Publications

The ALK(F1174L) mutation is associated with intrinsic and acquired resistance to crizotinib and cosegregates with MYCN in neuroblastoma. In this study, we generated a mouse model overexpressing ALK(F1174L) in the neural crest. Compared to ALK(F1174L) and MYCN alone, co-expression of these two oncogenes led to the development of neuroblastomas with earlier onset, higher penetrance, and enhanced lethality. ALK(F1174L)/MYCN tumors exhibited increased MYCN dosage due to ALK(F1174L)-induced activation of the PI3K/AKT/mTOR and MAPK pathways, coupled with suppression of MYCN pro-apoptotic effects. Combined treatment with the ATP-competitive mTOR inhibitor Torin2 overcame the resistance of ALK(F1174L)/MYCN tumors to crizotinib. Our findings demonstrate a pathogenic role for ALK(F1174L) in neuroblastomas overexpressing MYCN and suggest a strategy for improving targeted therapy for ALK-positive neuroblastoma.

(131)I-metaiodobenzylguanidine (MIBG) is a targeted radiopharmaceutical with activity in patients with relapsed or refractory neuroblastoma. Irinotecan is a known radiosensitizer with activity in neuroblastoma. This phase I study aimed to determine the recommended phase 2 dose of MIBG together with fixed doses of vincristine and irinotecan.

The proto-oncogene MYCN is mis-expressed in various types of human brain tumors. To clarify how developmental and regional differences influence transformation, we transduced wild-type or mutationally stabilized murine N-myc(T58A) into neural stem cells (NSCs) from perinatal murine cerebellum, brain stem, and forebrain. Transplantation of N-myc(WT) NSCs was insufficient for tumor formation. N-myc(T58A) cerebellar and brain stem NSCs generated medulloblastoma/primitive neuroectodermal tumors, whereas forebrain NSCs developed diffuse glioma. Expression analyses distinguished tumors generated from these different regions, with tumors from embryonic versus postnatal cerebellar NSCs demonstrating Sonic Hedgehog (SHH) dependence and SHH independence, respectively. These differences were regulated in part by the transcription factor SOX9, activated in the SHH subclass of human medulloblastoma. Our results demonstrate context-dependent transformation of NSCs in response to a common oncogenic signal.

Importance of the field: More effective drugs are needed to treat poor prognosis paediatric malignancies. Development of anticancer agents for childhood cancers faces several unique challenges compared with their adult counterparts.Areas covered in this review: We demonstrate how recent advances in preclinical drug development may overcome these difficulties and challenges. We explain the role of academia, regulators and industry in this field, address issues with preclinical models and illustrate several examples of biology-driven drug development in childhood cancers.What the reader will gain: Increased knowledge about preclinical drug development in paediatric oncology including different preclinical models, established preclinical research networks, and relationships among academia, industry and regulators, as illustrated by several examples of targeted agents in childhood solid malignancies.Take home message: It is anticipated that emerging advanced preclinical models and testing platforms will provide a more efficient, biologically-driven rationale to support the use of targeted therapies in several malignancies such as neuroblastoma, medulloblastoma or high grade glioma which account for the majority of deaths related to childhood cancer.

Genetically engineered mouse models (GEMM) have made major contributions to a molecular understanding of several adult cancers and these results are increasingly being translated into the pre-clinical setting where GEMM will very likely make a major impact on the development of targeted therapeutics in the near future. The relationship of pediatric cancers to altered developmental programs, and their genetic simplicity relative to adult cancers provides unique opportunities for the application of new advances in GEMM technology. In neuroblastoma the well-characterized TH-MYCN GEMM is increasingly used for a variety of molecular-genetic, developmental and pre-clinical therapeutics applications. We discuss: the present and historical application of GEMM to neuroblastoma research, future opportunities, and relevant targets suitable for new GEMM strategies in neuroblastoma. We review the potential of these models to contribute both to an understanding of the developmental nature of neuroblastoma and to improved therapy for this disease.

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Sonic Hedgehog (SHH) signaling drives a minority of MB, correlating with desmoplastic pathology and favorable outcome. The majority, however, arises independently of SHH and displays classic or large cell anaplastic (LCA) pathology and poor prognosis. To identify common signaling abnormalities, we profiled mRNA, demonstrating misexpression of MYCN in the majority of human MB and negligible expression in normal cerebella. We clarified a role in pathogenesis by targeting MYCN (and luciferase) to cerebella of transgenic mice. MYCN-driven MB showed either classic or LCA pathologies, with Shh signaling activated in approximately 5% of tumors, demonstrating that MYCN can drive MB independently of Shh. MB arose at high penetrance, consistent with a role for MYCN in initiation. Tumor burden correlated with bioluminescence, with rare metastatic spread to the leptomeninges, suggesting roles for MYCN in both progression and metastasis. Transient pharmacological down-regulation of MYCN led to both clearance and senescence of tumor cells, and improved survival. Targeted expression of MYCN thus contributes to initiation, progression, and maintenance of MB, suggesting a central role for MYCN in pathogenesis.

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