Simple, fast and efficient iTOP-mediated delivery of CRISPR/Cas9 RNP in difficult-to-transduce human cells including primary T cells

The advent of the CRISPR/Cas9 system has transformed the field of human genome engineering and has created new perspectives in the development of innovative cell therapies. However, the absence of a simple, fast and efficient delivery method of CRISPR/Cas9 into primary human cells has been limiting the progress of CRISPR/Cas9-based therapies. Here, we describe an optimized protocol for iTOP-mediated delivery of CRISPR/Cas9 in various human cells, including primary T cells, induced pluripotent stem cells (hiPSCs), Jurkat, ARPE-19 and HEK293 cells. We compare iTOP to other CRISPR/Cas9 delivery methods, such as electroporation and lipofection, and evaluate the corresponding gene-editing efficiencies and post-treatment cell viabilities. We demonstrate that the gene editing achieved by iTOP-mediated delivery of CRISPR/Cas9 is 40-95 % depending on the cell type, while post-iTOP cell viability remains high in the range of 70-95 %. Collectively, we present an optimized workflow for a simple, high-throughput and effective iTOP-mediated delivery of CRISPR/Cas9 to engineer difficult-to-transduce human cells. We believe that the iTOP technology® could contribute to the development of novel CRISPR/Cas9-based cell therapies.

International Consensus on Minimum Preclinical Testing Requirements for the Development of Innovative Therapies For Children and Adolescents with Cancer

Cancer remains the leading cause of disease-related death in children. For the many children who experience relapses of their malignant solid tumors, usually after very intensive first-line therapy, curative treatment options are scarce. Preclinical drug testing to identify promising treatment elements that match the molecular make-up of the tumor is hampered by the fact that (i) molecular genetic data on pediatric solid tumors from relapsed patients and thus our understanding of tumor evolution and therapy resistance are very limited to date and (ii) for many of the high-risk entities, no appropriate and molecularly well-characterized patient-derived models and/or genetic mouse models are currently available. However, recent regulatory changes enacted by the European Medicines Agency (class waiver changes) and the maturation of the RACE for Children act with the FDA, will require a significant increase in preclinical pediatric cancer research and clinical development must occur. We detail the outcome of a pediatric cancer international multistakeholder meeting whose output aims at defining an international consensus on minimum preclinical testing requirements for the development of innovative therapies for children and adolescents with cancer. Recommendations based on the experience of the NCI funded PPTP/C (www.ncipptc.org) and the EU funded ITCC-P4 public private partnership (www.itccp4.eu) are provided for the use of cell-based and mouse models for pediatric solid malignancies, as well as guidance on the scope and content of preclinical proof-of-concept data packages to inform clinical development dependent on clinical urgency. These recommendations can serve as a minimal guidance necessary to jumpstart preclinical pediatric research globally.

G-CSF as a suitable alternative to GM-CSF to boost dinutuximab-mediated neutrophil cytotoxicity in neuroblastoma treatment

BACKGROUND

Current immunotherapy for patients with high-risk neuroblastoma involves the therapeutic antibody dinutuximab that targets GD2, a ganglioside expressed on the majority of neuroblastoma tumors. Opsonized tumor cells are killed through antibody-dependent cellular cytotoxicity (ADCC), a process mediated by various immune cells, including neutrophils. The capacity of neutrophils to kill dinutuximab-opsonized tumor cells can be further enhanced by granulocyte-macrophage colony-stimulating factor (GM-CSF), which has been shown in the past to improve responses to anti-GD2 immunotherapy. However, access to GM-CSF (sargramostim) is limited outside of Northern America, creating a high clinical need for an alternative method to stimulate dinutuximab responsiveness in the treatment of neuroblastoma. In this in vitro study, we have investigated whether clinically well-established granulocyte colony-stimulating factor (G-CSF) can be a potentially suitable alternative for GM-CSF in the dinutuximab immunotherapy regimen of patients with neuroblastoma.

METHODS

We compared the capacity of neutrophils stimulated either in vitro or in vivo with GM-CSF or G-CSF to kill dinutuximab-opsonized GD2-positive neuroblastoma cell lines and primary patient tumor material. Blocking experiments with antibodies inhibiting either respective Fc gamma receptors (FcγR) or neutrophil integrin CD11b/CD18 demonstrated the involvement of these receptors in the process of ADCC. Flow cytometry and live cell microscopy were used to quantify and visualize neutrophil-neuroblastoma interactions.

RESULTS

We found that G-CSF was as potent as GM-CSF in enhancing the killing capacity of neutrophils towards neuroblastoma cells. This was observed with in vitro stimulated neutrophils, and with in vivo stimulated neutrophils from both patients with neuroblastoma and healthy donors. Enhanced killing due to GM-CSF or G-CSF stimulation was consistent regardless of dinutuximab concentration, tumor-to-neutrophil ratio and concentration of the stimulating cytokine. Both GM-CSF and G-CSF stimulated neutrophils required FcγRIIa and CD11b/CD18 integrin to perform ADCC, and this was accompanied by trogocytosis of tumor material by neutrophils and tumor cell death in both stimulation conditions.

CONCLUSIONS

Our preclinical data support the use of G-CSF as an alternative stimulating cytokine to GM-CSF in the treatment of high-risk neuroblastoma with dinutuximab, warranting further testing of G-CSF in a clinical setting.

High-Throughput Screening Identifies Idasanutlin as a Resensitizing Drug for Venetoclax-Resistant Neuroblastoma Cells

Neuroblastoma tumors frequently overexpress the anti-apoptotic protein B-cell lymphoma/leukemia 2 (BCL-2). We previously showed that treating BCL-2-dependent neuroblastoma cells with the BCL-2 inhibitor venetoclax results in apoptosis, but unfortunately partial therapy resistance is observed. The current study describes the identification of drugs capable of resensitizing venetoclax-resistant neuroblastoma cells to venetoclax. To examine these effects, venetoclax resistance was induced in BCL-2-dependent neuroblastoma cell lines KCNR and SJNB12 by continuous exposure to high venetoclax concentrations. Non-resistant and venetoclax-resistant neuroblastoma cell lines were exposed to a 209-compound library in the absence and presence of venetoclax to identify compounds that were more effective in the venetoclax-resistant cell lines under venetoclax pressure. Top hits were further validated in combination with venetoclax using BCL-2-dependent neuroblastoma model systems. Overall, high-throughput drug screening identified the MDM2 inhibitor idasanutlin as a promising resensitizing agent for venetoclax-resistant neuroblastoma cell lines. Idasanutlin treatment induced BAX-mediated apoptosis in venetoclax-resistant neuroblastoma cells in the presence of venetoclax, whereas it caused p21-mediated growth arrest in control cells. In vivo combination treatment showed tumor regression and superior efficacy over single-agent therapies in a BCL-2-dependent neuroblastoma cell line xenograft and a patient-derived xenograft. However, xenografts less dependent on BCL-2 were not sensitive to venetoclax-idasanutlin combination therapy. This study demonstrates that idasanutlin can overcome resistance to the BCL-2 inhibitor venetoclax in preclinical neuroblastoma model systems, which supports clinical development of a treatment strategy combining the two therapies.

High-throughput drug screening reveals Pyrvinium pamoate as effective candidate against pediatric MLL-rearranged acute myeloid leukemia

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Drug library screening identified pyrvinium to be effective against MLL-rearranged AML.

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Pyrvinium targets the mitochondria of MLL-rearranged AML cells.

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Pyrvinium does not antagonize with standard chemotherapy in MLL-rearranged AML.

Pediatric MLL-rearranged acute myeloid leukemia (AML) has a generally unfavorable outcome, primarily due to relapse and drug resistance. To overcome these difficulties, new therapeutic agents are urgently needed. Yet, implementing novel drugs for clinical use is a time-consuming, laborious, costly and high-risk process. Therefore, we applied a drug-repositioning strategy by screening drug libraries, comprised of >4000 compounds that are mostly FDA-approved, in a high-throughput format on primary MLL-rearranged AML cells. Here we identified pyrvinium pamoate (pyrvinium) as a novel candidate drug effective against MLL-rearranged AML, eliminating all cell viability at <1000 nM. Additional screening of identified drug hits on non-leukemic bone marrow samples, resulted in a decrease in cell viability of ∼50% at 1000 nM pyrvinium, suggesting a therapeutic window for targeting leukemic cells specifically. Validation of pyrvinium on an extensive panel of AML cell lines and primary AML samples showed comparable viabilities as the drug screen data, with pyrvinium achieving IC₅₀ values of <80 nM in these samples. Remarkably, pyrvinium also induced cell toxicity in primary MLL-AF10⁺ AML cells, an MLL-rearrangement associated with a poor outcome. While pyrvinium is able to inhibit the Wnt pathway in other diseases, this unlikely explains the efficacy we observed as β-catenin was not expressed in the AML cells tested. Rather, we show that pyrvinium co-localized with the mitochondrial stain in cells, and hence may act by inhibiting mitochondrial respiration. Overall, this study shows that pyrvinium is highly effective against MLL-rearranged AML in vitro, and therefore represents a novel potential candidate for further studies in MLL-rearranged AML.

Tumor to normal single-cell mRNA comparisons reveal a pan-neuroblastoma cancer cell

Neuroblastoma is a childhood cancer that resembles developmental stages of the neural crest. It is not established what developmental processes neuroblastoma cancer cells represent. Here, we sought to reveal the phenotype of neuroblastoma cancer cells by comparing cancer (n = 19,723) with normal fetal adrenal single-cell transcriptomes (n = 57,972). Our principal finding was that the neuroblastoma cancer cell resembled fetal sympathoblasts, but no other fetal adrenal cell type. The sympathoblastic state was a universal feature of neuroblastoma cells, transcending cell cluster diversity, individual patients, and clinical phenotypes. We substantiated our findings in 650 neuroblastoma bulk transcriptomes and by integrating canonical features of the neuroblastoma genome with transcriptional signals. Overall, our observations indicate that a pan-neuroblastoma cancer cell state exists, which may be attractive for novel immunotherapeutic and targeted avenues.

The immune landscape of neuroblastoma: Challenges and opportunities for novel therapeutic strategies in pediatric oncology

Immunotherapy holds great promise for the treatment of pediatric cancers. In neuroblastoma, the recent implementation of anti-GD2 antibody Dinutuximab into the standard of care has improved patient outcomes substantially. However, 5-year survival rates are still below 50% in patients with high-risk neuroblastoma, which has sparked investigations into novel immunotherapeutic approaches. T cell-engaging therapies such as immune checkpoint blockade, antibody-mediated therapy and adoptive T cell therapy have proven remarkably successful in a range of adult cancers but still meet challenges in pediatric oncology. In neuroblastoma, their limited success may be due to several factors. Neuroblastoma displays low immunogenicity due to its low mutational load and lack of MHC-I expression. Tumour infiltration by T and NK cells is especially low in high-risk neuroblastoma and is prognostic for survival. Only a small fraction of tumour-infiltrating lymphocytes shows tumour reactivity. Moreover, neuroblastoma tumours employ a variety of immune evasion strategies, including expression of immune checkpoint molecules, induction of immunosuppressive myeloid and stromal cells, as well as secretion of immunoregulatory mediators, which reduce infiltration and reactivity of immune cells. Overcoming these challenges will be key to the successful implementation of novel immunotherapeutic interventions. Combining different immunotherapies, as well as personalised strategies, may be promising approaches. We will discuss the composition, function and prognostic value of tumour-infiltrating lymphocytes (TIL) in neuroblastoma, reflect on challenges for immunotherapy, including a lack of TIL reactivity and tumour immune evasion strategies, and highlight opportunities for immunotherapy and future perspectives with regard to state-of-the-art developments in the tumour immunology space.

Combined targeting of the p53 and pRb pathway in neuroblastoma does not lead to synergistic responses

BACKGROUND

Despite intensive treatment protocols and recent advances, neuroblastomas still account for approximately 15% of all childhood cancer deaths. In contrast with adult cancers, p53 pathway inactivation in neuroblastomas is rarely caused by p53 mutation but rather by altered MDM2 or p14ARF expression. Moreover, neuroblastomas are characterised by high proliferation rates, frequently triggered by pRb pathway dysfunction due to aberrant expression of cyclin D1, CDK4 or p16INK4a. Simultaneous disturbance of these pathways can occur via co-amplification of MDM2 and CDK4 or homozygous deletion of CDKN2A, which encodes both p14ARF and p16INK4a.

METHODS AND RESULTS

We examined whether both single and combined inhibition of MDM2 and CDK4/6 is effective in reducing neuroblastoma cell viability. In our panel of ten cell lines with a spectrum of aberrations in the p53 and pRb pathway, idasanutlin and abemaciclib were the most potent MDM2 and CDK4/6 inhibitors, respectively. No correlation was observed between the genetic background and response to the single inhibitors. We confirmed this lack of correlation in isogenic systems overexpressing MDM2 and/or CDK4. In addition, combined inhibition did not result in synergistic effects. Instead, abemaciclib diminished the pro-apoptotic effect of idasanutlin, leading to slightly antagonistic effects. In vivo treatment with idasanutlin and abemaciclib led to reduced tumour growth compared with single drug treatment, but no synergistic response was observed.

CONCLUSION

We conclude that p53 and pRb pathway aberrations cannot be used as predictive biomarkers for neuroblastoma sensitivity to MDM2 and/or CDK4/6 inhibitors. Moreover, we advise to be cautious with combining these inhibitors in neuroblastomas.

Decitabine mildly attenuates MLL-rearranged acute lymphoblastic leukemia in vivo, and represents a poor chemo-sensitizer

MLL-rearranged acute lymphoblastic leukemia (ALL) represents a highly aggressive ALL subtype, characterized by aberrant DNA methylation patterns. DNA methyltransferase inhibitors, such as decitabine have previously been demonstrated to be effective in eradicating MLL-rearranged ALL cells in vitro. Here, we assessed the in vivo anti-leukemic potential of low-dose DNA methyltransferase inhibitor decitabine using a xenograft mouse model of human MLL-rearranged ALL. Furthermore, we explored whether prolonged exposure to low-dose decitabine could chemo-sensitize MLL-rearranged ALL cells toward conventional chemotherapy as well as other known epigenetic-based and anti-neoplastic compounds. Our data reveal that decitabine prolonged survival in xenograft mice of MLL-rearranged ALL by 8.5 days (P = .0181), but eventually was insufficient to prevent leukemia out-growth, based on the examination of the MLLAF4 cell line SEM. Furthermore, we observe that prolonged pretreatment of low-dose decitabine mildly sensitized toward the conventional drugs prednisolone, vincristine, daunorubicin, asparaginase, and cytarabine in a panel of MLL-rearranged cell lines. Additionally, we assessed synergistic effects of decitabine with other epigenetic-based or anticancer drugs using high-throughput drug library screens. Validation of the top hits, including histone deacetylase inhibitor panobinostat, BCL2 inhibitor Venetoclax, MEK inhibitor pimasertib, and receptor tyrosine kinase foretinib, revealed additive and moderate synergistic effects for the combination of each drug together with decitabine in a cell line-dependent manner.

Therapeutic vulnerabilities in the DNA damage response for the treatment of ATRX mutant neuroblastoma

BACKGROUND

In neuroblastoma, genetic alterations in ATRX, define a distinct poor outcome patient subgroup. Despite the need for new therapies, there is a lack of available models and a dearth of pre-clinical research.

METHODS

To evaluate the impact of ATRX loss of function (LoF) in neuroblastoma, we utilized CRISPR-Cas9 gene editing to generate neuroblastoma cell lines isogenic for ATRX. We used these and other models to identify therapeutically exploitable synthetic lethal vulnerabilities associated with ATRX LoF.

FINDINGS

In isogenic cell lines, we found that ATRX inactivation results in increased DNA damage, homologous recombination repair (HRR) defects and impaired replication fork processivity. In keeping with this, high-throughput compound screening showed selective sensitivity in ATRX mutant cells to multiple PARP inhibitors and the ATM inhibitor KU60019. ATRX mutant cells also showed selective sensitivity to the DNA damaging agents, sapacitabine and irinotecan. HRR deficiency was also seen in the ATRX deleted CHLA-90 cell line, and significant sensitivity demonstrated to olaparib/irinotecan combination therapy in all ATRX LoF models. In-vivo sensitivity to olaparib/irinotecan was seen in ATRX mutant but not wild-type xenografts. Finally, sustained responses to olaparib/irinotecan therapy were seen in an ATRX deleted neuroblastoma patient derived xenograft.

INTERPRETATION

ATRX LoF results in specific DNA damage repair defects that can be therapeutically exploited. In ATRX LoF models, preclinical sensitivity is demonstrated to olaparib and irinotecan, a combination that can be rapidly translated into the clinic.

FUNDING

This work was supported by Christopher's Smile, Neuroblastoma UK, Cancer Research UK, and the Royal Marsden Hospital NIHR BRC.

Neuroblastoma stage 4S: Tumor regression rate and risk factors of progressive disease

BACKGROUND

The clinical course of neuroblastoma stage 4S or MS is characterized by a high rate of spontaneous tumor regression and favorable outcome. However, the clinical course and rate of the regression are poorly understood.

METHODS

A retrospective cohort study was performed, including all patients with stage 4S neuroblastoma without MYCN amplification, from two Dutch centers between 1972 and 2012. We investigated the clinical characteristics, the biochemical activity reflected in urinary catecholamine excretion, and radiological imaging to describe the kinetics of tumor regression, therapy response and outcome.

RESULTS

The cohort of 31 patients reached a 10-year overall survival of 84% ± 7% (median follow-up 16 years; range, 3.3-39). During the regressive phase, liver size normalized in 91% of the patients and catecholamine excretion in 83%, both after a median of two months (liver size: range, 0-131; catecholamines: range, 0-158). The primary tumors completely regressed in 69% after 13 months (range, 6-73), and the liver architecture normalized in 52% after 15 months (range, 5-131). Antitumor treatment was given in 52% of the patients. Interestingly, regression rates were similar for treated and untreated patients. Four of seven patients < 4 weeks old died of rapid liver expansion and organ compression. Three patients progressed to stage 4, 3 to 13 months after diagnosis; all had persistently elevated catecholamines.

CONCLUSION

Patients < 4 weeks old with neuroblastoma stage 4S are at risk of fatal outcome caused by progression of liver metastases. In other patients, tumor regression is characterized by a rapid biochemical normalization that precedes radiological regression.

Systematic target actionability reviews of preclinical proof-of-concept papers to match targeted drugs to paediatric cancers

Background

Children with cancer are in urgent need of new therapies, as approximately 25% of patients experience a relapse and 20% succumb to their disease. Moreover, the majority of survivors suffer from clinically relevant health problems. Repurposing of targeted agents developed for adult indications could provide novel therapeutic options for paediatric cancer patients. To prioritise targeted drugs for paediatric clinical development, we applied a systematic review methodology to develop a Target Actionability Review (TAR) strategy. These TARs assess the strength and completeness of published preclinical proof-of-concept (PoC) data by structured critical appraisal of and summarising the available scientific literature for a specific target (pathway) and the associated drugs in paediatric tumours.

Methods

A sensitive literature search in PubMed was performed and relevant papers were identified. For each paper, the individual experimental findings were extracted, marked for paediatric tumour type and categorised into nine separate PoC data modules. Each experimental finding was scored for experimental outcome and quality independently by two reviewers; discrepancies were assessed by a third reviewer and resolved by adjudication. Scores corresponding to one PoC module were merged for each tumour type and visualised in a heat map matrix in the publicly available R2 data portal [r2.amc.nl].

Results and conclusions

To test our TAR methodology, we conducted a pilot study on MDM2 and TP53. The heat map generated from analysis of 161 publications provides a rationale to support drug development in specific paediatric solid and brain tumour types. Furthermore, our review highlights tumour types where preclinical data are incomplete or lacking and for which additional preclinical testing is advisable.

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A new strategy to review literature on targeted compounds in paediatric cancer.

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Results help to guide and prioritise clinical development of novel targeted agents.

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Outcomes are visualised in a publicly available, interactive heat map.

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We applied this unique methodology to MDM2 and TP53 and MDM2 inhibitors.

An organoid biobank for childhood kidney cancers that captures disease and tissue heterogeneity

Kidney tumours are among the most common solid tumours in children, comprising distinct subtypes differing in many aspects, including cell-of-origin, genetics, and pathology. Pre-clinical cell models capturing the disease heterogeneity are currently lacking. Here, we describe the first paediatric cancer organoid biobank. It contains tumour and matching normal kidney organoids from over 50 children with different subtypes of kidney cancer, including Wilms tumours, malignant rhabdoid tumours, renal cell carcinomas, and congenital mesoblastic nephromas. Paediatric kidney tumour organoids retain key properties of native tumours, useful for revealing patient-specific drug sensitivities. Using single cell RNA-sequencing and high resolution 3D imaging, we further demonstrate that organoid cultures derived from Wilms tumours consist of multiple different cell types, including epithelial, stromal and blastemal-like cells. Our organoid biobank captures the heterogeneity of paediatric kidney tumours, providing a representative collection of well-characterised models for basic cancer research, drug-screening and personalised medicine.

Pre-clinical cell culture models capturing the heterogeneity of childhood kidney tumours are limited. Here, the authors establish and characterise an organoid biobank of tumour and matched normal organoid cultures from over 50 children with different subtypes of kidney cancer.

Mesenchymal Neuroblastoma Cells Are Undetected by Current mRNA Marker Panels: The Development of a Specific Neuroblastoma Mesenchymal Minimal Residual Disease Panel

Patients with neuroblastoma in molecular remission remain at considerable risk for disease recurrence. Studies have found that neuroblastoma tissue contains adrenergic (ADRN) and mesenchymal (MES) cells; the latter express low levels of commonly used markers for minimal residual disease (MRD). We identified MES-specific MRD markers and studied the dynamics of these markers during treatment.

PATIENTS AND METHODS

Microarray data were used to identify genes differentially expressed between ADRN and MES cell lines. Candidate genes were then studied using real-time quantitative polymerase chain reaction in cell lines and control bone marrow and peripheral blood samples. After selecting a panel of markers, serial bone marrow, peripheral blood, and peripheral blood stem cell samples were obtained from patients with high-risk neuroblastoma and tested for marker expression; survival analyses were also performed.

RESULTS

PRRX1, POSTN, and FMO3 mRNAs were used as a panel for specifically detecting MES mRNA in patient samples. MES mRNA was detected only rarely in peripheral blood; moreover, the presence of MES mRNA in peripheral blood stem cell samples was associated with low event-free survival and overall survival. Of note, during treatment, serial bone marrow samples obtained from 29 patients revealed a difference in dynamics between MES mRNA markers and ADRN mRNA markers. Furthermore, MES mRNA was detected in a higher percentage of patients with recurrent disease than in those who remained disease free (53% v 32%, respectively; P = .03).

CONCLUSION

We propose that the markers POSTN and PRRX1, in combination with FMO3, be used for real-time quantitative polymerase chain reaction-based detection of MES neuroblastoma mRNA in patient samples because these markers have a unique pattern during treatment and are more prevalent in patients with poor outcome. Together with existing markers of MRD, these new markers should be investigated further in large prospective studies.

Molecular characteristics and therapeutic vulnerabilities across paediatric solid tumours

The spectrum of tumours arising in childhood is fundamentally different from that seen in adults, and they are known to be divergent from adult malignancies in terms of cellular origins, epidemiology, genetic complexity, driver mutations and underlying mutational processes. Despite the immense knowledge generated through sequencing efforts and functional characterization of identified (epi-)genetic alterations over the past decade, the clinical implications of this knowledge have so far been limited. Novel preclinical platforms such as the European Innovative Therapies for Children with Cancer-Paediatric Preclinical Proof-of-Concept Platform and the US-based Pediatric Preclinical Testing Consortium are being developed to try to change this by aiming to recapitulate the extensive heterogeneity of paediatric tumours and thereby, hopefully, improve the ability to predict clinical benefit. Numerous studies have also been established worldwide to provide patients with access to real-time molecular profiling and the possibility of more precise mechanism-of-action-based treatments. In addition to tumour-intrinsic findings and mechanisms, ongoing studies are investigating features such as the immune microenvironment of paediatric tumours in comparison with adult cancers - currently of very timely clinical relevance. However, there is an ongoing need for rigorous preclinical biomarker and target validation to feed into the next generation of molecularly stratified clinical trials. This Review aims to provide a comprehensive state-of-the-art overview of the molecular landscape of paediatric solid tumours, including their underlying genomic alterations and interactions with the microenvironment, complemented with our current understanding of potential therapeutic vulnerabilities and how these can be preclinically tested using more accurate predictive methods. Finally, we provide an outlook on the challenges and opportunities associated with translating this overwhelming scientific progress into real clinical benefit.

RAS-MAPK Pathway-Driven Tumor Progression Is Associated with Loss of CIC and Other Genomic Aberrations in Neuroblastoma

Mutations affecting the RAS-MAPK pathway frequently occur in relapsed neuroblastoma tumors, which suggests that activation of this pathway is associated with a more aggressive phenotype. To explore this hypothesis, we generated several model systems to define a neuroblastoma RAS-MAPK pathway signature. Activation of this pathway in primary tumors indeed correlated with poor survival and was associated with known activating mutations in ALK and other RAS-MAPK pathway genes. Integrative analysis showed that mutations in PHOX2B, CIC, and DMD were also associated with an activated RAS-MAPK pathway. Mutation of PHOX2B and deletion of CIC in neuroblastoma cell lines induced activation of the RAS-MAPK pathway. This activation was independent of phosphorylated ERK in CIC knockout systems. Furthermore, deletion of CIC caused a significant increase in tumor growth in vivo These results show that the RAS-MAPK pathway is involved in tumor progression and establish CIC as a powerful tumor suppressor that functions downstream of this pathway in neuroblastoma.Significance: This work identifies CIC as a powerful tumor suppressor affecting the RAS-MAPK pathway in neuroblastoma and reinforces the importance of mutation-driven activation of this pathway in cancer. Cancer Res; 78(21); 6297-307. ©2018 AACR.

Abstract 2630: Preclinical identification of Venetoclax combination strategies with Idasanutlin, CUDC-907, Prexasertib or Talazoparib for neuroblastoma treatment

BACKGROUND: The anti-apoptotic protein B cell lymphoma/leukaemia 2 (BCL-2) is highly expressed in the majority of all neuroblastomas. In previous preclinical studies, we have shown that treatment of BCL-2-dependent neuroblastoma with BCL-2 inhibitors leads to programmed cell death. These results have contributed to the initiation of a phase I trial to study the safety and pharmacokinetics of Venetoclax in children with relapsed or refractory neuroblastoma.

AIM: The current study aims to identify and validate targeted combination strategies to prevent or overcome neuroblastoma resistance to Venetoclax.

METHODS: Targeted drug candidates for combination treatment with Venetoclax were identified by high-throughput drug screening of non-resistant and Venetoclax-resistant BCL-2-dependent neuroblastoma cell lines. Top hits were subsequently tested more extensively in vitro and in vivo to validate the screening results.

RESULTS: High-throughput drug screens identified the MDM2 inhibitor Idasanutlin as one of the strongest re-sensitizers for Venetoclax in Venetoclax-resistant BCL-2-dependent neuroblastoma cells with wild-type p53. Subsequent in vitro validation showed that Idasanutlin induced cyclin dependent kinase inhibitor 1 (p21)-mediated growth arrest in non-resistant neuroblastoma cells, but induced a BCL-2-associated X protein (BAX)-mediated apoptotic response in Venetoclax-resistant neuroblastoma cells in the presence of Venetoclax. In vivo combination of Venetoclax with Idasanultin resulted in a remarkably improved anticancer effect compared to single agent therapy, with very good partial and complete responses in BCL-2-dependent neuroblastoma xenografts. Combination screens additionally revealed that the clinically studied targeted inhibitors CUDC-907 (PI3K/HDAC), Prexasertib (CHK1) and Talazoparib (PARP1/2) improved the efficacy of Venetoclax more potently than ALK inhibitors in BCL-2-dependent neuroblastoma cells harboring ALK mutations.

CONCLUSION: Our findings suggest that the clinical use of Venetoclax for the treatment of children with BCL-2-dependent neuroblastoma tumors can be improved by combination therapy with targeted inhibitors. The presence of additional neuroblastoma driving genomic events is not always predictive of the optimal combination strategy for BCL-2-dependent neuroblastoma subgroups. These findings should guide the design of combination Phase 2 trials of Venetoclax with other targeted compounds such as Idasanutlin, CUDC-907, Prexasertib and Talazoparib.

Citation Format: M. Emmy M. Dolman, Laurel T. Bate-Eya, Lindy Vernooij, Bianca Koopmans, Lindy K. Alles, Anke H. Essing, Daphne Lelieveld, David A. Egan, Mark Kerstjens, Ronald W. Stam, Huib N. Caron, Jan J. Molenaar. Preclinical identification of Venetoclax combination strategies with Idasanutlin, CUDC-907, Prexasertib or Talazoparib for neuroblastoma treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2630.

γ-Secretase inhibitor I inhibits neuroblastoma cells, with NOTCH and the proteasome among its targets

As high-risk neuroblastoma (NB) has a poor prognosis, new therapeutic modalities are needed. We therefore investigated the susceptibility of NB cells to γ-secretase inhibitor I (GSI-I). NOTCH signaling activity, the cellular effects of GSI-I and its mechanisms of cytotoxicity were evaluated in NB cells in vitro and in vivo. The results show that NOTCH signaling is relevant for human NB cells. Of the GSIs screened in vitro GSI-I was the most effective inhibitor of NB cells. Both MYCN-amplified and non-amplified NB cells were susceptible to GSI-I. Among the targets of GSI-I in NB cells were NOTCH and the proteasome. GSI-I caused G2/M arrest that was enhanced by acute activation of MYCN and led to mitotic dysfunction. GSI-I also induced proapoptotic NOXA. Survival of mice bearing an MYCN non-amplified orthotopic patient-derived NB xenograft was significantly prolonged by systemic GSI-I, associated with mitotic catastrophe and reduced angiogenesis, and without evidence of intestinal toxicity. In conclusion, the activity of GSI-I on multiple targets in NB cells and the lack of gastrointestinal toxicity in mice are advantageous and merit further investigations of GSI-I in NB.

Retinoblastoma and Neuroblastoma Predisposition and Surveillance

Retinoblastoma (RB) is the most common intraocular malignancy in childhood. Approximately 40% of retinoblastomas are hereditary and due to germline mutations in the RB1 gene. Children with hereditary RB are also at risk for developing a midline intracranial tumor, most commonly pineoblastoma. We recommend intensive ocular screening for patients with germline RB1 mutations for retinoblastoma as well as neuroimaging for pineoblastoma surveillance. There is an approximately 20% risk of developing second primary cancers among individuals with hereditary RB, higher among those who received radiotherapy for their primary RB tumors. However, there is not yet a clear consensus on what, if any, screening protocol would be most appropriate and effective. Neuroblastoma (NB), an embryonal tumor of the sympathetic nervous system, accounts for 15% of pediatric cancer deaths. Prior studies suggest that about 2% of patients with NB have an underlying genetic predisposition that may have contributed to the development of NB. Germline mutations in ALK and PHOX2B account for most familial NB cases. However, other cancer predisposition syndromes, such as Li-Fraumeni syndrome, RASopathies, and others, may be associated with an increased risk for NB. No established protocols for NB surveillance currently exist. Here, we describe consensus recommendations on hereditary RB and NB from the AACR Childhood Cancer Predisposition Workshop. Clin Cancer Res; 23(13); e98-e106. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Cancer Surveillance in Gorlin Syndrome and Rhabdoid Tumor Predisposition Syndrome

Gorlin syndrome and rhabdoid tumor predisposition syndrome (RTPS) are autosomal dominant syndromes associated with an increased risk of childhood-onset brain tumors. Individuals with Gorlin syndrome can manifest a wide range of phenotypic abnormalities, with about 5% of family members developing medulloblastoma, usually occurring in the first 3 years of life. Gorlin syndrome is associated with germline mutations in components of the Sonic Hedgehog pathway, including Patched1 (PTCH1) and Suppressor of fused (SUFU)SUFU mutation carriers appear to have an especially high risk of early-onset medulloblastoma. Surveillance MRI in the first years of life in SUFU mutation carriers is, therefore, recommended. Given the risk of basal cell carcinomas, regular dermatologic examinations and sun protection are also recommended. Rhabdoid tumors (RT) are tumors initially defined by the descriptive "rhabdoid" term, implying a phenotypic similarity with rhabdomyoblasts at the microscopic level. RTs usually present before the age of 3 and can arise within the cranium as atypical teratoid/rhabdoid tumors or extracranially, especially in the kidney, as malignant rhabdoid tumors. However, RTs of both types share germline and somatic mutations in SMARCB1 or, more rarely, SMARCA4, each of which encodes a chromatin remodeling family member. SMARCA4 mutations are particularly associated with small cell carcinoma of the ovary, hypercalcemic type (SCCOHT). The outcome following a diagnosis of any of these tumors is often poor, and the value of surveillance is unknown. International efforts to determine surveillance protocols are underway, and preliminary recommendations are made for carriers of SMARCB1 and SMARCA4 mutations. Clin Cancer Res; 23(12); e62-e67. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

High efficacy of the BCL-2 inhibitor ABT199 (venetoclax) in BCL-2 high-expressing neuroblastoma cell lines and xenografts and rational for combination with MCL-1 inhibition

The anti-apoptotic protein B cell lymphoma/leukaemia 2 (BCL-2) is highly expressed in neuroblastoma and plays an important role in oncogenesis. In this study, the selective BCL-2 inhibitor ABT199 was tested in a panel of neuroblastoma cell lines with diverse expression levels of BCL-2 and other BCL-2 family proteins. ABT199 caused apoptosis more potently in neuroblastoma cell lines expressing high BCL-2 and BIM/BCL-2 complex levels than low expressing cell lines. Effects on cell viability correlated with effects on BIM displacement from BCL-2 and cytochrome c release from the mitochondria. ABT199 treatment of mice with neuroblastoma tumors expressing high BCL-2 levels only resulted in growth inhibition, despite maximum BIM displacement from BCL-2 and the induction of a strong apoptotic response. We showed that neuroblastoma cells might survive ABT199 treatment due to its acute upregulation of the anti-apoptotic BCL-2 family protein myeloid cell leukaemia sequence 1 (MCL-1) and BIM sequestration by MCL-1. In vitro inhibition of MCL-1 sensitized neuroblastoma cell lines to ABT199, confirming the pivotal role of MCL-1 in ABT199 resistance. Our findings suggest that neuroblastoma patients with high BCL-2 and BIM/BCL-2 complex levels might benefit from combination treatment with ABT199 and compounds that inhibit MCL-1 expression.

p53 Nongenotoxic Activation and mTORC1 Inhibition Lead to Effective Combination for Neuroblastoma Therapy

Purpose: mTORC1 inhibitors are promising agents for neuroblastoma therapy; however, they have shown limited clinical activity as monotherapy, thus rational drug combinations need to be explored to improve efficacy. Importantly, neuroblastoma maintains both an active p53 and an aberrant mTOR signaling.Experimental Design: Using an orthotopic xenograft model and modulating p53 levels, we investigated the antitumor effects of the mTORC1 inhibitor temsirolimus in neuroblastoma expressing normal, decreased, or mutant p53, both as single agent and in combination with first- and second-generation MDM2 inhibitors to reactivate p53.Results: Nongenotoxic p53 activation suppresses mTOR activity. Moreover, p53 reactivation via RG7388, a second-generation MDM2 inhibitor, strongly enhances the in vivo antitumor activity of temsirolimus. Single-agent temsirolimus does not elicit apoptosis, and tumors rapidly regrow after treatment suspension. In contrast, our combination therapy triggers a potent apoptotic response in wild-type p53 xenografts and efficiently blocks tumor regrowth after treatment completion. We also found that this combination uniquely led to p53-dependent suppression of survivin whose ectopic expression is sufficient to rescue the apoptosis induced by our combination.Conclusions: Our study supports a novel highly effective strategy that combines RG7388 and temsirolimus in wild-type p53 neuroblastoma, which warrants testing in early-phase clinical trials. Clin Cancer Res; 23(21); 6629-39. ©2017 AACR.

Abstract 5815: The HBP1 tumor suppressor is a negative epigenetic regulator of MYCN driven neuroblastoma through interaction with the PRC2 complex

MYCN is a key driver in initiation and progression of neuroblastoma (NB) and represents a major target for novel drug strategies. We previously reported that the MYC repressor gene HBP1 was down regulated by mutant ALK via the PI3K-AKT-FOXO3 signaling axis1. Here, we further demonstrate that HBP1 upregulation suppresses proliferation of neuroblastoma cells by decreasing the MYCN signaling pathway. HBP1 levels were also shown to be repressed in neuroblastoma cells through MYC/MYCN driven upregulation of the miR-17~92 cluster, indicating that MYCN and mutant ALK both act to inhibit HBP1 expression in NB. Next, we tested the green tea polyphenol epigallocatechin gallate (EGCG), known to upregulate HBP1, and the BET inhibitor JQ1, which represses MYCN activity in neuroblastoma cells, and showed in vitro and in vivo synergistic effects on cell viability and tumor growth. Treatment with the PI3K/mTOR dual inhibitor BEZ-235 together with JQ1 also showed very strong synergistic effects. Further dissection of the HBP1 regulome using Gene Set Enrichment Analysis (GSEA) and iRegulon analysis (http://iregulon.aertslab.org) allowed identification of the PRC2 component SUZ12 as a central node in HBP1 regulated signaling, mainly through controlling the repression of MYCN regulated genes. In keeping with this finding, GSEA analysis of our HBP1 overexpression data set revealed also strong enrichment for genes that are differentially expressed upon EZH2 inhibition in neuroblastoma cells. Because HBP1 has previously been shown to interact with HDAC, we tested the effects of the HDAC inhibitors vorinostat and panobinostat as single agents and in combination with BEZ-235. Both combinations showed a strong synergistic effect on cell viability. The molecular mechanism of this synergism will be explored through RNAseq expression analysis. We conclude that HBP1 is a crucial component in MYCN controlled repression of gene activity through PRC2 interaction and demonstrate novel opportunities for precision drugging of MYCN overexpressing NB cells. 1Lambertz et al. Clin Cancer Res. (2015)

Citation Format: Geertrui Denecker, Shana Claeys, Irina Lambertz, Els Janssens, Suzanne Vanhauwaert, Bieke Decaesteker, Tom Van Maerken, Bram De Wilde, Genevieve Laureys, Kristina Althoff, Johannes Schulte, Jean-Baptiste Demoulin, Stephen S. Roberts, Laurel Bate-Eya, Jan J. Molenaar, Frank Westermann, Katleen De Preter, Frank Speleman. The HBP1 tumor suppressor is a negative epigenetic regulator of MYCN driven neuroblastoma through interaction with the PRC2 complex [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5815. doi:10.1158/1538-7445.AM2017-5815

From class waivers to precision medicine in paediatric oncology

New drugs are crucially needed for children with cancer. The European Paediatric Regulation facilitates paediatric class waivers for drugs developed for diseases only occurring in adults. In this Review, we retrospectively searched oncology drugs that were class waivered between June, 2012, and June, 2015. 147 oncology class waivers were confirmed for 89 drugs. Mechanisms of action were then assessed as potential paediatric therapeutic targets by both a literature search and an expert review. 48 (54%) of the 89 class-waivered drugs had a mechanisms of action warranting paediatric development. Two (2%) class-waivered drugs were considered not relevant and 16 (18%) required further data. In light of these results, we propose five initiatives: an aggregated database of paediatric biological tumour drug targets; molecular profiling of all paediatric tumours at diagnosis and relapse; a joint academic-pharmaceutical industry preclinical platform to help analyse the activity of new drugs (Innovative Therapy for Children with Cancer Paediatric Preclinical Proof-of-Concept Platform); paediatric strategy forums; and the suppression of article 11b of the European Paediatric Regulation, which allows product-specific waivers on the grounds that the associated condition does not occur in children. These initiatives and a mechanism of action-based approach to drug development will accelerate the delivery of new therapeutic drugs for front-line therapy for those children who have unmet medical needs.