Proteasome Inhibition to Maximize the Apoptotic Potential of Cytokine Therapy for Murine Neuroblastoma Tumors

Ubiquitination in the regulation of inflammatory cell death and cancer

The ubiquitin system is complex, multifaceted, and is crucial for the modulation of a vast number of cellular processes. Ubiquitination is tightly regulated at different levels by a range of enzymes including E1s, E2s, and E3s, and an array of DUBs. The UPS directs protein degradation through the proteasome, and regulates a wide array of cellular processes including transcription and epigenetic factors as well as key oncoproteins. Ubiquitination is key to the dynamic regulation of programmed cell death. Notably, the TNF signaling pathway is controlled by competing ubiquitin conjugation and deubiquitination, which governs both proteasomal degradation and signaling complex formation. In the inflammatory response, ubiquitination is capable of both activating and dampening inflammasome activation through the control of either protein stability, complex formation, or, in some cases, directly affecting receptor activity. In this review, we discuss the enzymes and targets in the ubiquitin system that regulate fundamental cellular processes regulating cell death, and inflammation, as well as disease consequences resulting from their dysregulation. Finally, we highlight several pre-clinical and clinical compounds that regulate ubiquitin system enzymes, with the aim of restoring homeostasis and ameliorating diseases.

Second-generation proteasome inhibitor carfilzomib sensitizes neuroblastoma cells to doxorubicin-induced apoptosis

Neuroblastoma (NB), which accounts for about 15% of cancer-related mortality in children, is the most common extracranial malignant neoplasm in children. Elevated level of proteasome activity promotes cancer development and the inhibition of proteasome activity is a promising strategy for cancer treatment. Therefore, targeting proteasome by small molecule inhibitors may be a viable option for NB therapy. Here in this study, we show that a novel proteasome inhibitor Carfilzomib (CFZ) exerts anti-tumor effect on NB. CFZ caused decreased cell viability and attenuated colony formation ability of a subset of NB cell lines. CFZ induced cell apoptosis in NB cells. Moreover, CFZ enhanced the cytotoxic effect of doxorubicin (Dox) on NB cells and Dox-induced p38 and JNK phosphorylation. In addition, CFZ inhibited Dox-induced NF-κB activation by stabilizing the protein level of IκBα. Furthermore, CFZ induced apoptosis and augmented Dox-induced apoptosis in NB tumor cells in orthotopic xenograft mouse models. In summary, our study suggests that proteasome is a therapeutic target in NB and proteasome inhibition by CFZ is a potential therapeutic strategy for treating NB patients.

Natural Killer Cell Response to Chemotherapy-Stressed Cancer Cells: Role in Tumor Immunosurveillance

Natural killer (NK) cells are innate cytotoxic lymphoid cells that actively prevent neoplastic development, growth, and metastatic dissemination in a process called cancer immunosurveillance. An equilibrium between immune control and tumor growth is maintained as long as cancer cells evade immunosurveillance. Therapies designed to kill cancer cells and to simultaneously sustain host antitumor immunity are an appealing strategy to control tumor growth. Several chemotherapeutic agents, depending on which drugs and doses are used, give rise to DNA damage and cancer cell death by means of apoptosis, immunogenic cell death, or other forms of non-apoptotic death (i.e., mitotic catastrophe, senescence, and autophagy). However, it is becoming increasingly clear that they can trigger additional stress responses. Indeed, relevant immunostimulating effects of different therapeutic programs include also the activation of pathways able to promote their recognition by immune effector cells. Among stress-inducible immunostimulating proteins, changes in the expression levels of NK cell-activating and inhibitory ligands, as well as of death receptors on tumor cells, play a critical role in their detection and elimination by innate immune effectors, including NK cells. Here, we will review recent advances in chemotherapy-mediated cellular stress pathways able to stimulate NK cell effector functions. In particular, we will address how these cytotoxic lymphocytes sense and respond to different types of drug-induced stresses contributing to anticancer activity.

Bortezomib augments lymphocyte stimulatory cytokine signaling in the tumor microenvironment to sustain CD8+T cell antitumor function

Tumor-induced immune tolerance poses a major challenge for therapeutic interventions aimed to manage cancer. We explored approaches to overcome T-cell suppression in murine breast and kidney adenocarcinomas, and lung fibrosarcoma expressing immunogenic antigens. We observed that treatment with a reversible proteasome inhibitor bortezomib (1 mg/kg body weight) in tumor-bearing mice significantly enhanced the expression of lymphocyte-stimulatory cytokines IL-2, IL-12, and IL-15. Notably, bortezomib administration reduced pulmonary nodules of mammary adenocarcinoma 4T1.2 expressing hemagglutinin (HA) model antigen (4T1HA) in mice. Neutralization of IL-12 and IL-15 cytokines with a regimen of blocking antibodies pre- and post-adoptive transfer of low-avidity HA518-526-specific CD8+T-cells following intravenous injection of 4T1HA cells increased the number of pulmonary tumor nodules. This neutralization effect was counteracted by the tumor metastasis-suppressing action of bortezomib treatments. In bortezomib-treated 4T1HA tumor-bearing mice, CD4+T-cells showed increased IL-2 production, CD11c+ dendritic cells showed increased IL-12 and IL-15 production, and HA-specific activated CD8+T-cells showed enhanced expression of IFNγ, granzyme-B and transcription factor eomesodermin. We also noted a trend of increased expression of IL-2, IL-12 and IL-15 receptors as well as increased phosphorylation of STAT5 in tumor-infiltrating CD8+T-cells following bortezomib treatment. Furthermore, bortezomib-treated CD8+T-cells showed increased phosphorylation of mitogen-activated protein kinase p38, and Akt, which was abrogated by phosphatidylinositide 3-kinase (PI3K) inhibitor. These data support the therapeutic potential of bortezomib in conjunction with other immunotherapies to augment the strength of convergent signals from CD8+T-cell signaling molecules including TCR, cytokine receptors and downstream PI3K/Akt/STAT5 pathways to sustain CD8+T-cell effector function in the tumor microenvironment.

Bortezomib Improves Adoptive T-cell Therapy by Sensitizing Cancer Cells to FasL Cytotoxicity

Cancer immunotherapy shows great promise but many patients fail to show objective responses, including in cancers that can respond well, such as melanoma and renal adenocarcinoma. The proteasome inhibitor bortezomib sensitizes solid tumors to apoptosis in response to TNF-family death ligands. Because T cells provide multiple death ligands at the tumor site, we investigated the effects of bortezomib on T-cell responses in immunotherapy models involving low-avidity antigens. Bortezomib did not affect lymphocyte or tissue-resident CD11c(+)CD8(+) dendritic cell counts in tumor-bearing mice, did not inhibit dendritic cell expression of costimulatory molecules, and did not decrease MHC class I/II-associated antigen presentation to cognate T cells. Rather, bortezomib activated NF-κB p65 in CD8(+) T cells, stabilizing expression of T-cell receptor CD3ζ and IL2 receptor-α, while maintaining IFNγ secretion to improve FasL-mediated tumor lysis. Notably, bortezomib increased tumor cell surface expression of Fas in mice as well as human melanoma tissue from a responsive patient. In renal tumor-bearing immunodeficient Rag2(-/-) mice, bortezomib treatment after adoptive T-cell immunotherapy reduced lung metastases and enhanced host survival. Our findings highlight the potential of proteasome inhibitors to enhance antitumor T-cell function in the context of cancer immunotherapy.

Synergistic Antivascular and Antitumor Efficacy with Combined Cediranib and SC6889 in Intracranial Mouse Glioma

Prognosis remains extremely poor for malignant glioma. Targeted therapeutic approaches, including single agent anti-angiogenic and proteasome inhibition strategies, have not resulted in sustained anti-glioma clinical efficacy. We tested the anti-glioma efficacy of the anti-angiogenic receptor tyrosine kinase inhibitor cediranib and the novel proteasome inhibitor SC68896, in combination and as single agents. To assess anti-angiogenic effects and evaluate efficacy we employed 4C8 intracranial mouse glioma and a dual-bolus perfusion MRI approach to measure K^trans, relative cerebral blood flow and volume (rCBF, rCBV), and relative mean transit time (rMTT) in combination with anatomical MRI measurements of tumor growth. While single agent cediranib or SC68896 treatment did not alter tumor growth or survival, combined cediranib/SC68896 significantly delayed tumor growth and increased median survival by 2-fold, compared to untreated. This was accompanied by substantially increased tumor necrosis in the cediranib/SC68896 group (p<0.01), not observed with single agent treatments. Mean vessel density was significantly lower, and mean vessel lumen area was significantly higher, for the combined cediranib/SC68896 group versus untreated. Consistent with our previous findings, cediranib alone did not significantly alter mean tumor rCBF, rCBV, rMTT, or K^trans. In contrast, SC68896 reduced rCBF in comparison to untreated, but without concomitant reductions in rCBV, rMTT, or K^trans. Importantly, combined cediranib/SC68896 substantially reduced rCBF, rCBV. rMTT, and K^trans. A novel analysis of K^trans/rCBV suggests that changes in K^trans with time and/or treatment are related to altered total vascular surface area. The data suggest that combined cediranib/SC68896 induced potent anti-angiogenic effects, resulting in increased vascular efficiency and reduced extravasation, consistent with a process of vascular normalization. The study represents the first demonstration that the combination of cediranib with a proteasome inhibitor substantially increases the anti-angiogenic efficacy produced from either agent alone, and synergistically slows glioma tumor growth and extends survival, suggesting a promising treatment which warrants further investigation.

Modulatory effects of bortezomib on host immune cell functions

Bortezomib is an inhibitor of the ubiquitin-proteasome proteolytic pathway responsible for intracellular protein turnover. Cellular proteins controlled by this pathway represent a diverse group of potential therapeutic targets, particularly in cancer cells, which exploit this proteasomal pathway to promote their growth and diminish apoptosis. Along with inhibiting the proteasome and thus sensitizing tumor cells to apoptosis, bortezomib may also have multiple effects on the host immune responses. This review summarizes the effects that bortezomib may play on immune cell subsets in various disease states in modifying lymphocyte receptors, ligands, the expression of various cytokines and chemokines and their downstream signaling. We also propose steps that can be taken to refine combinatorial strategies that include bortezomib to improve current immunotherapeutic approaches.

Powerful inner/outer controlled multi-target magnetic nanoparticle drug carrier prepared by liquid photo-immobilization

Nanomagnetic materials offer exciting avenues for advancing cancer therapies. Most researches have focused on efficient delivery of drugs in the body by incorporating various drug molecules onto the surface of nanomagnetic particles. The challenge is how to synthesize low toxic nanocarriers with multi-target drug loading. The cancer cell death mechanisms associated with those nanocarriers remain unclear either. Following the cell biology mechanisms, we develop a liquid photo-immobilization approach to attach doxorubicin, folic acid, tumor necrosis factor-α, and interferon-γ onto the oleic acid molecules coated Fe3O4 magnetic nanoparticles to prepare a kind of novel inner/outer controlled multi-target magnetic nanoparticle drug carrier. In this work, this approach is demonstrated by a variety of structural and biomedical characterizations, addressing the anti-cancer effects in vivo and in vitro on the HeLa, and it is highly efficient and powerful in treating cancer cells in a valuable programmed cell death mechanism for overcoming drug resistance.

Bortezomib antagonizes microtubule-interfering drug-induced apoptosis by inhibiting G2/M transition and MCL-1 degradation

Inhibition of the proteasome is considered as a promising strategy to sensitize cancer cells to apoptosis. Recently, we demonstrated that the proteasome inhibitor Bortezomib primes neuroblastoma cells to TRAIL-induced apoptosis. In the present study, we investigated whether Bortezomib increases chemosensitivity of neuroblastoma cells. Unexpectedly, we discover an antagonistic interaction of Bortezomib and microtubule-interfering drugs. Bortezomib significantly attenuates the loss of cell viability and induction of apoptosis on treatment with Taxol and different vinca alkaloids but not with other chemotherapeutics, that is, Doxorubicin and Cisplatinum. Importantly, Bortezomib inhibits G2/M transition by inhibiting proteasomal degradation of cell cycle regulatory proteins such as p21, thereby preventing cells to enter mitosis, the cell cycle phase in which they are most vulnerable to antitubulin chemotherapeutics. Consequently, Bortezomib counteracts Taxol-induced mitotic arrest and polyploidy, as shown by reduced expression of PLK1 and phosphorylated histone H3. In addition, Bortezomib antagonizes Taxol-mediated degradation of MCL-1 during mitotic arrest by preventing cells to enter mitosis and by inhibiting the proteasome. Downregulation of MCL-1 is critically required for Taxol-induced apoptosis, as overexpression of a phosphomutant MCL-1 variant, which is resistant to degradation, significantly diminishes Taxol-triggered apoptosis. Vice versa, attenuation of Bortezomib-mediated accumulation of MCL-1 by knockdown of MCL-1 significantly enhances Taxol/Bortezomib-induced apoptosis. Thus, Bortezomib rescues Taxol-induced apoptosis by inhibiting G2/M transition and mitigating MCL-1 degradation. The identification of this antagonistic interaction of Bortezomib and microtubule-targeted drugs has important implications for the design of Bortezomib-based combination therapies.

Characterization of the protein ubiquitination response induced by Doxorubicin

Doxorubicin is commonly considered to exert its anti-tumor activity by triggering apoptosis of cancer cells through DNA damage. Recent reports have shown that Doxorubicin elicits a marked heat shock response, and that either inhibition or silencing of heat shock proteins enhance the Doxorubicin apoptotic effect in neuroblastoma cells. In order to investigate whether Doxorubicin may also act through protein modification, we performed a proteomic analysis of ubiquitinated proteins. Here we show that nanomolar Doxorubicin treatment of neuroblastoma cells caused: (a) dose-dependent over-ubiquitination of a specific set of proteins in the absence of measurable inhibition of proteasome, (b) protein ubiquination patterns similar to those with Bortezomib, a proteasome inhibitor, (c) depletion and loss of activity of ubiquitinated enzymes such as lactate dehydrogenase and α-enolase, and (d) a decrease in HSP27 solubility, probably a consequence of its binding to denatured proteins. These data strongly reinforce the hypothesis that Doxorubicin may also exert its effect by damaging proteins.

Cell death in HeLa mediated by thermoplastic polyurethane with co-immobilized IFN-γ plus TNF-α

In order to prohibit the toxicity of free IFN-γ plus TNF-α in treating human cervical cancer HeLa cells, two kinds of thermoplastic polyurethane (polyester/polyether) biomaterials with co-immobilized IFN-γ plus TNF-α on the surfaces are prepared. The programmed cell death of HeLa induced by these biomaterials is investigated. The surface modification of these biomaterials with co-immobilized IFN-γ plus TNF-α is performed by the photo-immobilization method, and the surface structures are characterized by various techniques. The cell morphology, cell mortality, cell cycle arrest, and functional status of caspases, upon the treatment by these biomaterials, are characterized. The results show that the as-prepared biomaterials have high inhibition activity against the growth of HeLa cells. The HeLa cells mediated by the two kinds of biomaterials are mainly arrested in the G(1) phase, while those cells mediated directly by free IFN-γ plus TNF-α are mainly arrested in the S phase. It is suggested that the programmed cell death mechanism induced by these two kinds of biomaterials is both caspase-dependent and caspase-independent. Our data provide the knowledge of microscopic surface structures and cell biology basis for synthesizing the thermoplastic polyurethane biomaterials with co-immobilized IFN-γ plus TNF-α, which are promising for novel therapeutics (e.g. drug cup) design for cervical cancer patients.

Novel insights into the synergistic interaction of Bortezomib and TRAIL: tBid provides the link

The proteasome inhibitor Bortezomib has been identified as a potent enhancer of TRAIL-induced apoptosis in several human cancers. However, the identification of the underlying molecular mechanisms of this synergistic cell death induction has been ongoing over the last years. A recent study identifies a new mechanism of action for the synergism of TRAIL and Bortezomib.

Mode of action of epoxyphomalins A and B and characterization of related metabolites from the marine-derived fungus Paraconiothyrium sp

Epoxyphomalins A (1) and B (2) are highly potent cytotoxic fungal metabolites. During the course of purifying larger quantities of 1 and 2 from Paraconiothyrium sp. fermentation extracts, three new epoxyphomalins (3-5) were isolated and characterized, showing modifications to the oxidation pattern of the cyclohexene moiety or of C-9 of the decalin system. IC(50) values for cytotoxicity against a panel of 36 human tumor cell lines were determined for all new compounds. Compound 4 was found to be cytotoxic particularly toward prostate PC3M (IC(50) = 0.72 μM) and bladder BXF 1218 L (IC(50) = 1.43 μM) cancer cell lines. In addition, inhibition of chymotrypsin-, caspase-, and trypsin-like activity of purified 20S proteasomes was determined for epoxyphomalins A (1) and B (2). The results indicate that compounds 1 and 2 exert their cytotoxic effect through potent inhibition of the 20S proteasome.

Cylindrocyclophanes with proteasome inhibitory activity from the Cyanobacterium Nostoc sp

Material collected from a parkway in the city of Chicago afforded the isolation of a Nostoc species (UIC 10022A). The extract of this strain displayed significant inhibition of the 20S proteasome as well as antiproliferative activity against HT29, MCF7, NCI-H460, and SF268 cancer cell lines. A standardized dereplication protocol allowed for the rapid identification of three known (11-13) and nine new (1-9) chlorinated cylindrocyclophanes from less than 100 mg of organic extract. Scale-up isolation of 1-9 and 11-13 from a larger extract was guided by LC-UV-MS data. In addition, KBr enrichment of the culture media afforded the isolation of a brominated cylindrocyclophane (10). Biological evaluation of 1-5, 9, and 10-13 revealed a large range of activity against the 20S proteasome and allowed the determination of preliminary structure-activity relationships of the cylindrocyclophane pharmacophore.

Pharmacotherapy of neuroblastoma

IMPORTANCE OF THE FIELD

Neuroblastoma, a tumor of the sympathetic nervous system, is the most common extracranial solid tumor of early life. High risk disease in older children remains a therapeutic challenge, despite high-intensity therapy with correspondingly significant short- and long-term toxicities.

AREAS COVERED IN THIS REVIEW

We have reviewed therapy for neuroblastoma over the last three decades. This includes cytotoxic chemotherapy, immunotherapy, radionuclides, antiangiogenic compounds, and molecularly targeted agents. We provide a perspective on the incorporation of these drugs into therapy for neuroblastoma.

WHAT THE READER WILL GAIN

The reader will gain a better understanding of these novel agents and their targets in neuroblastoma. The reader will also gain insight into the need to define through sequential, carefully designed clinical trials, the roles and toxicities of these therapies, especially if the combination of targeted and conventional cytotoxic agents is used.

TAKE HOME MESSAGE

Advanced-stage neuroblastoma in older infants and children remains a disease that is difficult to cure. New, targeted agents may improve both the therapeutic index and the outcome, but are, for the most part, in early development and present a challenge for clinical trial design given both the rarity of this disease and its responsiveness (albeit incomplete) to currently used cytotoxic agents.

Proteasome inhibition causes regression of leukemia and abrogates BCR-ABL-induced evasion of apoptosis in part through regulation of forkhead tumor suppressors

BCR-ABL plays an essential role in the pathogenesis of chronic myeloid leukemia (CML) and some cases of acute lymphocytic leukemia (ALL). Although ABL kinase inhibitors have shown great promise in the treatment of CML, the persistence of residual disease and the occurrence of resistance have prompted investigations into the molecular effectors of BCR-ABL. Here, we show that BCR-ABL stimulates the proteasome-dependent degradation of members of the forkhead family of tumor suppressors in vitro, in an in vivo animal model, and in samples from patients with BCR-ABL-positive CML or ALL. As several downstream mediators of BCR-ABL are regulated by the proteasome degradation pathway, we also show that inhibition of this pathway, using bortezomib, causes regression of CML-like disease. Bortezomib treatment led to inhibition of BCR-ABL-induced suppression of FoxO proteins and their proapoptotic targets, tumor necrosis factor-related apoptosis-inducing ligand and BIM, thereby providing novel insights into the molecular effects of proteasome inhibitor therapy. We additionally show sensitivity of imatinib-resistant BCR-ABL T315I cells to bortezomib. Our data delineate the involvement of FoxO proteins in BCR-ABL-induced evasion of apoptosis and provide evidence that bortezomib is a candidate therapeutic in the treatment of BCR-ABL-induced leukemia.

The proteasome inhibitor bortezomib interacts synergistically with the histone deacetylase inhibitor suberoylanilide hydroxamic acid to induce T-leukemia/lymphoma cells apoptosis

Interactions between inhibitors of the proteasome and histone deacetylases have been examined in human T-leukemia/lymphoma cells both in vitro and in vivo. Co-exposure of cells to bortezomib and suberoylanilide hydroxamic acid (SAHA) synergistically induces T-leukemia/lymphoma cells to undergo apoptosis, consistent with a significant increase in mitochondrial injury and caspase activation. These events are accompanied by inhibition of cyto-protective signaling pathways, including the nuclear factor (NF)-kappaB, Raf-1/mitogen-induced extracellular kinase (MEK)/extracellular signal-related kinase (ERK) and AKT pathways, and activation of stress-related cascades, including the stress-activated kinases c-jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK). Moreover, bortezomib in conjunction with SAHA efficiently induces apoptosis of primary T-leukemia/lymphoma cells and inhibits tumor growth in a murine xenograft model established with subcutaneous injection of Jurkat cells. Taken together, these findings confirm the synergistic anti-tumor effect of the proteasome and histone deacetylase inhibitors, and provide an insight into the future clinical applications of bortezomib-SAHA combining regimen in treating T-cell malignancies.

Pediatric developmental therapies: interesting new drugs now in early-stage clinical trials

The current high cure rates for children diagnosed with cancer can be attributed in part to emphasis on large cooperative group clinical trials. The significant improvement in pediatric cancer survival over the past few decades is the result of optimized chemotherapy drug dosing, timing, and intensity; however, further alterations in traditional chemotherapy agents are unlikely to produce substantially better outcomes. Furthermore, there remains a subset of patients who have a very poor prognosis due to tumor type or stage at presentation, or who have a dismal prognosis with relapse or recurrence. As such, innovative approaches to therapy and new drugs are clearly needed for introduction into the current pediatric oncology arsenal. A variety of biologically targeted therapies that have shown promise in preclinical studies and early-phase adult clinical trials are now being explored in pediatric clinical trials. These novel agents hold the promise for continuing to drive forward improvements in patient survival, with potentially less toxicity than exists with traditional chemotherapy drugs.

Investigation of antimicrobial and protease-inhibitory activity from cultured cyanobacteria

A culture collection of cyanobacteria has been established at the University of Illinois at Chicago. This collection includes marine, terrestrial, and freshwater strains and contains representatives of the five orders of cyanobacteria: Chroococcales, Pleurocapsales, Oscillatoriales, Nostocales, and Stigonematales. In this study, extracts from a subset of 61 strains, 16 marine and 45 freshwater/terrestrial, were evaluated against three current protease targets, i.e. 20S proteasome and two SARS viral proteases, two important bacterial targets, i.e. Mycobacterium tuberculosis and Bacillus anthracis, and in the Artemia salina toxicity assay. In total, extracts of 12 strains possessed significant levels of activity in one or more targets. The overwhelming majority of active extracts (11 of 12) were from either freshwater or terrestrial forms of cyanobacteria, with the greater part of these (9 of 12) being heterocyst-forming strains. These results further support the use of cultured cyanobacteria as a source of biologically active natural products.

IFN-alpha and bortezomib overcome Bcl-2 and Mcl-1 overexpression in melanoma cells by stimulating the extrinsic pathway of apoptosis

We hypothesized that IFN-alpha would enhance the apoptotic activity of bortezomib on melanoma cells. Combined treatment with bortezomib and IFN-alpha induced synergistic apoptosis in melanoma and other solid tumor cell lines. Apoptosis was associated with processing of procaspase-3, procaspase-7, procaspase-8, and procaspase-9 and with cleavage of Bid and poly(ADP-ribose) polymerase. Bortezomib plus IFN-alpha was effective at inducing apoptosis in melanoma cells that overexpressed Bcl-2 or Mcl-1, suggesting that this treatment combination can overcome mitochondrial pathways of cell survival and resistance to apoptosis. The proapoptotic effects of this treatment combination were abrogated by a caspase-8 inhibitor, led to increased association of Fas and FADD before the onset of cell death, and were significantly reduced in cells transfected with a dominant-negative FADD construct or small interfering RNA targeting Fas. These data suggest that bortezomib and IFN-alpha act through the extrinsic pathway of apoptosis via FADD-induced caspase-8 activation to initiate cell death. Finally, bortezomib and IFN-alpha displayed statistically significant antitumor activity compared with either agent alone in both the B16 murine model of melanoma and in athymic mice bearing human A375 xenografts. These data support the future clinical development of bortezomib and IFN-alpha for malignant melanoma.

AKT pathway in neuroblastoma and its therapeutic implication

Neuroblastoma is a frequent pediatric tumor with a poor outcome in spite of aggressive treatment, even with autologous hematopoietic stem cell transplantation. The overall cure rate of 40% is unsatisfactory and new therapeutic strategies are urgently needed. AKT is a major mediator of survival signals that protect cells from apoptosis and regulate cell proliferation. The AKT signaling network is considered a key determinant of the biological aggressiveness of these tumors. In this article, the authors discuss the relation between activators of AKT in neuroblastoma, in particular, growth factors such as IGF-1, TRK, GDNF, VEGF and EGF, and their effects on tumoral proliferation, differentiation and apoptosis. Numerous other proteins interact with AKT in neuroblastoma. Several are relatively well characterized, such as PTEN and retinoic acid; others are new and potentially interesting, such as PKC and anaplastic lymphoma kinase. Specific inhibition of AKT has been studied, such as with LY249002, with significant effects on cell progression and apoptosis in tumoral cells. Moreover, a series of new drugs, such as geldanamycin and rapamycin, directly modify the expression of AKT in tumoral cells. Few specific inhibitors of AKT are available; less specific inhibitors are probably unsuitable therapeutic options in neuroblastoma. Drugs with a direct or indirect inhibitory effect on the AKT pathway, used alone or in combination with other drugs, seem to hold great promise as a new therapeutic modality in neuroblastoma.

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.

Bortezomib inhibits angiogenesis and reduces tumor burden in a murine model of neuroblastoma

BACKGROUND

Bortezomib is a proteasome inhibitor with pleiotropic antitumor activity. Here we investigate the antiangiogenic and antitumor efficacy of bortezomib against neuroblastoma both in vitro and in a murine model of localized and disseminated disease.

METHODS

In vitro activity of bortezomib was assessed by evaluating its effect on cell proliferation and cell cycle status. Localized tumor burden was followed with caliper measurements and total-body bioluminescence in mice with disseminated disease. The antiangiogenic activity was evaluated with immunohistochemistry and human vascular endothelial growth factor (VEGF) enzyme-linked immunosorbent assay on tumor protein extracts.

RESULTS

Bortezomib treatment resulted in dose and time-dependent decreases in cell proliferation and resulted in cell cycle arrest. In vivo, bortezomib restricted tumor growth in a model of localized disease and decreased bioluminescence in mice with disseminated disease. That decreased bioluminescence reflected decreased tumor burden was confirmed at necropsy by assessing disease in specific organs. In addition, treatment resulted in a decrease in intratumoral vessel counts and reduced tumor VEGF expression.

CONCLUSION

Bortezomib shows significant activity against neuroblastoma in vitro, and it inhibits tumor growth and angiogenesis in vivo. These results suggest that clinical studies of bortezomib are warranted for the treatment of this difficult disease.