MLN4924, an NAE inhibitor, suppresses AKT and mTOR signaling via upregulation of REDD1 in human myeloma cells.

The function and survival of normal and malignant plasma cells depends on the elaborately regulated ubiquitin proteasome system. Proteasome inhibitors such as bortezomib have proved to be highly effective in the treatment of multiple myeloma (MM), and their effects are related to normal protein homeostasis which is critical for plasma cell survival. Many ubiquitin ligases are regulated by conjugation with NEDD8. Therefore, neddylation may also impact survival and proliferation of malignant plasma cells. Here, we show that MLN4924, a potent NEDD8 activating enzyme (NAE) inhibitor, induced cytotoxicity in MM cell lines, and its antitumor effect is associated with suppression of the AKT and mammalian target of rapamycin (mTOR) signaling pathways through increased expression of REDD1. Combining MLN4924 with the proteasome inhibitor bortezomib induces synergistic apoptosis in MM cell lines which can overcome the prosurvival effects of growth factors such as interleukin-6 and insulin-like growth factor-1. Altogether, our findings demonstrate an important function for REDD1 in MLN4924-induced cytotoxicity in MM and also provide a promising therapeutic combination strategy for myeloma.

Mobilization of hematopoietic progenitors from normal donors using the combination of granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor results in fewer plasmacytoid dendritic cells in the graft and enhanced donor T cell engraftment with Th1 polarization: results from a randomized clinical trial.

Granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) both mobilize CD34(+) stem cells into the blood when administered before apheresis but have distinct effects on dendritic cell (DC) differentiation. We previously demonstrated that the combination of GM+G-CSF results in fewer plasmacytoid DCs (pDCs) when used to mobilize peripheral blood stem cells for autologous transplantation. To test the hypothesis that the content of pDCs in an allograft can be modulated with the cytokines used for mobilization, we randomized the human leukocyte antigen-matched sibling donors of 50 patients with hematological malignancies to a mobilization regimen of either GM+G-CSF (n = 25) or G-CSF alone (n = 25). Primary and secondary endpoints included the cellular constituents of the mobilized grafts, the kinetics of posttransplantation immune reconstitution, and clinical outcomes of the transplantation recipients. Grafts from donors receiving GM+G-CSF contained equivalent numbers of CD34(+) cells with fewer pDCs and T cells, with a higher fraction of Th1-polarized donor T cells than G-CSF mobilized grafts. Immune recovery was enhanced among recipients of GM+G-CSF. Survival was not significantly different between transplantation recipients in the two arms. The use of GM+G-CSF modulates immune function and recovery after allogeneic transplantation and should be explored in larger studies powered to evaluate clinical outcomes.

Tipifarnib sensitizes cells to proteasome inhibition by blocking degradation of bortezomib-induced aggresomes.

In this report, we investigated the mechanism responsible for synergistic induction of myeloma cell apoptosis induced by the combination of tipifarnib and bortezomib. Immunofluorescence studies revealed that bortezomib alone resulted in an accumulation of puncta of ubiquitinated proteins that was further enhanced by the addition of tipifarnib. These data suggest inhibition of the degradation of bortezomib-induced aggresomes; and consistent with this possibility, we also observed an increase in p62SQSTM1 in cells treated with the combination. However, autophagy in these cells appears to be normal as LC3BII is present, and autophagic flux appears to be unaffected as demonstrated by the addition of bafilomycin A1. Together, these data demonstrate that tipifarnib synergizes with bortezomib by inducing protein accumulation as a result of the uncoupling of the aggresome and autophagy pathways.

Regulation of alloimmune responses by dendritic cell subsets.

OBJECTIVE: Dendritic cells (DCs) are powerful mediators of immune responses. We have demonstrated that the content of plasmacytoid (type 2) dendritic cells (DC2) within allogeneic bone marrow grafts impacts survival and graft-vs-host disease following transplantation. In order to better understand the effect of DC subsets on regulation of immunity, we tested the effect of DC subsets on T cells in a model of indirect antigen presentation to mimic presentation of host-type alloantigen by donor-type DC. MATERIALS AND METHODS: Volunteers underwent apheresis without cytokine priming, and DC1, DC2, naïve, and memory T cells were purified by immunomagnetic bead and fluorescein-activated cell sorting. Purified DC1 and DC2 cells were cultured with third-party irradiated blood mononuclear cells and either naïve or memory homologous T cells in mixed lymphocyte reactions. RESULTS: Myeloid (type 1) dendritic cells (DC1) induced significant proliferation of homologous T cells and were more effective in priming naïve T-cell responses than memory T cells responding to alloantigen. DC2 cells induced minimal T-cell proliferation regardless of the T-cell subset used as the responding fraction. Secondary mixed lymphocyte reaction studies demonstrated that DC2 primed T cells remained hyporesponsive even when challenged with a third-party alloantigen. The immunostimulatory effect of DC1 required DC-to-T-cell contact, and induced interleukin-12 secretion, while DC2 cells induced interferon-gamma secretion. Polymerase chain reaction analysis of DC2-primed T cells demonstrated a significant increase in Foxp3 expression, supporting induction of a regulatory T-cell population. CONCLUSION: DC1 and DC2 cells induced divergent T-cell responses using homologous cells. Better understanding of DC2-mediated T-cell suppression may yield strategies that overcome tumor-specific immune tolerance and regulate graft-vs-host disease.

A phase I/II trial combining high-dose melphalan and autologous transplant with bortezomib for multiple myeloma: a dose- and schedule-finding study.

PURPOSE: We did a randomized phase I/II trial designed to evaluate the safety and efficacy of combining the proteasome inhibitor bortezomib with high-dose melphalan as the conditioning for high-dose therapy and autologous transplant for myeloma. EXPERIMENTAL DESIGN: Enrolled patients were limited to those who did not achieve a very good partial remission (VGPR) following one or more induction regimens, and were randomized to receive a single escalating dose of bortezomib (1.0, 1.3, or 1.6 mg/m(2)) either 24 hours before or 24 hours after high-dose melphalan. Dose escalation was based on the escalation with overdose control (EWOC), a Bayesian statistical model. Bone marrow aspirates were collected before initiation of therapy and at the time of transplant to evaluate which sequence resulted in maximal plasma cell apoptosis, and response to transplant was assessed by the International Myeloma Working Group criteria. RESULTS: Among 39 randomized patients, 20 received bortezomib after melphalan and 19 received bortezomib before melphalan. Toxicities and posttransplant hematopoietic recovery rates were similar between arms. The overall response rate for all patients was 87%, with 51% achieving a VGPR or better. Pharmacodynamic studies showed greater plasma cell apoptosis among patients who received bortezomib following melphalan. CONCLUSIONS: The use of bortezomib in conjunction with high-dose melphalan is safe, with data suggesting improved efficacy. A single dose of bortezomib administered after high-dose melphalan is the recommended dose and schedule for future clinical investigation.

Risk factors and kinetics of thrombocytopenia associated with bortezomib for relapsed, refractory multiple myeloma.

Bortezomib, a proteasome inhibitor with efficacy in multiple myeloma, is associated with thrombocytopenia, the cause and kinetics of which are different from those of standard cytotoxic agents. We assessed the frequency, kinetics, and mechanism of thrombocytopenia following treatment with bortezomib 1.3 mg/m2 in 228 patients with relapsed and/or refractory myeloma in 2 phase 2 trials. The mean platelet count decreased by approximately 60% during treatment but recovered rapidly between treatments in a cyclic fashion. Among responders, the pretreatment platelet count increased significantly during subsequent cycles of therapy. The mean percent reduction in platelets was independent of baseline platelet count, M-protein concentration, and marrow plasmacytosis. Plasma thrombopoietin levels inversely correlated with platelet count. Murine studies demonstrated a reduction in peripheral platelet count following a single bortezomib dose without negative effects on megakaryocytic cellularity, ploidy, or morphology. These data suggest that bortezomib-induced thrombocytopenia is due to a reversible effect on megakaryocytic function rather than a direct cytotoxic effect on megakaryocytes or their progenitors. The exact mechanism underlying bortezomib-induced thrombocytopenia remains unknown but it is unlikely to be related to marrow injury or decreased thrombopoietin production.

A randomized trial comparing the combination of granulocyte-macrophage colony-stimulating factor plus granulocyte colony-stimulating factor versus granulocyte colony-stimulating factor for mobilization of dendritic cell subsets in hematopoietic progenitor cell products.

The ability of granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) administration to increase the content of blood leucocytes and hematopoietic progenitor cells (HPCs) is well established, yet the effect of these cytokines on immune function is less well described. Recent data indicate that plasmacytoid dendritic cells (DC2) may inhibit cellular immune response. We hypothesized that administration of the combination of G-CSF and GM-CSF after chemotherapy would reduce the type 2, or plasmacytoid, DC2 content of the autologous blood HPC grafts compared with treatment with G-CSF alone. To test this hypothesis, 35 patients with lymphoma and myeloma were randomized to receive either G-CSF or the combination of G-CSF plus GM-CSF after chemotherapy, and blood HPC grafts were collected by apheresis. Cytokine-related adverse events between the 2 groups were similar. More than 2 x 10(6)CD34 + cells per kilogram were collected by apheresis in 14 of 18 subjects treated with G-CSF and in 16 of 17 subjects treated with GM-CSF plus G-CSF ( p = not significant). There were minor differences between the 2 groups with respect to the content of T cells and CD34 + cells in the apheresis products. However, grafts collected from recipients of the combination of GM-CSF plus G-CSF had significantly fewer DC2 cells and similar numbers of DC1 cells compared with recipients treated with G-CSF alone. A third cohort of patients received chemotherapy followed by the sequential administration of G-CSF and the addition of GM-CSF 6 days later. Grafts from these patients had a markedly reduced DC2 content compared with those from patients treated either with G-CSF alone or with the concomitant administration of both cytokines. These data, and recent data that cross-presentation of antigen by DC2 cells may induce antigen-specific tolerance among T cells, suggest that GM-CSF during mobilization of blood HPC grafts may be a clinically applicable strategy to enhance innate and acquired immunity after autologous and allogeneic HPC transplantation.