The transcriptional regulator gene E2 of the Human Papillomavirus (HPV) 16 influences the radiosensitivity of cervical keratinocytes

P53 and pRB induction improves response to radiation therapy in HPV-positive laryngeal squamous cell carcinoma

INTRODUCTION

Patients with Human Papillomavirus (HPV+)-associated Laryngeal Squamous Cell Carcinoma (LSCC) exhibit dramatically improved survival relative to those with HPV-Negative (HPV-) tumors. In this study, the authors aimed to investigate the radiosensitivity of all available confirmed HPV+ and HPV-LSCC cells in vitro and in vivo.

METHODS

Primary LSCC cells were generated from tumor specimens obtained from patients. Real-time PCR was performed to confirm HPV infection and the expression of HPV-related genes (E6 and E7), p53, and pRB. Clonogenic survival assays, western blotting, and flow cytometry were used to assess radiation sensitivity, apoptosis, and the expression of p53 and pRB. p53 and pRB knockout cells were generated using CRISPR/Cas9 technology.

RESULTS

HPV+ LSCC cells displayed enhanced radiation sensitivity compared to HPV- cells. Radiation-induced apoptosis in HPV+ LSCC cells, accompanied by increased levels of p53 and pRB. Knockout of p53 or pRB led to radiation resistance and attenuated radiation-induced apoptosis in HPV+ LSCC cells. In vivo experiments showed similar results, where knockout of p53 or pRB decreased radiosensitivity in tumor-bearing mice.

CONCLUSION

The present findings demonstrated that HPV+ LSCC cells displayed obvious inherent radiation sensitivity, corresponding to increased apoptosis following radiation exposure. Mechanism study showed that the expression of p53 and pRB in HPV+ cells are required for radiation sensitivity. These findings highlight a novel mechanism by which p53 and pRB play key roles in the radiation sensitivity of HPV+ LSCC compared to HPV-LSCC.

Molecular Markers to Predict Prognosis and Treatment Response in Uterine Cervical Cancer

Uterine cervical cancer is one of the leading causes of cancer-related mortality in women worldwide. Each year, over half a million new cases are estimated, resulting in more than 300,000 deaths. While less-invasive, fertility-preserving surgical procedures can be offered to women in early stages, treatment for locally advanced disease may include radical hysterectomy, primary chemoradiotherapy (CRT) or a combination of these modalities. Concurrent platinum-based chemoradiotherapy regimens remain the first-line treatments for locally advanced cervical cancer. Despite achievements such as the introduction of angiogenesis inhibitors, and more recently immunotherapies, the overall survival of women with persistent, recurrent or metastatic disease has not been extended significantly in the last decades. Furthermore, a broad spectrum of molecular markers to predict therapy response and survival and to identify patients with high- and low-risk constellations is missing. Implementation of these markers, however, may help to further improve treatment and to develop new targeted therapies. This review aims to provide comprehensive insights into the complex mechanisms of cervical cancer pathogenesis within the context of molecular markers for predicting treatment response and prognosis.

DNA repair gene expression is associated with differential prognosis between HPV16 and HPV18 positive cervical cancer patients following radiation therapy

Cervical cancers are almost always induced by HPV infections, of which HPV16 and HPV18 are predominant. Cancers associated with these strains are induced through DNA repair factors and have a differential response to radiation therapy. Hence this study focuses on finding DNA repair gene expression differences in HPV16 and HPV18 positive cervical cancers after radiation therapy. A higher number of somatic mutations were observed in HPV16 positive cervical tumours for patients that were disease free when compared to those who recurred/progressed. Moreover, hierarchal clustering of RNAseq data from The Cancer Genome Atlas was conducted to identify groups of DNA repair genes associated with a differential prognosis for cervical cancer following postoperative radiation therapy. TP53BP1, MCM9 (at higher than mean levels), POLR2F and SIRT6 (at lower than mean levels), were associated with an increase in patients experiencing cervical cancer recurrence/progression following postoperative radiation therapy when HPV18 positive, but not HPV16 positive. The expression patterns of these genes provide an explanation for the higher rate of postoperative radiation therapy resistance associated with HPV18 positive cervical cancer patients. Therefore, HPV18 positive cervical tumours may be more likely retain a greater non-homologous end joining and homologous recombination pathway activity, which could dampen the effect of postoperative radiation therapy. Moreover, greater susceptibility to postoperative radiation therapy could be caused by the reliance of cervical cancer cells upon the single-strand annealing and nucleotide excision pathways for repair of DNA damage.

The Presence of Human Papillomavirus DNA Integration is Associated with Poor Clinical Results in Patients with Third-Stage Cervical Cancer

The presence of virus DNA integration into the cell genome was studied for 47 primary HPV16-positive patients with morphologically verified stage III cervical cancer. By using ROC analysis, the patients were divided into two groups: with and without HPV DNA integration into the host cell genome. The differences between the groups by the histological type, degree of tumor differentiation, and primary response to therapy were statistically insignificant. Virus DNA integration more than 7-fold reduced 5-year relapse-free survival and 1.7-fold reduced overall survival rate in comparison with patients without HPV DNA integration (p=0.0002 and p=0.05, respectively). The relative risk of adverse outcome of the disease in patients with the presence of HPV16 DNA integration increases by 4 times over a period of less than 3 years (р=0.0006) at high AUC level. The probability of earlier progression of the disease in patients with of HPV DNA integration calculated according to the Cox proportional hazards model was 85.5% (hazard ratio 5.96; p=0.002). Thus, the results suggest that the presence of HPV16 DNA integration into the cell genome is an independent factor in predicting clinical outcome of advanced cervical cancer and can serve as an effective criterion for the individual choice of treatment tactics for the patients.

Carbon-ion irradiation overcomes HPV-integration/E2 gene-disruption induced radioresistance of cervical keratinocytes

To date, only few data exist on mechanisms underlying the human papillomavirus (HPV)-associated irradiation response. It has been suggested, that the viral E2 gene plays an important role in that context. The aim of the current study is to compare the effect of photon- and carbon-ion (12C)-radiation therapy (RT) on cells with different HPV and E2 gene status. We hypothesized that 12C-RT might overcome the radioresistance of E2 gene-disrupted cells. We analyzed four different cell lines that differed in HPV status or E2 gene status. Cells were irradiated with either photons or 12C. Clonogenic survival, cell cycle and expression of Rb and p53 were analyzed. Radiosensitivity seemed to be dependent on E2 gene status and type of RT. 12C-RT led to lower surviving fractions, indicating higher radiosensitivity even in cells with disrupted E2 gene. The observed relative biological effectiveness (RBE) of 12C-RT for C33a/Caski and W12/S12 was 1.3/4 and 2.7/2.5, respectively. Cell cycle regulation after both photon- and 12C-RT was dependent on HPV status and on E2 gene status. Furthermore, the effect of RT on expression of p53 and Rb seemed to be dependent on E2 gene status and type of RT. We showed that 12C-RT overcomes HPV-integration induced radioresistance. The effect of RT on cell cycle regulation as well as on expression of p53 and Rb seemed to be dependent on HPV status, E2 gene status and type of RT. Differences in Rb expression and cell cycle regulation may play a role for enhanced radiosensitivity to 12C-RT of cells with disrupted E2 gene.

miR-375 Modulates Radiosensitivity of HR-HPV-Positive Cervical Cancer Cells by Targeting UBE3A through the p53 Pathway

Background

Prediction of radioresistance of HR-HPV-positive (+) cervical cancer, especially before the course of radiotherapy, is quite beneficial to develop an optimal treatment strategy for individual patients. Unfortunately, the mechanisms responsible for radioresistance of cervical cancer are still largely unexplored. HR-HPV infection leads to a series of changes to normal biophysical process, including miRNAs expression. In this study, we explored the association between miR-375 and radioresistance in HR-HPV (+) cervical cancer.

Material/Methods

qRT-PCR analysis was performed to determine miR-375 expression in HR-HPV-positive (+) cervical cancer patients and in HPV-16-positive SiHa and HPV-18-positive HeLa cervical cancer cell lines. The influence of miR-375 on radiosensitivity and the downstream regulative network were further explored in the cell line models.

Results

The results verified a putative binding site between miR-375 and UBE3A. miR-375 overexpression could significantly reduce UBE3A expression. UBE3A knockdown led to significantly reduced cell survival under radiation treatment. miR-375 promoted radiosensitivity of HR-HPV (+) cancer through decreasing p53 degradation and thereby increasing radiation-induced apoptosis.

Conclusions

The miR-375-UBE3A axis is important in modulating radiosensitivity of HR-HPV (+) cervical cancer.

Situation of HPV16 E2 gene status during radiotherapy treatment of cervical carcinoma

BACKGROUND

Human papillomavirus (HPV) integration within the E2 gene has been proposed as a critical event in cervical carcinogenesis. This study concerned whether HPV16 status and E2 gene intactness are predictive of radiation response in patients with cervical cancer.

MATERIALS AND METHODS

Biopsies of 44 patients with cervical cancer were collected before or after radiotherapy. The presence of HPV16 was assessed by polymerase chain reaction (PCR) using specific primers for the L1 region. E2 disruption was detected by amplifying the entire E2 gene.

RESULTS

HPV16 DNA was found in 54.5% of the clinical samples. Overall, 62.5% of the HPV16 positive tumors had integrated viral genome and 37.5% had episomal genome. There was a tendency of increase of HPV16 E2 negative tumors compared with HPV16 L1 ones in advanced stages (75% versus 20% in stage III respectively). Detection of E2 gene appeared influenced by the radiotherapy treatment, as the percentage of samples containing an intact HPV16 E2 was more frequent in pretreated patients compared to radiotherapy treated patients (66.6% versus 20%). The radiation therapy caused an eight-fold [OR= 8; CI=1.22-52.25; p=0.03] increase in the risk of HPV16 genome disruption. The integration status is influenced by the irradiation modalities, interestingly E2 disruption being found widely after radiotherapy treatment (75%) with a total fractioned dose of 50 Gy.

CONCLUSIONS

This study reveals that the status of the viral DNA may be used as a marker to optimize the radiation treatment.

Human papillomavirus does not have a causal role in colorectal carcinogenesis

AIM: To investigate the presence of human papillomavirus (HPV) DNA along with the integration, the quantification and the expression of the HPV16 in colorectal cancers.

METHODS: A prospective series of colorectal tumors were genotyped for HPV DNA. The clinical and pathological variables of the HPV-positive tumors were compared to those of HPV-negative samples. The integration status of HPV16 was evaluated by calculating E2/E6 ng ratios. HPV16-positive tumors were also evaluated for (1) E2, E4, E5, E6 and E7 viral gene ng quantification; (2) relative quantification compared to W12 cells; and (3) viral E2, E4, E5, E6 and E7 mRNA transcripts by real-time polymerase chain reaction.

RESULTS: HPV infection was detected in 16.9% of all tumors examined, and HPV16 was the most frequent type detected (63.6% of positive tissues). Notably, the clinical and pathological features of HPV-positive colorectal cancers were not significantly different than those of HPV-negative cancers (χ² and t-test for all clinical and pathological features of HPV-positive vs HPV-negative colorectal cancers: p ns). HPV16 DNA was present exclusively in episomal form, and the HPV16 E2, E4, E5, E6 and E7 genes were detected in trace nanogram quantities. Furthermore, the HPV16 genes ranged from 10^-3 to 10^-9 compared to W12 cells at an episomal stage. Although the extractions were validated by housekeeping gene expression, all the HPV16 positive tissues were transcriptionally inactive for the E2, E4, E5, E6 and E7 mRNAs.

CONCLUSION: Based on our results, HPV is unlikely involved in colorectal carcinogenesis.

Human papilloma virus and survival of oropharyngeal cancer patients treated with surgery and adjuvant radiotherapy

Impact of p16 protein, a surrogate marker for human papilloma virus induced cancer, p53 and EGFR as well as clinical factors on survival in a patient cohort with oropharyngeal squamous cell carcinoma (OPSCC) treated by surgical resection and adjuvant radiotherapy (RT) ± concomitant chemotherapy (CT). This is a retrospective analysis of patient's charts and tumor tissue. 57 patients were consecutively included and their tumor tissue assembled on a tissue microarray following immunohistochemical analysis. Survival times were estimated by means of Kaplan-Meier analysis. The importance of clinical and immunohistochemical factors for outcome was estimated by cox proportional hazard models. With 88% 5-year overall survival, 91% 5-year disease-specific survival and 91% 5-year disease-free survival, respectively, we found excellent survival rates in this surgically treated patient cohort of mainly advanced OPSCC (93% AJCC stage III or IV). The only factors positively influencing survival were p16 overexpression as well as p53 negativity and even more pronounced the combination of those biomarkers. Survival analysis of patients classified into three risk categories according to an algorithm based on p16, smoking, T- and N-category revealed a low, intermediate and high-risk group with significant survival differences between the low and the high-risk group. Patients with OPSCC can be successfully treated by surgery and adjuvant RT ± CT with a clear survival benefit of p16 positive, p53 negative patients. We recommend considering a combination of immunohistochemical (p16, p53) and clinical factors (smoking, T- and N-category) for risk stratification.

Photon-induced cell migration and integrin expression promoted by DNA integration of HPV16 genome

BACKGROUND

Persistent human papilloma virus 16 (HPV16) infections are a major cause of cervical cancer. The integration of the viral DNA into the host genome causes E2 gene disruption which prevents apoptosis and increases host cell motility. In cervical cancer patients, survival is limited by local infiltration and systemic dissemination. Surgical control rates are poor in cases of parametrial infiltration. In these patients, radiotherapy (RT) is administered to enhance local control. However, photon irradiation itself has been reported to increase cell motility. In cases of E2-disrupted cervical cancers, this phenomon would impose an additional risk of enhanced tumor cell motility. Here, we analyze mechanisms underlying photon-increased migration in keratinocytes with differential E2 gene status.

METHODS

Isogenic W12 (intact E2 gene status) and S12 (disrupted E2 gene status) keratinocytes were analyzed in fibronectin-based and serum-stimulated migration experiments following single photon doses of 0, 2, and 10 Gy. Quantitative FACS analyses of integrin expression were performed.

RESULTS

Migration and adhesion are increased in E2 gene-disrupted keratinocytes. E2 gene disruption promotes attractability by serum components, therefore, effectuating the risk of local infiltration and systemic dissemination. In S12 cells, migration is further increased by photon RT which leads to enhanced expression of fibronectin receptor integrins.

CONCLUSION

HPV16-associated E2 gene disruption is a main predictor of treatment-refractory cancer virulence. E2 gene disruption promotes cell motility. Following photon RT, E2-disrupted tumors bear the risk of integrin-related infiltration and dissemination.

Integrative radiation systems biology

Maximisation of the ratio of normal tissue preservation and tumour cell reduction is the main concept of radiotherapy alone or combined with chemo-, immuno- or biologically targeted therapy. The foremost parameter influencing this ratio is radiation sensitivity and its modulation towards a more efficient killing of tumour cells and a better preservation of normal tissue at the same time is the overall aim of modern therapy schemas. Nevertheless, this requires a deep understanding of the molecular mechanisms of radiation sensitivity in order to identify its key players as potential therapeutic targets. Moreover, the success of conventional approaches that tried to statistically associate altered radiation sensitivity with any molecular phenotype such as gene expression proofed to be somewhat limited since the number of clinically used targets is rather sparse. However, currently a paradigm shift is taking place from pure frequentistic association analysis to the rather holistic systems biology approach that seeks to mathematically model the system to be investigated and to allow the prediction of an altered phenotype as the function of one single or a signature of biomarkers. Integrative systems biology also considers the data from different molecular levels such as the genome, transcriptome or proteome in order to partially or fully comprehend the causal chain of molecular mechanisms. An example for the application of this concept currently carried out at the Clinical Cooperation Group "Personalized Radiotherapy in Head and Neck Cancer" of the Helmholtz-Zentrum München and the LMU Munich is described. This review article strives for providing a compact overview on the state of the art of systems biology, its actual challenges, potential applications, chances and limitations in radiation oncology research working towards improved personalised therapy concepts using this relatively new methodology.