5-bp Classical Satellite DNA Loci from Chromosome-1 Instability in Cervical Neoplasia Detected by DNA Breakage Detection/Fluorescence in Situ Hybridization (DBD-FISH)

DBD-FISH Using Specific Chromosomal Region Probes for the Study of Cervical Carcinoma Progression

Genomic instability is an important biomarker in the progression of cervical carcinoma. DBD-FISH (DNA breakage detection-fluorescence in situ hybridization) is a sensitive method that detects strand breaks, alkali-labile sites, and incomplete DNA excision repair in cells of the cervical epithelium. This technique integrates the microgel immersion of cells from a vaginal lesion scraping and the DNA unwinding treatment with the capacity of FISH integrated into digital image analysis. Cells captured within an agarose matrix are lysed and submerged in an alkaline unwinding solution that generates single-stranded DNA motifs at the ends of internal DNA strand breaks. After neutralization, the microgel is dehydrated and the cells are incubated with DNA-labeled probes. The quantity of a hybridized probe at a target sequence corresponds to the measure of the single-stranded DNA produced during the unwinding step, which is equivalent to the degree of local DNA breakage. DNA damage does not show uniformly throughout the entire DNA of a cell; rather, it is confined to specific chromosomal sites. In this chapter, an overview of the technique is supplied, focusing on its ability for assessing the association between DNA damage in specific sequences and in the progressive stages of cervical carcinoma.

LINE-1 and Alu Methylation in hrHPV-Associated Precancerous Cervical Samples

OBJECTIVE

This study was conducted to determine global DNA methylation patterns in cervical cells cytologically identified as atypical squamous cells of unknown significance (ASCUS) with a normal, LSIL, or HSIL histopathological result.

METHODS

Methylation patterns of long interspersed nuclear elements (LINE-1) and short interspersed element (Alu) sequences were assessed using the combined bisulfite restriction analysis (COBRA) method in cervical samples with cytology-diagnosed cervical lesions.

RESULTS

In cervical precancerous lesions with hrHPV positive, the percentage of overall (^mC) and mCmC LINE-1 methylation levels showed a stepwise increase from hrHPV positive normal to HSIL with significant differences (p<0.001). However, both methylation levels were significantly higher in hrHPV negative normal than in hrHPV positive normal (p<0.001). The overall (^mC) Alu methylation in hrHPV positive LSIL and HSIL was lower than in hrHPV positive normal, with a significant difference (p<0.05). Remarkably, the percentage of uCmC and mCuC of LINE-1 and Alu in three different hrHPV positive cervical lesions showed a stepwise decrease from hrHPV positive normal, LSIL and HSIL, respectively. Furthermore, receiver operating characteristic (ROC) curve analyses revealed that the LINE-1 ^mC and ^mC^mC patterns have high sensitivity and specificity for distinguishing HSIL from normal/LSIL in hrHPV positive cases at the appropriate cutoff levels.

CONCLUSION

We have demonstrated the LINE-1 and Alu methylation data in normal and premalignant cervical epithelia. LINE-1 hypomethylation was found in hrHPV positive normal cells, with lower methylation levels associated with cancer features. In cytologically diagnosed Atypical Squamous Cells of Unknown Significance (ASCUS), the levels of ^mC and the ^mC^mC pattern could be utilized in concert with hrHPV detection to classify the ASCUS sample prior to colposcopy.

Assessment of micronuclei counts as tumour marker in cervical carcinogenesis: A follow-up study

OBJECTIVE

Micronuclei counts were performed in cervical smears with low-grade squamous intraepithelial lesions of the cervix (LSIL) to assess its potentiality as tumour marker in cervical carcinogenesis.

METHODS

The cases studied were from the ongoing rural cervical cancer screening in west Lucknow, India. Micronuclei counts were performed in the cervical smears of 100 LSIL cases, and the number of cells with micronuclei was defined as micronucleated cells (MNC) and the number of micronuclei per 1000 cells as MNC score. Human papillomavirus (HPV) DNA testing was also done in 100 LSIL cases by GeneNav qPCR test.

RESULTS

A high MNC score was found in 20 of the 100 LSIL cases while the counts were low in the remaining 80. Persistence of LSIL was seen in 19 of the 20 LSIL cases with high MNC score while only six cases of the 80 cases with low MNC score showed persistence. The persistence of LSIL was very high in cases with high MNC score. The multiple high-risk HPV types such as 18, 31, 33 and 35 were seen in 12 of the 100 LSIL cases and a high positivity rate was seen in women with high MNC score. The persistence of LSIL was also higher with HPV positivity.

CONCLUSION

The study revealed correlation between high MNC score, persistence of LSIL and HPV positivity. Hence, MNC score can prove to be very useful in discriminating high-risk LSIL cases that are less likely to regress and possibly may progress to high-grade squamous intraepithelial lesions or carcinoma.

Quick assessment of DNA damage in cervical epithelial cells using a chromatin dispersion test

PURPOSE

This study was aimed to quantify genomic DNA breakages in the cervical epithelium cells of patients diagnosed with different grades of cervical lesions using a quick test based on chromatin dispersion after controlled protein depletion. The association between the progressive stages of cervical dysplasia and the levels of DNA damage, taking into account the presence of papillomavirus human (HPV) infection, was investigated.

METHODS

A hospital-based unmatched case-control study was conducted during 2018 with a sample of 78 women grouped according to histological diagnosis as follows: 23 women with low grade-squamous intraepithelial lesion (LG-SIL), 34 women with high grade- squamous intraepithelial lesion (HG-SIL), and three women with cervical carcinoma (CC). In parallel, 15 women without cervical lesions were included as a Control cohort. DNA damage levels in cervical epithelial cells were assessed using the chromatin dispersion test (CDT) and controlled in parallel with DNA breakage detection coupled with florescent in situ hybridization (DBD‒FISH) using whole genomic DNA probes.

RESULTS

CDT produces different morphotypes in the cervical epithelium that can be associated with the level of DNA breakage revealed with DBD‒FISH. A significant increase of DNA damage was correlated with the histological progression of the patients and human papillomavirus (HPV) infection.

CONCLUSION

The CDT is a simple, accurate and inexpensive morphological bioassay to identify different levels DNA damage that can be associated with the level of abnormal cells present in the cervical epithelium in patients who commonly present HPV infection.

DBD-FISH, an effective marker for detecting genotoxicity in buccal mucosa exfoliated cells of patients with oral cancer

Oral squamous cell carcinoma (OSCC) is characterized by increased genetic instability as an essential variable of event of neoplastic transformation. The aim of this study was to evaluate genomic instability in exfoliated cells from the buccal mucosa of patients with OSCC vs. the control group, using DNA Breakage Detection/Fluorescence In Situ hybridization (DBD-FISH). Exfoliated cells from the buccal mucosa were obtained from 38 patients with oral cancer (case group) and from 10 individuals without oral lesions (control group). DNA damage was evaluated by DBD-FISH using the whole-genome DNA probe and digital imaging analysis. Collaterally, HPV infection was determined utilizing the INNO-LiPA HPV kit. Patients with OSCC showed an increase in the hybridization signal five times more intense than that of the baseline level of DNA damage detected in control individuals. The best cutoff value for predicting oral squamous cell carcinoma was 67.46, and an Odds Ratio (OR) value of 87. HPV detection analysis revealed than one patient with OSCC (2.6%) was positive for HPV. All controls were negative HPV. In conclusion, DBD-FISH permitted the clear visualization of level high of DNA damage in the buccal epithelial cells of patients with OSSC respect to control group. Chromosome instability in oral mucosa may be an individual marker of malignant transformation in OSCC.

Expression of the HPV18/E6 oncoprotein induces DNA damage

This study investigated possible variations in DNA damage in HeLa cells with silenced expression of the HPV/E6 oncogene compared with HeLa cells with normal expression of the E6 oncogene using the DNA breakage detection–fluorescence in situ hybridization (DBD–FISH) technique and a whole human genome DNA probe. The variable levels of DNA breaks present were measured quantitatively using image analysis after whole-genome DNA hybridization. HeLa cells with silenced expression of the HPV18/E6 oncogene showed a significant decrease in DNA damage compared with parental cells with normal expression of the E6 oncogene. These results were confirmed by alkaline comet assay. In conclusion, we demonstrated a decrease in DNA damage in HeLa clones associated with low expression of the HPV/E6 oncogene. The significance of this decrease regarding the HPV life cycle and carcinogenesis requires further exploration.

Use of DBD-FISH for the study of cervical cancer progression

DNA breakage detection-fluorescence in situ hybridization (DBD-FISH) is a procedure to detect and quantify DNA breaks in single cells, either in the whole genome or within specific DNA sequences. This methodology combines microgel embedding of cells and DNA unwinding procedures with the power of FISH coupled to digital image analysis. Cells trapped within an agarose matrix are lysed and immersed in an alkaline unwinding solution that produces single-stranded DNA motifs beginning at the ends of internal DNA strand breaks. After neutralization, the microgel is dehydrated and the cells are incubated with fluorescently labeled DNA probes. The amount of hybridized probe at a target sequence correlates with the amount of single-stranded DNA generated during the unwinding step, which is in turn proportional to the degree of local DNA breakage. A general view of the technique is provided, emphasizing its versatility for evaluating the association between DNA damage and progressive stages of cervical neoplasia.