Abstract PD5-06: PD5-06 CCN6 suppresses spindle metaplastic breast carcinoma in part via antagonizing Wnt/β-catenin signaling

Background: Metaplastic breast carcinomas (mBrCAs) are a rare and highly aggressive subtype of triple negative breast cancer, with histological evidence of non-glandular differentiation and frequent activation of the canonical (-catenin-dependent) Wnt pathway. Our laboratory has reported that CCN6 is expressed in normal mammary epithelium, but CCN6 expression is lost in 68% of spindle mBrCAs. We found mice with mammary epithelial cell-specific conditional deletion of Ccn6 (MMTV-Cre; Ccn6fl/fl mice) develop mammary tumors that recapitulate human spindle mBrCAs, including upregulation of Wnt pathway genes. We investigated if and how secreted CCN6 protein functions in tumor suppression in spindle mBrCA via effects on the canonical Wnt pathway. Methods: To investigate CCN6 binding to the Wnt co-receptors LRP6 and FZD8 proteins, we performed Flag-IPs on MDA-MB231 mesenchymal-like breast cancer cells expressing Flag-CCN6 or vector. Effects of CCN6 on b-catenin subcellular localization and gene and protein expression were studied by IHC, IF, qRT-PCR and immunoblot in human cell lines and MMTV-Cre;Ccn6fl/fl tumors. To test effects of recombinant CCN6 on canonical Wnt signaling, we used the Leading-Light Wnt Reporter Assay and also tested CCN6 effects in WNT3A- and WNT10B-mediated Wnt signaling activation and on MDA-MB231 cell invasion. To study b-catenin/TCF function in invasive growth of CCN6-deficient cancer cells, we employed two independent approaches: i) expression of a dominant-negative Tcf4 (dnTcf4) versus control vector in MMTV-Cre; Ccn6fl/fl tumor-derived cells; and ii) expression of a constitutively active mutant (S33Y) b-catenin in concert with treatment with recombinant human CCN6 (rhCCN6; 500 ug/ml) versus BSA control. Syngeneic orthotopic mammary tumor transplants of MMTV-Cre;Ccn6fl/fl were used in vivo for rescue experiments with i.p. injections of rhCCN6 or BSA. We monitored tumor growth and morphology, and performed IHC to determine b-catenin localization and expression. Results: We found in co-IPs that CCN6 interacts with LRP6 and FZD8 to form a complex that antagonizes canonical Wnt signaling. CCN6 ectopic expression in MDA-MB231 cells led to reduced nuclear and increased membrane localization of b-catenin and decreased invasive growth in vitro. In vivo, CCN6 protein administration to MMTV-Cre; Ccn6fl/fl mice reduced tumor growth and was linked to decreased nuclear b-catenin in the tumors. Conclusion: CCN6 antagonizes canonical Wnt/b-catenin in part by binding Wnt ligands, leading to reduced active b-catenin in the cytoplasm and nucleus. Our data indicate a critical role for b-catenin activation for CCN6-deficient mBrCA tumor phenotypes. In vivo, rhCCN6 protein reduces tumorigenesis in MMTV-Cre; Ccn6fl/fl mBrCA tumors, highlighting how CCN6 restoration or b-catenin inhibition could be new therapeutic approaches for mBrCAs.

Citation Format: Maria E. Gonzalez, Eric R. Fearon, Celina Kleer. PD5-06 CCN6 suppresses spindle metaplastic breast carcinoma in part via antagonizing Wnt/β-catenin signaling [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 PD5-06.

Microenvironmental ammonia enhances T cell exhaustion in colorectal cancer

Effective therapies are lacking for patients with advanced colorectal cancer (CRC). The CRC tumor microenvironment has elevated metabolic waste products due to altered metabolism and proximity to the microbiota. The role of metabolite waste in tumor development, progression, and treatment resistance is unclear. We generated an autochthonous metastatic mouse model of CRC and used unbiased multi-omic analyses to reveal a robust accumulation of tumoral ammonia. The high ammonia levels induce T cell metabolic reprogramming, increase exhaustion, and decrease proliferation. CRC patients have increased serum ammonia, and the ammonia-related gene signature correlates with altered T cell response, adverse patient outcomes, and lack of response to immune checkpoint blockade. We demonstrate that enhancing ammonia clearance reactivates T cells, decreases tumor growth, and extends survival. Moreover, decreasing tumor-associated ammonia enhances anti-PD-L1 efficacy. These findings indicate that enhancing ammonia detoxification can reactivate T cells, highlighting a new approach to enhance the efficacy of immunotherapies.

DOT1L affects colorectal carcinogenesis via altering T cell subsets and oncogenic pathway

Chronic inflammation and oncogenic pathway activation are key-contributing factors in colorectal cancer pathogenesis. However, colorectal intrinsic mechanisms linking these two factors in cancer development are poorly defined. Here, we show that intestinal epithelial cell (IEC)-specific deletion of Dot1l histone methyltransferase (Dot1l^ΔIEC) reduced H3K79 dimethylation (H3K79me2) in IECs and inhibited intestinal tumor formation in Apc^Min- and AOM-DSS-induced colorectal cancer models. IEC-Dot1l abrogation was accompanied by alleviative colorectal inflammation and reduced Wnt/β-catenin signaling activation. Mechanistically, Dot1l deficiency resulted in an increase in Foxp3⁺RORϒ⁺ regulatory T (Treg) cells and a decrease in inflammatory Th17 and Th22 cells, thereby reducing local inflammation in the intestinal tumor microenvironment. Furthermore, Dot1l deficiency caused a reduction of H3K79me2 occupancies in the promoters of the Wnt/β-catenin signaling genes, thereby diminishing Wnt/β-catenin oncogenic signaling pathway activation in colorectal cancer cells. Clinically, high levels of tumor H3K79me2 were detected in patients with colorectal carcinomas as compared to adenomas, and negatively correlated with RORϒ⁺FOXP3⁺ Treg cells. Altogether, we conclude that DOT1L is an intrinsic molecular node connecting chronic immune activation and oncogenic signaling pathways in colorectal cancer. Our work suggests that targeting the DOT1L pathway may control colorectal carcinogenesis. Significance: IEC-intrinsic DOT1L controls T cell subset balance and key oncogenic pathway activation, impacting colorectal carcinogenesis.

Reuterin in the healthy gut microbiome suppresses colorectal cancer growth through altering redox balance

Microbial dysbiosis is a colorectal cancer (CRC) hallmark and contributes to inflammation, tumor growth, and therapy response. Gut microbes signal via metabolites, but how the metabolites impact CRC is largely unknown. We interrogated fecal metabolites associated with mouse models of colon tumorigenesis with varying mutational load. We find that microbial metabolites from healthy mice or humans are growth-repressive, and this response is attenuated in mice and patients with CRC. Microbial profiling reveals that Lactobacillus reuteri and its metabolite, reuterin, are downregulated in mouse and human CRC. Reuterin alters redox balance, and reduces proliferation and survival in colon cancer cells. Reuterin induces selective protein oxidation and inhibits ribosomal biogenesis and protein translation. Exogenous Lactobacillus reuteri restricts colon tumor growth, increases tumor reactive oxygen species, and decreases protein translation in vivo. Our findings indicate that a healthy microbiome and specifically, Lactobacillus reuteri, is protective against CRC through microbial metabolite exchange.

Altering the Microbiome Inhibits Tumorigenesis in a Mouse Model of Oviductal High-Grade Serous Carcinoma

Studies have shown bacteria influence the initiation and progression of cancers arising in sites that harbor rich microbial communities, such as the colon. Little is known about the potential for the microbiome to influence tumorigenesis at sites considered sterile, including the upper female genital tract. The recent identification of distinct bacterial signatures associated with ovarian carcinomas suggests microbiota in the gut, vagina, or elsewhere might contribute to ovarian cancer pathogenesis. Here, we tested whether altering the microbiome affects tumorigenesis in a mouse model of high-grade serous carcinoma (HGSC) based on conditional oviduct-specific inactivation of the Brca1, Trp53, Rb1, and Nf1 tumor suppressor genes. Cohorts of control (n = 20) and antibiotic-treated (n = 23) mice were treated with tamoxifen to induce tumor formation and then monitored for 12 months. The antibiotic cocktail was administered for the first 5 months of the monitoring period in the treatment group. Antibiotic-treated mice had significantly fewer and less advanced tumors than control mice at study endpoint. Antibiotics induced changes in the composition of the intestinal and vaginal microbiota, which were durable in the fecal samples. Clustering analysis showed particular groups of microbiota are associated with the development of HGSC in this model. These findings demonstrate the microbiome influences HGSC pathogenesis in an in vivo model that closely recapitulates the human disease. Because the microbiome can modulate efficacy of cancer chemo- and immunotherapy, our genetically engineered mouse model system may prove useful for testing whether altering the microbiota can improve the heretofore poor response of HGSC to immunotherapies. SIGNIFICANCE: This study provides strong in vivo evidence for a role of the microbiome in ovarian cancer pathogenesis.

Abstract B50: Direct interrogation of the incessant ovulation hypothesis in a high-fidelity mouse model of high-grade serous cancer

The biologic basis for factors that modify risk of developing high-grade serous carcinoma remains understudied. In particular, the “Incessant Ovulation” hypothesis remains a plausible model to unify the observed risks associated with more ovulations (increasing age, early menarche/late menopause) as well as protection conferred by oral contraceptive use, multiparity, and breastfeeding. We used genetically engineered mouse models (GEMMs) of HGSC to directly interrogate the role of aging and multiparity as deleterious and protective risk factors, respectively, for HGSC development. Specifically, we utilized oviductal-restricted tamoxifen-inducible Cre recombinase to drive conditional bi-allelic inactivation of key tumor-suppressor genes (Brca1, Trp53, Rb1, Nf1) in the murine fallopian tube (oviduct). In our genetically engineered mice, autochthonous tumors arise with high penetrance in response to tamoxifen treatment, albeit with prolonged latency. As a consequence, the models allow us to evaluate effects of multiparity and aging on tumor development and progression. To test effects of multiparity, two cohorts of mice were tested, one with two floxed alleles of all 4 TSGs (BPRN), and another in which one allele of Nf1 was wild-type (BPRNfl/+). Mice were treated with tamoxifen and then continuously caged with a breeding male for a total of up to 9 pregnancies. Control mice were treated with tamoxifen and then remained nulliparous until sacrifice. The total number of pregnancies ranged from 5 to 9 for each mouse in the multiparous groups. Mice were euthanized 62 weeks post-TAM or earlier, if humane endpoints were reached. No apparent differences in diagnosis at study endpoint was observed in the multiparous BPRN versus nulliparous group (p=0.34, Mantel-Haenszel Chi-square test of association). Interestingly, the control mice showed a trend for worse diagnosis compared to the BPRNfl/+ mice at study endpoint (p=0.02). In the aging cohort, control BPRN mice were exposed to tamoxifen at 8 weeks of age and followed to humane endpoints. The experimental group was aged to 9 months, exposed to tamoxifen and then followed to humane endpoints. Survival post-TAM was observed to be shortened in the older animals (median 45.5 weeks versus 57 weeks in control mice, log rank test p=0.0033). Using Cox proportional hazard models, aging was associated with a hazard ratio of 2.8 with 95% CI of 1.4-5.9. Collectively these data suggest that multiple pregnancies alone delays HGSC development and progression in certain genetic contexts, while in contrast, tumor induction in aged mice is associated with significantly shorter survival. Together, these results help credential these GEMMs as useful tools with which to explore the biologic basis for risk factors presumed to underly the development of HGSC.

Citation Format: Yali Zhai, Kevin McCool, Rork Kuick, Lixing Chen, Eric R. Fearon, Kathleen R. Cho. Direct interrogation of the incessant ovulation hypothesis in a high-fidelity mouse model of high-grade serous cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B50.

Cancer: Context Is Key for E-cadherin in Invasion and Metastasis

A recent paper demonstrates how tissue context impacts the breast cancer cell phenotype. Loss of the E-cadherin tumor suppressor protein enhanced cell invasion, but inhibited multiple steps in metastatic spread due to the accumulation of reactive oxygen species and induction of apoptosis.

Murine Oviductal High-Grade Serous Carcinomas Mirror the Genomic Alterations, Gene Expression Profiles, and Immune Microenvironment of Their Human Counterparts

Robust preclinical models of ovarian high-grade serous carcinoma (HGSC) are needed to advance our understanding of HGSC pathogenesis and to test novel strategies aimed at improving clinical outcomes for women with the disease. Genetically engineered mouse models of HGSC recapitulating the likely cell of origin (fallopian tube), underlying genetic defects, histology, and biologic behavior of human HGSCs have been developed. However, the degree to which the mouse tumors acquire the somatic genomic changes, gene expression profiles, and immune microenvironment that characterize human HGSCs remains unclear. We used integrated molecular characterization of oviductal HGSCs arising in the context of Brca1, Trp53, Rb1, and Nf1 (BPRN) inactivation to determine whether the mouse tumors recapitulate human HGSCs across multiple domains of molecular features. Targeted DNA sequencing showed the mouse BPRN tumors, but not endometrioid carcinoma-like tumors based on different genetic defects (e.g., Apc and Pten), acquire somatic mutations and widespread copy number alterations similar to those observed in human HGSCs. RNA sequencing showed the mouse HGSCs most closely resemble the so-called immunoreactive and mesenchymal subsets of human HGSCs. A combined immuno-genomic analysis demonstrated the immune microenvironment of BPRN tumors models key aspects of tumor-immune dynamics in the immunoreactive and mesenchymal subtypes of human HGSC, with enrichment of immunosuppressive cell subsets such as myeloid-derived suppressor cells and regulatory T cells. The findings further validate the BPRN model as a robust preclinical experimental platform to address current barriers to improved prevention, diagnosis, and treatment of this often lethal cancer. SIGNIFICANCE: The acquired gene mutations, broad genomic alterations, and gene expression and immune cell-tumor axis changes in a mouse model of oviductal serous carcinoma closely mirror those of human tubo-ovarian high-grade serous carcinoma.

Abstract AP16: MODELING ENDOMETRIOID AND HIGH GRADE SEROUS CARCINOMAS IN THE MOUSE USING CRISPR/CAS9-MEDIATED SOMATIC GENE EDITING IN FALLOPIAN TUBE EPITHELIUM

Genetically engineered mouse models (GEMMs) have contributed significantly to our understanding of the role of specific gene defects in human cancers. GEMMs that recapitulate many of the molecular and biological characteristics of various histologic subtypes of ovarian carcinomas have already been developed. However, conventional methods of GEMM development based on Cre-lox technology require the time-consuming and labor-intensive processes of transgenic line production and cross-breeding, a problem that is exacerbated when developing cancer GEMMs based on multiple genetic defects. The RNA-guided Cas9 nuclease from the microbial clustered regularly interspaced short palindromic repeats (CRISPR) adaptive immune system potentially offers a more rapid and versatile alternative platform for tumor modeling in the mouse, as it can be used to target multiple genomic loci simultaneously by specifying a 20-nt targeting sequence for each gene of interest. The development of gynecological cancer GEMMs using CRISPR/Cas9-mediated conditional gene editing has not yet been reported. We have tested this approach to generate endometrioid carcinoma (EC) and high-grade serous carcinoma (HGSC) in the mouse oviductal epithelium.

We first selected potentially optimal 20-nt sequences (guide RNAs) targeting the murine orthologs of the Apc and Pten tumor suppressor genes for the EC model, and the Brca1, Trp53, Rb1, and Nf1 genes for the HGSC model. Efficient cutting mediated by each guide RNA was validated in vitro by the Surveyor nuclease assay in NIH3T3 mouse fibroblasts. Next, we generated two transgenic mouse lines: one carrying a transgene with guide RNAs targeting Apc and Pten in tandem as a single guide RNA (sgAP) and a second carrying a transgene with a single guide RNA targeting Brca1, Trp53, Rb1, and Nf1 (sgBPRN). These transgenic lines were then crossed with Ovgp1-iCre-ERT2 and Rosa26LSL-Cas9-EGFP (Jackson laboratory) mice to allow for conditional (Tamoxifen-regulated) inactivation of Apc-Pten or Brca1-Trp53-Rb1-Nf1 specifically in the FTE. Endometrioid carcinomas were identified in Ovgp1-iCreERT2;Rosa26LSL-Cas9-EGFP;sgAP mice by 20 weeks post tamoxifen and early HGSC was present in an Ovgp1-iCreERT2; Rosa26LSL-Cas9-EGFP;sgBPRN mouse 34 weeks post tamoxifen treatment. The tumors derived from Cre-CRISPR/Cas9-sgRNA technology showed similar morphology and immunophenotypic characteristics to tumors arising in the models using Cre-lox technology based on the same genetic defects. Insertions/deletions (Indels) in tumor DNA were found in all of the targeted genes near the expected cut-sites, and confirmed by Sanger sequencing of cloned PCR products. All of the Indels resulted in predicted premature protein truncation and loss of function. Our results show that CRISPR/Cas9-sgRNA system genome editing can be used successfully to model gynecological cancers in mice.

Citation Format: Rong Wu, Carmine Stolfi, Yali Zhai, Eric R. Fearon, and Kathleen R. Cho. MODELING ENDOMETRIOID AND HIGH GRADE SEROUS CARCINOMAS IN THE MOUSE USING CRISPR/CAS9-MEDIATED SOMATIC GENE EDITING IN FALLOPIAN TUBE EPITHELIUM [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr AP16.

Abstract GMM-061: MOLECULAR CHARACTERIZATION OF MOUSE MODELS OF HIGH-GRADE SEROUS CARCINOMA ARISING IN THE OVIDUCT

We recently developed genetically engineered mouse models (GEMMs) of oviductal high-grade serous carcinoma (HGSC) based on conditional inactivation of several different combinations of tumor suppressor genes (Brca1, Trp53, Rb1, and Nf1) that are recurrently mutated in human HGSCs. The histopathological features of the mouse tumors closely mimic their human tumor counterparts. In order to characterize how well the mouse tumors recapitulate the molecular characteristics of human HGSCs, targeted exome sequencing was used to analyze the 32 most commonly mutated genes in human HGSC, in 60 mouse tumors arising in the context of Brca1, Trp53, Rb1, and/or Nf1 inactivation. We employed the sequence data to assess DNA copy number alterations (CNAs) and single nucleotide variants (SNVs) in the mouse tumors.

Compared to 14 normal tissues and 8 oviductal tumors arising in the context of Apc, Pten, ± Arid1a inactivation, the mouse HGSCs showed a high level of genomic instability, with many widely distributed CNAs – very similar to the widespread CNAs observed in human HGSCs. Targeted exome sequencing also showed that a subset of the mouse tumors acquired alterations observed in human HGSCs, including amplification of cMyc, and deletion of Pten. Variant analysis identified nonsynonymous SNVs in Csmd3, Crebbp, Pten, Mettl17, and Zymynd8 and a frameshift deletion of Pten. Sanger sequencing confirmed the presence of these somatic mutations in the mouse tumors and their absence in matched normal tissues. Loss of PTEN expression was observed in those tumors that acquired somatic Pten alterations.

These data show that HGSCs arising in our GEMMs have very similar molecular characteristics to their human tumor counterparts. The somatic alterations are likely acquired during the relatively lengthy period (several months) between tumor initiation and progression to overt malignancy. These features render the models particularly well suited for studying the early phases of HGSC development and for translational applications aimed at identifying effective strategies for HGSC prevention and early detection.

Citation Format: Yali Zhai, Yisheng Wang, Stephanie M. Schulman, Kevin Hu, Albert Liu, Scott A. Tomlins, Eric R. Fearon, and Kathleen R. Cho. MOLECULAR CHARACTERIZATION OF MOUSE MODELS OF HIGH-GRADE SEROUS CARCINOMA ARISING IN THE OVIDUCT [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-061.

Induction of endoplasmic reticulum stress and inhibition of colon carcinogenesis by the anti-helmintic drug rafoxanide

Colorectal cancer (CRC) remains one of the leading causes of mortality worldwide. Drug repositioning is a promising approach for new cancer therapies, as it provides the opportunity to rapidly advance potentially promising agents into clinical trials. The FDA-approved anti-helminthic drug rafoxanide was recently reported to antagonize the oncogenic function of the BRAF V600E mutant protein, commonly found in CRCs, as well as to inhibit the proliferation of skin cancer cells. These observations prompted us to investigate the potential anti-cancer effects of rafoxanide in CRC models. We found rafoxanide inhibited proliferation in CRC cells, but not in normal colonic epithelial cells. Rafoxanide's anti-proliferative action was associated with marked reduction in cyclin D1 protein levels and accumulation of cells in the G0/G1 phase. These effects relied on selective induction of the endoplasmic reticulum stress (ERS) response in CRC cells and were followed by caspase-dependent cell death. Systemic administration of rafoxanide to Apc^min/+ mice induced to develop CRCs caused ERS activation, proliferation inhibition and apoptosis induction in the neoplastic cells. Collectively, our data suggest rafoxanide might be repurposed as an anti-cancer drug for the treatment of CRC.

Lineage tracing suggests that ovarian endosalpingiosis does not result from escape of oviductal epithelium

Most high-grade serous carcinomas are thought to arise from Fallopian tube epithelium (FTE), but some likely arise outside of the tube, perhaps from ectopic tubal-type epithelium known as endosalpingiosis. Importantly, the origin of endosalpingiosis is poorly understood. The proximity of the tubal fimbriae to the ovaries has led to the proposal that disruptions in the ovarian surface that occur during ovulation may allow detached FTE to implant in the ovary and form tubal-type glands and cysts. An alternative model suggests that cells present in ectopic locations outside the Müllerian tract retain the capacity for multi-lineage differentiation and can form glands with tubal-type epithelium. We used double transgenic Ovgp1-iCreER^T2 ;R26R^LSL-eYFP mice, which express an eYFP reporter protein in OVGP1-positive tissues following transient tamoxifen (TAM) treatment, to track the fate of oviductal epithelial cells. Cohorts of adult mice were given TAM to activate eYFP expression in oviductal epithelium, and ovaries were examined at time points ranging from 2 days to 12 months post-TAM. To test whether superovulation might increase acquisition of endosalpingiosis, additional cohorts of TAM-treated mice underwent up to five cycles of superovulation and ovaries were examined at 1, 6, and 12 months post-TAM. Ovaries were sectioned in their entirety to identify endosalpingiosis. Immunohistochemical staining for PAX8, tubulin, OVGP1, and eYFP was employed to study endosalpingiosis lesions. Ovarian endosalpingiosis was identified in 14.2% of TAM-treated adult mice. The endosalpingiotic inclusion glands and cysts were lined by secretory and ciliated cells and expressed PAX8, tubulin, OVGP1, and eYFP. Neither age nor superovulation was associated with a significant increase in endosalpingiosis. Endosalpingiosis was also occasionally present in the ovaries of pre-pubertal mice. The findings imply that ovarian endosalpingiosis in the mouse does not likely arise as a consequence of detachment and implantation of tubal epithelium and other mechanisms may be relevant. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Silencing the GUCA2A-GUCY2C tumor suppressor axis in CIN, serrated, and MSI colorectal neoplasia

Colorectal cancers (CRCs) initiate through distinct mutations, including in APC pathway components leading to tubular adenomas (TAs); in BRAF, with epigenetic silencing of CDX2, leading to serrated adenomas (SAs); and in the DNA mismatch repair machinery driving microsatellite instability (MSI). Transformation through the APC pathway involves loss of the hormone GUCA2A that silences the tumor-suppressing receptor GUCY2C. Indeed, oral hormone replacement is an emerging strategy to reactivate GUCY2C and prevent CRC initiation and progression. Moreover, retained expression by tumors arising from TAs has established GUCY2C as a diagnostic and therapeutic target to prevent and treat metastatic CRC. Here, we defined the potential role of the GUCA2A-GUCY2C axis and its suitability as a target in tumors arising through the SA and MSI pathways. GUCA2A hormone expression was eliminated in TAs, SAs, and MSI tumors compared to their corresponding normal adjacent tissues. In contrast to the hormone, the tumor-suppressing receptor GUCY2C was retained in TA and MSI tumors. Surprisingly, GUCY2C expression was nearly eliminated in SAs, reflecting loss of the transcription factor CDX2. Changes in the GUCA2A-GUCY2C axis in human SAs and MSI tumors were precisely recapitulated in genetic mouse models. These data reveal the possibility of GUCA2A loss silencing GUCY2C in the pathophysiology of, and oral hormone replacement to restore GUCY2C signaling to prevent, MSI tumors. Also, they highlight the potential for targeting GUCY2C to prevent and treat metastases arising from TA and MSI tumors. In contrast, loss of GUCY2C excludes patients with SAs as candidates for GUCY2C-based prevention and therapy.

Guanylate cyclase C (GUCY2C) as a preventative and therapeutic target in colorectal cancers (CRCs) arising through divergent genomic pathways

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Background: CRCs arise through distinct mutations, including in APC pathway leading to tubular adenomas (TAs); in BRAF, with epigenetic silencing of CDX2, leading to serrated adenomas (SAs); and in the DNA mismatch repair machinery driving microsatellite instability (MSI). The APC pathway involves loss of the hormone guanylin, silencing the tumor suppressing receptor GUCY2C. Indeed, oral hormone replacement is an emerging strategy to reactivate GUCY2C and prevent CRC. Moreover, retained expression by tumors arising from TAs has established GUCY2C as a therapeutic target to prevent and treat metastatic CRC. Here, we defined the potential role of the guanylin-GUCY2C axis, and its suitability as a target, in tumors arising through the SA and MSI pathways. Methods: We compared guanylin-GUCY2C protein and mRNA expression between human TAs (n = 18), SAs (n = 15), MSI tumors (n = 7) and their matched normal adjacent tissue. Genetic mouse models of serrated and MSI tumors were used to confirm findings and elucidate mechanisms. Results: Guanylin hormone was eliminated in TAs, SAs and MSI tumors compared to their normal adjacent tissues. In contrast to the hormone, the tumor suppressing receptor GUCY2C was retained in TAs and MSI tumors. Surprisingly, GUCY2C expression was nearly eliminated in SAs reflecting loss of the transcription factor CDX2. Changes in the guanylin-GUCY2C axis in human SAs and MSI tumors were precisely recapitulated in genetic mouse models. Conclusions: Guanylin is universally lost at the earliest stages of transformation in tumors arising through divergent genomic mechanisms suggesting its utility as a biomarker of CRC initiation. These data reveal the possibility of guanylin loss silencing GUCY2C in the pathophysiology of, and oral hormone replacement to restore GUCY2C signaling to prevent, MSI tumors. Also, they highlight the potential for targeting GUCY2C to prevent and treat metastases arising from TAs and MSI tumors. In contrast, loss of GUCY2C excludes patients with SAs as candidates for GUCY2C-based prevention and therapy.

Abstract B76: Oncogenic Kras and Pik3ca can cooperate with inactivation of various tumor suppressor genes to generate high-grade serous carcinomas in the mouse oviduct

Recent studies suggest that most “ovarian” high-grade serous carcinomas (HGSCs) actually originate from precursors in the fallopian tubal epithelium (FTE) known as serous tubal intraepithelial carcinomas (STICs). We have developed Ovgp1-iCreERT2 mice in which the Ovgp1 promoter controls expression of tamoxifen-regulated Cre recombinase in the oviductal epithelium—equivalent to human FTE. We recently employed Ovgp1-iCreERT2 mice to show that FTE-specific inactivation of several different combinations of tumor suppressor genes (TSGs) that are recurrently mutated in human HGSCs—namely Brca1, Trp53, Rb1, and Nf1---results in STICs that progress to HGSC or Müllerian carcinosarcoma over several months, and to widely metastatic disease in a subset of mice. The histopathologic features of the mouse tumors closely resemble those of their human tumor counterparts.

The PI3K and RAS signaling pathways are frequently dysregulated in human HGSCs, often via amplification (and much less frequently mutation) of PIK3CA and KRAS, respectively. We wished to determine if mutant Kras or Pik3ca can cooperate with inactivation of various combinations of the aforementioned TSGs to generate oviductal HGSCs in the mouse, and were particularly interested in generating tumors in the context of intact Brca1/2. We found that conditional mutation of Kras (G12D) can cooperate with Brca1, Trp53, Rb1, and/or Nf1 inactivation in the generation of HGSCs in the mouse. Only two TSGs alterations (Trp53 and Rb1) were required for tumor development in the context of mutant Kras. HGSCs and/or carcinosarcomas developed rapidly in the context of mutant Kras and bi-allelic inactivation of Trp53 and Rb1, even when Brca1 and Brca2 were intact. HGSC and/or carcinosarcoma also developed in the oviducts following conditional mutation of Pik3ca (E545K) and various combinations of inactivated Brca1, Trp53, Rb1, and/or Nf1 alleles. When compared to our prior study of mouse tumors arising in the context of TSG inactivation alone, our data show that that 1) oncogenic Kras or Pik3ca accelerates tumor development and progression in mice carrying floxed Brca1, Trp53, Rb1, and/or Nf1 alleles compared to mice with the same TSG defects but without mutant Kras or Pik3ca; 2) oviductal tumorigenesis in the mouse requires fewer TSGs defects when mutant Kras or Pik3ca is also present; and 3) oviductal HGSCs can arise in the context of wild-type Brca1/2. Collectively, these models recapitulate the heterogeneity of human HGSC and should prove useful for testing new approaches for prevention, early detection, and treatment.

Citation Format: Yali Zhai, Stephanie Schulman, Neil Khandwala, Eric R. Fearon, Kathleen R. Cho. Oncogenic Kras and Pik3ca can cooperate with inactivation of various tumor suppressor genes to generate high-grade serous carcinomas in the mouse oviduct. [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 B76.

Thiosulfate sulfurtransferase-like domain-containing 1 protein interacts with thioredoxin

Rhodanese domains are structural modules present in the sulfurtransferase superfamily. These domains can exist as single units, in tandem repeats, or fused to domains with other activities. Despite their prevalence across species, the specific physiological roles of most sulfurtransferases are not known. Mammalian rhodanese and mercaptopyruvate sulfurtransferase are perhaps the best-studied members of this protein superfamily and are involved in hydrogen sulfide metabolism. The relatively unstudied human thiosulfate sulfurtransferase-like domain-containing 1 (TSTD1) protein, a single-domain cytoplasmic sulfurtransferase, was also postulated to play a role in the sulfide oxidation pathway using thiosulfate to form glutathione persulfide, for subsequent processing in the mitochondrial matrix. Prior kinetic analysis of TSTD1 was performed at pH 9.2, raising questions about relevance and the proposed model for TSTD1 function. In this study, we report a 1.04 Å resolution crystal structure of human TSTD1, which displays an exposed active site that is distinct from that of rhodanese and mercaptopyruvate sulfurtransferase. Kinetic studies with a combination of sulfur donors and acceptors reveal that TSTD1 exhibits a low Km for thioredoxin as a sulfane sulfur acceptor and that it utilizes thiosulfate inefficiently as a sulfur donor. The active site exposure and its interaction with thioredoxin suggest that TSTD1 might play a role in sulfide-based signaling. The apical localization of TSTD1 in human colonic crypts, which interfaces with sulfide-releasing microbes, and the overexpression of TSTD1 in colon cancer provide potentially intriguing clues as to its role in sulfide metabolism.

Mutant p53R270H drives altered metabolism and increased invasion in pancreatic ductal adenocarcinoma

Pancreatic cancer is characterized by nearly universal activating mutations in KRAS. Among other somatic mutations, TP53 is mutated in more than 75% of human pancreatic tumors. Genetically engineered mice have proven instrumental in studies of the contribution of individual genes to carcinogenesis. Oncogenic Kras mutations occur early during pancreatic carcinogenesis and are considered an initiating event. In contrast, mutations in p53 occur later during tumor progression. In our model, we recapitulated the order of mutations of the human disease, with p53 mutation following expression of oncogenic Kras. Further, using an inducible and reversible expression allele for mutant p53, we inactivated its expression at different stages of carcinogenesis. Notably, the function of mutant p53 changes at different stages of carcinogenesis. Our work establishes a requirement for mutant p53 for the formation and maintenance of pancreatic cancer precursor lesions. In tumors, mutant p53 becomes dispensable for growth. However, it maintains the altered metabolism that characterizes pancreatic cancer and mediates its malignant potential. Further, mutant p53 promotes epithelial-mesenchymal transition (EMT) and cancer cell invasion. This work generates new mouse models that mimic human pancreatic cancer and expands our understanding of the role of p53 mutation, common in the majority of human malignancies.

This study shows that sequential mutations in Kras and Trp53 collaborate in pancreatic cancer and establishes effects of interrupting mutant Trp53 at different tumor stages.

Lymph Node Metastases in Colon Cancer Are Polyclonal

Purpose: Recent studies have highlighted the existence of subclones in tumors. Lymph nodes are generally the first location of metastasis for most solid epithelial tumors, including colorectal cancer. We sought to understand the genetic origin of lymph node metastasis in colorectal cancer by evaluating the relationship between colorectal cancer subclones present in primary tumors and lymph nodes.Experimental Design: A total of 33 samples from seven colorectal cancers, including two or three spatially disparate regions from each primary tumor and one to four matched lymph nodes for each tumor, underwent next-generation whole-exome DNA sequencing, Affymetrix OncoScan SNP arrays, and targeted deep confirmatory sequencing. We performed mapping between SNPs and copy number events from the primary tumor and matched lymph node samples, allowing us to profile heterogeneity and the mutational origin of lymph node metastases. The computational method PyClone was used to define subclones within each tumor. The method Clonality Inference in Tumors Using Phylogeny (CITUP) was subsequently used to infer phylogenetic relationships among subclones.Results: We found that there was substantial heterogeneity in mutations and copy number changes among all samples from any given patient. For each patient, the primary tumor regions and matched lymph node metastases were each polyclonal, and the clonal populations differed from one lymph node to another. In some patients, the cancer cell populations in a given lymph node originated from multiple distinct regions of a tumor.Conclusions: Our data support a model of lymph node metastatic spread in colorectal cancer whereby metastases originate from multiple waves of seeding from the primary tumor over time. Clin Cancer Res; 24(9); 2214-24. ©2017 AACRSee related commentary by Gerlinger, p. 2032.

High-grade serous carcinomas arise in the mouse oviduct via defects linked to the human disease

Recent studies have suggested that the most common and lethal type of 'ovarian' cancer, i.e. high-grade serous carcinoma (HGSC), usually arises from epithelium on the fallopian tube fimbriae, and not from the ovarian surface epithelium. We have developed Ovgp1-iCreER^T2 mice in which the Ovgp1 promoter controls expression of tamoxifen-regulated Cre recombinase in oviductal epithelium - the murine equivalent of human fallopian tube epithelium (FTE). We employed Ovgp1-iCreER^T2 mice to show that FTE-specific inactivation of several different combinations of tumour suppressor genes that are recurrently mutated in human HGSCs - namely Brca1, Trp53, Rb1, and Nf1 - results in serous tubal intraepithelial carcinomas (STICs) that progress to HGSC or carcinosarcoma, and to widespread metastatic disease in a subset of mice. The cancer phenotype is highly penetrant and more rapid in mice carrying engineered alleles of all four tumour suppressor genes. Brca1, Trp53 and Pten inactivation in the oviduct also results in STICs and HGSCs, and is associated with diffuse epithelial hyperplasia and mucinous metaplasia, which are not observed in mice with intact Pten. Oviductal tumours arise earlier in these mice than in those with Brca1, Trp53, Rb1 and Nf1 inactivation. Tumour initiation and/or progression in mice lacking conditional Pten alleles probably require the acquisition of additional defects, a notion supported by our identification of loss of the wild-type Rb1 allele in the tumours of mice carrying only one floxed Rb1 allele. Collectively, the models closely recapitulate the heterogeneity and histological, genetic and biological features of human HGSC. These models should prove useful for studying the pathobiology and genetics of HGSC in vivo, and for testing new approaches for prevention, early detection, and treatment. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Impact of oviductal versus ovarian epithelial cell of origin on ovarian endometrioid carcinoma phenotype in the mouse

Endometrioid carcinoma (EC) is a relatively indolent ovarian carcinoma subtype that is nonetheless deadly if detected late. Existing genetically engineered mouse models (GEMMs) of the disease, based on transformation of the ovarian surface epithelium (OSE), take advantage of known ovarian EC driver gene lesions, but do not fully recapitulate the disease features seen in patients. An EC model in which the Apc and Pten tumour suppressor genes are conditionally deleted in murine OSE yields tumours that are biologically more aggressive and significantly less differentiated than human ECs. Importantly, OSE is not currently thought to be the tissue of origin of most ovarian cancers, including ECs, suggesting that tumour initiation in Müllerian epithelium may produce tumours that more closely resemble their human tumour counterparts. We have developed Ovgp1-iCreER^T2 mice in which the Ovgp1 promoter controls expression of tamoxifen (TAM)-regulated Cre recombinase in oviductal epithelium - the murine equivalent of human Fallopian tube epithelium. Ovgp1-iCreER^T2 ;Apc^fl/fl ;Pten^fl/fl mice treated with TAM or injected with adenovirus expressing Cre into the ovarian bursa uniformly develop oviductal or ovarian ECs, respectively. On the basis of their morphology and global gene expression profiles, the oviduct-derived tumours more closely resemble human ovarian ECs than do OSE-derived tumours. Furthermore, mice with oviductal tumours survive much longer than their counterparts with ovarian tumours. The slow progression and late metastasis of oviductal tumours resembles the relatively indolent behaviour characteristic of so-called Type I ovarian carcinomas in humans, for which EC is a prototype. Our studies demonstrate the utility of Ovgp1-iCreER^T2 mice for manipulating genes of interest specifically in the oviductal epithelium, and establish that the cell of origin is an important consideration in mouse ovarian cancer GEMMs. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract TMEM-018: IN VITRO MODELS OF HGSC BASED ON MURINE OVIDUCTAL EPITHELIAL ORGANOIDS

Mouse models of high-grade serous carcinoma (HGSC) arising from oviductal epithelium provide excellent in vivo systems with which to define the cellular and molecular events associated with HGSC development and progression. However, tumors in mice typically develop over months rather than weeks, and tumor progression in vivo cannot be easily monitored. Murine organoid models that closely mimic the biology of fallopian tube epithelium would facilitate research exploring HGSC pathogenesis.

We have developed Ovgp1-iCreERT2 mice in which the Ovgp1 promoter controls expression of tamoxifen (TAM)-inducible Cre recombinase in the oviductal epithelium – the murine equivalent of human fallopian tube epithelium. We have established long-term, 3-dimensional oviductal epithelial organoid cultures from Ovgp1-iCreERT2;R26LSL-EYFP double transgenic mice, and show that the organoids contain both ciliated and secretory cells, and express oviductal epithelial markers including cytokeratin 8, ER, PAX8 and OVGP1. Organoids treated in vitro with 4-hydroxy-tamoxifen (4-OH-TAM) activate the EYFP reporter.

Oviductal epithelial organoids established from Ovgp1-iCreERT2;Brca1del/fl; Trp53mut/fl;Rb1fl/fl (BPR) mice and treated in vitro with 4-OH-TAM show selection for the recombined tumor suppressor gene alleles by passage 6, accompanied by morphological and behavioral changes associated with neoplastic transformation. Stable organoid cultures can also be established from the oviductal epithelium of BPR mice treated in vivo with Tamoxifen (TAM).

We show that long-lived 3-dimensional organoids can be generated from normal oviductal tissue; can undergo Cre-mediated recombination in vitro to inactivate tumor suppressor genes relevant to human HGSC pathogenesis; and can acquire properties associated with neoplastic transformation in a relatively short period of time (weeks). As we have already generated Ovgp1-iCreERT2 mice with various combinations of constitutional and Cre-inducible mutant tumor suppressor gene (Trp53, Rb1, Brca1, Pten, Nf1, Apc) and oncogene (PIK3CA, KRAS) alleles, the roles of specific genetic alterations in HGSC pathogenesis can be explored in a relatively rapid and controlled experimental system.

Citation Format: Yali Zhai, Eric R. Fearon, and Kathleen R. Cho. IN VITRO MODELS OF HGSC BASED ON MURINE OVIDUCTAL EPITHELIAL ORGANOIDS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr TMEM-018.

Autocrine lysophosphatidic acid signaling activates β-catenin and promotes lung allograft fibrosis

Tissue fibrosis is the primary cause of long-term graft failure after organ transplantation. In lung allografts, progressive terminal airway fibrosis leads to an irreversible decline in lung function termed bronchiolitis obliterans syndrome (BOS). Here, we have identified an autocrine pathway linking nuclear factor of activated T cells 2 (NFAT1), autotaxin (ATX), lysophosphatidic acid (LPA), and β-catenin that contributes to progression of fibrosis in lung allografts. Mesenchymal cells (MCs) derived from fibrotic lung allografts (BOS MCs) demonstrated constitutive nuclear β-catenin expression that was dependent on autocrine ATX secretion and LPA signaling. We found that NFAT1 upstream of ATX regulated expression of ATX as well as β-catenin. Silencing NFAT1 in BOS MCs suppressed ATX expression, and sustained overexpression of NFAT1 increased ATX expression and activity in non-fibrotic MCs. LPA signaling induced NFAT1 nuclear translocation, suggesting that autocrine LPA synthesis promotes NFAT1 transcriptional activation and ATX secretion in a positive feedback loop. In an in vivo mouse orthotopic lung transplant model of BOS, antagonism of the LPA receptor (LPA1) or ATX inhibition decreased allograft fibrosis and was associated with lower active β-catenin and dephosphorylated NFAT1 expression. Lung allografts from β-catenin reporter mice demonstrated reduced β-catenin transcriptional activation in the presence of LPA1 antagonist, confirming an in vivo role for LPA signaling in β-catenin activation.

BRAFV600E cooperates with CDX2 inactivation to promote serrated colorectal tumorigenesis

While 20–30% of colorectal cancers (CRCs) may arise from precursors with serrated glands, only 8–10% of CRCs manifest serrated morphology at diagnosis. Markers for distinguishing CRCs arising from ‘serrated’ versus ‘conventional adenoma’ precursors are lacking. We studied 36 human serrated CRCs and found CDX2 loss or BRAF mutations in ~60% of cases and often together (p=0.04). CDX2^Null/BRAF^V600E expression in adult mouse intestinal epithelium led to serrated morphology tumors (including carcinomas) and BRAF^V600E potently interacted with CDX2 silencing to alter gene expression. Like human serrated lesions, CDX2^Null/BRAF^V600E-mutant epithelium expressed gastric markers. Organoids from CDX2^Null/BRAF^V600E–mutant colon epithelium showed serrated features, and partially recapitulated the gene expression pattern in mouse colon tissues. We present a novel mouse tumor model based on signature defects seen in many human serrated CRCs – CDX2 loss and BRAF^V600E. The mouse intestinal tumors show significant phenotypic similarities to human serrated CRCs and inform about serrated CRC pathogenesis.

DOI:http://dx.doi.org/10.7554/eLife.20331.001

CDX2: Linking Cell and Patient Fates in Colon Cancer

Administering adjuvant chemotherapy to stage II colon cancer patients is controversial due to limited benefit observed for this subpopulation. Recently, Dalerba et al. (2016) identified a subgroup of stage II patients that might benefit from adjuvant chemotherapy based on lack of CDX2 expression in their cancer stem cells.

Iron Uptake via DMT1 Integrates Cell Cycle with JAK-STAT3 Signaling to Promote Colorectal Tumorigenesis

Dietary iron intake and systemic iron balance are implicated in colorectal cancer (CRC) development, but the means by which iron contributes to CRC are unclear. Gene expression and functional studies demonstrated that the cellular iron importer, divalent metal transporter 1 (DMT1), is highly expressed in CRC through hypoxia-inducible factor 2α-dependent transcription. Colon-specific Dmt1 disruption resulted in a tumor-selective inhibitory effect of proliferation in mouse colon tumor models. Proteomic and genomic analyses identified an iron-regulated signaling axis mediated by cyclin-dependent kinase 1 (CDK1), JAK1, and STAT3 in CRC progression. A pharmacological inhibitor of DMT1 antagonized the ability of iron to promote tumor growth in a CRC mouse model and a patient-derived CRC enteroid orthotopic model. Our studies implicate a growth-promoting signaling network instigated by elevated intracellular iron levels in tumorigenesis, offering molecular insights into how a key dietary component may contribute to CRC.

Abstract 2684: Modeling a prototypical type I ovarian carcinoma in the mouse based on oviductal versus ovarian epithelial transformation: which is superior

Type I ovarian carcinomas are relatively indolent tumors that are nonetheless deadly if detected too late. Endometrioid carcinoma (EC) is a prototypical Type I ovarian cancer subtype. Existing mouse models of the disease based on transformation of the ovarian surface epithelium (OSE) take advantage of known EC genetic signatures but fail to capture fully the clinical disease progression and tumor phenotype. We previously described a mouse ovarian EC model in which the Apc and Pten tumor suppressor genes are conditionally deleted in the OSE via bursal injection of adenovirus expressing Cre recombinase (AdCre). We now report a new mouse model of EC in which the Ovgp1 (oviductal glycoprotein) promoter regulates expression of tamoxifen-inducible Cre recombinase specifically in the mouse oviductal epithelium (equivalent to human fallopian tube epithelium [FTE]), and not in the OSE or endometrium. Ovgp1-iCreERT2;Apcfl/fl;Ptenfl/fl mice treated with tamoxifen (TAM) develop oviductal tumors over months rather than weeks. The oviductal EC morphology closely resembles that of human ovarian ECs, with overt gland formation throughout, whereas ovarian bursal injection of AdCre in Ovgp1-iCreERT2;Apcfl/fl;Ptenfl/fl mice results in OSE-derived ECs that are poorly differentiated and include a prominent spindle cell component, consistent with our prior work. OSE-derived tumors progress rapidly, with none of the mice surviving beyond 14 weeks post-AdCre injection. Littermates with FTE-derived tumors survive much longer (>30 weeks post TAM). The slow progression and late (typically >16 weeks post TAM) metastasis to ovary and omentum associated with the FTE-derived tumors are more akin to the relatively indolent behavior characteristic of Type I ovarian carcinoma in humans. To further evaluate which of the two types of mouse tumors more closely resemble human ovarian tumors, we profiled gene expression in 6 FTE- and 5 OSE-derived Apc/Pten-deficient tumors, and compared the groups to each other and to data from 99 human ovarian carcinomas we analyzed previously (including 37 endometrioid, 41 serous, and 13 clear cell, and 8 mucinous carcinomas). Based on gene expression, the FTE-derived tumors are more correlated to every class of human ovarian tumors (p < 2 X10−6 in all 4 comparisons), with highest correlation to human ECs (particularly those with mutant CTNNB1) and mucinous carcinomas. This new model of EC, based on transformation of Mullerian epithelium rather than the OSE, will likely prove more suitable for translational applications, including pre-clinical testing of novel therapeutics for ovarian EC.

Citation Format: Rong Wu, Yali Zhai, Rork Kuick, Paloma Garcia, Anum Naseem, Eric R. Fearon, kathleen R. Cho. Modeling a prototypical type I ovarian carcinoma in the mouse based on oviductal versus ovarian epithelial transformation: which is superior. [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 2684.

Abstract 672: Differential effects of p53 mutations on cancer invasion and metastasis in a mouse model of colon cancer

Inactivation of the APC (adenomatous polyposis coli) tumor suppressor gene plays an important role in initiating most adenomas and colorectal cancers (CRCs). Somatic mutations in the TP53 tumor suppressor gene and KRAS oncogene are found in roughly 60% and 40% of CRCs, respectively, and contribute to tumor progression. In the vast majority of human CRCs, TP53 missense mutations lead to high levels of mutant p53 protein expression and the loss of the other wild type TP53 allele. To evaluate the role of TP53 missense mutations in CRC progression, we generated a genetically engineered mouse model of colorectal carcinoma, via combined targeting of Apc, Kras, and Trp53 alleles in mouse colon epithelium, focusing on comparing phenotypic effects of the murine equivalent of the human R273H mutation (i.e., murine R270H mutation) or a large deletion mutation of mouse Trp53. Inactivation of one allele Apc and activation of an oncogenic Kras allele in colon epithelium generated serrated and hyperplastic morphologic epithelium and adenomas. The addition of either the R270H missense mutation or the Trp53 null mutation to the Apc and Kras mutations led to markedly shortened survival of the mice, due to the development of multiple colon tumors in each mouse ranging from adenomas to late stage adenocarcinomas. Evidence of invasion into the smooth muscle and serosa area was found in both compound mice with missense or deletion mutations in Trp53, with the Trp53R270H mutant mice displaying an increased prevalence of deeply invasive tumors relative to the mice with deletion of Trp53. Furthermore, we found that the missense mutant Trp53R270H allele in combination with Apc and Kras mutations, but not the null-mutant Trp53 allele, was strongly linked to metastases to lymph nodes and lung. We have developed a useful mouse model of metastatic colon cancer that recapitulates the role of TP53 mutations in cooperating with APC and KRAS mutations in human CRC development and progression. In addition, our findings strongly suggest a powerful role for missense mutant p53 proteins compared to TP53 null mutations in promoting invasion and metastasis in CRC progression.

Citation Format: Ying Feng, Naoya Sakamoto, Maranne Green, Megan Greenn, Kathleen R. Cho, Eric R. Fearon. Differential effects of p53 mutations on cancer invasion and metastasis in a mouse model of colon 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 672.

Activation of Wnt/β-Catenin in Ewing Sarcoma Cells Antagonizes EWS/ETS Function and Promotes Phenotypic Transition to More Metastatic Cell States

Ewing sarcomas are characterized by the presence of EWS/ETS fusion genes in the absence of other recurrent genetic alterations and mechanisms of tumor heterogeneity that contribute to disease progression remain unclear. Mutations in the Wnt/β-catenin pathway are rare in Ewing sarcoma but the Wnt pathway modulator LGR5 is often highly expressed, suggesting a potential role for the axis in tumor pathogenesis. We evaluated β-catenin and LGR5 expression in Ewing sarcoma cell lines and tumors and noted marked intra- and inter-tumor heterogeneity. Tumors with evidence of active Wnt/β-catenin signaling were associated with increased incidence of tumor relapse and worse overall survival. Paradoxically, RNA sequencing revealed a marked antagonism of EWS/ETS transcriptional activity in Wnt/β-catenin-activated tumor cells. Consistent with this, Wnt/β-catenin-activated cells displayed a phenotype that was reminiscent of Ewing sarcoma cells with partial EWS/ETS loss of function. Specifically, activation of Wnt/β-catenin induced alterations to the actin cytoskeleton, acquisition of a migratory phenotype, and upregulation of EWS/ETS-repressed genes. Notably, activation of Wnt/β-catenin signaling led to marked induction of tenascin C (TNC), an established promoter of cancer metastasis, and an EWS/ETS-repressed target gene. Loss of TNC function in Ewing sarcoma cells profoundly inhibited their migratory and metastatic potential. Our studies reveal that heterogeneous activation of Wnt/β-catenin signaling in subpopulations of tumor cells contributes to phenotypic heterogeneity and disease progression in Ewing sarcoma. Significantly, this is mediated, at least in part, by inhibition of EWS/ETS fusion protein function that results in derepression of metastasis-associated gene programs. Cancer Res; 76(17); 5040-53. ©2016 AACR.

Abstract A21: The metastasis-regulator Tenascin C is activated by Wnt/beta-catenin in Ewing sarcoma

A pathogenic role for Wnt/beta-catenin signaling in Ewing sarcoma, an aggressive and highly metastatic tumor characterized by pathognomonic EWS/ETS fusion proteins, has yet to be elucidated. To address the potential importance of Wnt/beta-catenin in Ewing sarcoma we performed immunohistochemical staining of primary tumor specimens and discovered that nuclear beta-catenin is highly heterogeneous, both within and between tumors, and that all tumors with evidence of beta-catenin activation were associated with clinical relapse. These studies led us to hypothesize that activation of Wnt/beta-catenin in Ewing sarcoma cells promotes acquisition of an aggressive phenotype. To test this hypothesis we generated TCF/LEF-reporter cells and performed RNA-seq and functional studies of Wnt/beta-catenin activated cells. Pathway activation was achieved by provision of Wnt3a, inhibition of GSK3b, and by ectopic expression of constitutively active beta-catenin. LGR5 expression was assessed by in situ hybridization and potentiation of the Wnt signal by R-spondin determined by reporter assays and qRT-PCR. Knockdown of gene expression was achieved by lentiviral transduction of targeted shRNAs. Migration was assessed in transwell assays and phalloidin and cortactin staining was used to visualize the cytoskeleton. Metastatic potential was determined by a tail vein injection model. Our results confirm that only subpopulations of Ewing sarcoma cells activate beta-catenin in response to exogenous Wnt ligand. Responsive cells were found to be more migratory than non-responsive cells and cytoskeleton changes, including increased cell spreading and formation of migration-associated podosome structures, were observed in the activated cell populations. RNA sequencing of Wnt/beta-catenin activated cells revealed changes in expression of over a thousand genes. Interestingly, gene set enrichment analysis (GSEA) showed that the Wnt/beta-catenin modulated genes were highly inversely correlated with EWS/ETS-regulated genes. Specifically, Wnt/beta-catenin induced genes are repressed by EWS/ETS and vice versa, thus revealing transcriptional antagonism between EWS/ETS and Wnt/beta-catenin signaling. Confirmation of this antagonism was demonstrated by the finding that the cytoskeletal phenotype of Wnt/beta-catenin activated cells in part phenocopies that of EWS/ETS knockdown cells. At a molecular level TNC (tenascin C) was identified to be among the most induced genes in Wnt-activated cells. A combination of pharmacologic and genetic approaches confirmed that TNC is a beta-catenin target in Ewing sarcoma cells and that it is also transcriptionally repressed by EWS/ETS. Tenascin C is a matricellular protein that is an established regulator of metastatic phenotypes including cancer cell migration, invasion, and survival during metastatic dissemination. Studies of TNC-knockdown cells showed that loss of TNC has no significant impact on cell proliferation but results in reduced cell migration and invasion. In addition, cells with reduced expression of TNC showed a significant reduction in metastatic potential in vivo. Together these studies reveal marked cellular heterogeneity of Wnt/beta-catenin activation in Ewing sarcoma and demonstrate that the distinct gene expression signature associated with Wnt pathway activation in tumor cells is associated with transcriptional antagonism of EWS/ETS. Paradoxically, this antagonism promotes transition to a more aggressive cellular phenotype with enhanced metastatic potential that is associated with changes in the cytoskeleton and upregulation of TNC. Together these data support the innovative hypothesis that, in Ewing sarcoma, cell plasticity between non-metastatic and metastatic cellular phenotypes is dependent on the balance between EWS/ETS and Wnt/beta-catenin signaling.

Citation Format: Elisabeth A. Pedersen, Rajasree Menon, Dafydd G. Thomas, Kelly M. Bailey, Raelene A. Van Noord, Rashmi Chugh, Eric R. Fearon, Elizabeth R. Lawlor. The metastasis-regulator Tenascin C is activated by Wnt/beta-catenin in Ewing sarcoma. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr A21.

Intra-tumor genetic heterogeneity in rectal cancer

Colorectal cancer arises in part from the cumulative effects of multiple gene lesions. Recent studies in selected cancer types have revealed significant intra-tumor genetic heterogeneity and highlighted its potential role in disease progression and resistance to therapy. We hypothesized the existence of significant intra-tumor genetic heterogeneity in rectal cancers involving variations in localized somatic mutations and copy number abnormalities. Two or three spatially disparate regions from each of six rectal tumors were dissected and subjected to the next-generation whole-exome DNA sequencing, Oncoscan SNP arrays, and targeted confirmatory sequencing and analysis. The resulting data were integrated to define subclones using SciClone. Mutant-allele tumor heterogeneity (MATH) scores, mutant allele frequency correlation, and mutation percent concordance were calculated, and copy number analysis including measurement of correlation between samples was performed. Somatic mutations profiles in individual cancers were similar to prior studies, with some variants found in previously reported significantly mutated genes and many patient-specific mutations in each tumor. Significant intra-tumor heterogeneity was identified in the spatially disparate regions of individual cancers. All tumors had some heterogeneity but the degree of heterogeneity was quite variable in the samples studied. We found that 67-97% of exonic somatic mutations were shared among all regions of an individual's tumor. The SciClone computational method identified 2-8 shared and unshared subclones in the spatially disparate areas in each tumor. MATH scores ranged from 7 to 41. Allele frequency correlation scores ranged from R(2)=0.69-0.96. Measurements of correlation between samples for copy number changes varied from R(2)=0.74-0.93. All tumors had some heterogeneity, but the degree was highly variable in the samples studied. The occurrence of significant intra-tumor heterogeneity may allow selected tumors to have a genetic reservoir to draw from in their evolutionary response to therapy and other challenges.

Tumor-selective proteotoxicity of verteporfin inhibits colon cancer progression independently of YAP1

Yes-associated protein 1 (YAP1) is a transcriptional coactivator in the Hippo signaling pathway. Increased YAP1 activity promotes the growth of tumors, including that of colorectal cancer (CRC). Verteporfin, a drug that enhances phototherapy to treat neovascular macular degeneration, is an inhibitor of YAP1. We found that verteporfin inhibited tumor growth independently of its effects on YAP1 or the related protein TAZ in genetically or chemically induced mouse models of CRC, in patient-derived xenografts, and in enteroid models of CRC. Instead, verteporfin exhibited in vivo selectivity for killing tumor cells in part by impairing the global clearance of high-molecular weight oligomerized proteins, particularly p62 (a sequestrome involved in autophagy) and STAT3 (signal transducer and activator of transcription 3; a transcription factor). Verteporfin inhibited cytokine-induced STAT3 activity and cell proliferation and reduced the viability of cultured CRC cells. Although verteporfin accumulated to a greater extent in normal cells than in tumor cells in vivo, experiments with cultured cells indicated that the normal cells efficiently cleared verteporfin-induced protein oligomers through autophagic and proteasomal pathways. Culturing CRC cells under hypoxic or nutrient-deprived conditions (modeling a typical CRC microenvironment) impaired the clearance of protein oligomers and resulted in cell death, whereas culturing cells under normoxic or glucose-replete conditions protected cell viability and proliferation in the presence of verteporfin. Furthermore, verteporfin suppressed the proliferation of other cancer cell lines even in the absence of YAP1, suggesting that verteporfin may be effective against multiple types of solid cancers.

Arid1a inactivation in an Apc- and Pten-defective mouse ovarian cancer model enhances epithelial differentiation and prolongs survival

Inactivation of the ARID1A tumour suppressor gene is frequent in ovarian endometrioid (OEC) and clear cell (OCCC) carcinomas, often in conjunction with mutations activating the PI3K-AKT and/or canonical Wnt signalling pathways. Prior work has shown that conditional bi-allelic inactivation of the Apc and Pten tumour suppressor genes in the mouse ovarian surface epithelium (OSE) promotes outgrowth of tumours that reflect the biological behaviour and gene expression profiles of human OECs harbouring comparable Wnt and PI3K-AKT pathway defects, although the mouse tumours are more poorly differentiated than their human tumour counterparts. We found that conditional inactivation of one or both Arid1a alleles in OSE concurrently with Apc and Pten inactivation unexpectedly prolonged the survival of tumour-bearing mice and promoted striking epithelial differentiation of the cancer cells, resulting in morphological features akin to those in human OECs. Enhanced epithelial differentiation was linked to reduced expression of the mesenchymal markers N-cadherin and vimentin, and increased expression of the epithelial markers Crb3 and E-cadherin. Global gene expression profiling showed enrichment for genes associated with mesenchymal-epithelial transition in the Arid1a-deficient tumours. We also found that an activating (E545K) Pik3ca mutation, unlike Pten inactivation or Pik3ca H1047R mutation, cannot cooperate with Arid1a loss to promote ovarian cancer development in the mouse. Our results indicate that the Arid1a tumour suppressor gene has a key role in regulating OEC differentiation, and paradoxically the mouse cancers with more initiating tumour suppressor gene defects had a less aggressive phenotype than cancers arising from fewer gene alterations. Microarray data have been deposited in NCBI's Gene Expression Omnibus (GSE67695).

Abstract AS06: Development and characterization of an oviduct-specific model of high-grade serous carcinoma

Recent studies suggest the most common and lethal type of “ovarian” cancer, high-grade serous carcinoma (HGSC), often arises from fallopian tube epithelium rather than the ovarian surface epithelium. Their intraperitoneal location and microscopic size make it very difficult to screen for, or study the biology of early tubal lesions in humans, as most are discovered incidentally in women with hereditary predisposition to ovarian cancer who elect prophylactic salpingo-oophorectomy for cancer risk-reduction. Although most cases of pelvic HGSC probably originate in the fallopian tube, roughly one-third lack evidence of tubal origin. These cases may arise from ectopic tubal-type epithelium (endosalpingiosis) present in the ovary, peritoneum, or at other sites. Mouse models that closely mimic the genetics and biology of human HGSCs may be useful for clarifying how tubal and non-tubal pelvic HGSCs develop and progress.

We have developed transgenic (Ovgp1-iCreERT2) mice allowing conditional (tamoxifen [TAM]-inducible) expression of Cre recombinase exclusively in the oviductal epithelium, using a single transgene. Using double transgenic Ovgp1-iCreERT2;R26LSL-eYFP mice in which TAM treatment activates eYFP reporter protein expression in oviductal epithelial cells, we have shown that tubal-type inclusion glands (endosalpingiosis) expressing both eYFP and OVGP1 are present in a subset of murine ovaries following treatment with TAM. The findings suggest that oviductal epithelium can detach from the oviduct and traffic to the ovaries, where it implants through breaks in the OSE and maintains its tubal-type differentiation. Preliminary data also suggest that the frequency of ovarian endosalpingiosis increases over time and by superovulating the mice. The latter finding raises the possibility that at least some of the protective effects of high parity and oral contraceptive use on human ovarian cancer risk is related to reduced likelihood of acquiring endosalpingiosis from which “ovarian” HGSCs may eventually arise.

We have further shown that Ovgp1-iCreERT2;Trp53fl/fl;Brca1fl/fl mice develop oviductal lesions identical to human serous tubal intraepithelial carcinomas (STICs) after TAM treatment and have identified additional genetic alterations that cooperate with Trp53 and Brca1 inactivation in oviductal HGSC pathogenesis in our model system. Murine models of HGSC that recapitulate their human tumor counterparts provide excellent in vivo systems with which to define the cellular and molecular events associated with HGSC development and progression.

Citation Format: Yali Zhai, Rong Wu, Tom C. Hu, Eric R. Fearon, Kathleen R. Cho. Development and characterization of an oviduct-specific model of high-grade serous carcinoma [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 AS06.

Regulation of Wnt signaling target gene expression by the histone methyltransferase DOT1L

The histone methyltransferase DOT1L, solely responsible for histone H3 lysine 79 (H3K79) methylation, is associated with gene activation. Human leukemias carrying MLL gene rearrangements aberrantly recruit DOT1L to leukemogenic genes leading to increased H3K79 methylation and their transcriptional activation. Recent studies suggest that Wnt-targeted genes also depend on H3K79 methylation. Employing a chemical biology approach, the requirement for H3K79 methylation was investigated in Wnt pathway-inducible HEK293 cells and human colon adenocarcinoma-derived cell lines by inhibiting DOT1L with EPZ004777, a selective and potent S-adenosylmethionine competitive inhibitor. Our findings indicate that H3K79 methylation is not essential for the canonical Wnt signaling pathway, in particular for maintenance or activation of Wnt pathway target gene expression. Furthermore, H3K79 methylation is not elevated in human colon carcinoma samples in comparison with normal colon tissue. Therefore, our findings indicate that inhibition of DOT1L histone methyltransferase activity is likely not a viable therapeutic strategy in colon cancer.

AXIN1 and AXIN2 variants in gastrointestinal cancers

Mutations in the APC (adenomatous polyposis coli) gene, which encodes a multi-functional protein with a well-defined role in the canonical Wnt pathway, underlie familial adenomatous polypsosis, a rare, inherited form of colorectal cancer (CRC) and contribute to the majority of sporadic CRCs. However, not all sporadic and familial CRCs can be explained by mutations in APC or other genes with well-established roles in CRC. The AXIN1 and AXIN2 proteins function in the canonical Wnt pathway, and AXIN1/2 alterations have been proposed as key defects in some cancers. Here, we review AXIN1 and AXIN2 sequence alterations reported in gastrointestinal cancers, with the goal of vetting the evidence that some of the variants may have key functional roles in cancer development.

An integrative analysis of colon cancer identifies an essential function for PRPF6 in tumor growth

The spliceosome machinery is composed of multimeric protein complexes that generate a diverse repertoire of mRNA. Here, Adler et al. discover that PRPF6, a member of the tri-snRNP spliceosome complex, drives cancer proliferation. Inhibition of PRPF6 and other tri-snRNP complex proteins selectively abrogated growth in cancer cells with high tri-snRNP levels. Reducing PRPF6 altered the splicing of a discrete number of genes, including an oncogenic isoform of the ZAK kinase. This study identifies an essential role for PRPF6 in cancer via splicing of distinct growth-related gene products.

The spliceosome machinery is composed of multimeric protein complexes that generate a diverse repertoire of mRNA through coordinated splicing of heteronuclear RNAs. While somatic mutations in spliceosome components have been discovered in several cancer types, the molecular bases and consequences of spliceosome aberrations in cancer are poorly understood. Here we report for the first time that PRPF6, a member of the tri-snRNP (small ribonucleoprotein) spliceosome complex, drives cancer proliferation by preferential splicing of genes associated with growth regulation. Inhibition of PRPF6 and other tri-snRNP complex proteins, but not other snRNP spliceosome complexes, selectively abrogated growth in cancer cells with high tri-snRNP levels. High-resolution transcriptome analyses revealed that reduced PRPF6 alters the constitutive and alternative splicing of a discrete number of genes, including an oncogenic isoform of the ZAK kinase. These findings implicate an essential role for PRPF6 in cancer via splicing of distinct growth-related gene products.

Biomarkers of coordinate metabolic reprogramming in colorectal tumors in mice and humans

BACKGROUND & AIMS

There are no robust noninvasive methods for colorectal cancer screening and diagnosis. Metabolomic and gene expression analyses of urine and tissue samples from mice and humans were used to identify markers of colorectal carcinogenesis.

METHODS

Mass spectrometry-based metabolomic analysis of urine and tissues from wild-type C57BL/6J and Apc(Min/+) mice, as well as from mice with azoxymethane-induced tumors, was employed in tandem with gene expression analysis. Metabolic profiling was also performed on colon tumor and adjacent nontumor tissues from 39 patients. The effects of β-catenin activity on metabolic profiles were assessed in mice with colon-specific disruption of Apc.

RESULTS

Thirteen markers were found in urine associated with development of colorectal tumors in Apc(Min/+) mice. Metabolites related to polyamine metabolism, nucleic acid metabolism, and methylation, identified tumor-bearing mice with 100% accuracy, and also accurately identified mice with polyps. Changes in gene expression in tumor samples from mice revealed that derangement of metabolites were a reflection of coordinate metabolic reprogramming in tumor tissue. Similar changes in urinary metabolites were observed in mice with azoxymethane-induced tumors and in mice with colon-specific activation of β-catenin. The metabolic alterations indicated by markers in urine, therefore, appear to occur during early stages of tumorigenesis, when cancer cells are proliferating. In tissues from patients, tumors had stage-dependent increases in 17 metabolites associated with the same metabolic pathways identified in mice. Ten metabolites that were increased in tumor tissues, compared with nontumor tissues (proline, threonine, glutamic acid, arginine, N1-acetylspermidine, xanthine, uracil, betaine, symmetric dimethylarginine, and asymmetric-dimethylarginine), were also increased in urine from tumor-bearing mice.

CONCLUSIONS

Gene expression and metabolomic profiles of urine and tissue samples from mice with colorectal tumors and of colorectal tumor samples from patients revealed pathways associated with derangement of specific metabolic pathways that are indicative of early-stage tumor development. These urine and tissue markers might be used in early detection of colorectal cancer.

Investigation of 3-aryl-pyrimido[5,4-e][1,2,4]triazine-5,7-diones as small molecule antagonists of β-catenin/TCF transcription

Nearly all colorectal cancers (CRCs) and varied subsets of other cancers have somatic mutations leading to β-catenin stabilization and increased β-catenin/TCF transcriptional activity. Inhibition of stabilized β-catenin in CRC cell lines arrests their growth and highlights the potential of this mechanism for novel cancer therapeutics. We have pursued efforts to develop small molecules that inhibit β-catenin/TCF transcriptional activity. We used xanthothricin, a known β-catenin/TCF antagonist of microbial origin, as a lead compound to synthesize related analogues with drug-like features such as low molecular weight and good metabolic stability. We studied a panel of six candidate Wnt/β-catenin/Tcf-regulated genes and found that two of them (Axin2, Lgr5) were reproducibly activated (9-10 fold) in rat intestinal epithelial cells (IEC-6) following β-catenin stabilization by Wnt-3a ligand treatment. Two previously reported β-catenin/TCF antagonists (calphostin C, xanthothricin) and XAV939 (tankyrase antagonist) inhibited Wnt-activated genes in a dose-dependent fashion. We found that four of our compounds also potently inhibited Wnt-mediated activation in the panel of target genes. We investigated the mechanism of action for one of these (8c) and demonstrated these novel small molecules inhibit β-catenin transcriptional activity by degrading β-catenin via a proteasome-dependent, but GSK3β-, APC-, AXIN2- and βTrCP-independent, pathway. The data indicate the compounds act at the level of β-catenin to inhibit Wnt/β-catenin/TCF function and highlight a robust strategy for assessing the activity of β-catenin/TCF antagonists.

Type I to type II ovarian carcinoma progression: mutant Trp53 or Pik3ca confers a more aggressive tumor phenotype in a mouse model of ovarian cancer

A dualistic pathway model of ovarian carcinoma (OvCA) pathogenesis has been proposed: type I OvCAs are low grade, genetically stable, and relatively more indolent than type II OvCAs, most of which are high-grade serous carcinomas. Endometrioid OvCA (EOC) is a prototypical type I tumor, often harboring mutations that affect the Wnt and phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin signaling pathways. Molecular and histopathologic analyses indicate type I and II OvCAs share overlapping features, and a subset of EOCs may undergo type I→type II progression accompanied by acquisition of somatic TP53 or PIK3CA mutations. We used a murine model of EOC initiated by conditional inactivation of the Apc and Pten tumor suppressor genes to investigate mutant Trp53 or Pik3ca alleles as key drivers of type I→type II OvCA progression. In the mouse EOC model, the presence of somatic Trp53 or Pik3ca mutations resulted in shortened survival and more widespread metastasis. Activation of mutant Pik3ca alone had no demonstrable effect on the ovarian surface epithelium but resulted in papillary hyperplasia when coupled with Pten inactivation. Our findings indicate that the adverse prognosis associated with TP53 and PIK3CA mutations in human cancers can be functionally replicated in mouse models of type I→type II OvCA progression. Moreover, the models should represent a robust platform for assessment of the contributions of Trp53 or Pik3ca defects in the response of EOCs to conventional and targeted drugs.

Adenoma-linked barrier defects and microbial products drive IL-23/IL-17-mediated tumour growth

Approximately 2% of colorectal cancer is linked to pre-existing inflammation known as colitis-associated cancer, but most develops in patients without underlying inflammatory bowel disease. Colorectal cancer often follows a genetic pathway whereby loss of the adenomatous polyposis coli (APC) tumour suppressor and activation of β-catenin are followed by mutations in K-Ras, PIK3CA and TP53, as the tumour emerges and progresses. Curiously, however, 'inflammatory signature' genes characteristic of colitis-associated cancer are also upregulated in colorectal cancer. Further, like most solid tumours, colorectal cancer exhibits immune/inflammatory infiltrates, referred to as 'tumour-elicited inflammation'. Although infiltrating CD4(+) T(H)1 cells and CD8(+) cytotoxic T cells constitute a positive prognostic sign in colorectal cancer, myeloid cells and T-helper interleukin (IL)-17-producing (T(H)17) cells promote tumorigenesis, and a 'T(H)17 expression signature' in stage I/II colorectal cancer is associated with a drastic decrease in disease-free survival. Despite its pathogenic importance, the mechanisms responsible for the appearance of tumour-elicited inflammation are poorly understood. Many epithelial cancers develop proximally to microbial communities, which are physically separated from immune cells by an epithelial barrier. We investigated mechanisms responsible for tumour-elicited inflammation in a mouse model of colorectal tumorigenesis, which, like human colorectal cancer, exhibits upregulation of IL-23 and IL-17. Here we show that IL-23 signalling promotes tumour growth and progression, and development of a tumoural IL-17 response. IL-23 is mainly produced by tumour-associated myeloid cells that are likely to be activated by microbial products, which penetrate the tumours but not adjacent tissue. Both early and late colorectal neoplasms exhibit defective expression of several barrier proteins. We propose that barrier deterioration induced by colorectal-cancer-initiating genetic lesions results in adenoma invasion by microbial products that trigger tumour-elicited inflammation, which in turn drives tumour growth.

Alleviation of gut inflammation by Cdx2/Pxr pathway in a mouse model of chemical colitis

Pregnane X Receptor (PXR), a master regulator of drug metabolism and inflammation, is abundantly expressed in the gastrointestinal tract. Baicalein and its O-glucuronide baicalin are potent anti-inflammatory and anti-cancer herbal flavonoids that undergo a complex cycle of interconversion in the liver and gut. We sought to investigate the role these flavonoids play in inhibiting gut inflammation by an axis involving PXR and other potential factors. The consequences of PXR regulation and activation by the herbal flavonoids, baicalein and baicalin were evaluated in vitro in human colon carcinoma cells and in vivo using wild-type, Pxr-null, and humanized (hPXR) PXR mice. Baicalein, but not its glucuronidated metabolite baicalin, activates PXR in a Cdx2-dependent manner in vitro, in human colon carcinoma LS174T cells, and in the murine colon in vivo. While both flavonoids abrogate dextran sodium sulfate (DSS)-mediated colon inflammation in vivo, oral delivery of a potent bacterial β-glucuronidase inhibitor eliminates baicalin’s effect on gastrointestinal inflammation by preventing the microbial conversion of baicalin to baicalien. Finally, reduction of gastrointestinal inflammation requires the binding of Cdx2 to a specific proximal site on the PXR promoter. Pharmacological targeting of intestinal PXR using natural metabolically labile ligands could serve as effective and potent therapeutics for gut inflammation that avert systemic drug interactions.

A p53/miRNA-34 axis regulates Snail1-dependent cancer cell epithelial-mesenchymal transition

Expression of the essential EMT inducer Snail1 is inhibited by miR-34 through a p53-dependent regulatory pathway.

Snail1 is a zinc finger transcriptional repressor whose pathological expression has been linked to cancer cell epithelial–mesenchymal transition (EMT) programs and the induction of tissue-invasive activity, but pro-oncogenic events capable of regulating Snail1 activity remain largely uncharacterized. Herein, we demonstrate that p53 loss-of-function or mutation promotes cancer cell EMT by de-repressing Snail1 protein expression and activity. In the absence of wild-type p53 function, Snail1-dependent EMT is activated in colon, breast, and lung carcinoma cells as a consequence of a decrease in miRNA-34 levels, which suppress Snail1 activity by binding to highly conserved 3′ untranslated regions in Snail1 itself as well as those of key Snail1 regulatory molecules, including β-catenin, LEF1, and Axin2. Although p53 activity can impact cell cycle regulation, apoptosis, and DNA repair pathways, the EMT and invasion programs initiated by p53 loss of function or mutation are completely dependent on Snail1 expression. These results identify a new link between p53, miR-34, and Snail1 in the regulation of cancer cell EMT programs.

Preclinical testing of PI3K/AKT/mTOR signaling inhibitors in a mouse model of ovarian endometrioid adenocarcinoma

PURPOSE

Genetically engineered mouse (GEM) models of ovarian cancer that closely recapitulate their human tumor counterparts may be invaluable tools for preclinical testing of novel therapeutics. We studied murine ovarian endometrioid adenocarcinomas (OEA) arising from conditional dysregulation of canonical WNT and PI3K/AKT/mTOR pathway signaling to investigate their response to conventional chemotherapeutic drugs and mTOR or AKT inhibitors.

EXPERIMENTAL DESIGN

OEAs were induced by injection of adenovirus expressing Cre recombinase (AdCre) into the ovarian bursae of Apc(flox/flox); Pten(flox/flox) mice. Tumor-bearing mice or murine OEA-derived cell lines were treated with cisplatin and paclitaxel, mTOR inhibitor rapamycin, or AKT inhibitors API-2 or perifosine. Treatment effects were monitored in vivo by tumor volume and bioluminescence imaging, in vitro by WST-1 proliferation assays, and in OEA tissues and cells by immunoblotting and immunostaining for levels and phosphorylation status of PI3K/AKT/mTOR signaling pathway components.

RESULTS

Murine OEAs developed within 3 weeks of AdCre injection and were not preceded by endometriosis. OEAs responded to cisplatin + paclitaxel, rapamycin, and AKT inhibitors in vivo. In vitro studies showed that response to mTOR and AKT inhibitors, but not conventional cytotoxic drugs, was dependent on the status of PI3K/AKT/mTOR signaling. AKT inhibition in APC(-)/Pten(-) tumor cells resulted in compensatory upregulation of ERK signaling.

CONCLUSIONS

The studies show the utility of this GEM model of ovarian cancer for preclinical testing of novel PI3K/AKT/mTOR signaling inhibitors and provide evidence for compensatory signaling, suggesting that multiple rather than single agent targeted therapy will be more efficacious for treating ovarian cancers with activated PI3K/AKT/mTOR signaling.

Mutant KRAS promotes hyperplasia and alters differentiation in the colon epithelium but does not expand the presumptive stem cell pool

BACKGROUND & AIMS

Adenomatous polyps are precursors to colorectal cancer (CRC), whereas hyperplastic polyps (HPPs) have low risk of progression to CRC. Mutations in KRAS are found in ∼40% of CRCs and large adenomas and a subset of HPPs. We investigated the reasons why HPPs with KRAS mutations lack malignant potential and compared the effects of Kras/KRAS activation with those of Apc/APC inactivation, which promotes adenoma formation.

METHODS

We activated a KrasG12D mutant allele or inactivated Apc alleles in mouse colon epithelium and analyzed phenotypes and expression of selected genes and proteins. The mouse data were validated using samples of human HPPs and adenomas. Signaling pathways and factors contributing to Kras/KRAS-induced phenotypes were studied in intestinal epithelial cells.

RESULTS

Activation of Kras led to hyperplasia and serrated crypt architecture akin to that observed in human HPPs. We also observed loss of Paneth cells and increases in goblet cell numbers. Abnormalities in Kras-mediated differentiation and proliferation required mitogen-activated protein kinase signaling and were linked to activation of the Hes1 transcription factor. Human HPPs also had activation of HES1. In contrast to Apc/APC inactivation, Kras/KRAS activation did not increase expression of crypt stem cell markers in colon epithelium or colony formation in vitro. Kras/KRAS activation was not associated with substantial induction of p16(INK4a) protein expression in mouse colon epithelium or human HPPs.

CONCLUSIONS

Although Kras/KRAS mutation promotes serrated and hyperplastic morphologic features in colon epithelium, it is not able to initiate adenoma development, perhaps in part because activated Kras/KRAS signaling does not increase the number of presumptive stem cells in affected crypts.

Molecular genetics of colorectal cancer

Over the past three decades, molecular genetic studies have revealed some critical mutations underlying the pathogenesis of the sporadic and inherited forms of colorectal cancer (CRC). A relatively limited number of oncogenes and tumor-suppressor genes-most prominently the APC, KRAS, and p53 genes-are mutated in a sizeable fraction of CRCs, and a larger collection of genes that are mutated in subsets of CRC have begun to be defined. Together with DNA-methylation and chromatin-structure changes, the mutations act to dysregulate conserved signaling networks that exert context-dependent effects on critical cell phenotypes, including the regulation of cellular metabolism, proliferation, differentiation, and survival. Much work remains to be done to fully understand the nature and significance of the individual and collective genetic and epigenetic defects in CRC. Some key concepts for the field have emerged, two of which are emphasized in this review. Specifically, the gene defects in CRC often target proteins and pathways that exert pleiotropic effects on the cancer cell phenotype, and particular genetic and epigenetic alterations are linked to biologically and clinically distinct subsets of CRC.

Molecular genetics of colorectal cancer

Over the past three decades, molecular genetic studies have revealed some critical mutations underlying the pathogenesis of the sporadic and inherited forms of colorectal cancer (CRC). A relatively limited number of oncogenes and tumor-suppressor genes-most prominently the APC, KRAS, and p53 genes-are mutated in a sizeable fraction of CRCs, and a larger collection of genes that are mutated in subsets of CRC have begun to be defined. Together with DNA-methylation and chromatin-structure changes, the mutations act to dysregulate conserved signaling networks that exert context-dependent effects on critical cell phenotypes, including the regulation of cellular metabolism, proliferation, differentiation, and survival. Much work remains to be done to fully understand the nature and significance of the individual and collective genetic and epigenetic defects in CRC. Some key concepts for the field have emerged, two of which are emphasized in this review. Specifically, the gene defects in CRC often target proteins and pathways that exert pleiotropic effects on the cancer cell phenotype, and particular genetic and epigenetic alterations are linked to biologically and clinically distinct subsets of CRC.