Human MLH1 status can potentially predict cisplatin sensitivity but not microsatellite instability in head and neck squamous cell carcinoma cells

Microsatellite Instability and Loss of Heterozygosity as Prognostic Markers in Oral Squamous Cell Carcinoma: Molecular Mechanisms, Detection Techniques, and Therapeutic Strategies

The aim of this study was to conduct a systematic review of research investigating the potential role of microsatellite instability (MSI) and loss of heterozygosity (LOH) in oral squamous cell carcinoma (OSCC), with a focus on molecular mechanisms, detection methods, and therapeutic approaches. Search for articles involved the PubMed and Scopus. Previous retrospective and prospective studies identified variations between oral cancers that exhibit microsatellite stability and LOH. In this search, 294 articles were initially retrieved. Of these, 70 were excluded due to duplication, 106 were identified as ineligible by automated tools, and 24 were excluded as they were published in languages other than English. An additional 94 articles were excluded, 32 of which focused on head and neck cancers broadly, and 8 could not be accessed due to withdrawal. Ultimately, a systematic review was conducted based on 54 selected articles. Among the chromosomes analyzed for MSI and LOH, the highest frequency of LOH was observed on chromosome 9p. The MSI subtype is particularly susceptible to immunotherapeutic methods, such as the use of anti-PD-L1 and anti-CTLA4 antibodies, owing to its strong immunogenicity and ubiquitous expression of immune checkpoint ligands. Given the distinct characteristics and clinical behavior of oral cancer with MSI compared to microsatellite stable disease, it is advisable to incorporate MSI testing into the diagnostic process for all stages of tumor development. This ensured that each patient had received precise and effective treatment.

Combined therapy with cisplatin and 5-AZA-2CdR modifies methylation and expression of DNA repair genes in oral squamous cell carcinoma

The methylation and expression of DNA repair system genes has been studied in several tumor types. These genes have been associated with resistance to chemotherapy treatments by epigenetic regulation. Studies have yet to show the effects of combined therapy using an epigenetic drug (5-aza-2CdR) and cisplatin (CDDP) on DNA repair genes in oral squamous cell carcinoma (OSCC). This study proposed to investigate the effects of CDDP in combination with 5-aza-2CdR on the methylation of MGMT and MLH1 genes in oral cancer cells. Oral squamous cell carcinoma cell lineages (SCC-9, SCC-15, and SCC-25) were submitted to 72 hours of treatment: 0.1 μM CDDP (or 4.44 μM SCC-9), 0.1 μM and 0.3 μM 5-aza-2CdR (or 1 μM and 3 μM SCC-9), and the drugs in combination. Cell viability was assessed by MTT, DNA methylation of MGMT and MLH1 genes by Methylation Sensitivity High-Resolution Melting (MS-HRM), and the relative expression of the genes by RT-qPCR. The results show that all treatments reduced cell viability; however, in SCC-15 and SCC-9 (IC50 value), 5-aza-2CdR promotes cell sensitization to cytotoxic effect of cisplatin. The MGMT promoter region was 100% demethylated in the SCC-15 and SCC-25 cells but partially (50%) methylated in SCC-9 before drug treatment. Treatment with IC50 CDDP value kept the methylation status and decreased MGMT expression in SCC-9; MGMT gene in SCC-15 and SCC-25 cells became downregulated after treatment with 5-aza-2CdR. MLH1 was demethylated, but the treatments with low-doses and combined drugs decreased the expression in SCC-9 and SCC-25; however high doses of 5-aza-2CdR and drug combination with IC50 value CDDP increased expression of MLH1 in SCC-9. The data presented suggest that epigenetic drugs associated with chemotherapy have clinical translational potential as a therapy strategy to avoid or reverse cancer resistance, requiring further investigation.

PMS2: a potential prognostic protein marker in oral squamous cell carcinoma

Background

An increase in oral squamous cell carcinoma (OSCC) cases was observed despite the reduction in exposure to classic risk factors. Although the exact cause of this trend remains unknown, epigenetic factors could be contributing to an increased occurrence of these tumors. This study aims to assess the influence of PMS2 protein immunoexpression on the prognosis of patients with OSCC.

Material and Methods

This study comprised 76 cases of OSCC treated between 2011 and 2016. Immunohistochemical staining for PMS2 was performed. For evaluation, 10 fields per histological section were photographed at a 400x magnification and positively-stained cells were counted with Image J. Mann-Whitney and Kruskal-Wallis tests were used to compare the immunolabeling pattern with the clinical-pathological and prognostic characteristics. Survival analysis was performed with Chi-square, Long-Rank Mantel-Cox and Cox regression tests (p<0.05).

Results

An overexpression of PMS2 was observed in N0/1 tumors and in oral cancers found in unusual locations. In patients ≤60 years of age, high levels of PMS2 ( >60%; p=0.041) were associated with low survival (p=0.029). In multivariate analysis, surgery combined with chemotherapy (p=0.030) and high PMS2 immunoexpression (p=0.042) significantly increased the risk of death for ≤60 years old patients.

Conclusions

The findings of this study indicate that PMS2 can be a potential prognostic protein marker in OSCC patients 60 years of age and younger.

Key words:Squamous cell carcinoma, mouth neoplasms, mismatch repair endonuclease PMS2, survival.

The Mismatch Repair System (MMR) in Head and Neck Carcinogenesis and Its Role in Modulating the Response to Immunotherapy: A Critical Review

Simple Summary

The dysfunction of the mismatch repair system, an important mechanism for the detection and correction of DNA replication mistakes, may often lead to instability in the length of specific genetic sequences, known as microsatellites, and to the accumulation of mutations. Microsatellite instability is a well-known risk factor for the development of colorectal cancers and other types of tumors but is also considered a positive predictor of the immunotherapy response. Malignancies harboring such a specific genomic instability are very immunogenic because of the great number of aberrant antigens they produce. Therapies based on the blockade of specific immune checkpoints have shown to induce an effective immune response against microsatellite-unstable cancer. Many studies proved that microsatellite instability has a decisive role in the carcinogenesis and the malignant progression of head and neck cancer and, in the near future, it may become a useful tool in tailoring immunotherapy also in this field of precision oncology.

Abstract

The mismatch repair (MMR) system has a major role in the detection and correction of DNA replication errors, resulting from DNA polymerase slippage or nucleotides misincorporation. Specific inherited/acquired alterations or epigenetic inactivation of MMR genes are associated with microsatellite instability (MSI): the loss of crucial function in repairing DNA alterations can promote carcinogenesis by favoring the accumulation of thousands of mutations in a broad spectrum of different anatomic sites such as colon, stomach, prostate, esophagus, endometrium, lung and head and neck. Recent extensive data suggest that tumor mutational burden strongly correlates with a clinical response to immunotherapy using checkpoint inhibitors and this response is influenced by MMR deficiency in a wide range of human solid cancers. In this context, few data about this crucial point are available for head and neck cancer (HNC). In this review, we discuss the role of MMR alterations and the resulting MSI in HNC pathogenesis. Furthermore, by summarizing the clinical available data on how they influence the progression of precancerous lesions and the risk of recurrence or second primary tumors, we want to define the current role of MSI in the management of HNC. Finally, we analyze the complex interaction between cancer cells and the immune system addressing the data now available about a potential correlation between microsatellite instability and immunotherapy response in HNC.

Tumour mismatch repair protein loss is associated with advanced stage in oral cavity squamous cell carcinoma

An unexplained increase in the incidence of oral cavity squamous cell carcinoma (oSCC) has been observed despite decreasing smoking rates, particularly in younger patients. Links to defects in the DNA mismatch repair (MMR) system are well established in early onset colorectal, urothelial and gynaecological malignancies. MMR deficient patients treated with immune checkpoint inhibitors have demonstrated improved response rates. Studies exploring MMR status in head and neck squamous cell carcinoma (HNSCC) demonstrate conflicting results. This study explores the incidence of MMR protein loss and its association with clinicopathological features and outcome in oSCC. Immunohistochemical staining using tissue microarrays to assess the expression of MMR proteins (hMLH1, hMSH2, hMSH6, and hPMS2) was performed on 285 consecutive oSCC cases between 2000 and 2016. Data on smoking, alcohol and metachronous malignancies were retrospectively collected. Proportional hazards regression models were used to compare survival in MMR intact and deficient patients. MMR deficiency was seen in 21 patients (7.4%). MMR deficient tumours were associated with bone invasion (52% vs 32%, p=0.05), higher pT stage (pT4 in 57% vs 35%, p<0.001) and a higher number of metachronous malignancies (p=0.05). MMR deficiency was not associated with younger age at presentation or absence of smoking or alcohol. There was no significant association between MMR status and survival (overall survival hazard ratio 1.36; p=0.32). The incidence of MMR loss in oSCC is low and is not associated with young age at presentation. MMR deficiency in oSCC is associated with an increase in the number of metachronous malignancies and more advanced primary tumours.

EBV infection is associated with histone bivalent switch modifications in squamous epithelial cells

Epstein-Barr virus (EBV) induces histone modifications to regulate signaling pathways involved in EBV-driven tumorigenesis. To date, the regulatory mechanisms involved are poorly understood. In this study, we show that EBV infection of epithelial cells is associated with aberrant histone modification; specifically, aberrant histone bivalent switches by reducing the transcriptional activation histone mark (H3K4me3) and enhancing the suppressive mark (H3K27me3) at the promoter regions of a panel of DNA damage repair members in immortalized nasopharyngeal epithelial (NPE) cells. Sixteen DNA damage repair family members in base excision repair (BER), homologous recombination, nonhomologous end-joining, and mismatch repair (MMR) pathways showed aberrant histone bivalent switches. Among this panel of DNA repair members, MLH1, involved in MMR, was significantly down-regulated in EBV-infected NPE cells through aberrant histone bivalent switches in a promoter hypermethylation-independent manner. Functionally, expression of MLH1 correlated closely with cisplatin sensitivity both in vitro and in vivo. Moreover, seven BER members with aberrant histone bivalent switches in the EBV-positive NPE cell lines were significantly enriched in pathway analysis in a promoter hypermethylation-independent manner. This observation is further validated by their down-regulation in EBV-infected NPE cells. The in vitro comet and apurinic/apyrimidinic site assays further confirmed that EBV-infected NPE cells showed reduced DNA damage repair responsiveness. These findings suggest the importance of EBV-associated aberrant histone bivalent switch in host cells in subsequent suppression of DNA damage repair genes in a methylation-independent manner.

Mismatch repair system proteins in oral benign and malignant lesions

Different environmental agents may cause DNA mutations by disrupting its double-strand structure; however, even normal DNA polymerase function may synthesize mismatch nucleotide bases, occasionally demonstrating failure in its proofreading activity. To overcome this issue, mismatch repair (MMR) system, a group of proteins specialized in finding mispairing bases and small loops of insertion or deletion, works to avoid the occurrence of mutations that could ultimately lead to innumerous human diseases. In the last decades, the role of MMR proteins in oral carcinogenesis and in the development of other oral cavity neoplasms has grown, but their importance in the pathogenesis and their prognostic potential for patients affected by oral malignancies, especially oral squamous cell carcinoma (OSCC), remain unclear. Therefore, in this manuscript we aimed to review and critically discuss the currently available data on MMR proteins expression in oral potentially malignant lesions, in OSCC, and in other oral neoplasms to better understand their relevance in these lesions.

Reduced expression of mutS homolog 2 and mutL homolog 1 affects overall survival in laryngeal squamous cell carcinoma patients: Investigation into a potential cause

The risk factors affecting the survival rates of laryngeal carcinoma are not well understood. In this study, we investigated the expression status of mutS homolog 2 (MSH2) and mutL homolog 1 (MLH1) and examined the relationship between these two molecules and overall survival rates in laryngeal cancer. We also explored the potential reason for the altered expression of these two genes. Using real-time polymerase chain reaction and western blotting, we detected MSH2 and MLH1 expression in laryngeal cancer tissue samples. We collected a retrospective cohort with 180 laryngeal cancer patients, and inspected MSH2 and MLH1 staining with tissue microarray immunohistochemistry. Prognostic value of clinicopathological characteristics was evaluated by statistical analysis. Laryngeal carcinoma cells were co-cultured with Helicobacter pylori (H. pylori) bacteria. MSH2 and MLH1 were expressed at lower levels compared to those of adjacent tissues in 21 laryngeal carcinoma patients. Patients with negative expression of MSH2 and MLH1 tended to have a higher risk of mortality compared to patients with positive expression (HR=4.38; HR=3.0, respectively). Cigarette smoking rate was higher in the MLH1 expression positive group. H. pylori infection reduced the MSH2 and MLH1 expression levels of laryngeal carcinoma cell lines within co-culture conditions. It is suggested that the altered expression levels of MSH2 and MLH1 probably affect the overall survival of laryngeal carcinoma patients. H. pylori infection may have an effect on the expression of MSH2 and MLH1 in laryngeal carcinoma patients.