombinant HSV-TK increased the intracellular concentration of GCV nucleotide, cells were rescued by the cytoprotective effect of MRP4. In cells that overexpressed MRP4, intracellular accumulation of GCV metabolites was reduced, efflux of these metabolites was increased, and resistance to bystander killing was increased. Therefore, MRP4 can strongly reduce the susceptibility of HSV-TK-expressing cells to GCV, and its overexpression in adjacent cells protects them from bystander cell death. These findings indicate that a nucleotide transporter, such as MRP4, modulates the cellular response to GCV and thus may influence not only the efficacy of antiviral therapy, but also prodrug-based gene therapy, which is critically dependent upon bystander cell killing.The multidrug resistance proteins (MRPs) 1 are a family of ATP-binding cassette transporters (ABC transporters; for an overview, see //nutrigene.4t.com/humanabc.html) that mediates drug efflux and multidrug resistance (1). We previously demonstrated that MRP4 (also known as ABCC4) severely reduces the antiviral efficacy of several nucleoside reverse transcriptase inhibitors, such as zidovudine (3Ј-azido-3Ј-deoxythymidine) (AZT)) and 9-(2-(phosphonomethoxy)ethyl)-adenine (PMEA), in mammalian cells and that this effect corresponds with increased ATP-dependent efflux of their nucleotide derivatives (2). These findings were, in part, replicated by Lee et al. (3). A better understanding of the role of MRP4 as a nucleotide efflux transporter may lead to improved nucleoside-based therapies for HIV, herpes viruses, and cancer. Ganciclovir (9-(1,3-dihydroxy-2-propoxymethyl)guanine (GCV)) is widely used against cytomegalovirus infection in patients with AIDS (4 -6) but is poorly tolerated in combination with AZT (7). Although the molecular basis of this interaction is unknown, in vitro studies indicate that the combination is extremely cytotoxic (8, 9). We therefore postulated that MRP4 might be involved in the cytotoxicity induced by the AZT-GCV combination. If so, such an interaction could have important therapeutic potential because of the widespread use of GCV as a prodrug in gene therapies for cancer (10,11). Transduction of tumor cells with the herpes simplex virus thymidine kinase (HSV-TK) gene and treatment with GCV is a common antica...

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We have investigated the interaction between tumor cells and specific cells in their microenvironment using myeloma as a model. The role of myeloma-induced osteoclastogenesis in the disease was studied ex vivo. Myeloma plasma cells freshly purified from patients' bone marrow attracted committed osteoclast (OC) precursors (n ‫؍‬ 9; P < 0.01) and in 22 experiments directly induced their differentiation to multinucleated, boneresorbing OCs (P < 0.00002) in a receptor activator of nuclear factor-B ligand-mediated mechanism that was inhibited by the receptor activator of nuclear factor-B (RANK-Fc) in 13 experiments by 71 ؎ 12% (P < 0.008). In contrast, myeloma cells did not induce differentiation of peripheral blood mononuclear cells. Myeloma plasma cells cocultured with OCs retained their viability and proliferative activity for >13 weeks. After 14 days in coculture, the plasma cells from 29 patients had higher viability (P < 2 ؋ 10 ؊6 ), fewer apoptotic cells (P < 4 ؋ 10 ؊15 ), and a higher bromodeoxyuridine labeling index (P < 0.0006) than controls. Physical contact between OCs and myeloma cells was required for these effects to take place. No differences were observed between OCs from healthy donors and those from myeloma patients. Blocking interleukin 6 activity, while reducing survival of myeloma cells, had no effect on their proliferative activity. These results support data obtained from animal models and clinical observations on the essential role of the microenvironment in tumor sustenance and progression.