Detection of human papillomavirus type 16 E6/E7 transcripts in fixed paraffin-embedded cervical cancers by the polymerase chain reaction

Human papillomavirus mRNA and p16 detection as biomarkers for the improved diagnosis of cervical neoplasia

Human papillomavirus (HPV) infection of the genital tract is very common and normally follows a benign clinical course; however, in an unfortunate minority of infected individuals, it can cause disease that sometimes leads to cancer. It is accepted that HPV DNA testing has a role in the management of cervical disease both in a prevaccination and postvaccination era; however, to improve the specificity of this approach, there is a requirement to develop and validate tools/assays that can identify women at risk for progressive disease. There is evidence to suggest that detection of viral gene expression both directly and indirectly may constitute a more specific approach for delineating clinically significant infection compared with HPV DNA-based assays. HPV oncogene expression and evidence of its deregulation can be monitored through direct detection of viral mRNA transcripts or through detection of the cellular protein p16. For both approaches, commercial assays have been introduced and numerous studies have been conducted. The present article describes the scientific theory underpinning these approaches, their amenability to routine-diagnostic specimens/settings, and the clinical data that has been garnered through their application thus far. Currently, there is promising data indicating that HPV mRNA and p16 might play an important role in future cervical cancer screening scenarios. Still, large randomized studies are necessary to confirm the preliminary data.

METHODS

PubMed and OVID were interrogated with search terms "HPV RNA;" "HPV mRNA;" "HPV transcript-detection, testing, and methods;" "p16" AND "cervical cancer;" "p16" AND "CIN;" "p16" AND "histology"; "p16" AND "cytology;" "p16;" and "screening."

The effect of vaginal microbes on in vivo and in vitro expression of human papillomavirus 16 E6-E7 genes

Since other viruses can influence expression of human papillomavirus (HPV) 16 E6-E7 genes in vitro, this study addressed whether specific vaginal bacteria do so as well. The vaginal microflora of 18 women with cervical intraepithelial neoplasia (CIN) or normal histology and HPV 16 infection, was evaluated by quantitative culture. Expression of HPV 16 E6-E7 oncogenes was assessed in exfoliated cervical cells by quantitative polymerase chain reaction. HPV 16 expression was also quantitated in CaSki carcinoma cell line cocultured with Bacteroides fragilis or Lactobacillus acidophilus. Isolation of Lactobacillus sp. (p = 0.05) and expression of the E6*II transcript (p = 0.03) were associated with low-grade CIN or normal histology. However, changes in E6-E7 expression were not associated independently with isolation of a specific microorganism. Similarly, expression of HPV 16 E6-E7 oncogenes in vitro was unaltered in the presence of bacteria. These results suggest that vaginal microorganisms are unlikely to alter the natural history of HPV-associated CIN by influencing HPV oncogene expression.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Application of the NASBA nucleic acid amplification method for the detection of human papillomavirus type 16 E6-E7 transcripts

Using a human papillomavirus type 16 (HPV-16) E6-E7 specific primer set in a nucleic acid sequence-based amplification (NASBA) reaction, detection of HPV-16 transcripts was accomplished in a single enzymatic reaction at 41 degrees C. The NASBA reaction product was visualized either by Northern bolt analysis with an HPV-16 E6-E7-specific 32P-labelled oligonucleotide probe or by a non-radioactive enzyme-linked gel assay (ELGA). In combination with a rapid nucleic acid extraction procedure this method appears to be very suitable for the sensitive and specific detection of HPV-16 transcripts on small amounts of HPV-16-expressing cells of various sources, including cervical smears.

Expression of human papillomavirus type 16 E6-E7 open reading frame varies quantitatively in biopsy tissue from different grades of cervical intraepithelial neoplasia

The proteins encoded by the human papillomavirus type 16 E6-E7 open reading frame are essential for transformation of the host cell. Two mRNA species, E6*I and E6*II, generated by alternative splicing of a polycistronic pre-mRNA, encode truncated E6 proteins and the E7 protein. Our investigation assessed whether or not the level of expression of E6*I and E6*II varies quantitatively in relation to the grade of cervical intraepithelial neoplasia (CIN). We used a quantitative reverse transcription PCR assay to quantify these transcripts in concurrently collected biopsy tissue and exfoliated cervical cells from 22 women with a normal cervix or various grades of CIN. We evaluated transcription profiles in relation to CIN grade and specimen type. The expression levels of E6*I and E6*II in exfoliated cervical cells did not vary significantly in relation to the grade of CIN. However, expression of E6*II was significantly diminished or absent in biopsy tissue obtained from CIN grade II and III lesions (P = 0.014). Our findings suggest that quantification of E6*I and E6*II expression in biopsy tissue may be more clinically relevant than analysis of exfoliated cells. The identification of distinct patterns of expression in association with low- and high-grade CIN suggests that quantification of E6*I and E6*II expression in biopsy tissue may have prognostic value as an indicator of CIN progression.

Absence of human papillomavirus type 16 E6 transcripts in HPV 16-infected, cytologically normal cervical scrapings

By a combination of reversed transcription and subsequent polymerase chain reaction (RNA-PCR), 23 cytologically normal cervical scrapings, positive for the presence of human papillomavirus type 16 (HPV 16) DNA, were analyzed for the presence of transcripts originating from the E6 region of the viral genome. This region is thought to be involved in transformational, tumorigenic events. No mRNAs of the E6 region were detectable using the most sensitive PCR-mediated procedure currently available. Since it was previously shown that in cytological abnormal cervical scrapings about one-half of the samples positive for HPV 16 DNA express mRNAs of the E6 region, a difference between normal and abnormal cervical scrapings, when the HPV 16 is present, exists. The observed difference between cytologically normal and abnormal, HPV-DNA-positive cervical scrapes may eventually be used as a prognostic marker for screening of women at risk for the development of cervical carcinoma. However, firm establishment of the putative correlation between tumor progression and the presence of E6 transcripts requires extensive follow-up analysis of HPV-positive patients.

Prevalence and distribution of human papillomavirus type-16 DNA in pelvic lymph nodes of patients with cervical cancer and in women with no history of cervical abnormality

The polymerase chain reaction (PCR) was used to investigate the prevalence and distribution of human papillomavirus (HPV)-16 DNA in paraffin sections of all pelvic lymph nodes removed from 14 patients with Stage Ib-cervical cancer at the time of resection of their primary tumours. The results were compared with those obtained from 8 women with no known history of cervical abnormality. In all, 22 cervical biopsies and 40 I lymph nodes (296 paraffin blocks) were examined. Nine of the 14 cervical cancer patients had primary tumours that were positive for HPV-16 DNA: only 3 of these had lymph nodes with histological evidence of metastasis, and HPV 16 DNA was detected in each of the corresponding paraffin blocks. HPV 16 DNA was also detected in varying proportions (8%-92%) of the histologically-negative lymph nodes from these women. There was no correlation between the HPV DNA-positive lymph nodes and their proximity to the primary tumour. HPV-16 DNA was not identified in any of the lymph nodes from the 5 women whose cancers were not HPV-16-related, or in those of women with no evidence of cervical abnormality. This preliminary survey suggests that HPV DNA is frequently transported from HPV-16-related cervical tumours to regional lymph nodes. However, its practical significance will not be clear until sufficient time has elapsed for correlation of the results with the clinical outcome.