Microsatellite Instability In Colorectal Cancer Research Articles

Gene mutation profiling in microsatellite instability colorectal cancer and its association with the efficacy of immunotherapy: A retrospective study.

Microsatellite instability-high (MSI-H) colorectal cancer (CRC) is known for its heightened responsiveness to immunotherapy. However, establishing robust predictive markers for immunotherapy efficacy remains imperative. This retrospective study aimed to elucidate the genetic landscape of MSI-H CRC and correlate these genetic alterations with immunotherapy outcomes in a cohort of 121 patients. We analyzed clinical and molecular data from 121 patients with MSI-H CRC. We conducted a thorough genetic analysis of MSI-H CRC patients, with a specific emphasis on the APC, TP53, RAS, and MMR genes. We further analyzed the relationship between gene mutations and immunotherapy efficacy. The primary endpoints analyzed were objective response rate (ORR) and progression-free survival (PFS). All statistical analysis was conducted using SPSS26.0 and R 4.2.0 software. Our findings underscored the complexity of the genetic landscape in MSI-H CRC, shedding light on the intricate interplay of these genes in CRC development. Notably, mutations in MMR genes exhibited a distinctive pattern, providing insights into the underlying mechanisms of MSI-H. Furthermore, our results revealed correlations between specific genetic alterations and immunotherapy outcomes, with a particular focus on treatment response rates and progression-free survival. This study represents a significant step toward unraveling the genetic nuances of MSI-H CRC. The distinctive pattern of MMR gene mutations not only adds depth to our understanding of MSI-H CRC but also hints at potential avenues for targeted therapies. This research sets the stage for future investigations aimed at refining therapeutic strategies and improving outcomes for patients with MSI-H CRC.

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.

Clinicopathological characteristics of Lynch-like syndrome.

Lynch-like syndrome (LLS) has recently been proposed as a third type of microsatellite instability (MSI) tumor after Lynch syndrome (LS) and sporadic MSI colorectal cancer (CRC) without either a germline variant of mismatch repair (MMR) genes or hypermethylation of the MLH1 gene. The present study aimed to clarify and compare the clinicopathological characteristics of LLS with those of the other MSI CRC subtypes. In total, 2634 consecutive patients with CRC who underwent surgical resection and subsequently received universal tumor screening (UTS), including MSI analysis were enrolled between January 2008 and November 2019. Genetic testing was performed in patients suspected of having Lynch syndrome. UTS of the cohort found 146 patients with MSI CRC (5.5%). Of these, excluding sporadic MSI CRC, 30 (1.1%) had a diagnosis of LS, and 19 (0.7%) had no germline pathogenic variants of the MMR gene. The CRC type in the latter group was identified as LLS. LLS occurred significantly more often in young patients, was left-sided, involved a KRAS variant and BRAF wild-type, and had a higher concordance rate with the Revised Bethesda Guidelines than sporadic MSI CRC. No significant differences were observed in terms of the clinicopathological factors between LLS and LS-associated MSI CRC; however, LLS had a lower frequency of LS-related neoplasms compared with LS. Distinguishing clinically between LS and LLS was challenging, but the incidence of neoplasms was higher in LS than in LLS, suggesting the need for different screening and surveillance methods for the two subtypes.

Inhibition of autophagy-related protein 7 enhances anti-tumor immune response and improves efficacy of immune checkpoint blockade in microsatellite instability colorectal cancer

BackgroundThe efficacy of anti-PD-1 therapy is primarily hindered by the limited T-cell immune response rate and immune evasion capacity of tumor cells. Autophagy-related protein 7 (ATG7) plays an important role in autophagy and it has been linked to cancer. However, the role of ATG7 in the effect of immune checkpoint blockade (ICB) treatment on high microsatellite instability (MSI-H)/mismatch repair deficiency (dMMR) CRC is still poorly understood.MethodsIn this study, patients from the cancer genome altas (TCGA) COAD/READ cohorts were used to investigate the biological mechanism driving ATG7 development. Several assays were conducted including the colony formation, cell viability, qRT-PCR, western blot, immunofluorescence, flow cytometry, ELISA, immunohistochemistry staining and in vivo tumorigenicity tests.ResultsWe found that ATG7 plays a crucial role in MSI-H CRC. Its knockdown decreased tumor growth and caused an infiltration of CD8+ T effector cells in vivo. ATG7 inhibition restored surface major histocompatibility complex I (MHC-I) levels, causing improved antigen presentation and anti-tumor T cell response by activating reactive oxygen species (ROS)/NF-κB pathway. Meanwhile, ATG7 inhibition also suppressed cholesterol accumulation and augmentation of anti-tumor immune responses. Combining ATG7 inhibition and statins improved the therapeutic benefit of anti-PD-1 in MSI-H CRC. Importantly, CRC patients with high expression of both ATG7 and recombinant 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) experienced worse prognosis compared to those with low ATG7 and HMGCR expression.ConclusionsInhibition of ATG7 leads to upregulation of MHC-I expression, augments immune response and suppresses cholesterol accumulation. These findings demonstrate that ATG7 inhibition has therapeutic potential and application of statins can increase the sensitivity to immune checkpoint inhibitors.

Significance of Microsatellite Instability in Colorectal Carcinoma- A Complete Review

The microsatellite instability (MSI-H) or mismatch repair deficient (dMMR) colorectal tumors recently have been reported that can benefit from immunotherapy, and MSI can be used as a genetic instability of a tumor detection index. Many studies have shown that there are many heterogeneous phenomena in patients with MSI tumors in terms of immunotherapy, prognosis and chemotherapy sensitivity. Here we mainly review the research results of MSI detection methods, its mechanisms, occurrence and its relationship with related tumors, aiming in such a way for brief analysis of the micro satellite instability. Microsatellites (MS) are the repeated sequences of DNA that play an important role in maintaining the tissue morphology. Any mutation of the DNA or chromosomes, lead to the instability of the microsatellites, thereby causing the microsatellite instability. There are three types of microsatellite instability (MSI). High microsatellite instability (MSI-H), low microsatellite instability (MSI-L) and microsatellite stability (MSS). Recent clinical research tends to classify MSS-L and MSS as similar. Microstaellite instability plays an important role in colorectal carcinoma. Based on different molecular mechanisms, MSI in colorectal cancer can be divided into colorectal cancer (CRC) with no obvious family genetic history and Lynch syndrome with non-polyposis with family genetic history. Lynch syndrome is an autosomal dominant disorder and syndrome caused by mutations in MMR strains, and it can also cause tumors in other parts of the colon and rectum. With the recent development of MSI detection technology and immunosuppressant in tumor therapy, researchers found that MSI-H tumors respond well to immunotherapy. There are several methods to detect the microsatellite instability. 1. Next Generation sequencing (NGS), 2. Fluoresence multiplex PCR and capillary electrophoresis. 3. Immunohistochemistry. 4. Single molecule- molecular inversion probes (SmMIP). The main mechanism of MSI includes, Slipped strand mispairing, MMR deficient.

Abstract 520: circBRIP1 RNA as a non-invasive target engagement pharmacodynamic biomarker for DHX9 inhibition

Abstract DHX9 is a multifunctional DEAH-box ATP-independent RNA helicase which has been reported to play important roles in replication, transcription, translation, RNA splicing and RNA processing which contribute to DHX9’s role in maintenance of genomic stability. DHX9 can bind specifically to inverted repeat Alu elements, preventing back-splicing events that lead to circular RNA and exon skipping of the linear transcript. Upon DHX9 inhibition, a robust induction of Alu-mediated circular RNA is observed. For example, circBRIP1 is an Alu-mediated circular RNA that is robustly elevated upon DHX9 loss, with no observed change to levels of linear BRIP1. Here we describe data demonstrating circBRIP1 as a DHX9 specific target engagement pharmacodynamic (PD) biomarker and its potential utility as a non-invasive clinical PD biomarker. We have previously demonstrated that DHX9 inhibition by novel small molecule inhibitors is efficacious in microsatellite instable (MSI) colorectal cancer (CRC) with defective mismatch repair (dMMR), both in vitro and in vivo. DHX9 inhibition in the HCT116 dMMR CRC cell line results in a robust dose dependent induction of the Alu-mediated circular RNA, circBRIP1, as early as 6 hours after compound treatment. The development of lead series DHX9 inhibitors exhibited a positive correlation between circBRIP1 EC50 and DHX9 biochemical activity, as well as proliferation inhibition in a dMMR CRC cell line. However, dose dependent induction of circBRIP1 following DHX9 inhibition occurs with similar potencies across DHX9i sensitive and insensitive CRC cell lines. This suggests that elevation of circBRIP1 is a unique proximal target engagement PD biomarker of DHX9 inhibition, but not a predictor of DHX9 sensitivity. Importantly, induction of circBRIP1 is observed intratumorally in human xenograft in vivo efficacy studies in mice. Induction in each individual tumor correlates with observed tool compound exposure, providing evidence of a predictable PK/PD relationship. We also observe dose dependent circBRIP1 induction in mouse peripheral blood mononuclear cells (PBMC). We have extended these studies to primary human whole blood, where we see robust dose dependent induction of circBRIP1 after ex vivo treatment with DHX9 inhibitor for 24 hours. Altogether, these studies show evidence for the utility of circBRIP1 as a non-invasive target engagement biomarker for DHX9 inhibitors in the clinic. Citation Format: David Brennan, Jennifer Castro, Matthew H. Daniels, Monique Laidlaw, Chuang Lu, Stephen J. Blakemore, Serena J. Silver, P. Ann Boriack-Sjodin, Kenneth W. Duncan, Jason A. Sager, Robert A. Copeland. circBRIP1 RNA as a non-invasive target engagement pharmacodynamic biomarker for DHX9 inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 520.

Abstract 1189: Modulation of the MSS and MSI colorectal cancer immune microenvironment with FOLFOX and FOLFIRI -/+ anti-PD-1 immunotherapy

Abstract Metastatic colorectal cancer (mCRC) is a deadly disease with a five-year survival rate of 14%. Most patients receive 5-FU (F) and folinic acid (FOL) combined with oxaliplatin (OX), irinotecan (IRI), or both (OXIRI). Immune checkpoint inhibitors (ICIs) are effective against microsatellite instable (MSI) tumors, but 95% of mCRC tumors are microsatellite stable (MSS) and ICI-resistant. Though the primary targets of 5-FU, irinotecan, and oxaliplatin are well-understood, their effects on the tumor microenvironment (TME) remain incompletely characterized. Chemotherapy-mediated immune stimulation in MSS CRC has been observed in preclinical models and clinical trials. We hypothesize that combination chemotherapy treatment modulates the immune microenvironment of CRC -/+ ICI, with differences across subtype and treatment regimen. Chemotherapy-dependent changes in cancer cell gene expression, PD-L1 levels, cytokine secretion, and T cell activation were measured using in vitro models of MSS and MSI CRC. A preliminary evaluation of spleen and tumor T cells and dendritic cells (DCs) in murine models of MSS and MSI CRC after immunotherapy -/+ chemotherapy was conducted. CD8+ T cells, DCs, PD-L1, CD69, and GM-CSF expression were measured in clinical specimens of chemotherapy-treated MSS mCRC patients. In MSS CRC, FOX increased GM-CSF and activated CD8+ T cells in vitro and activated splenic CD8+ and CD4+ T cells in vivo. FOX and FIRI suppressed an anti-PD-1-mediated enhancement of type 1 cDCs in the tumor in vivo. FOLFOX was associated with increased tumor CD8+ T cells and decreased GM-CSF in MSS mCRC biopsies. FIRI treatment increased PD-L1 in vitro. FOLFIRI was not associated with increased tumor CD8+ T cells in MSS mCRC biopsies. In MSI CRC, FOX increased tumor CD8+ T cells in vivo. Here, we elucidate novel effects of clinically relevant chemotherapy combinations on the TME in MSS and MSI CRC. These data point to a FOX-specific mechanism by which CD8+ T cell infiltration into MSS mCRC tumors is enhanced, but their activation is halted potentially by GM-CSF suppression and/or type 1 cDC depletion in the TME. These findings contribute to our understanding of the mechanisms of chemotherapy-dependent immune modulation and bring the field closer to harnessing these effects for therapeutic gain. Citation Format: Lindsey Carlsen, Maximilian Pinho-Schwermann, Leiqing Zhang, Andrew Elliott, Kelsey E. Huntington, William J. MacDonald, Brooke Verschleiser, Laura Jinxuan Wu, Wafik S. El-Deiry. Modulation of the MSS and MSI colorectal cancer immune microenvironment with FOLFOX and FOLFIRI -/+ anti-PD-1 immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1189.

Relationship Between ABO Blood Group and Microsatellite Instability in Colorectal Cancer: A Retrospective Single-Center Study.

Colorectal cancer (CRC) is the second most common cancer in both women and men. Microsatellite instability-high (MSI-H) CRC is a molecular subgroup and has distinct clinical and pathologic features from microsatellite stable (MSS) CRC. Studies have suggested an association between hereditary antigens in ABO blood group system and the risk of developing various cancers but the relationship between blood groups and MSI-H CRC has not been investigated. This study aimed to investigate this relationship and its possible effect on clinicopathological features in patients with CRC. This is a retrospective cross-sectional single-center study including pathology-confirmed CRC patients. Demographic and clinicopathological features, blood groups, and microsatellite status were examined among two groups. Microsatellite instability was examined by immunohistochemistry (IHC) in pathology specimen. A total of 144 patients, 72 patients with MSI-H CRC and 72 patients with MSS CRC, were included in the study. Among all patients, median age was 61.7 ± 12.9 (range 27-89) and 57.6% were male. MSI-H and MSS groups were similar in terms of age, gender distribution, and comorbidities. Patients with MSI-H CRC had significantly common O-blood group than control group (44.4% vs 18.1%, p: 0.001). In multivariate analysis, O-blood group was 4.2 times more common in the MSI-H patient group (95% CI: 1.514-11.819, p: 0.006). Also patients with MSI-H CRC were found to have significantly more right-sided, high-grade tumors and early-stage disease. MSI-H CRC is an important subgroup in colon cancer with different molecular and clinicopathological features. It was observed that O-blood group was 4.2 times more common in MSI-H CRC. We believe that clarifying the relationship between microsatellite instability and O-blood group and its possible genetic and epigenetic mechanismsin larger studies will enable us to better understand tumor behavior and prognosis, also affect our treatment choices of these patient groups.

Predicting mechanism of immune response in microsatellite instability colorectal cancer

Colorectal cancer (CRC), also known as colon cancer, is the third most common cancer and the fourth most cause of cancer-related death in the world. CRC can be classified into two major subtypes, including microsatellite instability (MSI) and microsatellite stability (MSS), which showed different characteristics in immunotherapy. Low sensitivity of diagnostic biomarkers and metastasis are still the principal cause of mortality, especially in MSI. Here, applying computational programs, we identified recurring expression programs based on single cell RNA sequencing (scRNA-Seq) data of CRC cell lines. Notably, three MSI specific recurring modules were identified by non-negative matrix factorization (NMF). High NMF score genes enriched in the function of metabolism and inflammatory response. Focusing on top specific active transcription factor (TF), RUNX3 (Runt-related transcription factor 3), our results suggest that T cell infiltration was increased in RUNX3 high MSI CRC samples. Unbiased Gene Set Enrichment Analysis (GSEA) showed that RUNX3 was strongly associated with immune and metastasis related functions, such as Interferon Gamma (IFN-γ) and EPITHELIAL MESENCHYMAL TRANSITION (EMT). In addition, RUNX3 shows specific highly activated at epigenetic level in MSI compared with other gastrointestinal carcinomas. Positive correlation between RUNX3 and most immune checkpoints further confirmed RUNX3 might have crucial roles in MSI cancer progression and immunotherapy. Taken together, these results indicate significant tumor heterogeneity of two CRC subtypes at single-cell level and epigenetic modification level. These results also linked transcriptional dysregulation with immune infiltration at single-cell level in MSI, which may advance the application of scRNA-Seq technology in immunotherapy and contribute to developing novel biomarkers of this malignancy.

RNA methylation-related genes INHBB and SOWAHA are associated with MSI status in colorectal cancer patients and may serve as prognostic markers for predicting immunotherapy efficacy.

The role of RNA methylation is vital in the advancement and spread of tumors. However, its exact role in microsatellite instability in colorectal cancer (CRC) is still not fully understood. To address this gap in knowledge, this study investigated the impact of genes associated with RNA methylation on the prognosis and response to immunotherapy in individuals diagnosed with low microsatellite instability (MSI-L) or microsatellite stable (MSS) CRC. The differentially expressed genes (DEGs) in two groups of patients: those with high microsatellite instability (MSI-H) and those with MSI-L/MSS was thoroughly investigated and compared in aims of exploring the association between them and the 60 RNA methylation regulators. We employed these genes and developed an MSI-RMscore to establish a risk signature capable of forecasting patient outcomes. Furthermore, an investigation of the immunophenotypic traits was conducted encompassing patients categorized as high-risk and low-risk. By combining the MSI-RMscore and clinicopathological features, a predictive nomogram was developed, which was subsequently validated using the GEO database. Furthermore, immunohistochemistry was employed to establish the correlation between INHBB and SOWAHA and the MSI status, as well as patient prognosis. Our findings indicated that the high-risk subgroup exhibited unfavorable overall survival rates, reduced responsiveness to immune checkpoint blockers, elevated estimate scores, and increased infiltration of macrophages and fibroblasts. We also confirmed that INHBB and SOWAHA were associated with CRC patient prognosis and MSI status, as well as immunotherapy response. These findings suggest that targeting INHBB and SOWAHA could be a promising strategy to enhance patient responsiveness to immunotherapy.

Aberrant PRDM2 methylation as an early event in serrated lesions destined to evolve into microsatellite-instable colorectal cancers.

Up to 30% of colorectal cancers (CRCs) develop from sessile serrated lesions (SSLs). Within the serrated neoplasia pathway, at least two principally distinct oncogenetic routes exist generating microsatellite-stable and microsatellite-instable CRCs, respectively. Aberrant DNA methylation (DNAm) is found early in the serrated pathway and might play a role in both oncogenetic routes. We studied a cohort of 23 SSLs with a small focus (<10 mm) of dysplasia or cancer, 10 of which were MLH1 deficient and 13 MLH1 proficient. By comparing, for each SSL, the methylation status of (1) the region of dysplasia or cancer (SSL-D), (2) the nondysplastic SSL (SSL), and (3) adjacent normal mucosa, differentially methylated probes (DMPs) and regions (DMRs) were assessed both genome-wide as well as in a tumor-suppressor gene-focused approach. By comparing DNAm of MLH1-deficient SSL-Ds with their corresponding SSLs, we identified five DMRs, including those annotating for PRDM2 and, not unexpectedly, MLH1. PRDM2 gene promotor methylation was associated with MLH1 expression status, as it was largely hypermethylated in MLH1-deficient SSL-Ds and hypomethylated in MLH1-proficient SSL-Ds. Significantly increased DNAm levels of PRDM2 and MLH1, in particular at 'critical' MLH1 probe sites, were to some extent already visible in SSLs as compared to normal mucosa (p = 0.02, p = 0.01, p < 0.0001, respectively). No DMRs, nor DMPs, were identified for SSLs destined to evolve into MLH1-proficient SSL-Ds. Our data indicate that, within both arms of the serrated CRC pathway, the majority of the epigenetic alterations are introduced early during SSL formation. Promoter hypermethylation of PRDM2 and MLH1 on the other hand specifically initiates in SSLs destined to transform into MLH1-deficient CRCs suggesting that the fate of SSLs may not necessarily result from a stochastic process but possibly is already imprinted and predisposed.

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.

The Efficacy of Immune Checkpoint Inhibitors in Microsatellite Stable Colorectal Cancer: A Systematic Review.

The use of immune checkpoint inhibitors (ICIs) has revolutionized cancer care, particularly in immune-inflamed tumors and tumors with a high mutational burden, like microsatellite instable colorectal cancer (CRC). However, their effectiveness in microsatellite stable (MSS) CRC is limited. This systematic review aims to evaluate the efficacy of ICIs in MSS CRC and explore promising combination strategies. A comprehensive search from the Web of Science, Medline, and Embase databases, for studies published until 14 November 2022, identified 53 clinical trials included in the review. ICI monotherapy or ICI-ICI combinations demonstrated limited clinical activity for patients with MSS CRC, with overall response rates below (ORR) 10% in most studies. The ICI and tyrosine kinase inhibitor (TKI) garnered ORRs ranging from 10% to 40% and indicated a higher benefit for patients, particularly those without active liver metastases. The combination of ICIs with anti-VEGF agents showed modest ORRs, especially in the earlier treatment lines and in combination with chemotherapy. While these combinations could lead to modest improvements, well-defined biomarkers for long-term benefit are yet to be delineated. Combinations involving BRAF inhibitors with ICIs were studied, showing promising responses with combination approaches in molecularly defined subgroups. In conclusion, while ICI monotherapy has limited efficacy in MSS CRC, combination strategies hold promise to enhance survival outcomes. Further research is necessary to identify optimal combination approaches, predictive biomarkers for treatment response, as well as enrollment according to tumor molecular characteristics.

Detecting microsatellite instability in colorectal cancer using Transformer-based colonoscopy image classification and retrieval.

Colorectal cancer (CRC) is a major global health concern, with microsatellite instability-high (MSI-H) being a defining characteristic of hereditary nonpolyposis colorectal cancer syndrome and affecting 15% of sporadic CRCs. Tumors with MSI-H have unique features and better prognosis compared to MSI-L and microsatellite stable (MSS) tumors. This study proposed establishing a MSI prediction model using more available and low-cost colonoscopy images instead of histopathology. The experiment utilized a database of 427 MSI-H and 1590 MSS colonoscopy images and vision Transformer (ViT) with different feature training approaches to establish the MSI prediction model. The accuracy of combining pre-trained ViT features was 84% with an area under the receiver operating characteristic curve of 0.86, which was better than that of DenseNet201 (80%, 0.80) in the experiment with support vector machine. The content-based image retrieval (CBIR) approach showed that ViT features can obtain a mean average precision of 0.81 compared to 0.79 of DenseNet201. ViT reduced the issues that occur in convolutional neural networks, including limited receptive field and gradient disappearance, and may be better at interpreting diagnostic information around tumors and surrounding tissues. By using CBIR, the presentation of similar images with the same MSI status would provide more convincing deep learning suggestions for clinical use.

Immunotherapy of microsatellite stable colorectal cancer: resistance mechanisms and treatment strategies.

In recent years, immunotherapy strategies based on immune checkpoint inhibitors have yielded good efficacy in colorectal cancer (CRC)especially in colorectal cancer with microsatellite instability-high. However, microsatellite-stable (MSS) CRCs account for about 85% of CRCs and are resistant to immunotherapy. Previous studies have shown that compared with MSS CRC, high microsatellite instability CRC possesses a higher frequency of mutations and can generate more neoantigens. Therefore, improving the sensitivity of immunotherapy to MSS CRC is a hot topic which is crucial for the treatment of MSS CRC. This review aims to discuss the factors contributing to MSS CRC insensitivity to immunotherapy and explored potential solutions to overcome immunotherapy resistance.

Icis Treatment for Different MSI Colorectal Cancer: Theoretical Basis, Status Quo And Outlook

As the third cancer worldwide, the incidence and the cancer-related mortality is both high in colorectal cancer (CRC) patients. The treatment of CRC has standard methods, including radiotherapy, chemotherapy and other general therapy. However, these systemic therapies are not specific, which are also toxic for normal cells and show many side effects in patients. New immunotherapeutic strategies have changed the landscape of treatment of metastatic CRC (mCRC), especially immune checkpoint inhibitors (ICIs). After research, the condition of microsatellite instability (MSI) has proven to be one of the main influencing factors of ICIs' efficacy. This review comprehensively analyses the possible mechanisms underlying the varying efficacy of ICIs in the treatment of different MSI tumors and evaluates potential therapeutic strategies that offer possible ways to overcome resistance mechanisms.

Prevalence and type of MMR expression heterogeneity in colorectal adenocarcinoma: therapeutic implications and reporting.

Mismatch repair (MMR) immunohistochemical (IHC) evaluation has entered pathology routine practice as the first-line screening method to identify patients with MMR deficient (MMRd)/microsatellite instability (MSI) colorectal cancer (CRC), and its misdiagnosis may significantly impact the personalization of CRC patient care. To determine the prevalence of MMR protein intratumor heterogeneity in real-world practice, we collected a series of 8282 CRCs tested for MMR proteins in the setting of Lynch syndrome universal screening. Four heterogenous cases were also investigated for tumor infiltrating lymphocytes count, MSI status, and consensus molecular subtypes by Nanostring nCounter® Platform. Overall, 1056 (12.8%) CRCs showed a MMR altered status, with 46 cases showing a heterogeneous MMR profile (0.56% of the total, and 4.36% of all MMRd cases). To conclude, the authors make some critical remarks regarding the approach to MMR heterogeneity in clinical practice and routine diagnostics.

Abstract C087: DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer

Abstract Background: DHX9 is a DEAH-box RNA helicase which has been reported to play important roles in replication, transcription, translation and RNA splicing/processing, all of which contribute to DHX9’s role in the maintenance of genomic stability. Functionally, DHX9 unwinds and/or resolves regions of double-stranded DNA and RNA helices but has a greater propensity for secondary structures such as DNA/RNA hybrids (R-loops), circular RNA (circRNA) and DNA/RNA G-quadraplexes. Overexpression of DHX9 is evident in multiple cancer types, including colorectal cancer (CRC) and lung cancer. In particular, microsatellite instable (MSI) tumors exhibiting defective mismatch repair (dMMR) show a strong dependence on DHX9, making this helicase an attractive target for oncology drug discovery. Here, we will demonstrate validation of DHX9 as a novel target for CRC-MSI, and the identification of potent and selective in vitro and in vivo small molecule inhibitors of DHX9. Materials and Methods: DHX9 targeted siRNA or DHX9 small molecule inhibitors were used to assess anti-proliferative activity in multiple different CRC-MSI and CRC-MSS cell lines through either CellTiter-Glo proliferation or colony formation assays. Downstream biological consequences of DHX9 knockdown or inhibition in vitro were determined using immuno-fluorescent imaging, western blot, flow cytometry to measure RNA/DNA secondary structure, cell cycle changes, apoptosis, and qPCR to measure circBRIP1 induction. CRC-MSI and CRC-MSS tumor xenografts were treated with DHX9 inhibitor ATX968 BID orally for 21-28 days. Tumor and plasma samples were collected for pharmacokinetics (PK) and pharmacodynamic (PD) (circBRIP1) measurement. Results: We demonstrate that DHX9 inhibition in CRC-MSI leads to an increase in RNA/DNA secondary structures such as R-loops, G-quadruplexes and Alu mediated circRNA such as circBRIP1, leads to subsequent DNA damage and increased replication stress. Cell lines that exhibit defective DNA repair pathways such as dMMR are unable to resolve this replication stress and demonstrate S-G2 phase cell cycle arrest prior to onset of apoptosis. We confirmed this selective dependency in a panel of cancer cell lines, where anti-proliferative effects mediated by DHX9 inhibition were associated with dMMR status. Furthermore, DHX9 tool compound ATX968 was well tolerated in vivo across a 28-day treatment period with robust and durable tumor regression observed in the MSI CRC tumor xenograft model. Following cessation of treatment, minimal tumor regrowth was observed in a 28-day post treatment window. Tumor and plasma concentrations of ATX968 and changes in PD markers of DHX9 inhibition were measured and resulting PK, PD and efficacy data were highly correlated. Conclusions: Together, these preclinical data validate DHX9 as a tractable new target with potential utility as a novel treatment for patients with CRC-MSI. Conflict of Interests: All authors are current or former employees and shareholders of Accent Therapeutics, Inc. Citation Format: Jennifer Castro, Matthew H Daniels, David Brennan, Brian T Johnston, Rishabh Bansal, Monique Laidlaw, Chuang Lu, Deepali Gotur, Young-Tae Lee, Kevin Knockenhauer, April Case, Jie Wu, Anugraha Raman, Jae Eun Cheong, Julie Liu, Shane M Buker, E. Allen Sickmier, Stephen J Blakemore, P. Ann Boriack-Sjodin, Kenneth W Duncan, Serena J Silver, Scott Ribich, Robert A Copeland. DHX9 inhibition as a novel therapeutic modality in microsatellite instable colorectal cancer [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 C087.

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.

Source, co-occurrence, and prognostic value of PTEN mutations or loss in colorectal cancer

Somatic PTEN mutations are common and have driver function in some cancer types. However, in colorectal cancers (CRCs), somatic PTEN-inactivating mutations occur at a low frequency (~8–9%), and whether these mutations are actively selected and promote tumor aggressiveness has been controversial. Analysis of genomic data from ~53,000 CRCs indicates that hotspot mutation patterns in PTEN partially reflect DNA-dependent selection pressures, but also suggests a strong selection pressure based on protein function. In microsatellite stable (MSS) tumors, PTEN alterations co-occur with mutations activating BRAF or PI3K, or with TP53 deletions, but not in CRC with microsatellite instability (MSI). Unexpectedly, PTEN deletions are associated with poor survival in MSS CRC, whereas PTEN mutations are associated with improved survival in MSI CRC. These and other data suggest use of PTEN as a prognostic marker is valid in CRC, but such use must consider driver mutation landscape, tumor subtype, and category of PTEN alteration.