Targeting ornithine decarboxylase reverses the LIN28/Let-7 axis and inhibits glycolytic metabolism in neuroblastoma

Polyamine depletion limits progression of acute leukaemia

Cancer cells are addicted to polyamines, polycations essential for cellular function. While dual targeting of cellular polyamine biosynthesis and polyamine uptake is under clinical investigation in solid cancers, preclinical and clinical studies into its potential in haematological malignancies are lacking. Here we investigated the preclinical efficacy of polyamine depletion in acute leukaemia. The polyamine biosynthesis inhibitor difluoromethylornithine (DFMO) inhibited growth of a molecularly diverse panel of acute leukaemia cell lines, while non-malignant cells were unaffected. Responsiveness to DFMO was linked to decreased levels of its molecular target, the rate-limiting polyamine biosynthesis enzyme ODC1, and of the polyamine transporters ATP13A2 and ATP13A3. DFMO increased polyamine uptake and upregulated expression of polyamine transporters in acute leukaemia cells, a compensatory effect abolished by treatment with the polyamine transport inhibitor AMXT 1501. This drug, currently in a phase 1 clinical trial in solid tumours in combination with DFMO, potentiated the inhibitory effects of DFMO, and their combination synergistically inhibited the growth of acute leukaemia cell lines by inducing apoptosis. DFMO and AMXT 1501 limited disease progression in highly aggressive xenograft models of infant KMT2A-rearranged leukaemia, even when treatment was initiated at high disease burden. Increased expression of c-MYC was associated with enhanced sensitivity to the combination of DFMO and AMXT 1501, suggesting this oncoprotein as a potential predictive marker of response to the drug combination. In conclusion, targeting polyamine biosynthesis and polyamine uptake limits disease progression in models of acute leukaemia, supporting further preclinical and clinical investigation into this approach for acute leukaemia.

Polyamine Inhibition with DFMO: Shifting the Paradigm in Neuroblastoma Therapy

Neuroblastoma is a common childhood malignancy, and high-risk presentations, including an MYCN amplified status, continue to result in poor survival. Difluoromethylornithine (DFMO) is a new and well-tolerated treatment for high-risk neuroblastoma. This review article discusses preclinical and clinical data that resulted in the establishment of DFMO as a treatment for neuroblastoma. The review of preclinical data includes a summary of the contribution of polyamine synthetic pathways to high-risk neuroblastoma, the effect that MYCN has on polyamine synthetic pathways, and the proposed mechanism by which DFMO inhibits tumorigenesis. This understanding has led to the discussion of various preclinical combination therapies that may result in a synergistic therapeutic response for high-risk neuroblastoma. We review the clinical trials that show the successful treatment of high-risk neuroblastoma with DFMO, including comparative analysis and traditional neuroblastoma trials using propensity score matching. We review the regulatory path by which DFMO gained approval from the Federal Drug Administration for use as a maintenance therapy following the traditional high-risk neuroblastoma therapy. Finally, we discuss the role of DFMO in future clinical research for neuroblastoma and additional pediatric cancers.

Metabolic targeting of neuroblastoma, an update

Neuroblastoma is a paediatric cancer of the sympathetic nervous system that originates from the neural crest and can be categorised into stages and risk groups. Risk groups inform treatment options and high-risk cases bear a 50 % probability of relapse post-treatment remission. In neuroblastoma, MYCN amplification is the strongest predictor of unfavourable patient prognosis; circa 50 % of high-risk cases display MYCN amplification. This dismal prognosis is perhaps influenced by the MYCN-driven metabolic rewiring of these cells since the MYC family is indicated in the regulation of proliferation, cell death, metabolism, differentiation, and protein synthesis. This review aims to capture the most recent studies that investigate metabolic rewiring in MYCN-amplified and MYCN-activated cells from the perspective of alterations to glycolysis, the TCA cycle, and oxidative phosphorylation, in addition to changes to amino acid, nucleotide, and lipid metabolism that can be relevant to therapy. A better understanding of the metabolic profile of MYCN-amplified disease will facilitate the identification of effective treatment options and improve the prognosis of high-risk neuroblastoma patients.

US Food and Drug Administration Approval Summary: Eflornithine for High-Risk Neuroblastoma After Prior Multiagent, Multimodality Therapy

On December 13, 2023, the US Food and Drug Administration (FDA) approved eflornithine (IWILFIN, US WorldMeds) to reduce the risk of relapse in adult and pediatric patients with high-risk neuroblastoma who have demonstrated at least a partial response to prior multiagent, multimodality therapy including anti-GD2 immunotherapy. The approval was based on an externally controlled trial (ECT) consisting of a single-arm trial, study 3(b), compared with an external control (EC) derived from a National Cancer Institute/Children's Oncology Group-sponsored clinical trial (Study ANBL0032) and supported by confirmatory evidence. In the protocol-specified primary analysis, the event-free survival hazard ratio (HR) was 0.48 (95% CI, 0.27 to 0.85) and overall survival HR was 0.32 (95% CI, 0.15 to 0.70). The most common adverse reactions (≥5%) were hearing loss, otitis media, pyrexia, pneumonia, and diarrhea. Notably, this is the first oncology drug approval which relies on an ECT as the primary clinical data to support substantial evidence of effectiveness. This was made possible by a distinctly high-quality, comparable EC data set with consistent treatment effect estimations demonstrated in multiple sensitivity and supportive analyses. Eflornithine's manageable safety profile and strong nonclinical and mechanistic data provided further support for the approval, and the evidentiary package was evaluated in the context of high unmet need in a rare, life-threatening cancer.

Polyamine Depletion by D, L-alpha-difluoromethylornithine Inhibits Ewing Sarcoma Metastasis by Inducing Ferroptosis

Polyamine metabolism and signaling play important roles in multiple cancers but have not previously been studied in Ewing sarcoma. Here, we show that blocking polyamine synthesis with D, L-alpha-difluoromethylornithine (DFMO) causes a G1 cell cycle arrest, dose-dependent decreases in sarcosphere formation from Ewing sarcoma cell lines growing in non-adherent conditions and a decrease in clonogenic growth in soft agar. Further, we utilized our orthotopic implantation/amputation model of Ewing sarcoma metastasis to demonstrate that DFMO slowed primary tumor growth in addition to limiting metastasis. RNA sequencing demonstrated gene expression patterns consistent with induction of ferroptosis caused by polyamine depletion. Induction of ferroptosis was validated in vitro by demonstrating that ferrostatin-1, an inhibitor of ferroptosis, allows sphere formation even in the presence of DFMO. Collectively, these results reveal a novel mechanism by which DFMO prevents metastasis - induction of ferroptosis due to polyamine depletion. Our results provide preclinical justification to test the ability of DFMO to prevent metastatic recurrence in Ewing sarcoma patients at high risk for relapse.

DFMO inhibition of neuroblastoma tumorigenesis

BACKGROUND

Most high-risk neuroblastoma patients who relapse succumb to disease despite the existing therapy. We recently reported increased event-free and overall survival in neuroblastoma patients receiving difluoromethylornithine (DFMO) during maintenance therapy. The effect of DFMO on cellular processes associated with neuroblastoma tumorigenesis needs further elucidation. Previous studies have shown cytotoxicity with IC50 values >5-15 mM, these doses are physiologically unattainable in patients, prompting further mechanistic studies at therapeutic doses.

METHODS

We characterized the effect of DFMO on cell viability, cell cycle, apoptosis, neurosphere formation, and protein expression in vitro using five established neuroblastoma cell lines (BE2C, CHLA-90, SHSY5Y, SMS-KCNR, and NGP) at clinically relevant doses of 0, 50, 100, 500, 1000, and 2500 μM. Limiting Dilution studies of tumor formation in murine models were performed. Statistical analysis was done using GraphPad and the level of significance set at p = 0.05.

RESULTS

There was not a significant loss of cell viability or gain of apoptotic activity in the in vitro assays (p > 0.05). DFMO treatment initiated G1 to S phase cell cycle arrest. There was a dose-dependent decrease in frequency and size of neurospheres and a dose-dependent increase in beta-galactosidase activity in all cell lines. Tumor formation was decreased in xenografts both with DFMO-pretreated cells and in mice treated with DFMO.

CONCLUSION

DFMO treatment is cytostatic at physiologically relevant doses and inhibits tumor initiation and progression in mice. This study suggests that DFMO, inhibits neuroblastoma by targeting cellular processes integral to neuroblastoma tumorigenesis at clinically relevant doses.

Impact of Difluoromethylornithine and AMXT 1501 on Gene Expression and Capsule Regulation in Streptococcus pneumoniae

Streptococcus pneumoniae (Spn), a Gram-positive bacterium, poses a significant threat to human health, causing mild respiratory infections to severe invasive conditions. Despite the availability of vaccines, challenges persist due to serotype replacement and antibiotic resistance, emphasizing the need for alternative therapeutic strategies. This study explores the intriguing role of polyamines, ubiquitous, small organic cations, in modulating virulence factors, especially the capsule, a crucial determinant of Spn's pathogenicity. Using chemical inhibitors, difluoromethylornithine (DFMO) and AMXT 1501, this research unveils distinct regulatory effects on the gene expression of the Spn D39 serotype in response to altered polyamine homeostasis. DFMO inhibits polyamine biosynthesis, disrupting pathways associated with glucose import and the interconversion of sugars. In contrast, AMXT 1501, targeting polyamine transport, enhances the expression of polyamine and glucose biosynthesis genes, presenting a novel avenue for regulating the capsule independent of glucose availability. Despite ample glucose availability, AMXT 1501 treatment downregulates the glycolytic pathway, fatty acid synthesis, and ATP synthase, crucial for energy production, while upregulating two-component systems responsible for stress management. This suggests a potential shutdown of energy production and capsule biosynthesis, redirecting resources towards stress management. Following DFMO and AMXT 1501 treatments, countermeasures, such as upregulation of stress response genes and ribosomal protein, were observed but appear to be insufficient to overcome the deleterious effects on capsule production. This study highlights the complexity of polyamine-mediated regulation in S. pneumoniae, particularly capsule biosynthesis. Our findings offer valuable insights into potential therapeutic targets for modulating capsules in a polyamine-dependent manner, a promising avenue for intervention against S. pneumoniae infections.

Eflornithine as Postimmunotherapy Maintenance in High-Risk Neuroblastoma: Externally Controlled, Propensity Score-Matched Survival Outcome Comparisons

PURPOSE

Long-term survival in high-risk neuroblastoma (HRNB) is approximately 50%, with mortality primarily driven by relapse. Eflornithine (DFMO) to reduce risk of relapse after completion of immunotherapy was investigated previously in a single-arm, phase II study (NMTRC003B; ClinicalTrials.gov identifier: NCT02395666) that suggested improved event-free survival (EFS) and overall survival (OS) compared with historical rates in a phase III trial (Children Oncology Group ANBL0032; ClinicalTrials.gov identifier: NCT00026312). Using patient-level data from ANBL0032 as an external control, we present new analyses to further evaluate DFMO as HRNB postimmunotherapy maintenance.

PATIENTS AND METHODS

NMTRC003B (2012-2016) enrolled patients with HRNB (N = 141) after standard up-front or refractory/relapse treatment who received up to 2 years of continuous treatment with oral DFMO (750 ± 250 mg/m2 twice a day). ANBL0032 (2001-2015) enrolled patients with HRNB postconsolidation, 1,328 of whom were assigned to dinutuximab (ch.14.18) treatment. Selection rules identified 92 NMTRC003B patients who participated in (n = 87) or received up-front treatment consistent with (n = 5) ANBL0032 (the DFMO/treated group) and 852 patients from ANBL0032 who could have been eligible for NMTRC003B after immunotherapy, but did not enroll (the NO-DFMO/control group). The median follow-up time for DFMO/treated patients was 6.1 years (IQR, 5.2-7.2) versus 5.0 years (IQR, 3.5-7.0) for NO-DFMO/control patients. Kaplan-Meier and Cox regression compared EFS and OS for overall groups, 3:1 (NO-DFMO:DFMO) propensity score-matched cohorts balanced on 11 baseline demographic and disease characteristics with exact matching on MYCN, and additional sensitivity analyses.

RESULTS

DFMO after completion of immunotherapy was associated with improved EFS (hazard ratio [HR], 0.50 [95% CI, 0.29 to 0.84]; P = .008) and OS (HR, 0.38 [95% CI, 0.19 to 0.76]; P = .007). The results were confirmed with propensity score-matched cohorts and sensitivity analyses.

CONCLUSION

The externally controlled analyses presented show a relapse risk reduction in patients with HRNB treated with postimmunotherapy DFMO.

Difluoromethylornithine (DFMO) and Neuroblastoma: A Review

Neuroblastoma is a type of cancer that affects the sympathetic nervous system and is the most common extracranial solid tumor in children. Difluoromethylornithine (DFMO) is a drug that has shown promise as a treatment option for high-risk neuroblastoma. This review aims to provide an overview of the current research on the use of DFMO in neuroblastoma treatment. The review includes a discussion of the mechanisms of action of DFMO, as well as its potential for use in combination with other treatments such as chemotherapy and immunotherapy. The review also examines the current clinical trials involving DFMO in high-risk neuroblastoma patients and provides insights into the challenges and future directions for the use of DFMO in neuroblastoma treatment. Overall, the review highlights the potential of DFMO as a promising therapy for neuroblastoma and highlights the need for further research to fully understand its potential benefits and limitations.

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.

A new 68Ga-labeled ornithine derivative for PET imaging of ornithine metabolism in tumors

Ornithine metabolism plays a vital role in tumorigenesis. For cancer cells, ornithine is mainly used as a substrate for ornithine decarboxylase (ODC) for the synthesis of polyamines. The ODC as a key enzyme of polyamine metabolism has become an important target for cancer diagnosis and treatment. To non-invasively detect the levels of ODC expression in malignant tumors, we have synthesized a novel ⁶⁸Ga-labeled ornithine derivative ([⁶⁸Ga]Ga-NOTA-Orn). The synthesis time of [⁶⁸Ga]Ga-NOTA-Orn was about 30 min with a radiochemical yield of 45-50% (uncorrected), and the radiochemical purity was > 98%. [⁶⁸Ga]Ga-NOTA-Orn was stable in saline and rat serum. Cellular uptake and competitive inhibition assays using DU145 and AR42J cells demonstrated that the transport pathway of [⁶⁸Ga]Ga-NOTA-Orn was similar to that of L-ornithine, and it could interact with the ODC after transporting into the cell. Biodistribution and micro-positron emission tomography (Micro-PET) imaging studies showed that [⁶⁸Ga]Ga-NOTA-Orn exhibited rapid tumor uptake and was rapidly excreted through the urinary system. All above results suggested that [⁶⁸Ga]Ga-NOTA-Orn is a novel amino acid metabolic imaging agent with great potential of tumor diagnosis.

CD203c is expressed by human fetal hepatoblasts and distinguishes subsets of hepatoblastoma

Background & Aims

Hepatocytic cells found during prenatal development have unique features compared to their adult counterparts, and are believed to be the precursors of pediatric hepatoblastoma. The cell-surface phenotype of hepatoblasts and hepatoblastoma cell lines was evaluated to discover new markers of these cells and gain insight into the development of hepatocytic cells and the phenotypes and origins of hepatoblastoma.

Methods

Human midgestation livers and four pediatric hepatoblastoma cell lines were screened using flow cytometry. Expression of over 300 antigens was evaluated on hepatoblasts defined by their expression of CD326 (EpCAM) and CD14. Also analyzed were hematopoietic cells, expressing CD45, and liver sinusoidal-endothelial cells (LSECs), expressing CD14 but lacking CD45 expression. Select antigens were further examined by fluorescence immunomicroscopy of fetal liver sections. Antigen expression was also confirmed on cultured cells by both methods. Gene expression analysis by liver cells, 6 hepatoblastoma cell lines, and hepatoblastoma cells was performed. Immunohistochemistry was used to evaluate CD203c, CD326, and cytokeratin-19 expression on three hepatoblastoma tumors.

Results

Antibody screening identified many cell surface markers commonly or divergently expressed by hematopoietic cells, LSECs, and hepatoblasts. Thirteen novel markers expressed on fetal hepatoblasts were identified including ectonucleotide pyrophosphatase/phosphodiesterase family member 3 (ENPP-3/CD203c), which was found to be expressed by hepatoblasts with widespread expression in the parenchyma of the fetal liver. In culture CD203c⁺CD326⁺⁺ cells resembled hepatocytic cells with coexpression of albumin and cytokeratin-19 confirming a hepatoblast phenotype. CD203c expression declined rapidly in culture whereas the loss of CD326 was not as pronounced. CD203c and CD326 were co-expressed on a subset of hepatoblastoma cell lines and hepatoblastomas with an embryonal pattern.

Conclusions

CD203c is expressed on hepatoblasts and may play a role in purinergic signaling in the developing liver. Hepatoblastoma cell lines were found to consist of two broad phenotypes consisting of a cholangiocyte-like phenotype that expressed CD203c and CD326 and a hepatocyte-like phenotype with diminished expression of these markers. CD203c was expressed by some hepatoblastoma tumors and may represent a marker of a less differentiated embryonal component.

MicroRNAs as prospective biomarkers, therapeutic targets and pharmaceuticals in neuroblastoma

Neuroblastomas, the most prevalent malignant solid neoplasms of childhood, originate from progenitor cells of the sympathetic nervous system. Their genetic causation is diverse and involves multiple molecular mechanisms. This review highlights multiple roles of microRNA in neuroblastoma pathogenesis and discusses the prospects of harnessing these important natural regulator molecules as biomarkers, therapeutic targets and pharmaceuticals in neuroblastoma.

Lin28 Regulates Cancer Cell Stemness for Tumour Progression

Tumours develop therapy resistance through complex mechanisms, one of which is that cancer stem cell (CSC) populations within the tumours present self-renewable capability and phenotypical plasticity to endure therapy-induced stress conditions and allow tumour progression to the therapy-resistant state. Developing therapeutic strategies to cope with CSCs requires a thorough understanding of the critical drivers and molecular mechanisms underlying the aforementioned processes. One such hub regulator of stemness is Lin28, an RNA-binding protein. Lin28 blocks the synthesis of let-7, a tumour-suppressor microRNA, and acts as a global regulator of cell differentiation and proliferation. Lin28also targets messenger RNAs and regulates protein translation. In this review, we explain the role of the Lin28/let-7 axis in establishing stemness, epithelial-to-mesenchymal transition, and glucose metabolism reprogramming. We also highlight the role of Lin28 in therapy-resistant prostate cancer progression and discuss the emergence of Lin28-targeted therapeutics and screening methods.

Compromised glycolysis contributes to foot process fusion of podocytes in diabetic kidney disease: Role of ornithine catabolism

INTRODUCTION

Compromised glycolysis in podocytes contributes to the initiation of diabetic kidney disease (DKD). Podocyte injury is characterized by cytoskeletal remodeling and foot process fusion. Compromised glycolysis in diabetes likely leads to switch of energy supply in podocyte. However, the underlying mechanism by which disturbed energy supply in podocytes affects the cytoskeletal structure of podocytes remains unclear.

METHODS

Metabolomic and transcriptomic analyses were performed on the glomeruli of db/db mice to examine the catabolism of glucose, fatty, and amino acids. Ornithine catabolism was targeted in db/db and podocyte-specific pyruvate kinase M2 knockout (PKM2-podoKO) mice. In vitro, expression of ornithine decarboxylase (ODC1) was modulated to investigate the effect of ornithine catabolism on mammalian target of rapamycin (mTOR) signaling and cytoskeletal remodeling in cultured podocytes.

RESULTS

Multi-omic analyses of the glomeruli revealed that ornithine metabolism was enhanced in db/db mice compared with that in db/m mice under compromised glycolytic conditions. Additionally, ornithine catabolism was exaggerated in podocytes of diabetic PKM2-podoKO mice compared with that in diabetic PKM2^flox/flox mice. In vivo, difluoromethylornithine (DFMO, inhibitor of ODC1) administration reduced urinary albumin excretion and alleviated podocyte foot process fusion in db/db mice. In vitro, 2-deoxy-d-glucose (2-DG) exposure induced mTOR signaling activation and cytoskeletal remodeling in podocytes, which was alleviated by ODC1-knockdown. Mechanistically, a small GTPase Ras homolog enriched in the brain (Rheb), a sensor of mTOR signaling, was activated by exposure to putrescine, a metabolic product of ornithine catabolism.

CONCLUSION

These findings demonstrate that compromised glycolysis in podocytes under diabetic conditions enhances ornithine catabolism. The metabolites of ornithine catabolism contribute to mTOR signaling activation via Rheb and cytoskeletal remodeling in podocytes in DKD.

Effect of Letrozole on hippocampal Let-7 microRNAs and their correlation with working memory and phosphorylated Tau protein in an Alzheimer's disease-like rat model

Background

Let-7 microRNAs (miRNAs) may contribute to neurodegeneration, including Alzheimer's disease (AD), but, they were not investigated in Streptozotocin (STZ)-induced AD. Letrozole increases the expression of Let-7 in cell lines, with conflicting evidence regarding its effects on memory. This study examined Let-7 miRNAs in STZ-induced AD, their correlation with memory and hyperphosphorylated Tau (p-Tau) and the effects of Letrozole on them.

Methods

Seven groups of adult Sprague Dawley rats were used: Negative control, Letrozole, Letrozole Vehicle, STZ (with AD induced by intracerebroventricular injection of STZ in artificial cerebrospinal fluid (aCSF)), CSF Control, STZ + Letrozole (STZ-L), and CSF + Letrozole Vehicle. Alternation percentage in T-maze was used as a measure of working memory. Let-7a, b and e and p-Tau levels in the hippocampus were estimated using quantitative real-time reverse transcription–polymerase chain reaction (qRT–PCR) and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Significant decreases in alternation percentage and increase in p-Tau concentration were found in the STZ, Letrozole and STZ-L groups. Expression levels of all studied microRNAs were significantly elevated in the Letrozole and the STZ-L groups, with no difference between the two, suggesting that this elevation might be linked to Letrozole administration. Negative correlations were found between alternation percentage and the levels of all studied microRNAs, while positive ones were found between p-Tau concentration and the levels of studied microRNAs.

Conclusions

This study shows changes in the expression of Let-7a, b and e miRNAs in association with Letrozole administration, and correlations between the expression of the studied Let-7 miRNAs and both the status of working memory and the hippocampal p-Tau levels. These findings might support the theory suggesting that Letrozole aggravates pre-existing lesions. They also add to the possibility of Let-7’s neurotoxicity.

A pilot study of genomic-guided induction therapy followed by immunotherapy with difluoromethylornithine maintenance for high-risk neuroblastoma

BACKGROUND

Survival for patients with high-risk neuroblastoma (HRNB) remains poor despite aggressive multimodal therapies.

AIMS

To study the feasibility and safety of incorporating a genomic-based targeted agent to induction therapy for HRNB as well as the feasibility and safety of adding difluoromethylornithine (DFMO) to anti-GD2 immunotherapy.

METHODS

Twenty newly diagnosed HRNB patients were treated on this multicenter pilot trial. Molecular tumor boards selected one of six targeted agents based on tumor-normal whole exome sequencing and tumor RNA-sequencing results. Treatment followed standard upfront HRNB chemotherapy with the addition of the selected targeted agent to cycles 3-6 of induction. Following consolidation, DFMO (750 mg/m² twice daily) was added to maintenance with dinutuximab and isotretinoin, followed by continuation of DFMO alone for 2 years. DNA methylation analysis was performed retrospectively and compared to RNA expression.

RESULTS

Of the 20 subjects enrolled, 19 started targeted therapy during cycle 3 and 1 started during cycle 5. Eighty-five percent of subjects met feasibility criteria (receiving 75% of targeted agent doses). Addition of targeted agents did not result in toxicities requiring dose reduction of chemotherapy or permanent discontinuation of targeted agent. Following standard consolidation, 15 subjects continued onto immunotherapy with DFMO. This combination was well-tolerated and resulted in no unexpected adverse events related to DFMO.

CONCLUSION

This study demonstrates the safety and feasibility of adding targeted agents to standard induction therapy and adding DFMO to immunotherapy for HRNB. This treatment regimen has been expanded to a Phase II trial to evaluate efficacy.

The Roles of the Let-7 Family of MicroRNAs in the Regulation of Cancer Stemness

Cancer has long been viewed as a disease of normal development gone awry. Cancer stem-like cells (CSCs), also termed as tumor-initiating cells (TICs), are increasingly recognized as a critical tumor cell population that drives not only tumorigenesis but also cancer progression, treatment resistance and metastatic relapse. The let-7 family of microRNAs (miRNAs), first identified in C. elegans but functionally conserved from worms to human, constitutes an important class of regulators for diverse cellular functions ranging from cell proliferation, differentiation and pluripotency to cancer development and progression. Here, we review the current state of knowledge regarding the roles of let-7 miRNAs in regulating cancer stemness. We outline several key RNA-binding proteins, long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) involved in the regulation of let-7 biogenesis, maturation and function. We then highlight key gene targets and signaling pathways that are regulated or mutually regulated by the let-7 family of miRNAs to modulate CSC characteristics in various types of cancer. We also summarize the existing evidence indicating distinct metabolic pathways regulated by the let-7 miRNAs to impact CSC self-renewal, differentiation and treatment resistance. Lastly, we review current preclinical studies and discuss the clinical implications for developing let-7-based replacement strategies as potential cancer therapeutics that can be delivered through different platforms to target CSCs and reduce/overcome treatment resistance when applied alone or in combination with current chemo/radiation or molecularly targeted therapies. By specifically targeting CSCs, these strategies have the potential to significantly improve the efficacy of cancer therapies.

Advances in pharmacotherapy for neuroblastoma

INTRODUCTION

Neuroblastoma is the most prevalent cancer type diagnosed within the first year after birth and accounts for 15% of deaths from pediatric cancer. Despite the improvements in survival rates of patients with neuroblastoma, the incidence of the disease has increased over the last decade. Neuroblastoma tumor cells harbor a vast range of variable and heterogeneous histochemical and genetic alterations which calls for the need to administer individualized and targeted therapies to induce tumor regression in each patient.

AREAS COVERED

This paper provides reviews the recent clinical trials which used chemotherapeutic and/or targeted agents as either monotherapies or in combination to improve the response rate in patients with neuroblastoma, and especially high-risk neuroblastoma. It also reviews some of the prominent preclinical studies which can provide the rationale for future clinical trials.

EXPERT OPINION

Although some distinguished advances in pharmacotherapy have been made to improve the survival rate and reduce adverse events in patients with neuroblastoma, a more comprehensive understanding of the mechanisms of tumorigenesis, resistance to therapies or relapse, identifying biomarkers of response to each specific drug, and developing predictive preclinical models of the tumor can lead to further breakthroughs in the treatment of neuroblastoma.

Metabolism and function of polyamines in cancer progression

Polyamines are essential for the proliferation, differentiation, and development of eukaryotes. They include spermine, spermidine, and the diamine precursor putrescine, and are low-molecular-weight, organic polycations with more than two amino groups. Their intracellular concentrations are strictly maintained within a specific physiological range through several regulatory mechanisms in normal cells. In contrast, polyamine metabolism is dysregulated in many neoplastic states, including cancer. In various types of cancer, polyamine levels are elevated, and crosstalk occurs between polyamine metabolism and oncogenic pathways, such as mTOR and RAS pathways. Thus, polyamines might have potential as therapeutic targets in the prevention and treatment of cancer. The molecular mechanisms linking polyamine metabolism to carcinogenesis must be unraveled to develop novel inhibitors of polyamine metabolism. This overview describes the nature of polyamines, their association with carcinogenesis, the development of polyamine inhibitors and their potential, and the findings of clinical trials.

Probenecid increases renal retention and antitumor activity of DFMO in neuroblastoma

BACKGROUND

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Interference with the polyamine biosynthesis pathway by inhibition of MYCN-activated ornithine decarboxylase (ODC) is a validated approach. The ODC inhibitor α-difluoromethylornithine (DFMO, or Eflornithine) has been FDA-approved for the treatment of trypanosomiasis and hirsutism and has advanced to clinical cancer trials including NB as well as cancer-unrelated human diseases. One key challenge of DFMO is its rapid renal clearance and the need for high and frequent drug dosing during treatment.

METHODS

We performed in vivo pharmacokinetic (PK), antitumorigenic, and molecular studies with DFMO/probenecid using NB patient-derived xenografts (PDX) in mice. We used LC-MS/MS, HPLC, and immunoblotting to analyze blood, brain tissue, and PDX tumor tissue samples collected from mice.

RESULTS

The organic anion transport 1/3 (OAT 1/3) inhibitor probenecid reduces the renal clearance of DFMO and significantly increases the antitumor activity of DFMO in PDX of NB (P < 0.02). Excised tumors revealed that DFMO/probenecid treatment decreases polyamines putrescine and spermidine, reduces MYCN protein levels and dephosphorylates retinoblastoma (Rb) protein (p-Rb^Ser795), suggesting DFMO/probenecid-induced cell cycle arrest.

CONCLUSION

Addition of probenecid as an adjuvant to DFMO therapy may be suitable to decrease overall dose and improve drug efficacy in vivo.

Molecular Genetics in Neuroblastoma Prognosis

In recent years, much research has been carried out to identify the biological and genetic characteristics of the neuroblastoma (NB) tumor in order to precisely define the prognostic subgroups for improving treatment stratification. This review will describe the major genetic features and the recent scientific advances, focusing on their impact on diagnosis, prognosis, and therapeutic solutions in NB clinical management.

Arginine Metabolism and Its Potential in Treatment of Colorectal Cancer

Colorectal cancer is the leading cause of death from cancer globally. The current treatment protocol still heavily relies on early detection and surgery. The molecular mechanisms underlying development of colorectal cancer are clinically important and determine the prognosis and treatment response. The arginine metabolism pathway is hyperactive in colorectal cancer and several molecules involved in the pathway are potential targets for chemoprevention and targeted colorectal cancer therapy. Endothelial nitric oxide synthase (eNOS), argininosuccinate synthetase and ornithine decarboxylase (ODC) are the main enzymes for arginine metabolism. Limiting arginine-rich meat consumption and inhibiting ODC activity largely reduces polyamine synthesis and the incidence of colorectal cancer. Arginine transporter CAT-1 and Human member 14 of the solute carrier family 6 (SLC6A14) are overexpressed in colorectal cancer cells and contributes to intracellular arginine levels. Human member 9 of the solute carrier family 38 (SLC38A9) serves as a component of the lysosomal arginine-sensing machinery. Pharmaceutical inhibition of single enzyme or arginine transporter is hard to meet requirement of restoring of abnormal arginine metabolic network. Apart from application in early screening for colorectal cancer, microRNA-based therapeutic strategy that simultaneously manipulating multiple targets involved in arginine metabolism brings promising future in the treatment of colorectal cancer.

Non-Coding RNAs Participate in the Pathogenesis of Neuroblastoma

Neuroblastoma is one of the utmost frequent neoplasms during the first year of life. This pediatric cancer is believed to be originated during the embryonic life from the neural crest cells. Previous studies have detected several types of chromosomal aberrations in this tumor. More recent studies have emphasized on expression profiling of neuroblastoma samples to identify the dysregulated genes in this type of cancer. Non-coding RNAs are among the mostly dysregulated genes in this type of cancer. Such dysregulation has been associated with a number of chromosomal aberrations that are frequently detected in neuroblastoma. In this study, we explain the role of non-coding transcripts in the malignant transformation in neuroblastoma and their role as biomarkers for this pediatric cancer.

Dual targeting of polyamine synthesis and uptake in diffuse intrinsic pontine gliomas

Diffuse intrinsic pontine glioma (DIPG) is an incurable malignant childhood brain tumor, with no active systemic therapies and a 5-year survival of less than 1%. Polyamines are small organic polycations that are essential for DNA replication, translation and cell proliferation. Ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme in polyamine synthesis, is irreversibly inhibited by difluoromethylornithine (DFMO). Herein we show that polyamine synthesis is upregulated in DIPG, leading to sensitivity to DFMO. DIPG cells compensate for ODC1 inhibition by upregulation of the polyamine transporter SLC3A2. Treatment with the polyamine transporter inhibitor AMXT 1501 reduces uptake of polyamines in DIPG cells, and co-administration of AMXT 1501 and DFMO leads to potent in vitro activity, and significant extension of survival in three aggressive DIPG orthotopic animal models. Collectively, these results demonstrate the potential of dual targeting of polyamine synthesis and uptake as a therapeutic strategy for incurable DIPG.

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.

Molecular targeting therapies for neuroblastoma: Progress and challenges

There is an urgent need to identify novel therapies for childhood cancers. Neuroblastoma is the most common pediatric solid tumor, and accounts for ~15% of childhood cancer‐related mortality. Neuroblastomas exhibit genetic, morphological and clinical heterogeneity, which limits the efficacy of existing treatment modalities. Gaining detailed knowledge of the molecular signatures and genetic variations involved in the pathogenesis of neuroblastoma is necessary to develop safer and more effective treatments for this devastating disease. Recent studies with advanced high‐throughput “omics” techniques have revealed numerous genetic/genomic alterations and dysfunctional pathways that drive the onset, growth, progression, and resistance of neuroblastoma to therapy. A variety of molecular signatures are being evaluated to better understand the disease, with many of them being used as targets to develop new treatments for neuroblastoma patients. In this review, we have summarized the contemporary understanding of the molecular pathways and genetic aberrations, such as those in MYCN, BIRC5, PHOX2B, and LIN28B, involved in the pathogenesis of neuroblastoma, and provide a comprehensive overview of the molecular targeted therapies under preclinical and clinical investigations, particularly those targeting ALK signaling, MDM2, PI3K/Akt/mTOR and RAS‐MAPK pathways, as well as epigenetic regulators. We also give insights on the use of combination therapies involving novel agents that target various pathways. Further, we discuss the future directions that would help identify novel targets and therapeutics and improve the currently available therapies, enhancing the treatment outcomes and survival of patients with neuroblastoma.

ETMR: a tumor entity in its infancy

Embryonal tumor with Multilayered Rosettes (ETMR) is a relatively rare but typically deadly type of brain tumor that occurs mostly in infants. Since the discovery of the characteristic chromosome 19 miRNA cluster (C19MC) amplification a decade ago, the methods for diagnosing this entity have improved and many new insights in the molecular landscape of ETMRs have been acquired. All ETMRs, despite their highly heterogeneous histology, are characterized by specific high expression of the RNA-binding protein LIN28A, which is, therefore, often used as a diagnostic marker for these tumors. ETMRs have few recurrent genetic aberrations, mainly affecting the miRNA pathway and including amplification of C19MC (embryonal tumor with multilayered rosettes, C19MC-altered) and mutually exclusive biallelic DICER1 mutations of which the first hit is typically inherited through the germline (embryonal tumor with multilayered rosettes, DICER1-altered). Identification of downstream pathways affected by the deregulated miRNA machinery has led to several proposed potential therapeutical vulnerabilities including targeting the WNT, SHH, or mTOR pathways, MYCN or chromosomal instability. However, despite those findings, treatment outcomes have only marginally improved, since the initial description of this tumor entity. Many patients do not survive longer than a year after diagnosis and the 5-year overall survival rate is still lower than 30%. Thus, there is an urgent need to translate the new insights in ETMR biology into more effective treatments. Here, we present an overview of clinical and molecular characteristics of ETMRs and the current progress on potential targeted therapies.

Structure based design of inhibitory peptides targeting ornithine decarboxylase dimeric interface and in vitro validation in human retinoblastoma Y79 cells

Polyamine synthesis in human cells is initiated by catalytic action of Ornithine decarboxylase (ODC) on Ornithine. Elevated levels of polyamines are manifested proliferating cancer cells and are found to promote tumour cell adhesion. Di-flouro methyl orninthine is a known inhibitor of ODC, however its usage is limited due its low affinity quick clearance and incompetent cellular uptake, thus posing a need for potential inhibitors. Currently, peptides are substituting drugs, as these are highly selective, specific and potent. Hence, in this study, the interacting interfaces of native homodimeric form of ODC and its heterodimer with Antizyme were probed to design inhibitory peptides targeting ODC. The designed peptides were validated for structural fitness by extensive molecular dynamics simulations and Circular dichroism studies. Finally, these peptides were validated in Y79 retinoblastoma cells for impact on ODC activity, cytotoxicity cell cycle and cell adhesion. On collective analysis, Peptide3 (Pep 3) and Peptide4 (Pep 4) were found to be potentially targeting ODC, as these peptides showed significant decrease in intracellular polyamine levels, cell adhesion and cell cycle perturbation in Y79 cells. Thus, Pep 3 and Pep 4 shall be favourably considered as therapeutic agents for targeting ODC mediated proliferation in retinoblastoma.Communicated by Ramaswamy H. Sarma.

Cell surface vimentin-positive circulating tumor cell-based relapse prediction in a long-term longitudinal study of postremission neuroblastoma patients

Neuroblastoma (NB) is a deadly childhood disease that carries a 50% chance of relapse for anyone in remission and similar level of 5-year survival. We investigated the value of our proprietary approach-cell surface vimentin (CSV) positive circulating tumor cells (CTC) to monitor treatment response and predict relapse in NB patients under remission in a Phase II long-term preventative clinical trial. We longitudinally analyzed peripheral blood samples from 93 patients for 27 cycles (~25 months) and discovered that the presence of CSV⁺ CTCs in the first two sequential samples (baseline, cycle 4 [month 3-4]) was a significant indicator of earlier relapse. We observed strong correlation between relapse-free survival (RFS) and lack of CSV⁺ CTCs in first 4 cycles of therapy (95%). There was sensitivity reaching 100% in predicting RFS in patients who had neither CSV⁺ CTCs nor MycN amplification. Of note, the low number of CSV⁺ CTCs seems equivalent to low tumor load because the prevention therapy difluoromethylornithine yields faster reduction of relapse risk when none or only 1-2 CSV⁺ CTCs (every 6 mL) are present in the blood samples compared to >3 CSV⁺ CTCs. To the best of our knowledge, this is the first study that directly observes CTCs in under remission NB patients for relapse prediction and the first to gather sequential CSV⁺ CTC data in any study in a long-term longitudinal manner.

A subset analysis of a phase II trial evaluating the use of DFMO as maintenance therapy for high-risk neuroblastoma

Neuroblastoma is a sympathetic nervous system tumor, primarily presenting in children under 6 years of age. The long-term prognosis for patients with high-risk neuroblastoma (HRNB) remains poor despite aggressive multimodal therapy. This report provides an update to a phase II trial evaluating DFMO as maintenance therapy in HRNB. Event-free survival (EFS) and overall survival (OS) of 81 subjects with HRNB treated with standard COG induction, consolidation and immunotherapy followed by 2 years of DFMO on the NMTRC003/003b Phase II trial were compared to a historical cohort of 76 HRNB patients treated at Beat Childhood Cancer Research Consortium (BCC) hospitals who were disease-free after completion of standard upfront therapy and did not receive DFMO. The 2- and 5-year EFS were 86.4% [95% confidence interval (CI) 79.3%-94.2%] and 85.2% [77.8%-93.3%] for the NMTRC003/003b subset vs 78.3% [69.5%-88.3%] and 65.6% [55.5%-77.5%] for the historical control group. The 2- and 5-year OS were 98.8% [96.4-100%] and 95.1% [90.5%-99.9%] vs 94.4% [89.3%-99.9%] and 81.6% [73.0%-91.2%], respectively. DFMO maintenance for HRNB after completion of standard of care therapy was associated with improved EFS and OS relative to historical controls treated at the same institutions. These results support additional investigations into the potential role of DFMO in preventing relapse in HRNB.

Upregulating Lin28a Promotes Axon Regeneration in Adult Mice with Optic Nerve and Spinal Cord Injury

Severed CNS axons fail to regenerate in adult mammals and there are no effective regenerative strategies to treat patients with CNS injuries. Several genes, including phosphatase and tensin homolog (PTEN) and Krüppel-like factors, regulate intrinsic growth capacity of mature neurons. The Lin28 gene is essential for cell development and pluripotency in worms and mammals. In this study, we evaluated the role of Lin28a in regulating regenerative capacity of diverse populations of CNS neurons in adult mammals. Using a neuron-specific Thy1 promoter, we generated transgenic mice that overexpress Lin28a protein in multiple populations of projection neurons, including corticospinal tracts and retinal ganglion cells. We demonstrate that upregulation of Lin28a in transgenic mice induces significant long distance regeneration of both corticospinal axons and the optic nerve in adult mice. Importantly, overexpression of Lin28a by post-injury treatment with adeno-associated virus type 2 (AAV2) vector stimulates dramatic regeneration of descending spinal tracts and optic nerve axons after lesions. Upregulation of Lin28a also enhances activity of the Akt signaling pathway in mature CNS neurons. Therefore, Lin28a is critical for regulating growth capacity of multiple CNS neurons and may become an important molecular target for treating CNS injuries.

Drug repurposing towards targeting cancer stem cells in pediatric brain tumors

In the pediatric population, brain tumors represent the most commonly diagnosed solid neoplasms and the leading cause of cancer-related deaths globally. They include low-grade gliomas (LGGs), medulloblastomas (MBs), and other embryonal, ependymal, and neuroectodermal tumors. The mainstay of treatment for most brain tumors includes surgical intervention, radiation therapy, and chemotherapy. However, resistance to conventional therapy is widespread, which contributes to the high mortality rates reported and lack of improvement in patient survival despite advancement in therapeutic research. This has been attributed to the presence of a subpopulation of cells, known as cancer stem cells (CSCs), which reside within the tumor bulk and maintain self-renewal and recurrence potential of the tumor. An emerging promising approach that enables identifying novel therapeutic strategies to target CSCs and overcome therapy resistance is drug repurposing or repositioning. This is based on using previously approved drugs with known pharmacokinetic and pharmacodynamic characteristics for indications other than their traditional ones, like cancer. In this review, we provide a synopsis of the drug repurposing methodologies that have been used in pediatric brain tumors, and we argue how this selective compilation of approaches, with a focus on CSC targeting, could elevate drug repurposing to the next level.

Targeting metabolic dependencies in pediatric cancer

PURPOSE OF REVIEW

In an attempt to identify potential new therapeutic targets, efforts to describe the metabolic features unique to cancer cells are increasingly being reported. Although current standard of care regimens for several pediatric malignancies incorporate agents that target tumor metabolism, these drugs have been part of the therapeutic landscape for decades. More recent research has focused on the identification and targeting of new metabolic vulnerabilities in pediatric cancers. The purpose of this review is to describe the most recent translational findings in the metabolic targeting of pediatric malignancies.

RECENT FINDINGS

Across multiple pediatric cancer types, dependencies on a number of key metabolic pathways have emerged through study of patient tissue samples and preclinical modeling. Among the potentially targetable vulnerabilities are glucose metabolism via glycolysis, oxidative phosphorylation, amino acid and polyamine metabolism, and NAD metabolism. Although few agents have yet to move forward into clinical trials for pediatric cancer patients, the robust and promising preclinical data that have been generated suggest that future clinical trials should rationally test metabolically targeted agents for relevant disease populations.

SUMMARY

Recent advances in our understanding of the metabolic dependencies of pediatric cancers represent a source of potential new therapeutic opportunities for these diseases.

Exploring the Potential of MicroRNA Let-7c as a Therapeutic for Prostate Cancer

Prostate cancer (PCa) is one of the leading causes of mortality worldwide and often presents with aberrant microRNA (miRNA) expression. Identifying and understanding the unique expression profiles could aid in the detection and treatment of this disease. This review aims to identify miRNAs as potential therapeutic targets for PCa. Three bio-informatic searches were conducted to identify miRNAs that are reportedly implicated in the pathogenesis of PCa. Only hsa-Lethal-7 (let-7c), recognized for its role in PCa pathogenesis, was common to all three databases. Three further database searches were conducted to identify known targets of hsa-let-7c. Four targets were identified, HMGA2, c-Myc (MYC), TRAIL, and CASP3. An extensive review of the literature was undertaken to assess the role of hsa-let-7c in the progression of other malignancies and to evaluate its potential as a therapeutic target for PCa. The heterogeneous nature of cancer makes it logical to develop mechanisms by which the treatment of malignancies is tailored to an individual, harnessing specific knowledge of the underlying biology of the disease. Resetting cellular miRNA levels is an exciting prospect that will allow this ambition to be realized.

Polyamines in mammalian pathophysiology

Polyamines (PAs) are essential organic polycations for cell viability along the whole phylogenetic scale. In mammals, they are involved in the most important physiological processes: cell proliferation and viability, nutrition, fertility, as well as nervous and immune systems. Consequently, altered polyamine metabolism is involved in a series of pathologies. Due to their pathophysiological importance, PA metabolism has evolved to be a very robust metabolic module, interconnected with the other essential metabolic modules for gene expression and cell proliferation/differentiation. Two different PA sources exist for animals: PA coming from diet and endogenous synthesis. In the first section of this work, the molecular characteristics of PAs are presented as determinant of their roles in living organisms. In a second section, the metabolic specificities of mammalian PA metabolism are reviewed, as well as some obscure aspects on it. This second section includes information on mammalian cell/tissue-dependent PA-related gene expression and information on crosstalk with the other mammalian metabolic modules. The third section presents a synthesis of the physiological processes described as modulated by PAs in humans and/or experimental animal models, the molecular bases of these regulatory mechanisms known so far, as well as the most important gaps of information, which explain why knowledge around the specific roles of PAs in human physiology is still considered a "mysterious" subject. In spite of its robustness, PA metabolism can be altered under different exogenous and/or endogenous circumstances so leading to the loss of homeostasis and, therefore, to the promotion of a pathology. The available information will be summarized in the fourth section of this review. The different sections of this review also point out the lesser-known aspects of the topic. Finally, future prospects to advance on these still obscure gaps of knowledge on the roles on PAs on human physiopathology are discussed.

Short-term efficacy and safety of MR-guided focused ultrasound surgery for analgesia in children with metastatic bone tumors

Short-term efficacy and safety of magnetic resonance-guided focused ultrasound surgery (MRgFUS) for analgesia in children with metastatic bone tumors were studied. Thirty children with pediatric bone metastases admitted to Jinan Maternity and Child Care Hospital from March 2015 to March 2018 and who received MRgFUS treatment of the bone metastasis lesions were collected. The postoperative efficacy was assessed. The observation indicators included the Numerical Rating Scale (NRS) scores, European Organization for Research and Treatment of Cancer (EORTC) and Quality of Life Questionnaire (QLQ) scores before surgery, and 1 week, 1, 2, and 3 months after surgery and the Karnofsky Performance Status (KPS) scores before surgery, and 1 week and 3 months after surgery. The adverse reactions and medications of the children after the surgery were also under observation. NRS and VAS scores of all different observation time-points after surgery were statistically lower than those before surgery (P<0.05), and the NRS scores and Visual Analog Scale (VAS) scores 3 months after surgery were lower than those 1 week after surgery (P<0.05). Compared with the preoperative conditions, the QLQ-C30 scores of terms like physical function, cognitive function, nausea and vomiting, and degree of pain 1 week, 1, 2, and 3 months after surgery were decreased, and the clinical symptoms of the children were relieved (P<0.05). There was a statistical difference between the total QLQ-C30 scores 3 months after operation and the total QLQ-C30 scores 3 months before operation (P<0.05). No serious adverse reactions related to treatment were reported, and the application of analgesics was reduced. MRgFUS relieves bone metastasis pain in children with good curative effect and high safety.

Cancer Stem Cells in Neuroblastoma: Expanding the Therapeutic Frontier

Neuroblastoma (NB) is the most common extracranial solid tumor often diagnosed in childhood. Despite intense efforts to develop a successful treatment, current available therapies are still challenged by high rates of resistance, recurrence and progression, most notably in advanced cases and highly malignant tumors. Emerging evidence proposes that this might be due to a subpopulation of cancer stem cells (CSCs) or tumor-initiating cells (TICs) found in the bulk of the tumor. Therefore, the development of more targeted therapy is highly dependent on the identification of the molecular signatures and genetic aberrations characteristic to this subpopulation of cells. This review aims at providing an overview of the key molecular players involved in NB CSCs and focuses on the experimental evidence from NB cell lines, patient-derived xenografts and primary tumors. It also provides some novel approaches of targeting multiple drivers governing the stemness of CSCs to achieve better anti-tumor effects than the currently used therapeutic agents.

A Regulator of Metabolic Reprogramming: MicroRNA Let-7

Let-7, a gene firstly known to control the timing of Caenorhabditis elegans larval development does not code for a protein but instead produces small non-coding RNAs, microRNAs. Higher animals have multiple isoforms of mature let-7 microRNAs. Mature let-7 family members share the same “seed sequence” and distinct from each other slightly by ‘non-seed’ sequence region. Let-7 has emerged as a central regulator of systemic energy homeostasis and it displays remarkable plasticity in metabolic responses to nutrients availability and physiological activities. In this review, we discuss recent studies highlighting post-transcriptional mechanisms that govern metabolic reprogramming in distinct cells by let-7. We focus on the participation of the let-7 clusters in immune cells, and suggest that tissue-specific regulation of the let-7 clusters by engineered mouse models might impact metabolic homeostasis and will be required to elucidate their physiological and pathological roles in the in vivo disease models.

Polyamine synthesis as a target of MYC oncogenes

This paper is in recognition of the 100th birthday of Dr. Herbert Tabor, a true pioneer in the polyamine field for over 70 years, who served as the editor-in-chief of the Journal of Biological Chemistry from 1971 to 2010. We review current knowledge of MYC proteins (c-MYC, MYCN, and MYCL) and focus on ornithine decarboxylase 1 (ODC1), an important bona fide gene target of MYC, which encodes the sentinel, rate-limiting enzyme in polyamine biosynthesis. Although notable advances have been made in designing inhibitors against the "undruggable" MYCs, their downstream targets and pathways are currently the main avenue for therapeutic anticancer interventions. To this end, the MYC-ODC axis presents an attractive target for managing cancers such as neuroblastoma, a pediatric malignancy in which MYCN gene amplification correlates with poor prognosis and high-risk disease. ODC and polyamine levels are often up-regulated and contribute to tumor hyperproliferation, especially of MYC-driven cancers. We therefore had proposed to repurpose α-difluoromethylornithine (DFMO), an FDA-approved, orally available ODC inhibitor, for management of neuroblastoma, and this intervention is now being pursued in several clinical trials. We discuss the regulation of ODC and polyamines, which besides their well-known interactions with DNA and tRNA/rRNA, are involved in regulating RNA transcription and translation, ribosome function, proteasomal degradation, the circadian clock, and immunity, events that are also controlled by MYC proteins.

Maintenance DFMO Increases Survival in High Risk Neuroblastoma

High risk neuroblastoma (HRNB) accounts for 15% of all pediatric cancer deaths. Despite aggressive therapy approximately half of patients will relapse, typically with only transient responses to second-line therapy. This study evaluated the ornithine decarboxylase inhibitor difluoromethylornithine (DFMO) as maintenance therapy to prevent relapse following completion of standard therapy (Stratum 1) or after salvage therapy for relapsed/refractory disease (Stratum 2). This Phase II single agent, single arm multicenter study enrolled from June 2012 to February 2016. Subjects received 2 years of oral DFMO (750 ± 250 mg/m² twice daily). Event free survival (EFS) and overall survival (OS) were determined on an intention-to-treat (ITT) basis. 101 subjects enrolled on Stratum 1 and 100 were eligible for ITT analysis; two-year EFS was 84% (±4%) and OS 97% (±2%). 39 subjects enrolled on Stratum 2, with a two-year EFS of 54% (±8%) and OS 84% (±6%). DFMO was well tolerated. The median survival time is not yet defined for either stratum. DFMO maintenance therapy for HRNB in remission is safe and associated with high EFS and OS. Targeting ODC represents a novel therapeutic mechanism that may provide a new strategy for preventing relapse in children with HRNB.

Genetic susceptibility to neuroblastoma: current knowledge and future directions

Neuroblastoma, a malignancy of the developing peripheral nervous system that affects infants and young children, is a complex genetic disease. Over the past two decades, significant progress has been made toward understanding the genetic determinants that predispose to this often lethal childhood cancer. Approximately 1-2% of neuroblastomas are inherited in an autosomal dominant fashion and a combination of co-morbidity and linkage studies has led to the identification of germline mutations in PHOX2B and ALK as the major genetic contributors to this familial neuroblastoma subset. The genetic basis of "sporadic" neuroblastoma is being studied through a large genome-wide association study (GWAS). These efforts have led to the discovery of many common susceptibility alleles, each with modest effect size, associated with the development and progression of sporadic neuroblastoma. More recently, next-generation sequencing efforts have expanded the list of potential neuroblastoma-predisposing mutations to include rare germline variants with a predicted larger effect size. The evolving characterization of neuroblastoma's genetic basis has led to a deeper understanding of the molecular events driving tumorigenesis, more precise risk stratification and prognostics and novel therapeutic strategies. This review details the contemporary understanding of neuroblastoma's genetic predisposition, including recent advances and discusses ongoing efforts to address gaps in our knowledge regarding this malignancy's complex genetic underpinnings.

Polyamine Deacetylase Structure and Catalysis: Prokaryotic Acetylpolyamine Amidohydrolase and Eukaryotic HDAC10

Polyamines such as putrescine, spermidine, and spermine are small aliphatic cations that serve myriad biological functions in all forms of life. While polyamine biosynthesis and cellular trafficking pathways are generally well-defined, only recently has the molecular basis of reversible polyamine acetylation been established. In particular, enzymes that catalyze polyamine deacetylation reactions have been identified and structurally characterized: histone deacetylase 10 (HDAC10) from Homo sapiens and Danio rerio (zebrafish) is a highly specific N⁸-acetylspermidine deacetylase, and its prokaryotic counterpart, acetylpolyamine amidohydrolase (APAH) from Mycoplana ramosa, is a broad-specificity polyamine deacetylase. Similar to the greater family of HDACs, which mainly serve as lysine deacetylases, both enzymes adopt the characteristic arginase-deacetylase fold and employ a Zn²⁺-activated water molecule for catalysis. In contrast with HDACs, however, the active sites of HDAC10 and APAH are sterically constricted to enforce specificity for long, slender polyamine substrates and exclude bulky peptides and proteins containing acetyl-l-lysine. Crystal structures of APAH and D. rerio HDAC10 reveal that quaternary structure, i.e., dimer assembly, provides the steric constriction that directs the polyamine substrate specificity of APAH, whereas tertiary structure, a unique 3₁₀ helix defined by the P(E,A)CE motif, provides the steric constriction that directs the polyamine substrate specificity of HDAC10. Given the recent identification of HDAC10 and spermidine as mediators of autophagy, HDAC10 is rapidly emerging as a biomarker and target for the design of isozyme-selective inhibitors that will suppress autophagic responses to cancer chemotherapy, thereby rendering cancer cells more susceptible to cytotoxic drugs.

Virtual screening of natural inhibitors targeting ornithine decarboxylase with pharmacophore scaffolding of DFMO and validation by molecular dynamics simulation studies

Ornithine decarboxylase (ODC) is an enzyme that initiates polyamine synthesis in human. Polyamines play key roles in cell-cell adhesion, cell motility and cell cycle regulation. Higher synthesis of polyamines also occurs in rapidly proliferating cancer cells are mediated by ODC. As per earlier studies, di-flouro-methyl-orninthine (DFMO) is a proven efficient inhibitor ODC targeting the catalytic activity, however, its usage is limited due to side effects. Targeting ODC is considered as a potential therapeutic modality in the treatment of cancer. In this study, it is attempted to use DFMO scaffold to build a ligand-based pharmocophore query using MOE to screen similar active compounds from Universal Natural Products Database with better ADMET properties. The identified compounds were virtually screened against the active cavity of ODC using Glide. Further, potential natural hits targeting ODC were shortlisted based on Molecular Mechanics/Generalized-Born/Surface Area (MM-GBSA) score. Finally, molecular dynamics simulations were performed for the natural molecule hit and DFMO in complex with ODC using Desmond. Among the hits shortlisted, 2-amino-5, 9, 13, 17-tetramethyloctadeca-8, 16-diene-1, 3, 14-triol (UNPD208110) was found to be highly potential, as it showed a higher binding affinity in terms of interactions with key active cavity residues, and also showed better ADMET property, HUMO-LUMO gap energy and more stable complex formation with ODC compared to DFMO. Hence, the proposed molecule (UNPD208110) shall be favourably considered as a potential natural inhibitor targeting ODC-mediated disease conditions.

Synergistic drug combination GC7/DFMO suppresses hypusine/spermidine-dependent eIF5A activation and induces apoptotic cell death in neuroblastoma

The eukaryotic initiation factor 5A (eIF5A), which contributes to several crucial processes during protein translation, is the only protein that requires activation by a unique post-translational hypusine modification. eIF5A hypusination controls cell proliferation and has been linked to cancer. eIF5A hypusination requires the enzymes deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase and uniquely depends on the polyamine (PA) spermidine as the sole substrate. Ornithine decarboxylase (ODC) is the rate-limiting enzyme in PA biosynthesis. Both ODC and PAs control cell proliferation and are frequently dysregulated in cancer. Since only spermidine can activate eIF5A, we chose the hypusine-PA nexus as a rational target to identify new drug combinations with synergistic antiproliferative effects. We show that elevated mRNA levels of the two target enzymes DHPS and ODC correlate with poor prognosis in a large cohort of neuroblastoma (NB) tumors. The DHPS inhibitor GC7 (N1-guanyl-1,7-diaminoheptane) and the ODC inhibitor α-difluoromethylornithine (DFMO) are target-specific and in combination induced synergistic effects in NB at concentrations that were not individually cytotoxic. Strikingly, while each drug alone at higher concentrations is known to induce p21/Rb- or p27/Rb-mediated G1 cell cycle arrest, we found that the drug combination induced caspase 3/7/9, but not caspase 8-mediated apoptosis, in NB cells. Hypusinated eIF5A levels and intracellular spermidine levels correlated directly with drug treatments, signifying specific drug targeting effects. This two-pronged GC7/DFMO combination approach specifically inhibits both spermidine biosynthesis and post-translational, spermidine-dependent hypusine-eIF5A activation, offering an exciting clue for improved NB drug therapy.

Insights on ornithine decarboxylase silencing as a potential strategy for targeting retinoblastoma

Ornithine Decarboxylase (ODC) is a key enzyme involved in polyamine synthesis and is reported to be up regulated in several cancers. However, the effect of ODC gene silencing in retinoblastoma is to be understood for utilization in therapeutic applications. Hence, in this study, a novel siRNA (small interference RNA) targeting ODC was designed and validated in Human Y79 retinoblastoma cells for its effects on intracellular polyamine levels, Matrix Metalloproteinase 2 & 9 activity and Cell cycle. The designed siRNA showed efficient silencing of ODC mRNA expression and protein levels in Y79 cells. It also showed significant reduction of intracellular polyamine levels and altered levels of oncogenic LIN28b expression. By this study, a regulatory loop is proposed, wherein, ODC silencing in Y79 cells to result in decreased polyamine levels, thereby, leading to altered protein levels of Lin28b, MMP-2 and MMP-9, which falls in line with earlier studies in neuroblastoma. Thus, by this study, we propose ODC silencing as a prospective strategy for targeting retinoblastoma.

MicroRNA-125b-5p mediates post-transcriptional regulation of hepatitis B virus replication via the LIN28B/let-7 axis

MicroRNAs (miRNAs) are able to modulate hepatitis B virus (HBV) replication and play an important role in the pathogenesis of HBV infection. Recently, we have identified that serum miR-125b-5p levels correlated with HBV DNA levels and liver necroinflammation. In the present study, we addressed how miR-125b-5p regulated HBV replication at the different steps, inclduing viral transcription, assembly, and virion production and investigated the underlying mechanisms. We found that miR-125b-5p overexpression increased HBV replication without altering HBV transcription. This is the first demonstration of post-transcriptional miRNA regulation of HBV replication. In contrast, transfection of miR-125b-5p inhibitor resulted in downregulation of HBV replication in hepatoma cells. Further, miR-125b-5p inhibited the phosphorylation of retinoblastoma protein and blocked cell cycle progression at the G1/S phase in hepatoma cell lines. Our results indicate that certain miRNAs are able to arrest the cell cycle at G1 phase and may increase HBV replication. RNA sequencing revealed several liver-specific metabolic pathways regulated by miR-125b-5p, which was also found to suppress LIN28B and induce let-7 family members. Additional data demonstrated that miR-125b-5p targeted the LIN28B/let-7 axis to stimulate HBV replication at a post-transcriptional step.

Difluoromethylornithine in cancer: new advances

Difluoromethylornithine (DFMO; eflornithine) is an irreversible suicide inhibitor of the enzyme ornithine decarboxylase which is involved in polyamine synthesis. Polyamines are important for cell survival, thus DFMO was studied as an anticancer agent and as a chemoprevention agent. DFMO exhibited mainly cytostatic activity and had single agent efficacy as well as activity in combination with other chemotherapeutic drugs for some cancers and leukemias. Herewith, we summarize the current knowledge of the anticancer and chemopreventive properties of DFMO and assess the status of clinical trials.

Ornithine and its role in metabolic diseases: An appraisal

Ornithine is a non-essential amino acid produced as an intermediate molecule in urea cycle. It is a key substrate for the synthesis of proline, polyamines and citrulline. Ornithine also plays an important role in the regulation of several metabolic processes leading to diseases like hyperorithinemia, hyperammonemia, gyrate atrophy and cancer in humans. However, the mechanism of action behind the multi-faceted roles of ornithine is yet to be unraveled completely. Several types of cancers are also characterized by excessive polyamine synthesis from ornithine by different rate limiting enzymes. Hence, in this review we aim to provide extensive insights on potential roles of ornithine in many of the disease related cellular processes and also on the structural features of ornithine interacting proteins, enabling development of therapeutic modalities.