Cancer stem cells in neuroblastoma therapy resistance

Dickopff 1 inhibits cancer stem cell properties and promotes neuronal differentiation of human neuroblastoma cell line SH-SY5Y

Neuroblastomas are pediatric tumors arising from undifferentiated cells of neural crest origin with stem cell-like characteristics. Dysregulation of Wnt/β-catenin signaling has been shown to be linked to the development of various tumors. Activated Wnt signaling results in β-catenin accumulation in the nucleus to support pro-neoplastic traits. DKK1, a secreted glycoprotein, is an inhibitor of Wnt signaling, and the addition of DKKI to the culture medium has been used to suppress the Wnt pathway. This study aimed to analyze the role of Dickopff-1 as a potential differentiating agent for the neuroblastoma cell line SH-SY5Y and neurospheres derived from it. The treatment of SH-5Y5Y derived neurospheres by DKK1 resulted in their disintegration and reduced proliferation markers like Ki67, PCNA. DKK1 treatment to the neurospheres also resulted in the loss of cancer stem cell markers like CD133, KIT and pluripotency markers like SOX2, OCT4, NANOG. DKK1 treatment caused reduction in mRNA expression of β-catenin and TCF genes like TCF4, TCF12. When the SH-SY5Y cancer cells were grown under differentiating conditions, DKKI caused neuronal differentiation by itself, and in synergy with retinoic acid. This was verified by the expression of markers like MAPT, DCX, GAP43, ENO2 and also with changes in neurite length. We concluded that Wnt inhibition, as exemplified by DKK1 treatment, is therefore a possible differentiating condition and also suppresses the proliferative and cancer stemness related properties of SH-SY5Y neuroblastoma cells.

An overview of the past decade of bufalin in the treatment of refractory and drug-resistant cancers: current status, challenges, and future perspectives

Profound progress has been made in cancer treatment in the past three decades. However, drug resistance remains prevalent and a critical challenge. Drug resistance can be attributed to oncogenes mutations, activated defensive mechanisms, ATP-bind cassette transporters overexpression, cancer stem cells, etc. Chinese traditional medicine toad venom has been used for centuries for different diseases, including resistant cancers. Bufalin is one of the bufadienolides in toad venom that has been extensively studied for its potential in refractory and drug-resistant cancer treatments in vitro and in vivo. In this work, we would like to critically review the progress made in the past decade (2013-2022) of bufalin in overcoming drug resistance in cancers. Generally, bufalin shows high potential in killing certain refractory and resistant cancer cells via multiple mechanisms. More importantly, bufalin can work as a chemo-sensitizer that enhances the sensitivity of certain conventional and targeted therapies at low concentrations. In addition, the development of bufalin derivatives was also briefly summarized and discussed. We also analyzed the obstacles and challenges and provided possible solutions for future perspectives. We hope that the collective information may help evoke more effort for more in-depth studies and evaluation of bufalin in both lab and possible clinical trials.

Prognostic significance of NT5E/CD73 in neuroblastoma and its function in CSC stemness maintenance

Cluster of differentiation 73 (CD73), a cell surface enzyme that catalyzes adenosine monophosphate (AMP) breakdown to adenosine, is differentially expressed in cancers and has prognostic significance. We investigated its expression profile in neuroblastoma (NB), its association with NB clinical outcomes, and its influence in the regulation of cancer stem cells' (CSCs) stemness maintenance. RNA-Seq data mining (22 independent study cohorts, total n = 3836) indicated that high CD73 can predict good NB prognosis. CD73 expression (immunohistochemistry) gauged in an NB patient cohort (n = 87) showed a positive correlation with longer overall survival (OS, P = 0.0239) and relapse-free survival (RFS, P = 0.0242). Similarly, high CD73 correlated with longer OS and RFS in advanced disease stages, MYCN non-amplified (MYCN-na), and Stage-4-MYCN-na subsets. Despite no definite association in children < 2 years old (2Y), high CD73 correlated with longer OS (P = 0.0294) and RFS (P = 0.0315) in children > 2Y. Consistently, high CD73 was associated with better OS in MYCN-na, high-risk, and stage-4 subsets of children > 2Y. Multivariate analysis identified CD73 as an independent (P = 0.001) prognostic factor for NB. Silencing CD73 in patient-derived (stage 4, progressive disease) CHLA-171 and CHLA-172 cells revealed cell-line-independent activation of 58 CSC stemness maintenance molecules (QPCR profiling). Overexpressing CD73 in CHLA-20 and CHLA-90 cells with low CD73 and silencing in CHLA-171 and CHLA-172 cells with high CD73 showed that CD73 regulates epithelial to mesenchymal transition (E-Cadherin, N-Cadherin, Vimentin), stemness maintenance (Sox2, Nanog, Oct3/4), self-renewal capacity (Notch), and differentiation inhibition (leukemia inhibitory factor, LIF) proteins (confocal-immunofluorescence). These results demonstrate that high CD73 can predict good prognosis in NB, and further suggest that CD73 regulates stemness maintenance in cells that defy clinical therapy.

Chemoprevention of neuroblastoma: progress and promise beyond uncertainties

Neuroblastoma is the most common extracranial solid tumor in children and comprises one-tenth of all childhood cancer deaths. The current clinical therapy for this deadly disease is multimodal, involving an induction phase with alternating regimens of high-dose chemotherapeutic drugs and load reduction surgery; a consolidation phase with more intensive chemotherapy, radiotherapy, and stem cell transplant; and a maintenance phase with immunotherapy and immune-activating cytokine treatment. Despite such intensive treatment, children with neuroblastoma have unacceptable life quality and survival, warranting preventive measures to regulate the cellular functions that orchestrate tumor progression, therapy resistance, metastasis, and tumor relapse/recurrence. Globally, active efforts are underway to identify novel chemopreventive agents, define their mechanism(s) of action, and assess their clinical benefit. Some chemoprevention strategies (e.g., retinoids, difluoromethylornithine) have already been adopted clinically as part of maintenance phase therapy. Several agents are in the pipeline, while many others are in preclinical characterization. Here we review the classes of chemopreventive agents investigated for neuroblastoma, including cellular events targeted, mode(s) of action, and the level of development. Our review: (i) highlights the pressing need for new and improved chemopreventive strategies for progressive neuroblastoma; (ii) lists the emerging classes of chemopreventive agents for neuroblastoma; and (iii) recognizes the relevance of targeting dynamically evolving hallmark functions of tumor evolution (e.g., survival, differentiation, lineage transformation). With recent gains in the understanding of tumor evolution processes and preclinical and clinical efforts, it is our strong opinion that effective chemopreventive strategies for aggressive neuroblastoma are a near reality.

Neural crest cells development and neuroblastoma progression: Role of Wnt signaling

Neuroblastoma (NB) is one of the most common heterogeneous extracranial cancers in infancy that arises from neural crest (NC) cells of the sympathetic nervous system. The Wnt signaling pathway, both canonical and noncanonical pathway, is a highly conserved signaling pathway that regulates the development and differentiation of the NC cells during embryogenesis. Reports suggest that aberrant activation of Wnt ligands/receptors in Wnt signaling pathways promote progression and relapse of NB. Wnt signaling pathways regulate NC induction and migration in a similar manner; it regulates proliferation and metastasis of NB. Inhibiting the Wnt signaling pathway or its ligands/receptors induces apoptosis and abrogates proliferation and tumorigenicity in all major types of NB cells. Here, we comprehensively discuss the Wnt signaling pathway and its mechanisms in regulating the development of NC and NB pathogenesis. This review highlights the implications of aberrant Wnt signaling in the context of etiology, progression, and relapse of NB. We have also described emerging strategies for Wnt-based therapies against the progression of NB that will provide new insights into the development of Wnt-based therapeutic strategies for NB.

Therapy resistance in neuroblastoma: Mechanisms and reversal strategies

Neuroblastoma is one of the most common pediatric solid tumors that threaten the health of children, accounting for about 15% of childhood cancer-related mortality in the United States. Currently, multiple therapies have been developed and applied in clinic to treat neuroblastoma including chemotherapy, radiotherapy, targeted therapy, and immunotherapy. However, the resistance to therapies is inevitable following long-term treatment, leading to treatment failure and cancer relapse. Hence, to understand the mechanisms of therapy resistance and discover reversal strategies have become an urgent task. Recent studies have demonstrated numerous genetic alterations and dysfunctional pathways related to neuroblastoma resistance. These molecular signatures may be potential targets to combat refractory neuroblastoma. A number of novel interventions for neuroblastoma patients have been developed based on these targets. In this review, we focus on the complicated mechanisms of therapy resistance and the potential targets such as ATP-binding cassette transporters, long non-coding RNAs, microRNAs, autophagy, cancer stem cells, and extracellular vesicles. On this basis, we summarized recent studies on the reversal strategies to overcome therapy resistance of neuroblastoma such as targeting ATP-binding cassette transporters, MYCN gene, cancer stem cells, hypoxia, and autophagy. This review aims to provide novel insight in how to improve the therapy efficacy against resistant neuroblastoma, which may shed light on the future directions that would enhance the treatment outcomes and prolong the survival of patients with neuroblastoma.

Doxorubicin-Induced TrkAIII Activation: A Selection Mechanism for Resistant Dormant Neuroblastoma Cells

Patients with advanced neuroblastoma (NB) receive multimodal clinical therapy, including the potent anthracycline chemotherapy drug doxorubicin (Dox). The acquisition of Dox resistance, however, is a major barrier to a sustained response and leads to a poor prognosis in advanced disease states, reinforcing the need to identify and inhibit Dox resistance mechanisms. In this context, we report on the identification and inhibition of a novel Dox resistance mechanism. This mechanism is characterized by the Dox-induced activation of the oncogenic TrkAIII alternative splice variant, resulting in increased Dox resistance, and is blocked by lestaurtinib, entrectinib, and crizotinib tyrosine kinase and LY294002 IP3-K inhibitors. Using time lapse live cell imaging, conventional and co-immunoprecipitation Western blots, RT-PCR, and inhibitor studies, we report that the Dox-induced TrkAIII activation correlates with proliferation inhibition and is CDK1- and Ca²⁺-uniporter-independent. It is mediated by ryanodine receptors; involves Ca²⁺-dependent interactions between TrkAIII, calmodulin and Hsp90; requires oxygen and oxidation; occurs within assembled ERGICs; and does not occur with fully spliced TrkA. The inhibitory effects of lestaurtinib, entrectinib, crizotinib, and LY294002 on the Dox-induced TrkAIII and Akt phosphorylation and resistance confirm roles for TrkAIII and IP3-K consistent with Dox-induced, TrkAIII-mediated pro-survival IP3K/Akt signaling. This mechanism has the potential to select resistant dormant TrkAIII-expressing NB cells, supporting the use of Trk inhibitors during Dox therapy in TrkAIII-expressing NBs.

High-Risk Neuroblastoma: Poor Outcomes Despite Aggressive Multimodal Therapy

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Neuroblastoma (NBL) is a highly malignant embryonal tumor that originates from the primordial neural crest cells. NBL is the most common tumor in infants and the most common extracranial solid tumor in children. The tumor is more commonly diagnosed in children of 1-4 years of age. NBL is characterized by enigmatic clinical behavior that ranges from spontaneous regression to an aggressive clinical course leading to frequent relapses and death. Based on the likelihood of progression and relapse, the International Neuroblastoma Risk Group classification system categorized NBL into very low risk, low risk, intermediate risk, and high risk (HR) groups. HR NBL is defined based on the patient's age (> 18 months), disease metastasis, tumor histology, and MYCN gene amplification. HR NBL is diagnosed in nearly 40% of patients, mainly those > 18 months of age, and is associated with aggressive clinical behavior. Treatment strategies involve the use of intensive chemotherapy (CTR), surgical resection, high dose CTR with hematopoietic stem cell support, radiotherapy, biotherapy, and immunotherapy with Anti-ganglioside 2 monoclonal antibodies. Although HR NBL is now better characterized and aggressive multimodal therapy is applied, the outcomes of treatment are still poor, with overall survival and event-free survival of approximately 40% and 30% at 3-years, respectively. The short and long-term side effects of therapy are tremendous. HR NBL carries a high mortality rate accounting for nearly 15% of pediatric cancer deaths. However, most mortalities are attributed to the high frequency of disease relapse (50%) and disease reactiveness to therapy (20%). Newer treatment strategies are therefore urgently needed. Recent discoveries in the field of biology and molecular genetics of NBL have led to the identification of several targets that can improve the treatment results. In this review, we discuss the different aspects of the epidemiology, biology, clinical presentations, diagnosis, and treatment of HR NBL, in addition to the recent developments in the management of the disease.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Novel second-generation rexinoid induces growth arrest and reduces cancer cell stemness in human neuroblastoma patient-derived xenografts

INTRODUCTION

The poor therapeutic efficacy seen with current treatments for neuroblastoma may be attributed to stem cell-like cancer cells (SCLCCs), a subpopulation of cancer cells associated with poor prognosis and disease recurrence. Retinoic acid (RA) is a differentiating agent used as maintenance therapy for high-risk neuroblastoma but nearly half of children treated with RA relapse. We hypothesized that 6-Methyl-UAB30 (6-Me), a second-generation rexinoid recently developed with a favorable toxicity profile compared to RA, would reduce cancer cell stemness in human neuroblastoma patient-derived xenografts (PDXs).

METHODS

Cells from three neuroblastoma PDXs were treated with 6-Me and proliferation, viability, motility, and cell-cycle progression were assessed. CD133 expression, sphere formation, and mRNA abundance of stemness and differentiation markers were evaluated using flow cytometry, in vitro extreme limiting dilution analysis, and real-time PCR, respectively.

RESULTS

Treatment with 6-Me decreased proliferation, viability, and motility, and induced cell-cycle arrest and differentiation in all three neuroblastoma PDXs. In addition, 6-Me treatment led to decreased CD133 expression, decreased sphere-forming ability, and decreased mRNA abundance of Oct4, Nanog, and Sox2, indicating decreased cancer cell stemness.

CONCLUSIONS

6-Me decreased oncogenicity and reduced cancer cell stemness of neuroblastoma PDXs, warranting further exploration of 6-Me as potential novel therapy for neuroblastoma.

Transepithelial Anti-Neuroblastoma Response to Kale among Four Vegetable Juices Using In Vitro Model Co-Culture System

Juicing vegetables is thought to be an anticancer treatment. Support exists for a rank order of anticancer greens (kale > dandelion > lettuce > spinach) based on degrees of bioavailability of different phytochemicals, also offset by some noxious molecules (i.e., calcium-oxalate). We developed a new in vitro transepithelial anti-neuroblastoma model system. The juices were diluted as predicted once in the small intestine. They were applied to apical Caco-2Bbe1 cells atop dividing SH-SY5Y neuroblastoma cells, and changes in transepithelial electrical resistance (TEER) and cell growth were considered with juice spectroscopies. Studied first in monoculture, kale and dandelion were the most cytostatic juices on SH-SY5Ys, lettuce showed no effect, and high (4.2%) spinach was cytotoxic. In co-culture, high (4.2%) kale was quickest (three days) to inhibit neuroblastoma growth. By five days, dandelion and kale were equally robust. Lettuce showed small anti-proliferative effects at five days and spinach remained cytotoxic. Spinach’s cytotoxicity corresponded with major infrared bands indicative of oxalate. Kale juice uniquely induced reactive oxygen species and S-phase cell cycle arrest in SH-SY5Y. The superiority of kale and dandelion was also apparent on the epithelium, because raising TEER levels is considered healthy. Kale’s unique features corresponded with a major fluorescent peak that co-eluted with kaempferol during high performance liquid chromatography. Because the anticancer rank order was upheld, the model appears validated for screening anticancer juices.

MicroRNAs at the Crossroad of the Dichotomic Pathway Cell Death vs. Stemness in Neural Somatic and Cancer Stem Cells: Implications and Therapeutic Strategies

Stemness and apoptosis may highlight the dichotomy between regeneration and demise in the complex pathway proceeding from ontogenesis to the end of life. In the last few years, the concept has emerged that the same microRNAs (miRNAs) can be concurrently implicated in both apoptosis-related mechanisms and cell differentiation. Whether the differentiation process gives rise to the architecture of brain areas, any long-lasting perturbation of miRNA expression can be related to the occurrence of neurodevelopmental/neuropathological conditions. Moreover, as a consequence of neural stem cell (NSC) transformation to cancer stem cells (CSCs), the fine modulation of distinct miRNAs becomes necessary. This event implies controlling the expression of pro/anti-apoptotic target genes, which is crucial for the management of neural/neural crest-derived CSCs in brain tumors, neuroblastoma, and melanoma. From a translational point of view, the current progress on the emerging miRNA-based neuropathology therapeutic applications and antitumor strategies will be disclosed and their advantages and shortcomings discussed.

Tideglusib attenuates growth of neuroblastoma cancer stem/progenitor cells in vitro and in vivo by specifically targeting GSK-3β

BACKGROUND

Neuroblastoma (NB) is the most frequently diagnosed extracranial solid tumor among the pediatric population. It is an embryonic tumor with high relapse rates pertaining to the presence of dormant slowly dividing cancer stem cells (CSC) within the tumor bulk that are responsible for therapy resistance. Therefore, there is a dire need to develop new therapeutic approaches that specifically target NB CSCs. Glycogen synthase kinase (GSK)-3β is a serine/threonine kinase that represents a common signaling node at the intersection of many pathways implicated in NB CSCs. GSK-3β sustains the survival and maintenance of CSCs and renders them insensitive to chemotherapeutic agents and radiation.

METHODS

In our study, we aimed at evaluating the potential anti-tumor effect of Tideglusib (TDG), an irreversible GSK-3β inhibitor drug, on three human NB cell lines, SK-N-SH, SH-SY5Y, and IMR-32.

RESULTS

Our results showed that TDG significantly reduced cell proliferation, viability, and migration of the NB cells, in a dose- and time-dependent manner, and also significantly hindered the neurospheres formation eradicating the self-renewal ability of highly resistant CSCs. Besides, TDG potently reduced CD133 cancer stem cell marker expression in both SH-SY5Y cells and G1 spheres. Lastly, TDG inhibited NB tumor growth and progression in vivo.

CONCLUSION

Collectively, we concluded that TDG could serve as an effective treatment capable of targeting the NB CSCs and hence overcoming therapy resistance. Yet, future studies are warranted to further investigate its potential role in NB and decipher the subcellular and molecular mechanisms underlying this role.

9-cis-UAB30, a novel rexinoid agonist, decreases tumorigenicity and cancer cell stemness of human neuroblastoma patient-derived xenografts

Retinoic acid (RA) therapy has been utilized as maintenance therapy for high-risk neuroblastoma, but over half of patients treated with RA relapse. Neuroblastoma stem cell-like cancer cells (SCLCCs) are a subpopulation of cells characterized by the expression of the cell surface marker CD133 and are hypothesized to contribute to drug resistance and disease relapse. A novel rexinoid compound, 9-cis-UAB30 (UAB30), was developed having the same anti-tumor effects as RA but a more favorable toxicity profile. In the current study, we investigated the efficacy of UAB30 in neuroblastoma patient-derived xenografts (PDX). Two PDXs, COA3 and COA6, were utilized and alterations in the malignant phenotype were assessed following treatment with RA or UAB30. UAB30 significantly decreased proliferation, viability, and motility of both PDXs. UAB30 induced cell-cycle arrest as demonstrated by the significant increase in percentage of cells in G1 (COA6: 33.7 ± 0.7 vs. 43.3 ± 0.7%, control vs. UAB30) and decrease in percentage of cells in S phase (COA6: 44.7 ± 1.2 vs. 38.6 ± 1%, control vs. UAB30). UAB30 led to differentiation of PDX cells, as evidenced by the increase in neurite outgrowth and mRNA abundance of differentiation markers. CD133 expression was decreased by 40% in COA6 cells after UAB30. The ability to form tumorspheres and mRNA abundance of known stemness markers were also significantly decreased following treatment with UAB30, further indicating decreased cancer cell stemness. These results provide evidence that UAB30 decreased tumorigenicity and cancer cell stemness in neuroblastoma PDXs, warranting further exploration as therapy for high-risk neuroblastoma.

Significance of hematopoietic surface antigen CD34 in neuroblastoma prognosis and the genetic landscape of CD34-expressing neuroblastoma CSCs

High-risk neuroblastoma (HR-NB) is branded with hematogenous metastasis, relapses, and dismal long-term survival. Intensification of consolidation therapy with tandem/triple autologous stem cell (SC) rescue (with bone marrow [BM]/peripheral blood [PB] CD34⁺ selection) after myeloablative chemotherapy has improved long-term survival. However, the benefit is limited by the indication of NB cells in CD34⁺ PBSCs, CD34 expression in NB cells, and the risk of reinfusing NB cancer stem cells (NB CSCs) that could lead to post-transplant relapse. We investigated the association of CD34 surface expression (92 patients) with NB evolution/clinical outcomes. CD34 gene-level status in NB was assessed through RNA-Seq data mining (18 cohorts, n, 3324). Genetic landscape of CD34-expressing NB CSCs (CD133⁺CD34⁺) was compared with CD34^- CSCs (CD133⁺CD34^-). RNA-seq data revealed equivocal association patterns of CD34 expression with patient survival. Our immunohistochemistry data revealed definite, but rare (mean, 0.73%; range 0.00-7.87%; median, 0.20%) CD34 positivity in NB. CD34⁺ significantly associated with MYCN amplification (p, 0.003), advanced disease stage (p, 0.016), and progressive disease (PD, p < 0.0009) after clinical therapy. A general high-is-worse tendency was observed in patients with relapsed disease. High CD34⁺ correlated with poor survival in patients with N-MYC-amplified HR-NB. Gene expression analysis of CD34⁺-NB CSCs identified significant up (4631) and downmodulation (4678) of genes compared with NB CSCs that lack CD34. IPA recognized the modulation of crucial signaling elements (EMT, stemness maintenance, differentiation, inflammation, clonal expansion, drug resistance, metastasis) that orchestrate NB disease evolution in CD34⁺ CSCs compared with CD34^- CSCs. While the function of CD34 in NB evolution requires further in-depth investigation, careful consideration should be exercised for autologous stem cell rescue with CD34⁺ selection in NB patients. Graphical abstract.

Bioinformatic Identification of Neuroblastoma Microenvironment-Associated Biomarkers with Prognostic Value

The microenvironment plays a vital role in the tumor recurrence of neuroblastoma. This research aimed at exploring prognostic genes that are involved in neuroblastoma microenvironment. We used “estimate” R package to calculate the immune/stromal/ESTIMATE scores of each sample of ArrayExpress dataset E-MTAB-8248 based on the ESTIMATE algorithm. Then we found that immune/stromal/ESTIMATE scores were not correlated with age/chromosome 11q, but tumor stage, MYCN gene amplifications, and chromosome 1p. Samples were then divided into high- and low-score groups, and 280 common differentially expressed genes (DEGs) were identified. 64 potential prognostic genes were harvested through overall survival analysis from the common DEGs. 14 prognostic genes (ABCA6, SEPP1, SLAMF8, GPR171, ABCA9, ARHGAP15, IL7R, HLA-DPB1, GZMA, GPR183, CCL19, ITK, FGL2, and CD1C) were obtained after screening in two independent cohorts. GO and KEGG analysis discovered that common DEGs and 64 potential prognostic genes are mainly involved in T-cell activation, lymphocyte activation regulation, leukocyte migration, and the interaction of cytokines and cytokine receptors. Correlation analysis showed that all prognostic genes were negatively correlated with MYCN amplification. Cox analysis identified 5 independent prognostic genes (ARHGAP15, ABCA9, CCL19, SLAMF8, and CD1C).

Emerging therapeutic targets for neuroblastoma

INTRODUCTION

Neuroblastoma (NB) is the prime cancer of infancy, and accounts for 9% of pediatric cancer deaths. While children diagnosed with clinically stable NB experience a complete cure, those with high-risk disease (HR-NB) do not recover, despite intensive therapeutic strategies. Development of novel and effective targeted therapies is needed to counter disease progression, and to benefit long-term survival of children with HR-NB.

AREAS COVERED

Recent studies (2017-2020) pertinent to NB evolution are selectively reviewed to recognize novel and effective therapeutic targets. The prospective and promising therapeutic targets/strategies for HR-NB are categorized into (a) targeting oncogene-like and/or reinforcing tumor suppressor (TS)-like lncRNAs; (b) targeting oncogene-like microRNAs (miRs) and/or mimicking TS-miRs; (c) targets for immunotherapy; (d) targeting epithelial-to-mesenchymal transition and cancer stem cells; (e) novel and beneficial combination approaches; and (f) repurposing drugs and other strategies in development.

EXPERT OPINION

It is highly unlikely that agents targeting a single candidate or signaling will be beneficial for an HR-NB cure. We must develop efficient drug deliverables for functional targets, which could be integrated and advance clinical therapy. Fittingly, the looming evidence indicated an aggressive evolution of promising novel and integrative targets, development of efficient drugs, and improvised strategies for HR-NB treatment.

Structural Optimization and Enhanced Prodrug-Mediated Delivery Overcomes Camptothecin Resistance in High-Risk Solid Tumors

Camptothecins are potent topoisomerase I inhibitors used to treat high-risk pediatric solid tumors, but they often show poor efficacy due to intrinsic or acquired chemoresistance. Here, we developed a multivalent, polymer-based prodrug of a structurally optimized camptothecin (SN22) designed to overcome key chemoresistance mechanisms. The ability of SN22 vs. SN38 (the active form of irinotecan/CPT-11) to overcome efflux pump-driven drug resistance was tested. Tumor uptake and biodistribution of SN22 as a polymer-based prodrug (PEG-[SN22]₄) compared with SN38 was determined. The therapeutic efficacy of PEG-[SN22]₄ to CPT-11 was compared in: (i) spontaneous neuroblastomas (NB) in transgenic TH-MYCN mice; (ii) orthotopic xenografts of a drug-resistant NB line SK-N-BE(2)C (mutated TP53); (iii) flank xenografts of a drug-resistant NB-PDX; and (iv) xenografts of Ewing sarcoma and rhabdomyosarcoma. Unlike SN38, SN22 inhibited NB cell growth regardless of ABCG2 expression levels. SN22 prodrug delivery resulted in sustained intratumoral drug concentrations, dramatically higher than those of SN38 at all time points. CPT-11/SN38 treatment had only marginal effects on tumors in transgenic mice, but PEG-[SN22]₄ treatment caused complete tumor regression lasting over 6 months (tumor free at necropsy). PEG-[SN22]₄ also markedly extended survival of mice with drug-resistant, orthotopic NB and it caused long-term (6+ months) remissions in 80% to 100% of NB and sarcoma xenografts. SN22 administered as a multivalent polymeric prodrug resulted in increased and protracted tumor drug exposure compared with CPT-11, leading to long-term "cures" in NB models of intrinsic or acquired drug resistance, and models of high-risk sarcomas, warranting its further development for clinical trials. SIGNIFICANCE: SN22 is an effective and curative multivalent macromolecular agent in multiple solid tumor mouse models, overcoming common mechanisms of drug resistance with the potential to elicit fewer toxicities than most cancer therapeutics.

Differential sequences and single nucleotide polymorphism of exosomal SOX2 DNA in cancer

Glioblastoma multiforme (GBM) is the most common form of brain cancer, with an average life expectancy of fewer than two years post-diagnosis. We have previously reported that cancer cell originated exosomes, including GBM, have NANOG and NANOGP8 DNA associated with them. The exosomal NANOG DNA has certain differences as compared to its normal counterpart that are of immense importance as a potential cancer biomarker. NANOG has been demonstrated to play an essential role in the maintenance of embryonic stem cells, and its pseudogene, NANOGP8, is suggested to promote the cancer stem cell phenotype. Similarly, SOX2 is another stemness gene highly expressed in cancer stem cells with an intimate involvement in GBM progression and metastasis as well as promotion of tumorigenicity in Neuroblastoma (NB). Since exosomes are critical in intercellular communication with a role in dissipating hallmark biomolecules responsible for cancer, we conducted a detailed analysis of the association of the SOX2 gene with exosomes whose sequence modulations with further research and appropriate sample size can help to identify diagnostic markers for cancer. We have detected SOX2 DNA associated with exosomes and have identified some of the SNPs and nucleotide variations in the sequences from a GBM and SH-SY5Y sample. Although a further systematic investigation of exosomal DNA from GBM and NB patient's blood is needed, finding of SOX2 DNA in exosomes in the current study may have value in clinical research. SOX2 is known to be misregulated in cancer cells by changes in miRNA function, such as SNPs in the binding sites. Our finding of cancer-specific SNPs in exosomal SOX2 DNA sequence may reflect those changes in the cancer stem cells as well as cancer cells. A series of our study on embryonic stem cell gene analysis in exosomal DNA may lead to a minimally invasive exosome-based diagnosis, and give us a key in understanding the mechanisms of cancer formation, progression, and metastasis.