Current and future direction in treatment of HPV-related cervical disease

Human papillomavirus (HPV) is the most common sexually transmitted virus in the world. About 70% of cervical cancers are caused by the most oncogenic HPV genotypes of 16 and 18. Since available prophylactic vaccines do not induce immunity in those with established HPV infections, the development of therapeutic HPV vaccines using E6 and E7 oncogenes, or both as the target antigens remains essential. Also, knocking out the E6 and E7 oncogenes in host genome by genome-editing CRISPR/Cas system can result in tumor growth suppression. These methods have shown promising results in both preclinical and clinical trials and can be used for controlling the progression of HPV-related cervical diseases. This comprehensive review will detail the current treatment of HPV-related cervical precancerous and cancerous diseases. We also reviewed the future direction of treatment including different kinds of therapeutic methods and vaccines, genome-editing CRISPR/Cas system being studied in clinical trials. Although the progress in the development of therapeutic HPV vaccine has been slow, encouraging results from recent trials showed vaccine-induced regression in high-grade CIN lesions. CRISPR/Cas genome-editing system is also a promising strategy for HPV cancer therapy. However, its safety and specificity need to be optimized before it is used in clinical setting.

Regulation of HPV transcription

Human papillomavirus infection is associated with the development of malignant and benign neoplasms. Approximately 40 viral types can infect the anogenital mucosa and are categorized into high- and low-risk oncogenic human papillomavirus, depending on their association with the development of cervical carcinoma. High-risk human papillomavirus 16 and 18 are detected in 55% and 15% of all invasive cervical squamous cell carcinomas worldwide, respectively. Low-risk human papillomavirus 6 and 11 are responsible for 90% of genital warts and are also associated with the development of recurrent respiratory papillomatosis. Human papillomavirus preferentially infects mitotic active cells of the basal layer from both mucosal and cutaneous epithelium through microabrasions. The viral life cycle synchronizes with the epithelial differentiation program, which may be due, in part, to the binding of differentially expressed cellular transcription factors to the long control region throughout the various epithelial layers. This review aimed to summarize the current knowledge regarding the mechanisms by which viral gene expression is regulated and the influence of human papillomavirus heterogeneity upon this phenomenon. A better understanding of the regulatory mechanisms may elucidate the particularities of human papillomavirus-associated pathogenesis and may provide new tools for antiviral therapy.

HPV DNA methylation at the early promoter and E1/E2 integrity: A comparison between HPV16, HPV18 and HPV45 in cervical cancer

Objectives

To compare and describe type-specific characteristics of HPV16, HPV18 and HPV45 in cervical cancer with respect to 3′LCR methylation and disruption of E1/E2.

Methods

The methylation level of 137 cervical cancer samples (70 with HPV16, 37 with HPV18, and 30 with HPV45) of Brazilian patients was analyzed by pyrosequencing. PCR amplifications were performed to characterize E1 and E2 disruption as an episomal surrogate.

Results

The 3′LCR of HPV16 showed a higher methylation at all CpG sites (7%, 9%, 11%, 10% and 10%) than homologous HPV18 regions (4%, 5%. 6%, 9% and 5%) and HPV45 regions (7%, 7% and 5%). Presence of intact E1/E2 was associated with higher HPV16 and HPV18 methylation levels at all CpG sites (p < 0.05). Disruption of E1/E2 was more frequently found in HPV45 (97%) and HPV18 (84%) than in HPV16 DNA (30%). HPV16 disruption was more frequently found in E1 (48%) unlike HPV18, where it was found in E2 (61%). Concomitant disruption of E1/E2 was most frequent in HPV45 (72%).

Conclusions

The findings showed a higher methylation associated with intact E1/E2 for HPV16 and HPV18. The closely phylogenetic related HPV18 and HPV45 share a similar methylation level and the frequency of viral genome disruption.

Quantitative methylation analysis of human papillomavirus 16L1 gene reveals potential biomarker for cervical cancer progression

Human papillomavirus 16 is the most prevalent type found in cervical cancer worldwide, accounting for >50% of all cases. Quantitative methylation analysis of human papillomavirus 16L1 gene within 5' (CpGs 5600, 5606, 5609, 5615) and 3' (7136 and 7145) regions to determine potential biomarker for cervical cancer progression was performed in exfoliated cervical cells collected from 101 Thai women of precancerous and cancerous lesions. Intermediate to high methylation levels (>20%) were detected in HPV16 5'L1 regions especially CpG 5600 of all cancerous (100%) and 50% of CIN3 samples, whereas normal/CIN1 samples (80%) showed methylation levels <20%. Our results indicate the potential use of HPV 16L1 gene methylation at specific site as a biomarker for prognostic cervical cancer screening, however, suitable cutoff should be further evaluated in a larger sample size.

Construction of a Transcription Map for Papillomaviruses using RACE, RNase Protection, and Primer Extension Assays

Papillomaviruses are a family of small, non-enveloped DNA tumor viruses. Knowing a complete transcription map of each papillomavirus genome can provide guidance for various papillomavirus studies. This unit provides detailed protocols to construct a transcription map of human papillomavirus type 18. The same approach can be easily adapted to other transcription map studies of any other papillomavirus genotype due to the high degree of conservation in genome structure, organization, and gene expression among papillomaviruses. The focused methods are 5'- and 3'-rapid amplification of cDNA ends (RACE), which are techniques commonly used in molecular biology to obtain full-length RNA transcript or to map a transcription start site (TSS) or an RNA polyadenylation (pA) cleavage site. Primer walking RT-PCR is a method for studying the splicing junction of RACE products. In addition, RNase protection assay and primer extension are also introduced as alternative methods in the mapping analysis.

Human papillomavirus vaccine trials and tribulations: Clinical perspectives

Human papillomavirus (HPV) affects hundreds of millions of people worldwide and is associated with both benign and malignant neoplasms in men and women. It is a double-stranded DNA virus with an icosahedral capsid. Forty HPV types are known to infect mucosal keratinocytes. If not cured by the immune system, the infection can lead to genital warts, mucosal dysplasia, or cancer. The most common oncogenic types are 16 and 18. The vaccine to prevent HPV and its associated morbidity and mortality has existed since 2006. Several variations protect against an increasing number of HPV types. The recommended vaccination age is before sexual exposure; administration of the vaccine to children has been controversial. This continuing medical education review evaluates the current HPV vaccines available to clinicians. Part I focuses on the debate over who should be vaccinated, at what age, and in which populations.

Modeling HPV early promoter regulation

In high risk forms, human papillomaviruses (HPV) can either induce or promote cancerous lesions, especially cervical cancer which is considered the second most common cancer in the women worldwide. HPV life cycle is tightly linked to the infected cell differentiation program and its evolution is strictly joined to the switch between the early and the late viral polycistronic promoters.The aim of this study is to develop a novel mathematical model which collects and structures the available biologic knowledge on the early promoter regulation for HPV in episomal form. The model includes the main regulation by E2 viral protein as well as a novel discovered co-regulation function mediated by the viral E1 protein. Only by including both E2 and E1 regulatory effect the model is able to correctly predict the temporal behaviour of the early promoter switching off. A possible use of the model as in silico tool to evaluate new antiviral therapies is discussed.

Differences in Transcriptional Activity of Human Papillomavirus Type 6 Molecular Variants in Recurrent Respiratory Papillomatosis

A significant proportion of recurrent respiratory papillomatosis (RRP) is caused by human papillomavirus type 6 (HPV-6). The long control region (LCR) contains cis-elements for regulation of transcription. Our aim was to characterize LCR HPV-6 variants in RRP cases, compare promoter activity of these isolates and search for cellular transcription factors (TFs) that could explain the differences observed. The complete LCR from 13 RRP was analyzed. Transcriptional activity of 5 variants was compared using luciferase assays. Differences in putative TFs binding sites among variants were revealed using the TRANSFAC database. Chromatin immunoprecipation (CHIP) and luciferase assays were used to evaluate TF binding and impact upon transcription, respectively. Juvenile-onset RRP cases harbored exclusively HPV-6vc related variants, whereas among adult-onset cases HPV-6a variants were more prevalent. The HPV-6vc reference was more transcriptionally active than the HPV-6a reference. Active FOXA1, ELF1 and GATA1 binding sites overlap variable nucleotide positions among isolates and influenced LCR activity. Furthermore, our results support a crucial role for ELF1 on transcriptional downregulation. We identified TFs implicated in the regulation of HPV-6 early gene expression. Many of these factors are mutated in cancer or are putative cancer biomarkers, and must be further studied.

Gene Silencing and Activation of Human Papillomavirus 18 Is Modulated by Sense Promoter Associated RNA in Bidirectionally Transcribed Long Control Region

Background

Recently various studies have demonstrated the role of promoter associated non-coding RNAs (pRNA) in dsRNA induced transcriptional gene silencing and activation. However the exact mechanistic details of these processes with respect to the orientation of pRNAs are poorly defined.

Methodology/Principal Findings

We have identified novel sense and antisense long control region (LCR) associated RNAs (pRNAs) in HPV18 positive cervical cancer cell lines HeLa, C-4 I and C-4 II. Using dsRNAs against these pRNAs, we were able to achieve upregulation or downregulation of the sense and antisense pRNAs and the downstream E6 and E7 oncogenes. We present evidence that knockdown of the sense pRNA is associated with reduction in E6 and E7 oncogenes and an upregulation of antisense pRNA. Conversely upregulation of sense pRNA is accompanied by an induction of the oncogenes and a concomitant reduction in antisense pRNA. Moreover, the exact role of sense and antisense pRNAs in dsRNA mediated gene modulation was confirmed by their selective degradation using antisense phosphorothioate oligodeoxynucleotides (ODN). Degradation of sense pRNA with antisense ODN led to loss of dsRNA induced silencing and activation, suggesting that dsRNA mediated gene modulation requires sense pRNA. Both processes were accompanied with congruent changes in the methylation pattern of activating and repressive histones.

Conclusion/Significance

Thus this data identifies and demonstrates the role of previously unknown important regulatory transcripts in HPV18 gene expression which can prove valuable targets in cervical cancer therapeutics. This mode of gene regulation by bidirectional transcription could be operational in other promoters as well and serve as a mechanism of regulating gene expression.

Viral load, integration and methylation of E2BS3 and 4 in human papilloma virus (HPV) 16-positive vaginal and vulvar carcinomas

Objective

To investigate if viral load, integration and methylation of E2BS3 and 4 represent different ways of tumor transformation in vaginal and vulvar carcinoma and to elucidate its clinical impact.

Methods

Fifty-seven samples, positive for HPV16, were selected for the study. Detection of viral load was made with realtime-PCR using copy numbers of E6 and integration was calculated from comparing E2 to E6-copies. Methylation of E2BS3 and 4 was analysed using bisulphite treatment of tumor DNA, followed by PCR and pyrosequencing.

Results

Vaginal tumors were found to have a higher viral load (p = 0.024) compared to vulvar tumors but a high copy number (> median value, 15 000) as well as high methylation (>50%) was significantly (p = 0.010 and p = 0.045) associated with a worse cancer-specific survival rate in vulvar carcinoma, but not in vaginal carcinoma. Four groups could be defined for the complete series using a Cluster Two step analysis; (1) tumors holding episomal viral DNA, viral load below 150 000 copies not highly methylated (n = 25, 46.3%); (2) tumors harboring episomal viral DNA and being highly methylated (>50%; n = 6, 11.1%); (3) tumors with viral DNA fully integrated (n = 11, 20.4%), and (4) tumors harboring episomal viral DNA and being medium- or unmethylated (<50%) and having a high viral load (> total mean value 150 000; n = 12, 22.2%). The completely integrated tumors were found to be distinct group, whilst some overlap between the groups with high methylation and high viral load was observed.

Conclusion

HPV16- related integration, methylation in E2BS3 and 4 and viral load may represent different viral characteristics driving vaginal and vulvar carcinogenesis. HPV16- related parameters were found to be of clinical importance in the vulvar series only.

Folate and vitamin B12 may play a critical role in lowering the HPV 16 methylation-associated risk of developing higher grades of CIN

We previously reported that a higher degree of methylation of CpG sites in the promoter (positions 31, 37, 43, 52, and 58) and enhancer site 7862 of human papillomavirus (HPV) 16 was associated with a lower likelihood of being diagnosed with HPV 16-associated CIN 2+. The purpose of this study was to replicate our previous findings and, in addition, to evaluate the influence of plasma concentrations of folate and vitamin B12 on the degree of HPV 16 methylation (HPV 16m). The study included 315 HPV 16-positive women diagnosed with either CIN 2+ or ≤CIN 1. Pyrosequencing technology was used to quantify the degree of HPV 16m. We reproduced the previously reported inverse association between HPV 16m and risk of being diagnosed with CIN 2+. In addition, we observed that women with higher plasma folate and HPV 16m or those with higher plasma vitamin B12 and HPV 16m were 75% (P < 0.01) and 60% (P = 0.02) less likely to be diagnosed with CIN 2+, respectively. With a tertile increase in the plasma folate or vitamin B12, there was a 50% (P = 0.03) and 40% (P = 0.07) increase in the odds of having a higher degree of HPV 16m, respectively. This study provides initial evidence that methyl donor micronutrients, folate and vitamin B12, may play an important role in maintaining a desirably high degree of methylation at specific CpG sites in the HPV E6 promoter and enhancer that are associated with the likelihood of being diagnosed with CIN 2+.

Human papillomavirus DNA methylation as a potential biomarker for cervical cancer

Sexually transmitted carcinogenic human papillomavirus (HPV) infections are extraordinarily prevalent worldwide. However, most incident HPV infections clear within a few years, whereas a small minority persists to invasive cancer. Recent studies indicate that detection of methylated viral DNA may distinguish women with cervical intraepithelial neoplasia grade 2+ (CIN2+) from those with a carcinogenic HPV-type infection that shows no evidence of CIN2+. Several studies have reported a positive association between methylation of CpG sites in the L1 gene and CIN2+, although there are inconclusive results about methylation of CpG sites in the upstream regulatory region (URR). In this review, we summarize the current state of knowledge on HPV DNA methylation in cervical carcinogenesis, and discuss the merits of different methods used to measure HPV DNA methylation. To follow the promising leads, we suggest future studies to validate the use of methylated carcinogenic HPV DNA as a predictive and/or diagnostic biomarker for risk of cervical cancer among HPV-positive women.

Nitric oxide induces early viral transcription coincident with increased DNA damage and mutation rates in human papillomavirus-infected cells

High-risk human papillomavirus (HPV) infections are necessary but insufficient causes of cervical cancers. Other risk factors for cervical cancer (e.g., pregnancy, smoking, infections causing inflammation) can lead to high and sustained nitric oxide (NO) concentrations in the cervix, and high NO levels are related to carcinogenesis through DNA damage and mutation. However, the effects of NO exposure in HPV-infected cells have not been investigated. In this study, we used the NO donor DETA-NO to model NO exposure to cervical epithelium. In cell culture media, 24-hour exposure to 0.25 to 0.5 mmol/L DETA-NO yielded a pathologically relevant NO concentration. Exposure of cells maintaining episomal high-risk HPV genomes to NO increased HPV early transcript levels 2- to 4-fold but did not increase viral DNA replication. Accompanying increased E6 and E7 mRNA levels were significant decreases in p53 and pRb protein levels, lower apoptotic indices, increased DNA double-strand breaks, and higher mutation frequencies when compared with HPV-negative cells. We propose that NO is a molecular cofactor with HPV infection in cervical carcinogenesis, and that modifying local NO cervical concentrations may constitute a strategy whereby HPV-related cancer can be reduced.

Recent Advances in the Search for Antiviral Agents against Human Papillomaviruses

Infection by human papillomavirus (HPV) is extremely common and associated with the development of benign warts or malignant lesions of the skin and mucosa. Infection by a high-risk (oncogenic) anogenital HPV type, most often through sexual contacts, is the starting point of virtually all cases of cervical cancers and the majority of anal cancers. The same viral types are also increasingly being linked with a subset of head-and-neck and non-melanoma skin cancers. Although prophylactic vaccines are now available to protect against the four types most commonly found in cervical and anal cancers (HPV16 and HPV18) and anogenital warts (HPV6 and HPV11), these neither protect against all genital HPVs nor are of therapeutic utility for already infected patients. Thus, the need for antiviral agents to treat HPV-associated diseases remains great, but none currently exist. This article reviews the recent progress made towards the development of antiviral agents to treat HPV infections, from target identification and validation to the discovery of lead compounds with therapeutic potential. Emphasis has been placed on novel low-molecular-weight compounds that antagonize HPV proteins or, alternatively, inhibit cellular proteins which have been usurped by papillomaviruses and are mediating their pathogenic effects.