Effect of bortezomib on human neuroblastoma: analysis of molecular mechanisms involved in cytotoxicity

Spatial sequestration of activated-caspase 3 in aggresomes mediates resistance of neuroblastoma cell to bortezomib treatment

Neuroblastoma (NB) is the most common pediatric tumor and is currently treated by several types of therapies including chemotherapies, such as bortezomib treatment. However, resistance to bortezomib is frequently observed by mechanisms that remain to be deciphered. Bortezomib treatment leads to caspase activation and aggresome formation. Using models of patients-derived NB cell lines with different levels of sensitivity to bortezomib, we show that the activated form of caspase 3 accumulates within aggresomes of NB resistant cells leading to an impairment of bortezomib-induced apoptosis and increased cell survival. Our findings unveil a new mechanism of resistance to chemotherapy based on an altered subcellular distribution of the executioner caspase 3. This mechanism could explain the resistance developed in NB patients treated with bortezomib, emphasizing the potential of drugs targeting aggresomes.

Purification, characterization and biological functions of metalloprotein isolated from haemolymph of mud crab Scylla serrata (Forskal, 1775)

In recent years, an enormous number of naturally occurring biological macromolecules has been reported worldwide due to its antibacterial and anticancerous potential. Among them, in this study, the copper containing respiratory protein namely haemocyanin (HC) was isolated from the haemolymph of mud crab Scylla serrata. The isolated metalloprotein HC was purified using Sepharose column by gel filtration chromatography. The purified HC was separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and molecular weight of the protein was identified as 95 kDa. Fourier transform infrared spectrophotometer (FT-IR) and nuclear magnetic resonance (¹H NMR) spectral data revealed the presence of amino acid constituents. Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis based mass ion search exposed that the purified protein was HC. HC exhibited an in vitro bacteriostatic effects against the bacterial pathogens and also elevated ROS levels in the treated samples. The half maximal (50%) inhibitory concentration (IC₅₀) of HC was found to be 80 μg/mL against lung cancer cells (A549). Our study collectively addressed the potential antibacterial and anti-cancerous activity of HC. The results obtained from this study suggest that HC can be used for therapeutical application in the near future.

Inhibition of Ubiquitin-Specific Protease 14 Suppresses Cell Proliferation and Synergizes with Chemotherapeutic Agents in Neuroblastoma

Neuroblastoma is the most common extracranial malignant solid tumor in children, and drug resistance is a major reason for poor outcomes. Elevated proteasome activity plays an important role in neuroblastoma tumor development and resistance to conventional chemotherapy. Ubiquitin-specific protease 14 (USP14), one of three deubiquitinases associated with the regulatory subunit of the proteasome, is emerging as a potential therapeutic target in multiple tumor types. However, the role of USP14 in neuroblastoma is yet to be elucidated. We found that USP14 inhibition in neuroblastoma via knockdown or a specific inhibitor such as b-AP15 suppressed cell proliferation by inducing cell apoptosis. Furthermore, b-AP15 significantly inhibited neuroblastoma tumor growth in NGP and SH-SY5Y xenograft mouse models. For combination treatment, b-AP15 plus conventional chemotherapeutic agents such as doxorubicin or VP-16 resulted in synergistic antitumor effects on neuroblastoma. Our study demonstrates that USP14 is required for cell viability and is a novel therapeutic target in neuroblastoma. Moreover, USP14 inhibition may add value in combination therapy due to its powerful synergistic effects in treating neuroblastoma.

POH1 Knockdown Induces Cancer Cell Apoptosis via p53 and Bim

The ubiquitin-proteasome system is implicated in cell apoptosis that is frequently dysregulated in human cancers. POH1/rpn11/PSMD14, as a part of the 19S proteasomal subunit, contributes to the progression of malignancy, but its role in apoptosis remains unclear. Here, we showed that POH1 expression was increased and associated with poor outcomes in three independent cohorts of patients with hepatocellular carcinoma (HCC), esophageal cancer (EC), and colorectal cancer (CRC). The knockdown of POH1 significantly inhibited tumor cell proliferation and induced apoptosis mediated by the mitochondrial pathway in vitro. Intratumoral injection of POH1 small interfering RNA (siRNA) significantly reduced the progression of tumor growth and induced apoptosis in vivo. Furthermore, p53 or Bim siRNA markedly attenuated the apoptosis induced by POH1 depletion. POH1 depletion resulted in cell apoptosis by increasing the stability of p53 and Bim and inhibiting their ubiquitination. Overall, POH1 knockdown induced cell apoptosis through increased expression of p53 and Bim via enhanced protein stability and attenuated degradation. Thus, POH1 may serve as a potential prognostic marker and therapeutic target in human cancers.

Microenvironment-Driven Shift of Cohesion/Detachment Balance within Tumors Induces a Switch toward Metastasis in Neuroblastoma

Neuroblastoma (NB) is a childhood cancer arising from sympatho-adrenal neural crest cells. Disseminated forms have high frequency of multiple tumoral foci whose etiology remains unknown; NB embryonic origin limits investigations in patients and current models. We developed an avian embryonic model driving human NB tumorigenesis in tissues homologous to patients. We found that aggressive NBs display a metastatic mode, secondary dissemination via peripheral nerves and aorta. Through tumor transcriptional profiling, we found that NB dissemination is induced by the shutdown of a pro-cohesion autocrine signal, SEMA3C, which constrains the tumoral mass. Lowering SEMA3C levels shifts the balance toward detachment, triggering NB cells to collectively evade the tumor. Together with patient cohort analysis, this identifies a microenvironment-driven pro-metastatic switch for NB.

The mitochondrial apoptotic pathway is induced by Cu(II) antineoplastic compounds (Casiopeínas®) in SK-N-SH neuroblastoma cells after short exposure times

The family of Copper(II) coordination compounds Casiopeínas^® (Cas) has shown antiproliferative activity in several tumour lines by oxidative cellular damage and mitochondrial dysfunction that lead to cell death through apoptotic pathways. The goal of this work is looking for the functional mechanism of CasIIgly, CasIIIia and CasIIIEa in neuroblastoma metastatic cell line SK-N-SH, a paediatric extra-cranial tumour which is refractory to several anti-carcinogenic agents. All Cas have shown higher antiproliferative activity than cisplatin (IC₅₀ = 123 μM) with IC₅₀ values of 18, 22 and 63 µM for CasIIgly, CasIIIEa and CasIIIia, respectively. At low concentrations and early times (4 h), these compounds cause a disruption of the mitochondrial transmembrane potential (Δψm). Concomitantly, an important depletion of intracellular glutathione and an increase of reactive oxygen species (ROS) hydrogen peroxide and radical superoxide were observed. On the other side, the lower cytotoxic effect of Casiopeínas on cultures of human peripheral blood lymphocytes (IC_50CasIIgly  = 1720 µM, IC_{50 CasIIIEa}  = 3860 µM and IC_{50 CasIIIia}  = 4700 µM) show the selectivity of these compounds over the tumour cells compared with the non-transformed cells. Chemically, glutathione (GSH) interacts with Casiopeínas^® through the coordination of sulphur atom to the metal centre, process which facilitates the electron transfer to get Cu(I), GSSG and the posterior production of ROS. Additionally, the molecular structure of CasIIIia as nitrate is reported. These results have shown that the anticarcinogenic activity of Casiopeínas^® on neuroblastoma SK-N-SH is through mitochondrial apoptosis due to the enhanced pro-oxidant environment promoted by the presence of the coordination copper compounds.

Integrative omics reveals MYCN as a global suppressor of cellular signalling and enables network-based therapeutic target discovery in neuroblastoma

Despite intensive study, many mysteries remain about the MYCN oncogene's functions. Here we focus on MYCN's role in neuroblastoma, the most common extracranial childhood cancer. MYCN gene amplification occurs in 20% of cases, but other recurrent somatic mutations are rare. This scarcity of tractable targets has hampered efforts to develop new therapeutic options. We employed a multi-level omics approach to examine MYCN functioning and identify novel therapeutic targets for this largely un-druggable oncogene. We used systems medicine based computational network reconstruction and analysis to integrate a range of omic techniques: sequencing-based transcriptomics, genome-wide chromatin immunoprecipitation, siRNA screening and interaction proteomics, revealing that MYCN controls highly connected networks, with MYCN primarily supressing the activity of network components. MYCN's oncogenic functions are likely independent of its classical heterodimerisation partner, MAX. In particular, MYCN controls its own protein interaction network by transcriptionally regulating its binding partners.

Our network-based approach identified vulnerable therapeutically targetable nodes that function as critical regulators or effectors of MYCN in neuroblastoma. These were validated by siRNA knockdown screens, functional studies and patient data. We identified β-estradiol and MAPK/ERK as having functional cross-talk with MYCN and being novel targetable vulnerabilities of MYCN-amplified neuroblastoma. These results reveal surprising differences between the functioning of endogenous, overexpressed and amplified MYCN, and rationalise how different MYCN dosages can orchestrate cell fate decisions and cancerous outcomes. Importantly, this work describes a systems-level approach to systematically uncovering network based vulnerabilities and therapeutic targets for multifactorial diseases by integrating disparate omic data types.

Tideglusib induces apoptosis in human neuroblastoma IMR32 cells, provoking sub-G0/G1 accumulation and ROS generation

Neuroblastoma is the most common tumor amongst children amounting to nearly 15% of cancer deaths. This cancer is peculiar in its characteristics, exhibiting differentiation, maturation and metastatic transformation leading to poor prognosis and low survival rates among children. Chemotherapy, though toxic to normal cells, has shown to improve the survival of the patient with emphasis given more towards targeting angiogenesis. Recently, Tideglusib was designed as an 'Orphan Drug' to target the neurodegenerative Alzheimer's disease and gained significant momentum in its function during clinical trials. Duffy et al. recently reported a reduction in cell viability of human IMR32 neuroblastoma cells when treated with Tideglusib at varying concentrations. We investigated the effects of Tideglusib, at various concentrations, compared to Lithium chloride at various concentrations, on IMR32 cells. Lithium, a known GSK-3 inhibitor, was used as a standard to compare the efficiency of Tideglusib in a dose-dependent manner. Cell viability was assessed by MTT assay. The stages of apoptosis were evaluated by AO/EB staining and nuclear damage was determined by Hoechst 33258 staining. Reactive oxygen species (ROS) and mitochondrial membrane potential (ΔΨm) were assessed by DCFDA dye and Rhodamine-123 dye, respectively. Tideglusib reported a significant dose-dependent increase in pro-apoptotic proteins (PARP, Caspase-9, Caspase-7, Caspase-3) and tumor-related genes (FasL, TNF-α, Cox-2, IL-8, Caspase-3). Anti-GSK3 β, pGSK3 β, Bcl-2, Akt-1, p-Akt1 protein levels were observed with cells exposed to Tideglusib and Lithium chloride. No significant dose-dependent changes were observed for the mRNA expression of collagenase MMP-2, the tumor suppressor p53, or the cell cycle protein p21. Our study also reports Tideglusib reducing colony formation and increasing the level of sub-G0/G1 population in IMR32 cells. Our investigations report the significance of Tideglusib as a promising apoptotic inducer in human neuroblastoma IMR32 cells. Our study also reports that LiCl reduced cell viability in IMR32 cells inducing apoptosis mediated by ROS generation.

Loss of lysosome-associated membrane protein 3 (LAMP3) enhances cellular vulnerability against proteasomal inhibition

The family of lysosome-associated membrane proteins (LAMP) includes the ubiquitously expressed LAMP1 and LAMP2, which account for half of the proteins in the lysosomal membrane. Another member of the LAMP family is LAMP3, which is expressed only in certain cell types and differentiation stages. LAMP3 expression is linked with poor prognosis of certain cancers, and the locus where it is encoded was identified as a risk factor for Parkinson's disease (PD). Here, we investigated the role of LAMP3 in the two main cellular degradation pathways, the proteasome and autophagy. LAMP3 mRNA was not detected in mouse models of PD or in the brain of human patients. However, it was strongly induced upon proteasomal inhibition in the neuroblastoma cell line SH-SY5Y. Induction of LAMP3 mRNA following proteasomal inhibition was dependent on UPR transcription factor ATF4 signaling and induced autophagic flux. Prevention of LAMP3 induction enhanced apoptotic cell death. In summary, these data demonstrate that LAMP3 regulation as part of the UPR contributes to protein degradation and cell survival during proteasomal dysfunction. This link between autophagy and the proteasome may be of special importance for the treatment of tumor cells with proteasomal inhibitors.

The naturally born fusariotoxin enniatin B and sorafenib exert synergistic activity against cervical cancer in vitro and in vivo

During the last decades substantial progress has been made in developing systemic cancer therapy. However, tumors are frequently intrinsically resistant against structurally and mechanistically unrelated drugs. Thus, it is of predominant interest to overcome drug resistance and to encourage the research for novel chemotherapeutic approaches. Recently, we have introduced enniatins, naturally occurring cyclohexadepsipeptides produced by filamentous fungi of the genus Fusarium, as potential anticancer drugs. Here, we expend this approach by demonstrating antiangiogenic properties for enniatin B (Enn B) indicated by a strong inhibition of human endothelial cell migration and tube formation. Moreover, combination of Enn B with the clinically approved multi-kinase inhibitor sorafenib (Sora) displayed profound synergistic in vitro and in vivo anticancer effects against cervical cancer. Subsequent studies showed that this strong synergism is accompanied by a marked increase in mitochondrial injury and apoptosis induction reflected by mitochondrial membrane depolarization, caspase-7 activation, and subsequent cleavage of PARP. Additionally, cells were shown to stop DNA synthesis and accumulate in S and G2/M phase of the cell cycle. The multifaceted characteristics underlying this strong synergism were suggested to be based on interference with the p38 MAPK as well as the ERK signaling pathways. Finally, also in vivo studies revealed that the combination treatment is distinctly superior to single drug treatments against the KB-3-1 cervix carcinoma xenograft model. Taken together, our data confirm the anticancer benefits of the naturally occurring fusariotoxin Enn B and further present Enn B/Sora as a novel combination strategy especially for the treatment of cervical cancer.

Bortezomib-induced unfolded protein response increases oncolytic HSV-1 replication resulting in synergistic antitumor effects

BACKGROUND

Bortezomib is an FDA-approved proteasome inhibitor, and oncolytic herpes simplex virus-1 (oHSV) is a promising therapeutic approach for cancer. We tested the impact of combining bortezomib with oHSV for antitumor efficacy.

EXPERIMENTAL DESIGN

The synergistic interaction between oHSV and bortezomib was calculated using Chou-Talalay analysis. Viral replication was evaluated using plaque assay and immune fluorescence. Western blot assays were used to evaluate induction of estrogen receptor (ER) stress and unfolded protein response (UPR). Inhibitors targeting Hsp90 were utilized to investigate the mechanism of cell killing. Antitumor efficacy in vivo was evaluated using subcutaneous and intracranial tumor xenografts of glioma and head and neck cancer. Survival was analyzed by Kaplan-Meier curves and two-sided log-rank test.

RESULTS

Combination treatment with bortezomib and oHSV (34.5ENVE), displayed strong synergistic interaction in ovarian cancer, head and neck cancer, glioma, and malignant peripheral nerve sheath tumor (MPNST) cells. Bortezomib treatment induced ER stress, evident by strong induction of Grp78, CHOP, PERK, and IRE1α (Western blot analysis) and the UPR (induction of hsp40, 70, and 90). Bortezomib treatment of cells at both sublethal and lethal doses increased viral replication (P < 0.001), but inhibition of Hsp90 ablated this response, reducing viral replication and synergistic cell killing. The combination of bortezomib and 34.5ENVE significantly enhanced antitumor efficacy in multiple different tumor models in vivo.

CONCLUSIONS

The dramatic synergy of bortezomib and 34.5ENVE is mediated by bortezomib-induced UPR and warrants future clinical testing in patients.

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.

Targeting neuroblastoma stem cells with retinoic acid and proteasome inhibitor

Background

Neuroblastma cell lines contain a side-population of cells which express stemness markers. These stem-like cells may represent the potential underlying mechanism for resistance to conventional therapy and recurrence of neuroblastoma in patients.

Methodology/Principal Findings

To develop novel strategies for targeting the side-population of neurobastomas, we analyzed the effects of 13-cis-retinoic acid (RA) combined with the proteasome inhibitor MG132. The short-term action of the treatment was compared with effects after a 5-day recovery period during which both chemicals were withdrawn. RA induced growth arrest and differentiation of SH-SY5Y and SK-N-BE(2) neuroblastoma cell lines. Inhibition of the proteasome caused apoptosis in both cell lines, thus, revealing the critical role of this pathway in the regulated degradation of proteins involved in neuroblastoma proliferation and survival. The combination of RA with MG132 induced apoptosis in a dose-dependent manner, in addition to promoting G2/M arrest in treated cultures. Interestingly, expression of stem cell markers such as Nestin, Sox2, and Oct4 were reduced after the recovery period of combined treatment as compared with untreated cells or treated cells with either compound alone. Consistent with this, neurosphere formation was significantly impaired by the combined treatment of RA and MG132.

Conclusions

Given that stem-like cells are associated with resistant to conventional therapy and are thought to be responsible for relapse, our results suggest that dual therapy of RA and proteasome inhibitor might be beneficial for targeting the side-population of cells associated residual disease in high-risk neuroblastoma.

BAK and NOXA are critical determinants of mitochondrial apoptosis induced by bortezomib in mesothelioma

Based on promising preclinical efficacy associated with the 20S proteasome inhibitor bortezomib in malignant pleural mesothelioma (MPM), two phase II clinical trials have been initiated (EORTC 08052 and ICORG 05–10). However, the potential mechanisms underlying resistance to this targeted drug in MPM are still unknown. Functional genetic analyses were conducted to determine the key mitochondrial apoptotic regulators required for bortezomib sensitivity and to establish how their dysregulation may confer resistance. The multidomain proapoptotic protein BAK, but not its orthologue BAX, was found to be essential for bortezomib-induced apoptosis in MPM cell lines. Immunohistochemistry was performed on tissues from the ICORG-05 phase II trial and a TMA of archived mesotheliomas. Loss of BAK was found in 39% of specimens and loss of both BAX/BAK in 37% of samples. However, MPM tissues from patients who failed to respond to bortezomib and MPM cell lines selected for resistance to bortezomib conserved BAK expression. In contrast, c-Myc dependent transactivation of NOXA was abrogated in the resistant cell lines. In summary, the block of mitochondrial apoptosis is a limiting factor for achieving efficacy of bortezomib in MPM, and the observed loss of BAK expression or NOXA transactivation may be relevant mechanisms of resistance in the clinic.

Effect of bortezomib in combination with cisplatin and 5‑fluorouracil on 4T1 breast cancer cells

Bortezomib is a highly selective and reversible inhibitor of the 26S proteasome. It has been approved for the treatment of patients with relapsed and refractory multiple myeloma. A number of studies have been conducted to evaluate the activity and safety of bortezomib either alone or in combination with several cytotoxic agents and radiation. In the current study, the efficacy of bortezomib alone or in combination with cisplatin and 5‑fluorouracil was evaluated in 4T1 breast cancer cells, a highly metastatic murine cancer cell line. Using MTT assay, IC50 values of cisplatin and 5‑fluorouracil were determined to be 14.2 and 8.9 µM for cisplatin and 5‑fluorouracil, respectively. The effects of different concentrations of cisplatin and 5‑fluorouracil in combination with two different concentrations of bortezomib were examined in the 4T1 cells. Statistically significant differences were found when 1 or 5 µM cisplatin was combined with 10 or 50 nM bortezomib. Similarly, 1 µM 5‑fluorouracil or 5 µM 5‑fluorouracil in combination with 10 nM bortezomib caused significant cell death as compared to treatment with single agents. However, 1 or 5 µM 5‑fluorouracil did not potentiate the effects of higher concentrations of bortezomib (50 nM). The effect of the combination of cisplatin, 5‑fluorouracil and bortezomib was determined by soft agar assay. It was confirmed that a combination of cisplatin and bortezomib was more effective than each drug as a monotherapy. Therefore, the combination of cisplatin and bortezomib should be tested further in clinical settings.

The p53-independent induction of apoptosis in breast cancer cells in response to proteasome inhibitor bortezomib

An important hallmark of cancer cells is acquired resistance toward apoptosis. The apoptotic pathway is the most well-defined cell death program and is characterized by several morphological and biochemical features. The tumor suppressor protein p53 is a critical regulator of apoptosis in many cell types. p53 stimulates a wide network of signals that act through either extrinsic or intrinsic pathways of apoptosis. However, a number of studies have shown that apoptosis can be induced in a p53-independent manner as well. In this study, we examined the mechanism of apoptosis in p53-null breast cancer cells in response to the proteasome inhibitor bortezomib. Initially, we determined the p53 status of 4T1 breast carcinoma and 4THMpc (a highly mestatic derivative of 4T1) cells and verified that both cells are p53 deficient. It was subsequently shown that apoptosis can be induced in both cells in a dose-dependent manner in response to bortezomib treatment, based on DNA fragmentation evidence. Western blot analyses of ubiquitin-protein conjugates additionally showed that the proteasome is potently inhibited by bortezomib in p53-null 4T1 and 4THMpc cells. The results presented in the current study also show that caspase-3 is significantly activated in response to the treatment with bortezomib, implying that induction of apoptosis in these p53-deficient cells is occurring via caspase-3. The additional results presented here suggest that the pro-apoptotic proteins Bad, Noxa, and Puma are not critical regulators of apoptosis induction in p53-null 4T1 and 4THMpc cells. Similarly, there was no difference in the expression level of Mcl-1 in treated cells, suggesting that this anti-apoptotic protein is also uninvolved in the apoptotic response resulting from bortezomib treatment. In contrast, a very significant upregulation of the anti-apoptotic protein Hsp25/27 was detected in these p53-deficient cells after treatment with bortezomib. If the increased expression of Hsp25/27 protein levels are muting the apoptotic effects of the bortezomib treatment, then the apoptosis-inducing effects of such proteasome inhibitors might be increased with approaches simultaneously inhibiting Hsp25/27 protein in p53-deficient cells.

HSPA2 overexpression protects V79 fibroblasts against bortezomib-induced apoptosis

Human HSPA2 is a member of the HSPA (HSP70) family of heat-shock proteins, encoded by the gene originally described as testis-specific. Recently, it has been reported that HSPA2 can be also expressed in human somatic tissues in a cell-type specific manner. The aim of the present study was to find out whether HSPA2 can increase the resistance of somatic cells to the toxic effect of heat shock, proteasome inhibitors, and several anticancer cytostatics. We used a Chinese hamster fibroblast V79 cell line because these cells do not express the HSPA2 and cytoprotective HSPA1 proteins under normal culture conditions and show limited ability to express HSPA1 in response to heat shock and proteasome inhibitors. We established, by retroviral gene transfer, a stable V79/HSPA2 cell line, which constitutively overexpressed HSPA2 protein. The major observation of our study was that HSPA2 increased long-term survival of cells subjected to heat shock and proteasome inhibitors. We found, that HSPA2 confers resistance to bortezomib-induced apoptosis. Thus, we showed for the first time that in somatic cells HSPA2 can be a part of a system protecting cells against cytotoxic stimuli inducing proteotoxic stress.

Synergistic effects of combination treatment with bortezomib and doxorubicin in human neuroblastoma cell lines

BACKGROUND

Neuroblastoma (NB) is the most common extracranial solid tumor in infants. Currently, the mainstay of NB chemotherapy is combination treatment with some traditional drugs, but these combination regimens are always inefficient.

METHODS

The aim of this study was to evaluate the inhibitory effect of a combination of doxorubicin and bortezomib, a novel anticancer drug and the first prote-asome inhibitor approved for the treatment of human malignant tumors, on the proliferation of two human NB cell lines, SK-N-SH and SH-SY5Y. The general mechanism underlying this combined effect was also investigated. Synergistic inhibitory effects on human NB cell proliferation were evaluated using the median-effect principle. The pro-apoptotic effects of these drugs were evaluated using double staining with annexin-V-FITC and propidium iodide.

RESULTS

Synergistic inhibitory effects on proliferation were observed when a combination of bortezomib and doxorubicin was applied to cultured NB cells. A similar synergistic effect on apoptosis was also observed when the two drugs were used concurrently, which suggested that the possible mechanism underlying the observed synergistic inhibitory effect might be related to apoptosis.

CONCLUSION

The combination of bortezomib and doxorubicin appears to be a promising strategy to treat NB.

Inducible hsp70 in the regulation of cancer cell survival: analysis of chaperone induction, expression and activity

Understanding the mechanisms that control stress is central to realize how cells respond to environmental and physiological insults. All the more important is to reveal how tumour cells withstand their harsher growth conditions and cope with drug-induced apoptosis, since resistance to chemotherapy is the foremost complication when curing cancer. Intensive research on tumour biology over the past number of years has provided significant insights into the molecular events that occur during oncogenesis, and resistance to anti-cancer drugs has been shown to often rely on stress response and expression of inducible heat shock proteins (HSPs). However, with respect to the mechanisms guarding cancer cells against proteotoxic stresses and the modulatory effects that allow their survival, much remains to be defined. Heat shock proteins are molecules responsible for folding newly synthesized polypeptides under physiological conditions and misfolded proteins under stress, but their role in maintaining the transformed phenotype often goes beyond their conventional chaperone activity. Expression of inducible HSPs is known to correlate with limited sensitivity to apoptosis induced by diverse cytotoxic agents and dismal prognosis of several tumour types, however whether cancer cells survive because of the constitutive expression of heat shock proteins or the ability to induce them when adapting to the hostile microenvironment remains to be elucidated. Clear is that tumours appear nowadays more "addicted" to heat shock proteins than previously envisaged, and targeting HSPs represents a powerful approach and a future challenge for sensitizing tumours to therapy. This review will focus on the anti-apoptotic role of heat shock 70kDa protein (Hsp70), and how regulatory factors that control inducible Hsp70 synthesis, expression and activity may be relevant for response to stress and survival of cancer cells.

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.

Pharmacologic management of high-risk neuroblastoma in children

Neuroblastoma is the most common extracranial solid tumor of childhood. It accounts for 15% of pediatric cancer deaths. Children with high-risk disease have a 3-year event-free survival rate of only 20%. Chemotherapy is the mainstay of treatment in children with advanced neuroblastoma. The aim of this article was to review and critically evaluate the pharmacotherapy of neuroblastoma, using peer reviewed and review literature from 2000-11. All peer reviewed, published human subject studies of therapy for neuroblastoma in children were included. Animal model and in vitro studies were included only if they added to the understanding of the mechanism of a proposed or existing human neuroblastoma therapy. Current therapeutic options for neuroblastoma involve insufficient differentiation of normal from neoplastic tissue. Critically needed new approaches will increasingly exploit targeting of therapy for unique characteristics of the neuroblastoma cell. Pharmacotherapy for neuroblastoma still suffers from an inadequate therapeutic window. Enhancement of toxicity for tumor and safety for normal tissues will entail innovation in targeting neuroblastoma cells and rescuing or protecting normal tissue elements.

Snake venom toxin inhibits cell growth through induction of apoptosis in neuroblastoma cells

Snake venom toxin from Vipera lebetina turanica can induce apoptosis in many cancer cell lines, but there is no study about the apoptotic effect of snake venom toxin on human neuroblastoma cells. In this study, we investigated the apoptotic effect of snake venom toxin in human neuroblastoma SK-N-MC and SK-N-SH cells. Our result showed that cell detachment and apoptotic cell death were increased by snake venom toxin (1.25-10 microg/mL), but normal neuronal cells were not affected. Consistent with the induction of apoptosis, the level of reactive oxygen species (ROS) was increased, but mitochondrial membrane potential (MMP) was disrupted by treatment with snake venom toxin. However, the glutathione prevented snake venom toxin-induced cell growth inhibition. Snake venom toxin also increased the expression of pro-apoptotic protein Bax, but down-regulated anti-apoptotic protein Bcl-2. Therefore, these results showed that snake venom toxin from Vipera lebetina turanica causes apoptotic cell death of neuroblastoma cells through ROS dependent MMP disruption, and suggested that snake venom toxin may be applicable as an anti-cancer agent for neuroblastoma.

Triptolide therapy for neuroblastoma decreases cell viability in vitro and inhibits tumor growth in vivo

BACKGROUND

Heat shock protein (Hsp)-70 is overexpressed in several human malignancies, and its inhibition has been shown to kill cancer cells. Our objectives were to assess the effectiveness of triptolide, an Hsp-70 inhibitor, in treating neuroblastoma in vitro and in vivo, and to measure the associated effects on Hsp-70 levels and apoptosis markers.

METHODS

After exposing N2a and SKNSH cell lines to triptolide, cell viability was assessed. Caspase-3 and -9 activities were measured and annexin staining performed to determine if cell death occurred via apoptosis. Hsp-70 protein and mRNA levels were determined using Western blot and real-time polymerase chain reaction. In an orthotopic tumor model, mice received daily triptolide injections and were humanely killed at study completion with tumor measurement.

RESULTS

Triptolide treatment resulted in dose- and time-dependent N2a cell death and dose-dependent SKNSH killing. Triptolide exposure was associated with dose-dependent increases in caspase activity and annexin staining. Triptolide decreased Hsp-70 protein and mRNA levels in a dose-dependent fashion. Mice receiving triptolide therapy had significantly smaller tumors than controls.

CONCLUSION

Triptolide therapy decreased neuroblastoma cell viability in vitro and inhibited tumor growth in vivo. Our studies suggest that triptolide killed cells via apoptosis and in association with inhibition of Hsp-70 expression. Triptolide may provide a novel therapy for neuroblastoma.

New therapeutic targets for the treatment of high-risk neuroblastoma

High-risk neuroblastoma remains a major problem in pediatric oncology, accounting for 15% of childhood cancer deaths. Although incremental improvements in outcome have been achieved with the intensification of conventional chemotherapy agents and the addition of 13-cis-retinoic acid, only one-third of children with high-risk disease are expected to be long-term survivors when treated with current regimens. In addition, the cost of cure can be quite high, as surviving children remain at risk for additional health problems related to long-term toxicities of treatment. Further advances in therapy will require the targeting of tumor cells in a more selective and efficient way so that survival can be improved without substantially increasing toxicity. In this review we summarize ongoing clinical trials and highlight new developments in our understanding of the molecular biology of neuroblastoma, emphasizing potential targets or pathways that may be exploitable therapeutically.

An alternative in vivo system for testing angiogenic potential of human neuroblastoma cells

In this study we purposed an alternative method to study the angiogenic and invasive potential of neuroblastoma cell suspensions implanted on the chick embryo chorioallantoic membrane (CAM) surface. Neuroblastoma cells were seeded in Matrigel and thereafter the suspension was pipetted onto the CAM surface at day 8 of incubation inside a silicon ring previously loaded onto the CAM surface. Four days after implantation, the silicon ring was removed and the angiogenic and invasive response were studied morphologically at macroscopic and microscopic levels and by reverse transcriptase-polymerase chain reaction (RT-PCR) by using human and chicken primers for several angiogenic cytokines, namely vascular endothelial growth factor-A (VEGF-A), fibroblast growth factor-2 (FGF-2), angiopoietin-1 (ANG-1), hypoxia inducible factor-2alpha (HIF-2alpha), and for an endogenous angiostatic molecule, namely endostatin. Results showed that: (1) Neuroblastoma cells induced an angiogenic response in the CAM assay comparable to that induced by FGF-2; (2) neuroblastoma cells are packed inside Matrigel or are recognizable in the CAM mesenchyme; (3) Angiogenic activity of neuroblastoma cells is associated to an high expression of the transcripts of human VEGF-A, FGF-2, ANG-1 and HIF-2alpha and to a low expression in the transcript of a human endostatin while in the control specimens there is no expression of both angiogenic and angiostatic molecules; and (4) the expression of the transcripts of the same chicken angiogenesis stimulators and inhibitor is unmodified in treated and control specimens. Overall, these data indicate that neuroblastoma cells growth on the chick CAM express characteristics of the human disease. This experimental model could be employed for further research on human tumor progression and anti-angiogenic molecules screening.