Macrophage-mediated anti-tumor immunity against high-risk neuroblastoma

Neuroblastoma is the most common extracranial childhood solid tumor. The majority of high-risk neuroblastoma is resistant/refractory to the current high intensity therapy. Neuroblastoma lacks classical HLA Class I expression and exhibits low mutation burden, allowing neuroblastoma cells to evade CD8+ T cell-mediated immunity. Neuroblastoma cells do not express PD-L1, and tumor-associated macrophages are the predominant PD-L1+ cells in the tumor. In this study, we performed gene expression profiling and survival analyses on large neuroblastoma datasets to address the prognostic effect of PD-L1 gene expression and the possible involvement of the SLAMF7 pathway in the anti-neuroblastoma immunity. High-level expression of PD-L1 was found significantly associated with better outcome of high-risk neuroblastoma patients; two populations of PD-1+ PD-L1+ macrophages could be present in high-risk tumors with PD-1/PD-L1 ratios, ≈1 and >1. Patients with the PD-1/PD-L1 ratio >1 tumor showed inferior survival. High-level co-expression of SLAMF7 and SH2D1B was significantly associated with better survival of the high-risk neuroblastoma patients. Together, this study supports the hypothesis that macrophages are important effector cells in the anti-high-risk neuroblastoma immunity, that PD-1 blockade therapy can be beneficial to the high-risk neuroblastoma subset with the PD-1/PD-L1 expression ratio >1, and that SLAMF7 is a new therapeutic target of high-risk neuroblastoma.

Stage 4S Neuroblastoma: Molecular, Histologic, and Immunohistochemical Characteristics and Presence of 2 Distinct Patterns of MYCN Protein Overexpression-A Report From the Children's Oncology Group

Stage 4S neuroblastoma (4SNB) is associated with spontaneous tumor regression and an excellent prognosis. However, a small group of the patients have a poor prognosis. One hundred eighty-five stage 4SNB cases filed at the Children's Oncology Group Neuroblastoma Pathology Reference Laboratory were studied. MYCN oncogene status [non-amplified (NA) vs. Amplified (A)] determined by fluorescence in situ hybridization, MYC-family (MYCN/MYC) protein expression [no-overexpression(-)/(+/-) vs. overexpression(+)] by immunohistochemistry and histopathology by International Neuroblastoma Pathology Classification [Favorable Histology (FH) vs. Unfavorable Histology (UH)] with particular attention to nucleolar hypertrophy [NH(-) vs. (+)] were assessed with patient survival. One hundred forty-seven (79.5%) tumors were MYCN-NA, FH, MYC-family protein(-)/(+/-), and NH(-) with a good prognosis [88.5±3.1% 3-y event-free survival (EFS); 94.1±2.3% 3-y overall survival (OS)]. Among MYCN-NA tumors, 11 demonstrated MYCN protein(+) with a moderate and uniform (M/U) staining pattern: they were FH(10/11), NH(-), 1 showed MYC protein(+) simultaneously, and all patients are alive. Also found were 5 MYC protein(+) and MYCN(-)/(+/-) tumors; they were FH without NH (4/5), and all patients are alive. Among MYCN-A tumors, 18 had MYCN protein(+) with a strong and heterogeneous (S/H) staining pattern, 9 had UH (44.4±23.4% EFS/OS) and 9 had FH (68.6±19.2% EFS/OS), and 15 showed NH(+). Two tumors had MYCN protein(-)/(+/-) despite MYCN-A; both were FH and NH(-), and 1 patient died. S/H staining pattern of MYCN protein overexpression by immunohistochemistry was associated with MYCN amplification, NH(+) and a poor prognosis. In contrast, the M/U staining pattern was associated with MYCN nonamplification and NH(-), and had no adverse prognostic effects for the stage 4SNB patients.

Clinical Relevance of CD4 Cytotoxic T Cells in High-Risk Neuroblastoma

Neuroblastoma is the most common extracranial childhood solid tumor. The majority of high-risk neuroblastoma is resistant/refractory to the current high intensity therapy, and the survival of these patients remains poor for the last three decades. To effectively treat these extremely unfavorable neuroblastomas, innovative immunotherapy approaches would be the most promising. In this article, we discuss the identity of tumor-infiltrating effector cells and immunosuppressive cells in high-risk neuroblastoma. Neuroblastoma is unique in that it expresses little or no classical HLA Class I and II. In contrast, high-risk neuroblastomas express the stress-responsive non-classical Class I, HLA-E molecule. HLA-E is the ligand of activating receptors NKG2C/E that are expressed on memory NK cells, CD8+T cells and CD4 CTLs. By examining a comprehensive RNA-seq gene expression dataset, we detected relatively high levels of CD4 expression in high-risk neuroblastoma tissues. The majority of CD4+ cells were CD3+, and thus they were likely tumor-associated CD4+T cells. In addition, high-level of both CD4 and NKG2C/E expression was associated with prolonged survival of the high-risk neuroblastoma patients, but CD8 levels were not, further suggesting that the CD4+ NKG2C/E+ T cells or CD4 CTL conferred cytotoxicity against the neuroblastoma cells. However, this T cell mediated- "protective effect" declined over time, in part due to the progressive formation of immunosuppressive tumor microenvironment. These observations suggest that to improve survival of high-risk neuroblastoma patients, it is essential to gain insights into how to enhance CD4 CTL cytotoxicity and control the immunosuppressive tumor microenvironment during the course of the disease.

Combined Replenishment of miR-34a and let-7b by Targeted Nanoparticles Inhibits Tumor Growth in Neuroblastoma Preclinical Models

Neuroblastoma (NB) tumor substantially contributes to childhood cancer mortality. The design of novel drugs targeted to specific molecular alterations becomes mandatory, especially for high-risk patients burdened by chemoresistant relapse. The dysregulated expression of MYCN, ALK, and LIN28B and the diminished levels of miR-34a and let-7b are oncogenic in NB. Due to the ability of miRNA-mimics to recover the tumor suppression functions of miRNAs underexpressed into cancer cells, safe and efficient nanocarriers selectively targeted to NB cells and tested in clinically relevant mouse models are developed. The technology exploits the nucleic acids negative charges to build coated-cationic liposomes, then functionalized with antibodies against GD₂ receptor. The replenishment of miR-34a and let-7b by NB-targeted nanoparticles, individually and more powerfully in combination, significantly reduces cell division, proliferation, neoangiogenesis, tumor growth and burden, and induces apoptosis in orthotopic xenografts and improves mice survival in pseudometastatic models. These functional effects highlight a cooperative down-modulation of MYCN and its down-stream targets, ALK and LIN28B, exerted by miR-34a and let-7b that reactivate regulatory networks leading to a favorable therapeutic response. These findings demonstrate a promising therapeutic efficacy of miR-34a and let-7b combined replacement and support its clinical application as adjuvant therapy for high-risk NB patients.

Local delivery of dinutuximab from lyophilized silk fibroin foams for treatment of an orthotopic neuroblastoma model

Immunotherapy targeting GD2 is a primary treatment for patients with high-risk neuroblastoma. Dinutuximab is a monoclonal antibody with great clinical promise but is limited by side effects such as severe pain. Local delivery has emerged as a potential mechanism to deliver higher doses of therapeutics into the tumor bed, while limiting systemic toxicity. We aim to deliver dinutuximab locally in a lyophilized silk fibroin foam for the treatment of an orthotopic neuroblastoma mouse model. Dinutuximab-loaded silk fibroin foams were fabricated through lyophilization. In vitro release profile and bioactivity of the release through complement-dependent cytotoxicity were characterized. MYCN-amplified neuroblastoma cells (KELLY) were injected into the left gland of mice to generate an orthotopic neuroblastoma model. Once the tumor volume reached 100 mm³ , dinutuximab-, human IgG-, or buffer-loaded foams were implanted into the tumor and growth was monitored using high-resolution ultrasound. Post-resection histology was performed on tumors. Dinutuximab-loaded silk fibroin foams exhibited a burst release, with slow release thereafter in vitro with maintenance of bioactivity. The dinutuximab-loaded foam significantly inhibited xenograft tumor growth compared to IgG- and buffer-loaded foams. Histological analysis revealed the presence of dinutuximab within the tumor and neutrophils and macrophages infiltrating into dinutuximab-loaded silk foam. Tumors treated with local dinutuximab had decreased MYCN expression on histology compared to control or IgG-treated tumors. Silk fibroin foams offer a mechanism for local release of dinutuximab within the neuroblastoma tumor. This local delivery achieved a significant decrease in tumor growth rate in a mouse orthotopic tumor model.

Replicating and identifying large cell neuroblastoma using high-dose intra-tumoral chemotherapy and automated digital analysis

PURPOSE

Large cell neuroblastomas (LCN) are frequently seen in recurrent, high-risk neuroblastoma but are rare in primary tumors. LCN, characterized by large nuclei with prominent nucleoli, predict a poor prognosis. We hypothesize that LCN can be created with high-dose intra-tumoral chemotherapy and identified by a digital analysis system.

METHODS

Orthotopic mouse xenografts were created using human neuroblastoma and treated with high-dose chemotherapy delivered locally via sustained-release silk platforms, inducing tumor remission. After recurrence, LCN populations were identified on H&E sections manually. Clusters of typical LCN and non-LCN cells were divided equally into training and test sets for digital analysis. Marker-controlled watershed segmentation was used to identify nuclei and characterize their features. Logistic regression was developed to distinguish LCN from non-LCN.

RESULTS

Image analysis identified 15,000 nuclei and characterized 70 nuclear features. A 19-feature model provided AUC >0.90 and 100% accuracy when >30% nuclei/cluster were predicted as LCN. Overall accuracy was 87%.

CONCLUSIONS

We recreated LCN using high-dose chemotherapy and developed an automated method for defining LCN histologically. Features in the model provide insight into LCN nuclear phenotypic changes that may be related to increased activity. This model could be adapted to identify LCN in human tumors and correlated with clinical outcomes.

Correction to Design, Synthesis, and Biological Evaluation of Tetrahydroisoquinoline-Based Histone Deacetylase 8 Selective Inhibitors

[This corrects the article DOI: 10.1021/acsmedchemlett.7b00126.].

Down-regulation of MYCN protein by CX-5461 leads to neuroblastoma tumor growth suppression

PURPOSE

MYCN oncogene amplification is an independent predictor of poor prognosis in neuroblastoma. CX-5461 is a small molecular inhibitor that prevents initiation of ribosomal RNA (rRNA) synthesis by RNA Pol I, down-regulating MYCN/MYC proteins. We hypothesize that neuroblastoma tumor growth can be suppressed by CX-5461.

METHODS

MYCN-amplified (KELLY, IMR5) and nonamplified (SY5Y, SKNAS) neuroblastoma cells were treated with CX-5461. MYCN/MYC expression after 24-48 h was determined by Western blot. Orthotopic neuroblastoma tumors created in mice using KELLY cells were treated with CX-5461-loaded silk films implanted locally. Tumor growth was monitored using ultrasound. Histologic evaluation of tumors was performed.

RESULTS

IC₅₀ for KELLY, IMR5, SY5Y, and SKNAS cells to CX-5461 was 0.75 μM, 0.02 μM, 0.8 μM, and 1.7 μM, respectively. CX-5461 down-regulated MYCN and MYC proteins at 0.25-1.0 μM on Western blot analysis. CX-5461-loaded silk film released 23.7±3 μg of the drug in 24 h and 48.2±3.9 μg at 120 h. KELLY tumors treated with CX-5461-loaded film reached 800 mm³ after 7.8±1.4 days, while those treated with control film reached the same size on 5.1±0.6 days (p=0.03). CX-5461-treated tumors showed collapse of nucleolar hypertrophy and MYCN protein downregulation.

CONCLUSION

We demonstrated that local delivery of CX-5461 via sustained release platform can suppress orthotopic neuroblastoma tumor growth, especially those with MYCN/MYC overexpression.

Silk Reservoirs for Local Delivery of Cisplatin for Neuroblastoma Treatment: In Vitro and In Vivo Evaluations

Neuroblastoma is the most common extracranial childhood tumor, and current treatment requires surgical resection and multidrug chemotherapy. Local, perioperative delivery of chemotherapeutics is a promising treatment method for solid tumors that require surgical removal. In this study, we have aimed to develop a controlled-release implant system to deliver cisplatin in tumor or tumor resection area. Silk fibroin, a biodegradable, nonimmunogenic biopolymer was used to encapsulate different doses of cisplatin in a reservoir system. The physical integrity of the reservoirs was characterized by evaluating the crystalline structure of silk secondary structure using FTIR spectroscopy. The in vitro release of cisplatin was evaluated in phosphate-buffered saline at 37°C, and the reservoirs were able to release the drug up to 30 days. The cytotoxicity of cisplatin and cisplatin reservoirs were tested on KELLY cells. Cytotoxicity data showed 3.2 μg/mL cisplatin was required to kill 50% of the cell population, and the released cisplatin from the silk reservoirs showed significant cytotoxicity up to 21 days. Intratumoral implantation of silk reservoirs into an orthotopic neuroblastoma mouse model decreased tumor growth significantly when compared with control subjects. These results suggest that silk reservoirs are promising carriers for cisplatin delivery to the tumor site.

Disseminated injection of vincristine-loaded silk gel improves the suppression of neuroblastoma tumor growth

BACKGROUND

Advanced-stage neuroblastoma patients require multiagent chemotherapy. Intratumoral implantation of vincristine-loaded silk gel uses local diffusion to decrease orthotopic neuroblastoma tumor growth in mice. We hypothesize that injecting vincristine-loaded silk gel into 8 locations within the tumor, instead of only centrally, decreases the diffusion distance and improves tumor growth suppression.

METHODS

Human neuroblastoma cells, KELLY, were injected into mouse adrenal glands to create orthotopic tumors. After the tumors reached 100 mm³ by ultrasound, silk gels loaded with 50 µg vincristine were injected centrally or in 8 areas throughout the tumor. Drug-release profile was measured in vitro. Endpoints were tumor size >1,000 mm³ and histologic examination.

RESULTS

Vincristine-loaded silk gels suppressed tumor growth up to an inflection point (458.7 ± 234.4 mm³ for central, 514.3 ± 165.8 mm³ for 8-point injection) before tumor growth accelerated >200 mm³ over 3 days. The time to inflection point was 6.6 days for central, 13.3 days for 8-point injection (P < .05). Using the sphere volume equation to approximate tumor volume, splitting the volume into 1/8 decreased the diffusion radius by 1/2. Histologic examination confirmed tumor necrosis adjacent to vincristine-loaded silk gel.

CONCLUSION

Injecting vincristine-loaded sustained release silk gel at 8 separate locations halved the diffusion distance and doubled the time for the tumor to reach the growth inflexion point.

In vitro and in vivo evaluation of etoposide - silk wafers for neuroblastoma treatment

High-risk neuroblastoma requires surgical resection and multi-drug chemotherapy. This study aimed to develop an extended release, implantable and degradable delivery system for etoposide, commonly used for neuroblastoma treatment. Different concentrations of silk, a biodegradable, non-toxic, non-immunogenic material were employed to prepare etoposide-loaded wafer formulations. Secondary structure of silk in the formulations was characterized using Fourier Transform Infrared (FTIR) spectroscopy and optimized based on the crystalline structure. Accelerated in vitro degradation studies under different conditions such as acidic, alkaline, oxidizing mediums and high temperature, were performed. The integrity of the silk wafer structure was maintained unless exposed to 0.1 N NaOH for 24 h. In vitro release of etoposide was performed in PBS (phosphate buffered saline) at 37 °C. Silk coated 6% wafers released the drug up to 45 days, while uncoated wafers released the drug for 30 days. Cytotoxicity study was performed on KELLY cells to evaluate the etoposide cytotoxicity (LC50) and the long-term efficacy of the etoposide wafer formulations. The results showed that etoposide killed 50% of the cells at 1 μg/mL concentration and the wafer formulations demonstrated significant cytotoxicity up to 22 days when compared to untreated cells. Using an orthotopic neuroblastoma mouse model, intra-tumoral implantation of the coated 6%, uncoated 6%, or uncoated 3% silk wafers were all effective at decreasing tumor growth. Histological examination revealed tumor cell necrosis adjacent to the drug-loaded silk wafer.

Abstract 2497: Inhibitors of RNA Pol I and an aminoacyl-tRNA synthetase result in MYC and MYCN downregulation in MYC family protein-driven neuroblastoma cells

We have previously reported histologic variants among unfavorable histology neuroblastomas (NB), having large cell appearance with vesicular nuclei and or prominent nucleolar (PN) formation, indicating hyperactive rRNA synthesis and protein translation. These features appear to be associated with dismal outcome and high-level MYC family protein expression. PN formation could provide critical prognostic and risk-stratification information for NB. At the same time, this observation could open up an opportunity for innovative therapy for aggressive NB. To assess this possibility, we examined the effect of two potent and specific small-molecule inhibitors of RNA Pol I activity and an aminoacyl tRNA synthetase (CX-5461 and Halofuginone, respectively) on growth and MYC family protein expression in NB cell lines. These small-molecule inhibitors inhibited growth of NB cell lines at low to submicromolar concentrations in vitro in 48 hours. Moreover, the inhibitors destabilized MYC and MYCN proteins in NB cells. Interestingly, halofuginone showed a rapid effect on the stability of MYC family proteins at 500 nM-1 uM (&lt;3 hours). In contrast, CX-5461 at 1 uM was less effective at the 3-hour time. At the concentration of 100 nM-250 nM for halofuginone and 1 uM for CX-5461 for up to 48 hours of the drug treatments, MYC and MYCN expression were both downregulated. We further examined the preclinical efficacy of halofuginone in orthotopic Kelly human NB xenografts in mice using a silk film as the drug delivery device. Halofuginone showed a significant growth-suppressive effect on the xenografts, as indicated by the time periods to reach certain tumor sizes being significantly longer in the halofuginone-treated group than those in the control group. Moreover, histologic examination of the xenografts showed a marked suppression of MYCN protein expression in the halofuginone-treated xenograft at day 17 of the drug treatment. Specific inhibition of hyperactive rRNA synthesis and protein translation was shown to be an effective way to suppress MYC/MYCN protein expression and NB growth. Together, MYC-family protein overexpression and PN formation should be included in new NB risk stratification and considered for potential therapeutic targets.

Citation Format: Naohiko Ikegaki, Jasmine Zeki, Bill Chiu, Hiroyuki Shimada. Inhibitors of RNA Pol I and an aminoacyl-tRNA synthetase result in MYC and MYCN downregulation in MYC family protein-driven neuroblastoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2497.

Rare MYC-amplified Neuroblastoma With Large Cell Histology

Background Although MYCN (aka N-myc) amplification is reported in ∼20% of neuroblastomas, MYC (aka C-myc) amplification appears to be a rare event in this disease. As of today, only 2 MYC-amplified neuroblastomas have been briefly mentioned in the literature. Methods We studied here the clinicopathological features of 3 MYC-amplified neuroblastomas. Results All 3 patients (2 females and 1 male) had stage 4 disease. One female is currently alive and well 52 months after the diagnosis, while the other female and male patients died of disease 24 and 20 months after the diagnosis, respectively. Further analysis on 2 tumors revealed unfavorable histology with MYC protein overexpression but with neither MYCN amplification nor MYCN protein overexpression. Both of these tumors exhibited "large cell neuroblastoma" histology with enlarged, uniquely open nuclei and nucleolar hypertrophy, along with "aberrant" desmin expression. Conclusions MYC-amplified neuroblastomas are extremely rare and seem to present with distinct clinicopathological features.

Design, Synthesis, and Biological Evaluation of Tetrahydroisoquinoline-Based Histone Deacetylase 8 Selective Inhibitors

Histone deacetylase 8 (HDAC8) is a promising drug target for multiple therapeutic applications. Here, we describe the modeling, design, synthesis, and biological evaluation of a novel series of C1-substituted tetrahydroisoquinoline (TIQ)-based HDAC8 inhibitors. Minimization of entropic loss upon ligand binding and use of the unique HDAC8 "open" conformation of the binding site yielded a successful strategy for improvement of both HDAC8 potency and selectivity. The TIQ-based 3g and 3n exhibited the highest 82 and 55 nM HDAC8 potency and 330- and 135-fold selectivity over HDAC1, respectively. Selectivity over other class I isoforms was comparable or better, whereas inhibition of HDAC6, a class II HDAC isoform, was below 50% at 10 μM. The cytotoxicity of 3g and 3n was evaluated in neuroblastoma cell lines, and 3n displayed concentration-dependent cytotoxicity similar to or better than that of PCI-34051. The selectivity of 3g and 3n was confirmed in SH-SY5Y cells as both did not increase the acetylation of histone H3 and α-tubulin. Discovery of the novel TIQ chemotype paves the way for the development of HDAC8 selective inhibitors for therapeutic applications.

Implantable chemotherapy-loaded silk protein materials for neuroblastoma treatment

Neuroblastoma is the most common extracranial childhood solid tumor. Treatment of high risk tumors require intense multicycle chemotherapies, resulting in short- and long-term toxicities. Here, we present treatment of an orthotopic neuroblastoma mouse model, with silk fibroin materials loaded with vincristine, doxorubicin or the combination as a intratumoral, sustained release system. The materials, loaded with vincristine with or without doxorubicin, significantly decreased neuroblastoma tumor growth compared to materials loaded without drug or doxorubicin only as well as intravenous (IV) drug treatment. The intratumoral drug concentration was significantly higher with intratumoral delivery versus IV. Furthermore, intratumor delivery decreased the maximum plasma concentration compared to IV delivery, reducing systemic exposure and possibly reduing long-term side effects of chemotherapy exposure. Histopathologically, tumors with remission periods >25 days before recurrence transformed from a "small-round-blue cell" (SBRC) to predominantly "large cell" neuroblastoma (LCN) histopathology, a more aggressive tumor subtype with unfavorable clinical outcomes. These results show that intratumoral chemotherapy delivery may be a treatment strategy for pediatric neuroblastoma, potentially translatable to other focal tumors types. Furthermore, this treatment modality allows for a clinically relevant mouse model of tumor transformation that may be used for studying the phenotypical tumor recurrence and developing more effective treatment strategies for recurrent tumors.

Abstract 1139: Translational control of MYC protein stability as a target of small molecules

It is well established that MYC family proteins drive tumor growth and sustain the malignant phenotype. However, MYC family proteins have gained the reputation of being “un-druggable” by small molecule inhibitors. This is because MYC proteins lack intrinsic enzymatic activities or appropriate molecular grooves to which small molecules may bind and inhibit their function. Nonetheless, previous studies suggest that MYC family proteins (MYC, MYCN, MYCL) can be “targetable” indirectly by accelerating their turnover rate at different biochemical pathways that regulate the steady state level of the proteins. These include transcriptional-inhibition of the corresponding genes and acceleration of their proteasome-dependent degradation. The goal of this study is to gain a better understanding of how the MYC family protein turnover is regulated, which in turn might help develop future new drugs against “MYC family-driven” cancers. We have used neuroblastoma, a childhood cancer, as a disease model and identified several small molecules that rapidly destabilize MYC and MYCN proteins in MYC-driven neuroblastoma cells. The small molecules include FCCP, OSU-03012 and Salinomycin. Preliminary data suggest that the common target of these compounds is mitochondria. Recently, we have also found Halofuginone, an FDA approved orphan drug for Scleroderma treatment exhibits a similar MYC-destabilizing activity. At submicromolar concentrations and less than one hour of drug-treatment, Halofuginone rapidly causes significant down-regulation of MYC proteins in neuroblastoma cells. Halofuginone is known to activate the eIF2α pathway, which controls translation. Activation of the eIF2α pathway is initiated by the activation of eIF2a kinases (GCN2, HRI, PERK, PKR) via autophosphorylation by various stress-related stimuli such as reactive oxygen species and misfolded proteins. The activated eIF2α kinases then inactivates eIF2α by phosphorylation, which subsequently halts translation globally. Interestingly, FCCP, OSU-03012 and Salinomycin treatments also caused eIF2α phosphorylation. These observations suggest that activation of the eIF2α pathway results in translational block of the MYC family protein expression in tumor cells. Because half-lives of MYC family proteins are very short, a sudden attenuation in protein translation can cause rapid down-regulation of the proteins. Hence, activation of the eIF2α pathway by small molecules may prove effective for rapid down-regulation of MYC family proteins in MYC-driven cancer cells.

Citation Format: Naohiko Ikegaki, Luqman Baloch, Christopher Chu, Joshua Lomahan, Jamie Harris, Bill Chiu. Translational control of MYC protein stability as a target of small molecules. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1139.

Abstract A37: Immunohistochemical detection of MYCN protein and MYC protein identifies highly aggressive neuroblastomas

Background:MYCN amplification with subsequent MYCN protein (MYCN-P) over-expression is a powerful indicator of a poor prognosis of neuroblastoma patients. Little is known regarding the prognostic significance of the homologous MYC protein (MYC-P) expression in this disease.

Methods: Immunohistochemical study for MYCN-P and MYC-P expression was conducted using a total of 357 cases of neuroblastoma, undifferentiated (20) or poorly differentiated (337) subtype with available unstained slides. The cases were collected and reviewed during one-year period of 2009 at the COG (Children's Oncology Group) Neuroblastoma Pathology Reference Laboratory. Relationship between these protein expressions and other prognostic markers [Clinical stage (stage 4, N=161 vs. non-stage 4, N=196); Age at diagnosis (&lt;18months, N=210 vs. ≥18months, N=147);MYCN status (amplified, N=82 vs. non-amplified, N=272); International Neuroblastoma Pathology Classification (FH-favorable histology, N=176 vs. UH-unfavorable histology, N=181); MKI (mitosis-karyorrhexis index, Low, N=159; Intermediate, N=103 vs. High, N=81); and prominent nucleolar (PN) formation (+, N=110 vs. -, N=247)] were analyzed.

Findings: Of 357 cases, there were 67 (19%) MYCN-P (+) tumors, 37 (10%) MYC-P (+) tumors, and only one (0.3%) tumor expressing both proteins. Both MYCN-P (+) and MYC-P (+) tumors were more likely diagnosed in older children with stage 4 disease. MYCN-P (+) tumors were associated with amplified MYCN and UH, and often had High MKI. MYC-P (+) tumors were also frequently UH but not associated with MYCN amplification, and more likely to have Low or Intermediate MKI. PN formation was significantly associated with either MYCN-P or MYC-P expression. FH patients without MYC-P/MYCN-P expressions exhibited the best survival (N=167, 89.7+/-5.5% 3-year EFS, 97.0+/-3.2% 3-year OS), followed by UH patients without MYC-P/MYCN-P expressions (N=84, 63.1+/-13.6% 3-year EFS, 83.5+/-9.4% 3-year OS). While MYCN-P (+) patients and MYC-P (+) patients had similar and significantly low (p&lt;0•0001) survival rates (46.2+/-12.0% 3-year EFS, 63.2+/-12.1% 3-year OS and 43.4+/-23.1% 3-year EFS, 63.5+/-19.2% 3-year OS, respectively). Notably, prognostic impact by MYC-P expression was independent from other factors.

Interpretation: In summary, about 30% of neuroblastoma cases in the undifferentiated and poorly differentiated subtypes expressed either MYCN protein (2/3 of the tumors) or MYC protein (1/3 of the tumors) in this series of cases. Those tumors were highly aggressive clinically: patients with MYC-protein expressing tumor had similarly low 3-year EFS and 3-year OS rate to those with MYCN-protein expressing tumor. MYCN-P expression was associated with MYCN amplification. In contrast, MYC-P expression was not associated with MYCN amplification, and its prognostic impact was independent from other standard prognostic factors in this disease. With the results of this report, we should move on to a prospective study of MYC-P expression as a new biomarker for high-risk neuroblastomas.

Citation Format: Larry L. Wang, Risa Teshiba, Naohiko Ikegaki, Xao X. Tang, Arlene Naranjo, Wendy B. London, Michael D. Hogarty, Julie M. Gastier-Foster, A. Thomas Look, Julie R. Park, John M. Maris, Susan L. Cohn, Robert C. Seeger, Shahab Asgharzadeh, Hiroyuki Shimada. Immunohistochemical detection of MYCN protein and MYC protein identifies highly aggressive neuroblastomas. [abstract]. In: Proceedings of the AACR Special Conference on Myc: From Biology to Therapy; Jan 7-10, 2015; La Jolla, CA. Philadelphia (PA): AACR; Mol Cancer Res 2015;13(10 Suppl):Abstract nr A37.

Abstract 1218: A biological crosstalk between p53 and MYCN/MYC in neuroblastoma

We previously showed that TSA (an HDAC inhibitor) and Epoxomycin (a proteasome inhibitor) as single agents and in combination significantly suppressed growth of MYCN-amplified neuroblastoma cells. However, these compounds had contrasting effects on MYCN expression. TSA down-regulated MYCN expression, but Epoxomycin and the TSA/Epoxomycin combination led to MYCN hyper-expression (defined as markedly increased expression beyond that observed in the untreated cells). The expression of p53 was also increased in MYCN-amplified cells treated with Epoxomycin or the TSA/Epoxomycin combination. In an independent study, we also found that treatment of neuroblastoma cells (MYCN-amplified or non-MYCN amplified) with 17-DMAG and S(+) Ibuprofen resulted in an increase in p53 expression and a reduction in MYCN or MYC expression. In this study, we examined (i) the pattern of gene expression induced by MYCN hyper-expression in MYCN-amplified cells, and (ii) a potential functional relationship between p53 and MYCN/MYC in neuroblastoma. Transient transfection of MYCN and TP53 into neuroblastoma cells was done by electroporation. Gene expression profiling, TaqMan real-time PCR, and Western blot assays were used to detect expression patterns of genes and proteins. It was observed that ectopic over MYCN expression in MYCN-amplified IMR5 cells resulted in growth suppression. Gene expression profiling analysis revealed that the hyper-expression of MYCN in the MYCN-transfected IMR5 cells led to an increased expression of genes involved in growth suppression and apoptosis, including EGR1, EPHA2, KLF2, PERP and SEL1L. The expression of PERP and EPHA2 was confirmed by TaqMan real-time PCR and Western blot assay, respectively. Interestingly, co-transfection of TP53 and MYCN in IMR5 cells led to high p53 expression but a reduction in MYCN expression (below the levels of endogenous MYCN). Transfection of TP53 into IMR5, SY5Y, and SKNAS reduced endogenous MYCN and MYC expression in these cells. Consistent with these observations, treatment of IMR5 and SY5Y cells with known p53-inducers, Doxorubicin and CoCl2, resulted in an increased p53 expression and a reduction of MYCN and MYC expression. Although high MYCN expression sustains growth of MYCN-amplified neuroblastoma, the hyper-expression of MYCN is deleterious to survival of these cells. In addition, augmented p53 expression may elicit a negative feedback regulation of MYCN/MYC expression in neuroblastoma.

Citation Format: Naohiko Ikegaki, Xao Tang. A biological crosstalk between p53 and MYCN/MYC in neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1218. doi:10.1158/1538-7445.AM2015-1218

Abstract 4215: Small molecule compounds that destabilize stem cell factors

Cancer stem cells (CSCs) are thought to be present in malignant tumors at various proportions, and their phenotype can drift over time. Based on the current view, this elusive population of cancer cells is likely responsible for distant metastases, drug resistance and recurrence. However, the process by which such cell population is generated and maintained in a tumor mass has been unclear. Based on our previous study (PNAS Vol. 110: 6097-102 2013) and others, this process may involve the elevated expression of stem cell factors (SOX2, OCT4, NANOG, LIN28, KLF4, MYC, MYCN and those with equivalent functions). If so, it is conceivable that destabilization of these proteins would facilitate the eradication of CSC compartments in tumor mass. We have previously identified several small molecule compounds that confer the anti-growth effect on the stem cell-like neuroblastoma cells via screening of the Prestwick Chemical Library®, containing 1200 FDA-approved small molecules and of other selected experimental small molecules by using MTS assays. These compounds were structurally and biologically diverse molecules, including Alexidine (Alex), Benzethonium (Benz), Ketoconazole (Keto), Flubendazole (Flu), Auranofin (Aura), Nifuroxazide (Nif), Itraconazole (Itac) and JQ1. In this study, we investigated the effects of these selected small molecules on the expression of stem cell factors using the human teratocarcinoma cell lines NT2 and NCCIT as model systems, because these cells retain the expression of the majority of stem cell factors. The teratocarcinoma cell lines were treated with the small molecules at 0.5 to 10 μM for 24 hours and subjected to Western blot analysis. The expression of stem cell factors was down-regulated in NT2 cells by the several small molecules tested. The expression of SOX2 was down-regulated by Benz (5 μM), Flu (10 μM), Nif (10 μM), Aura (1 μM) and JQ1 (5 μM); the expression of OCT4 was down-regulated by Benz, Flu, Nif, Alex and JQ1; the NANOG expression was down-regulated by the all compounds tested; the expression of LIN28 was down-regulated by Benz, Flu and Aura; the expression of MYC/MYCN was down-regulated by Benz, Flu, Nif, Alex, Keto and JQ1. Interestingly, Auranofin treatment augmented the expression of MYC/MYCN, although the compound was growth suppressive to NT2 cells. Unlike the stem cell factors, the expression of LIN28B, which is the homologue of LIN28, was not affected by any of the compounds tested. A similar observation was made for NCCIT cells, but the effect of the compounds on the expression of stem cell factors appeared to be weaker. Collectively, the data suggest that small molecules identified via the process described could become useful lead chemicals for developing drug-like compounds that can target the most malignant stem cell-like cancer cells.

Citation Format: Naohiko Ikegaki, Sarah Lomahan, Xao Tang. Small molecule compounds that destabilize stem cell factors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4215. doi:10.1158/1538-7445.AM2015-4215

Abstract 3910: Identification of lead organic compounds active against stem cell-like neuroblastoma cells by high throughput screening

Cancer stem cells (CSCs) are plastic in nature, a characteristic that hampers cancer therapeutics. We previously reported the establishment of induced neuroblastoma (NB) stem cells (iCSC), which were stable stem cell-like NB cells in sphere culture. These cells recapitulated the in vivo histological phenotypes of Large-Cell NB (LCN), the most aggressive and deadly subset of NB, including vesicular nuclei and two to three prominent nucleoli (PNAS Vol. 110: 6097-102 2013). In addition to the LCN phenotype, high-level expression MYC or MYCN is the consistent feature of the iCSC xenografts grown in immune-compromised mice. The goal of this study is to identify lead organic compounds active against NB iCSCs by high throughput screening. By using MTS assays, the SKNAS iCSC and the parental monolayer cells were used to screen the Prestwick Chemical Library®, containing 1200 FDA-approved small molecules. Growth suppressive compounds were defined as they exhibited cell survival reduction of greater than 80% compared to DMSO control. There were unexplored compounds with significant antineoplastic activity among existing antibacterial, antifungal, antiprotozoal, and anthelmintic compounds. Among the compounds screened, we identified a dozen of small molecules that were preferentially growth suppressive to the SKNAS iCSC over the monolayer cells. The secondary MTS assay confirmed so far that Chlorhexidine (antiseptic), Benzethonium (antiseptic) and Digoxin (cardiac glycoside) were potential anti-NB iCSC agents: they were more effective in suppressing growth of the SKNAS iCSC than the monolayer cells. In addition, these compounds exhibited MYC destabilizing activity in the SKNAS iCSC. Notably, JQ1, the recently identified MYC destabilizer, was less effective than Chlorhexidine, Benzethonium and Digoxin in suppressing growth of SKNAS iCSC. The above three compounds also showed the MYCN destabilizing effect in another pair of MYCN-amplified SKNBE(2)C iCSCs and SKNBE(2)C monolayer cells. We are currently completing characterization of the small molecules identified with focus on their anti- iCSC growth and anti-MYC/MYCN effects. This study would reveal specific pathways that regulate biological activities of the CSCs. In addition, it is a promising approach that could lead to development of safe and effective anti-cancer therapeutics not only for NB but also other cancer types.

Citation Format: Naohiko Ikegaki, Kiira Ratia, Ruth Hsiao, Mariko M. Limpar, Sarah Lomahan, Xao X. Tang. Identification of lead organic compounds active against stem cell-like neuroblastoma cells by high throughput screening. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3910. doi:10.1158/1538-7445.AM2014-3910

Abstract 3858: Implications of the downregulation of stemness/reprogramming factor expression by ibuprofen and biguanides

Cancer stem cells (CSCs) are thought to have the capacity to renew indefinitely, to initiate tumor formation, and to give rise to multiple non-tumorigenic progenies via asymmetric cell division. As a result of this phenotypic drift, an established tumor would consist of a mixture of CSC and non-CSC. Based on the current view, the CSC population is likely responsible for distant metastases, drug resistance and recurrence. However, the process by which this cell population is generated in a tumor mass has continued to be unclear. Based on our previous study (PNAS Vol. 110: 6097-6102, 2013), this process may involve nuclear reprogramming, namely the elevated expression of stemness/reprogramming factors (SOX2, OCT4, NANOG, LIN28, KLF4, MYC/MYCN, and those with equivalent functions). If so, it is conceivable that destabilization of these proteins would prevent or substantially slow down the generation of CSC compartment(s) within a tumor mass. Recently, we have reported that anti-inflammatory Ibuprofen and anti-diabetic biguanides destabilize MYC and MYCN in neuroblastoma cells. In this study, we have investigated the effects of Ibuprofen and Phenformin on stemness phenotypes of cancer cells (i.e., the expression of stemness factors) using the teratocarcinoma cell line NT2. NT2 cells were chosen as the experimental system because unlike many other cancer cell lines, they retain the expression of stemness/reprogramming factors. Furthermore, they express both MYC and MYCN proteins. Our data showed that high-dose/short-term treatment of NT2 cells with Phenformin and Ibuprofen significantly down-regulated the expression of MYC/MYCN, OCT4, SOX2, and NANOG. Moreover, the anti-stemness effect of Ibuprofen in the low-dose/long-term treatment was also evident (0.15 mM at Day 7 of the drug-treatment or 0.15 mM and 0.25 mM at Day 4). Experiments are underway to address the similar effect of low-dose/long-term treatment of Metformin and Phenformin in NT2 cells. We are also investigating a change in global gene expression in the drugs-treated NT2 cells, with the emphasis on stem cell-related genes and pathways. Results of these studies will help us better understand how these common drugs (anti-inflammation and diabetes medications) can be used in anti-cancer therapeutics, and more importantly, in cancer prevention, which is the key to eradication of this disease.

Citation Format: Laura Grenlin, Tuan-Anh Tran, Sarah Lomahan, Naohiko Ikegaki, Xao X. Tang. Implications of the downregulation of stemness/reprogramming factor expression by ibuprofen and biguanides. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3858. doi:10.1158/1538-7445.AM2014-3858

Aurora kinase A is a possible target of OSU‑03012 to destabilize MYC family proteins

OSU-03012, a 3-phosphoinositide-dependent kinase-1 (PDK1) inhibitor, destabilizes MYCN and MYC proteins in neuroblastoma cells. However, AKT phosphorylation is barely detectable in neuroblastoma cells under normal culture conditions whether treated with OSU-03012 or not. This observation suggests that PDK1 is not the main target of OSU-03012 to destabilize MYC and MYCN in neuroblastoma cells. In the present study, we explored one of the possible mechanisms by which OSU-03012 destabilizes MYC and MYCN. Since Aurora kinase A is reported to phosphorylate GSK3β, leading to its inactivation, we hypothesized that one of the targets of OSU-03012 is Aurora kinase A. Comparative analysis of OSU-03012 and VX-680, a potent and specific inhibitor of Aurora kinases, showed that both inhibitors destabilized MYC and MYCN and were significantly growth suppressive to neuroblastoma cell lines. In silico molecular docking analysis further showed that the calculated interaction energy between Aurora kinase A and OSU-03012 was −109.901 kcal/mol, which was lower than that (−89.273 kcal/mol) between Aurora kinase A and FXG, an Aurora kinase-specific inhibitor. Finally, an in vitro Aurora kinase A inhibition assay using a recombinant Aurora kinase A showed that OSU-03012 significantly inhibited Aurora kinase A, although it was weaker in potency than that of VX-680. Thus, OSU-03012 has a likelihood of binding to and inhibiting Aurora kinase A in vivo. These results suggest that OSU-03012 affects multiple cellular targets, including Aurora kinase A, to exhibit its growth suppressive and MYC and MYCN-destabilizing effects on neuroblastoma and other cancer cells.

Destabilization of MYC/MYCN by the mitochondrial inhibitors, metaiodobenzylguanidine, metformin and phenformin

In the present study, we investigated the anticancer effects of the mitochondrial inhibitors, metaiodobenzylguanidine (MIBG), metformin and phenformin. ¹³¹I-MIBG has been used for scintigraphic detection and the targeted radiotherapy of neuroblastoma (NB), a pediatric malignancy. Non-radiolabeled MIBG has been reported to be cytotoxic to NB cells in vitro and in vivo. However, the mechanisms behind its growth suppressive effects have not yet been fully elucidated. Metformin and phenformin are diabetes medications that are being considered in anticancer therapeutics. We investigated the anticancer mechanisms of action of MIBG and metformin in NB. Our data revealed that both drugs suppressed NB cell growth and that the combination drug treatment was more potent. MIBG reduced MYCN and MYC expression in MYCN-amplified and non-MYCN-amplified NB cells in a dose- and time-dependent manner. Metformin was less effective than MIBG in destabilizing MYC/MYCN. The treatment of NB cells with metformin or MIBG resulted in an increased expression of genes encoding biomarkers for favorable outcome in NB [(ephrin (EFN)B2, EFNB3, EPH receptor B6 (EPHB6), neurotrophic tyrosine kinase, receptor, type 1 (NTRK1), CD44 and Myc-interacting zinc finger protein (MIZ-1)] and tumor suppressor genes [(early growth response 1 (EGR1), EPH receptor A2 (EPHA2), growth arrest and DNA-damage-inducible, beta (GADD45B), neuregulin 1 (NRG1), TP53 apoptosis effector (PERP) and sel-1 suppressor of lin-12-like (C. elegans) (SEL1L)]. Accordingly, metformin and MIBG augmented histone H3 acetylation in these cells. Phenformin also exhibited histone modification and was more effective than metformin in destabilizing MYC/MYCN in NB cells. Our data suggest that the destabilization of MYC/MYCN by MIBG, metformin and phenformin and their effects on histone modification are important mechanisms underlying their anticancer effects.

S(+)-ibuprofen destabilizes MYC/MYCN and AKT, increases p53 expression, and induces unfolded protein response and favorable phenotype in neuroblastoma cell lines

Neuroblastoma is a common pediatric solid tumor that exhibits a striking clinical bipolarity favorable and unfavorable. The survival rate of children with unfavorable neuroblastoma remains low among all childhood cancers. MYCN and MYC play a crucial role in determining the malignancy of unfavorable neuroblastomas, whereas high-level expression of the favorable neuroblastoma genes is associated with a good disease outcome and confers growth suppression of neuroblastoma cells. A small fraction of neuroblastomas harbors TP53 mutations at diagnosis, but a higher proportion of the relapse cases acquire TP53 mutations. In this study, we investigated the effect of S(+)-ibuprofen on neuroblastoma cell lines, focusing on the expression of the MYCN, MYC, AKT, p53 proteins and the favorable neuroblastoma genes in vitro as biomarkers of malignancy. Treatment of neuroblastoma cell lines with S(+)-ibuprofen resulted in a significant growth suppression. This growth effect was accompanied by a marked decrease in the expression of MYC, MYCN, AKT and an increase in p53 expression in neuroblastoma cell lines without TP53 mutation. In addition, S(+)-ibuprofen enhanced the expression of some favorable neuroblastoma genes (EPHB6, CD44) and genes involved in growth suppression and differentiation (EGR1, EPHA2, NRG1 and SEL1L). Gene expression profile and Ingenuity pathway analyses using TP53-mutated SKNAS cells further revealed that S(+)-ibuprofen suppressed molecular pathways associated with cell growth and conversely enhanced those of cell cycle arrest and the unfolded protein response. Collectively, these results suggest that S(+)-ibuprofen or its related compounds may have the potential for therapeutic and/or palliative use for unfavorable neuroblastoma.

Neuroblastoma of undifferentiated subtype, prognostic significance of prominent nucleolar formation, and MYC/MYCN protein expression: a report from the Children's Oncology Group

BACKGROUND

This study sought to investigate biological/clinicopathological characteristics of neuroblastoma, undifferentiated subtype (NBUD).

METHODS

This study examined 157 NBUD cases filed at the Children's Oncology Group Neuroblastoma Pathology Reference Laboratory, and survival rates of the patients were analyzed with known prognostic factors. Immunostainings for MYCN and MYC protein were performed on 68 tumors.

RESULTS

NBUD cases had a poor prognosis (48.4% ± 5.0% 3-year event-free survival [EFS]; 56.5% ± 5.0% overall survival [OS]), and were often associated with high mitosis-karyorrhexis index (MKI, 65%), prominent nucleoli (PN, 83%), ≥ 18 months of age (75%), MYCN amplification (MYCN-A, 83%), diploid pattern (63%), and 1pLOH (loss of heterozygosity (72%). However, these prognostic indicators, except for MYCN status, had no significant impact on survival. Surprisingly, EFS for patients with MYCN-A tumors (53.4% ± 5.6%) was significantly better (P=.0248) than for patients with MYCN-nonamplified (MYCN-NA) tumors (31.7% ± 11.7%), with MYCN-NA and PN (+) tumors having the worst prognosis (9.3%  ± 8.8%, P=.0045). Immunohistochemically, MYCN expression was found in 42 of 48 MYCN-A tumors. In contrast, MYC expression was almost exclusively found in the MYCN-NA tumors (9 of 20) especially when they had PN (8 of 11). Those patients with only MYC-positive tumors had the worst EFS (N=8, 12.5% ± 11.7%) compared with only MYCN-positive (N=39, 49.9% ± 17.7%) and both negative tumors (N=15, 70.0% ± 17.1%) (P= .0029). High MKI was often found in only MYCN-positive (30 of 38) but rarely in only MYC-positive (2 of 8) tumors.

CONCLUSIONS

NBUD represents a unique subtype of neuroblastoma associated with a poor prognosis. In this subtype, MYC protein expression may be a new prognostic factor indicating more aggressive clinical behavior than MYCN amplification and subsequent MYCN protein expression.

Abstract 2654: Induced stable neuroblastoma stem cells recapitulate in vivo highly aggressive large-cell neuroblastomas

Neuroblastoma (NB) is a pediatric tumor of neural crest origin, and half of the cases are highly aggressive. Based on the degree of neuronal differentiation, NB is histopathologically divided into undifferentiated (UD), poorly differentiated (PD) and differentiating subtypes. Recently, a unique histological subset of NBs within the UD and PD subtypes has been identified. These tumors are uniformly composed of large cells having vesicular nuclei with sharply outlined nuclear membranes, and one to four prominent nucleoli, which are referred to as “Large-Cell Neuroblastomas” or LCNs. Patients with the UD neuroblastoma with the LCN appearance had a very poor prognosis regardless of age at diagnosis, clinical stage, and DNA index. Surprisingly, non-MYCN amplified UDs behaved significantly worse than MYCN amplified UDs. Our hypothesis is that the histological features and the clinical behavior of LCNs are the reminiscence of a malignancy likely driven by stem cell-like cancer cells. To gain better understanding of the nature of LCNs, we have generated phenotypically stablilized stem cell-like NB cells by treating monolayer NB cell lines with epigenetic modifiers for a short time. Without further exposure to epigenetic modifiers, stemness phenotypes of the NB cells were maintained over a year in sphere-forming culture conditions. Hence, we referred to these spheres as induced CSCs (iCSCs). We previously presented that the SKNAS iCSC had a very high tumor-initiating ability in SCID/Beige mice and SKNAS iCSC xenografts recapitulated the histological appearance of totally undifferentiated “large-cell” NBs. A cancer stem cell marker, CXCR4, was preferentially expressed in the iCSC xenografts over the monolayer counterparts. In this study, we established additional iCSCs from three NB cell lines [SKNBE(2)C, CHP134, SY5Y]. The expression of stemness factors was augmented in these NB iCSCs compared to conventional monolayer counterparts. In addition, the expression of stem cell markers (CD24, CD133) and neural crest stem cell markers (SOX9, SLUG, Musashi, p75NTR) was elevated in these NB iCSCs. Notably, SCID/Beige mice subcutaneously injected with one hundred SKNBE(2)C iCSCs formed tumors, and in some cases, SKNBE(2)C iCSCs metastasized to adrenal gland, liver, spleen, kidney, indicating an increased tumor invasiveness of these cells. CXCR4 and p75NTR expression was positive in the iCSC xenografts, although not uniformly. By histopathological and immunohistochemical examinations, we confirmed that the xenografts established from SKNAS iCSC, SKNBE(2)C iCSC, CHP134 iCSC, and SY5Y iCSC shared two common and consistent features: the LCN phenotype and high-level expression of MYC/MYCN. These characteristics may help identify the presence of CSC compartment in patients’ specimens. The established NB iCSCs may also serve as useful tools for the development of effective therapeutics against NB.

Citation Format: Naohiko Ikegaki, Hiroyuki Shimada, Xao X. Tang. Induced stable neuroblastoma stem cells recapitulate in vivo highly aggressive large-cell neuroblastomas. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2654. doi:10.1158/1538-7445.AM2013-2654

Abstract 766: Phenformin is a MYCN/MYC destabilizer that can specifically target neural crest derived tumors

We have been interested in identifying MYCN/MYC destabilizers that can specifically target neural crest derived tumors (neuroblastoma, melanoma, and malignant pheochromocytoma). MYCN amplification and its over-expression are associated with the worst neuroblastoma disease outcome. Non-MYCN amplified neuroblastomas express high-levels of MYC, and prognosis of these neuroblastomas is very poor. Melanoma and malignant pheochromocytoma are also known for high MYC expression. Interestingly, these neural crest derived tumors characteristically express the norepinephrine transporter (NET). This feature can be used to specifically target the tumor cells with agonists of NET, such as Meta-Iodo-BenzylGuanidine (MIBG). In the previous AACR meeting, we presented our finding that non-radio-labeled MIBG can suppress growth of neuroblastoma cells in vitro, and this effect is in part related to its ability to destabilize MYC and MYCN. We have also shown that FCCP, a well-known mitochondrial respiration inhibitor, destabilized MYCN and MYC in neuroblastoma cells and caused growth suppression. Recently, it has been reported that Phenformin, a Type II diabetic drug, binds NET, suggesting that NET positive cells preferentially uptake Phenformin. It is also known that Phenformin inhibits the mitochondrial electron transfer system. In this study, we have investigated a possible effect of Phenformin on growth and MYC/MYCN stability in neuroblastoma cells in vitro. SKNBE(2)C and CHP134 neuroblastoma cell lines were treated with various doses (0-2.5mM) of Phenformin for two days. MTS assay was used to assess the effect of Phenformin on growth of the cells. There was a dose-dependent growth suppression of the NB cell lines tested. Phenformin was more effective against growth of SKNBE(2)C than CHP134 cells. The effect of Phenformin on MYC/MYCN expression in four neuroblastoma cell lines [SKNBE(2)C, CHP134, SKNAS, and SY5Y] was also examined by Western blot assay. SKNBE(2)C and CHP134 express MYCN, whereas SKNAS and SY5Y express MYC at high levels. Treatment of these cells with Phenformin at the dose of 1mM for 24 hours resulted in destabilization of MYCN/MYC, suggesting that the growth suppressive effect of Phenformin on neuroblastoma cells was in part due to reduction in MYC/MYCN expression. We are currently examining whether the above observations made in neuroblastoma are also applicable to other neural crest derived tumors. In addition, we are investigating how Phenformin-related mitochondrial dysfunction causes destabilization of MYC/MYCN in neuroblastoma cells.

Citation Format: Naohiko Ikegaki, Srah Lomahan, Xao X. Tang. Phenformin is a MYCN/MYC destabilizer that can specifically target neural crest derived tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 766. doi:10.1158/1538-7445.AM2013-766

Abstract 2875: Meta-iodo-benzylguanidine (MIBG) is a MYCN/MYC destabilizer that specifically targets neural crest derived tumors

Melanoma and malignant pheochromocytoma are known for high MYC expression. MYCN amplification and its over-expression are associated with the worst neuroblastoma disease outcome. Meta-iodo-benzylguanidine (MIBG) is a norepinephrine analogue and a mitochondrial respiration inhibitor. 131I-MIBG has been used for scintigraphic detection of neural crest derived tumors (neuroblastoma, pheochromocytoma and melanoma) that specifically uptake MIBG by norepinephrine transporters (NET). 131I-MIBG is also used for targeted radiotherapy of neuroblastoma and pheochromocytoma. Non-radiolabeled MIBG had been reported to be cytotoxic to neuroblastoma cells in vitro and in vivo. However, the molecular mechanism of its growth suppressive effect was not elucidated. Our previous studies showed that FCCP, a well-known mitochondrial respiration inhibitor, destabilized MYCN and MYC in neuroblastoma cells and caused growth suppression. In this study we confirmed that MIBG suppressed growth of neuroblastoma cell lines (SKNBE(2)C, IMR5, Nb69, and SKNAS), and its growth suppressive effect in each cell line correlated with NET expression in these cells. In addition, MIBG suppressed growth of neuroblastoma stem cells derived from SKNBE(2)C. MIBG treatment of SKNBE(2)C and SKNAS resulted in an increase expression of growth suppressive gene (GADD45B) and genes encoding for biomarkers of favorable neuroblastoma (CD44, EPHB6, EFNB2, EFNB3, NTRK1). Treatment of MYCN amplified (SKNBE(2)C, IMR5) and non-MYCN amplified (Nb69, SKNAS) neuroblastoma cells with MIBG resulted in marked reduction of MYCN and MYC expression, respectively in dose and time dependent fashions. Collectively, our studies suggest that MIBG not only targets neural crest derived tumors, but also is a MYCN/MYC destabilizing agent.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2875. doi:1538-7445.AM2012-2875

Abstract LB-142: Regulation of MYCN stability by reactive oxygen species in neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Amplification of the MYCN proto-oncogene is associated with older age, rapid tumor progression, and the worst outcome of this disease. As MYCN amplification leads to its over-expression, high-level expression of MYCN is thought to cause an aggressive behavior of MYCN amplified tumors. In fact, the forced reduction of MYCN protein expression by siRNA results in growth suppression and apoptosis of NB cells with MYCN amplification. We have identified several compounds that can rapidly destabilize the MYCN protein (within a few hours), in NB cells and cause growth suppression. The compounds include FCCP, OSU-03012, and Salinomycin. Our recent data suggest that a common effect of the above compounds appears to be the inhibition of mitochondrial functions.

Moreover, ascorbic acid, an anti-oxidant, abolishes the effect of these compounds on MYCN protein stability. It is known that inhibition of mitochondrial oxidative phosphorylation increases the production of reactive oxygen species (ROS), which include superoxide (O2-), hydroxyl radical (•OH), and hydrogen peroxide (H2O2). Anti-oxidants are also known to quench ROS. Preliminary data showed that ROS was detected when the IMR5 NB cells were treated with OSU-03012 for three hours. In addition, we have found that forced over-expression of pVHL, an E3 ubiquitin ligase, in NB cell lines results in reduction of MYCN protein levels. We are currently testing whether ROS regulates MYCN stability by hydroxylation of proline residues on MYCN, and whether pVHL recognizes the ROS-modified MYCN, which is then subjected to rapid proteasome-dependent degradation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-142. doi:10.1158/1538-7445.AM2011-LB-142

Biological effects of induced MYCN hyper-expression in MYCN-amplified neuroblastomas

Neuroblastoma is a childhood malignancy of the sympathetic nervous system. The tumor exhibits two different phenotypes: favorable and unfavorable. MYCN amplification is associated with rapid tumor progression and the worst neuroblastoma disease outcome. We have previously reported that inhibitors of histone deacetylase (HDAC) and proteasome enhance favorable neuroblastoma gene expression in neuroblastoma cell lines and inhibit growth of these cells. In this study, we investigated the effect of trichostatin A or TSA (an HDAC inhibitor), and epoxomycin (a proteasome inhibitor) on MYCN and p53 expression in MYCN-amplified neuroblastoma cells. It was found that TSA down-regulated MYCN expression, but Epoxomycin and the TSA/Epoxomycin combination led to MYCN hyper-expression in MYCN-amplified neuroblastoma cell lines. Despite their contrasting effects on MYCN expression, TSA and Epoxomycin caused growth suppression and cell death of the MYCN-amplified cell lines examined. Consistent with these data, forced hyper-expression of MYCN in MYCN-amplified IMR5 cells via transfection resulted in growth suppression and the increased expression of several genes known to suppress growth or induce cell death. Furthermore, Epoxomycin as a single agent and its combination with TSA enhance p53 expression in the MYCN-amplified neuroblastoma cell lines. Unexpectedly, co-transfection of TP53 and MYCN in IMR5 cells resulted in high p53 expression but a reduction of MYCN expression. Together our data suggest that either down regulation or hyper-expression of MYCN results in growth inhibition and/or apoptosis of MYCN-amplified neuroblastoma cells. In addition, elevated p53 expression has a suppressive effect on MYCN expression in these cells.

Biological significance of EPHA2 expression in neuroblastoma

Neuroblastoma is a pediatric solid tumor that exhibits striking clinical bipolarity. Despite extensive efforts to treat unfavorable neuroblastoma, survival rate of children with the disease is among the lowest. Previous studies suggest that EPHA2, a member of the EPH family receptor kinases, can either promote or suppress cancer cell growth depending on cellular contexts. In this study, we investigated the biological significance of EPHA2 in neuroblastoma. It was found that tumorigenic N-type neuroblastoma cell lines expressed low levels of EPHA2, whereas hypo-tumorigenic S-type neuroblastoma cell lines expressed high levels of EPHA2 (p<0.005). Notably, inhibitors of DNA methylation and histone deacetylase enhanced EPHA2 expression in N-type cells, suggesting that EPHA2 is epigenetically silenced in unfavorable neuroblastoma cells. Furthermore, ectopic high-level expression of EPHA2 in N-type neuroblastoma cell lines resulted in significant growth suppression. However, Kaplan-Meier survival analysis showed that high EPHA2 expression was not associated with a good disease outcome of neuroblastoma, indicating that EPHA2 is not a favorable neuroblastoma gene, but a growth suppressive gene for neuroblastoma. Accordingly, EPHA2 expression was markedly augmented in vitro in neuroblastoma cells treated with doxorubicin, which is commonly used for treating unfavorable neuroblastoma. Taken together, EPHA2 is one of the effectors of chemotherapeutic agents (e.g., gene silencing inhibitors and DNA damaging agents). EPHA2 expression may thus serve as a biomarker of drug responsiveness for neuroblastoma during the course of chemotherapy. In addition, pharmaceutical enhancement of EPHA2 by non-cytotoxic agents may offer an effective therapeutic approach in the treatment of children with unfavorable neuroblastoma.

De novo identification of MIZ-1 (ZBTB17) encoding a MYC-interacting zinc-finger protein as a new favorable neuroblastoma gene

PURPOSE

Neuroblastoma is a childhood cancer that exhibits either a favorable or an unfavorable phenotype. Favorable neuroblastoma genes (EPHB6, EFNB2, EFNB3, NTRK1, and CD44) are genes whose high-level expression predicts favorable neuroblastoma disease outcome. Accordingly, the forced expression of these genes or their reactivation by gene silencing inhibitors in unfavorable neuroblastoma cells results in suppression of tumor growth and metastases. This study was undertaken to design an experimental strategy to identify additional favorable neuroblastoma genes.

EXPERIMENTAL DESIGN

Favorable neuroblastoma gene candidates were first identified by gene expression profiling analysis on IMR5 neuroblastoma cells treated with inhibitors of DNA methylation and histone deacetylase against the untreated control cells. Among the candidates, we focused on MIZ-1, which encodes a MYC-interacting zinc-finger protein, because it is known to enhance the expression of growth suppressive genes, such as CDKN1A.

RESULTS

High-level MIZ-1 expression was associated with favorable disease outcome of neuroblastoma (P = 0.0048). Forced MIZ-1 expression suppressed in vitro growth of neuroblastoma cell lines. High MIZ-1 expression was correlated with the small-size neuroblastoma xenografts treated with gene silencing inhibitors or a glucocorticoid. In addition, forced MIZ-1 expression enhanced the expression of CD44 and EFNB2 in neuroblastoma cell lines in vitro. Furthermore, MIZ-1 expression was positively correlated with the expression of favorable neuroblastoma genes (EFNB2, EFNB3, EPHB6, and NTRK1) in the human neuroblastoma xenograft therapeutic models.

CONCLUSION

MIZ-1 is a new favorable neuroblastoma gene, which may directly or indirectly regulate the expression of other favorable neuroblastoma genes.

The MYCN Enigma: Significance of MYCN Expression in Neuroblastoma

MYCN amplification strongly predicts adverse outcome of neuroblastoma. However, the significance of MYCN expression in the clinical and biological behavior of neuroblastoma has been unclear. To address this question, we first examined the expression of MYCN in combination with TrkA (a favorable prognostic indicator of neuroblastoma) in 91 primary neuroblastoma by quantitative reverse transcription-PCR and investigated the relationship among patient survival, MYCN, and TrkA expressions. Three subsets of neuroblastoma were defined based on MYCN and TrkA expression. Neuroblastoma expressing the highest level of MYCN but little TrkA were MYCN-amplified cases, which had a 5-year survival of 9.3%. Interestingly, MYCN and TrkA expression showed a linear correlation (r = 0.5664, P < 0.00005) in neuroblastoma lacking MYCN amplification, and the 5-year survival of neuroblastoma patients with low MYCN and low TrkA expressions was 63.7%, whereas those with high expression of both had a 5-year survival of 88.1% (P < 0.00005). This nonlinear distribution of disease outcome relative to MYCN expression in neuroblastoma explains why MYCN expression is not predictive of neuroblastoma disease outcome by dichotomous division of the neuroblastoma cohort. However, high-level MYCN expression is associated with favorable outcome in neuroblastoma lacking MYCN amplification. Furthermore, forced expression of MYCN significantly suppresses growth of neuroblastoma cells lacking MYCN amplification by inducing apoptosis and enhancing favorable neuroblastoma gene expression. Collectively, these data suggest that high-level MYCN expression in neuroblastoma lacking MYCN amplification results in a benign phenotype. Thus, the high MYCN expression confers the opposite biological consequence in neuroblastoma, depending on whether or not MYCN is amplified.

Favorable neuroblastoma genes and molecular therapeutics of neuroblastoma

PURPOSE AND EXPERIMENTAL DESIGN

Neuroblastoma (NB) is a common pediatric solid tumor that exhibits a striking clinical bipolarity: favorable and unfavorable. Favorable NB genes (EPHB6, EFNB2, EFNB3, NTRK1, and CD44) are genes whose high-level expression predicts favorable NB outcome, and forced expression of these genes inhibits growth of unfavorable NB cells. In this study, we investigated whether favorable NB gene expression could be augmented in unfavorable NB cells by chemical compounds and whether an increased expression of these genes was associated with suppression of NB growth and metastasis.

RESULTS

We found that inhibitors of DNA methylation [5-aza-2'-deoxycytidine (5AdC)], histone deacetylase (HDAC) [4-phenylbutyrate (4PB)], and proteasome (MG262) enhanced the expression of favorable NB genes in NB cell lines and inhibited the growth of these cells in vitro (P < 0.0005). The growth-inhibitory effects of 5AdC and 4PB in vitro were in part due to caspase-dependent cell death and inhibition of DNA synthesis. Administration of 5AdC and/or 4PB also suppressed growth of subcutaneous NB xenografts in nude mice (P < 0.001), which was accompanied by enhanced favorable NB gene expression and an increase in apoptosis. Moreover, 4PB suppressed bone marrow and liver metastases of NB cells in severe combined immunodeficient/Beige mice (P = 0.007 and P = 0.008, respectively). The growth-suppressive activity of HDAC inhibitors on NB was further confirmed by the efficacy of trichostatin A, a potent and specific HDAC inhibitor.

CONCLUSIONS

Collectively, these observations further emphasize the link between the elevated favorable NB gene expression and a benign phenotype of NB.

Effect of 20-epi-1alpha,25-dihydroxyvitamin D3 on the proliferation of human neuroblastoma: role of cell cycle regulators and the Myc-Id2 pathway

The antiproliferative effects of 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] and its epimer, 20-epi-1alpha,25-dihydroxyvitamin D(3) [20-epi-1,25(OH)(2)D(3)], in six human neuroblastoma (NB) cell lines (SH-SY5Y, NB69, SK-N-AS, IMR5, CHP134, and NGP) were investigated. We determined the ability of 1,25(OH)(2)D(3) and 20-epi-1,25(OH)(2)D(3) to influence cell viability by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell proliferation by bromodeoxyuridine (BrdU) incorporation, and their antineoplastic effect on colony formation in a soft agar assay. A concentration-dependent decrease in cell viability, inhibition of DNA synthesis, and suppression of clonal proliferation was observed with both compounds. 20-epi-1,25(OH)(2)D(3) was more potent in suppressing the proliferation of all six NB cell lines. To understand the mechanisms of action, we examined the effect of 20-epi-1,25(OH)(2)D(3) on the Myc-Id2 cell proliferative network and also on key regulators of the cell cycle. For the first time, we show that 20-epi-1,25(OH)(2)D(3) down-regulated Myc and Id2 expression by western blot analysis. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that 20-epi-1,25(OH)(2)D(3) induced the expression of retinoic acid receptor-beta and p21(Cip1), and down-regulated the expression of cyclin D1 resulting in decreased phosphorylation of retinoblastoma protein (pRB). In sum, we show that 20-epi-1,25(OH)(2)D(3) exerts strong antiproliferative effects by regulating key growth control networks (Myc-Id2-pRB) in NB cells.

Anti-proliferative effects of 20-epi-vitamin-D3 analogue, KH1060 in human neuroblastoma: induction of RAR-beta and p21(Cip1)

We determined the in vitro biological activities of 1 alpha, 25-dihdroxyvitamin D(3) (1,25-D(3)) and its analogue, 20-epi-22-oxa-24a, 26a, 27a-trihomo-1 alpha, 25 (OH)(2) vitamin D(3) (KH1060) in six human neuroblastoma (NB) cell lines (SH-SY5Y, NB69, SK-N-AS, IMR5, CHP-134, NGP). The ability of these compounds to inhibit cell growth and DNA synthesis was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and BrdU incorporation, respectively. The induction of cell death was monitored by caspase-3 activity. Their antineoplastic effect was assessed by clonal proliferation in soft agar. KH1060 was more effective than 1,25 D(3) in inhibiting cell growth and DNA synthesis. The IC-(50) (inhibition of 50% cell viability) indicated that KH1060 was about 10-20-fold more potent than 1,25 D(3). This growth inhibition was also accompanied by induction of caspase-3 activity, indicating that these compounds induce cell death in a caspase-dependent fashion. Moreover, KH1060 exerted potent antineoplastic activity by suppressing the clonal proliferation of the six NB cells. For the first time we demonstrate that KH1060 induces the expression of retinoic acid receptor-beta and p21(Cip1) suggesting that these proteins in part mediate the growth inhibitory effects. Taken together, all the six NB cells were more susceptible to growth inhibition by KH1060 than 1,25-D(3), suggesting its possible use in NB to potentiate the action of retinoids, which are in clinical use for this disease.

Resistance to chemotherapy mediated by TrkB in neuroblastomas

Neuroblastoma is a common childhood tumor derived from the peripheral nervous system. Favorable neuroblastomas usually express TrkA, the receptor for nerve growth factor (NGF), whereas unfavorable, MYCN-amplified neuroblastomas usually express TrkB and its ligand, brain-derived neurotrophic factor (BDNF). Here, we provide evidence that the TrkB-BDNF pathway is associated with enhanced survival and resistance to chemotherapy in neuroblastoma. We transfected the neuroblastoma line SH-SY5Y, which has endogenous expression of BDNF, with a full-length TrkB expression vector, and obtained clones with moderate or high levels of expression. Cells were exposed in vitro to chemotherapy agents used to treat neuroblastomas: doxorubicin, etoposide (VP16), and cisplatin. Chemoresistance was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for cell survival and by ELISA for cell death. In all cases, the TrkB-expressing subclones were more resistant to treatment than the parent line. Furthermore, when the TrkB tyrosine kinase was blocked with the Trk-specific inhibitor CEP-2563, or by neutralizing antibody to BDNF, sensitivity to chemotherapy was significantly increased. We also found constitutive phosphorylation of AKT at the Ser-473 site in TrkB transfectants, whereas there was only a minimal level of constitutive phosphorylation of AKT in SY5Y cells. These results show that the TrkB-BDNF pathway provides a survival advantage when exposed to DNA-damaging reagents, and, therefore, this autocrine pathway may play an important role in mediating the drug-resistant phenotype associated with TrkB-expressing neuroblastomas. Activation of PI3K/AKT survival pathway may contribute to the increased drug resistance in TrkB-expressing neuroblastomas.

Expression of the neurotrophin receptor TrkA down-regulates expression and function of angiogenic stimulators in SH-SY5Y neuroblastoma cells

Angiogenesis is essential for tumor growth and metastasis and depends on the production of angiogenic factors. Mechanisms regulating the expression of angiogenic factors in tumor cells are largely unknown. High expression of the neurotrophin receptor TrkA in neuroblastomas (NBs) is associated with a favorable prognosis, whereas TrkB is mainly expressed on aggressive, MYCN-amplified NBs. To investigate the biological effects of TrkA and TrkB expression on angiogenesis in NB, we examined the expression of angiogenic factors in the human NB cell line SY5Y and its TrkA and TrkB transfectants. In comparison with parental SY5Y cells, mRNA and protein levels of the examined angiogenic factors were significantly reduced in SY5Y-TrkA cells, whereas SY5Y-TrkB cells did not demonstrate a significant change. Conditioned medium of TrkB transfectants and parental SY5Y cells induced endothelial cell proliferation and migration, but this effect was completely absent in SY5Y-TrkA cells. TrkA expression also resulted in severely impaired tumorigenicity in a mouse xenograft model and was associated with reduced angiogenic factor expression and vascularization of tumors, as determined by immunohistochemistry and an in vivo Matrigel assay. TrkA expression inhibits angiogenesis and tumor growth in SY5Y NB cells by down-regulation of angiogenic factors, whereas expression of TrkB does not down-regulate the production of these angiogenic factors. The biologically different behavior of TrkA- and TrkB-expressing NBs may be explained in part by their effects on angiogenesis.

Expression of Apo-3 and Apo-3L in primitive neuroectodermal tumours of the central and peripheral nervous system

Deregulation of apoptosis has been implicated in the pathogenesis, spontaneous regression and treatment resistance of neuroblastoma. A newly recognised member of the tumour necrosis factor (TNF)-family of death receptors known as Apo-3 has been mapped to human chromosome 1p36.3, a region commonly deleted in aggressive neuroblastoma. Based on its localisation and function, Apo-3 is a candidate for the putative neuroblastoma tumour suppressor gene. Therefore we analysed mRNA expression of the Apo-3 receptor/ligand (Apo-3/Apo-3L) system in a representative panel of 18 neuroblastoma cell lines, 41 primary neuroblastoma and 13 ganglioneuromas/ganglioneuroblastomas by semi-quantitative RT-PCR. We compared the level of expression with the well-established prognostic factors age, stage, histology, MYCN-amplification and TrkA expression, as well as outcome. For comparison, we studied Apo-3/Apo-3L expression in 27 central nervous system (CNS) primitive neuroectodermal tumours/medulloblastomas (PNET/medulloblastoma) and in six normal brain samples. Neuroblastoma cell lines with 1p deletion and MYCN-amplification expressed significantly lower levels of Apo-3 (P=0.009 and P=0.03, respectively) compared with neuroblastoma cell lines without 1p deletion or MYCN-amplification. The mean expression level of Apo-3L was significantly higher in ganglioneuromas/ganglioneuroblastomas compared with neuroblastomas (P=0.001) and in normal brain compared with PNET/medulloblastoma (P<0.0001). Expression of Apo-3L was significantly associated with survival in neuroblastomas (P<0.049) and in PNET/medulloblastomas (P=0.01). Expression of Apo-3 was significantly associated with survival in PNET/medulloblastomas (P=0.03). Thus, the Apo-3 receptor/ligand system might be involved in the regulation of apoptosis in neuroblastomas and PNET.

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in neuroblastoma cells correlates with a loss of caspase-8 expression

Disruption of apoptotic pathways may be involved in tumor formation, regression, and treatment resistance of neuroblastoma (NB). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in cancer cell lines, whereas normal cells are not sensitive to TRAIL-mediated apoptosis. In this study we analyzed the expression and function of TRAIL and its agonistic and antagonistic receptors as well as expression of cellular FLICE-like inhibitory protein and caspase-2, -3, -8, -9, and -10 in 18 NB cell lines. Semiquantitative RT-PCR revealed that TRAIL-R2 and TRAIL-R3 are the main TRAIL-receptors used by NB cells. Sensitivity to TRAIL-induced apoptosis did not correlate with mRNA expression of TRAIL receptors or cellular FLICE-like inhibitory protein. Surprisingly, caspase-8 and caspase-10 mRNA expression was detected in only 5 of 18 NB cell lines. Interestingly, only these five NB cell lines were susceptible to TRAIL-induced apoptosis in a time- and dose-dependent manner. Treatment with 5-aza-2'-deoxycytidine restored mRNA and protein expression of caspase-8 and TRAIL sensitivity of resistant cell lines, suggesting that gene methylation is involved in caspase inactivation. The TRAIL system seems to be functional in NB cells expressing caspase-8 and/or caspase-10. Because many cytotoxic drugs induce caspase-dependent apoptosis, failure to express caspase-8 and/or caspase-10 might be an important mechanism of resistance to chemotherapy in NB.

Inhibition of N-myc expression and induction of apoptosis by iron chelation in human neuroblastoma cells

Neuroblastoma is the second most common solid malignancy of childhood. Enhanced expression of the amplified N-myc gene in the tumor cells may be associated with poor patient prognosis and may contribute to tumor development and progression. The use of deferoxamine mesylate (DFO), an iron chelator, to treat neuroblastoma is being investigated in national clinical studies. We show here by TUNEL assay and DNA laddering that DFO induces apoptosis in cultured human neuroblastoma cells, which is preceded by a decrease in the expression of N-myc and the altered expression of some other oncogenes (up-regulating c-fos and down-regulating c-myb) but not housekeeping genes. The decrease in N-myc expression is iron-specific but does not result from inhibition of ribonucleotide reductase, because specific inhibition of this iron-containing enzyme by hydroxyurea does not affect N-myc protein levels. Nuclear run-on and transient reporter gene expression experiments show that the decrease in N-myc expression occurs at the level of initiation of transcription and by inhibiting N-myc promoter activity. Comparison across neuroblastoma cell lines of the amount of residual cellular N-myc protein with the extent of apoptosis measured as pan-caspase activity after 48 h of iron chelation reveals no correlation, suggesting that the decrease in N-myc expression is unlikely to mediate apoptosis. In conclusion, chelation of cellular iron by DFO may alter the expression of multiple genes affecting the malignant phenotype by multiple pathways. Given the clinical importance of N-myc overexpression in neuroblastoma malignancy, decreasing N-myc expression by DFO might be useful as an adjunct to current

Expression of the neurotrophin receptor TrkB is associated with unfavorable outcome in Wilms' tumor

PURPOSE

Neurotrophins and their receptors regulate the proliferation, differentiation, and death of neuronal cells, and they have been implicated in the pathogenesis and prognosis of neuroblastomas and medulloblastomas. Tyrosine kinase (Trk) receptors also are expressed in extraneural tissues.

PATIENTS AND METHODS

To study the role of neurotrophin receptors and ligands in Wilms' tumor (WT), we determined their expression by semiquantitative duplex reverse transcriptase polymerase chain reaction in 39 patients with primary WT. Comparison of mRNA expression levels with clinical variables was performed by use of Cox regression analysis.

RESULTS

Children with WT that expressed high levels of full-length TrkB mRNA (TrkBfull) had a significantly greater risk of death than children whose tumors had little or no TrkBfull expression (hazard ratio, 9.7; P =.02). The 5-year relapse-free survival was 100% versus 65% for patients with low versus high tumor expression of TrkBfull (P <.003). Conversely, children with tumors that expressed high mRNA levels of a functionally inactive truncated TrkB receptor (TrkBtrunc) had a greater chance of survival than children with low levels of TrkBtrunc (hazard ratio, 0.08; P =.005). The 5-year relapse-free survival was 95% versus 68% for patients with high versus low levels of TrkBtrunc (P =.01). The hazard ratios for TrkBfull and TrkBtrunc remained significant after they were adjusted for tumor stage (P =.01 and P =.017, respectively). All WTs with high levels of TrkB expression also expressed the brain-derived nerve growth factor ligand.

CONCLUSION

Expression of TrkBfull in WT is associated with worse outcome, perhaps because it provides an autocrine survival pathway. Conversely, TrkBtrunc expression is associated with excellent outcome, perhaps as a result of a dominant negative effect.

Association among EPHB2, TrkA, and MYCN expression in low-stage neuroblastomas

BACKGROUND

The EPH family is the largest subfamily of receptor protein-tyrosine kinases, consisting of EPHA and EPHB subgroups. Ligands of EPH family receptors are called ephrins, which include ephrin-A and ephrin-B subgroups. We recently found that transcripts encoding the EPHB subgroup (EPHB) and the ephrin-B subgroup (EFNB) were expressed together in neuroblastoma (NB) cell lines.

PROCEDURE

In this study, we examined the expression of EPHB and EFNB transcripts in 24 NB specimens representing all clinical stages. We found that several EPHB and EFNB transcripts were expressed together in all NBs examined.

RESULTS

Among the transcripts examined, EPHB6 expression was most significantly associated with low stage tumors (stages 1, 2, and 4S; P = 0.0048). TrkA expression was significantly correlated with EPHB6, EFNB2, and EFNB3 expression (P < 0.01 in each case). Taken together, these data indicate that the expression of EPHB6, EFNB2, and EFNB3 may serve as prognostic indicators of favorable NBs. In the low-stage NBs without MYCN amplification, EPHB2 expression was correlated both with MYCN expression and with TrkA expression (P < 0.01 in each case). Moreover, MYCN expression was correlated with TrkA expression (P < 0.01) in the low-stage NBs.

CONCLUSIONS

This observation points to the possibility that MYCN expression might contribute to favorable outcome of low-stage NBs.

Effect of CEP-751 (KT-6587) on neuroblastoma xenografts expressing TrkB

BACKGROUND

The compound CEP-751 (KT-6587), a potent and selective inhibitor of the Trk family of tyrosine kinases, has been shown to inhibit the growth of human neuroblastoma (NB) xenografts in nude mice [1].

PROCEDURE

To address its mechanism of action, we studied SY5Y, a human NB cell line with no detectable Trk expression, and two subclones transfected with TrkB. The transfected clones, SY5Y (G8) and SY5Y (G12), expressed moderate and high levels, respectively, of TrkB mRNA and protein. These TrkB-expressing subclones and the parental line were then grown as xenografts in nude mice, and CEP-751 was used to inhibit TrkB tyrosine kinase activity in these xenografts. Animals were treated twice a day with CEP-751 (21 mg/kg), or with the carrier vehicle as a control. TrkB expression in the resultant tumors was examined by quantitative RT-PCR. The effect of CEP-751 on TrkB activation by BDNF was examined in G12 cells in culture by immunoprecipitation with antipan Trk antiserum, followed by Western blot analysis using antiphosphotyrosine antibodies. To determine if CEP-751 was causing apoptosis, the TUNEL assay was used.

RESULTS

CEP-751 had little effect on the growth of SY5Y tumors, but did slow the growth rate of the C8 and G12 tumors. The daily growth rate of the treated tumors was 0.16, 0.13, and 0.10 cm3, respectively, for the SY5Y, G8, and G12 tumors. RT PCR analysis confirmed the expression of TrkB in G8 and G12, but not in SY5Y tumors. Activation of TrkB by BDNF in G12 cells was inhibited by CEP-751 in a dose dependent fashion. The treated tumors showed marked evidence of apoptosis.

CONCLUSIONS

These data suggest that the effect of CEP-751 is due, at least in part, to its inhibition of TrkB kinase, and that CEP-751 may become a useful therapeutic tool for the treatment of aggressive neuroblastomas, which often express TrkB.

TrkA signal transduction pathways in neuroblastoma

BACKGROUND

Favorable neuroblastomas frequently express high levels of the TrkA receptor, and these tumors have a propensity to either differentiate or regress, but the mechanisms responsible for these two fates are unclear.

PROCEDURE

To study TrkA signal transduction in neuroblastoma (nb), we stably expressed wild-type TrkA and five TrkA mutants in the human nb cell line SH-SY5Y. Resulting single cell clones were characterized by TrkA mRNA and protein expression and by autophosphorylation of the receptor.

RESULTS

Introduction of TrkA restored nerve growth factor (NGF) responsiveness of SH-SY5Y cells, demonstrated by morphological differentiation and induction of immediate-early genes. TrkA overexpression leads to growth inhibition in the absence of NGF, whereas NGF treatment results in increased proliferation.

CONCLUSIONS

Analysis of downstream signaling elements in mutated TrkA receptors indicates that NGF-induced differentiation is dependent on TrkA kinase activity, but several redundant pathways seem to be used farther downstream. This suggests differences from TrkA pathways identified in PC12 cells.

Resistance to TRAIL-induced apoptosis in neuroblastoma cells correlates with a loss of caspase-8 expression

BACKGROUND

Disruption of apoptotic pathways may be involved in tumor formation, regression, and treatment resistance of neuroblastoma (NB). TNF-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in cancer cell lines.

PROCEDURE

In this study we analyzed the expression and function of TRAIL, its agonistic and antagonistic receptors, and important intracellular signaling elements in 18 NB cell lines.

RESULTS

Semiquantitative RT-PCR revealed that TRAIL-R2 and TRAIL-R3 are the main TRAIL-receptors used by NB cells. Sensitivity to TRAIL-induced apoptosis did not correlate with mRNA expression of TRAIL receptors or cFLIP. Surprisingly, caspase-8 and caspase-10 mRNA was detected in only 5 of 18 NB cell lines. Interestingly, only these five NB cell lines were susceptible to TRAIL-induced apoptosis in a time- and dose-dependent manner.

CONCLUSIONS

Treatment with 5-aza-2'-deoxycytidine restored mRNA expression of caspase-8 and -10 and TRAIL sensitivity of resistant cell lines, suggesting that gene methylation is involved in caspase inactivation. Since many cytotoxic drugs induce caspase-dependent apoptosis, failure to express caspase-8 and/or caspase-10 might be an important mechanism of resistance to chemotherapy in NB.

Different effects of TrkA expression in neuroblastoma cell lines with or without MYCN amplification

BACKGROUND

Expression of the neurotrophin receptor TrkA is associated with a favorable prognosis in neuroblastoma (NB) and promotes growth inhibition and neuronal differentiation. Aggressive, MYCN-amplified NB tumors express little or no TrkA mRNA, suggesting that MYCN overexpression may inhibit TrkA expression.

PROCEDURE

To study the interactions of TrkA expression and MYCN amplification in NB, we stably expressed the TrkA receptor in the MYCN single copy cell lines SH-SY5Y and NB69 as well as in the MYCN amplified cell lines CHP134 and IMR5.

RESULTS

All four transfected cell lines demonstrated high TrkA expression and similar activation of the TrkA receptor and of mitogen-activated protein kinases as well as induction of immediate-early genes in response to nerve growth factor (NGF). Introduction of TrkA restored NGF responsiveness of SH-SY5Y and NB69 cells, as demonstrated by morphologic differentiation, growth inhibition, and enhanced survival in serum-free medium. However, no morphologic, growth, or survival responses to NGF were detected in MYCN-amplified CHP134 and IMR5 TrkA transfectants.

CONCLUSIONS

Thus, transfection of TrkA into MYCN amplified NB cell lines only partly restored the TrkA/NGF signaling pathway, suggesting additional inhibitory effects of MYCN overexpression on TrkA signaling.