Abstract 6130: Cancer sensitivity to therapy is constrained by apoptosis regulation in cells of origin

Many chemotherapeutic agents target cellular components or processes that are present in all cancers, yet clinical responses to these agents vary greatly between cancer types and even patient age - the basis for these broad-scale differences are unclear. The vast majority of targeted and cytotoxic cancer therapies including ionizing radiation produce pro-apoptotic signaling in exposed cells, suggesting that the mitochondrial apoptosis sensitivity of cancer cells could act as a central signaling “node” to broadly impact therapy outcomes. To test this, we used BH3 profiling and complementary chemosensitivity assays to analyze hundreds of primary cancer specimens across twelve major cancer types. We find that cancers with typically favorable outcomes including certain hematologic malignancies, testicular cancer, and some pediatric cancers contain mitochondria that are highly primed for apoptosis, which renders them hypersensitive to cytotoxic as well as targeted agents and radiation therapy. Priming levels in many epithelial cancers including ovarian cancer and non-small cell lung cancer are highly heterogeneous, mirroring their variability in clinical outcomes. Finally, many tumor types that are typically chemoresistant including adult soft tissue sarcomas, hepatocellular carcinoma and pancreatic cancer are almost completely resistant to pro-apoptotic signaling. By analyzing in vitro and in vivo pancreatic, ovarian, hepatocellular and sarcoma tumorigenesis models, we find that apoptotic priming generally increases during neoplastic transformation, in part due to consistent upregulation of pro-apoptotic proteins BAX and BAK. However, the level of apoptotic priming in cancer cells is constrained by the baseline apoptosis sensitivity of normal cells prior to transformation. Remarkably, we find that apoptotic priming is dynamically regulated by cell lineage and differentiation state but can also be modulated by oncogenes. For instance, Myc activation typically increases apoptotic priming while activation of mutant Ras signaling decreases it - these changes in priming alter the chemosensitivity of cancer cells. Finally, we use inducible mouse tumor models to demonstrate that neoplastic transformation of cells from developmentally immature tissues yields pediatric tumors that are more primed for apoptosis than equivalent tumors arising in adults. This difference in priming causes pediatric tumors to be more sensitive to front-line therapies and BH3 mimetics targeting pro-survival BCL-2 family proteins in vitro and in vivo. Thus, lineage-determined regulation of apoptosis prior to and during neoplastic transformation leads to broad-scale differences in cancer cell chemosensitivity and can be exploited therapeutically by targeting BCL-2 family proteins.

Citation Format: Cameron Fraser, Xingping Qin, Kenichi Shimada, Johan Spetz, Mary Heather Florido, Rumani Singh, Stacey Yu, Adam Presser, Zintis Inde, Gaurav Joshi, Jennifer Guerriero, Francisco Sanchez-Rivera, Alison Karst, Omar Lopez, Chendi Li, Peter Winter, Ying Yue, Peter Sorger, Jingwei Cheng, Izidore Lossos, Aaron Hata, Ronny Drapkin, Adam Palmer, James Decaprio, Manisha Thakuria, Charles Yoon, Ursula Matulonis, Matthew Meyerson, Elizabeth Stover, Diana Cardona, Kris Wood, Shayna Sarosiek, David Kirsch, Joseph Mancias, Andrew Cherniack, Anthony Letai, Kristopher Sarosiek. Cancer sensitivity to therapy is constrained by apoptosis regulation in cells of origin. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6130.

Abstract 2079: Tumor cell intrinsic inactivation of TREX1 increases type I IFN signaling and immune cell recruitment

Tumor cells employ mechanisms to evade anti-tumor immune responses that can include the downregulation or silencing of cytosolic nucleic acid sensing pathway components to dampen Type I IFN signaling. It has been documented that genomic instability and mitotic stress in malignant cells can lead to aberrant cytosolic DNA accumulation and activation of the cGAS-STING pathway. A key negative regulator of cytosolic DNA is the DNA exonuclease TREX1. TREX1 assists in removing DNA from the cytosol, in turn reducing cGAS-STING mediated type I IFN induction. Not surprisingly, TREX1 is overexpressed in several tumor types when compared to normal tissue. The functional importance of TREX1 in cytoplasmic nucleic acid surveillance is evidenced by inactivating TREX1 mutations having an association with Type I inteferonopathies such as Aicardi-Goutières syndrome and SLE. Specifically, most of these mutations impact the enzymatic function of TREX1, underscoring the importance of its exonuclease function. To directly assess TREX1 function in cancer, we inactivated TREX1 in a panel of tumor cell lines. Loss of TREX1 resulted in reduced proliferation and increased expression of the Type I IFN-stimulated gene CXCL10. This finding was validated with CRISPR knockout of TREX1, which also led to the activation of IRF3 and a Type I IFN associated gene signature. To characterize the role of TREX1 function in curbing anti-tumor immunity in vivo, we inactivated Trex1 in the murine syngeneic B16F10 melanoma model. TREX1 knockout together with PD1 blockade resulted in slower tumor growth when compared to PD1 blockade alone. This was accompanied by an increase in CD8+ T and NK cell infiltration in tumors. In addition, gene expression profiling of whole tumors revealed that TREX1 loss resulted in increased type I IFN signaling within the tumor microenvironment. In summary, our data strongly suggest a critical role for TREX1 in suppressing anti-tumor immunity and indicate it would be an attractive target for therapeutic intervention.

Citation Format: Haritha Mathsyaraja, Benjamin Wolf, Chari Cortez, Adam Kashishian, Alison Karst, Madelyn Cueva, Min Wang, Kathleen S. Keegan, Jennifer Cain. Tumor cell intrinsic inactivation of TREX1 increases type I IFN signaling and immune cell recruitment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2079.

Abstract PR01: Cyclin E: Targeting cell cycle dependencies in CCNE1-amplified tumors

Genomic instability is a hallmark of high-grade serous ovarian carcinoma (HGSOC). Based on The Cancer Genome Atlas (TCGA), it is estimated that approximately 50% of HGSOCs harbor a defect in the homologous recombination (HR) pathway of DNA repair. In contrast, the 20% that harbor CCNE1 amplifications appear to have an intact HR pathway. These tumors are associated with shorter overall survival and resistance to platinum-based chemotherapy. Cyclin E is the activating partner of cyclin-dependent kinase 2 (CDK2), which controls cell cycle progression from G1 to S phase.

Our previous data showed that CCNE1 amplification and overexpression occurs early in serous tumorigenesis. Importantly, in immortalized human fallopian tube secretory epithelial cells (FTSEC), constitutive Cyclin E overexpression imparts malignant characteristics to these cells. This leads to an accumulation of DNA damage and altered gene expression of genes involved in DNA replication and fork protection. However, in the setting of hTERT expression and a p53 mutant, Cyclin E overexpression alone was not capable of fully transforming the FTSECs. Therefore, in order to identify cooperating genetic alterations, we performed an in vitro gain-of-function (GOF) screen. One of those identified hits was the RAD51 paralog XRCC2, which is known to be involved in the homologous recombination DNA repair pathway and in fork protection. We could show that XRCC2 expression is upregulated in response to Cyclin E overexpression in FTSECs and when analyzing the TCGA patient cohorts, we found a strong correlation between RNAseq expression of XRCC2 and Cyclin E. We could further demonstrate that the knockdown of XRCC2 is synthetic lethal in CCNE1 amplified ovarian cancer cell lines but not in cells that harbor no CCNE1 amplification, indicating that the upregulation of XRCC2 creates a dependency in CCNE1-amplified tumors.

Since overexpression of Cyclin E leads to unscheduled S-phase entry and stress on the replication fork, we speculated that one of the roles of XRCC2 might be to stabilize the replication fork in CCNE1-overexpressing cells. We found that the knockdown of XRCC2 in Cyclin E-overexpressing cells leads to a strong reduction in fork speed and fork recovery.

To further understand this mechanism we analyzed the binding partners of XRCC2 in CCNE1 amplified cells by mass spectrometry. Interestingly, we found that XRCC2 interacts with the minichromosome maintenance deficient 7 (MCM7) protein. MCM7 is part of the MCM complex that unwinds the DNA during replication. Surprisingly, the downregulation XRCC2 also led to a strong reduction in MCM7 protein expression, indicating that XRCC2 may play an important role in stabilization of the MCM complex. This is especially interesting since CCNE1-amplified cells are more dependent on active MCM complexes and are more sensitive to MCM complex reduction compared to normal cells. Further defining the factors that contribute to the XRCC2-MCM7 interaction at the replication fork may define novel vulnerabilities in CCNE1-amplified tumors.

This abstract is also being presented as Poster A03.

Citation Format: Kai Doberstein, Alison Karst, Paul T. Kroeger, Jr., Paul Jones, William Hahn, Ronny Drapkin. Cyclin E: Targeting cell cycle dependencies in CCNE1-amplified tumors. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr PR01.

Abstract 1425: Targeting cell cycle dependencies in CCNE1 amplified tumors

Genomic instability is a hallmark of high grade serous ovarian carcinoma (HGSOC). Based on The Cancer Genome Atlas (TCGA), it is estimated that approximately 50% of HGSOCs harbor a defect in the homologous recombination (HR) pathway of DNA repair. In contrast, the 20% that harbor CCNE1 amplifications appear to have an intact HR pathway. These tumors are associated with shorter overall survival and resistance to chemotherapy. Cyclin E is the activating partner of cyclin-dependent kinase 2 (CDK2) which controls cell cycle progression from G1 to S phase. Our previous data showed that CCNE1 amplification and overexpression occurs early in serous tumorigenesis. Importantly, in immortalized human fallopian tube secretory epithelial cells (FTSEC), constitutive Cyclin E overexpression imparts malignant characteristics to these cells. This leads to an accumulation of DNA damage and altered gene expression of genes involved in DNA replication and fork protection. However, in the setting of hTERT expression and a p53 mutant, Cyclin E overexpression alone was not capable of fully transforming the FTSECs. Therefore, in order to identify cooperating genetic alterations, we performed an in vitro gain-of-function (GOF) screen. One of those identified hits was the RAD51 paralog XRCC2, which is known to be involved in the HR DNA repair pathway and in fork protection. We could show that XRCC2 expression is upregulated in response to Cyclin E overexpression in FTSECs and we found a strong correlation between RNAseq expression of XRCC2 and Cyclin E in the TCGA patient cohorts. We could further demonstrate that the knock down of XRCC2 is synthetic lethal in CCNE1 amplified ovarian cancer cell lines but not in cells that harbor no CCNE1 amplification, indicating that the upregulation of XRCC2 creates a dependency in CCNE1 amplified tumors. Since overexpression of Cyclin E leads to unscheduled S-phase entry and stress on the replication fork, we speculated that one of the roles of XRCC2 might be to stabilize the replication fork in Cyclin E overexpressing cells. We found that the knock down of XRCC2 in Cyclin E overexpressing cells leads to a strong reduction in fork speed and fork recovery. To further understand this mechanism we analyzed the binding partners of XRCC2 in CCNE1 amplified cells by mass spectrometry. Interestingly, we found that XRCC2 interacts with the minichromosome maintenance deficient 7 (MCM7) protein. MCM7 is part of the MCM complex that unwinds the DNA during replication. Surprisingly, the downregulation XRCC2 also led to a strong reduction in MCM7 protein expression indicating that XRCC2 may play an important role in stabilization the MCM complex. This is especially interesting since CCNE1 amplified cells are more dependent on active MCM complexes and are more sensitive to MCM complex reduction compared to normal cells. Further defining the factors that contribute to the XRCC2-MCM7 interaction at the replication fork may define novel vulnerabilities in CCNE1 amplified tumors.

Citation Format: Kai Doberstein, Alison Karst, Paul Jones, Azra Ligon, Michelle Hirsch, Dariush Etemadmoghadam, William Hahn, David Bowtell, Ronny Drapkin. Targeting cell cycle dependencies in CCNE1 amplified tumors [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 1425. doi:10.1158/1538-7445.AM2017-1425

Abstract PR05: Identifying potential targets in Cyclin E-amplified tumors

Genomic instability is a hallmark of high grade serous ovarian carcinoma (HGSOC). Based on The Cancer Genome Atlas (TCGA), it is estimated that approximately 50% of HGSOCs harbour a defect in the homologous recombination (HR) pathway of DNA repair. A majority of these cases are due to the germline and/or somatic inactivation of the BRCA1 or BRCA2 genes. In contrast, the 20% of HGSOC that harbor CCNE1 amplifications are mutually exclusive with BRCA mutations and appear to have an intact HR pathway. These tumors are associated with shorter overall survival and resistance to platinum-based chemotherapy. Cyclin E is the activating partner of cyclin-dependent kinase 2 (CDK2) which controls cell cycle progression through phosphorylation of pRB and induction of E2F transcriptional activity.

Our previous data showed that CCNE1 amplification and overexpression occurs early in serous tumorigenesis. Importantly, in immortalized human fallopian tube secretory epithelial cells (FTSEC), constitutive cyclin E overexpression imparts malignant characteristics to these cells, including increased proliferation, loss of contact inhibition and clonogenicity. This leads to an accumulation of DNA damage and altered gene expression of genes involved in DNA replication fork protection and the BRCA-Fanconi Anemia pathway. However, in the setting of hTERT expression and a p53 mutant, Cyclin E overexpression alone was not capable of fully transforming the FTSECs. Therefore, in order to identify cooperating genetic alterations, we performed an in vitro gain-of-function (GOF) screen using an open reading frame (ORF) library of approximately 800 genes that are recurrently amplified in HGSOC. The transduced cells were then tested for anchorage independent colony formation on ultra-low attachment (ULA) plates and soft agar. A total of 92 genes were identified between the two assays, with 28 genes registering as a “hit” in both assays. A subset was then retested for in vivo growth in immunocompromised mice using the empty vector as the negative control. Positive hits included CHD2, GAB2, AKT, PITRM1, PTPRB, XRCC2, PSME4, and SLC38A1.

Interestingly, by using RNA interference we found that knock-down of some of the genes found in the GOF screen is synthetic lethal in cancer cells that overexpress Cyclin E or have a CCNE1 amplification. The identified hits included genes involved in the DNA damage response pathways and the Fanconi Anemia pathway. Underlining the importance of these genes, analysis of the TCGA revealed that both pathways are strongly upregulated in Cyclin E overexpressing tumors. These results suggest that targeting cooperating genetic dependencies in CCNE1 amplified tumors may be a novel therapeutic avenue. We are currently using our panel of patient-derived tumor xenograft and cell lines to address this possibility.

This abstract is also presented as Poster A06.

Citation Format: Kai Doberstein, Alison Karst, Dariush Etemadmoghadam, Paul Jones, Gavin Dunn, William Hahn, David Bowtell, Ronny Drapkin. Identifying potential targets in Cyclin E-amplified tumors. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr PR05.

Cis-eQTL analysis and functional validation of candidate susceptibility genes for high-grade serous ovarian cancer

Genome-wide association studies have reported 11 regions conferring risk of high-grade serous epithelial ovarian cancer (HGSOC). Expression quantitative trait locus (eQTL) analyses can identify candidate susceptibility genes at risk loci. Here we evaluate cis-eQTL associations at 47 regions associated with HGSOC risk (P≤10(-5)). For three cis-eQTL associations (P<1.4 × 10(-3), FDR<0.05) at 1p36 (CDC42), 1p34 (CDCA8) and 2q31 (HOXD9), we evaluate the functional role of each candidate by perturbing expression of each gene in HGSOC precursor cells. Overexpression of HOXD9 increases anchorage-independent growth, shortens population-doubling time and reduces contact inhibition. Chromosome conformation capture identifies an interaction between rs2857532 and the HOXD9 promoter, suggesting this SNP is a leading causal variant. Transcriptomic profiling after HOXD9 overexpression reveals enrichment of HGSOC risk variants within HOXD9 target genes (P=6 × 10(-10) for risk variants (P<10(-4)) within 10 kb of a HOXD9 target gene in ovarian cells), suggesting a broader role for this network in genetic susceptibility to HGSOC.

YAP induces high-grade serous carcinoma in fallopian tube secretory epithelial cells

Accumulating evidence indicates that ovarian high-grade serous carcinoma (HGSC) originates from fallopian tube secretory epithelial cells (FTSECs). However, the molecular mechanisms underlying the initiation and progression of HGSC derived from FTSECs remains unclear. In this study, we found that the Hippo/Yes-associated protein (YAP) signaling pathway has a critical role in the initiation and progression of fallopian tube and ovarian HGSC. Importantly, YAP was overexpressed in inflammatory and cancerous fallopian tube tissues. Further, overexpression of wild-type YAP, or constitutively active YAP in immortalized FTSECs, induced cell proliferation, migration, colony formation and tumorigenesis. Moreover, the Hippo/YAP and the fibroblast growth factor (FGF) signaling pathways formed an autocrine/paracrine-positive feedback loop to drive the progression of the FTSEC-derived HGSC. Evidence in this study strongly suggests that combined therapy with inhibitors of YAP (such as verteporfin) and FGF receptors (such as BGJ398) can provide a novel therapeutic strategy to treat fallopian tube and ovarian HGSC.

Abstract POSTER-BIOL-1324A: Loss of DYRK1A promotes transformation of the fallopian tube epithelial cells by oncogenic ras

Purpose of the study: High-grade serous ovarian carcinoma (HGSOC) is an aggressive form of ovarian cancer that is characterized by nearly ubiquitous presence of somatic mutations in TP53 gene and widespread gene copy number variations. It is likely that some of these genetic alterations cooperate with TP53 mutations in the pathogenesis of HGSOC; however, the specific roles of individual genes that are frequently gained or lost in HGSOC are only beginning to emerge. We have previously characterised an important role of DYRK1A protein kinase in the ability of human cells to undergo G0/G1 cell cycle arrest and oncogenic-Ras induced senescence. DYRK1A is required for the assembly of the DREAM repressor complex that controls the genes involved in cell cycle progression; this function of DYRK1A could be promoted by LATS kinases of the Hippo tumor suppressor pathway. Analysis of the The Cancer Genome Atlas (TCGA) ovarian dataset revealed loss of heterozygosity (LOH) of DYRK1A gene in over 25% HGSOC tumors. Therefore, we sought to determine whether loss of DYRK1A function can contribute to ovarian carcinogenesis.

Experimental Procedures: A panel of human ovarian cancer cell lines was used to determine the levels of DYRK1A and its ability to suppress cell proliferation. The fallopian tube epithelial cell (FTEC) cell lines with stable shRNA knock-down of DYRK1A were used in transformation assays with ovarian cancer-relevant oncogenes. Bioinformatics analysis of the TGCA ovarian oncogenomic dataset was applied to determine whether DYRK1A loss in HGSOC could lead to perturbation of any specific gene expression programs.

Summary of Data: It was found that depletion of DYRK1A promotes oncogenic transformation of the FTEC cells expressing mutant p53R175H and oncogenic HRASG12V. Rescue of DYRK1A expression in these cells resulted in arrest of proliferation and senescence. DYRK1A protein levels were reduced in a subset of ovarian cancer cell lines; overexpression of active but not the kinase-inactive DYRK1A suppressed the proliferation of these cells. Gene Set Enrichment Analysis (GSEA) of the TCGA HGSOC dataset revealed upregulated expression of the DREAM target genes in a subset of samples with LOH of both DYRK1A and LATS1 genes.

Conclusion: Our findings support the role of DYRK1A as an ovarian tumor supressor and suggest that loss of DYRK1A function in HGSOC could lead to activation of transcription of the genes involved in cell proliferation.

Citation Format: Larisa Litovchick, Siddharth Saini, Alison Karst, Lan Hu, Ronny Drapkin, James A. DeCaprio. Loss of DYRK1A promotes transformation of the fallopian tube epithelial cells by oncogenic ras [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1324A.

Abstract 970: Broad therapy resistance is induced by suppression of apoptotic priming by lineage programs and oncogenic activation

Understanding the mechanisms of resistance to anticancer therapies may improve personalized treatment regimens and responses to therapy. The mitochondrial apoptosis pathway is activated by most targeted and cytotoxic therapies and represents a node that may be modulated for broad therapy resistance. It has been shown that some cancers, especially those of hematopoietic origin, are primed for apoptosis (as measured by BH3 Profiling) and consequently undergo apoptosis readily in response to therapies while others are unprimed and resistant. However, despite the importance of apoptotic priming in governing response to anticancer therapies, the upstream molecular determinants of apoptotic priming are unknown. Prior work has shown that oncogenes, including c-Myc, can sensitize some cells to apoptosis. We therefore hypothesized that lineage programming and activation of oncogenes may modulate apoptotic priming in normal cells undergoing neoplastic transformation.

Using numerous in vitro and in vivo ovarian, breast, kidney and liver tumorigenesis models we discovered that the strongest determinant of apoptotic priming and chemosensitivity in a cancer cell is the level of priming measured in the cell of origin. To illustrate, ovarian adenocarcinomas, which originate from primed ovarian or fallopian tube epithelia, are considerably more primed than hepatocellular carcinomas originating from unprimed precursors. Notably, we also found that activation of certain oncogenes can meaningfully increase apoptotic priming and chemosensitivity while others decrease it. For example, transformation of normal epithelial cells via forced expression of the c-Myc oncogene increased priming and chemosensitivity. In contrast, activation of Ras in isogenic cells dramatically decreased both priming and chemosensitivity. We have systematically characterized the effects of 27 oncogenes on apoptotic priming and chemosensitivity including PI3K, Notch, Src, BRAF, β-catenin, Akt, and Aurora B kinase. Certain subsets of oncogenes consistently reduced apoptotic priming in cells undergoing transformation and, in combination with cell lineage programs, established broad resistance to targeted and cytotoxic therapies. Importantly, our experimental findings are complemented by clinical correlates. Overall, this work may aid efforts to deploy personalized and efficacious cancer treatments and enhance our knowledge of how cancers evade cell death, which is a hallmark of cancer.

Citation Format: Kristopher A. Sarosiek, Alison Karst, Peter Winter, Antonio Sorrentino, Sourav Bandyopadhyay, Andrei Goga, Kris C. Wood, Ronny Drapkin, Anthony Letai. Broad therapy resistance is induced by suppression of apoptotic priming by lineage programs and oncogenic activation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 970. doi:10.1158/1538-7445.AM2015-970

Cell-type-specific enrichment of risk-associated regulatory elements at ovarian cancer susceptibility loci

Understanding the regulatory landscape of the human genome is a central question in complex trait genetics. Most single-nucleotide polymorphisms (SNPs) associated with cancer risk lie in non-protein-coding regions, implicating regulatory DNA elements as functional targets of susceptibility variants. Here, we describe genome-wide annotation of regions of open chromatin and histone modification in fallopian tube and ovarian surface epithelial cells (FTSECs, OSECs), the debated cellular origins of high-grade serous ovarian cancers (HGSOCs) and in endometriosis epithelial cells (EECs), the likely precursor of clear cell ovarian carcinomas (CCOCs). The regulatory architecture of these cell types was compared with normal human mammary epithelial cells and LNCaP prostate cancer cells. We observed similar positional patterns of global enhancer signatures across the three different ovarian cancer precursor cell types, and evidence of tissue-specific regulatory signatures compared to non-gynecological cell types. We found significant enrichment for risk-associated SNPs intersecting regulatory biofeatures at 17 known HGSOC susceptibility loci in FTSECs (P = 3.8 × 10(-30)), OSECs (P = 2.4 × 10(-23)) and HMECs (P = 6.7 × 10(-15)) but not for EECs (P = 0.45) or LNCaP cells (P = 0.88). Hierarchical clustering of risk SNPs conditioned on the six different cell types indicates FTSECs and OSECs are highly related (96% of samples using multi-scale bootstrapping) suggesting both cell types may be precursors of HGSOC. These data represent the first description of regulatory catalogues of normal precursor cells for different ovarian cancer subtypes, and provide unique insights into the tissue specific regulatory variation with respect to the likely functional targets of germline genetic susceptibility variants for ovarian cancer.

Mesenchymal gene program-expressing ovarian cancer spheroids exhibit enhanced mesothelial clearance

Metastatic dissemination of ovarian tumors involves the invasion of tumor cell clusters into the mesothelial cell lining of peritoneal cavity organs; however, the tumor-specific factors that allow ovarian cancer cells to spread are unclear. We used an in vitro assay that models the initial step of ovarian cancer metastasis, clearance of the mesothelial cell layer, to examine the clearance ability of a large panel of both established and primary ovarian tumor cells. Comparison of the gene and protein expression profiles of clearance-competent and clearance-incompetent cells revealed that mesenchymal genes are enriched in tumor populations that display strong clearance activity, while epithelial genes are enriched in those with weak or undetectable activity. Overexpression of transcription factors SNAI1, TWIST1, and ZEB1, which regulate the epithelial-to-mesenchymal transition (EMT), promoted mesothelial clearance in cell lines with weak activity, while knockdown of the EMT-regulatory transcription factors TWIST1 and ZEB1 attenuated mesothelial clearance in ovarian cancer cell lines with strong activity. These findings provide important insights into the mechanisms associated with metastatic progression of ovarian cancer and suggest that inhibiting pathways that drive mesenchymal programs may suppress tumor cell invasion of peritoneal tissues.

Abstract 4290: c-Myc and Ras differentially regulate mitochondrial apoptotic priming and chemosensitivity

Successful treatment of most human cancers is dependent on tumor cell sensitivity to chemotherapy yet the basis for chemosensitivity is poorly understood. We have previously shown that a cancer's proximity to the apoptotic threshold, a property we call "apoptotic priming," governs its chemosensitivity in patients with multiple myeloma, ALL, AML and ovarian cancer. The genetic and molecular events that underlie the differential priming in tumors, however, are currently unknown. Utilizing in vitro ovarian, kidney and lung tumorigenesis models we find that oncogenes are powerful modulators of apoptotic priming and are consequently responsible for differential chemosensitivity. For example, forced expression of the c-Myc oncogene increases priming and chemosensitivity of immortalized normal epithelium. In contrast, Ras activation in isogenic cells dramatically decreases both priming and chemosensitivity. Our in vitro findings are validated by clinical observations. Apoptotic priming, an important determinant of patient outcomes, is modulated in contrasting manners by oncogenes.

Citation Format: Kristopher A. Sarosiek, Triona Ni Chonghaile, Alison Karst, Luv Patel, Ronny Drapkin, Anthony Letai. c-Myc and Ras differentially regulate mitochondrial apoptotic priming and chemosensitivity. [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 4290. doi:10.1158/1538-7445.AM2013-4290

Abstract PR5: Treatment of ovarian cancer with targeted tumor-penetrating siRNA nanocomplexes

Whole-genome analysis of cancer samples is identifying many potential therapeutic targets, by virtue of their being frequently mutated or functionally essential in specific types of cancer. However, we lack efficient ways to test the therapeutic benefit of modulating targets in vivo. RNAi offers one potential solution; however, approaches to deliver siRNA in vivo have been challenging due to their susceptibility to serum nucleases, endosomal entrapment, and stimulation of innate immunity. Furthermore, nanoparticle- and antibody-based siRNA delivery approaches have historically suffered from limited tumor penetration and low transvascular transit, thereby limiting the applicability of parenchymal siRNA targets. Here we describe a tumor penetrating nanocomplex (TPN) comprised of siRNA complexed to a tandem tumor-penetrating and membrane-translocating peptide, which enables the homing of siRNA deep into tumor parenchyma. Upon complexation with siRNA, the resulting nanocomplex is stable, non-immunostimulatory, displays homing peptides in a multivalent fashion that increases their binding avidity and delivers siRNA to the cytosol of tumor cells through receptor-specific interactions and membrane translocation. Upon systemic administration into mice, this nanocomplex penetrates into the parenchyma of metastatic peritoneal tumors and silences target genes in cells of interest in a receptor-specific manner. We employed TPNs in vivo to evaluate ID4, a novel candidate oncogene in ovarian cancer, which we identified by combining genome-scale RNAi screening of cancer cell lines with genome-scale sequence analysis of patient tumors. We show that treatment of tumor-bearing mice with ID4-specific TPNs suppresses tumor growth and significantly improved survival. These findings provide a framework for the identification, credentialing, and understanding of novel cancer targets as well as validating a specific therapeutic target in ovarian cancer.

This abstract is also presented as Poster B2.

Citation Format: Yin Ren, Hiu Wing Cheung, Ronny Drapkin, David Root, Justin Lo, Valentina Fogal, Erkki Ruoslahti, William Hahn, Sangeeta Bhatia, Geoffrey von Maltzahn, Amit Agrawal, Glenn Cowley, Barbara Weir, Jesse Boehm, Pablo Tamayo, Jill Mesirov, Alison Karst. Treatment of ovarian cancer with targeted tumor-penetrating siRNA nanocomplexes [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr PR5.

'Dosimetric breast size': a new and useful parameter for the prediction of local recurrence after breast conservative treatment

To evaluate the risk of local recurrence following breast-conserving therapy for breast cancer, we measured the distance between each entry point of the irradiation on the surface of the breast in line with the axis of the external and internal tangential fields (dosimetric breast size). 652 breast cancer patients were retrospectively analysed, with a median age of 51 years and a median follow-up of 99 months (range 84-192). There were 50 local recurrences, 44 isolated and 6 associated with nodal recurrence or metastases. The global rates of local recurrences at 5 and 10 years were 5.3% and 9%, respectively (Kaplan-Meier analysis). Following a Cox's multivariate analysis, the only significant and independent parameters related to local recurrence were quality of excision, age at diagnosis and dosimetric breast size. For a small dosimetric breast size (< or = 10 cm), the rate of local recurrence was 14.1 compared with 11.8 for medium dosimetric breast size (> 10 cm-< or = 12 cm) and 5.2 for large dosimetric breast size (> 12 cm). If the analysis was restricted to only those with complete excision, then the relative risk for a patient with a small dosimetric breast size was three times that for a large breast size.

Apolipoprotein E genotypes in Parkinson's disease with and without dementia

The apolipoprotein E gene (Apo E) type 4 allele is a genetic risk factor influencing the development and age of onset of Alzheimer's disease. Because Parkinson's disease shares many characteristics of Alzheimer's disease, we studied the frequencies of Apo E genotypes in a cohort of 52 Parkinson's disease patients with dementia and 61 patients without dementia. Dementia was determined per National Institute of Neurological and Communicative Disorders and Stroke criteria and Mattis Dementia Rating Scale (DRS) < 126. Normal cognition was defined as DRS > 132. Apo E genotype and allele frequencies did not differ between demented and nondemented parkinsonian patients. Neither group's genotype and allele frequencies differed from that of a nondemented population of 78 controls. We conclude that the Apo E epsilon 4 allele influences neither the development of Parkinson's disease nor the dementia associated with Parkinson's disease.

Temperature dependence of the activity of DNA-modifying enzymes: endonucleases and DNA ligase

The activities of 17 endonucleases: the restriction endonucleases AvaI, Bam HI, EcoRI, HindIII, PstI and SalI, which cleave pBR322 DNA once: AluI, AvaII, CfoI, HaeIII, HhaI, HinfI, HpaII and TaqI, which cut pBR322 DNA several times, and three 'unspecific' nucleases (S1 nuclease, staphylococcal nuclease and DNase I from bovine pancreas) were determined between 0 degrees and 65 degrees C. The reaction was followed by the disappearance of covalently closed circular pBR322 DNA, using the alkaline ethidium fluorescence assay of Morgan et al. [Nucleic Acids Res. (1979) 7, 547-594]; the activity of T4 DNA ligase was similarly measured by the conversion of nicked circular DNA to closed circular DNA. For each enzyme, small aliquots of the same solution were incubated at different temperatures simultaneously in a temperature gradient device, resulting in a high relative precision. The experimental results are summarized by the simplest possible theoretical description, using linear or exponential kinetics and apparent activation energies Ea for the enzymatic reaction, Ei for the enzyme inactivation and Ti for the inactivation temperature. To a good approximation these three parameters suffice for describing the temperature dependence of the activity of most of the enzymes.