Low-dose decitabine enhances the effect of PD-1 blockade in colorectal cancer with microsatellite stability by re-modulating the tumor microenvironment

PD-1 blockade has demonstrated impressive clinical outcomes in colorectal cancers that have high microsatellite instability. However, the therapeutic efficacy for patients with tumors with low microsatellite instability or stable microsatellites needs further improvement. Here, we have demonstrated that low-dose decitabine could increase the expression of immune-related genes such as major histocompatibility complex genes and cytokine-related genes as well as the number of lymphocytes at the tumor site in CT26 colorectal cancer-bearing mice. A more significant inhibition of tumor growth and a prolongation of survival were observed in the CT26 mouse model after treatment with a combination of PD-1 blockade and decitabine than in mice treated with decitabine or PD-1 blockade alone. The anti-tumor effect of the PD-1 blockade was enhanced by low-dose decitabine. The results of RNA sequencing and whole-genome bisulfite sequencing of decitabine-treated CT26 cells and tumor samples with microsatellite stability from the patient tumor-derived xenograft model have shown that many immune-related genes, including antigen-processing and antigen-presenting genes, were upregulated, whereas the promoter demethylation was downregulated after decitabine exposure. Therefore, decitabine-based tumor microenvironment re-modulation could improve the effect of the PD-1 blockade. The application of decitabine in PD-1 blockade-based immunotherapy may elicit more potent immune responses, which can provide clinical benefits to the colorectal cancer patients with low microsatellite instability or stable microsatellites.

Combination Immunotherapies to Overcome Intrinsic Resistance to Checkpoint Blockade in Microsatellite Stable Colorectal Cancer

Although immune checkpoint inhibitors (ICIs) have shown promising results in the treatment of treating various malignancies, progress has been severely limited in metastatic colorectal cancer (mCRC). ICIs are effective in a fraction of patients with microsatellite instability-high mCRC but have little clinical efficacy in patients with microsatellite stable (MSS) mCRC, which accounts for 95% of mCRC cases. MSS mCRCs are considered to have intrinsic resistance to ICI monotherapy through multiple mechanisms. (1) They are poorly immunogenic because of their low tumor mutation burden; (2) frequent activation of the WNT/β-catenin signaling pathway excludes intratumoral CD8+ T cell immunity; (3) the tumor microenvironment is immunosuppressive because of the presence of various immunosuppressive cells, including tumor-associated macrophages and regulatory T cells; and (4) frequent liver metastasis in MSS mCRC may reduce the efficacy of ICIs. To overcome these resistance mechanisms, combination approaches using various agents, including STING agonists, MEK inhibitors, VEGF/R inhibitors, WNT/β-catenin inhibitors, oncolytic viruses, and chemo/radiotherapy, are actively ongoing. Preliminary evidence of the efficacy of some has been shown in early clinical trials. This review summarizes novel combination immunotherapy strategies described in recent preclinical and clinical studies to overcome the limitations of ICI monotherapy in MSS mCRC.

Low-dose immunogenic chemotherapeutics promotes immune checkpoint blockade in microsatellite stability colon cancer

More than 85% of colorectal cancer (CRC) patients, who are with microsatellite stability (MSS), are resistant to immune checkpoint blockade (ICB) treatment. To overcome this resistance, combination therapy with chemotherapy is the most common choice. However, many CRC patients do not benefit more from combination therapy than chemotherapy alone. We hypothesize that severe immunosuppression, caused by chemotherapy administered at the maximum tolerated dose, antagonizes the ICB treatment. In this study, we found that low-dose oxaliplatin (OX), an immunogenic cell death (ICD)-induced drug, increased the antitumor response of TIGIT blockade against CT26 tumor, which is regarded as a MSS tumor. Combined treatment with OX and TIGIT blockade fostered CD8+ T-cell infiltration into tumors and delayed tumor progression. Importantly, only low-dose immunogenic chemotherapeutics successfully sensitized CT26 tumors to TIGIT blockade. In contrast, full-dose OX induces severe immunosuppression and impaired the efficacy of combination therapy. Further, we also found that lack of synergy between nonimmunogenic chemotherapeutics and TIGIT blockade. Consequently, this study suggests that the strategies of combination treatment of chemotherapy and ICB should be re-evaluated. The chemotherapeutics should be chosen for the potential to ICD and the dosage and regimen should be also optimized.

Metastatic Colorectal Cancer Patient With Microsatellite Stability and BRAFV600E Mutation Showed a Complete Metabolic Response to PD-1 Blockade and Bevacizumab: A Case Report

A vast majority of colorectal cancer (CRC) patients with microsatellite stability (MSS) or proficient mismatch repair (pMMR) are refractory to immunotherapeutic strategies. The current research focusses on the combined treatment strategies for identification and optimization in order to improve the efficacy of immunotherapy among patients with microsatellite stability (MSS), who account for the majority of metastatic colorectal cancer (mCRC) cases. mCRC patients harboring MSS and the BRAFV600E mutation show a worse prognosis and barely benefit from immunotherapy. In this report, we discuss the case of a mCRC patient with MSS and BRAFV600E mutation, who exhibited significant response to the combined treatment with nivolumab and bevacizumab, and has been exhibiting a progression-free survival (PFS) of more than 17 months. Our findings indicate that combined anti-angiogenic therapy can improve the efficacy of immunotherapy, which results in the prolong survival of the patient. This is a case report on MSS and BRAFV600E colorectal cancer which presents with a response to immunotherapy and anti-angiogenic therapy.

Effects of OsMSH6 Mutations on Microsatellite Stability and Homeologous Recombination in Rice

DNA mismatch repair (MMR) system is important for maintaining DNA replication fidelity and genome stability by repairing erroneous deletions, insertions and mis-incorporation of bases. With the aim of deciphering the role of the MMR system in genome stability and recombination in rice, we investigated the function of OsMSH6 gene, an import component of the MMR system. To achieve this goal, homeologous recombination and endogenous microsatellite stability were evaluated by using rice mutants carrying a Tos17 insertion into the OsMSH6 gene. Totally 60 microsatellites were analyzed and 15 distributed on chromosome 3, 6, 8, and 10 showed instability in three OsMSH6 mutants, D6011, NF7784 and NF9010, compared with the wild type MSH6WT (the control). The disruption of OsMSH6 gene is associated with modest increases in homeologous recombination, ranging from 2.0% to 32.5% on chromosome 1, 3, 9, and 10 in the BCF2 populations of the mutant ND6011 and NF9010. Our results suggest that the OsMSH6 plays an important role in ensuring genome stability and genetic recombination, providing the first evidence for the MSH6 gene in maintaining microsatellite stability and restricting homeologous recombination in plants.

The different roles of hRAD50 in microsatellite stable and unstable colorectal cancers

RAD50 protein is essential for DNA double-strand break repair and maintaining genomic integrity. In this study, we investigated the clinicopathological significance of hRAD50 expression and mutation in microsatellite stable (MSS) and unstable (MSI) colorectal cancers (CRCs). hRAD50 expression was examined in primary CRC (n=268), the corresponding distant (n=69) and adjacent normal mucosa (n=138), and lymph node metastasis (n=44) by immunohistochemistry. hRAD50 mutation was analyzed in 87 primary CRCs by PCR-SSCP-DNA sequencing. hRAD50 expression was increased in MSS primary CRCs, but not MSI ones, compared with distant/adjacent normal mucosa (p<0.05). There was no difference in the hRAD50 expression between primary and metastatic CRCs. The increased hRAD50 expression in MSS primary CRCs was related (p<0.05) or tended to be related (p=0.05) to early tumor stage, better differentiation, high inflammatory infiltration, p53 overexpression. Frameshift mutations of (A)(9) at coding region of hRAD50 were only found in MSI CRCs. Our results suggest that hRAD50 may play different roles in the development of MSS and MSI CRCs: increased hRAD50 expression in MSS CRCs {may be a cellular response against tumor from further progression}, while hRAD50 mutation may be involved in the development of MSI CRCs.

Role of LATS1/2 in Prognosis of Advanced Gastric Cancer and Its Relationship With the Tumor Immune Microenvironment

Background: Gastric cancer (GC) remains a refractory cancer particularly in Eastern Asia. Large tumor suppressor kinases 1/2 (LATS1/2) are core members of the Hippo pathway. The role of LATS1/2 in the prognosis of different subtypes of advanced gastric cancer and its relationship with the tumor immune microenvironment in GC remain unknown. Exploring the role of LATS1/2 in GC might provide potential immunotherapeutic approaches for treating GC. Methods: Four hundred and ninety surgically resected primary GC samples were assessed for LATS1/2, CD8, FOXP3, and CD163. Correlations between LATS1/2 expression and immune-related markers were investigated and the prognoses of patients with different GC subtypes were analyzed. Results: CD8 and CD163 appeared to be favorable and adverse prognostic factors, respectively. LATS1/2 and FOXP3 did not predict patients' overall survival. However, in microsatellite-stable GC patients, high LATS1/2 and FOXP3 expression and low CD8 expression predicted poor prognoses. Furthermore, high LATS1/2 expression was significantly correlated with decreased CD8 and increased FOXP3. Combined analysis of LATS1/2, CD8, and FOXP3 had better prognostic accuracy than did each marker individually. Conclusions: Different biological molecules can predict the prognoses of different types of GC patients. LATS1/2, core kinases in the Hippo pathway, are closely related to CD8 and FOXP3. Further understanding the mechanisms of LATS1/2 in CD8⁺ T cells and FOXP3⁺ Treg cells provides further theoretical basis and potential targets for GC immunotherapy.

Homologous recombination repair gene mutations in colorectal cancer favors treatment of immune checkpoint inhibitors

Immune checkpoint inhibitor (ICI) therapy is insensitive for Colorectal cancer (CRC) patients with microsatellite stable (MSS). Genomic data of three CRC cohort, n = 35), and the Cancer Genome Atlas (TCGA CRC cohort, n = 377), were analyzed. A cohort treated with ICIs from Memorial Sloan Kettering Cancer Center (MSKCC CRC cohort, n = 110) and two cases from the local hospital were characterized the impact of the HRR mutation on prognosis of CRC. Homologous recombination repair (HRR) gene mutations were more common in CN and HL cohorts (27.85%; 48.57%) than in TCGA CRC cohort (15.92%), especially in the MSS populations, the frequencies of HRR mutation were higher in CN and HL cohort (27.45%, 51.72%) than in TCGA cohort (6.85%). HRR mutations were associated with high tumor mutational burden (TMB-H). Although HRR mutation uncorrelated with an improved overall survival in the MSKCC CRC cohort (p = 0.97), HRR mutated patients had a significantly improved OS compared to the HRR wildtype population particularly in MSS subgroups (p = 0.0407) under ICI treatment. It probably contributed by a higher neoantigen and increased CD4+ T cell infiltration which found in the TCGA MSS HRR mutated CRC cohort. The similar phenomenon on cases was observed that MSS metastatic CRC patient with HRR mutation seemed more sensitive to ICI after multi-line chemotherapy in clinical practice than HRR wildtype. This finding suggests the feasibility of HRR mutation as an immunotherapy response predictor in MSS CRC, which highlights a potential therapeutic approach for these patients.

Characterization and clinical evaluation of microsatellite instability and loss of heterozygosity in tumor-related genes in gastric cancer

Microsatellite instability (MSI) detection is widely used in the diagnosis and prognosis evaluation of colorectal cancer. However, for gastric cancer (GC), there is no standard panel of microsatellites (MSs) used in clinical guidance. The present study aimed to identify useful predictors of the clinical features and for the prognosis of GC, based on an investigation of MSI and loss of heterozygosity (LOH) in tumor-related genes. First, from 20 tumor-related genes which were proven to be important to the development of GC, 91 MSs were identified, and PCR amplification, short tandem repeat scanning analysis and TA clone sequencing were used to analyze MSI and LOH in the first set of 90 GC samples. Subsequently, the same method was used to detect the MSI/LOH of the optimized loci in the second set of 136 GC samples. MSI/LOH in the mismatch repair genes was highly consistent with that in oncogenes and tumor suppressor genes, respectively. The length of the core sequence was a main factor for the MSI/LOH rate. The MSI of 12 single loci was significantly associated with lymph node metastasis. The MSI in TP53-1 and the LOH in MGMT-10 were significantly associated with early stages of tumor infiltration depth. The LOH in MGMT-10, PTN-2 and MCC-17 was significantly associated with TNM stage. The LOH in TP53-1 and ERBB2-12 was associated with adenocarcinoma. The MSI/LOH in 6 single loci of 5 tumor-related genes was associated with poor prognosis of GC. The present study demonstrated that the MSI/LOH of loci in tumor-associated genes was associated with 4 clinicopathological characteristics and outcomes of GC. These results may provide potential specific biomarkers for the clinical prediction and treatment of GC.

Microsatellite Status and IκBα Expression Levels Predict Sensitivity to Pharmaceutical Curcumin in Colorectal Cancer Cells

Clinical utilization of curcumin in colorectal cancer (CRC) was revived as a result of the development of novel curcumin formulations with improved bioavailability. Additionally, identification of biomarkers for curcumin sensitivity would also promote successful clinical applications. Here, we wanted to identify such biomarkers in order to establish a predictive model for curcumin sensitivity. Thirty-two low-passage CRC cell lines with specified tumor characteristics were included. Curcumin suppressed cell proliferation, yet sensitivity levels were distinct. Most curcumin-sensitive CRC cell lines were microsatellite stable and expressed high levels of IκBα. The predictive capacity of this biomarker combination possessed a statistical significance of 72% probability to distinguish correctly between curcumin-sensitive and -resistant CRC cell lines. Detailed functional analyses were performed with three sensitive and three resistant CRC cell lines. As curcumin's mode of action, inhibition of NF-κB p65 activation via IκBα was identified. In consequence, we hypothesize that novel curcumin formulations-either alone or, more likely, in combination with standard therapeutics-can be expected to prove clinically beneficial for CRC patients with high IκBα expression levels.

Immunocheckpoint Inhibitors in Microsatellite-Stable or Proficient Mismatch Repair Metastatic Colorectal Cancer: Are We Entering a New Era?

Colorectal cancer (CRC) is the third most frequent cancer and the second leading cause of cancer-related deaths in Europe. About 5% of metastatic CRC (mCRC) are characterized by high microsatellite instability (MSI) due to a deficient DNA mismatch repair (dMMR), and this condition has been related to a high sensitivity to immunotherapy, in particular to the Immune Checkpoint Inhibitors (ICIs). In fact, in MSI-H or dMMR mCRC, treatment with ICIs induced remarkable response rates and prolonged survival. However, the majority of mCRC cases are mismatch-repair-proficient (pMMR) and microsatellite-stable (MSS), and unfortunately these conditions involve resistance to ICIs. This review aims to provide an overview of the strategies implemented to overcome ICI resistance and/or define subgroups of patients with MSS or dMMR mCRC who may benefit from immunotherapy.

Differential Analyses of Peripheral Blood Parameters in CCR5 Inhibition-treated Colorectal Cancer Patients Reveal Dynamic Changes Linked to Clinical Outcomes

BACKGROUND/AIM

Chemokine receptor inhibition is an immunotherapy that modulates the innate arm of the immune system. Previous work in microsatellite-stable metastatic colorectal cancer showed an exploitive loop that could be successfully targeted via C-C-motive-chemokine-receptor 5 (CCR5) specific blocking, resulting in a selective anti-tumoral activation of macrophages. In the respective trial (MARACON trial, NCT01736813) the peripheral blood laboratory markers and cytokine values were measured over time. Little is known on their role as biomarkers or stratification parameters in immunotherapy trials.

PATIENTS AND METHODS

Systematic analyses of key laboratory parameters are presented, highlighting specific dynamics of lymphocyte and monocyte percentages, lactate dehydrogenase as well as interleukin-6 and interleukin-8 levels as parameters of a systemic inflammatory readout.

RESULTS

Specific dynamical changes of lymphocyte and monocyte compositions were noted between different patients, showing a stabilization (or increase) versus decreased numbers over time for monocytes. While lactate dehydrogenase, interleukin-6 and interleukin-8 showed almost uniformly rising levels over time, the systemic monocyte patterns prompted a further evaluation. Stabilized or increasing monocyte percentages were associated with improved overall survival (Kaplan Meier analysis, p=0.025) and with induced overt radiologic necrosis in patients.

CONCLUSION

The observed association between monocyte dynamics and imaging findings as well as overall survival suggests that analyses of dynamical parameters in the peripheral blood should be implemented in immunotherapy trials.

Long-term response to sintilimab, bevacizumab and chemotherapy in heavily pretreated microsatellite stable colon cancer

Most advanced colorectal cancer patients with proficient DNA mismatch repair or microsatellite stability (MSS) are insensitive to immune checkpoint inhibitor therapy. This report describes a heavily pretreated refractory colon adenocarcinoma patient with MSS. After experiencing four lines of treatment, the patient received the fifth-line therapy with the combined sintilimab, bevacizumab and chemotherapy. She achieved a long-term clinical outcome. The patient's progression-free survival after the fifth-line therapy was approximately 9.3 months, and her overall survival was approximately 57 months. To the best of our knowledge, this case represents the first report of durable clinical benefit from combination of an immune checkpoint inhibitor, bevacizumab and chemotherapy in a heavily pretreated patient with refractory metastatic colon adenocarcinoma with MSS.

The Current and Evolving Role of Immunotherapy in Metastatic Colorectal Cancer

Immunotherapy can be considered a therapeutic revolution in oncology, with great impact on many tumor types, such as melanoma and non-small cell lung cancer. However, in metastatic colorectal cancer, the benefits in terms of prolonged tumor control and high response rate are limited to the rare subgroup of tumors with high mutation burden - mostly tumors that harbor microsatellite instability (MSI) or a deficient mismatch repair system (dMMR), or tumor microsatellite stability and damaging mutations in the exonuclease domains of POLE or POLD. The KEYNOTE-028 uncontrolled phase II trial demonstrated an impressive antitumor activity of pembrolizumab in patients with treatment-refractory Lynch-associated tumors, including colorectal cancer. Nivolumab with or without ipilimumab confirmed the efficacy of immune checkpoint inhibitors in patients with previously treated dMMR / MSI metastatic colorectal cancer. The recent KEYNOTE-177 phase III trial demonstrated that pembrolizumab significantly reduced the relative risk of disease progression or death and improved progression-free survival in patients with treatment-naive dMMR / MSI metastatic colorectal cancer in comparison with first-line chemotherapy with or without biologics. Unfortunately, current pharmacological strategies with immunotherapy have not been successful for most patients with microsatellite stable metastatic colorectal cancer. In this review we critically appraise the applicability of immune checkpoint inhibitors in dMMR/MSI metastatic colorectal cancer. We also discuss the recent negative trials of immunotherapy combinations in microsatellite stable tumors and the more mature immunotherapy ongoing studies in the field of advanced colorectal cancer.

Efficacy and safety of combining short-course neoadjuvant chemoradiotherapy with envafolimab in locally advanced rectal cancer patients with microsatellite stability: a phase II PRECAM experimental study

BACKGROUND

Conventional neoadjuvant chemoradiotherapy (nCRT) yields a pathologic complete response (pCR) rate of 15-30% for locally advanced rectal cancer (LARC). This study ventures to shift this paradigm by incorporating short-course nCRT with immunotherapy, specifically Envafolimab, to achieve improved treatment efficacy and possibly redefine the standard of care for LARC.

MATERIALS AND METHODS

The PRECAM study is a prospective, single-arm, phase 2 clinical trial for LARC in patients with microsatellite stable (MSS) tumors. Participants received short-course radiotherapy (25Gy/5f), followed by two cycles of CAPEOX chemotherapy and six weekly doses of Envafolimab, a PD-L1 antibody, before total mesorectal excision surgery. The primary endpoint was the pCR rate.

RESULTS

From April to December 2022, 34 patients were enrolled, of whom 32 completed the study, each diagnosed with an MSS rectal adenocarcinoma. All patients underwent preoperative CRT combined with Envafolimab. Remarkably, a pCR rate of 62.5% (20/32) was attained, and a significant pathologic response rate of 75% (24/32) was achieved. Additionally, 21 of 32 participants achieved a neoadjuvant rectal (NAR) score below 8, suggesting an effective treatment response. Common adverse events included tenesmus (78.1%), diarrhea (62.5%), and leukocyte decrease (40.6%). Two Grade 3 adverse events were noted, one related to liver function abnormality and the other to a decrease in platelet count. Surgical procedures were performed in all cases, with minor complications, including ileus, infections, and anastomotic leakage. As of this report, there have been no reported cases of recurrence or death during the follow-up period, ranging from 12 to 20 months.

CONCLUSION

In LARC patients exhibiting MSS tumors, combining short-course nCRT with Envafolimab demonstrated favorable efficacy, leading to a significant pCR rate. Minor adverse effects and surgical complications were observed. These preliminary but promising results underscore the potential of this approach and call for further exploration and validation through a randomized controlled trial.

Case Report: Systemic treatment for breast and vulvar metastases from resected rectal signet ring cell carcinoma

BACKGROUND

Breast and vulvar metastases from rectal signet ring cell carcinoma (SRCC) represent a rare and obscure clinical entity associated with poor survival. Managing patients with metastatic rectal SRCC is extremely challenging due to the absence of high-quality evidence.

CASE PRESENTATION

A 26-year-old woman presented with progressively worsening anal pain, constipation, and hematochezia for approximately two years. Following the diagnosis of locally advanced rectal cancer (cT3N0-1M0), she received neoadjuvant chemotherapy with modified FOLFOX6 regimen and underwent laparoscopic abdominoperineal resection. Metastases to the breast and vulva developed during postoperative chemotherapy. Genetic testing revealed RAS/BRAF wild-type and microsatellite instability (MSI)-low status. Though sequential administration of irinotecan plus tegafur and tegafur plus raltitrexed-based chemotherapy in combination with bevacizumab, the disease progressed rapidly. Sadly, the patient passed away 15 months after initial diagnosis due to rapidly progressive disease.

CONCLUSION

Rectal SRCC is associated with younger on-set, aggressive behaviors, and worse survival outcomes. Due to poor cohesiveness, SRCC tends to develop metastases. A patient's medical history and immunohistochemical staining (such as CK20, CK7, and CDX-2) can aid in identifying the tumor origin of breast and vulvar metastases. Mutations and signaling pathways predominant in the tumorigenesis of SRCC remains unveiled. There is poor effect of conventional chemotherapies, targeted and immunotherapies for colorectal adenocarcinoma on SRCC, so novel therapies are needed to treat this patient population.

Construction of ferroptosis and pyroptosis model to assess the prognosis of gastric cancer patients based on bioinformatics

Background

Gastric cancer (GC) is a malignancy with a grim prognosis, ranking as the second most common cause of cancer-related deaths globally. Various investigations have demonstrated the substantial involvement of ferroptosis and pyroptosis in the advancement of tumors. Nevertheless, the precise molecular mechanisms by which distinct genes associated with ferroptosis and pyroptosis influence the tumor microenvironment (TME) in GC remain elusive. Therefore, this study aims to elucidate the role of ferroptosis and pyroptosis in GC and provide insigths for GC therapy and prognosis evaluation.

Methods

The data including gene expression, clinicopathological characteristics and survival information of GC samples from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) cohorts were collected, and the expression level of ferroptosis and pyroptosis genes (FPGs) in GC samples were analyzed. Consensus clustering analysis, Cox logistic regression, principal component analysis (PCA), and the "survival", "survminer", "limma", "ggplot2" and other packages in R were utilized to compare the differences among different groups. In the level of GC cells, cell viability experiments were conducted by Cell Counting Kit-8 (CCK-8) assay.

Results

Through the analysis of the expression level of FPGs in GC samples from the TCGA and GEO cohorts, twenty-three prognostic-related and differentially expressed FPGs were collected for further analysis. Through consensus clustering analysis, three distinct patterns of FPGs were identified and found to be correlated with clinicopathological characteristics, immune cell infiltration, and prognosis in patients with GC. Subsequently, 684 prognostic-related genes from 1,082 pattern-related differentially expressed genes (DEGs) were screened for constructing the FPG_Score system to quantify FPGs patterns in individual GC patients and predict the prognosis. The analysis indicated that GC patients with high FPG_Score exhibited improved survival rates, increased tumor mutation burden (TMB), higher microsatellite instability (MSI), and elevated programmed cell death protein ligand 1 (PD-L1) expression. These patients with high FPG_Score were more likely to benefit from immunotherapy and had a more favorable prognosis.

Conclusions

Our study innovatively provided a comprehensive analysis of FPGs in GC, and constructed the FPG_Score system for stratification of individual patients, so as to predict its benefit from immunotherapy and prognosis.

Metabolic Singularities in Microsatellite-Stable Colorectal Cancer: Identifying Key Players in Immunosuppression to Improve the Immunotherapy Response

Although immune checkpoint inhibitor (ICI) therapy is currently the standard of care in microsatellite-unstable (MSI) metastatic colorectal cancer (CRC), ICI therapy, alone or in combination with other therapies, is not a treatment approach in microsatellite-stable (MSS) CRC, which is present in 95% of patients. In this review, we focus on metabolic singularities-at the transcriptomic (either bulk or single cell), proteomic, and post-translational modification levels-that induce immunosuppression in cancer and specifically in MSS CRC. First, we evaluate the current efficacy of ICIs in limited and metastatic disease in MSS CRC. Second, we discuss the latest findings on the potential biomarkers for evaluating ICI efficacy in MSS CRC using strict REMARK criteria. Third, we review the current evidence on metabolic patterns in CRC tumors and immune cell metabolism to advance our understanding of metabolic crosstalk and to pave the way for the development of combination strategies to enhance ICI efficacy.

A Case of Complete Remission in Proficient Mismatch Repair (pMMR) Advanced Colon Cancer Treated with Sintilimab and XELOX

Introduction

Colorectal cancer (CRC) is the 3rd most common malignant tumors after breast cancer and lung cancer, accounting for 9.4% of patients. Some patients had distant metastasis at the time of diagnosis without surgery opportunity. It is particularly important to prolong patient survival and improve quality of life.

Patient Concerns

A 73-year-old female was admitted with discomfort over 2 months. Enlarged lymph nodes in the left supraclavicular fossa were observed in chest computed tomography (CT). Enhanced abdominal CT showed thickening of the right colon wall with multiple metastatic lymph nodes in the abdomen. Colonoscopy showed ileocecal mass and pathology showed moderately and poorly differentiated adenocarcinoma. Physical examination showed a 2*2 cm lymph node could be touched in the left supraclavicular fossa. The patient was diagnosed advanced colon cancer by the histopathological examination and imaging findings. Actually, it is hardly to resect radically.

Intervention

Sintilimab combined with XELOX was initiated. Two period of treatment after initial therapy, laparoscopic radical resection of right colon cancer was performed successfully.

Outcomes

After conversion treatment, the enlarged lymph nodes and primary tumor were significantly reduced. The patient was discharged successfully three weeks after surgery. Both specimen and 14 lymph nodes dissected showed no malignancy in pathology. Tumor regression grading (TRG) is 0, which indicate complete regression with no residual tumor cells including lymph nodes. The patient obtained a pathological complete response (pCR).

Lessons

The patient achieved a great therapeutic benefit with the above-mentioned chemotherapy in this case. The case provides a potential reference for pMMR CRC patients treating with immune checkpoint inhibitors (ICIs).

The next bastion to be conquered in immunotherapy: microsatellite stable colorectal cancer

Colorectal cancer (CRC) is the second leading cause of cancer-related deaths worldwide, and its incidence continues to rise, particularly in developing countries. The advent of immune checkpoint inhibitors (ICIs) has represented a significant advancement in CRC treatment. Deficient mismatch repair (dMMR) or high microsatellite instability (MSI-H) serves as a biomarker for immunotherapy, with dMMR/MSI-H CRC exhibiting significantly better response rates to immunotherapy compared to proficient mismatch repair (pMMR)or microsatellite stable (MSS) CRC. While some progress has been made in the treatment of pMMR/MSS CRC in recent years, it remains a challenging issue in clinical practice. The tumor microenvironment (TME) plays a crucial role not only in the development and progression of CRC but also in determining the response to immunotherapy. Understanding the characteristics of the TME in pMMR/MSS CRC could offer new insights to enhance the efficacy of immunotherapy. In this review, we provide an overview of the current research progress on the TME characteristics and advancements in immunotherapy for pMMR/MSS CRC.

Metastatic Colorectal Cancer Patient with Microsatellite Stability and Germline BRAC2 Mutation Shows a Complete Response to Olaparib in Combination with a PD-1 Inhibitor and Bevacizumab: A Case Report and Review of the Literature

Metastatic colorectal cancer (mCRC) has a poor prognosis. Combining chemotherapy with targeted therapy constitutes a basic form of mCRC treatment. Immune checkpoint inhibitors have been recommended for microsatellite instability mCRC, while most patients harboring microsatellite stability (MSS) or proficient mismatch repair (pMMR) are less responsive to immunotherapy. Combinational targeted therapy, including poly-ADP ribose polymerase (PARP) inhibitors, has been considered a promising way to reverse immunotherapy resistance; however, there is no clear and consistent conclusions can be drawn from the current research. Here, we report the case of a 59-year-old woman diagnosed with stage IVB MSS mCRC who received three courses of capecitabine/oxaliplatin chemotherapy combined with bevacizumab as a first-line treatment, resulting in an overall evaluation of stable disease (-25.7%). However, the occurrence of adverse events of intolerable grade 3 diarrhea and vomiting forced the cessation of this therapy. A germline BRCA2 mutation was found by next-generation sequencing, and the patient further received a combination of olaparib, tislelizumab, and bevacizumab. This treatment regime resulted in a complete metabolic response and a partial response (-50.9%) after 3 months of treatment. Mild asymptomatic interstitial pneumonia and manageable hematologic toxicity were two adverse events associated with this combination therapy. This study provides new insights into the combination of PARP inhibitors and immunotherapy for MSS mCRC patients carrying germline BRCA2 mutations.

Fruquintinib Combined With PD-1 Inhibitors for the Treatment of the Patients With Microsatellite Stability Metastatic Colorectal Cancer: Real-World Data

AIMS

Programmed death-1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitors have shown limited effectiveness in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC). Combining anti-angiogenesis inhibitors with PD-1 inhibitors has the potential to reverse the immunosuppressive tumour microenvironment, synergistically enhancing the anti-tumour immune response in MSS mCRC. The goal is to present real-world data that prove the clinical efficacy and safety of fruquintinib combined with PD-1 inhibitors in MSS mCRC.

MATERIALS AND METHODS

We conducted a real-world retrospective study in patients with MSS mCRC who received treatment with fruquintinib combined with PD-1 inhibitors between May 2019 and March 2023 in our centre.

RESULTS

Seventy seven patients with MSS mCRC received fruquintinib combined with PD-1 inhibitors. In total, 5.2% of patients (4/77) achieved a partial response (PR), while 50.6% (39/77) had a stable disease (SD). Notably, three lesions achieving PR were all lung metastases and the overall disease control rate (DCR) reached 55.8% (43/77). Median progression-free survival (PFS) and overall survival (OS) reached 5.1 months (95% CI: 3.6-6.7) and 14.6 months (95% CI: 9.6-15.6), respectively. Multivariate Cox analysis showed that prior treatment without vascular endothelial growth factor (VEGF) inhibitors was significantly associated with PFS and OS (p < 0.05). Further analysis indicated that total- or polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) significantly decreased after treatment (P = 0.039), especially in the PR/SD group (P = 0.003). Most adverse events included abdominal pain, rash, oedema, diarrhoea, and immunotherapy-associated hypothyroidism, yet symptoms were controllable.

CONCLUSION

Our results provided additional evidence that patients with MSS mCRC could benefit from the combination of fruquintinib and PD-1 inhibitors, especially those with lung metastases or without prior treatment with VEGF inhibitors. The detection of MDSCs may be an immune indicator for predicting of the combined therapy.

Identification of the molecular characteristics associated with microsatellite status of colorectal cancer patients for the clinical application of immunotherapy

Background: Mismatch repair-proficient (pMMR) microsatellite stability (MSS) in colorectal cancer (CRC) indicates an unfavorable therapeutic response to immunotherapy with immune checkpoint inhibitors (ICIs). However, the molecular characteristics of CRC patients with pMMR MSS remain largely unknown. Methods: Heterogeneities between mismatch repair-deficient (dMMR) microsatellite instability (MSI) and pMMR MSS CRC patients were investigated at the single-cell level. Next, an MSS-related risk score was constructed by single-sample gene set enrichment analysis (ssGSEA). The differences in immune and functional characteristics between the high- and low-score groups were systematically analyzed. Results: Based on the single-cell RNA (scRNA) atlas, an MSS-specific cancer cell subpopulation was identified. By taking the intersection of the significant differentially expressed genes (DEGs) between different cancer cell subtypes of the single-cell training and validation cohorts, 29 MSS-specific cancer cell marker genes were screened out for the construction of the MSS-related risk score. This risk score signature could efficiently separate pMMR MSS CRC patients into two subtypes with significantly different immune characteristics. The interactions among the different cell types were stronger in the MSS group than in the MSI group, especially for the outgoing signals of the cancer cells. In addition, functional differences between the high- and low-score groups were preliminarily investigated. Conclusion: In this study, we constructed an effective risk model to classify pMMR MSS CRC patients into two completely different groups based on the specific genes identified by single-cell analysis to identify potential CRC patients sensitive to immunotherapy and screen effective synergistic targets.

Alternating Oxaliplatin and Irinotecan Chemotherapy Combined With Capecitabine and Bevacizumab for Microsatellite-stable Stage IV Metastatic Colon Cancer With a BRAF V600E Mutation: Two Case Reports Indicating Survival Improvement over Standard Therapy

BACKGROUND/AIM

Colorectal cancer (CRC) has the third-highest incidence among human cancers. Advancements in chemotherapy and targeted therapy have improved the treatment outcomes for patients with CRC. However, the management of patients with unresectable metastatic CRC (mCRC) continues to be a significant challenge for clinicians worldwide, particularly for those with microsatellite stability (MSS) and the BRAF V600E mutation, as they are associated with the poorest prognosis.

CASE REPORTS

The present study describes two patients with unresectable MSS, BRAF V600E-mutated stage IV metastatic CRC using a biweekly alternating regimen of irinotecan and oxaliplatin combined with capecitabine and bevacizumab. Case 1 stabilized after alternating treatment, whereas Case 2 progressed after alternating treatment, with progression-free survival (PFS) of 20+ and 24.5 months, respectively. Circulating levels of carcinoemryonic antigen (CEA) dropped to near normal in both cases. A partial response (PR) was determined for both cases.

CONCLUSION

The two cases suggest that an alternating chemotherapy regimen of oxaliplatin and irinotecan, combined with capecitabine and bevacizumab is effective in the treatment of MSS, BRAF V600E-mutated stage IV metastatic CRC. The progression-free survival was significantly prolonged (both exceeding 20 months) compared to the first-line standard chemotherapy regimen for this disease. With a good balance between toxicity and efficacy, this alternating chemotherapy regimen can be considered as a potential first-line option for microsatellite-stable metastatic colon cancer.

SET facilitates immune escape of microsatellite stability colorectal cancer by inhibiting c-Myc degradation

Microsatellite stability (MSS) colorectal cancer (CRC) exhibits a low mutation load and poor immunogenicity, contributing to immune escape of tumor cells and less benefit from immune checkpoint blockade (ICB) treatment. The mechanisms underlying immunotherapeutic resistance in MSS CRC remain to be elucidated. Here, we identified that nuclear proto-oncogene SET is significantly higher expressed in MSS CRC compared to microsatellite instability (MSI) CRC and facilitates immune escape of MSS CRC. Mechanistically, SET represses the expression of C-C motif chemokine ligand 5 (CCL5) and upregulates mismatch repair (MMR) proteins expression in a c-Myc-dependent manner, which inhibits infiltration and migration of CD8+ T cells to tumor tissues and results in low immunogenicity in MSS CRC. In addition, we found that SET impairs ubiquitination and proteasomal degradation of c-Myc by disrupting the interaction between E3 ligase FBXW7 and c-Myc. Moreover, SET inhibition enhances the response to immunotherapy in MSS CRC in vivo. Overall, this study reveals the critical roles and posttranslational regulatory mechanism of SET in immune escape and highlights the SET/c-Myc axis as a potential target for immunotherapy of MSS CRC that have implications for targeting a unique aspect of this disease.