Tschida, Barbara R

Abstract Glioblastoma (GBM) remains a deadly cancer driven in part by invasion of tumor cells into the brain. Transcriptomic analyses have identified distinct molecular subtypes, but mechanistic differences that account for clinical differences are not clear. In this study, we show that, as predicted by the motor-clutch model of cell migration, mesenchymal glioma cells are more spread, generate larger traction forces, and migrate faster in brain tissue compared with proneural cells. Despite their rapid migration and comparable proliferation rates in vitro, mice with mesenchymal tumors survive longer than those with proneural tumors. This improved survival correlated with an immune response in mesenchymal tumors, including T cell–mediated. Consistently, inducing mesenchymal tumors in immunodeficient mice resulted in shorter survival, supporting a protective immune role in mesenchymal tumors. Thus, mesenchymal tumors have aggressive migration but are immunologically “hot,” which suppresses net proliferation. These two features counteract each other and may explain the lack of a strong survival difference between subtypes clinically, while also opening up new opportunities for subtype-specific therapies. Significance: This study highlights new mechanical and immunologic insights into GBM molecular subtypes using an integrated modeling–genome engineering strategy, which can potentially facilitate GBM subtype-specific therapeutic strategies.

Abstract Glioblastoma remains a deadly cancer driven in part by invasion of tumor cells into the brain. Transcriptomic analyses have identified distinct molecular subtypes, but mechanistic differences that account for clinical differences are not clear. Here, we show that, as predicted by the motor-clutch model of cell migration, mesenchymal glioma cells are more spread, generate larger traction forces, and migrate faster in brain tissue compared to proneural cells. Despite their rapid migration and comparable proliferation rates in vitro, mice with mesenchymal tumors survive longer than those with proneural tumors. This improved survival correlated with an immune response in the mesenchymal tumors, including T cell-mediated. Consistently, inducing mesenchymal tumors in immunodeficient mice resulted in shorter survival supporting a protective immune role in mesenchymal tumors. Thus, mesenchymal tumors have aggressive migration, but are immunologically ‘hot’ which suppresses net proliferation. These two features counteract each other and may explain the lack of a strong survival difference between subtypes clinically, while also opening up new opportunities for subtype-specific therapies. Significant Statement This study highlights new mechanical and immunological insights into glioblastoma molecular subtypes using an integrated modeling-genome engineering strategy, which can potentially facilitate glioblastoma subtype-specific therapeutic strategies.

Abstract 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.

Abstract Medulloblastoma and central nervous system primitive neuroectodermal tumors (CNS-PNET) are aggressive, poorly differentiated brain tumors with limited effective therapies. Using Sleeping Beauty (SB) transposon mutagenesis, we identified novel genetic drivers of medulloblastoma and CNS-PNET. Cross-species gene expression analyses classified SB-driven tumors into distinct medulloblastoma and CNS-PNET subgroups, indicating they resemble human Sonic hedgehog and group 3 and 4 medulloblastoma and CNS neuroblastoma with FOXR2 activation. This represents the first genetically induced mouse model of CNS-PNET and a rare model of group 3 and 4 medulloblastoma. We identified several putative proto-oncogenes including Arhgap36, Megf10, and Foxr2. Genetic manipulation of these genes demonstrated a robust impact on tumorigenesis in vitro and in vivo. We also determined that FOXR2 interacts with N-MYC, increases C-MYC protein stability, and activates FAK/SRC signaling. Altogether, our study identified several promising therapeutic targets in medulloblastoma and CNS-PNET. Significance: A transposon-induced mouse model identifies several novel genetic drivers and potential therapeutic targets in medulloblastoma and CNS-PNET.

Abstract Hepatic steatosis is a strong risk factor for the development of hepatocellular carcinoma (HCC), yet little is known about the molecular pathology associated with this factor. In this study, we performed a forward genetic screen using Sleeping Beauty (SB) transposon insertional mutagenesis in mice treated to induce hepatic steatosis and compared the results to human HCC data. In humans, we determined that steatosis increased the proportion of female HCC patients, a pattern also reflected in mice. Our genetic screen identified 203 candidate steatosis-associated HCC genes, many of which are altered in human HCC and are members of established HCC-driving signaling pathways. The protein kinase A/cyclic AMP signaling pathway was altered frequently in mouse and human steatosis-associated HCC. We found that activated PKA expression drove steatosis-specific liver tumorigenesis in a mouse model. Another candidate HCC driver, the N-acetyltransferase NAT10, which we found to be overexpressed in human steatosis–associated HCC and associated with decreased survival in human HCC, also drove liver tumorigenesis in a steatotic mouse model. This study identifies genes and pathways promoting HCC that may represent novel targets for prevention and treatment in the context of hepatic steatosis, an area of rapidly growing clinical significance. Cancer Res; 77(23); 6576–88. ©2017 AACR.

Abstract Hepatocellular carcinoma (HCC), or liver cancer, is the second leading cause of death from cancer worldwide (Ferlay et al, Lyon, France: International Agency for Research on Cancer, 2013). HCC is linked with hepatic steatosis, or fatty liver disease, the most common chronic liver disease in the US. Both hepatic steatosis and HCC are increasing in prevalence in the US. However, the molecular mechanisms that cause HCC in a steatotic liver are not entirely understood. To uncover mutations promoting cancer in fatty livers and elucidate the role of steatosis in HCC, we performed a forward genetic screen using the conditional Sleeping Beauty (SB) transposon insertional mutagenesis system in mice treated with ethanol and a choline deficient diet to induce steatosis. Mice developed hepatic steatosis and liver cancer without sex bias, modeling the pattern seen in humans in whom HCC's with steatosis as a preceding condition are represented by a nearly equal number of males and females. We found that hepatic steatosis caused a downregulation of liver Foxa1 expression and increased Foxa2 inactivating phosphorylation, thus providing a molecular explanation for the loss of gender bias in our mouse model. Transposon insertion sites were mapped from the mouse HCC tumors, and genes near or in which more insertions were observed than expected by chance were identified as common insertion sites (CIS), which we consider putative steatosis-associated liver cancer genes. Wnt/b-catenin signaling, which defines a subclass of HCC and can induce tumors in mice without sex bias, was one of the top CIS associated pathways identified. Interestingly, alpha-adrenergic and dopamine signaling were also among the top steatosis-specific CIS associated pathways, suggesting a role for the sympathetic nervous system and cAMP signaling in fatty liver-associated cancer. Further studies are underway to test the roles of the pathways and individual genes identified in this study in driving HCC. Our studies implicate Wnt/beta-catenin and sympathetic nervous system signaling in steatosis-associated HCC and suggest methods for treatment or prevention in such cases. Citation Format: Barbara R. Tschida, N. Alpay Temiz, Ju D. Yang, Vincent W. Keng, David A. Largaespada. A transposon-based forward genetic screen for steatosis-associated liver cancer drivers. [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 63.