Proteasome inhibitor bortezomib modulates TLR4-induced dendritic cell activation

Sorafenib, but not sunitinib, affects function of dendritic cells and induction of primary immune responses

The tyrosine kinase inhibitors sorafenib and sunitinib are approved for the treatment of patients with malignant diseases. To analyze the possible use of these compounds in combination with immunotherapeutic approaches, we analyzed the effects of both inhibitors on the immunostimulatory capacity of human dendritic cells (DCs) and the induction of primary immune responses in vivo. Sorafenib, but not sunitinib, inhibits function of DCs, characterized by reduced secretion of cytokines and expression of CD1a, major histocompatibility complex, and costimulatory molecules in response to TLR ligands as well as by their impaired ability to migrate and stimulate T-cell responses. These inhibitory effects are mediated by inhibition of PI3 and MAP kinases and NFκB signaling. In contrast, sorafenib had no influence on the phenotype and proliferation of T cells. To analyze the effects of both TKIs on cytotoxic T-cell induction in vivo, C57BL/6 mice were pretreated with sorafenib or sunitinib and immunized with OVA257-264 peptide. Sorafenib, but not sunitinib, application significantly reduced the induction of antigen-specific T cells. Numbers of regulatory T cells were reduced in peripheral blood mononuclear cells from mice treated with sunitinib. These results indicate that sunitinib, but not sorafenib, is suitable for combination with immunotherapeutic approaches for treatment of cancer patients.

The proteasome inhibitor bortezomib depletes plasma cells and protects mice with lupus-like disease from nephritis

Autoantibody-mediated diseases like myasthenia gravis, autoimmune hemolytic anemia and systemic lupus erythematosus represent a therapeutic challenge. In particular, long-lived plasma cells producing autoantibodies resist current therapeutic and experimental approaches. Recently, we showed that the sensitivity of myeloma cells toward proteasome inhibitors directly correlates with their immunoglobulin synthesis rates. Therefore, we hypothesized that normal plasma cells are also hypersensitive to proteasome inhibition owing to their extremely high amount of protein biosynthesis. Here we show that the proteasome inhibitor bortezomib, which is approved for the treatment of multiple myeloma, eliminates both short- and long-lived plasma cells by activation of the terminal unfolded protein response. Treatment with bortezomib depleted plasma cells producing antibodies to double-stranded DNA, eliminated autoantibody production, ameliorated glomerulonephritis and prolonged survival of two mouse strains with lupus-like disease, NZB/W F1 and MRL/lpr mice. Hence, the elimination of autoreactive plasma cells by proteasome inhibitors might represent a new treatment strategy for antibody-mediated diseases.

Treating metastatic solid tumors with bortezomib and a tumor necrosis factor-related apoptosis-inducing ligand receptor agonist antibody

BACKGROUND

Resistance of tumors to cell death signals poses a complex clinical problem. We explored the therapeutic potential and in vivo toxicity of a combination of bortezomib, a proteasome inhibitor, and MD5-1, a tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor (DR5) agonist monoclonal antibody, in mouse carcinomas. METHODS; Mice bearing Renca-FLAG (renal) or 4T1 (mammary) tumors were treated with bortezomib and/or MD5-1 and examined for lung metastases (Renca-FLAG: n = 93; 4T1: n = 40) or monitored for survival (Renca-FLAG: n = 143). Toxicity was assessed by histopathology and hematology. Viability and apoptotic signaling in Renca-FLAG and 4T1 cells treated with bortezomib alone or in combination with TRAIL were analyzed using 3-[4,5-dimethyiazol-2-yl-5]-[3-carboxymethyloxyphenyl]-2-[4-sulfophenyl]-2H tetrazolium assay and by measuring mitochondrial membrane depolarization and caspase-8 and caspase-3 activation. All statistical tests were two-sided.

RESULTS

Bortezomib (20 nM) sensitized Renca-FLAG and 4T1 cells to TRAIL-mediated apoptosis (mean percent decrease in numbers of viable cells, bortezomib + TRAIL vs TRAIL: Renca-FLAG, 95% vs 34%, difference = 61%, 95% confidence interval [CI] = 52% to 69%, P < .001; 4T1, 85% vs 20%, difference = 65%, 95% CI = 62% to 69%, P < .001). Sensitization involved activation of caspase-8 and caspase-3 but not mitochondrial membrane depolarization, suggesting an amplified signaling of the extrinsic cell death pathway. Treatment with bortezomib and MD5-1 reduced lung metastases in mice carrying Renca and 4T1 tumors (mean number of metastases, bortezomib + MD5-1 vs MD5-1: Renca-FLAG, 1 vs 8, difference = 7, 95% CI = 5 to 9, P < .001; 4T1, 1 vs 12, difference = 11, 95% CI = 9 to 12, P < .001) and increased median survival of mice bearing Renca-FLAG tumors (bortezomib + MD5-1 vs bortezomib + control isotype antibody: 22 of 30 [73%] were still alive at day 180 vs median survival of 42 days [95% CI = 41 to 44 days, P < .001]) in the absence of obvious toxicity.

CONCLUSION

Bortezomib combined with DR5 agonist monoclonal antibody may be a useful treatment for metastatic solid tumors.

Potential role of novel nucleoside analogs in the treatment of acute myeloid leukemia

PURPOSE OF REVIEW

Nucleoside analogs remain a cornerstone in acute myeloid leukemia therapy. As many new nucleosides are being investigated in clinical trials, this review aims to update the current state of experience with these new compounds and where they may fit into treatment strategies for acute myeloid leukemia.

RECENT FINDINGS

Many new nucleoside analogs are emerging with novel metabolic properties and mechanisms of action. Some have entered clinical trials and are actively investigated in the context of acute myeloid leukemia therapy. Clofarabine is the most-developed compound, and single-agent experience and combinations with other active agents in acute myeloid leukemia are being explored. Troxacitabine and sapacitabine are still in single-agent phases of their development and clinical experience is accumulating quickly.

SUMMARY

Nucleosides remain the most important class of drugs in acute myeloid leukemia and the interest in new compounds is strong. The plethora of new analogs continues to provide ample opportunity to expand the effectiveness of these drugs in acute myeloid leukemia therapy. Furthermore, their unique mechanisms of action provide possibilities for mechanism-based combinations.

DHMEQ, a novel nuclear factor-kappaB inhibitor, induces selective depletion of alloreactive or phytohaemagglutinin-stimulated peripheral blood mononuclear cells, decreases production of T helper type 1 cytokines, and blocks maturation of dendritic cells

Dehydroxymethylepoxyquinomicin (DHMEQ), a novel nuclear factor kappaB (NF-kappaB) inhibitor, has been shown to be active against variety types of solid tumours as well as haematological malignant cells. This study explored the anti-inflammatory effects of DHMEQ in vitro. DHMEQ inhibited the proliferation of phytohaemagglutinin (PHA)-stimulated or alloreactive peripheral blood mononuclear cells (PBMC) in mixed lymphocyte cultures as measured using a 3-(4,5-dimethylithiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay. In contrast, DHMEQ did not affect the viability of resting PBMC. In addition, real-time polymerase chain reaction showed that DHMEQ decreased PHA-stimulated expression of T helper type 1 (Th1) cytokines, including interleukin-2, interferon-gamma, and tumour necrosis factor alpha, in PBMC as well as Jurkat T-lymphoblastic leukaemia cells, and also decreased levels of p65 isoforms of NF-kappaB in the nucleus. Furthermore, we found that DHMEQ inhibited the endocytic capacity of dendritic cells (DCs) and down-regulated the expression of cell surface antigen CD40, suggesting that DHMEQ blocked the maturation as well as the function of DCs. Taken together, the results suggest that DHMEQ may be useful for treatment of inflammatory diseases, including graft-versus-host disease after allogenic haematopoietic stem cell transplantation.

Proteasome inhibition suppresses essential immune functions of human CD4+ T cells

The proteasome constitutes the central proteolytic component of the highly conserved ubiquitin-proteasome system, which is required for the maintenance and regulation of basic cellular processes, including differentiation, proliferation, cell cycling, gene transcription and apoptosis. Here we show that inhibition of proteasomal proteolytic activity by the proteasome inhibitors bortezomib and lactacystin suppresses essential immune functions of human CD4(+) T cells activated by allogeneic dendritic cells (DCs). In activated CD4(+) T cells, proteasome inhibition induces apoptosis accompanied by rapid accumulation and stabilization of the tumour suppressor protein p53. Activated CD4(+) T cells surviving proteasome inhibition undergo inhibition of proliferation by induction of G(1) phase cell-cycle arrest. Induction of G(1) arrest is accompanied by the accumulation of cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(KIP1) and the disappearance of cyclin A, cyclin D2 and proliferating cell nuclear antigen, proteins known to regulate G(1) to S phase cell-cycle transitions. Expression of the activation-associated cell surface receptors CD25, CD28, CD120b and CD134 as well as production of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-4 (IL-4) and IL-5 is suppressed in response to proteasome inhibition in CD4(+) T cells activated by DCs. Expression of CD25, IFN-gamma, TNF-alpha, IL-4 and IL-5 is known to be mediated by the transcriptional activity of nuclear factor of activated T cells (NFAT), and we show here that proteasome inhibition suppresses activation and nuclear translocation of NFATc2 in activated CD4(+) T cells. Thus, the proteasome is required for essential immune functions of activated CD4(+) T cells and can be defined as a molecular target for the suppression of deregulated and unwanted T-cell-mediated immune responses.

Doxorubicin cardiomyopathy via TLR-2 stimulation: potential for prevention using current anti-retroviral inhibitors such as ritonavir and nelfinavir

Doxorubicin remains a useful anti-cancer drug but as lifetime dose approaches 500 mg/m2 and particularly when this dose is exceeded, iatrogenic life-threatening cardiomyopathy becomes progressively more likely. This note reviews evidence indicating that doxorubicin induced cardiomyopathy is partly mediated by stimulation of Toll-like receptors (TLR) 2 and 4 which are expressed on cardiomyocytes. Indinavir, nelfinavir, ritonavir, and saquinavir are currently marketed protease inhibitors used to suppress human immunodeficiency virus. They have recently been shown to inhibit signalling at TLR 2 and 4 as well as intracellular events downstream from these receptors. It is possible that these FDA-approved anti-retroviral protease inhibitors could be used off-label to diminish likelihood of doxorubicin cardiotoxicity permitting higher doxorubicin doses. We suggest that currently marketed anti-viral protease inhibitors be investigated in animal models of doxorubicin cardiomyopathy and if such studies do indeed show protection, human studies be initiated.

Bortezomib significantly impairs the immunostimulatory capacity of human myeloid blood dendritic cells

Bortezomib is a potent drug for the treatment of multiple myeloma. Its anti-tumor activity is mediated by proteasome inhibition leading to decreased cell proliferation and induction of apoptosis. However, an unimpaired proteasomal function plays a crucial role for the induction of anti-tumor immunity by dendritic cells (DCs), which are currently used for therapeutic vaccination against various tumors including myeloma. In the present study, we investigated the impact of bortezomib on the immunostimulatory capacity of 6-sulfo LacNAc (slan) DCs, which represent a major subset of human blood DCs. We demonstrated that this proteasome inhibitor efficiently impairs the spontaneous in vitro maturation of slanDCs and the release of tumor necrosis factor (TNF)-alpha as well as interleukin (IL)-12 upon lipopolysaccharide (LPS) stimulation. Functional data revealed that bortezomib profoundly inhibits slanDC-induced proliferation and differentiation of CD4(+) T cells. In addition, the capacity of slanDCs to promote interferon-gamma secretion and tumor-directed cytotoxicity of natural killer (NK) cells is markedly impaired by bortezomib. These results provide evidence that bortezomib significantly reduces the ability of native human blood DCs to regulate innate and adaptive anti-tumor immunity and may have implications for the design of therapeutic strategies combining DC vaccination and bortezomib treatment.

Liver X receptors regulate dendritic cell phenotype and function through blocked induction of the actin-bundling protein fascin

Liver X receptors (LXRs) are nuclear receptors regulating lipid and cholesterol metabolism. Recent data revealed a cross talk between LXR and Toll-like receptor signaling in macrophages, indicating a role in immunity. Here, we show that LXRalpha is expressed in human myeloid dendritic cells (DCs) and induced during differentiation of monocyte-derived DCs, whereas LXRbeta is expressed constitutively at a very low level. LXR activation by 2 different LXR agonists strongly interfered with lipopolysaccharide (LPS)-induced but not with CD40L-induced DC maturation by altering DC morphology and suppressing interleukin-12-but enhancing interleukin-10-secretion. LXR activation in DCs largely blocked their T-cell stimulatory ability despite essentially unaltered expression of various antigen-presenting and costimulatory molecules. Immunologic synapse formation was significantly inhibited by LXR activation along with a complete block in LPS- but not CD40L-induced expression of the actin-bundling protein fascin. Notably, overexpression of fascin in LXR agonist-treated DCs restored immunologic synapse formation and restored their ability to activate T cells. In conclusion, our data reveal LXR as a potent modulator of DC maturation and function mediated in part by blocking the expression of fascin. Due to the central position of DCs in immunity, LXRalpha could be a potential novel target for immunomodulation.

Dendritic cell maturation stage determines susceptibility to the proteasome inhibitor bortezomib

The proteasome inhibitor bortezomib has been used successfully in the treatment of non-Hodgkin lymphomas in humans, and in the treatment of graft versus host disease (GVHD) and autoimmune diseases in animal models. The mechanism of growth inhibition and immunosuppression is only partly understood. Here, we have evaluated the differential effect of bortezomib on human monocyte derived immature and mature dendritic cells (DCs) as the maturation stage of DCs determines their function. We found bortezomib to induce apoptotic cell death in immature DCs and to a much lesser extent, in mature DCs. Furthermore, cytokine-induced maturation of immature DCs was inhibited by bortezomib, whereas already matured DCs remained unaffected as seen by phenotype and allo-stimulatory capacity. This corresponded to a decreased NF-kappaB activity in immature DCs, whereas NF-kappaB activity of mature DCs was not affected. In conclusion, our data expand on previous reports on the effects of proteasome inhibitors on human monocyte-derived DCs by demonstrating a differential effect of bortezomib on immature versus mature DCs. Our findings suggest a potential role of bortezomib in modulating immune responses in humans through inhibition of DC maturation.

Proteasome inhibitors: antitumor effects and beyond

Proteasome inhibitors are emerging as effective drugs for the treatment of multiple myeloma and possibly certain subtypes of non-Hodgkin's lymphoma. Bortezomib (Velcade) is the first proteasome inhibitor proven to be clinically useful and will soon be followed by a second generation of small molecule inhibitors with improved pharmacological properties. Although it is now understood that certain types of malignancies have an exquisite dependence on a functional proteasome for their survival, the underlying reason(s) remain unclear as of now. In this context, addiction to nuclear factor-kappaB (NF-kappaB)-induced survival signals, activation of the unfolded protein response as well as a reduced proteasomal activity in differentiated plasma cells have all been proposed to justify proteasome inhibitors' activity in susceptible tissues. In addition to their anticancer properties, bortezomib and related drugs modulate inflammatory and immune responses by affecting function and survival of immune cells such as lymphocytes and dendritic cells. The present review offers an overview of the biological effects that have been involved in proteasome inhibitors' antitumor activity and suggests prospective future applications for these drugs based on their recently characterized anti-inflammatory and immunomodulatory effects.