Drug resistance in human neuroblastoma cell lines correlates with clinical therapy

Mitoribosomal synthetic lethality overcomes multidrug resistance in MYC-driven neuroblastoma

Mitochondria are central for cancer responses to therapy-induced stress signals. Refractory tumors often show attenuated sensitivity to apoptotic signaling, yet clinically relevant molecular actors to target mitochondria-mediated resistance remain elusive. Here, we show that MYC-driven neuroblastoma cells rely on intact mitochondrial ribosome (mitoribosome) processivity and undergo cell death following pharmacological inhibition of mitochondrial translation, regardless of their multidrug/mitochondrial resistance and stem-like phenotypes. Mechanistically, inhibiting mitoribosomes induced the mitochondrial stress-activated integrated stress response (ISR), leading to downregulation of c-MYC/N-MYC proteins prior to neuroblastoma cell death, which could be both rescued by the ISR inhibitor ISRIB. The ISR blocks global protein synthesis and shifted the c-MYC/N-MYC turnover toward proteasomal degradation. Comparing models of various neuroectodermal tumors and normal fibroblasts revealed overexpression of MYC proteins phosphorylated at the degradation-promoting site T58 as a factor that predetermines vulnerability of MYC-driven neuroblastoma to mitoribosome inhibition. Reducing N-MYC levels in a neuroblastoma model with tunable MYCN expression mitigated cell death induction upon inhibition of mitochondrial translation and functionally validated the propensity of neuroblastoma cells for MYC-dependent cell death in response to the mitochondrial ISR. Notably, neuroblastoma cells failed to develop significant resistance to the mitoribosomal inhibitor doxycycline over a long-term repeated (pulsed) selection. Collectively, we identify mitochondrial translation machinery as a novel synthetic lethality target for multidrug-resistant MYC-driven tumors.

Adaptation of the Th-MYCN Mouse Model of Neuroblastoma for Evaluation of Disseminated Disease

High-risk neuroblastoma remains a profound clinical challenge that requires eradication of neuroblastoma cells from a variety of organ sites, including bone marrow, liver, and CNS, to achieve a cure. While preclinical modeling is a powerful tool for the development of novel cancer therapies, the lack of widely available models of metastatic neuroblastoma represents a significant barrier to the development of effective treatment strategies. To address this need, we report a novel luciferase-expressing derivative of the widely used Th-MYCN mouse. While our model recapitulates the non-metastatic neuroblastoma development seen in the parental transgenic strain, transplantation of primary tumor cells from disease-bearing mice enables longitudinal monitoring of neuroblastoma growth at distinct sites in immune-deficient or immune-competent recipients. The transplanted tumors retain GD2 expression through many rounds of serial transplantation and are sensitive to GD2-targeted immune therapy. With more diverse tissue localization than is seen with human cell line-derived xenografts, this novel model for high-risk neuroblastoma could contribute to the optimization of immune-based treatments for this deadly disease.

Potential Treatment Options for Neuroblastoma with Polyphenols through Anti-Proliferative and Apoptotic Mechanisms

Neuroblastoma (NB) is an extracranial tumor of the peripheral nervous system arising from neural crest cells. It is the most common malignancy in infants and the most common extracranial solid tumor in children. The current treatment for high-risk NB involves chemotherapy and surgical resection followed by high-dose chemotherapy with autologous stem-cell rescue and radiation treatment. However, those with high-risk NB are susceptible to relapse and the long-term side effects of standard chemotherapy. Polyphenols, including the sub-class of flavonoids, contain more than one aromatic ring with hydroxyl groups. The literature demonstrates their utility in inducing the apoptosis of neuroblastoma cells, mostly in vitro and some in vivo. This review explores the use of various polyphenols outlined in primary studies, underlines the pathways involved in apoptotic activity, and discusses the dosage and delivery of these polyphenols. Primary studies were obtained from multiple databases with search the terms “neuroblastoma”, “flavonoid”, and “apoptosis”. The in vitro studies showed that polyphenols exert an apoptotic effect on several NB cell lines. These polyphenols include apigenin, genistein, didymin, rutin, quercetin, curcumin, resveratrol, butein, bisphenols, and various plant extracts. The mechanisms of the therapeutic effects include calpain-dependent pathways, receptor-mediated apoptosis, and, notably, and most frequently, mitochondrial apoptosis pathways, including the mitochondrial proteins Bax and Bcl-2. Overall, polyphenols demonstrate potency in decreasing NB proliferation and inducing apoptosis, indicating significant potential for further in vivo research.

Reduced ER-mitochondria connectivity promotes neuroblastoma multidrug resistance

Most cancer deaths result from progression of therapy resistant disease, yet our understanding of this phenotype is limited. Cancer therapies generate stress signals that act upon mitochondria to initiate apoptosis. Mitochondria isolated from neuroblastoma cells were exposed to tBid or Bim, death effectors activated by therapeutic stress. Multidrug‐resistant tumor cells obtained from children at relapse had markedly attenuated Bak and Bax oligomerization and cytochrome c release (surrogates for apoptotic commitment) in comparison with patient‐matched tumor cells obtained at diagnosis. Electron microscopy identified reduced ER–mitochondria‐associated membranes (MAMs; ER–mitochondria contacts, ERMCs) in therapy‐resistant cells, and genetically or biochemically reducing MAMs in therapy‐sensitive tumors phenocopied resistance. MAMs serve as platforms to transfer Ca²⁺ and bioactive lipids to mitochondria. Reduced Ca²⁺ transfer was found in some but not all resistant cells, and inhibiting transfer did not attenuate apoptotic signaling. In contrast, reduced ceramide synthesis and transfer was common to resistant cells and its inhibition induced stress resistance. We identify ER–mitochondria‐associated membranes as physiologic regulators of apoptosis via ceramide transfer and uncover a previously unrecognized mechanism for cancer multidrug resistance.

Clinically Relevant Biomarker Discovery in High-Risk Recurrent Neuroblastoma

Neuroblastoma is a pediatric cancer of the developing sympathetic nervous system. High-risk neuroblastoma patients typically undergo an initial remission in response to treatment, followed by recurrence of aggressive tumors that have become refractory to further treatment. The need for biomarkers that can select patients not responding well to therapy in an early phase is therefore needed. In this study, we used next generation sequencing technology to determine the expression profiles in high-risk neuroblastoma cell lines established before and after therapy. Using partial least squares-discriminant analysis (PLS-DA) with least absolute shrinkage and selection operator (LASSO) and leave-one-out cross-validation, we identified a panel of 55 messenger RNAs and 17 long non-coding RNAs (lncRNAs) which were significantly altered in the expression between cell lines isolated from primary and recurrent tumors. From a neuroblastoma patient cohort, we found 20 of the 55 protein-coding genes to be differentially expressed in patients with unfavorable compared with favorable outcome. We further found a twofold increase or decrease in hazard ratios in these genes when comparing patients with unfavorable and favorable outcome. Gene set enrichment analysis (GSEA) revealed that these genes were involved in proliferation, differentiation and regulated by Polycomb group (PcG) proteins. Of the 17 lncRNAs, 3 upregulated (NEAT1, SH3BP5-AS1, NORAD) and 3 downregulated lncRNAs (DUBR, MEG3, DHRS4-AS1) were also found to be differentially expressed in favorable compared with unfavorable outcome. Moreover, using expression profiles on both miRNAs and mRNAs in the same cohort of cell lines, we found 13 downregulated and 18 upregulated experimentally observed miRNA target genes targeted by miR-21, -424 and -30e, -29b, -138, -494, -181a, -34a, -29b, respectively. The advantage of analyzing biomarkers in a clinically relevant neuroblastoma model system enables further studies on the effect of individual genes upon gene perturbation. In summary, this study identified several genes, which may aid in the prediction of response to therapy and tumor recurrence.

FAK and S6K1 Inhibitor, Neferine, Dually Induces Autophagy and Apoptosis in Human Neuroblastoma Cells

Human neuroblastoma cancer is the most typical extracranial solid tumor. Yet, new remedial treatment therapies are demanded to overcome its sluggish survival rate. Neferine, isolated from the lotus embryos, inhibits the proliferation of various cancer cells. This study aimed to evaluate the anti-cancer activity of neferine in IMR32 human neuroblastoma cells and to expose the concealable molecular mechanisms. IMR32 cells were treated with different concentrations of neferine, followed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay to assess cell viability. In an effort to determine the molecular mechanisms in neferine-incubated IMR32 cells, cell cycle arrest, cell migration, and focal adhesion kinase (FAK), the 70-kDa ribosomal S6 kinase 1 (S6K1), poly (ADP-ribose) polymerase (PARP), caspase-3, Beclin-1, and microtubule-associated protein 1A/1B-light chain 3 (LC3) protein expressions were investigated. Neferine strongly disrupted the neuroblastoma cell growth via induction of G2/M phase arrest. Furthermore, neferine provoked autophagy and apoptosis in IMR32 cells, confirmed by p-FAK, and p-S6K1 reduction, LC3-II accumulation, Beclin-1 overexpression, and cleaved caspase-3/PARP improvement. Finally, neferine markedly retarded cell migration of neuroblastoma cancer cells. As a result, our findings for the first time showed an explicit anti-cancer effect of neferine in IMR32 cells, suggesting that neferine might be a potential candidate against human neuroblastoma cells to improve clinical outcomes with further in vivo investigation.

Vincristine resistance in relapsed neuroblastoma can be efficiently overcome by Smac mimetic LCL161 treatment

PURPOSE

In spite of good initial therapy response neuroblastomas often spread to distant organs or relapse after periods of remission. Dysregulation of apoptosis, a hallmark of cancer, is often effected by elevated levels of antiapoptotic signals leading to resistance against chemotherapeutic drugs. Inhibitors of apoptosis proteins (IAPs) are crucial cellular apoptosis regulators. Targeting IAPs with Smac mimetics has been demonstrated as a promising strategy for treatment of neuroblastoma and other tumors.

METHODS

In paired neuroblastoma cell lines, obtained from the same patient at time of diagnosis (CHLA-15) and postchemotherapy during progressive disease (CHLA-20), expression of crucial IAPs was determined. Furthermore, effects of vincristine on viability, cytotoxicity, apoptosis induction and caspase-3/7 activation were determined.

RESULTS

Cellular IAP-1 (cIAP-1) and X-linked IAP (XIAP) expression was increased in cell line CHLA-20. Moreover, biological effects of vincristine were significantly lower in these cells. Treatment of cells with Smac mimetic LCL161 increased the effects of vincristine in CHLA-15 cells and more importantly was able to overcome vincristine resistance in CHLA-20 cells.

CONCLUSIONS

These findings demonstrate the potential of Smac mimetics for the development of novel therapeutic approaches for the treatment of relapsed/resistant neuroblastoma.

Power frequency magnetic field promotes a more malignant phenotype in neuroblastoma cells via redox-related mechanisms

In accordance with the classification of the International Agency for Research on Cancer, extremely low frequency magnetic fields (ELF-MF) are suspected to promote malignant progression by providing survival advantage to cancer cells through the activation of critical cytoprotective pathways. Among these, the major antioxidative and detoxification defence systems might be targeted by ELF-MF by conferring cells significant resistance against clinically-relevant cytotoxic agents. We investigated whether the hyperproliferation that is induced in SH-SY5Y human neuroblastoma cells by a 50 Hz, 1 mT ELF magnetic field was supported by improved defence towards reactive oxygen species (ROS) and xenobiotics, as well as by reduced vulnerability against both H2O2 and anti-tumor ROS-generating drug doxorubicin. ELF-MF induced a proliferative and survival advantage by activating key redox-responsive antioxidative and detoxification cytoprotective pathways that are associated with a more aggressive behavior of neuroblastoma cells. This was coupled with the upregulation of the major sirtuins, as well as with increased signaling activity of the erythroid 2-related nuclear transcription factor 2 (NRF2). Interestingly, we also showed that the exposure to 50 Hz MF as low as 100 µT may still be able to alter behavior and responses of cancer cells to clinically-relevant drugs.

The small molecule inhibitor YK-4-279 disrupts mitotic progression of neuroblastoma cells, overcomes drug resistance and synergizes with inhibitors of mitosis

Neuroblastoma is a biologically and clinically heterogeneous pediatric malignancy that includes a high-risk subset for which new therapeutic agents are urgently required. As well as MYCN amplification, activating point mutations of ALK and NRAS are associated with high-risk and relapsing neuroblastoma. As both ALK and RAS signal through the MEK/ERK pathway, we sought to evaluate two previously reported inhibitors of ETS-related transcription factors, which are transcriptional mediators of the Ras-MEK/ERK pathway in other cancers. Here we show that YK-4-279 suppressed growth and triggered apoptosis in nine neuroblastoma cell lines, while BRD32048, another ETV1 inhibitor, was ineffective. These results suggest that YK-4-279 acts independently of ETS-related transcription factors. Further analysis reveals that YK-4-279 induces mitotic arrest in prometaphase, resulting in subsequent cell death. Mechanistically, we show that YK-4-279 inhibits the formation of kinetochore microtubules, with treated cells showing a broad range of abnormalities including multipolar, fragmented and unseparated spindles, together leading to disrupted progression through mitosis. Notably, YK-4-279 does not affect microtubule acetylation, unlike the conventional mitotic poisons paclitaxel and vincristine. Consistent with this, we demonstrate that YK-4-279 overcomes vincristine-induced resistance in two neuroblastoma cell-line models. Furthermore, combinations of YK-4-279 with vincristine, paclitaxel or the Aurora kinase A inhibitor MLN8237/Alisertib show strong synergy, particularly at low doses. Thus, YK-4-279 could potentially be used as a single-agent or in combination therapies for the treatment of high-risk and relapsing neuroblastoma, as well as other cancers.

Next generation sequencing of microRNAs from isogenic neuroblastoma cell lines isolated before and after treatment

Neuroblastoma is a pediatric cancer of the developing sympathetic nervous system. High risk neuroblastoma patients typically undergo an initial remission in response to treatment, followed by recurrence of aggressive tumors that have become refractory to further treatment. Recent works have underlined the involvement of microRNAs (miRNAs) in neuroblastoma development and evolution of drug resistance. In this study we have used deep sequencing technology to identify miRNAs differentially expressed in neuroblastoma cell lines isolated from 6 patients at diagnosis and at relapse after intensive treatments. This approach revealed a panel of 42 differentially expressed miRNAs, 8 of which were upregulated and 34 were downregulated. Most strikingly, the 14q32 miRNA clusters encode 22 of the downregulated miRNAs. Reduced expression of 14q32 miRNAs in tumors associated with poor prognosis factors was confirmed in a cohort consisting of 226 primary neuroblastomas. In order to gain insight into the nature of the genes that may be affected by the differentially expressed miRNAs we utilized Ingenuity Pathway Analysis (IPA). This analysis revealed several biological functions and canonical pathways associated with cancer progression and drug resistance. The results of this study contribute to the identification of miRNAs involved in the complex processes of surviving therapeutic treatment and developing drug resistance in neuroblastoma.

Assessment of the chemosensitizing activity of TAT-RasGAP317-326 in childhood cancers

Although current anti-cancer protocols are reasonably effective, treatment-associated long-term side effects, induced by lack of specificity of the anti-cancer procedures, remain a challenging problem in pediatric oncology. TAT-RasGAP317-326 is a RasGAP-derived cell-permeable peptide that acts as a sensitizer to various anti-cancer treatments in adult tumor cells. In the present study, we assessed the effect of TAT-RasGAP317-326 in several childhood cancer cell lines. The RasGAP-derived peptide-induced cell death was analyzed in several neuroblastoma, Ewing sarcoma and leukemia cell lines (as well as in normal lymphocytes). Cell death was evaluated using flow cytometry methods in the absence or in the presence of the peptide in combination with various genotoxins used in the clinics (4-hydroperoxycyclophosphamide, etoposide, vincristine and doxorubicin). All tested pediatric tumors, in response to at least one genotoxin, were sensitized by TAT-RasGAP317-326. The RasGAP-derived peptide did not increase cell death of normal lymphocytes, alone or in combination with the majority of the tested chemotherapies. Consequently, TAT-RasGAP317-326 may benefit children with tumors by increasing the efficacy of anti-cancer therapies notably by allowing reductions in anti-cancer drug dosage and the associated drug-induced side effects.

DNA demethylation increases sensitivity of neuroblastoma cells to chemotherapeutic drugs

Neuroblastoma is a common embryonal malignancy in which high-stage cases have a poor prognosis, often associated with resistance to chemotherapeutic drugs. DNA methylation alterations are frequent in neuroblastoma and can modulate sensitivity to chemotherapeutic drugs in other cancers, suggesting that manipulation of epigenetic modifications could provide novel treatment strategies for neuroblastoma. We evaluated neuroblastoma cell lines for DNA demethylation induced by 5-Aza-2'-deoxycytidine, using genome-wide and gene-specific assays. Cytotoxic effects of chemotherapeutic agents (cisplatin, doxorubicin and etoposide), with and without 5-Aza-2'-deoxycytidine, were determined by morphological and biochemical apoptosis assays. We observed that the extent of genome-wide DNA demethylation induced by 5-Aza-2'-deoxycytidine varied between cell lines and was associated with expression differences of genes involved in the uptake and metabolism of 5-Aza-2'-deoxycytidine. Treatment of neuroblastoma cells with a combination of chemotherapeutic drugs and 5-Aza-2'-deoxycytidine significantly increased the levels of apoptosis induced by cisplatin, doxorubicin and etoposide, compared to treatment with chemotherapeutic drugs alone. The variable demethylation of cell lines in response to 5-Aza-2'-deoxycytidine suggests that epigenetic modifiers need to be targeted to suitably susceptible tumours for maximum therapeutic benefit. Epigenetic modifiers, such as 5-Aza-2'-deoxycytidine, could be used in combination with chemotherapeutic drugs to enhance their cytotoxicity, providing more effective treatment options for chemoresistant neuroblastomas.

A Three-Stage-Integrative Approach for the Identification of Potential Hepatotoxic Compounds From Botanical Products

With the increasing use of herbal medicines and dietary supplements, intensive concerns about their potential toxicities have been raised. Screening and identifying the toxic compounds from these botanical products composed by hundreds of components have become a critical but challenging problem. In this study, 3 methods, including fraction separation, an in-house-developed fluorescein diacetate-based automatic microscopy screening (FAMS) platform, and liquid chromatography-mass spectrometry-based compounds identification were integrated within the Three-Stage-Integrative (TSI) approach for the identification of potential hepatotoxicants from botanical products. The sensitivity and linear range of FAMS assay was validated and compared with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay by previously reported hepatotoxic compounds. The success of TSI approach was further demonstrated by its application to Fructus aristolochiae. Aristolochic acid IVa and aristolodione were tentatively identified to be potential hepatotoxicants in this plant. These applications suggested that our TSI approach provides an effective tool for identifying potential toxic compounds from botanical products.

Myc proteins as therapeutic targets

Myc proteins (c-myc, Mycn and Mycl) target proliferative and apoptotic pathways vital for progression in cancer. Amplification of the MYCN gene has emerged as one of the clearest indicators of aggressive and chemotherapy-refractory disease in children with neuroblastoma, the most common extracranial solid tumor of childhood. Phosphorylation and ubiquitin-mediated modulation of Myc protein influence stability and represent potential targets for therapeutic intervention. Phosphorylation of Myc proteins is controlled in-part by the receptor tyrosine kinase/phosphatidylinositol 3-kinase/Akt/mTOR signaling, with additional contributions from Aurora A kinase. Myc proteins regulate apoptosis in part through interactions with the p53/Mdm2/Arf signaling pathway. Mutation in p53 is commonly observed in patients with relapsed neuroblastoma, contributing to both biology and therapeutic resistance. This review examines Myc function and regulation in neuroblastoma, and discusses emerging therapies that target Mycn.

Chemotherapy-induced apoptosis in a transgenic model of neuroblastoma proceeds through p53 induction

Chemoresistance in neuroblastoma is a significant issue complicating treatment of this common pediatric solid tumor. MYCN-amplified neuroblastomas are infrequently mutated at p53 and are chemosensitive at diagnosis but acquire p53 mutations and chemoresistance with relapse. Paradoxically, Myc-driven transformation is thought to require apoptotic blockade. We used the TH-MYCN transgenic murine model to examine the role of p53-driven apoptosis on neuroblastoma tumorigenesis and the response to chemotherapy. Tumors formed with high penetrance and low latency in p53-haploinsufficient TH-MYCN mice. Cyclophosphamide (CPM) induced a complete remission in p53 wild type TH-MYCN tumors, mirroring the sensitivity of childhood neuroblastoma to this agent. Treated tumors showed a prominent proliferation block, induction of p53 protein, and massive apoptosis proceeding through induction of the Bcl-2 homology domain-3-only proteins PUMA and Bim, leading to the activation of Bax and cleavage of caspase-3 and -9. Apoptosis induced by CPM was reduced in p53-haploinsufficient tumors. Treatment of MYCN-expressing human neuroblastoma cell lines with CPM induced apoptosis that was suppressible by siRNA to p53. Taken together, the results indicate that the p53 pathway plays a significant role in opposing MYCN-driven oncogenesis in a mouse model of neuroblastoma and that basal inactivation of the pathway is achieved in progressing tumors. This, in part, explains the striking sensitivity of such tumors to chemotoxic agents that induce p53-dependent apoptosis and is consistent with clinical observations that therapy-associated mutations in p53 are a likely contributor to the biology of tumors at relapse and secondarily mediate resistance to therapy.

Onconase induces caspase-independent cell death in chemoresistant neuroblastoma cells

The efficacy of Onconase on the growth of a panel of chemosensitive and chemoresistant neuroblastoma cell lines was investigated. Onconase decreased cell viability of chemosensitive (IMR-32, UKF-NB-3) and chemoresistant neuroblastoma cell lines characterised by high expression of P-glycoprotein (P-gp) (UKF-NB-3(r)DOX(20)) or by high P-gp expression in combination with mutated p53 (UKF-NB-3(r)VCR(10), Be(2)-C), in a similar manner. Moreover, Onconase caused cell cycle block in G1 phase and induced caspase-independent cell death. Transmission electron microscope investigations suggested that Onconase-induced autophagy contributes to Onconase-induced cell death. Antitumour activity of Onconase against naïve and drug-resistant neuroblastoma xenografts was confirmed in animals.

WP744 is a novel anthracycline with enhanced activity against neuroblastoma

BACKGROUND

Doxorubicin (Dox) is one of the most useful chemotherapeutic agents for patients with advanced neuroblastoma (NB). A series of Dox analogs with bulky substitutions at the C-4' at amino-sugar have been designed to impair interactions between the drug and P-glycoprotein (P-gp), a multidrug drug resistance (MDR) transporter. Two analogs, WP744 and WP769, were selected and their biological properties were compared with Dox and the daunorubicin-based bisintercalator WP631. These novel Dox analogs may have antitumor activity beyond MDR evasion.

MATERIALS AND METHODS

MTT assays were used to determine the potency of three structurally altered Dox analogs against a panel of NB cell lines with and without amplification of the MYCN oncogene. Flow cytometry (FCM) was used to analyze apoptosis and cell death and phenotype cell lines for surface expression of the MDR protein P-gp.

RESULTS

The 4'-O-benzylated Dox analogs WP744 and WP769 were 2 to 36 times more cytotoxic than Dox for the NB cell lines tested. The bis-intercalator WP631, despite its significantly greater affinity for DNA (>10,000-fold), was generally less potent against NB than Dox. In Tet21N cells, which conditionally express MYCN, greatly enhanced (nearly 6-fold) sensitivity to WP744 killing was seen when this oncogene was induced, while enhanced sensitivity to Dox was more modest (2-fold) under MYCN-induced conditions. Treatment with WP744 also resulted in enhanced apoptosis. Apoptosis, but not cell death, in response to either WP744 or Dox was inhibited by caspase inhibition, suggesting that cell death was not completely dependent upon apoptosis. P-gp expression was detectable on five NB cell lines. WP744 was more cytotoxic than Dox against both P-gp+ and P-gp- cells.

CONCLUSIONS

These findings demonstrate that 4'-O-benzylation of the anthracycline molecule significantly enhances potency against NB independent of MYCN status, caspase activation, and MDR phenotype. However, WP744 demonstrated a unique synergy with MYCN for cell killing when this oncogene was specifically induced. WP744 may be more useful than conventional agents for the treatment of tumor clones that harbor defects in apoptotic pathways, in those with MYCN amplification, and in those with drug-resistant tumors.

Synergistic cytotoxicity of buthionine sulfoximine (BSO) and intensive melphalan (L-PAM) for neuroblastoma cell lines established at relapse after myeloablative therapy

Patients with high-risk neuroblastoma (NB) initially respond to aggressive, alkylator-based therapy only to die from recurrent disease that is refractory to chemotherapy, including alkylating agents. We examined the ability of buthionine sulfoximine (BSO)-mediated glutathione (GSH) depletion to modulate melphalan (L-PAM) resistance in five NB cell lines established after progressive disease following myeloablative therapy (high-dose melphalan, carboplatin, etoposide and total body irradiation) supported by autologous hematopoietic stem cell transplant (AHSCT), and in 15 NB cell lines established at diagnosis or after non-myeloablative therapy (pre-AHSCT). Four of five post-AHSCT NB cell lines and 10 of 15 pre-AHSCT NB cell lines were sensitive to single agent BSO (LC(90) <300 microM BSO), while two of five post-AHSCT lines and one of 15 pre-AHSCT lines showed high-level resistance to L-PAM (LC(90)>30 microM). Fixed ratio analysis demonstrated BSO/L-PAM synergy (combination index <1) for all five post-AHSCT and for all 15 pre-AHSCT cell lines tested. Multi-log cytotoxicity (often exceeding four logs of cell kill) was observed in post-AHSCT L-PAM-resistant cell lines (including p53 non-functional lines) only when clinically achievable concentrations of BSO were combined with myeloablative concentrations of L-PAM. We conclude that most neuroblastoma cell lines, including post-AHSCT NB cell lines that are highly resistant to myeloablative levels of L-PAM and lack p53 function, are sensitive to clinically achievable concentrations of L-PAM and BSO. However, some L-PAM-resistant NB cell lines (especially those lacking p53 function) require dose escalation of L-PAM to myeloablative concentrations in order to demonstrate significant synergistic cytotoxicity. Thus, optimal clinical application of BSO/L-PAM may require AHSCT.

Sphingolipids in neuroblastoma: their role in drug resistance mechanisms

Disseminated neuroblastoma usually calls for chemotherapy as the primary approach for treatment. Treatment failure is often attributable to drug resistance. This involves a variety of cellular mechanisms, including increased drug efflux through expression of ATP-binding cassette transporters (e.g., P-glycoprotein) and the inability of tumor cells to activate or propagate the apoptotic response. In recent years it has become apparent that sphingolipid metabolism and the generation of sphingolipid species, such as ceramide, also play a role in drug resistance. This may involve an autonomous mechanism, related to direct effects of sphingolipids on the apoptotic response, but also a subtle interplay between sphingolipids and ATP-binding cassette transporters. Here, we present an overview of the current understanding of the multiple levels at which sphingolipids function in drug resistance, with an emphasis on sphingolipid function in neuroblastoma and how modulation of sphingolipid metabolism may be used as a novel treatment paradigm.

Buthionine sulfoximine and myeloablative concentrations of melphalan overcome resistance in a melphalan-resistant neuroblastoma cell line

BACKGROUND

Alkylator resistance contributes to treatment failure in high-risk neuroblastoma. Buthionine sulfoximine (BSO) can deplete glutathione and synergistically enhance in vitro sensitivity to the alkylating agent melphalan (L-PAM) for many neuroblastoma cell lines, but optimal use of this combination needs to be defined because clinical responses have been less frequent and not durable.

PATIENTS AND METHODS

The authors established and characterized a neuroblastoma cell line (CHLA-171) from a patient who died of progressive disease after treatment with BSO and low-dose L-PAM.

RESULTS

CHLA-171 lacks MYCN amplification, expresses PGP (P-glycoprotein) 9.5 RNA, and shows cell surface antigen expression (human leukocyte antigen class I weakly positive, but HSAN 1.2 (hybridoma, SAN 1.2) and anti-GD2 (anti-ganglioside GD2 antibody) strongly positive) characteristic of neuroblastoma cell lines. Twenty-four hours of BSO treatment (0-1,000 micromol/L) maximally depleted CHLA-171 glutathione to 36% of baseline. The cytotoxic response of CHLA-171 to BSO and L-PAM, alone and in combination, was measured by digital image microscopy (DIMSCAN) over a range of drug concentrations and compared with drug levels obtained in the patient during BSO/L-PAM therapy. As single agents, CHLA-171 was highly resistant to L-PAM (LD90 = 42 micromol/L; peak plasma concentration in the patient equals 3.9 micromol/L) and moderately resistant to BSO (LD90 = 509 micromol/L; steady-state concentration in the patient equals 397 micromol/L). Treatment with a 10:1 (BSO:L-PAM) fixed ratio combination synergistically overcame resistance (3-4 logs of cell kill, combination index <1) at clinically achievable levels of BSO (100-400 micromol/L) and levels of L-PAM (10-40 micromol/L) clinically achievable only with hematopoietic stem cell support.

CONCLUSIONS

The in vitro results obtained for CHLA-171 suggest that BSO/L-PAM therapy may be optimally effective for drug-resistant neuroblastoma using myeloablative doses of L-PAM.

Synergism of buthionine sulfoximine and melphalan against neuroblastoma cell lines derived after disease progression

BACKGROUND

Despite intensive-alkylator based regimens, >50% of patients with high-risk neuroblastoma (NB) die from recurrent disease that is probably due, in part, to acquired alkylator resistance.

PROCEDURE

Using buthionine sulfoximine (BSO)-mediated, glutathione (GSH) depletion to modulate melphalan (L-PAM) resistance, we examined six NB cell lines established after progressive disease following either standard chemotherapy, BSO/L-PAM therapy, or myeloablative therapy and autologous hematopoietic stem cell transplant (AHSCT).

RESULTS

Four of the six cell lines (three p53-nonfunctional and one p53-functional) showed high-level L-PAM resistance.

CONCLUSIONS

Fixed ratio analysis demonstrated BSO/L-PAM synergy (combination index >1) for all cell lines tested. In L-PAM-resistant cell lines, the minimal cytotoxicity observed for BSO combined with nonmyeloablative concentrations of L-PAM was markedly enhanced (>4 logs total cell kill) when BSO was combined with myeloablative concentrations of L-PAM. In alkylator-resistant NB, the optimal use of BSO may require dose escalation of L-PAM to levels requiring AHSCT.

A phase I dose escalation of combination chemotherapy with granulocyte-macrophage-colony stimulating factor in patients with neuroblastoma

BACKGROUND

Dose intensity is important in the response to chemotherapy in patients with advanced neuroblastoma. The aim of the current study was to determine the maximum tolerated dose of a combination chemotherapy regimen in the treatment of patients with recurrent neuroblastoma and peripheral neuroepithelioma (primitive neuroectodermal tumor [PNET]) and whether the use of growth factor would allow increased dose intensity.

METHODS

Twenty-nine patients diagnosed with recurrent neuroblastoma or PNET were treated with a combination chemotherapy regimen of cisplatin, 160 mg/m(2)/96 hours; doxorubicin, 40 mg/m(2)/96 hours; and escalated doses of etoposide and ifosfamide. Granulocyte-macrophage-colony stimulating factor (GM-CSF) was administered beginning 24 hours after the completion of the chemotherapy. Courses were repeated at 28-day intervals. Once the maximum tolerated dose (MTD) was defined the interval between courses was shortened by administering the next course as soon as the patient's neutrophil and platelet counts had recovered to > 1500/microL and > 75,000/microL, respectively.

RESULTS

Sixteen patients were treated at 3 dose levels. The MTD was defined as 10 g/m(2)/96 hours of ifosfamide and 800 mg/m(2)/96 hours of etoposide. Thirteen additional patients then were treated at 1 level below the MTD to try and decrease the interval between courses. A total of 12 of 29 patients developed a dose-limiting toxicity (DLT) after the first course of therapy. The most common DLT was gastrointestinal toxicity followed by hematologic toxicity. Twenty-seven patients developed standard National Cancer Institute criteria Grade 3 or 4 toxicity after the first course of treatment and 7 patients achieved a complete or partial response to the first course. The use of GM-CSF did not allow further dose intensification.

CONCLUSIONS

This chemotherapy combination achieved a 31% overall response rate. A further increase in the dose intensity of this regimen may require supportive measures other than GM-CSF to decrease toxicity.

Molecular biology of neuroblastoma

PURPOSE AND RESULTS: Neuroblastoma, the most common solid extracranial neoplasm in children, is remarkable for its clinical heterogeneity. Complex patterns of genetic abnormalities interact to determine the clinical phenotype. The molecular biology of neuroblastoma is characterized by somatically acquired genetic events that lead to gene overexpression (oncogenes), gene inactivation (tumor suppressor genes), or alterations in gene expression. Amplification of the MYCN proto-oncogene occurs in 20% to 25% of neuroblastomas and is a reliable marker of aggressive clinical behavior. No other oncogene has been shown to be consistently mutated or overexpressed in neuroblastoma, although unbalanced translocations resulting in gain of genetic material from chromosome bands 17q23-qter have been identified in more than 50% of primary tumors. Some children have an inherited predisposition to develop neuroblastoma, but a familial neuroblastoma susceptibility gene has not yet been localized. Consistent areas of chromosomal loss, including chromosome band 1p36 in 30% to 35% of primary tumors, 11q23 in 44%, and 14q23-qter in 22%, may identify the location of neuroblastoma suppressor genes. Alterations in the expression of the neurotrophins and their receptors correlate with clinical behavior and may reflect the degree of neuroblastic differentiation before malignant transformation. Alterations in the expression of genes that regulate apoptosis also correlate with neuroblastoma behavior and may help to explain the phenomenon of spontaneous regression observed in a well-defined subset of patients.

CONCLUSION

The molecular biology of neuroblastoma has led to a combined clinical and biologic risk stratification. Future advances may lead to more specific treatment strategies for children with neuroblastoma.

Depletion of glutathione by buthionine sulfoxine is cytotoxic for human neuroblastoma cell lines via apoptosis

Buthionine sulfoximine (BSO) selectively inhibits glutathione (GSH) synthesis and has been used to sensitize tumor cells to alkylating agents, but has minimal single-agent cytotoxicity for most cell types. We determined the cytotoxicity of BSO for 18 (12 MYCN amplified; 6 MYCN nonamplified) human neuroblastoma cell lines using DIMSCAN, a digital image microscopy cytotoxicity assay. D-L(R:S) BSO was highly cytotoxic (>3 logs of cell kill) for most neuroblastoma cell lines, with 17/18 cell lines having IC90 values (range 2. 1->1000 microM) below equivalent steady state plasma levels of L(R:S) BSO reported in adult human trials. Cell lines with genomic amplification of MYCN were more sensitive to BSO than MYCN nonamplified cell lines (P = 0.04). D-L(R:S) BSO (500 microM for 72 h) induced apoptosis as detected by DNA laddering, nuclear morphology, and TUNEL staining of DNA fragments using flow cytometry. Maximal cell killing occurred within 48 h and was antagonized byic value in neuroblastoma.