Michael D. Taylor - US grants

DESCRIPTION (provided by applicant): Brain tumors are the most common solid malignancies and the leading cause of cancer- related death in children. Medulloblastoma (MB) is the most common pediatric brain tumor. Dissemination (metastasis) of MB through the cerebrospinal fluid seeds the leptomeningeal membranes that cover the brain and spinal cord. Metastases in MB are refractory to treatment, essentially defining children with incurable tumor. We mobilized the transposable element Sleeping Beauty (SB) in a genetically engineered mouse model of MB driven by Sonic Hedgehog (Shh) signaling and observed robust metastases. Genetic analyses of matched primary and metastatic lesions indicate that tumors undergo parallel evolution and harbor distinct, clonally selected mutations generated by transposition. This is among the first mouse models enabling identification of genes driving metastases. We hypothesize that SB can uncover clonal organization and genes underlying progression/metastasis, and that these data will inform human MB. We propose experiments characterizing paired primary and metastatic tumors from patients with MB. We also propose additional SB based experiments to identify metastases genes in a novel MYCN-driven model for MB which arises largely independently of Shh signaling and which models both classic (60% of human MB) and large cell, anaplastic pathologies (10% of human MB). Because classic human MB can be driven either by myc or by loss of p53, we will also mobilize SB in p53 deficient mice. The use of 3 models minimizes biological effects due to background, characterizes a broad genetic subset of MB, and facilitates identification and prioritization of: 1). Genes driving metastases in 3 distinct models for MB. 2). Candidates metastases genes altered in human MB. 3). Potential therapeutic targets. These data have profound implications for therapy, which assumes that metastases are biologically similar to the primary tumor. A.1.To recover transposon insertion site sequences from matched primary/metastatic GEM MB in two models in order to identify genes and pathways important for MB pathogenesis. A.2.To validate the functional importance of candidate metastases genes identified by SB insertion. A.3.To evaluate hierarchical structures, genes and pathways important for leptomeningeal dispersion using human genomic data, and paired tumors and metastases from human MB.

Brain tumors are the most common solid tumor and the leading cause of cancer-related death in children. Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Dissemination (metastasis) of MB results in seeding the leptomeningeal membranes that cover the brain and spinal cord. In prior work, we demonstrated that metastases are biologically distinct from their matched primary tumor that metastases are the overwhelming cause of death in children with MB, and that metastatic disease which frequently develops post-therapy is highly clonally divergent to therapy naïve metastases. Group 3 medulloblastoma (G3 MB) is responsible for the majority of deaths among MB patients. While only a third of G3 MB patients have visible metastases at diagnosis, almost 100% of patients with recurrent disease have metastases. The major source of morbidity in MB survivors is irradiation of the entire developing brain and spinal cord, performed to prevent metastatic recurrence, but leaving survivors with cognitive delay, growth failure, and secondary cancers. Modest decreases in the dose of craniospinal radiation would significantly improve quality of life for survivors. Understanding the biological basis of leptomeningeal dissemination, progression, and recurrence in G3 MB could therefore allow the development of therapies to supplement craniospinal radiation, enabling radiation dose reductions without an increased rate of recurrence. We have shown previously that, whereas most SHH tumors recur locally, G3 almost always recurs metastatically. This proposal leverages a well-validated GEMM model of G3 MB made collaboratively in the PIs labs, to discover genes that drive up-front metastatic initiation/progression and metastatic recurrence after radiation therapy. Identifying these genes should enable us to test novel therapies in a mouse hospital setting, to prevent metastatic recurrence in the setting of reduced craniospinal radiation. Our aims are to: Aim 1. Discover genes and pathways that initiate and drive progression of up-front metastases in G3 MB utilizing our animal model (functional genomics), followed by validation in human samples (cancer genomics) and functional validation using in vivo mouse models. Aim 2. Discover genes and pathways that initiate and drive progression of post-treatment metastases in G3 MB in response to radiation. We will use functional genomics and cancer genomics in a humanized mouse hospital setting, delivering both microneurosurgery and image guided multifractionated craniospinal radiotherapy. Aim 3. Initiate murine clinical trials to prophylactically prevent metastatic recurrence of G3 MB after surgery and reduced dose craniospinal irradiation, through delivery of novel agents targeting of mTOR, aneuploidy, and additional targets discovered in Aims #1 and #2.

PROJECT SUMMARY Brain tumors are the most common solid tumor and the leading cause of cancer-related death in children. Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Dissemination (metastasis) of MB results in seeding the leptomeningeal membranes that cover the brain and spinal cord. The unique pattern of dissemination leads to a relatively non-empirically supported model in which medulloblastoma was assumed to spread through passive shedding of cells into the cerebrospinal fluid, followed by distal implantation on the surface of the nervous system. We have now demonstrated experimentally, that medulloblastoma in fact disseminates through the blood circulation just like every other known type of human cancer, with hematogenously disseminated circulating tumor cells (CTCs) re-homing to the leptomeningeal compartment of the nervous system. CTCs reseed the leptomeninges almost exclusively, only rarely seeding organs outside the central nervous system. Hematogenous dissemination of medulloblastoma is an exciting development that offers the chance for novel approaches to the diagnosis, prevention, and treatment of metastatic medulloblastoma. The vast majority of medulloblastoma patients experience a `metastasis free' interval by imaging before their metastatic recurrence, which may offer a window to prevent metastatic recurrence. In patients with established metastatic disease, identifying the genes enabling CTCs to drive metastases could prevent or ameliorate disease progression, offering novel diagnostic and therapeutic opportunities for medulloblastoma patients. Therefore we will: Aim 1). Isolate and analyze circulating tumor cells from humans and mice with MB to determine the utility of CCL2 and CCR2 as biomarkers for the development of metastases within distinct MB subgroups. Aim 2). Manipulate CCL2/CCR2 expression using genetic/cell biology techniques to determine the contribution of each to MB metastasis in human xenograft and genetically modified mouse models that recapitulate distinct MB subgroups. Aim 3). Use established FDA approved drugs and antibodies, as well as emerging drugs and tool compounds, to block CCL2/CCR2, individually, together, and in combination with chemotherapy and craniospinal radiation in mouse models, to determine if we can prevent, and/or treat the dissemination of MB preclinically. There are no drugs or therapies for medulloblastoma metastases, despite the fact that metastases are the overwhelming cause of death, and the major source of long-term morbidity. We present a series of experiments that clarify how brain tumors can spread hematogenously, identify markers to improve diagnosis, and develop therapies applicable in near term to the treatment of metastatic MB in children.