Microsatellite Instability Cell Research Articles

Discovery of WRN inhibitor HRO761 with synthetic lethality in MSI cancers

The Werner syndrome RecQ helicase WRN was identified as a synthetic lethal target in cancer cells with microsatellite instability (MSI) by several genetic screens1–6. Despite advances in treatment with immune checkpoint inhibitors7–10, there is an unmet need in the treatment of MSI cancers11–14. Here we report the structural, biochemical, cellular and pharmacological characterization of the clinical-stage WRN helicase inhibitor HRO761, which was identified through an innovative hit-finding and lead-optimization strategy. HRO761 is a potent, selective, allosteric WRN inhibitor that binds at the interface of the D1 and D2 helicase domains, locking WRN in an inactive conformation. Pharmacological inhibition by HRO761 recapitulated the phenotype observed by WRN genetic suppression, leading to DNA damage and inhibition of tumour cell growth selectively in MSI cells in a p53-independent manner. Moreover, HRO761 led to WRN degradation in MSI cells but not in microsatellite-stable cells. Oral treatment with HRO761 resulted in dose-dependent in vivo DNA damage induction and tumour growth inhibition in MSI cell- and patient-derived xenograft models. These findings represent preclinical pharmacological validation of WRN as a therapeutic target in MSI cancers. A clinical trial with HRO761 (NCT05838768) is ongoing to assess the safety, tolerability and preliminary anti-tumour activity in patients with MSI colorectal cancer and other MSI solid tumours.

Cold atmospheric plasma stabilizes mismatch repair for effective, uniform treatment of diverse colorectal cancer cell types

Mismatch Repair (MMR) mechanisms play a pivotal role in rectifying DNA replication errors and maintaining the stability of DNA microsatellite structure. Colorectal cancer (CRC) can be characterized into microsatellite stability (MSS) and microsatellite instability (MSI) subtypes based on the functionality of MMR. MSI CRC notably exhibits enhanced chemotherapy resistance, attributable to diminished MMR-related protein expression. Cold atmospheric plasma (CAP) has emerged as a promising treatment modality, demonstrating efficacy in inducing apoptosis in various cancer cells. However, the therapeutic impact of CAP on MSI colorectal cancer, and the underlying mechanisms remain elusive. In this study, we investigated the effects of CAP on MSI (MC38, HCT116, and LOVO) and MSS (CT26 and HT29) CRC cell lines. We are probing into the products of CAP treatment. Our findings indicate that CAP treatment induces comparable effects on apoptosis, reactive oxygen species (ROS), and reactive nitrogen species (RNS), as well as the expression of apoptosis-related proteins in both MSI and MSS cells. Mechanistically, CAP treatment led to an elevation in the expression of mismatch repair proteins (MLH1 and MSH2), particularly in MSI cells, which notably have been proven to facilitate the activation of apoptosis-related proteins. Collectively, our study reveals that CAP enhances apoptotic signaling and induces apoptosis in MSI colorectal cancer cells by upregulating the expression of MMR-related proteins, thereby reinforcing MMR stabilization.

A pan-cancer analysis of TTC9A expression level and its correlation with prognosis and immune microenvironment

To investigate the expression level of tetratricopeptide repeat protein 9A in tumors and its association with the patients' prognosis and immune infiltration. TTC9A expression in different tumor tissues and its association with prognosis, DNA methylation, tumor mutation burden (TMB), and microsatellite instability (MSI) were analyzed based on data from TCGA and GTEx. TIMER and xCell were used to analyze the relationship between TTC9A expression and immune infiltration. Western blotting and RT-qPCR were used to detect the expression of TTC9A in 4 types of cancer cell lines. TTC9A expressions were significantly increased in many tumors and down-regulated in a few cancer types (P < 0.05). Western blotting and RT-qPCR showed that TTC9A expressions were elevated in lung, colon and liver cancer cells but decreased in bladder cancer cells. In head and neck squamous cell carcinoma, renal clear cell carcinoma, renal papillary cell carcinoma, low-grade glioma, malignant mesothelioma, and endometrial carcinoma tumors, a high expression of TTC9A was strongly correlated with better overall survival (OS), disease-specific survival (DSS), and progression-free interval (PFI) (P < 0.05), but was correlated with worse OS, DSS, and PFI in lung adenocarcinoma, pancreatic adenocarcinoma, adrenal carcinoma, and rectal adenocarcinoma (P < 0.05). TTC9A hypermethylation was associated with a more favorable prognosis of glioblastoma multiforme, low- grade glioma, uveal melanoma, and ovarian plasmacytoid cystadenocarcinoma (P < 0.05) but with poor prognosis of squamous cell carcinoma of the uterine cervix and intracervical adenocarcinoma, squamous cell carcinoma of head and neck, squamous cell carcinoma of the lungs, adrenal carcinoma, and endometrial carcinoma (P < 0.05). In most of the cancer types, TTC9A was significantly correlated with the level of immune cell infiltration (P < 0.05). TTC9A can be used as a prognostic marker for a variety of cancers and is strongly associated with TBM, MSI and immune cell infiltration.

Abstract PR007: Discovery of HRO761, a novel, first-in-class clinical stage WRN inhibitor with potent and selective anti-tumor activity in cancers with microsatellite instability

Abstract The RecQ DNA helicase WRN was identified as a synthetic lethal target in tumors with microsatellite instability (MSI) by several genetic screens. Despite recent advances in the treatment of MSI tumors by immune checkpoint inhibitors, a significant proportion of patients still fails to respond to or relapses after single agent anti-PD1 or combination of anti-PD1 plus anti-CTLA4 treatments. We present the biochemical, cellular and pharmacological characterization of the first potent and selective WRN helicase inhibitor, HRO761. We show that HRO761 is an allosteric WRN inhibitor that binds at the interface of the D1 and D2 helicase domains, locking WRN in an inactive conformation. Pharmacological inhibition of WRN by HRO761 recapitulates the phenotype observed by WRN genetic suppression, leading to activation of the DNA damage response and inhibition of tumor cell growth selectively in MSI but not in MSS cells. We further show that WRN inhibition leads to WRN protein degradation only in MSI tumor cells. Although HRO761 activates a p53-related response, anti-proliferative effects were observed in both p53 wild-type as well as p53 null or mutated tumor cells. HRO761 exposure in mice is linear with oral dose and results in dose-dependent in vivo DNA damage induction and tumor growth inhibition in MSI cell- and patient-derived xenograft models. Altogether these findings represent preclinical pharmacological validation of WRN as a selective therapeutic target in MSI cancers. A global first in human clinical trial with HRO761 (NCT05838768) is currently ongoing to assess the safety, tolerability and preliminary anti-tumor activity in patients with MSI colorectal cancer and other MSI solid tumors. Citation Format: Marta Cortes-Cros, Henrik Moebitz, Stephanie Barbe, Jutta Blank, Vincent Bordas, Giorgia Clementi, Ernesta Dammassa, Andrea Decker, Noemi Di Nanni, Ruben de Kanter, Marion Dourdoigne, Elena Gavioli, Stephane Ferretti, Marc Hattenberger, Christelle Hemmerlin, Jacques Hamon, Juergen Hinrichs, Isabel Jaco, Dragana Jankovic, Eloisa Jimenez Nunez, Yifang Li, Hans-Joerg Martus, Michele Moschetta, Cornelia Quadt, Markus Reschke, Vincent Romanet, Clemens Scheufler, Joseph Schoepfer, Ross Strang, Maxime Therier, Hans Voshol, Markus Wartmann, Sarah Welly, Monica Pham, Laurent Laborde. Discovery of HRO761, a novel, first-in-class clinical stage WRN inhibitor with potent and selective anti-tumor activity in cancers with microsatellite instability [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr PR007.

Pan-cancer analysis of SYNGR2 with a focus on clinical implications and immune landscape in liver hepatocellular carcinoma

BackgroundSynaptogyrin-2 (SYNGR2), as a member of synaptogyrin gene family, is overexpressed in several types of cancer. However, the role of SYNGR2 in pan-cancer is largely unexplored.MethodsFrom the TCGA and GEO databases, we obtained bulk transcriptomes, and clinical information. We examined the expression patterns, prognostic values, and diagnostic value of SYNGR2 in pan-cancer, and investigated the relationship of SYNGR2 expression with tumor mutation burden (TMB), microsatellite instability (MSI), immune infiltration, and immune checkpoint (ICP) genes. The gene set enrichment analysis (GSEA) software was used to perform pathway analysis. Besides, we built a nomogram of liver hepatocellular carcinoma patients (LIHC) and validated its prediction accuracy.ResultsSYNGR2 was highly expressed in most cancers. The high expression of SYNGR2 significantly reduced the overall survival (OS), disease-specific survival (DSS), disease-free interval (DFI), and progression-free interval (PFI) in multiple types of cancer. Also, receiver operating characteristic (ROC) curve analysis demonstrated that SYNGR2 showed high accuracy in distinguishing cancerous tissues from normal ones. Moreover, SYNGR2 expression was correlated with TMB, MSI, immune scores, and immune cell infiltrations. We also analyzed the association of SYNGR2 with immunotherapy response in LIHC. Finally, a nomogram including SYNGR2 and pathologic T, N, M stage was built and exhibited good predictive power for the OS, DSS, and PFI of LIHC patients.ConclusionOverall, SYNGR2 is a critical oncogene in various tumors. SYNGR2 participates in the carcinogenic progression, and may contribute to the immune infiltration in tumor microenvironment. Our study suggests that SYNGR2 can serve as a predictor related to prognosis in pan-cancer, especially LIHC.

Pan-cancer analysis of the oncogenic role of HNRNPR in human tumors.

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are potential cancer biomarkers. Little is known about the role of HNRNPR, an essential member of the hnRNP family, in human tumours. This study aims to explore the potential value of HNRNPR across cancers, based on The Cancer Genome Atlas (TCGA). The expression level, mutation, DNA methylation, phosphorylation status, survival status, pathological stage, tumor mutation burden (TMB), microsatellite instability (MSI), immune cell infiltration, and immune signature related to HNRNPR were analyzed. HNRNPR expression level was increased in several types of cancer and was associated with poor prognosis, especially in liver hepatocellular carcinoma (LIHC). HNRNPR was also correlated with antitumour immunity, and associated with TMB, MSI, and immune cell activation status across cancers. Furthermore, nomograms were established to predict the prognosis of LIHC, based on HNRNPR and other clinical characteristics. Functional enrichment analysis showed the mechanisms of HNRNPR-mediated LIHC progression. Loss-of-function experiments demonstrated that inhibition of HNRNPR could remarkably suppress hepatocellular carcinoma (HCC) cell proliferation, migration, invasion, and Epithelial-Mesenchymal Transition abilities. Our study offers a comprehensive understanding of the oncogenic roles of HNRNPR across different tumours, and demonstrates that HNRNPR might foster the proliferation, migration, and invasion abilities of HCC cells.

A prognostic and immunological analysis of 7B-containing Kelch structural domain (KLHDC7B) in pan-cancer: a potential target for immunotherapy and survival.

KLHDC7B is a member of Kelch family, with a Kelch domain in the C-terminal half, which plays a role in various cellular events, such as cytoskeletal arrangement, protein degradation, gene expression. Although there is increasing evidence supporting KLHDC7B's vital role in tumorigenesis, a systematic analysis of KLHDC7B in cancers remains lacking. Therefore, we intended to investigate the prognostic value for KLHDC7B across 33 cancer types and explore its potential immunological function. GEO (Gene Expression Omnibus database) and TCGA (The Cancer Genome Atla) database were used to explore the role of KLHDC7B in 33 cancers. TIMER2, GEPIA2 and Kaplan-Meier plotter were utilized to explore the KLHDC7B expression level and prognostic value in different cancers. The pan cancer genetic variation and DNA methylation of KLHDC7B were analyzed by cBioPortal and MEXPRESS. TIMER2 was employed to investigate the correlation between KLHDC7B expression and immune infiltration. The relationship of KLHDC7B expression with TMB (tumor mutational burden) and MSI (microsatellite instability) were evaluated using Spearman correlation analysis. Finally, by GO and KEGG enrichment analysis, the underlying mechanisms of KLHDC7B in tumor pathophysiology were further investigated. KLHDC7B expression level was related to pathological stages, MSI, TMB, immune checkpoint and immune cell infiltration in most cancers. Especially, we found that the KLHDC7B expression was negatively correlated with the immune infiltration of Myeloid derived suppressor cells into TGCT and GBM. Additionally, survival analysis showed that the expression of KLHDC7B was connected with overall survival (OS) in 3 cancers and disease-free survival (DFS) in 5 cancers. Furthermore, the enrichment analysis revealed that the KLHDC7B collecting genes and binding proteins are related to the function of proteins and immune response. KLHDC7B demonstrates strong clinical utility as markers of prognostic and immune response in pan-cancer.

Systematic pan-cancer analysis identifies transmembrane protein 158 as a potential therapeutic, prognostic and immunological biomarker.

The purpose of this study was to investigate the expression significance, predictive value, immunologic function, and biological role of transmembrane protein 158 (TMEM158) in the development of pan-cancer. To achieve this, we utilized data from multiple databases, including TCGA, GTEx, GEPIA, and TIMER, to collect gene transcriptome, patient prognosis, and tumor immune data. We evaluated the association of TMEM158 with patient prognosis, tumor mutational burden (TMB), and microsatellite instability (MSI) in pan-cancer samples. We performed immune checkpoint gene co-expression analysis and gene set enrichment analysis (GSEA) to better understand the immunologic function of TMEM158. Our findings revealed that TMEM158 was significantly differentially expressed between most types of cancer tissues and their adjacent normal tissues and was associated with prognosis. Moreover, TMEM158 was significantly correlated with TMB, MSI, and tumor immune cell infiltration in multiple cancers. Co-expression analysis of immune checkpoint genes showed that TMEM158 was related to the expression of several common immune checkpoint genes, especially CTLA4 and LAG3. Gene enrichment analysis further revealed that TMEM158 was involved in multiple immune-related biological pathways in pan-cancer. Overall, this systematic pan-cancer analysis suggests that TMEM158 is generally highly expressed in various cancer tissues and is closely related to patient prognosis and survival across multiple cancer types. TMEM158 may serve as a significant predictor of cancer prognosis and modulate immune responses to various types of cancer.

Glutathione peroxidase 2: A key factor in the development of microsatellite instability in colon cancer.

Much research has focused on detecting microsatellite instability (MSI), which is frequently employed in the diagnosis and treatment of patients with colon cancer. However, the causes and progression of MSI in colon cancer have not yet been thoroughly elucidated. In this study, we screened and validated the genes associated with MSI in colorectal adenocarcinoma (COAD) using bioinformatics analysis. MSI-related genes of COAD were obtained from the Gene Expression Omnibus dataset, Search Tool for the Retrieval of Interaction Gene/Proteins, Gene Set Enrichment Analysis, and Human Protein Atlas. The function, prognostic value, and immune connection of MSI-related genes in COAD were examined using Cytoscape 3.9.1, the Human Gene Database, and the Tumor IMmune Estimation Resource. Key genes were verified using The Cancer Genome Atlas database and immunohistochemistry of clinical tumor samples. We identified 59 MSI-related genes in patients with colon cancer. The protein interaction network of these genes was developed, and numerous functional modules associated with MSI were discovered. Pathways related to MSI were identified using KEGG enrichment analysis, and these included chemokine signaling, thyroid hormone synthesis, cytokine receptor interaction, estrogen signaling, and Wnt signaling pathways. Further analyses were used to identify the MSI-related gene, glutathione peroxidase 2 (GPX2), which was closely related to the occurrence of COAD and tumor immunity. In COAD, GPX2 may be crucial for the establishment of MSI and tumor immunity, and its deficiency may result in MSI and immune cell infiltration in colon cancer.

Clinical implication and immunological landscape analyses of ANLN in pan-cancer: A new target for cancer research.

Anillin is a F-actin binding protein (ANLN) mainly involved in the process of cytokinesis and known to be dysregulated in diverse cancers. However, the role of ANLN in pan-cancer prognosis and tumor immunity remains unclear. Gene expression profiles of 31 solid tumors were downloaded from The Cancer Genome Atlas (TCGA) database. ANLN mRNA and protein expression were quantified using quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC). Protein expression of ANLN was further confirmed in Human Protein Atlas (HPA) database. Cox regression and Kaplan-Meier analysis were utilized to assess the prognostic value of ANLN in pan-cancer. The correlation between ANLN and different immune gene markers and infiltration cells was analyzed via ESTIMATE and CIBERSORT. A BLCA immunotherapy cohort: IMvigor (210) was used to confirm the role of ANLN in immune response. ANLN upregulation was detected in 21 types of cancers and was associated with poor overall survival (OS), disease-free interval (DFI), and progression-free interval (PFI) in most cancers except in THYM (Thymoma). Additionally, correlation analysis revealed a significantly positive association between ANLN expression and tumor mutation burden (TMB), microsatellite instability (MSI), immune cells infiltration. and immune checkpoint genes in various cancers. The BLCA immunotherapy cohort confirmed that patients with higher ANLN level had better immune responses and longer OS. ANLN may serve as a prognostic biomarker for pan-cancer. ANLN upregulation is associated with higher TMB, MSI, and immune cell infiltration in multiple types of tumors, shedding new light for cancer treatment.

A systematic analysis of C5ORF46 in gastrointestinal tumors as a potential prognostic and immunological biomarker.

Background: Chromosome 5 open reading frame 46 (C5ORF46), also known as antimicrobial peptide with 64 amino acid residues (AP-64) and skin and saliva-secreted protein 1 (SSSP1), belongs to the family of open reading frame genes and encodes a small exosomal protein. C5ORF46 has been implicated in antibacterial activity and associated with patient prognosis in pancreatic cancer, colorectal cancer, and stomach cancer. These findings highlight the importance of C5ORF46 in gastrointestinal (GI) tumor inception and development. However, the prognostic and immunological value of C5ORF46 in human GI tumors remains largely unknown. In this study, we sought to explore the potential value of C5ORF46 in GI tumor prognosis and immunology. Method: RNA sequencing (RNA-seq) was performed on the tumor and tumor-adjacent normal samples we collected to identify potential target genes for GI tumors. Apart from our RNA-seq data, all original data were downloaded from The Cancer Genome Atlas (TCGA) database and integrated via Strawberry Perl (v 5.32.0) and R (v 4.1.1). The differential expression of C5ORF46 was examined with Oncomine, Tumor Immune Estimation Resource (TIMER), Gene Expression Profiling Interactive Analysis (GEPIA), Cancer Cell Line Encyclopedia (CCLE), the Human Protein Atlas (HPA) and TCGA databases. The c-BioPortal database was used to investigate the genomic alterations of C5ORF46. The effect of C5ORF46 on prognosis and clinical phenotypes was explored via bioinformatics analyses on the TCGA and GEPIA databases. We used the bioinformatics analyses based on the TCGA database to analyze tumor mutational burden (TMB), microsatellite instability (MSI), tumor immune cell infiltration, and the correlations between C5ORF46 expression and several immune-related genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was carried out via the DAVID website and presented as bubble charts using ShengXinRen online tools. Gene set enrichment analysis (GSEA) was performed using R scripts based on data downloaded from the GSEA website. Immunohistochemistry (IHC) was used to validate the expression of C5ORF46 in GI tumors. Results: The results of our RNA-seq data indicated a critical role for C5ORF46 in colon carcinogenesis. Consistently, we demonstrated that C5ORF46 was highly expressed in tumor tissues compared to normal tissues in human GI tumors. Moreover, a strong correlation was observed between C5ORF46 expression levels and patient prognosis, staging, TMB, MSI, and immune cell infiltration. Further, C5ORF46 presented as an important regulator in the tumor microenvironment (TME) and was active in the regulation of cancer immune functions. C5ORF46 is significantly correlated with genes regulating inflammation and immune responses. Conclusion: C5ORF46 may serve as a biomarker for GI tumor prognosis and immunology. C5ORF46 could be a novel target for GI tumor immunotherapy.

A Pan-Cancer Analysis Revealing the Dual Roles of Lysine (K)-Specific Demethylase 6B in Tumorigenesis and Immunity.

Introduction: Epigenetic-targeted therapy has been increasingly applied in the treatment of cancers. Lysine (K)-specific demethylase 6B (KDM6B) is an epigenetic enzyme involved in the coordinated control between cellular intrinsic regulators and the tissue microenvironment whereas the pan-cancer analysis of KDM6B remains unavailable. Methods: The dual role of KDM6B in 33 cancers was investigated based on the GEO (Gene Expression Omnibus) and TCGA (The Cancer Genome Atlas) databases. TIMER2 and GEPIA2 were applied to investigate the KDM6B levels in different subtypes or stages of tumors. Besides, the Human Protein Atlas database allowed us to conduct a pan-cancer study of the KDM6B protein levels. GEPIA2 and Kaplan–Meier plotter were used for the prognosis analysis in different cancers. Characterization of genetic modifications of the KDM6B gene was analyzed by the cBioPortal. DNA methylation levels of different KDM6B probes in different TCGA tumors were analyzed by MEXPRESS. TIMER2 was applied to determine the association of the KDM6B expression and immune infiltration and DNA methyltransferases. Spearman correlation analysis was used to assess the association of the KDM6B expression with TMB (tumor mutation burden) and MSI (microsatellite instability). The KEGG (Kyoto encyclopedia of genes and genomes) pathway analysis and GO (Gene ontology) enrichment analysis were used to further investigate the potential mechanism of KDM6B in tumor pathophysiology. Results: KDM6B was downregulated in 11 cancer types and upregulated across five types. In KIRC (kidney renal clear cell carcinoma) and OV (ovarian serous cystadenocarcinoma), the KDM6B level was significantly associated with the pathological stage. A high level of KDM6B was related to poor OS (overall survival) outcomes for THCA (thyroid carcinoma), while a low level was correlated with poor OS and DFS (disease-free survival) prognosis of KIRC. The KDM6B expression level was associated with TMB, MSI, and immune cell infiltration, particularly cancer-associated fibroblasts, across various cancer types with different correlations. Furthermore, the enrichment analysis revealed the relationship between H3K4 and H3K27 methylation and KDM6B function. Conclusion: Dysregulation of the DNA methyltransferase activity and methylation levels of H3K4 and H3K27 may involve in the dual role of KDM6B in tumorigenesis and development. Our study offered a relatively comprehensive understanding of KDM6B’s dual role in cancer development and response to immunotherapy.

Pan-Cancer Analysis of the Characteristics of LY96 in Prognosis and Immunotherapy Across Human Cancer.

Lymphocyte antigen 96 (LY96) is implicated in tumorigenesis by modulating host immunity. However, an integrated pan-cancer analysis of LY96 in prognosis and immunotherapy across human cancers is still lacking. Therefore, we analyzed the LY96 expression and its prognostic role in tumors by multiple databases. We also investigated the correlation between LY96 and copy number, DNA methylation, somatic mutation, microsatellite instability (MSI), tumor mutation burden (TMB), tumor microenvironment (TME), and immune cell infiltration across human cancers. In addition, the biological processes related to LY96 across various tumors and the correlation between LY96 and 50% inhibitive concentration (IC50) of various drugs were investigated. We found that LY96 was differently expressed between tumor and normal tissues and was significantly upregulated in most types of cancers. LY96 was gradually upregulated from stages I to IV in several cancers. Moreover, we found LY96 may play a prognostic role in most cancers, and patients with high or low LY96 expression often show different clinical outcomes. LY96 was also associated with copy number, DNA methylation, somatic mutation, MSI, TMB, TME characteristics, and immune cell infiltration in cancers. LY96 may also regulate classic tumor-associated pathways in several cancers and is related to drug resistance. This article may help to elucidate the role of LY96 in tumorigenesis, which may promote the development of immunotherapy and targeted therapy in cancers.

Irinotecan or Oxaliplatin: Which is the First Move for the Mate?

The aim of the present review is to discuss the potential link between RAS, BRAF and microsatellite instability (MSI) mutational patterns and chemotherapeutic agent efficacy [Irinotecan (IRI) vs. Oxaliplatin (OXA)], and how this can potentially influence the choice of the chemotherapy backbone. Following a review of the research literature, all pertinent articles published in the core journals were selected for the study. The inclusion criteria regarded relevant clinical and pre-clinical studies on the topic of interest (Relationship of OXA and IRI to KRAS/BRAF mutations and MSI). Excision repair cross complementation group 1 (ERCC1) expression is inhibited by KRAS mutation, making tumor cells more sensitive to OXA. Results from OPUS, COIN and PRIME trials support that no conclusive data are available for BRAF mutant population because of the small number of patients. Enhanced IRI cytotoxicity to MSI cell lines is due to the participation of some of the mismatch repair (MMR) components in various DNA repair processes and their role in the maintenance of the pro-apoptotic effect of IRI and G2/M cell arrest. OXA and IRI are indispensable drugs for mCRC treatment and their selection must be as careful as that of targeted agents. We suggest taking into consideration the interaction between known genomic alterations and OXA and IRI activity to personalize chemotherapy in mCRC patients.

TGFBR2‑dependent alterations of microRNA profiles in extracellular vesicles and parental colorectal cancer cells.

In colorectal cancer (CRC) with microsatellite instability (MSI), >90% of cases are affected by inactivating frameshift mutations of transforming growth factor β receptor type2 (TGFBR2). TGFBR2 deficiency is considered to drive MSI tumor progression by abrogating downstream TGF‑β signaling. This pathway can alter the expression of coding and non‑coding RNAs, including microRNAs (miRNAs), which are also present in extracellular vesicles (EVs) as post‑transcriptional modulators of gene expression. In our previous study, it was shown that TGFBR2 deficiency alters the protein composition and function of EVs in MSI tumors. To investigate whether mutant TGFBR2 may also affect the miRNA cargo of EVs, the present study characterized miRNAs in EVs and their parental MSI tumor cells that differed only in TGFBR2 expression status. The HCT116‑TGFBR2 MSI cell line model enables the doxycycline (dox)‑inducible reconstituted expression of TGFBR2 in an isogenic background (‑dox, TGFBR2 deficient; +dox, TGFBR2 proficient). Small RNA sequencing of cellular and EV miRNAs showed that the majority of the miRNAs (263/471; 56%) were shared between MSI tumor cells and their EVs. Exploratory data analysis revealed the TGBFR2‑dependent cluster separation of miRNA profiles in EVs and MSI tumor cells. This segregation appeared to result from two subsets of miRNAs, the expression of which were regulated in a TGFBR2‑dependent manner (EVs: n=10; MSI cells: n=15). In the EV subset, 7/10 miRNAs were downregulated and 3/10 were upregulated by TGFBR2 deficiency. In the cellular subset, 13/15 miRNAs were downregulated and 2/15 miRNAs were upregulated in the TGFBR2‑deficient cells. The present study emphasizes the general overlap of miRNA profiles in MSI tumor cells and their EVs, but also highlights the impact of a single tumor driver mutation on the expression of individual miRNAs, as exemplified by the downregulation of miR‑381‑3p in TGFBR2‑deficient MSI tumor cells and their secreted EVs.

Epigenetic changes in localized gastric cancer: the role of RUNX3 in tumor progression and the immune microenvironment.

Gastric cancer (GC) pathogenesis involves genetic, epigenetic and environmental factors. Epigenetic alterations, such as DNA methylation are considered pivotal in the inactivation of tumor-related genes. We assessed a methylation panel of 5 genes to study their association to GC progression and microsatellite instability (MSI), and studied the role of RUNX3 in GC pathogenesis and the tumor immune microenvironment.The methylation status of 47 promoter-CpG islands was studied through MALDI-TOF mass spectrometry analysis in 35 Microsatellite stable (MSS) GC, 26 MSI, and 18 cancer-free samples (CFS), and 6 MSS GC and 4 MSI GC cell lines. We also studied RUNX3 expression by immunohistochemistry (IHC) in 40 samples, and validated differences in methylation levels between tumor, normal, and immune tissue in 14 additional samples.Unsupervised hierarchical clustering of methylation levels revealed no distinct subgroups between MSI and MSS samples or cell lines. CFSs clustered together showing higher levels of RUNX3 methylation compared to GC samples. RUNX3 showed protein silencing in cancer and normal mucosa, compared to inflammatory peritumoural infiltrate in almost all cases, showing a non-lymphocytic predominant pattern and being correlated with epigenetic silencing.Our results show aberrant promoter's methylation in APC, CDH1, CDKN2A, MLH1 and RUNX3 associated with GC, as well as a non-lymphocytic predominant infiltrate with high expression of RUNX3. Deep study of RUNX3 inflammation signaling could help in understanding inflammation and immune activation in the tumor microenvironment.

Abstract 3708: Targeting synthetic lethality with PARP inhibition in colorectal cancer

Abstract Background: Small molecule poly ADP-ribose (PAR) polymerase (PARP) inhibitors (PARPi) purportedly result in DNA damage and are promising agents in the treatment of cancer. In a quest to identify best “synthetic lethality” for treatment, we have screened various combination therapies in colorectal cancer (CRC) cell lines. In addition, we have interrogated if the presence of microsatellite instability (MSI) status favor susceptibility of cells to synthetic lethality and thus acts as a prognostic marker of combination therapy. Methods: Using the SRB assay, the 12 combinations of the PARPi, veliparib (V), rucaparib (R), olaparib (Ol) and PJ34, and the cytotoxic drugs, irinotecan (I), 5-fluorouracil (5-FU) and oxaliplatin (Ox) were screened in HCT116 and LIM2405 cell lines. We assessed the effect of the combination using the CalcuSyn software for combination index (CI). We next evaluated the effectiveness and sequence dependence of combination in an additional 2 cell lines that had MSI status (RKO and HCT15) and 2 that had microsatellite stable (MSS) status (HT29 and SW837) and in 7 HCT116 isogenic lines (mutants of Bax, p21, p53, PTEN, Kras and DNMT and wild type of PIK). The combination of I and R was confirmed by FACS analysis in HCT116 and LIM2405. Results: Ol and R showed synergy in combination with I, whereas, V and PJ34 showed antagonism with Ox, including in Ox-sensitive cells. Single agent cytotoxicity was observed at 200nM for R, whereas V required more than 30uM. Early PARP-1 protein upregulation was observed upon Ox administration; but the changes were not reversed with either R or V. Nevertheless, R at 200nM and V 1uM significantly reduced PAR formation in Ox-sensitive cell lines. FACS analysis showed S phase arrest in SW837 (MSS) (p = 0.03) whereas G2-M arrest was observed in LIM2405 (MSI) (non-significant) upon treatment with R 400nM and I 200nM. In addition, studies using isogenic cell lines revealed the importance of p21, p53 and PTEN in exerting synergistic effect while combining R and I. Administration of I prior to R (24h each) was more cytotoxic than vice versa and simultaneous treatment in MSI cell lines. Conclusion: Among the various combinations studied, R with I was the most synergistic. The effect appears to be more pronounced when I precedes R, particularly in MSI cell lines. Alteration in cell cycle is MSI status dependent. Further work to identify mechanism of synergy is ongoing. Citation Format: Titto Augustine, Radhashree Maitra, Jinghang Zhang, Jay Nayak, Sanjay Goel. Targeting synthetic lethality with PARP inhibition in colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3708.

Treatment with the PARP inhibitor, niraparib, sensitizes colorectal cancer cell lines to irinotecan regardless of MSI/MSS status.

BackgroundCells with homologous recombination (HR) deficiency, most notably caused by mutations in the BRCA1 or BRCA2 genes, are sensitive to PARP inhibition. Microsatellite instability (MSI) accounts for 10-15% of colorectal cancer (CRC) and is hypothesized to lead to HR defects due to altered expression of Mre11, a protein required for double strand break (DSB) repair. Indeed, others have reported that PARP inhibition is efficacious in MSI CRC.MethodsHere we examine the response to niraparib, a potent PARP-1/PARP-2 inhibitor currently under clinical evaluation, in MSI versus microsatellite stable (MSS) CRC cell lines in vitro and in vivo. We compiled a large panel of MSI and MSS CRC cell lines and evaluated the anti-proliferative activity of niraparib. In addition to testing single agent cytotoxic activity of niraparib, we also tested irinotecan (or SN-38, the active metabolite of irinotecan) activity alone and in combination with niraparib in vitro and in vivo.ResultsIn contrast to earlier reports, MSI CRC cell lines were not more sensitive to niraparib than MSS CRC cell lines¸ suggesting that the MSI phenotype does not sensitize CRC cell lines to PARP inhibition. Moreover, even the most sensitive MSI cell lines had niraparib EC50s greater than 10 fold higher than BRCA-deficient cell lines. However, MSI lines were more sensitive to SN-38 than MSS lines, consistent with previous findings. We have also demonstrated that combination of niraparib and irinotecan was more efficacious than either agent alone in both MSI and MSS cell lines both in vitro and in vivo, and that niraparib potentiates the effect of irinotecan regardless of MSI status.ConclusionsOur results support the clinical evaluation of this combination in all CRC patients, regardless of MSI status.

Protein kinase C β inhibition by enzastaurin leads to mitotic missegregation and preferential cytotoxicity toward colorectal cancer cells with chromosomal instability (CIN)

Enzastaurin is a selective inhibitor of protein kinase C β and a potent inhibitor of tumor angiogenesis. In addition, enzastaurin shows direct cytotoxic activity toward a subset of tumor cells including colorectal cancer cells (CRC). In spite of promising results in animal models, the clinical activity of enzastaurin in CRC patients has been disappointing although a subset of patients seems to derive benefit. In the present study we investigated the biological and cytotoxic activities of enzastaurin toward a panel of well-characterized CRC cell lines in order to clarify the mechanistic basis for the cytotoxic activity. Our results show that enzastaurin is significantly more cytotoxic toward CRC cells with chromosome instability (CIN) compared to cells with microsatellite instability (MSI). Since CIN is usually attributed to mitotic dysfunction, the influence of enzastaurin on cell cycle progression and mitotic transit was characterized for representative CIN and MSI cell lines. Enzastaurin exposure was accompanied by prolonged metaphase arrest in CIN cells followed by the appearance of tetraploid and micronuclei-containing cells as well as by increased apoptosis, whereas no detectable mitotic dysfunctions were observed in MSI cells exposed to isotoxic doses of enzastaurin. Our study identifies enzastaurin as a new, context dependent member of a heterogeneous group of anticancer compounds that induce “mitotic catastrophe," that is mitotic dysfunction accompanied by cell death. These data provide novel insight into the mechanism of action of enzastaurin and may allow the identification of biomarkers useful to identify CRC patients particularly likely, or not, to benefit from treatment with enzastaurin.

A Novel Approach for Characterizing Microsatellite Instability in Cancer Cells

Microsatellite instability (MSI) is characterized by the expansion or contraction of DNA repeat tracts as a consequence of DNA mismatch repair deficiency (MMRD). Accurate detection of MSI in cancer cells is important since MSI is associated with several cancer subtypes and can help inform therapeutic decisions. Although experimental assays have been developed to detect MSI, they typically depend on a small number of known microsatellite loci or mismatch repair genes and have limited reliability. Here, we report a novel genome-wide approach for MSI detection based on the global detection of insertions and deletions (indels) in microsatellites found in expressed genes. Our large-scale analyses of 20 cancer cell lines and 123 normal individuals revealed striking indel features associated with MSI: there is a significant increase of short microsatellite deletions in MSI samples compared to microsatellite stable (MSS) ones, suggesting a mechanistic bias of repair efficiency between insertions and deletions in normal human cells. By incorporating this observation into our MSI scoring metric, we show that our approach can correctly distinguish between MSI and MSS cancer cell lines. Moreover, when we applied this approach to primal tumor samples, our metric is also well consistent with diagnosed MSI status. Thus, our study offers new insight into DNA mismatch repair system, and also provides a novel MSI diagnosis method for clinical oncology with better reliability.