Cutaneous Neurofibroma Heterogeneity: Factors that Influence Tumor Burden in Neurofibromatosis Type 1

Neurofibromatosis type 1 is one of the most common genetic disorders of the nervous system and predisposes patients to develop benign and malignant tumors. Cutaneous neurofibromas (cNFs) are NF1-associated benign tumors that affect nearly 100% of patients with NF1. cNFs dramatically reduce patients' QOL owing to their unaesthetic appearance, physical discomfort, and corresponding psychological burden. There is currently no effective drug therapy option, and treatment is restricted to surgical removal. One of the greatest hurdles for cNF management is the variability of clinical expressivity in NF1, resulting in intrapatient and interpatient cNF tumor burden heterogeneity, that is, the variability in the presentation and evolution of these tumors. There is growing evidence that a wide array of factors are involved in the regulation of cNF heterogeneity. Understanding the mechanisms underlying this heterogeneity of cNF at the molecular, cellular, and environmental levels can facilitate the development of innovative and personalized treatment regimens.

Abstract P3-08-04: Discovery of cancer genes and pathways operative in PI3K-activated mammary cancer reveals clinically relevant genotype-phenotype correlations

Human breast cancer (BRCA) shows tremendous genomic, gene expression, clinical, and phenotypic heterogeneity. Known driver gene alterations can only explain a portion of this heterogeneity, some of which likely arise from variation in the target cell for transformation, in addition to incompletely understood gene copy number and epigenetic alterations. These factors are difficult to identify with certainty using human patient samples due to widely varying germline genetic backgrounds, thousands of gene copy and epigenetic changes per sample, and, unknown target cell transformation. Activating mutations in the p110α catalytic subunit of PI3K are one of the most common genetic alterations in human BRCA. Here, we report results from two Sleeping Beauty (SB) transposon-accelerated mouse models of Pik3ca-mutant mammary cancer showing how genotype-phenotype correlations can be drawn providing strong candidates for mediating tumor phenotypes, including estrogen-receptor (ER)-dependent gene expression, high cell cycle activity, and immune cell exclusion. We used SB transposon mutagenesis in mice on a Pik3caH1047R activated mutant background to model mammary cancer development in two different mammary epithelial compartments. Both the target cell for mutagenesis and the specific transposon-induced mutations correlated with specific tumor phenotypes, including whether the tumors were ER positive or negative. RNA sequencing of tumors revealed novel genotype-phenotype correlations implicating specific transposon-altered gene drivers of high cell cycle activity, ER-dependent gene expression, and white blood cell exclusion from the tumor. Many transposon-implicated genes are altered at the gene copy number or epigenetic/methylation level in human BRCA, and several were functionally validated. These models provide a source of genetically heterogenous mouse mammary tumors with a uniform initiating mutation, Pik3caH1047R, useful for identifying cooperating pathways and drivers of specific tumor phenotypes.

Citation Format: Morito Kurata, Emiily Pope, Jingmin Shu, Wenlin Yuan, Wendy Hudson, Mark Sokolowski, Setareh Bagherzadeh, Zora Modrusan, Eric Stawiski, Steffen Durinck, Sekar Seshigiri, Aaron Sarver, Nuri Temiz, David Largaespada. Discovery of cancer genes and pathways operative in PI3K-activated mammary cancer reveals clinically relevant genotype-phenotype correlations. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-08-04.

Abstract A010: Methylation profiling reveals the role of PRC2 in regulating DNA methylome stochasticity in malignant peripheral nerve sheath tumors

Neurofibromatosis type 1 (NF1) syndrome is an autosomal dominant cancer predisposition syndrome defined by germline deletion of one NF1 allele. Somatic loss of heterozygosity in the remaining NF1 allele in Schwann lineage cells gives rise to benign tumors known as plexiform neurofibromas. These tumors have a high risk of developing into cancerous lesions known as malignant peripheral nerve sheath tumors (MPNST) through the sequential deletion of CDKN2A/B followed by recurrent mutations in SUZ12 or EED, constituting the inactivation of polycomb repressor complex 2 (PRC2). PRC2 is a transcriptional repressor complex involved in the silencing of several genes throughout cell development and differentiation. Loss of this complex leads to a depletion in trimethylation marks on Histone H3 Lysine 27 (H3K27me3) and the subsequent gain of acetylation marks on the same lysine residue (H3K27Ac). However, full range of epigenetic consequences of these events are currently not well characterized, especially with respect to MPNST formation and development. The Largaespada lab has developed Schwann cell lines engineered to harbor deletions in NF1 and either SUZ12 or EED and assayed the methylation status of 850,000 CpG sites using the EPIC array. The resulting methylation profiles reveal a large degree of change in promoter methylation between cell lines with and without PRC2 inactivation. These changes, however, appear to be inconsistent. To further understand this phenomenon, I have quantified methylation entropy of individual epialleles across PRC2-deficient and -proficient lines using the methylation state of each CpG site. This analysis reveals a variety of regions in which methylation becomes highly stochastic upon PRC2 loss, tending toward a bistable state in which CpG sites can be methylated or unmethylated across isogenic cell populations. Additionally, the deletion of EED specifically leads to an increase in hemi-methylation distinct from the deletion of SUZ12, implying differential roles for these subunits in mediating DNA methylation beyond the context of PRC2 activity. Finally, pathway analysis of genes whose promoters are differentially methylated upon PRC2 reveals a bias towards developmental modules such as morphogenesis and neuronal differentiation, suggesting that DNA methylation is a mechanism by which PRC2 loss promotes stemness in Schwann lineage cells prior to MPNST formation. These findings underline the importance of DNA methylation in contributing to tumor formation and define unique functions by which PRC2 specifically leverages diverse methylation states to drive malignant transformation in Schwann lineage cells.

Citation Format: Christopher M. Stehn, Minu Bhunia, Suganth Suppiah, Adam Herman, Gelareh Zadeh, David Largaespada. Methylation profiling reveals the role of PRC2 in regulating DNA methylome stochasticity in malignant peripheral nerve sheath tumors. [abstract]. In: Proceedings of the AACR Special Conference: Cancer Epigenomics; 2022 Oct 6-8; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_2):Abstract nr A010.

Abstract 1300: Identification of efficacious treatment for glioblastoma (GBM) by applying computational drug sensitivity imputation to novel GBM avatars and GBM clinical datasets

Glioblastoma (GBM) is a debilitating disease associated with poor prognosis and a limited response to therapies. At present, patients receive chemotherapy with temozolomide, following radiation therapy and surgery; however, none of the treatments are curative, and clinical trials are recommended as the preferred option for eligible patients. Regrettably, only 3-5% of GBM patients survive 3 years or more. Therefore, it is imperative to develop efficacious therapies. To achieve this goal, we have developed a computation method that allows us to impute drug sensitivity when transcriptome data is available. We have applied this imputation method to several publicly available normal brain tissue, low grade glioma (LGG), and GBM patient datasets to identify compounds of interest. We also compared the leads from these patient/in vivo data analyses with those generated from previous imputations made using a novel GBM avatar model; this model was created by introducing different genetic driver mutations using CRISPR-Cas9 into human induced pluripotent stem cells, followed by differentiation to GBM-associated mutations containing neural progenitor cells (NPC) and animal engraftment to develop human adult GBM models. We applied the drug imputation to over 1200 human normal brain, LGG and GBM samples as well as 18 NPC, tumor sphere and engrafted GBM tumor avatar samples. For each sample, we imputed over 700 drug sensitivity scores. Our model was trained independently using one of two separate high throughput in vitro drug screening datasets (GDSC and CTRP). To identify drugs showing higher sensitivity in GBM than in normal tissues, we compared the imputed drug sensitivity for each compound between samples belonging to the precancerous or the non-high grade glioma state (represented by the normal tissue and LGG data) and samples representing the cancerous or high grade glioma state (GBM). We identified a number of compounds showing higher imputed sensitivity in samples belonging to the cancerous state when compared to those in the precancerous or LGG state. We were also able to cross check compounds of interest with our avatar data. Among them, some agents have been used in the clinic to treat GBM, supporting the validity of integration of our computational tool with novel ex vivo GBM avatars and GBM clinical data in the development of new therapeutic strategy for GBM. More importantly, we have identified other compounds with various mechanism of action that show higher efficacy in GBM and will be further evaluated with the goal to quickly translate into clinic. Therefore, we can successfully integrate ovel experimental and computational models to speed up drug discovery with the goal of finding new therapeutics for GBM.

Citation Format: Danielle Maeser, Robert Gruener, Robert Galvin, Tomoyuki Koga, Frank B. Furnari, David Largaespada, Clark C. Chen, Stephanie R. Huang. Identification of efficacious treatment for glioblastoma (GBM) by applying computational drug sensitivity imputation to novel GBM avatars and GBM clinical datasets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1300.

Abstract 1823: Directing T cells using multivalent, bispecific chemically self-assembling nanorings (CSANs) to target brain tumors overexpressing EGFR and B7H3 antigens

Introduction: CNS solid tumors have few therapeutic options and disease progression is rapid especially in pediatrics. Current standard-of-care strategies with radiation and surgery typically result in severe neuroendocrine and cognitive deficiencies. Therapies that target select antigens overexpressed on only the malignant cells would alleviate some of these off-target side-effects. The Wagner lab has developed a non-genetic approach to facilitate selective cell-cell interactions using Chemically Self-Assembled Nanorings (CSANs). We have shown that functionalizing the CSAN construct with a cancer antigen-targeting protein and a T-cell targeting single chain antibody fragment (antiCD3 scfv) forms a multivalent, bispecific nanoring with the ability to traffic T-cells to the tumor. We therefore hypothesize that targeting overexpressed cancer antigens on medulloblastoma and/or glioblastoma using our technology would address many of the concerns associated with permanent genetic engineering such as CAR T cells.

Methods/Results: B7H3 (CD276) is a checkpoint molecule that is overexpressed on a wide variety of solid tumor types. For this study, we developed a new bispecific CSAN able to effectively direct human T cells to B7H3 overexpressing medulloblastoma. The Wagner lab is also currently able to produce CSANs that facilitate T cell interactions with many other solid tumor antigens such as EGFR and EpCAM. Therefore, we characterized the expression of EGFR, B7H3, and EpCAM on ONS76 and Daoy medulloblastoma and U87 glioblastoma in 2D and 3D models in vitro. We show that treating a B7H3+/EGFR+ allograft of ONS76 medulloblastoma with antiB7H3-CD3 or antiEGFR-CD3 CSANs resulted in ONS76 cytotoxicity and increased T cell lytic activity. We are currently analyzing the efficacy of our CSANs against orthotopically injected medulloblastoma in immunodeficient mice. We plan to probe the ways in which targeting these specific antigens induces changes in their expression within the tumor and identify potential modes of immune escape mechanisms such as antigen expression loss.

Conclusion: We show that bispecific CSANs are able to non-genetically direct T cells to selectively eradicate cancer cells overexpressing the targeted antigen. The conclusion of in vivo orthotopic models of medulloblastoma are required to demonstrate the ability of the CSANs to effectively cross the BBB and the efficacy of specifically targeting the checkpoint molecule B7H3.

Citation Format: Ellie Mews, Pauline Jackson, Ozgun Kilic, Justine Delgado, Mahathi Patchava, David Largaespada, Carston R. Wagner. Directing T cells using multivalent, bispecific chemically self-assembling nanorings (CSANs) to target brain tumors overexpressing EGFR and B7H3 antigens [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1823.

Epigenomic, genomic, and transcriptomic landscape of schwannomatosis

Schwannomatosis (SWNTS) is a genetic cancer predisposition syndrome that manifests as multiple and often painful neuronal tumors called schwannomas (SWNs). While germline mutations in SMARCB1 or LZTR1, plus somatic mutations in NF2 and loss of heterozygosity in chromosome 22q have been identified in a subset of patients, little is known about the epigenomic and genomic alterations that drive SWNTS-related SWNs (SWNTS-SWNs) in a majority of the cases. We performed multiplatform genomic analysis and established the molecular signature of SWNTS-SWNs. We show that SWNTS-SWNs harbor distinct genomic features relative to the histologically identical non-syndromic sporadic SWNs (NS-SWNS). We demonstrate the existence of four distinct DNA methylation subgroups of SWNTS-SWNs that are associated with specific transcriptional programs and tumor location. We show several novel recurrent non-22q deletions and structural rearrangements. We detected the SH3PXD2A-HTRA1 gene fusion in SWNTS-SWNs, with predominance in LZTR1-mutant tumors. In addition, we identified specific genetic, epigenetic, and actionable transcriptional programs associated with painful SWNTS-SWNs including PIGF, VEGF, MEK, and MTOR pathways, which may be harnessed for management of this syndrome.

EPCO-02. MOLECULAR CHARACTERIZATION OF TWO NOVEL MPNST SUBGROUPS IDENTIFIES THERAPEUTIC OPPORTUNITIES

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive Schwann-cell derived sarcomas. These tumors are resistant to all current therapies, with exception to gross total surgical resection, and unresectable or metastatic tumors are considered incurable. Our understanding of the molecular alterations driving malignant transformation is limited, and to date, targeted therapies have proven ineffective. In this study, we leverage multi-platform genomic and epigenomic profiling of human MPNSTs and neurofibromas to identify targetable molecular pathways that lead to malignant transformation. Unsupervised consensus hierarchical clustering of the top 20K most variable methylated probes yielded seven stable and robust subgroups that are clinically relevant. The high-grade MPNSTs formed two distinct methylation-based clusters (MPNST-G1 and MPNST-G2). MPNST-G1 had worse prognosis compared to MPNST-G2 (0.6 years versus 1.4 years, p < 0.05). PTCH1 loss or SMO gain was prevalent in MPNST-G1 compared to MPNST-G2 (75% vs 12.5%, p < 0.05). In addition, MPNST-G1 harbored PTCH1 CpG island promoter hypermethylation in (87.5% vs 12.5%, p < 0.001). Transcriptome profiling recapitulated the two distinct MPNST subgroups. We next demonstrated that that RB1 signaling pathways are aberrant in both MPNST-G1 and MPNST-G2. However, SHH pathway activation is observed in MPNST-G1, while WNT/CCND1/ ß-catenin pathway activation is observed in MPNST-G2. Network-based drug-disease proximity analysis identified SMO inhibitors as a potential FDA approved drug as a potential targeted therapy. To determine if SHH pathway activation is sufficient for malignant transformation, we knocked out PTCH1 in immortalized neurofibroma cells lines. In 3 different cell lines with PTCH1 knockout, we observed induction of a malignant phenotype, with increased cellular proliferation and invasion. Most importantly, in-vitro and in-vivo models confirm that targeting the SHH pathway, with sonidegib, was effective in inhibiting tumor growth proving SMO inhibition to be a novel therapeutic option in these lethal cancers.

TAMI-28. DIFFERENTIAL MIGRATION MECHANICS AND IMMUNE RESPONSES OF GLIOMA SUBTYPES

In Glioblastoma (GBM), tumor spreading is driven by tumor cells’ ability to infiltrate healthy brain parenchyma, which prevents complete surgical resection and contributes to tumor recurrence. GBM molecular subtypes, classical, proneural and mesenchymal, were shown to strongly correlate with specific genetic alterations (Mesenchymal: NF1; Classical: EGFRVIII; Proneural: PDGFRA). Here we tested the hypothesis that a key mechanistic difference between GBM molecular subtypes is that proneural cells are slow migrating and mesenchymal cells are fast migrating. Using Sleeping Beauty transposon system, immune-competent murine brain tumors were induced by SV40-LgT antigen in combination with either NRASG12V (NRAS) or PDGFB (PDGF) overexpression. Cross-species transcriptomic analysis revealed NRAS and PDGF-driven tumors correlate with human mesenchymal and proneural GBM, respectively. Similar to human GBM, CD44 expression was higher in NRAS tumors and, consistent with migration simulations of varying CD44 levels, ex vivo brain slice live imaging showed NRAS tumors cells migrate faster than PDGF tumors cells (random motility coefficient = 30µm2/hr vs. 2.5µm2/hr, p < 0.001). Consistent with CD44 function as an adhesion molecule, migration phenotype was independent of the tumor microenvironment. NRAS and human PDX/MES tumor cells were found to migrate faster and have larger cell spread area than PDGF and human PDX/PN tumors cells, respectively, in healthy mouse brain slices. Furthermore, traction force microscopy revealed NRAS tumor cells generate larger traction forces than PDGF tumors cells which further supports our theoretical mechanism driving glioma migration. Despite increased migration, NRAS cohort had better survival than PDGF which was attributed to enhanced antitumoral immune response in NRAS tumors, consistent with increased immune cell infiltration found in human mesenchymal GBM. Overall our work identified a potentially actionable difference in migration mechanics between GBM subtypes and establishes an integrated biophysical modeling and experimental approach to mechanically parameterize and simulate distinct molecular subtypes in preclinical models of cancer.

EXTH-08. MINIPIG MODELS OF NEUROFIBROMATOSIS TYPE 1 FOR THERAPEUTIC DEVELOPMENT

Neurofibromatosis Type 1 (NF1) is a genetic disease caused by mutations in the neurofibromin 1 (NF1) gene. NF1 patients present with a variety of clinical manifestations and are predisposed to cancer development. Many NF1 animal models have been developed, yet none display the spectrum of disease seen in patients and the translational impact of these models has been limited. Using gene-editing technology, we have developed a minipig model of NF1 that exhibits clinical hallmarks of the disease, including café au lait macules, neurofibromas, and optic pathway glioma. We have conducted pharmacological studies in our NF1 minipigs to assess the pharmacokinetic and pharmacodynamic properties of MEK inhibitors for NF1. We have demonstrated that oral administration of several MEK inhibitors results in clinically relevant plasma concentrations and consequent inhibition of Ras signaling in immune cells, and certain MEK inhibitors can cross the blood brain barrier and have a pharmacodynamic effect, suggesting that they may be effective in treating NF1-associated brain tumors. Because over 20% of NF1 patients harbor NF1 nonsense mutations, we are assessing safety and efficacy of nonsense mutation suppressors that may be effective in treating NF1. We evaluated six drugs known to induce nonsense mutation suppression in several primary cell types isolated from NF1 minipigs and show that several of these drugs have the propensity to induce the production of full length neurofibromin protein, leading to a subsequent reduction in MAPK signaling. Information acquired from this NF1 minipig preclinical model will be leveraged towards initiating a clinical trial in NF1 patients. The NF1 minipig provides an unprecedented opportunity to study the complex biology and natural history of NF1 and could prove indispensable for development of imaging methods, biomarkers, and evaluation of safety and efficacy of NF1 therapies.

EPCO-04. GENOMIC AND EPIGENOMIC HALLMARKS OF SCHWANNOMATOSIS SCHWANNOMAS

Schwannomatosis (SWNTS) is a genetic cancer predisposition syndrome that manifests as multiple and often, painful neuronal tumors called schwannomas (SWNs). Very little is known about the epigenomic and genomic alterations in SWNTS related SWNs (SWNTS-SWNs) other than germline mutations in SMARCB1 and LZTR1 plus somatic mutations in NF2 and loss of heterozygosity in chromosome 22q. Herein, we have comprehensively established the specific molecular signatures of SWNTS-SWNs. We found that tumor anatomic location was associated with pain and distinct DNA methylation and transcriptional signatures. DNA sequencing revealed several novel non-22q deletions, specifically in LZTR1-mutant cases. Whole-genome sequencing identified novel recurrent structural rearrangements. Further, chromosomal aberrations in SWNTS-SWNs were accompanied by increased transcription of mismatch repair genes. Our transcriptome analysis detected the SH3PXD2A-HTRA1 gene fusion in SWNTS-SWNs, more commonly in LZTR1-mutant tumors. In addition, we identified the specific genetic, epigenetic, and transcriptional hallmarks of painful SWNs that may be harnessed to develop new treatments for this debilitating syndrome.

TMOD-23. PRECLINICAL DRUG EVALUATION IN A GENETICALLY ENGINEERED MINIPIG MODEL OF NEUROFIBROMATOSIS TYPE 1

We have employed gene-editing technology to create a Neurofibromatosis Type 1 (NF1) minipig that replicates the broad spectrum of disease that develops in NF1 patients and meets the National Institute of Health’s diagnostic criteria for NF1. The NF1 boars are fertile and the NF1 mutant allele is transmitted at a Mendelian rate with no reduction in fitness of offspring that inherit this allele. To date, we have observed 100% penetrance of café au lait macules, a phenotype that occurs in nearly every NF1 patient, but has never been demonstrated in any other animal model. The NF1 minipig develops cutaneous neurofibromas and optic pathway glioma, that histologically resemble human tumors. Additionally, we have observed other NF1-associated phenotypes including Lisch nodules, tibial dysplasia, white matter decompaction, hypopigmentation, and freckling of the skin. The FDA has emphasized the need for development and testing of new therapies in large animal disease models prior to human studies. Therefore, we have conducted pharmacological studies in our NF1 swine to look at the pharmacokinetic and pharmacodynamic properties MEK inhibitors, currently in clinical trials for NF1. We have demonstrated that oral administration of the MEK inhibitors results in clinically relevant plasma levels of the drug and inhibition of Ras signaling, and that certain MEK inhibitors can cross the blood brain barrier and have a pharmacodynamic effect, suggesting that they may be effective in treating NF1-associated brain tumors. We envision this large animal model of NF1 will become a standard in the evaluation of the safety and efficacy of new drugs prior to Phase I clinical trials. Further, an NF1 minipig may enable researchers to better understand the biological and genetic mechanisms underlying this complex disease, detect NF1-related tumors earlier, identify biomarkers, discover novel drug targets, and test new drugs and combination therapies for safety and efficacy.

PDTM-19. MYC AND FAK/SRC COMBINATION TREATMENT OF FOXR2-HIGH BRAIN TUMORS

Brain tumors are the leading cause of cancer-related deaths in children. To identify novel therapeutic targets in two types of pediatric brain tumors, medulloblastoma (MB) and central nervous system primitive neuroectodermal tumors (CNS-PNETs), we performed a Sleeping Beauty transposon mutagenesis screen in mice. In doing this, we identified FOXR2 (Forkhead box R2) as a candidate oncogene in MB. FOXR2 is expressed at high levels in a subset of human MB and increased FOXR2 expression drives MB formation in mice. FOXR2 has been implicated as an oncogene in several cancers of neural original, including CNS-PNET, adult and pediatric high-grade glioma, and malignant peripheral nerve sheath tumors. We have also found that FOXR2 is upregulated in non-MYCN amplified high-risk neuroblastoma. Therefore, we propose that FOXR2 represents a strong candidate for targeted therapy across multiple brain tumor entities. We have uncovered a dual role of FOXR2 in stabilization of CMYC protein and activation of the FAK/SRC signaling pathway. We are working to further define the mechanism of FOXR2-mediated MYC stabilization and FAK/SRC activation. We plan to treat FOXR2-high tumors with combinations of drugs effective against tumors with high MYC, FAK, or SRC in clinical development. Inhibitors or combinations of that score well in vitro will be used to treat mice with orthotopically injected FOXR2-high tumor cells (MB, neuroblastoma, and glioma). In addition, we are working to construct mouse models of FOXR2-driven neural tumors for use in drug testing. We hypothesize that FOXR2-high tumors will be sensitive to MYC and FAK/SRC inhibitor combination therapy, establishing FOXR2 as a molecular marker for treatment success of MYC and FAK/SRC inhibitors in patients.

Abstract 3399: Comparative genomic analyses of osteosarcoma etiology reveal a chromosomal structural rationale for the increased incidence of osteosarcoma in dogs

Risk of osteosarcoma is significantly higher in large and giant breed dogs than in any other animal, including humans. To identify the reason for this observation, we used a comparative genomic approach to identify aberrations responsible for osteosarcoma etiology in a Sleeping Beauty transposon-accelerated mouse model, in human patients, and in naturally occurring canine tumors, using RNA-Seq and exome paired tumor normal analyses. Fusions identified in Sleeping Beauty-mutagenized tumors revealed a role for Cdkn2a disruption in Trp53 signaling, and for numerous genes which cooperate with disrupted TrpP53 signaling, indicating the existence of many diverse routes to osteosarcoma tumor formation. Similarly, human tumors showed TP53 pathway disruption associated with a high level of diversity of additional driver mechanisms, supporting multiple independent routes to tumor formation. However, in the majority of canine tumors, observed TP53 pathway aberrations co-occurred with loss of both copies of the region containing the PTEN tumor suppressor. In human osteosarcoma, only heterozygous PTEN loss was observed, and in both humans and mice, PTEN aberration was observed in a much smaller percentage of the tumor population. We hypothesize that increased osteosarcoma incidence in dogs is partly due to a syntenic rearrangement of the peri-PTEN locus in the canine genome. The PTEN gene is part of a small synteny block that localized in the distal end of canine chromosome 26 (CFA 26) during evolution. We hypothesize that this location change creates a high risk of loss in the context of cytogenetic instability caused by disruption of TP53, thereby providing a structural genetic rational for the higher incidence of osteosarcoma in dogs. Consistent with these results and with the powerful nature of PTEN as a tumor suppressor, canine osteosarcomas with homozygous loss of PTEN are associated with worse outcomes than canine osteosarcomas with intact PTEN. These results suggest that engineering genomes to minimize cancer risk may be a realistic approach to the prevention of cancer.

Citation Format: Aaron L. Sarver, Lauren Mills, Nuri Temiz, MIlcah Scott, Anne Sarver, Logan Spector, Jinhua Wang, Mathew Breen, Subbaya Subramanian, Branden Moriarity, Jaime Modiano, David Largaespada. Comparative genomic analyses of osteosarcoma etiology reveal a chromosomal structural rationale for the increased incidence of osteosarcoma in dogs [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 3399.

Abstract 1121: Validation of FOXR2 and ARHGAP36 as oncogenes in medulloblastoma

We are working to validate two putative oncogenes in medulloblastoma (MB), ARHGAP36 and FOXR2. These genes were identified as MB drivers using a Sleeping Beauty mutagenesis screen in mice and are overexpressed in subsets of human MB. We are using gain (GOF) and loss of function (LOF) studies both in vitro and in vivo to understand the roles of FOXR2 and ARHGAP36 in MB genesis. In GOF studies, both genes individually drove anchorage independent growth in a mouse cerebellar progenitor cell line (C17.2) and a human MB cell line (ONS76). When overexpressed individually in C17.2 cells, both FOXR2 and ARHGAP36 drove tumor formation in the flank of NU/J mice. We are also using an orthotopic injection model with C17.2 cells overexpressing either ARHGAP36 or FOXR2 individually to determine if these genes drive tumor formation in a more relevant setting. RNA sequencing and reverse-phase protein array analyses were also performed on WT and C17 cells overexpressing each oncogene to identify their effects in an unbiased manner. We are working to validate those effects using RT-PCR and Western analysis. In LOF studies, the CRISPR/Cas system is being used to create mutations in either the ARHGAP36 or FOXR2 locus in human MB cell lines (ONS76, MED8A, Daoy). This has been accomplished with ARHGAP36 in ONS76 cells, and we are currently characterizing those cells using proliferation, soft agar colony formation, and tumor formation assays. Lastly, we are working to create GOF and LOF mouse models of both FOXR2 and ARHGAP36 to characterize their oncogenic potential in vivo. We identified ARHGAP36 and FOXR2 as putative oncogenes in MB and our findings may elucidate novel targets for therapeutic efforts aimed at treating patients with MB.

Citation Format: Pauline Jackson, Alex Larsson, Paramita Das, David Largaespada. Validation of FOXR2 and ARHGAP36 as oncogenes in medulloblastoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1121.

Abstract 3665: WAC: A candidate tumor suppressor gene in colorectal cancer

Our lab recently performed a DNA transposon forward genetic screen in mice that was designed to identify low-frequency mutations that contribute to colorectal cancer (CRC) initiation and progression. Results from this screen identified the WW domain-containing adaptor with coiled-coil (WAC) gene as a top DNA transposon insertion site. WAC has previously been implicated in several cellular processes including amino acid starvation-induced autophagy, golgi biogenesis, and transcription associated histone modification but has never before been linked to tumorigenesis. Transposon mutagenesis screens performed by others (Takeda et al. Nature Genetics 2015) have also identified Wac as a common insertion site, a result that further implicates WAC as a candidate CRC driver gene. Analyses of transposon insertion patterns within Wac predict loss of gene function and a role as a tumor suppressor. Soft agar colony formation assays reveal that shRNA mediated silencing of Wac cooperates with Apc mutations in mouse colorectal cells to promote cellular transformation. Additional colony formation assays using immortalized human colonic epithelial cells and the adenoma derived AAC1 cell line also shows that silencing WAC is protumorigenic. Using a zebrafish model we demonstrated that overexpression of wild type but not cancer-associated mutant forms of WAC induce expression of the cell cycle inhibitor p21, which suggests that loss of WAC may lead to uncontrolled cellular proliferation. Finally, using publicly available mutation data we determined that WAC is somatically mutated in both breast and lung cancers; a finding that indicates WAC may serve a critical tumor suppressive role in several tissues. Currently we are developing a conditional knockout mouse to further investigate the role of WAC in CRC tumor formation.

Citation Format: Christopher R. Clark, Caitlin Conboy, Makayla Maile, Callie Janik, Julia Hatler, Robert Cormier, David Largaespada, Timothy K. Starr. WAC: A candidate tumor suppressor gene in colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3665.

Abstract 1621: SRGAP2 expression levels may induce a biphasic metastatic phenotype in osteosarcoma cell lines

The purpose of this study is to characterize the role of Slit-Robo GTPase-Activating Protein 2 (SRGAP2) in osteosarcoma (OS) metastasis. OS is the most common primary bone tumor and the eighth leading pediatric cancer. Despite combined therapies, treatment failure is experienced within 5 years of diagnosis by over 40% of patients, generally due to metastatic disease. Using the conditional Sleeping Beauty transposon mutagenesis system, our laboratory recently identified candidate tumor promoting genes in transgenic mice that develop OS, including the potential tumor suppressor SRGAP2 involved in regulating actin dynamics. We hypothesized that loss of SRGAP2 would increase the metastatic potential of OS cell lines in vitro and in vivo, whereas gain would decrease metastatic potential. Gene expression was amplified with a stably integrated, tetracycline-inducible over expression vector containing SRGAP2 cDNA and gene silencing was accomplished with a clustered regularly interspaced short palindromic repeat (CRISPR) targeting the gene. Studies were conducted in the well-characterized murine osteosarcoma cell lines K12 and its more aggressive derivative K7M2 and human osteosarcoma cell lines HOS and its more aggressive derivative 143B. Compared to luciferase-controls, overexpression and knockout of SRGAP2 had no effect on cell proliferation in K12, K7M2, HOS, and 143B (n = 4). A reduction of soft agar colony formation was observed in knockout cell lines but not in cell lines with SRGAP2 overexpression for K12 and 143B (n = 3); HOS cell lines did not form colonies in soft agar. Interestingly, overexpression of SRGAP2 decreased wound-healing closure in 143B and K12 lines, but increased closure time in HOS (n = 4). Tail vein injections in NRG mice are currently being investigated. Overexpression of SRGAP2 in K12 decreased development of macrometastases in lungs, whereas knockout of SRGAP2 eliminated gross detection of lung masses (n = 3). Future studies include imaging fixed cells to determine if SRGAP2 knockout and overexpression affects cell morphology and completing studies with K7M2 lines. These results suggest that SRGAP2 has a biphasic phenotype in osteosarcoma cell lines, with an optima in expression for efficient metastasis. It's dual role of deforming cell membranes independent of its ability to activate Rac GTPases and alter actin dynamics may be responsible for the observed results.

Citation Format: Tracy Marko, Ghaidan Shamsan, David Largaespada. SRGAP2 expression levels may induce a biphasic metastatic phenotype in osteosarcoma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1621.

Abstract A175: Design and evaluation of novel natural killer cell chimeric antigen receptors

Chimeric Antigen Receptors (CARs) are used to direct and activate cytotoxic lymphocytes against virally infected or malignant cells. They have been heavily investigated in cytotoxic T cells, and, to a much lesser extent, in natural killer (NK) cells with promising results, especially for anti-CD19 CARs to mediate killing of B cell leukemias. To date, CARs that have been utilized in NK cells have primarily employed the same intracellular signaling components as T cell CARs. However, this may not be the optimal approach for CAR-expressing NK cells due to differences in key signaling pathways. To improve the activity of NK cell-CARs targeted against solid tumors, the intracellular signaling domains of an anti-mesothelin CAR were modified to express NK cell specific signaling molecules and evaluated for activity in NK-92 cells against ovarian cancer cell lines. CARs were assembled using gBlocks encoding various transmembrane, co-activating, and signaling domains. NK cell specific CARs were then transfected into NK-92 cells, a human NK cell tumor line, using Sleeping Beauty. Positive cells were selected for using a drug resistance marker and CAR surface expression was evaluated using flow cytometry. CAR expressing NK-92 cells were then evaluated for degranulation, as indicated by CD107a production, and interferon (INF)-γ release when challenged with mesothelin negative, MA148, and mesothelin positive, A1847, ovarian cell lines. In addition, beads conjugated to mesothelin were used to measure NK cell activation via the CAR alone.

In total 10 novel CARs were assembled and transfected into NK-92 cells, 6 of which were properly expressed on the cell surface. All 6 properly expressed CARs enhanced both CD107a and INF-γ production. When CAR activity alone was evaluated using mesothelin conjugated protein A beads, non-transfected NK-92 cells or cells that did not properly express the CAR all had <3% positive cells for CD107a and INF-γ. In contrast, NK-92 cells expressing CARs had between 8 and 16% positive cells for CD107a, with 5-12% positive for INF-γ. Since CAR4, expressing an NKG2D transmembrane, 2B4 co-activation, and CD3ζ signaling domain had the greatest activity, individual domains were mutated to assess their function. Mutation of the key binding residue in NKG2D for DAP10 resulted in a drastic decrease in the percentage of INF-γ producing cells, while mutation of the tyrosine residues in the CD3ζ signaling domain greatly abrogated CD107a production. As expected, mutation of all domains resulted in an inactive CAR. These studies demonstrate that CARs containing NK cell receptor domains function properly and may lead to better NK-92 cell activation. In addition, mutating CAR domains allows for dissecting the different pathways leading to either degranulation or cytokine release in NK cells. To better assess CAR activation potential in non-transformed NK cells, we are currently expressing the most promising CAR constructs into induced pluripotent stem cells (iPSCs) followed by differentiation into mature NK cells that will be tested for activity against ovarian cancer cells both in vitro and in vivo. These iPSC-NK cells will have the potential to create an “off-the-shelf” immunotherapy with the capability of targeting multiple malignancies.

Citation Format: David L. Hermanson, Branden Moriarity, Trevor Argall, Melissa A. Geller, David Largaespada, Dan S. Kaufman. Design and evaluation of novel natural killer cell chimeric antigen receptors. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A175.

Abstract PR02: Somatic CRISPR/Cas9-mediated tumor suppressor disruption enables versatile brain tumor modeling

Modeling cancer in mice through engineering of candidate genes in the germline has long been the gold standard for the validation of putative oncogenes or tumor suppressor genes (TSGs). For TSGs, whereby loss-of-function (LOF) mutations act as a driver for malignant transformation, this has traditionally been accomplished using constitutive or cell type-specific knockout strategies mediated by homologous recombination in embryonic stem cells. While this allows evaluation of cell type-specific susceptibility to malignant transformation, generation of genetically engineered mouse models (GEMMs) is a time consuming process. For in vivo investigation of a large number of molecular alterations, such as the many new candidates currently emerging from large-scale tumor genome sequencing efforts, a faster and more flexible method is required. We therefore sought to adapt the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9-guided endonuclease technique for the somatic disruption of candidate TSGs and thereby complement aforementioned already existing models like GEMM.

To provide a flexible and effective method for investigating somatic LOF alterations and their influence on tumorigenesis in vivo, we established in vivo somatic gene transfer of CRISPR/Cas9-encoding vectors using polyethylenimine or in utero electroporation, respectively, allowing for in vivo targeting of TSGs in the developing murine brain. We demonstrate the utility of this approach by deleting the tumor suppressor Ptch1, which resulted in the development of cerebellar tumors resembling sonic hedgehog (SHH) subgroup medulloblastoma both at the histopathological as well as the molecular level. Furthermore, we show that multiple genes can be disrupted with this approach, using in utero electroporation of guide RNAs (gRNAs) targeting Trp53, Pten and Nf1 into the forebrain of mice. This resulted in induction of glioblastoma with 100% penetrance. Using whole genome sequencing (WGS) we characterized the MB-driving Ptch1 deletions in detail and show that no off-targets were detected in these tumors.

Taken together, these approaches provide a fast and convenient way for validating the emerging wealth of novel candidate TSGs and the generation of faithful animal models of human cancer.

Citation Format: Marc Zuckermann, Volker Hovestadt, Christiane B. Knobbe-Thomsen, Marc Zapatka, Paul A. Northcott, Kathrin Schramm, Jelena Belic, David T.W. Jones, Barbara Tschida, Branden Moriarity, David Largaespada, Martine F. Roussel, Andrey Korshunov, Guido Reifenberger, Stefan M. Pfister, Peter Lichter, Daisuke Kawauchi, Jan Gronych. Somatic CRISPR/Cas9-mediated tumor suppressor disruption enables versatile brain tumor modeling. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr PR02.

A Genome-Wide Scan Identifies Variants in NFIB Associated with Metastasis in Patients with Osteosarcoma

Metastasis is the leading cause of death in patients with osteosarcoma, the most common pediatric bone malignancy. We conducted a multistage genome-wide association study of osteosarcoma metastasis at diagnosis in 935 osteosarcoma patients to determine whether germline genetic variation contributes to risk of metastasis. We identified an SNP, rs7034162, in NFIB significantly associated with metastasis in European osteosarcoma cases, as well as in cases of African and Brazilian ancestry (meta-analysis of all cases: P = 1.2 × 10(-9); OR, 2.43; 95% confidence interval, 1.83-3.24). The risk allele was significantly associated with lowered NFIB expression, which led to increased osteosarcoma cell migration, proliferation, and colony formation. In addition, a transposon screen in mice identified a significant proportion of osteosarcomas harboring inactivating insertions in Nfib and with lowered NFIB expression. These data suggest that germline genetic variation at rs7034162 is important in osteosarcoma metastasis and that NFIB is an osteosarcoma metastasis susceptibility gene.

SIGNIFICANCE

Metastasis at diagnosis in osteosarcoma is the leading cause of death in these patients. Here we show data that are supportive for the NFIB locus as associated with metastatic potential in osteosarcoma.

Expression of FGFR3 and FGFR4 and clinical risk factors associated with progression-free survival in synovial sarcoma

Although rare, synovial sarcoma (SS) is one of the most common soft tissue sarcomas affecting young adults. To investigate potential tumor markers related to synovial sarcoma prognosis, we carried out a single-institution retrospective analysis of 103 patients diagnosed with SS between 1980 and 2009. Clinical outcome data were obtained from medical records, and archived tissue samples were used to evaluate the relationship between progression-free survival (PFS) and several prognostic factors, including tumor expression of FGFR3 and FGFR4. No associations were found between PFS and gender, body mass index, tumor site, SS18-SSX translocation, or FGFR4 expression. As seen in previous studies, age at diagnosis (<35, 63% versus ≥35 years, 31% 10-year PFS; P = .033), histologic subtype (biphasic, 75% versus monophasic 34% 10-year PFS; P = .034), and tumor size (≤5 cm, 70% versus >5 cm, 22% 10-year PFS; P < .0001) were associated with PFS in SS patients. In addition, in a subset of patients with available archived tumor samples taken prior to chemotherapy or radiation (n = 34), higher FGFR3 expression was associated with improved PFS (P = .030). To the best of our knowledge, this is the largest study of SS to date to suggest a potential clinical role for FGFR3. While small numbers make this investigation somewhat exploratory, the findings merit future investigation on a larger scale.

B cell transcription factors define a novel tumor suppressor gene network in acute lymphoblastic leukemia (P4410)

We recently found that STAT5 activation correlates with poor response to therapy in B-ALL. To identify genetic defects that cooperate with STAT5 activation to initiate transformation we carried out a forward genetic screen involving the mutagenic transposon Sleeping Beauty. This screen identified a number of cooperating partners including gain-of-function mutations in Sos1 and loss-of-function mutations in Ebf1 and Ikzf1 (i.e., Ikaros). Haploinsufficiency of Ebf1 or the related transcription factor Pax5 synergized with STAT5 to rapidly induce progenitor B-ALL in 100% of mice. The leukemic cells displayed reduced expression of Ebf1 and Pax5, which affected a small subset of EBF1 or PAX5 target genes, including tumor suppressor genes and oncogenes. To test whether compound haploinsufficiency of Ebf1 and Pax5 alone is sufficient to cause transformation, we generated Ebf1+/- x Pax5+/- mice. Over 80% of these mice developed progenitor B-ALL. We observed similar results in Ebf1+/- x Ikzf1+/-, Pax5+/- x Ikzf1+/-, and Pax5+/- x Ebf1+/- x Ikzf1+/- mice; interestingly, although most leukemias were B-ALL we also observed T-ALL suggesting that T-All may arise from a B cell progenitor. Our findings suggest a model in which STAT5 activation cooperates with small perturbations in a self-reinforcing network of transcription factors critical for B cell development to initiate ALL and that loss of any two alleles in the network results in a loss of network tumor suppressor function.

Abstract 1970: Validation of candidate gastrointestinal cancer genes with ion channel functions, identified from Sleeping Beauty transposon-mediated mutagenesis screens in mice

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths in the US. To identify the genetic alterations contributing to CRC, our labs have used Sleeping Beauty (SB)-transposon-mediated mutagenesis screens in Apc+/+ and ApcMin mice. These screens have identified a set of common insertion site (CIS) associated candidate cancer genes, that when dysregulated, may contribute to CRC development. Depletion of several CIS genes identified from an SB screen in ApcMin mice resulted in a significant decrease in human CRC cell viability. The SB screen in Apc+/+ mice has generated a list of CIS genes including two ion-channel encoding genes: Kcnq1 (potassium voltage-gated channel, KQT-like subfamily, member 1) and Cftr (cystic fibrosis transmembrane conductance regulator, ATP-binding cassette sub-family C, member 7) which act together to promote chloride ion secretion in the normal colon. We hypothesize that these candidate genes, when dysregulated, contribute to the development of CRC. The function of the candidate genes is being tested in a mouse model of Kcnq1 haploinsufficiency that was introgressed into the ApcMin model of GI cancer and in human CRC cell line DLD-1. In the mouse model, Kcnq1 expression is abrogated by targeted germline mutagenesis, resulting in a null allele. In cell culture, expression of each candidate gene is depleted by siRNA knockdown, confirmed by quantitative real time PCR and followed by measurements of cancer-related phenotypes which include cell viability measured by the MTT assay. We found that haploinsufficiency for Kcnq1 significantly enhances tumorigenesis in ApcMin mice. In support of this result, a 60% knockdown of KCNQ1 in DLD-1 cells resulted in ∼1.4x increase in cell viability, compared with a control siRNA treatment at day seven after transfection. The normal physiological functions of KCNQ1 indicate it may work with CFTR to prevent inflammation in the GI tract, thus suggesting that loss of KCNQ1 or CFTR may be oncogenic via an inflammatory mechanism. To begin testing this idea, colon tissues of Kcnq1+/+ and Kcnq1−/− mice were compared for expression of the inflammatory mediator Nfkb. Nfkb mRNA level was increased by ∼1.6x in Kcnq1−/− mice. To begin testing the potential connections between KCNQ1 and CFTR, CFTR was successfully depleted by 40% in DLD-1 cells and the effect on cell viability and inflammatory mediators’ expression is being determined. In summary, our results of both in vivo and in vitro studies confirm a tumor suppressor role for Kcnq1 in the GI tract. Current work is focused on investigating the model that genetic alterations of KCNQ1 and CFTR promote oncogenesis by a common pathway, possibly by an inflammatory mechanism.

Citation Format: Bich L. N. Than, M. Gerald O'Sullivan, Tim Starr, David Largaespada, Robert T. Cormier, Patricia M. Scott. Validation of candidate gastrointestinal cancer genes with ion channel functions, identified from Sleeping Beauty transposon-mediated mutagenesis screens in mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1970. doi:10.1158/1538-7445.AM2013-1970

Interweaving the strands: β-catenin, an HIV co-receptor, and Schwann cell tumors

WNT/β-catenin signaling is critical to the development of many cancer types. A paper by Mo and colleagues in a recent issue of Cell shows that autocrine CXCL12/CXCR4 chemokine signaling activates β-catenin signaling in a rare peripheral nerve sarcoma. Together with the availability of small molecules targeting CXCR4, this finding suggests new avenues for cancer therapy.

Abstract 812: Maternal folic acid supplementation and risk of medulloblastoma in offspring

Background: Epidemiological studies can give important insights into factors that modulate disease risk. However, the inherent limitations of observational studies make causal relationships difficult to infer. For example, several case-control studies have indicated that prenatal vitamins may protect against childhood brain tumors, including medulloblastoma, and folic acid (FA) is speculated to be the modulating factor. Using a murine model, we are testing whether low maternal dietary FA during the peri-gestational period increases medulloblastoma risk in offspring. We are using a well-defined transgenic mouse model of Gorlin syndrome, which is characterized by an autosomal dominant mutation in the PTCH1 gene. Heterozygous C57BL/6 strain Ptc1+/− mice have a medulloblastoma incidence of ∼40% at one year, making this transgenic model highly suitable for childhood brain cancer etiologic studies.

Methods. A total of 126 female wild-type C57BL/6 mice were randomized to one of three amino acid defined FA diets: 1) 0.3 mg/kg (low), 2) 2.0 mg/kg (control), and 3) 8.0 mg/kg (high), one month prior to mating with Ptc1+/− C57BL/6 males and maintained on their respective diets until weaning of their pups. Red blood cell (RBC) folate measurements were obtained from the dams at weaning and their association with the assigned dietary FA dose was determined using one-way ANOVA. The offspring have been genotyped and weaned heterozygotes are being followed for tumor development for one year. Interim hazard ratios (HRs) and 95% confidence intervals (CIs) were computed using Cox proportional hazards regression to examine the association between the assigned maternal dietary FA dose and offspring tumor incidence.

Results. In a total of 381 offspring, the overall Ptc1+/− genotype frequency is similar to previous reports with no significant differences between dietary groups (low: 40%, control: 40%, high: 42%). RBC folate concentrations in the dams at weaning increased significantly with increasing FA dose (p&lt;0.0001). Ptc1+/− offspring from each of the dietary groups have been followed for a mean of ∼6 months. To date, 25%, 35%, and 37% of Ptc1+/− offspring have developed tumors in the low, control, and high FA groups, respectively.Compared to the control group, the hazard for tumor development was non-significantly decreased in offspring in the low FA group (HR=0.7; 95% CI 0.3-1.4) and similar in the high FA group (HR=1.0; 95% CI 0.5-1.8).

Conclusions. In contrast to our hypothesis, these preliminary results indicate that higher doses of maternal dietary FA may increase offspring brain tumor incidence. We speculate that higher dietary FA levels during the peri-gestational period may influence brain tumor progression in mice predisposed to tumor development. The implications of these findings with respect to human populations will be discussed. Supported by R03CA141440, T32CA099936, and the Children's Cancer Research Fund, Minneapolis, MN.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 812. doi:10.1158/1538-7445.AM2011-812

Abstract 2859: Identification of driver mutations in colon cancer using Sleeping Beauty mutagenesis

Human colon tumors contain hundreds of genetic and epigenetic anomalies, of which only a handful are responsible for the growth and development of the tumor. We have developed a forward genetic screen in mice that can identify those mutations capable of causing gastrointestinal tract tumors. By comparing the mutations identified in our screen with those found in human colon tumors we can pinpoint the drivers of carcinogenesis. The forward genetic screen uses the Sleeping Beauty (SB) DNA transposon as a random mutagen capable of both activating and inactivating genes. Using Cre recombinase under the control of the Villin promoter we can selectively activate this mutagenesis in intestinal epithelial cells in the mouse. Tumors generated in these mice are analyzed for transposon insertion sites using linker mediated-PCR in combination with high-throughput sequencing. This analysis provides us with genomic sequence that can be mapped to the mouse genome. Candidate cancer driver genes are identified because they are located in areas of the genome that are recurrently mutated by the SB transposon in multiple tumors.

We conducted the screen in wild-type mice and identified 77 candidate cancer genes, of which six were previously known human colon cancer genes (APC, BMPR1A, SMAD4, PTEN, FBXW7, CDK8). More importantly, we identified many novel candidate drivers that can now serve as potential targets in colon cancer therapy. We have extended our studies by conducting three more screens using mice that already contain a known driver mutation. The purpose of these new screens is to gain a better understanding of the genetic changes that cooperate with common mutations found in colon cancer. The three screens used mice that have a mutation in Apc (ApcMin), carry a dominant negative acting Trp53 (p53R270H), or are null for the tumor suppressor gene p19ARF. We have completed the screen in ApcMin mice and found an additional 30 candidate drivers of colon cancer that may specifically cooperate with the Apc mutation. The two final screens are in the process of completion and should uncover genes that cooperate with mutations in Trp53 and p19ARF. The results of these studies will greatly expand the list of potential therapeutic targets and will enhance our understanding of the genetic etiology of colon cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2859. doi:10.1158/1538-7445.AM2011-2859

Isolation and preliminary characterization of the human and mouse homologues of the bacterial cell cycle gene era

Era is an essential GTPase that is required for proper cell cycle progression and cell division in Escherichia coli and is found in nearly all bacteria sequenced to date. To determine whether Era is also present in eukaryotic organisms, we searched the dbEST database and found EST clones coding for proteins that were similar to Era. Full sequencing of these ESTs from human and mouse identified a conserved homologue, ERAL1 (Era-like 1). ERAL1 maps to 17q11.2 in human and is located in the syntenic region of mouse chromosome 11. ERAL1 may be an attractive candidate for a tumor suppressor gene since ERAL1 is located in a chromosomal region where loss of heterozygosity is often associated with various types of cancer.