APC Tumor Suppressor Gene Research Articles

Short-term post-fast refeeding enhances intestinal stemness via polyamines.

For over a century, fasting regimens have improved health, lifespan and tissue regeneration in diverse organisms, including humans1-6. However, how fasting and post-fast refeeding affect adult stem cells and tumour formation has yet to be explored in depth. Here we demonstrate that post-fast refeeding increases intestinal stem cell (ISC) proliferation and tumour formation; post-fast refeeding augments the regenerative capacity of Lgr5+ ISCs, and loss of the tumour suppressor gene Apc in post-fast-refed ISCs leads to a higher tumour incidence in the small intestine and colon than in the fasted or ad libitum-fed states, demonstrating that post-fast refeeding is a distinct state. Mechanistically, we discovered that robust mTORC1 induction in post-fast-refed ISCs increases protein synthesis via polyamine metabolism to drive these changes, as inhibition of mTORC1, polyamine metabolite production or protein synthesis abrogates the regenerative or tumorigenic effects of post-fast refeeding. Given our findings, fast-refeeding cycles must be carefully considered and tested when planning diet-based strategies for regeneration without increasing cancer risk, as post-fast refeeding leads to a burst in stem-cell-driven regeneration and tumorigenicity.

Abstract SY07-02: Cell competition vs cell cooperation: Unlocking oncogenic potential of mutant clones in the gut

Abstract The epithelial monolayer of the intestine is one of the fastest renewing tissues of the human body. Every week, the entire epithelium is replaced by intestinal stem cells (ISCs) that reside in crypt-like structures within the monolayer. Within these crypts, a small number of ISCs continuously divide to provide all specialized cell types necessary to maintain normal intestinal homeostasis, while simultaneously competing with each other for a position within the crypt bottom. This competition, characterized by neutral loss-and-replacement events, can be drastically disturbed when one of the ISCs acquires a mutation that confers a competitive advantage. As a result, mutant ISCs will replace all normal ISCs, colonize the intestinal crypt, and facilitate the initiation of colorectal cancer (CRC). CRC development is a stepwise process characterized by the accumulation of mutations in cancer driver genes over time. Almost 80% of all CRCs present with early mutations in the tumor suppressor gene APC, leading to constitutive activation of the Wnt pathway and the formation of pre-malignant adenomas. We have previously demonstrated that, within individual crypts, Apc-mutant ISCs have a competitive advantage over normal ISCs, although the mechanism underlying this unequal competition remained unclear. Recently, we revealed that Apc-mutant ISCs in fact act as "supercompetitors" by secreting Wnt antagonists such as NOTUM, WIF1 and DKK2, that actively disadvantage neighboring wild type ISCs by forcing them do differentiate. We demonstrated that boosting wild type fitness by downstream pharmacological activation of the Wnt signaling pathway by GSK3β-inhibitor lithium rendered wild type ISCs resistant to the Wnt antagonists, reduced the number of Apc-mutant crypts, and prevented adenoma formation. Together, this work highlights that modulating cell competition between normal and mutant cells within the crypt can provide a novel approach to prevent CRC development. Our findings are particularly relevant for familial adenomatous polyposis (FAP) patients, that carry germline mutations in APC and are predisposed to the development of CRC. Based on our fundamental discoveries, we are currently performing a clinical trial to assess the chemopreventive effect of lithium on the expansion of APC-mutant clones in FAP patients [ClinicalTrials.gov: NCT05402891]. Importantly, it is becoming increasingly evident that intestinal adenomas do not form from a single Apc-mutant crypt, but require fields of multiple mutant crypts to facilitate tumor initiation. Although field cancerization by enhanced crypt fission has been observed for several oncogenic mutants in the gut (e.g. KrasG12D, PIK3CAH1047R), Apc-mutant cells are often contained within individual crypts. This indicates that multiple independent mutant clones may act cooperatively to facilitate tumorigenesis, thereby pointing towards a polyclonal origin of intestinal adenomas. Our current work investigates how Apc-mutant clones interact by modifying their local environment through reciprocal signalling with stromal and epithelial cells to escape the anatomical constraints of the crypt, thereby unlocking their oncogenic potential in the gut. Ultimately, unravelling the molecular mechanisms underlying clonal cooperation will inform potential chemoprevention strategies for CRC. Citation Format: Sanne van Neerven. Cell competition vs cell cooperation: Unlocking oncogenic potential of mutant clones in the gut [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr SY07-02.

RET is a sex-biased regulator of intestinal tumorigenesis.

Ret is implicated in colorectal cancer (CRC) as both a proto-oncogene and a tumor suppressor. We asked whether RET signaling regulates tumorigenesis in an Apc-deficient preclinical model of CRC. We observed a sex-biased phenotype: Apc Min/+ Ret+/- females had significantly greater tumor burden than Apc Min/+Ret+/- males, a phenomenon not seen in Apc Min/+ mice, which had equal distributions by sex. Dysfunctional RET signaling was associated with gene expression changes in diverse tumor signaling pathways in tumors and normal-appearing colon. Sex-biased gene expression differences mirroring tumor phenotypes were seen in 26 genes, including the Apc tumor suppressor gene. Ret and Tlr4 expression were significantly correlated in tumor samples from female but not male Apc Min/+ Ret+/- mice. Antibiotics resulted in reduction of tumor burden, inverting the sex-biased phenotype such that microbiota-depleted Apc Min/+ Ret+/- males had significantly more tumors than female littermates. Reconstitution of the microbiome rescued the sex-biased phenotype. Our findings suggest that RET represents a sexually dimorphic microbiome-mediated "switch" for regulation of tumorigenesis.

Investigation of iso-propylchaetominine anticancer activity on apoptosis, cell cycle and Wnt signaling pathway in different cancer models

Dysregulation of the Wnt signaling pathway contributes to the development of many cancer types. Natural compounds produced with biotechnological systems have been the focus of research for being a new drug candidate both with unlimited resources and cost-effective production.In this study, it was aimed to reveal the effects of isopropylchaetominine on cytotoxic, cytostatic, apoptotic and Wnt signaling pathways in brain, pancreatic and prostate cancer.The IC50 values of isopropylchaetominine in U-87 MG, PANC1, PC3 and LNCaP cells were calculated as 91.94 μM, 41.68 μM, 54.54 μM and 7.86 μM in 72nd h, respectively. The metabolite arrests the cell cycle in G0/G1 phase in each cancer cells. Iso-propylchaetominine induced a 4.3-fold and 1.9-fold increase in apoptosis in PC3 and PANC1 cells, respectively. The toxicity of isopropylchaetominine in healthy fibroblast cells was assessed using the annexin V method, and no significant apoptotic activity was observed between the groups treated with the active substance and untreated. In U-87 MG, PANC1, PC3, and LNCaP cells under treatment with isopropylchaetominin, the expression levels of DKK3, TLE1, AES, DKK1, FRZB, DAB2, AXIN1/2, PPARD, SFRP4, APC and SOX17 tumor suppressor genes increased significantly. Decreases in expression of Wnt1, Wnt2, Wnt3, Wnt4, Wnt5, Wnt6, Wnt10, Wnt11, FRZ2, FRZ3, FRZ7, TCF7L1, BCL9, PYGO, CCND2, c-MYC, WISP1 and CTNNB1 oncogenic genes were detected.All these result shows that isopropylchaetominine can present promising new treatment strategy in different cancer types.

A Mouse Model for the Rapid and Binomial Assessment of Putative WNT/β-Catenin Signalling Inhibitors.

Specific signalling thresholds of the WNT/β-catenin pathway affect embryogenesis and tissue homeostasis in the adult, with mutations in this pathway frequently occurring in cancer. Excessive WNT/β-catenin activity inhibits murine anterior development associated with embryonic lethality and accounts for the driver event in 80% of human colorectal cancers. Uncontrolled WNT/β-catenin signalling arises primarily from impairment mutation in the tumour suppressor gene APC that otherwise prevents prolonged stabilisation of β-catenin. Surprisingly, no inhibitor compounds for WNT/β-catenin signalling have reached clinical use in part owing to the lack of specific in vivo assays that discriminate between on-target activities and dose-limiting toxicities. Here, we present a simple in vivo assay with a binary outcome whereby the administration of candidate compounds to pregnant and phenotypically normal Apcflox/flox mice can rescue in utero death of Apcmin/flox mutant conceptus without subsequent post-mortem assessment of WNT/β-catenin signalling. Indeed, the phenotypic plasticity of born Apcmin/flox conceptus enables future refinement of our assay to potentially enable dosage finding and cross-compound comparisons. Thus, we show for the first time the suitability of endogenous WNT/β-catenin signalling during embryonic development to provide an unambiguous and sensitive mammalian in vivo model to assess the efficacy and bioavailability of potential WNT/β-catenin antagonists.

WIF1 promoter hypermethylation induce endometrial carcinogenesis through the Wnt/β-catenin signaling pathway.

This study explores the mechanism underlying WIF1 promoter methylation and its relationship with the pathogenesis of endometrial carcinoma. WIF1 promoter methylation was detected using methylation-specific polymerase chain reaction (MSP). WIF1 expression was examined through qRT-PCR and western blotting. Furthermore, 5-aza-2'-deoxycytidine (5-Aza) was used to demethylate the WIF1 promoter. The roles of WIF1 were investigated using in vitro loss- and gain-of-function assays. Xenograft models were used to analyze WIF1 expression and downstream genes, and results were confirmed using immunofluorescence and western blotting. WIF1 promoter methylation in endometrial cancer cells was significantly higher than that in normal cells, but the WIF1 mRNA and protein levels were reduced. The expression of WIF1 increased significantly after 5-Aza treatment (p<.05). Thus, 5-Aza treatment can inhibit the proliferation of endometrial cancer cells and induce apoptosis, while knockdown of WIF1 significantly inhibits the effects of 5-Aza. 5-Aza treatment can also inhibit Wnt pathway genes, including phosphorylation of β-catenin protein, c-Myc, and CyclinD1, inhibit downstream functional genes, and activate the tumor suppressor gene APC, which can be blocked by WIF1 knockdown in endometrial carcinoma cells. Finally, 5-Aza inhibited the proliferation of subcutaneous tumor-bearing nude mice with endometrial cancer cells, but the effect was weaker than that of WIF1 overexpression. Our research shows that WIF1 promoter hypermethylation may promote the progression of endometrial cancer by downregulating WIF1 expression, activating the Wnt/β-catenin pathway, and promoting proliferation and inhibiting apoptosis. WIF1 may be a potential biological target for gene therapy and drug development for the treatment of endometrial cancer.

Methylation study of tumor suppressor genes in human aberrant crypt foci, colorectal carcinomas, and normal colon.

Aberrant crypt foci (ACF) are the earliest preneoplastic lesions in human colon, identifiable on chromoendoscopic screening. Our objective was to evaluate the %methylation of APC, CDKN2A, MLH1, RASSF1, MGMT, and WIF1 tumor suppressor genes (TSG) in ACF, corresponding colorectal carcinomas (CRC), and normal colonic mucosal controls. In this study, macroscopically normal-appearing mucosal flaps were sampled 5-10 cm away from the tumor mass from 302 fresh colectomy specimens to identify ACF-like lesions. Thirty-five cases with multiple ACFs were selected (n 35) as the main study group, with corresponding sections from CRC (n 35) as disease controls, and mucosal tissue blocks from 20 colectomy specimens (normal controls), operated for non-neoplastic pathologies. Genomic DNA was extracted, and methylation-specific polymerase chain reaction (PCR) was performed on a customized methylation array model. %Methylation data were compared among the groups and with clinicopathological parameters. Selected target mRNA and protein expression studies were performed. %Methylation of TSGs in ACF was intermediate between normal colon and CRC, although a statistically significant difference was observed only for the WIF1 gene (P < 0.01). Also, there was increased nuclear β-catenin expression and upregulation of CD44-positive cancer-stem cells in ACF and CRCs than in controls. Right-sided ACFs and dysplastic ACFs had a higher %methylation of CDKN2A (P < 0.01), whereas hyperplastic ACFs had a higher %methylation of RASSF1 (P 0.04). The topographic characteristics of ACFs did not correlate with TSG %methylation. Early epigenetic methylation of WIF1 gene is one of the mechanisms for ACF development in human colon.

Anti-Cancer Effect of Dorema Ammoniacum Gum by Targeting Metabolic Reprogramming by Regulating APC, P53, KRAS Gene Expression in HT-29 Human Colon Cancer Cells.

Colorectal cancer is a heterogeneous disease that leads to metabolic disorders due to multiple upstream genetic and molecular changes and interactions. The development of new therapies, especially herbal medicines, has received much global attention. Dorema ammoniacum is a medicinal plant. Its gum is used in healing known ailments. Studying metabolome profiles based on nuclear magnetic resonance 1HNMR as a non-invasive and reproducible tool can identify metabolic changes as a reflection of intracellular fluxes, especially in drug responses. This study aimed to investigate the anti-cancer effects of different gum extracts on metabolic changes and their impact on gene expression in HT-29 cell. Extraction of Dorema ammoniacum gum with hexane, chloroform, and dichloromethane organic solvents was performed. Cell inhibition growth percentage and IC50 were assessed. Following treating the cells with dichloromethane extract, p53, APC, and KRAS gene expression were determined. 1HNMR spectroscopy was conducted. Eventually, systems biology software tools interpreted combined metabolites and genes simultaneously. The lowest determined IC50 concentration was related to dichloromethane solvent, and the highest was hexane and chloroform. The expression of the KRAS oncogene gene decreased significantly after treatment with dichloromethane extract compared to the control group, and the expression of tumor suppressor gene p53 and APC increased significantly. Most gene-altered convergent metabolic phenotypes. This study's results indicate that the dichloromethane solvent of Dorema ammoniacum gum exhibits its antitumor properties by altering the expression of genes involved in HT-29 cells and the consequent change in downstream metabolic reprogramming.

Sequential Accumulation of ‘Driver’ Pathway Mutations Induces the Upregulation of Hydrogen-Sulfide-Producing Enzymes in Human Colonic Epithelial Cell Organoids

Recently, a CRISPR-Cas9 genome-editing system was developed with introduced sequential ‘driver’ mutations in the WNT, MAPK, TGF-β, TP53 and PI3K pathways into organoids derived from normal human intestinal epithelial cells. Prior studies have demonstrated that isogenic organoids harboring mutations in the tumor suppressor genes APC, SMAD4 and TP53, as well as the oncogene KRAS, assumed more proliferative and invasive properties in vitro and in vivo. A separate body of studies implicates the role of various hydrogen sulfide (H2S)-producing enzymes in the pathogenesis of colon cancer. The current study was designed to determine if the sequential mutations in the above pathway affect the expression of various H2S producing enzymes. Western blotting was used to detect the expression of the H2S-producing enzymes cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST), as well as several key enzymes involved in H2S degradation such as thiosulfate sulfurtransferase/rhodanese (TST), ethylmalonic encephalopathy 1 protein/persulfide dioxygenase (ETHE1) and sulfide-quinone oxidoreductase (SQR). H2S levels were detected by live-cell imaging using a fluorescent H2S probe. Bioenergetic parameters were assessed by Extracellular Flux Analysis; markers of epithelial-mesenchymal transition (EMT) were assessed by Western blotting. The results show that the consecutive mutations produced gradual upregulations in CBS expression—in particular in its truncated (45 kDa) form—as well as in CSE and 3-MST expression. In more advanced organoids, when the upregulation of H2S-producing enzymes coincided with the downregulation of the H2S-degrading enzyme SQR, increased H2S generation was also detected. This effect coincided with the upregulation of cellular bioenergetics (mitochondrial respiration and/or glycolysis) and an upregulation of the Wnt/β-catenin pathway, a key effector of EMT. Thus sequential mutations in colon epithelial cells according to the Vogelstein sequence are associated with a gradual upregulation of multiple H2S generating pathways, which, in turn, translates into functional changes in cellular bioenergetics and dedifferentiation, producing more aggressive and more invasive colon cancer phenotypes.

Abstract IA007: Outcompeting cancer in the intestine

Abstract Cancers develop in a stepwise fashion as mutations in oncogenes and tumor suppressor genes accumulate. The mutations provide the cells in which they occur typically an advantage over the surrounding wild type neighbors, resulting in clonal expansion. Understanding the nature of the competitive benefit of oncogenic cells might result in the identification of targets for prevention of cancer. In particular in individuals affected by hereditary cancer syndromes, in which the initiating mutations are well-described, this is a promising strategy. I will discuss our work on intestinal carcinogenesis and the impact on stem cell properties of mutations associated with familial cancer syndromes affecting the gut. In particular I will discuss how inactivation of the tumor suppressor gene APC, which is affected in individuals suffering from Familial Adenomatous Polyposis (FAP), generates supercompetitor cells that actively suppress their neighbors. As we will see, the uncovered mechanism directly suggests a potent chemopreventive strategy that is currently being tested in a proof-of-concept clinical trial in FAP individuals. Citation Format: Louis Vermeulen. Outcompeting cancer in the intestine [abstract]. In: Proceedings of the AACR Special Conference on the Evolutionary Dynamics in Carcinogenesis and Response to Therapy; 2022 Mar 14-17. Philadelphia (PA): AACR; Cancer Res 2022;82(10 Suppl):Abstract nr IA007.

CRISPR-SID: Identifying EZH2 as a druggable target for desmoid tumors via in vivo dependency mapping

Cancer precision medicine implies identification of tumor-specific vulnerabilities associated with defined oncogenic pathways. Desmoid tumors are soft-tissue neoplasms strictly driven by Wnt signaling network hyperactivation. Despite this clearly defined genetic etiology and the strict and unique implication of the Wnt/β-catenin pathway, no specific molecular targets for these tumors have been identified. To address this caveat, we developed fast, efficient, and penetrant genetic Xenopus tropicalis desmoid tumor models to identify and characterize drug targets. We used multiplexed CRISPR/Cas9 genome editing in these models to simultaneously target a tumor suppressor gene (apc) and candidate dependency genes. Our methodology CRISPR/Cas9 selection-mediated identification of dependencies (CRISPR-SID) uses calculated deviations between experimentally observed gene editing outcomes and deep-learning-predicted double-strand break repair patterns to identify genes under negative selection during tumorigenesis. This revealed EZH2 and SUZ12, both encoding polycomb repressive complex 2 components, and the transcription factor CREB3L1 as genetic dependencies for desmoid tumors. In vivo EZH2 inhibition by Tazemetostat induced partial regression of established autochthonous tumors. In vitro models of patient desmoid tumor cells revealed a direct effect of Tazemetostat on Wnt pathway activity. CRISPR-SID represents a potent approach for invivo mapping of tumor vulnerabilities and drug target identification.

Single-cell DNA and RNA sequencing reveals the dynamics of intra-tumor heterogeneity in a colorectal cancer model

BackgroundIntra-tumor heterogeneity (ITH) encompasses cellular differences in tumors and is related to clinical outcomes such as drug resistance. However, little is known about the dynamics of ITH, owing to the lack of time-series analysis at the single-cell level. Mouse models that recapitulate cancer development are useful for controlled serial time sampling.ResultsWe performed single-cell exome and transcriptome sequencing of 200 cells to investigate how ITH is generated in a mouse colorectal cancer model. In the model, a single normal intestinal cell is grown into organoids that mimic the intestinal crypt structure. Upon RNAi-mediated downregulation of a tumor suppressor gene APC, the transduced organoids were serially transplanted into mice to allow exposure to in vivo microenvironments, which play relevant roles in cancer development. The ITH of the transcriptome increased after the transplantation, while that of the exome decreased. Mutations generated during organoid culture did not greatly change at the bulk-cell level upon the transplantation. The RNA ITH increase was due to the emergence of new transcriptional subpopulations. In contrast to the initial cells expressing mesenchymal-marker genes, new subpopulations repressed these genes after the transplantation. Analyses of colorectal cancer data from The Cancer Genome Atlas revealed a high proportion of metastatic cases in human subjects with expression patterns similar to the new cell subpopulations in mouse. These results suggest that the birth of transcriptional subpopulations may be a key for adaptation to drastic micro-environmental changes when cancer cells have sufficient genetic alterations at later tumor stages.ConclusionsThis study revealed an evolutionary dynamics of single-cell RNA and DNA heterogeneity in tumor progression, giving insights into the mesenchymal-epithelial transformation of tumor cells at metastasis in colorectal cancer.

Apc-mutant cells act as supercompetitors in intestinal tumour initiation.

A delicate equilibrium of WNT agonists and antagonists in the intestinal stem cell (ISC) niche is critical to maintaining the ISC compartment, as it accommodates the rapid renewal of the gut lining. Disruption of this balance by mutations in the tumour suppressor gene APC, which are found in approximately 80% of all human colon cancers, leads to unrestrained activation of the WNT pathway1,2. It has previously been established that Apc-mutant cells have a competitive advantage over wild-type ISCs3. Consequently, Apc-mutant ISCs frequently outcompete all wild-type stem cells within a crypt, thereby reaching clonal fixation in the tissue and initiating cancer formation. However, whether the increased relative fitness of Apc-mutant ISCs involves only cell-intrinsic features or whether Apc mutants are actively involved in the elimination of their wild-type neighbours remains unresolved. Here we show that Apc-mutant ISCs function as bona fide supercompetitors by secreting WNT antagonists, thereby inducing differentiation of neighbouring wild-type ISCs. Lithium chloride prevented the expansion of Apc-mutant clones and the formation of adenomas by rendering wild-type ISCs insensitive to WNT antagonists through downstream activation of WNT by inhibition of GSK3β. Our work suggests that boosting the fitness of healthy cells to limit the expansion of pre-malignant clones may be a powerful strategy to limit the formation of cancers in high-risk individuals.

P041 CDKN2B-AS1 (ANRIL) expression is decreased in Inflammatory Bowel Disease epithelia and in Celiac, and its reduction is linked with induced cells proliferation

Abstract Background Long non-coding RNAs (lncRNAs) have attenuated expression in several immune-mediated disorders. Using mRNAseq of intestinal biopsies, we identified a widespread dysregulation of 459 lncRNAs in the ileum of treatment-naïve pediatric Crohn Disease (CD) patients. We noted that large fraction of downregulated lncRNAs were correlated with epithelial functions. CDKN2B-AS1 (ANRIL) is one of the top most down-regulated lncRNA in CD, and showed decreased expression in Ulcerative Colitis (UC) colon tissues in recent studies. Methods Transcriptomics data is used to evaluate CDKN2B-AS1 expression in mucosal biopsies datasets and in gut epithelia. siRNA oligonucleotides targeting most CDKN2B-AS1 transcripts using Lipofectamine RNAiMAX is used to modulate CDKN2B-AS1 function, and RT-PCR to evaluate mRNA expression. xCELLigence system with gold microelectrodes in plate base is used to measure the impedance as an indicator for cell index. Results CDKN2B-AS1 is down-regulated in bulk mucosal biopsies obtained from CD ileum [fold change (FC) -8, corrected p=1.6E-5], in UC rectum (FC -9.4, corrected p=3.9E-18), and in celiac duodenum (FC -2.3, corrected p=0.03) in comparison to controls. CDKN2B-AS1 is detected under basal conditions in HT-29 cells. Two sets of CDKN2B-AS1 siRNA oligonucleotides (targeting most transcripts) achieved up to 60% reduction in CDKN2B-AS1 expression in HT-29 cells (p=1E-04) as confirmed by RT-PCR using two sets of primers. CDKN2B-AS1 reduction significantly increased cell index as measured by xCELLigence (doubled the index, p=1.7E-03). mRNAseq of the CDKN2B-AS1 reduced HT-29, showed reduction of the tumor suppressor gene APC in CDKN2B-AS1 siRNA treated cells (FC=-1.75, p=0.04) and of TGFBR2 (FC=-1.75, p=0.04). In contrast, reduction of CDKN2B-AS1 resulted in increase in WNT11 (FC=2.1, p=0.02) and TGFB1 (FC=1.9, p=0.04), and induction of the replication associated topoisomerase TOP1MT (FC=2.7, p=0.001). We confirmed these mRNAseq results using RT-PCR. Finally, mimicking inflammation by treating HT-29 with IL1β and LPS, reduced CDKN2B-AS1 expression (by 70%, p=6.3E-04) and doubled the cell index (p=1.8E-03). Conclusion We detected reduced CDKN2B-AS1 expression in three inflammatory disease affecting the gut in different location along the GI tract. Using HT-29 model system we were able to show, as was previously shown, an increase in cell index in CDKN2B-AS1 siRNA treated cells. We supplement those showing effect on down-stream genes that may be relevant in controlling cell proliferation. We further show that upon inflammatory triggering of HT-29 cells, CDKN2B-AS1 expression is reduced and cell index is increased, which may suggest a potential role in epithelial renewal in inflammation.

Familial Adenomatous Polyposis Associated With Bilateral Adrenocortical Tumors and Agressive Desmoid Tumor

Background: Familial adenomatous polyposis (FAP) is an autosomal dominant condition caused by germline mutation in the tumor suppressor gene APC. FAP occurs in 1 to 10.000 individuals, and is characterized by hundreds to thousands of colonic adenomatous polyps with a high risk of developing into colorectal cancer. Extracolonic manifestations can be malignant or benign. The major causes of morbidity and mortality in patients with FAP are abdominal desmoid tumors, with incidences ranging between 7% and 17%. Adrenal incidentaloma are frequently discovered in these patients, generally as benign lesions when they undergo abdominal CT-scan in the course of surveillance. Adrenal lesions in FAP ranged from 7.4% to 16%. We described an unusual patient with FAP, associated with autonomous cortisol production due to bilateral adrenal tumors and the development of aggressive desmoid tumor after unilateral adrenalectomy. Clinical Case: A 33-years-old female FAP-patient presented with abdominal pain, weight gain (10kgs), humor instability, paroxysmal of chest pain, dizziness and tremors. The abdominal MRI showed a heterogeneous, left adrenal mass (9.0 x 7.9 x 6.7cm), suspected for malignant tumor, and right adrenal mass with 3.6 x 1.8 cm suggestive of adenoma. Abdominal CT and PETCTFDG revealed on the left adrenal lesion with 33UH and maxSUV 3.9 and a right adrenal lesion 13UH and maxSUV 3.1. Serum hormone levels were as follows: cortisol after DST (1mg-dexamethasone) 4.8 ug/Dl, ACTH 8,8pg/Ml with no other abnormal hormone secretion detected. Patient underwent left adrenalectomy. Histological analysis revealed Weiss 1, modified Weiss 2 and Ki67 <1% compatible with adenoma. On follow-up, abdominal MRI revealed a 4.3cm-solid-homogeneous mass at the surgical incision, suspected of malignance. The mass progressively enlarged to 6.3 cm in diameter. Histological analysis of the biopsy identified a desmoid tumor. The contralateral adrenal tumor maintained stable during the follow-up; however, it began to produce cortisol autonomous secretion as observed on DST. The patient developed metabolic syndrome and did not present classical Cushing’ syndrome. Contralateral adrenalectomy was contraindicated because of concern of emergence of a new desmoid tumor. Discussion: FAP-associated with adrenal tumors can produce mineralocorticoids, corticosteroids, or both. Although adrenal cortical tumors have been reported frequently in FAP patients, the presence of bilateral commitment tumors on adrenal glands is extremely rare. Conclusion: We reported a woman with FAP and bilateral adrenal tumors with non-synchronic cortisol secretion associated with an aggressive desmoid tumor developing after the adrenalectomy. The patient is taking an adrenal inhibitor of steroidogenesis to control cortisol secretion and to provide clinical improvement.

Getting a Grip on the Undrugged: Targeting β-Catenin with Fragment-Based Methods.

Aberrant WNT pathway activation, leading to nuclear accumulation of β‐catenin, is a key oncogenic driver event. Mutations in the tumor suppressor gene APC lead to impaired proteasomal degradation of β‐catenin and subsequent nuclear translocation. Restoring cellular degradation of β‐catenin represents a potential therapeutic strategy. Here, we report the fragment‐based discovery of a small molecule binder to β‐catenin, including the structural elucidation of the binding mode by X‐ray crystallography. The difficulty in drugging β‐catenin was confirmed as the primary screening campaigns identified only few and very weak hits. Iterative virtual and NMR screening techniques were required to discover a compound with sufficient potency to be able to obtain an X‐ray co‐crystal structure. The binding site is located between armadillo repeats two and three, adjacent to the BCL9 and TCF4 binding sites. Genetic studies show that it is unlikely to be useful for the development of protein–protein interaction inhibitors but structural information and established assays provide a solid basis for a prospective optimization towards β‐catenin proteolysis targeting chimeras (PROTACs) as alternative modality.

A RAC-GEF network critical for early intestinal tumourigenesis

RAC1 activity is critical for intestinal homeostasis, and is required for hyperproliferation driven by loss of the tumour suppressor gene Apc in the murine intestine. To avoid the impact of direct targeting upon homeostasis, we reasoned that indirect targeting of RAC1 via RAC-GEFs might be effective. Transcriptional profiling of Apc deficient intestinal tissue identified Vav3 and Tiam1 as key targets. Deletion of these indicated that while TIAM1 deficiency could suppress Apc-driven hyperproliferation, it had no impact upon tumourigenesis, while VAV3 deficiency had no effect. Intriguingly, deletion of either gene resulted in upregulation of Vav2, with subsequent targeting of all three (Vav2−/−Vav3−/−Tiam1−/−), profoundly suppressing hyperproliferation, tumourigenesis and RAC1 activity, without impacting normal homeostasis. Critically, the observed RAC-GEF dependency was negated by oncogenic KRAS mutation. Together, these data demonstrate that while targeting RAC-GEF molecules may have therapeutic impact at early stages, this benefit may be lost in late stage disease.

Genes regulating membrane-associated E-cadherin and proliferation in adenomatous polyposis coli mutant colon cancer cells: High content siRNA screen.

Truncating mutations in the tumour suppressor gene APC occur frequently in colorectal cancers and result in the deregulation of Wnt signalling as well as changes in cell-cell adhesion. Using quantitative imaging based on the detection of membrane-associated E-cadherin, we undertook a protein coding genome-wide siRNA screen to identify genes that regulate cell surface E-cadherin in the APC-defective colorectal cancer cell line SW480. We identified a diverse set of regulators of E-cadherin that offer new insights into the regulation of cell-cell adhesion, junction formation and genes that regulate proliferation or survival of SW480 cells. Among the genes whose depletion promotes membrane-associated E-cadherin, we identified ZEB1, the microRNA200 family, and proteins such as a ubiquitin ligase UBE2E3, CDK8, sorting nexin 27 (SNX27) and the matrix metalloproteinases, MMP14 and MMP19. The screen also identified 167 proteins required for maintaining E-cadherin at cell-cell adherens junctions, including known junctional proteins, CTNND1 and CTNNA1, as well as signalling enzymes, DUSP4 and MARK2, and transcription factors, TEAD3, RUNX2 and TRAM2. A better understanding of the post-translational regulation of E-cadherin provides new opportunities for restoring cell-cell adhesion in APC-defective cells.

Abstract 6007: Post-fasting refeeding enhances intestinal stem cell-mediated regeneration and tumorigenesis

Abstract Although short-term fasting interventions improve intestinal stem cell (ISC) function, little is known about how much of this benefit comes from fasting versus the post-fasting refeeding response. Given the central role that ISCs play in driving injury-induced repair and in initiating early intestinal tumors, it is possible that fasting by boosting ISC function not only improves regeneration but also unexpectedly elevates intestinal tumorigenesis. To understand how fasting/refeeding interventions influence the role of ISCs in regeneration and early tumor formation, we assessed the function of ISCs to repair the intestinal lining after injury and to contribute to intestinal tumors. Notably, we find that 24 hours post-fasting refeeding boosts intestinal stem and progenitor cells proliferation and increases ISC function in organoid and in fate mapping assays compared to AL and fasted cohorts. Mechanistically, elevated mammalian target of rapamycin (mTOR) activity mediates the effects of refeeding in ISCs as treatment with mTOR inhibitor blocks these effects. Surprisingly, loss of the APC tumor suppressor gene in ISCs increased intestinal tumor numbers in the refed state compared to the AL and fasted states in an mTOR dependent manner. We propose that refeeding through mTOR signaling stimulates ISC function and in a context-dependent manner this can either improve repair after injury or promote intestinal tumorigenesis. Citation Format: Shinya Imada. Post-fasting refeeding enhances intestinal stem cell-mediated regeneration and tumorigenesis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6007.

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

Abstract 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.