Human papillomavirus type 16 E7 oncoprotein causes a delay in repair of DNA damage

Human papillomavirus E7 protein induces homologous recombination defects and PARPi sensitivity

PURPOSE

Cervical cancer is a common gynecological malignancy, pathologically associated with persistent infection of high-risk types of human papillomavirus (HPV). Previous studies revealed that HPV-positive cervical cancer displays genomic instability; however, the underlying mechanism is not fully understood.

METHODS

To investigate if DNA damage responses are aggravated in precancerous lesions of HPV-positive cervical epithelium, cervical tissues were biopsied and cryosectioned, and subjected to immunofluorescent staining. Cloned HA-tagged E6 and E7 genes of HPV16 subtype were transfected into HEK293T or C33A cells, and indirect immunofluorescent staining was applied to reveal the competency of double strand break (DSB) repair. To test the synthetic lethality of E7-indued HRD and PARP inhibitor (PARPi), we expressed E7 in C33A cells in the presence or absence of olaparib, and evaluated cell viability by colony formation.

RESULTS

In precancerous lesions, endogenous DNA lesions were elevated along with the severity of CIN grade. Expressing high-risk viral factor (E7) in HPV-negative cervical cells did not impair checkpoint activation upon genotoxic insults, but affected the potential of DSB repair, leading to homologous recombination deficiency (HRD). Based on this HPV-induced genomic instability, the viability of E7-expressing cells was reduced upon exposure to PARPi in comparison with control cells.

CONCLUSION

In aggregate, our findings demonstrate that HPV-E7 is a potential driver for genome instability and provides a new angle to understand its role in cancer development. The viral HRD could be employed to target HPV-positive cervical cancer via synthetic lethality.

HPV16 E6 induces chromosomal instability due to polar chromosomes caused by E6AP-dependent degradation of the mitotic kinesin CENP-E

Chromosome segregation during mitosis is highly regulated to ensure production of genetically identical progeny. Recurrent mitotic errors cause chromosomal instability (CIN), a hallmark of tumors. The E6 and E7 oncoproteins of high-risk human papillomavirus (HPV), which causes cervical, anal, and head and neck cancers (HNC), cause mitotic defects consistent with CIN in models of anogenital cancers, but this has not been studied in the context of HNC. Here, we show that HPV16 induces a specific type of CIN in patient HNC tumors, patient-derived xenografts, and cell lines, which is due to defects in chromosome congression. These defects are specifically induced by the HPV16 oncogene E6 rather than E7. We show that HPV16 E6 expression causes degradation of the mitotic kinesin CENP-E, whose depletion produces chromosomes that are chronically misaligned near spindle poles (polar chromosomes) and fail to congress. Though the canonical oncogenic role of E6 is the degradation of the tumor suppressor p53, CENP-E degradation and polar chromosomes occur independently of p53. Instead, E6 directs CENP-E degradation in a proteasome-dependent manner via the E6-associated ubiquitin protein ligase E6AP/UBE3A. This study reveals a mechanism by which HPV induces CIN, which may impact HPV-mediated tumor initiation, progression, and therapeutic response.

Fu Fang Gang Liu aqueous extract inhibits the proliferation of HeLa cells by causing deoxyribonucleic acid damage

ETHNOPHARMACOLOGICAL RELEVANCE

Fu Fang Gang Liu (FFGL) is an effective formula for treating wart proliferation caused by human papillomavirus (HPV) infection and has the potential to treat HPV-related cancers. However, scientific evidence of its anti-tumor activity against cervical cancer, the most common cancer caused by HPV, is lacking.

AIM OF THE STUDY

To clarify the anti-tumor effect of an FFGL aqueous extract on human cervical cancer and its possible mechanism of cell cycle arrest in HeLa cells.

MATERIALS AND METHODS

The anti-proliferative effect of FFGL on cervical cancer cells was assessed using the cell counting kit-8 assay. The proportion of apoptotic cells, cell cycle distribution, and cell division rate were determined using flow cytometry. Quantitative proteomics was used to identify differentially expressed proteins after FFGL treatment, and bioinformatics analysis was used to identify key nodal proteins affected by FFGL. Immunofluorescence and western blot analyses were used to explore changes in the expression of related proteins in the cell cycle and DNA damage pathways to elucidate the potential mechanism of action of FFGL against HeLa cell proliferation.

RESULTS

FFGL inhibited cervical cancer cell proliferation and caused cell cycle arrest. According to quantitative proteomics, CyclinB1 may play an important role in the anti-proliferative effect of FFGL on HeLa cells. Additional experiments showed that FFGL aqueous extract caused ATM-mediated DNA damage, further phosphorylated CHK2, led to the inactivation of Cdc25C, inhibited the activity of the CDK1/CyclinB1 complex, and resulted in cell cycle arrest.

CONCLUSIONS

FFGL can inhibit cervical cancer cell proliferation. Furthermore, it can increase CDK1 phosphorylation, block the cell cycle by causing DNA damage, and inhibit HeLa cell proliferation.

Therapeutic implications of transcriptomics in head and neck cancer patient-derived xenografts

There are currently no clinical strategies utilizing tumor gene expression to inform therapeutic selection for patients with head and neck squamous cell carcinoma (HNSCC). One of the challenges in developing predictive biomarkers is the limited characterization of preclinical HNSCC models. Patient-derived xenografts (PDXs) are increasingly recognized as translationally relevant preclinical avatars for human tumors; however, the overall transcriptomic concordance of HNSCC PDXs with primary human HNSCC is understudied, especially in human papillomavirus-associated (HPV+) disease. Here, we characterized 64 HNSCC PDXs (16 HPV+ and 48 HPV-) at the transcriptomic level using RNA-sequencing. The range of human-specific reads per PDX varied from 64.6%-96.5%, with a comparison of the most differentially expressed genes before and after removal of mouse transcripts revealing no significant benefit to filtering out mouse mRNA reads in this cohort. We demonstrate that four previously established HNSCC molecular subtypes found in The Cancer Genome Atlas (TCGA) are also clearly recapitulated in HNSCC PDXs. Unsupervised hierarchical clustering yielded a striking natural division of HNSCC PDXs by HPV status, with C19orf57 (BRME1), a gene previously correlated with positive response to cisplatin in cervical cancer, among the most significantly differentially expressed genes between HPV+ and HPV- PDXs. In vivo experiments demonstrated a possible relationship between increased C19orf57 expression and superior anti-tumor responses of PDXs to cisplatin, which should be investigated further. These findings highlight the value of PDXs as models for HPV+ and HPV- HNSCC, providing a resource for future discovery of predictive biomarkers to guide treatment selection in HNSCC.

DNA Damage Response Mechanisms in Head and Neck Cancer: Significant Implications for Therapy and Survival

Head and neck cancer (HNC) is a term collectively used to describe a heterogeneous group of tumors that arise in the oral cavity, larynx, nasopharynx, oropharynx, and hypopharynx, and represents the sixth most common type of malignancy worldwide. Despite advances in multimodality treatment, the disease has a recurrence rate of around 50%, and the prognosis of metastatic patients remains poor. HNCs are characterized by a high degree of genomic instability, which involves a vicious circle of accumulating DNA damage, defective DNA damage repair (DDR), and replication stress. Nonetheless, the damage that is induced on tumor cells by chemo and radiotherapy relies on defective DDR processes for a successful response to treatment, and may play an important role in the development of novel and more effective therapies. This review summarizes the current knowledge on the genes and proteins that appear to be deregulated in DDR pathways, their implication in HNC pathogenesis, and the rationale behind targeting these genes and pathways for the development of new therapies. We give particular emphasis on the therapeutic targets that have shown promising results at the pre-clinical stage and on those that have so far been associated with a therapeutic advantage in the clinical setting.

Plasma membrane proteoglycans syndecan-2 and syndecan-4 engage with EGFR and RON kinase to sustain carcinoma cell cycle progression

Epidermal growth factor receptor (EGFR) is a causal factor in carcinoma, yet many carcinoma patients are resistant to EGFR inhibitors. Potential insight into this resistance stems from prior work that showed EGFR in normal epithelial cells docks to the extracellular domain of the plasma membrane proteoglycan syndecan-4 (Sdc4) engaged with α3β1 and α6β4 integrins. We now report that this receptor complex is modified by the recruitment of syndecan-2 (Sdc2), the Recepteur d'Origine Nantais (RON) tyrosine kinase, and the cellular signaling mediator Abelson murine leukemia viral oncogene homolog 1 (ABL1) in triple-negative breast carcinoma and head and neck squamous cell carcinoma, where it contributes to EGFR kinase-independent proliferation. Treatment with a peptide mimetic of the EGFR docking site in the extracellular domain of Sdc4 (called SSTNEGFR) disrupts the entire complex and causes a rapid, global arrest of the cell cycle. Normal epithelial cells do not recruit these additional receptors to the adhesion mechanism and are not arrested by SSTNEGFR. Although EGFR docking with Sdc4 in the tumor cells is required, cell cycle progression does not depend on EGFR kinase. Instead, progression depends on RON kinase, activated by its incorporation into the complex. RON activates ABL1, which suppresses p38 mitogen-activated protein kinase and prevents a p38-mediated signal that would otherwise arrest the cell cycle. These findings add to the growing list of receptor tyrosine kinases that support tumorigenesis when activated by their association with syndecans at sites of matrix adhesion and identify new potential targets for cancer therapy.

Small DNA tumor viruses and human cancer: Preclinical models of virus infection and disease

Human tumor viruses cause various human cancers that account for at least 15% of the global cancer burden. Among the currently identified human tumor viruses, two are small DNA tumor viruses: human papillomaviruses (HPVs) and Merkel cell polyomavirus (MCPyV). The study of small DNA tumor viruses (adenoviruses, polyomaviruses, and papillomaviruses) has facilitated several significant biological discoveries and established some of the first animal models of virus-associated cancers. The development and use of preclinical in vivo models to study HPVs and MCPyV and their role in human cancer is the focus of this review. Important considerations in the design of animal models of small DNA tumor virus infection and disease, including host range, cell tropism, choice of virus isolates, and the ability to recapitulate human disease, are presented. The types of infection-based and transgenic model strategies that are used to study HPVs and MCPyV, including their strengths and limitations, are also discussed. An overview of the current models that exist to study HPV and MCPyV infection and neoplastic disease are highlighted. These comparative models provide valuable platforms to study various aspects of virus-associated human disease and will continue to expand knowledge of human tumor viruses and their relationship with their hosts.

Cervical cancer therapies: current challenges and future perspectives

Cervical cancer is the fourth most common female cancer worldwide and results in over 300 000 deaths globally. The causative agent of cervical cancer is persistent infection with high-risk subtypes of the human papillomavirus and the E5, E6 and E7 viral oncoproteins cooperate with host factors to induce and maintain the malignant phenotype. Cervical cancer is a largely preventable disease and early-stage detection is associated with significantly improved survival rates. Indeed, in high-income countries with established vaccination and screening programs it is a rare disease. However, the disease is a killer for women in low- and middle-income countries who, due to limited resources, often present with advanced and untreatable disease. Treatment options include surgical interventions, chemotherapy and/or radiotherapy either alone or in combination. This review describes the initiation and progression of cervical cancer and discusses in depth the advantages and challenges faced by current cervical cancer therapies, followed by a discussion of promising and efficacious new therapies to treat cervical cancer including immunotherapies, targeted therapies, combination therapies, and genetic treatment approaches.

Expression of DNA-damage response and repair genes after exposure to DNA-damaging agents in isogenic head and neck cells with altered radiosensitivity

BACKGROUND

Increased radioresistance due to previous irradiation or radiosensitivity due to human papilloma virus (HPV) infection can be observed in head and neck squamous cell carcinoma (HNSCC). The DNA-damage response of cells after exposure to DNA-damaging agents plays a crucial role in determining the fate of exposed cells. Tightly regulated and interconnected signaling networks are activated to detect, signal the presence of and repair the DNA damage. Novel therapies targeting the DNA-damage response are emerging; however, an improved understanding of the complex signaling networks involved in tumor radioresistance and radiosensitivity is needed.

MATERIALS AND METHODS

In this study, we exposed isogenic human HNSCC cell lines with altered radiosensitivity to DNA-damaging agents: radiation, cisplatin and bleomycin. We investigated transcriptional alterations in the DNA-damage response by using a pathway-focused panel and reverse-transcription quantitative PCR.

RESULTS

In general, the isogenic cell lines with altered radiosensitivity significantly differed from one another in the expression of genes involved in the DNA-damage response. The radiosensitive (HPV-positive) cells showed overall decreases in the expression levels of the studied genes. In parental cells, upregulation of DNA-damage signaling and repair genes was observed following exposure to DNA-damaging agents, especially radiation. In contrast, radioresistant cells exhibited a distinct pattern of gene downregulation after exposure to cisplatin, whereas the levels in parental cells were unchanged. Exposure of radioresistant cells to bleomycin did not significantly affect the expression of DNA-damage signaling and repair genes.

CONCLUSIONS

Our analysis identified several possible targets: NBN, XRCC3, ATR, GADD45A and XPA. These putative targets should be studied and potentially exploited for sensibilization to ionizing radiation and/or cisplatin in HNSCC. The use of predesigned panels of DNA-damage signaling and repair genes proved to offer a convenient and quick approach to identify possible therapeutic targets.

Viral Modulation of the DNA Damage Response and Innate Immunity: Two Sides of the Same Coin

The DDR consists of multiple pathways that sense, signal, and respond to anomalous DNA. To promote efficient replication, viruses have evolved to engage and even modulate the DDR. In this review, we will discuss a select set of diverse viruses and the range of mechanisms they evolved to interact with the DDR and some of the subsequent cellular consequences. There is a dichotomy in that the DDR can be both beneficial for viruses yet antiviral. We will also review the connection between the DDR and innate immunity. Previously believed to be disparate cellular functions, more recent research is emerging that links these processes. Furthermore, we will discuss some discrepancies in the literature that we propose can be remedied by utilizing more consistent DDR-focused assays. By doing so, we hope to obtain a much clearer understanding of how broadly these mechanisms and phenotypes are conserved among all viruses. This is crucial for human health since understanding how viruses manipulate the DDR presents an important and tractable target for antiviral therapies.

Head and Neck Squamous Cell Carcinoma: Risk Factors, Molecular Alterations, Immunology and Peptide Vaccines

Head and neck squamous cell carcinoma (HNSCC) arises from the epithelial lining of the oral cavity, hypopharynx, oropharynx, and larynx. There are several potential risk factors that cause the generation of HNSCC, including cigarette smoking, alcohol consumption, betel quid chewing, inadequate nutrition, poor oral hygiene, HPV and Epstein–Barr virus, and Candida albicans infections. HNSCC has causative links to both environmental factors and genetic mutations, with the latter playing a more critical role in cancer progression. These molecular changes to epithelial cells include the inactivation of cancer suppressor genes and proto-oncogenes overexpression, resulting in tumour cell proliferation and distant metastasis. HNSCC patients have impaired dendritic cell (DC) and natural killer (NK) cell functions, increased production of higher immune-suppressive molecules, loss of regulatory T cells and co-stimulatory molecules and major histocompatibility complex (MHC) class Ι molecules, lower number of lymphocyte subsets, and a poor response to antigen-presenting cells. At present, the standard treatment modalities for HNSCC patients include surgery, chemotherapy and radiotherapy, and combinatorial therapy. Despite advances in the development of novel treatment modalities over the last few decades, survival rates of HNSCC patients have not increased. To establish effective immunotherapies, a greater understanding of interactions between the immune system and HNSCC is required, and there is a particular need to develop novel therapeutic options. A therapeutic cancer vaccine has been proposed as a promising method to improve outcome by inducing a powerful adaptive immune response that leads to cancer cell elimination. Compared with other vaccines, peptide cancer vaccines are more robust and specific. In the past few years, there have been remarkable achievements in peptide-based vaccines for HNSCC patients. Here, we summarize the latest molecular alterations in HNSCC, explore the immune response to HNSCC, and discuss the latest developments in peptide-based cancer vaccine strategies. This review highlights areas for valuable future research focusing on peptide-based cancer vaccines.

Hypoxia and Its Influence on Radiotherapy Response of HPV-Positive and HPV-Negative Head and Neck Cancer

Head and neck squamous cancers are a heterogeneous group of cancers that arise from the upper aerodigestive tract. Etiologically, these tumors are linked to alcohol/tobacco abuse and infections with high-risk human papillomavirus (HPV). HPV-positive HNSCCs are characterized by a different biology and also demonstrate better therapy response and survival compared to alcohol/tobacco-related HNSCCs. Despite this advantageous therapy response and the clear biological differences, all locally advanced HNSCCs are treated with the same chemo-radiotherapy schedules. Although we have a better understanding of the biology of both groups of HNSCC, the biological factors associated with the increased radiotherapy response are still unclear. Hypoxia, i.e., low oxygen levels because of an imbalance between oxygen demand and supply, is an important biological factor associated with radiotherapy response and has been linked with HPV infections. In this review, we discuss the effects of hypoxia on radiotherapy response, on the tumor biology, and the tumor microenvironment of HPV-positive and HPV-negative HNSCCs by pointing out the differences between these two tumor types. In addition, we provide an overview of the current strategies to detect and target hypoxia.

4NQO enhances differential activation of DNA repair proteins in HPV positive and HPV negative HNSCC cells

Tobacco exposure and human papillomavirus (HPV) infection are among the main risk factors for the development of head and neck squamous cell carcinoma (HNSCC). Interestingly, recent studies show that tumors from HPV positive (HPV+) smokers and non-smokers have similar mutational profiles, which suggests that HPV could prevent mutation induction or accumulation in the intermediate risk group composed of HPV+ smokers. Hence, we tested this observation by analyzing the effects of 4-Nitroquinoline N-oxide (4NQO), a mutagen and smoking mimetic, in NOK (normal oral keratinocytes), NOK^E6.E7 (NOK cells transfected with E6.E7 oncogenes of HPV), HPV+ and HPV negative (HPV-) HNSCC cells. Oxidative DNA damage, γH2AX foci formation, DNA repair protein activation, cell cycle phase analysis, apoptotic cell death, cell viability and clonogenic cell survival were analyzed after 4NQO treatment in NOK, NOK^E6.E7, HPV+ and HPV- HNSCC cells. 4NQO increased oxidative base damage and γH2AX foci formation in NOK^E6.E7, HPV+ and HPV- HNSCC cells. Phosphorylation of homologous recombination (HR) repair proteins was higher in NOK^E6.E7 and HPV+ HNSCC cells compared to NOK and HPV- HNSCC cells respectively. HPV+ and HPV- HNSCC cells showed differential activation of cell cycle regulatory proteins, increased apoptosis, and decreased cell viability upon 4NQO-induced DNA damage. Taken together, 4NQO (a smoking mimetic), induced higher activation of HR repair in HPV+ HNSCC cells compared to HPV- HNSCC cells. This may allow for increased mutational resistance and help explain why HPV+ smokers have a worse prognosis than HPV+ non-smokers.

Genomic Signatures in HPV-Associated Tumors

Papillomaviruses dysregulate the G1/S cell cycle transition in order to promote DNA synthesis in S phase, which is a requirement for viral replication. The human papillomaviruses (HPV) E6 and E7 oncoproteins mediate degradation of the cell cycle regulators p53 and Rb, which are two of the most universally disrupted tumor-suppressor genes in all of cancer. The G1/S checkpoint is activated in normal cells to allow sufficient time for DNA repair in G1 before proceeding to replicate DNA and risk propagating unrepaired errors. The TP53 pathway suppresses a variety of such errors, including translocation, copy number alterations, and aneuploidy, which are thus found in HPV-associated tumors similarly to HPV-negative tumors with other mechanisms of TP53 disruption. However, E6 and E7 maintain a variety of other virus–host interactions that directly disrupt a growing list of other DNA repair and chromatin remodeling factors, implying HPV-specific repair deficiencies. In addition, HPV-associated squamous cell carcinomas tumors clinically respond differently to DNA damaging agents compared to their HPV negative counterparts. The focus of this review is to integrate three categories of observations: (1) pre-clinical understanding as to the effect of HPV on DNA repair, (2) genomic signatures of DNA repair in HPV-associated tumor genomes, and (3) clinical responses of HPV-associated tumors to DNA damaging agents. The goals are to try to explain why HPV-associated tumors respond so well to DNA damaging agents, identify missing pieces, and suggest clinical strategies could be used to further improve treatment of these cancers.

Biology of the Radio- and Chemo-Responsiveness in HPV Malignancies

In multiple anatomic sites, patients with cancers associated with the Human Papillomavirus (HPV) experience better locoregional control and overall survival after radiotherapy and/or chemoradiotherapy than patients with HPV-negative cancers. These improved outcomes suggest that relatively unique biological features in HPV-positive cancers may increase sensitivity to DNA damaging agents as well as an impaired DNA damage response. This review will address potential biological mechanisms driving this increased sensitivity of HPV-positive cancer to radiation and/or chemotherapy. This review will discuss the clinical and preclinical observations that support the intrinsic radiosensitivity and/or chemosensitivity of HPV-positive cancers. Furthermore, this review will highlight the molecular mechanisms for increased radiation sensitivity using the classical "4 Rs" of radiobiology: repair, reassortment, repopulation, and reoxygenation. First, HPV-positive cancers have increased DNA damage due to increased oxidative stress and impaired DNA damage repair due to the altered activity TP53, p16, TIP60, and other repair proteins. Second, irradiated HPV-positive cancer cells display increased G2/M arrest leading to reassortment of cancer cells in more radiosensitive phases of the cell cycle. In addition, HPV-positive cancers have less radioresistant cancer stem cell subpopulations that may limit their repopulation during radiotherapy. Finally, HPV-positive cancers may also have less hypoxic tumor microenvironments that make these cancers more sensitive to radiation than HPV-negative cells. We will also discuss extrinsic immune and microenvironmental factors enriched in HPV-positive cancers that facilities responses to radiation. Therefore, these potential biological mechanisms may underpin the improved clinical outcomes often observed in these virally induced cancers.

Targeted Therapy as a Potential De-Escalation Strategy in Locally Advanced HPV-Associated Oropharyngeal Cancer: A Literature Review

The treatment landscape of locally advanced HPV-oropharyngeal squamous cell carcinoma (OPSCC) is undergoing transformation. This is because the high cures rates observed in OPSCC are paired with severe treatment-related, long-term toxicities. These significant adverse effects have led some to conclude that the current standard of care is over-treating patients, and that de-intensifying the regimens may achieve comparable survival outcomes with lower toxicities. Consequently, several de-escalation approaches involving locally advanced OPSCC are underway. These include the reduction of dosage and volume of intensive cytotoxic regimens, as well as elimination of invasive surgical procedures. Such de-intensifying treatments have the potential to achieve efficacy and concurrently alleviate morbidity. Targeted therapies, given their overall safer toxicity profiles, also make excellent candidates for de-escalation, either alone or alongside standard treatments. However, their role in these endeavors is currently limited, because few targeted therapies are currently in clinical use for head and neck cancers. Unfortunately, cetuximab, the only FDA-approved targeted therapy, has shown inferior outcomes when paired with radiation as compared to cisplatin, the standard radio-sensitizer, in recent de-escalation trials. These findings indicate the need for a better understanding of OPSCC biology in the design of rational therapeutic strategies and the development of novel, OPSCC-targeted therapies that are safe and can improve the therapeutic index of standard therapies. In this review, we summarize ongoing research on mechanism-based inhibitors in OPSCC, beginning with the salient molecular features that modulate tumorigenic processes and response, then exploring pharmacological inhibition and pre-clinical validation studies of candidate targeted agents, and finally, summarizing the progression of those candidates in the clinic.

The DNA Damage Response Is Differentially Involved in HPV-Positive and HPV-Negative Radioresistant Head and Neck Squamous Cell Carcinoma

Simple Summary

Head and neck cancers can be divided in two major groups according to their risk factors, being high-risk human papillomavirus related (HPV-positive) and alcohol and tobacco related (HPV-negative) head and neck cancers. The majority of the locally advanced patients are treated with radiotherapy. However, up to 50% of these patients show local recurrences. The majority of these recurrences are linked to resistance to radiotherapy treatment. It is known that the response to DNA damage, also a process called the DNA damage response, is an important factor that determines the effectivity of radiotherapy. Here, we assessed the role of the DNA damage response in the resistance process to radiotherapy of head and neck cancers, by generating head and neck cancer cells resistant to radiotherapy. We show that the DNA damage response is differentially involved in the resistance process of HPV-positive and HPV-negative head and neck cancer cells. More specifically, HPV-positive radiotherapy-resistant cells showed increased ability to repair the DNA damage induced by radiotherapy. HPV-negative radiotherapy-resistant cells showed increased capacity to replicate after radiotherapy treatment. Despite this difference, inhibition of the DNA damage response enhanced the effect of radiotherapy in both groups.

Abstract

Radioresistance is a major cause of recurrences and radiotherapy (RT) failure in head and neck squamous cell carcinoma (HNSCC). DNA damage response (DDR) is known to be important for RT response, but its role in radioresistance is not fully understood. Here, we assessed the role of DDR in the radioresistance process of HNSCC by generating radioresistant clones from both HPV-positive SCC154 and HPV-negative SCC61 cells. We show that fractionated RT decreased RT response of HPV-positive and HPV-negative radioresistant clones in vitro and in vivo. Moreover, HPV-positive and HPV-negative radioresistant clones were characterized by differential DDR response. HPV-positive radioresistant clones showed less residual double-strand break damage and increased G2/M arrest recovery after RT, indicating an acquisition of increased DDR kinetics. In contrast, HPV-negative radioresistant clones showed less micronucleated cells after RT and increased survival upon checkpoint inhibition, indicating an increased replicative capacity. Inhibiting key factors of DDR in combination with RT rescued the radioresistant phenotype of both HPV-positive and HPV-negative radioresistant clones. Altogether, our results not only highlight the importance of DDR response in the radioresistance process of HPV-positive and HPV-negative HNSCC, but also provide possibilities for new therapies for HNSCC patients in recurrent settings.

Combined Inhibition of Rad51 and Wee1 Enhances Cell Killing in HNSCC Through Induction of Apoptosis Associated With Excessive DNA Damage and Replication Stress

Despite advances in surgery, chemotherapy, and radiation, there are limited treatment options for advanced head and neck squamous cell carcinoma (HNSCC) and survival remains very poor. Therefore, effective therapies are desperately needed. Recently, selective exploitation of DNA damage and replication stress responses has become a novel approach for cancer treatment. Wee1 kinase and Rad51 recombinase are two proteins involved in regulating replication stress and homologous recombination repair in cancer cells. In this study, we investigated the combined effect of Rad51 inhibitor (B02) and Wee1 inhibitor (AZD1775) in vitro and in vivo in various HNSCC cell lines. Clonogenic survival assays demonstrated that B02 synergized with AZD1775 in vitro in all HNSCC cell lines tested. The synergy between these drugs was associated with forced CDK1 activation and reduced Chk1 phosphorylation leading to induction of excessive DNA damage and replication stress, culminating in aberrant mitosis and apoptosis. Our results showed that elevated Rad51 mRNA expression correlated with worse survival in HNSCC patients with HPV-positive tumors. The combination of B02 and AZD1775 significantly inhibited tumor growth in vivo in mice bearing HPV-positive HNSCC tumors as compared to HPV-negative HNSCC. This differential sensitivity appears to be linked to HPV-positive tumors having more in vivo endogenous replication stress owing to transformation by E6 and E7 oncogenes. Furthermore, addition of B02 radiosensitized the HPV-negative HNSCC tumors in vitro and in vivo In conclusion, our data implicate that a novel rational combination with Rad51 and Wee1 inhibitors holds promise as synthetic lethal therapy, particularly in high-risk HPV-positive HNSCC.

Expression of miR-34a and miR-15b during the progression of cervical cancer in a murine model expressing the HPV16 E7 oncoprotein

The high-risk human papillomavirus (HR-HPV) E7 oncoprotein appears to be a major determinant for cell immortalization and transformation altering critical processes such as cell proliferation, apoptosis, and immune response. This oncoprotein plays an essential role in cervical carcinogenesis, but other cofactors such as long-term use of hormonal contraceptives are necessary to modulate the risk of cervical cancer (CC). The role of HR-HPVs in the alteration of microRNA (miRNA) levels in persistent viral infections currently remains unclear. The aim of this study was to evaluate the miR-34a and miR-15b expression levels in the murine HPV16K14E7 (K14E7) transgenic model after chronic estrogen (E₂) treatment and their involvement in CC. Interestingly, results showed that, although miR-34a expression is elevated by the HPVE7 oncogene, this expression was downregulated in the presence of both the E7 oncoprotein and chronic E₂ in cervical carcinoma. On the other hand, miR-15b expression was upregulated along cervical carcinogenesis mainly by the effect of E₂. These different changes in the expression levels of miR-34a and miR-15b along cervical carcinogenesis conduced to low apoptosis levels, high cell proliferation and finally, to cancerous cervical tissue development. In this work, we also determined the relative mRNA expression of Cyclin E2 (Ccne2), Cyclin A2 (Ccna2), and B cell lymphoma 2 (Bcl-2) (target genes of miR-34a and miR-15b); Sirtuin 1 (Sirt1), Cmyc, and Bax (miR-34a target genes); and p21/WAF1 (mir15b target gene) and the H-ras oncogene. Given the modifications in the expression levels of miR-34a and miR-15b during the development of cervical cancer, it will be useful to carry out further investigation to confirm them as molecular biomarkers of cancer.

Genomic heterogeneity and copy number variant burden are associated with poor recurrence-free survival and 11q loss in human papillomavirus-positive squamous cell carcinoma of the oropharynx

BACKGROUND

Human papillomavirus-positive (HPV+) squamous cell carcinoma of the oropharynx (OPSCC) is the most prevalent HPV-associated malignancy in the United States. Favorable treatment outcomes have led to increased interest in treatment de-escalation to reduce treatment morbidity as well as the development of prognostic markers to identify appropriately low-risk patients. Intratumoral genomic heterogeneity and copy number alteration burden have been demonstrated to be predictive of poor outcomes in many other cancers; therefore, we sought to determine whether intratumor heterogeneity and genomic instability are associated with poor outcomes in HPV+ OPSCC.

METHODS

Tumor heterogeneity estimates were made based on targeted exome sequencing of 45 patients with HPV+ OPSCC tumors. Analysis of an additional cohort of HPV+ OPSCC tumors lacking matched normal sequencing allowed copy number analysis of 99 patient tumors.

RESULTS

High intratumorally genomic heterogeneity and high numbers of copy number alterations were strongly associated with worse recurrence-free survival. Tumors with higher heterogeneity and frequent copy number alterations were associated with loss of distal 11q, which encodes key genes related to double-strand break repair, including ATM and MRE11A.

CONCLUSIONS

Both intratumor genomic heterogeneity and high-burden copy number alterations are strongly associated with poor recurrence-free survival in patients with HPV+ OPSCC. The drivers of genomic instability and heterogeneity in these tumors remains to be elucidated. However, 11q loss and defective DNA double-strand break repair have been associated with genomic instability in other solid tumors. Copy number alteration burden and intratumoral heterogeneity represent promising avenues for risk stratification of patients with HPV+OPSCC.

Cell death in head and neck cancer pathogenesis and treatment

Many cancer therapies aim to trigger apoptosis in cancer cells. Nevertheless, the presence of oncogenic alterations in these cells and distorted composition of tumour microenvironment largely limit the clinical efficacy of this type of therapy. Luckily, scientific consensus describes about 10 different cell death subroutines with different regulatory pathways and cancer cells are probably not able to avoid all of cell death types at once. Therefore, a focused and individualised therapy is needed to address the specific advantages and disadvantages of individual tumours. Although much is known about apoptosis, therapeutic opportunities of other cell death pathways are often neglected. Molecular heterogeneity of head and neck squamous cell carcinomas (HNSCC) causing unpredictability of the clinical response represents a grave challenge for oncologists and seems to be a critical component of treatment response. The large proportion of this clinical heterogeneity probably lies in alterations of cell death pathways. How exactly cells die is very important because the predominant type of cell death can have multiple impacts on the therapeutic response as cell death itself acts as a second messenger. In this review, we discuss the different types of programmed cell death (PCD), their connection with HNSCC pathogenesis and possible therapeutic windows that result from specific sensitivity to some form of PCD in some clinically relevant subgroups of HNSCC.

Improved local control in p16 negative oropharyngeal cancers with hypermethylated MGMT

INTRODUCTION

Patients with oropharyngeal cancers that are p16 negative (p16-) have worse outcomes than those who are p16 positive (p16+) and there is an unmet need for prognostic markers in this population. O6-Methylguanine (O6-MG)-DNA-methyltransferase (MGMT) gene methylation has been associated with response to chemoradiotherapy (CRT) in glioblastoma. We sought to find if MGMT promoter methylation was associated with outcomes of locally advanced oropharyngeal and oral cavity squamous cell carcinoma (OOSCC) in patients treated with definitive concurrent CRT.

METHODS

Patients were identified with primary OOSCC, known p16 status, retrievable pre-treatment biopsies, and at least 6 months of follow-up who received definitive concurrent CRT from 2004 to 2015. Biopsies were tested for MGMT hypermethylation (MGMT+) using a Qiagen pyrosequencing kit (Catalog number 970061). Outcomes were subsequently recorded and analyzed.

RESULTS

Fifty-eight patients were included with a median follow up of 78 (range 6-196) months. Fourteen patients (24.1%) had oral cavity cancer and 44 (75.9%) had oropharyngeal cancer. A significant difference was found for local recurrence free survival (LRFS) by combined MGMT and p16 status (p = 0.0004). Frequency of LR in MGMT+/p16+, MGMT+/p16-, MGMT-/p16+, and MGMT-p16- patients was 14.3%, 14.3%, 13.0%, and 69.2%, respectively (p = 0.0019). A significant difference was not found for distant recurrence free survival (p = 0.6165) or overall survival (p = 0.1615). LRFS remained significant on analysis restricted to oropharyngeal cancer patients (p-value = 0.0038).

CONCLUSION

Patients who are p16- and MGMT+ with oropharyngeal and oral cavity squamous cell carcinoma have significantly better LC with definitive CRT than those who are p16- and MGMT-. Prospective studies are needed to verify these findings.

Effect of ATR Inhibition in RT Response of HPV-Negative and HPV-Positive Head and Neck Cancers

Radiotherapy (RT) has a central role in head and neck squamous cell carcinoma (HNSCC) treatment. Targeted therapies modulating DNA damage response (DDR) and more specific cell cycle checkpoints can improve the radiotherapeutic response. Here, we assessed the influence of ataxia-telangiectasia mutated and Rad3-related (ATR) inhibition with the ATR inhibitor AZD6738 on RT response in both human papillomavirus (HPV)-negative and HPV-positive HNSCC. We found that ATR inhibition enhanced RT response in HPV-negative and HPV-positive cell lines independent of HPV status. The radiosensitizing effect of AZD6738 was correlated with checkpoint kinase 1 (CHK1)-mediated abrogation of G2/M-arrest. This resulted in the inhibition of RT-induced DNA repair and in an increase in the percentage of micronucleated cells. We validated the enhanced RT response in HPV-negative and HPV-positive xenograft models. These data demonstrate the potential use of ATR inhibition in combination with RT as a treatment option for both HPV-negative and HPV-positive HNSCC patients.

[18F]PARPi Imaging Is Not Affected by HPV Status In Vitro

Background

Human papillomavirus- (HPV-) associated oropharyngeal squamous cell carcinomas (OPSCCs) are clinically and pathologically distinct from HPV-negative tumors. Here, we explore whether HPV affects functional biomarkers, including γH2AX, RAD51, and PARP1. Moreover, the role of [18F]PARPi as a broadly applicable imaging tool for head and neck carcinomas is investigated.

Methods

HPV-positive and HPV-negative cell lines were used to evaluate the γH2AX, RAD51, and PARP1 expression with immunoblotting and immunofluorescence. Effects of external beam ionizing radiation were investigated in vitro, and survival was investigated via colony-formation assay. [18F]PARPi uptake experiments were performed on HPV-negative and HPV-positive cell lines to quantify PARP1 expression. PARP1 IHC and γH2AX foci were quantified using patient-derived oropharyngeal tumor specimens.

Results

Differences in DNA repair were detected, showing higher RAD51 and γH2AX expression in HPV-positive cell lines. Clonogenic assays confirm HPV-positive cell lines to be significantly more radiosensitive. PARP1 expression levels were similar, irrespective of HPV status. Consequently, [18F]PARPi uptake assays demonstrated that this tracer is internalized in cell lines independently from their HPV status.

Conclusion

The HPV status, often used clinically to stratify patients, did not affect PARP1 levels, suggesting that PARP imaging can be performed in both HPV-positive and HPV-negative patients. This study confirms that the PET imaging agent [18F]PARPi could serve as a general clinical tool for oropharyngeal cancer patients.

Precision Radiotherapy: Reduction in Radiation for Oropharyngeal Cancer in the 30 ROC Trial

BACKGROUND

Patients with human papillomavirus-related oropharyngeal cancers have excellent outcomes but experience clinically significant toxicities when treated with standard chemoradiotherapy (70 Gy). We hypothesized that functional imaging could identify patients who could be safely deescalated to 30 Gy of radiotherapy.

METHODS

In 19 patients, pre- and intratreatment dynamic fluorine-18-labeled fluoromisonidazole positron emission tomography (PET) was used to assess tumor hypoxia. Patients without hypoxia at baseline or intratreatment received 30 Gy; patients with persistent hypoxia received 70 Gy. Neck dissection was performed at 4 months in deescalated patients to assess pathologic response. Magnetic resonance imaging (weekly), circulating plasma cell-free DNA, RNA-sequencing, and whole-genome sequencing (WGS) were performed to identify potential molecular determinants of response. Samples from an independent prospective study were obtained to reproduce molecular findings. All statistical tests were 2-sided.

RESULTS

Fifteen of 19 patients had no hypoxia on baseline PET or resolution on intratreatment PET and were deescalated to 30 Gy. Of these 15 patients, 11 had a pathologic complete response. Two-year locoregional control and overall survival were 94.4% (95% confidence interval = 84.4% to 100%) and 94.7% (95% confidence interval = 85.2% to 100%), respectively. No acute grade 3 radiation-related toxicities were observed. Microenvironmental features on serial imaging correlated better with pathologic response than tumor burden metrics or circulating plasma cell-free DNA. A WGS-based DNA repair defect was associated with response (P = .02) and was reproduced in an independent cohort (P = .03).

CONCLUSIONS

Deescalation of radiotherapy to 30 Gy on the basis of intratreatment hypoxia imaging was feasible, safe, and associated with minimal toxicity. A DNA repair defect identified by WGS was predictive of response. Intratherapy personalization of chemoradiotherapy may facilitate marked deescalation of radiotherapy.

Interplay Between KSHV and the Host DNA Damage Response

Interactions between viruses and cellular factors are essential for viral replication or host defense. The DNA damage response (DDR) orchestrates a molecular network of cellular mechanisms that integrates cell cycle regulation and DNA repair or apoptosis. Numerous studies have revealed that the DDR is activated by virus infection, aberrant DNA structures generated by viral DNA replication, or the integration of retroviruses. Although the DDR is an essential function for maintaining the genomic integrity of cells, viruses may utilize this mechanism to build a convenient environment for themselves, and the resulting perturbation of the DDR has been shown to increase the risk of tumorigenesis. There have been many studies investigating the roles of the DDR in oncogenic viruses such as Epstein-Barr virus (EBV), human papillomavirus (HPV), hepatitis B virus (HBV), human T-cell leukemia virus type 1 (HTLV-1), and Kaposi’s sarcoma-associated herpesvirus (KSHV). This review summarizes current knowledge on the roles of DDR in the KSHV lifecycle.

De-intensification strategies in HPV-related oropharyngeal squamous cell carcinoma-a narrative review

Human papillomavirus-related (HPV+) oropharyngeal squamous cell carcinoma (OPSCC) is a relatively new clinical entity that is dramatically on the rise globally. HPV+ OPSCC is thought to be a separate clinical entity compared to HPV− OPSCC with a distinct tumor biology. Patients with HPV associated disease have been shown to have a substantially better prognosis and overall survival than those patients with the HPV negative (HPV−) counterpart. The standard of care for OPSCC is definitive radiation therapy (RT) and concurrent chemoradiation therapy (CRT), for lower and higher stage disease, respectively. However, traditional CRT is also associated with severe acute and late toxicities affecting patient quality of life, such as severe mucositis, dry mouth and dysphagia. Considering that HPV+ OPSCC is on the rise in a younger, healthier patient population and the good prognosis of HPV-related disease, there has been a focus on reducing treatment toxicities and optimizing quality of life while maintaining favorable oncologic outcomes. A variety of such de-escalation regimens are currently being explored in recently completed and ongoing clinical trials. Alterations to the standard chemotherapy, radiation and surgical regimens are being explored. This review will provide an overview of the rationale for and available results of the major de-intensification strategies in the treatment of locally advanced HPV+ OPSCC.

Biological and clinical aspects of HPV-related cancers

Cancer-related diseases represent the second overall cause of death worldwide. Human papilloma virus (HPV) is an infectious agent which is mainly sexually transmitted and may lead to HPV-associated cancers in both men and women. Almost all cervical cancers are HPV-associated, however, an increasing number of head and neck cancers (HNCs), especially oropharyngeal cancer, can be linked to HPV infection. Moreover, anogenital cancers, including vaginal, vulvar, penial, and anal cancers, represent a subset of HPV-related cancers. Whereas testing and prevention of cervical cancer have significantly improved over past decades, anogenital cancers remain more difficult to confirm. Current clinical trials including patients with HPV-related cancers focus on finding proper testing for all HPV-associated cancers as well as improve the currently applied treatments. The HPV viral oncoproteins, E6 and E7, lead to degradation of, respectively, p53 and pRb resulting in entering the S phase without G1 arrest. These high-risk HPV viral oncogenes alter numerous cellular processes, including DNA repair, angiogenesis, and/or apoptosis, which eventually result in carcinogenesis. Additionally, a comprehensive analysis of gene expression and alteration among a panel of DNA double strand breaks (DSB) repair genes in HPV-negative and HPV-positive HNC cancers reveals differences pointing to HPV-dependent modifications of DNA repair processes in these cancers. In this review, we discuss the current knowledge regarding HPV-related cancers, current screening, and treatment options as well as DNA damage response-related biological aspects of the HPV infection and clinical trials.

Role of gene signatures combined with pathology in classification of oropharynx head and neck cancer

Treatment personalisation remains an unmet need in oropharynx cancer (OPC). We aimed to determine whether gene expression signatures improved upon clinico-pathological predictors of outcome in OPC. The clinico-pathological predictors, AJCC version 7 (AJCC 7), AJCC 8, and a clinical algorithm, were assessed in 4 public series of OPC (n = 235). Literature review identified 16 mRNA gene expression signatures of radiosensitivity, HPV status, tumour hypoxia, and microsatellite instability. We quality tested signatures using a novel sigQC methodology, and added signatures to clinico-pathological variables as predictors of survival, in univariate and multivariate analyses. AJCC 7 Stage was not predictive of recurrence-free survival (RFS) or overall survival (OS). AJCC 8 significantly predicted RFS and OS. Gene signature quality was highly variable. Among HPV-positive cases, signatures for radiosensitivity, hypoxia, and microsatellite instability revealed significant underlying inter-tumour biological heterogeneity, but did not show prognostic significance when adjusted for clinical covariates. Surprisingly, among HPV-negative cases, a gene signature for HPV status was predictive of survival, even after adjustment for clinical covariates. Across the whole series, several gene signatures representing HPV and microsatellite instability remained significant in multivariate analysis. However, quality control and independent validation remain to be performed to add prognostic information above recently improved clinico-pathological variables.

An Integrated Approach for Preventing Oral Cavity and Oropharyngeal Cancers: Two Etiologies with Distinct and Shared Mechanisms of Carcinogenesis

Head and neck squamous cell carcinoma (HNSCC) was the 7th most common malignancy worldwide in 2018 and despite therapeutic advances, the overall survival rate for oral squamous cell carcinoma (OSCC; ∼50%) has remained unchanged for decades. The most common types are OSCC and oropharyngeal squamous cell carcinoma (OPSCC, survival rate ∼85%). Tobacco smoking is a major risk factor of HNSCC. In the developed world, the incidence of OSCC is declining as a result of tobacco cessation programs. However, OPSCC, which is also linked to human papillomavirus (HPV) infection, is on the rise and now ranks as the most common HPV-related cancer. The current state of knowledge indicates that HPV-associated disease differs substantially from other types of HNSCC and distinct biological differences between HPV-positive and HPV-negative HNSCC have been identified. Although risk factors have been extensively discussed in the literature, there are multiple clinically relevant questions that remain unanswered and even unexplored. Moreover, existing approaches (e.g., tobacco cessation, vaccination, and chemoprevention) to manage and control this disease remain a challenge. Thus, in this review, we discuss potential future basic research that can assist in a better understanding of disease pathogenesis which may lead to novel and more effective preventive strategies for OSCC and OPSCC.

Molecular mechanisms underlying increased radiosensitivity in human papillomavirus-associated oropharyngeal squamous cell carcinoma

Oropharyngeal squamous cell carcinoma (OPSCC) is an important type of head and neck squamous cell carcinoma (HNSCC). The traditional risk factors for OPSCC include carcinogen intake, smoking, alcohol consumption, and lifestyle. In recent years, cases of human papillomavirus (HPV)-related OPSCC have gradually increased. At present, HPV-related OPSCC in developed Western countries comprise up to 90% of all OPSCC cases, while in other developing countries, the proportion of HPV-related OPSCC cases is also gradually increasing. Compared with HPV-negative OPSCC, HPV-positive OPSCC patients have better overall survival rates and local control rates and this improved prognosis may be related to the increased radiosensitivity of HPV-positive tumors. Due to this more favorable prognosis, many downgraded treatment schemes are gradually emerging, including simple radiotherapy instead of concurrent radiotherapy or reduced radiotherapy dose. However, there is insufficient theoretical basis for such schemes. Some studies have shown that delayed repair of DNA damage after radiation, G2/M arrest, increased hypoxia, and decreased proliferation capacity are the main reasons for the increased radiosensitivity of HPV-positive tumor cells. In this review, we discuss the four principles of tumor cell damage caused by radiation, including repair, reoxygenation, redistribution, and regeneration in order to reveal the mechanism whereby HPV increases the radiosensitivity of tumor cells. An attempt was made to provide sufficient information to facilitate more individualized treatment for HPV-positive OPSCC patients, under the premise of good tumor control.

Catching HPV in the Homologous Recombination Cookie Jar

To replicate, the human papillomaviruses (HPVs) that cause anogenital and oropharyngeal malignancies must simultaneously activate DNA repair pathways and avoid the cell cycle arrest that normally accompanies DNA repair. For years it seemed that HPV oncogenes activated the homologous recombination pathway to facilitate the HPV lifecycle. However, recent developments show that, although homologous recombination gene expression and markers of pathway activation are increased, homologous recombination itself is attenuated. This review provides an overview of the diverse ways that HPV oncogenes manipulate homologous recombination and ideas on how the resulting dysregulation and inhibition offer opportunities for improved therapies and biomarkers.

Inhibition of CDK4/CDK6 Enhances Radiosensitivity of HPV Negative Head and Neck Squamous Cell Carcinomas

PURPOSE

Human papillomavirus negative (HPV-ve) head and neck squamous cell carcinoma (HNSCC) has a poor prognosis compared with HPV+ve HNSCCs. Expression of p16 in HPV+ve HNSCC is thought to mediate radiosensitivity via inhibition of cyclin-dependent kinase (CDK) 4/6. We used a clinically approved CDK4/CDK6 inhibitor, palbociclib, and assessed its effect on radiosensitivity in HNSCC.

METHODS AND MATERIALS

The effect of palbociclib on radiosensitivity was determined in HPV-ve and HPV+ve HNSCC cell lines using colony survival assays, immunofluorescent staining of repair proteins, homologous recombination assays, cell cycle, and metaphase spread analyses.

RESULTS

Only HPV-ve HNSCC cells were radiosensitized by palbociclib, which also occurred at hypoxic levels associated with radioresistance. Palbociclib led to decreased induction of BRCA1 and RAD51 after irradiation. Homologous recombination was diminished and repair of radiation-induced DNA damage was delayed in the presence of palbociclib, leading to increased chromosomal damage. Failure to repair radiation-induced damage led to cell death as a result of mitotic catastrophe.

CONCLUSIONS

Here, we highlight a therapeutic strategy to improve the radiosensitivity of HPV-ve HNSCC, a patient group that has an unmet and urgent need for improved radiation therapy efficacy.

Human papillomavirus 16 promotes microhomology-mediated end-joining

Squamous cell carcinomas (SCCs) arising from aerodigestive or anogenital epithelium that are associated with the human papillomavirus (HPV) are far more readily cured with radiation therapy than HPV-negative SCCs. The mechanism behind this increased radiosensitivity has been proposed to be secondary to defects in DNA repair, although the specific repair pathways that are disrupted have not been elucidated. To gain insight into this important biomarker of radiosensitivity, we first examined genomic patterns reflective of defects in DNA double-strand break repair, comparing HPV-associated and HPV-negative head and neck cancers (HNSCC). Compared to HPV-negative HNSCC genomes, HPV+ cases demonstrated a marked increase in the proportion of deletions with flanking microhomology, a signature associated with a backup, error-prone double-strand break repair pathway known as microhomology-mediated end-joining (MMEJ). Then, using 3 different methodologies to comprehensively profile double-strand break repair pathways in isogenic paired cell lines, we demonstrate that the HPV16 E7 oncoprotein suppresses canonical nonhomologous end-joining (NHEJ) and promotes error-prone MMEJ, providing a mechanistic rationale for the clinical radiosensitivity of these cancers.

Radiosensitization approaches for HPV-positive and HPV-negative head and neck squamous carcinomas

Radiotherapy is one of the most used treatment approaches for head and neck squamous cell carcinoma (HNSCC). Targeted inhibition of DNA repair machinery has the potential to improve treatment response by tailoring treatment to cancer cells lacking specific DNA repair pathways. Human papillomavirus (HPV)‐negative and HPV‐positive HNSCCs respond differently to radiotherapy treatment, suggesting that different approaches of DNA repair inhibition should be employed for these HNSCC groups. Here, we searched for optimal radiosensitization approaches for HPV‐positive and HPV‐negative HNSCCs by performing a targeted CRISPR‐Cas9 screen. We found that inhibition of base excision repair resulted in a better radiotherapy response in HPV‐positive HNSCC, which is correlated with upregulation of genes involved in base excision repair. In contrast, inhibition of nonhomologous end‐joining and mismatch repair showed strong effects in both HNSCC groups. We validated the screen results by combining radiotherapy with targeted inhibition of DNA repair in several preclinical models including primary and recurrent patient‐derived HNSCC xenografts. These findings underline the importance of stratifying HNSCC patients for combination treatments.

What's new?

The combination of radiotherapy and targeted inhibition of DNA repair pathways can potentially improve therapeutic response in patients with head and neck squamous cell carcinoma (HNSCC). Here, a targeted CRISPR‐Cas9 screen was used to identify optimal radiosensitization approaches for human papillomavirus (HPV)‐positive and HPV‐negative HNSCC. Inhibition of base excision repair was associated with improved radiotherapy response in HPV‐positive HNSCC cells. By comparison, inhibition of non‐homologous end‐joining and mismatch repair was effective in both HPV‐positive and HPV‐negative cells. The screen results were validated in patient‐derived xenograft models, suggesting that stratification of HNSCC patients by HPV status may benefit therapeutic outcome.

The Antiviral Agent Cidofovir Induces DNA Damage and Mitotic Catastrophe in HPV-Positive and -Negative Head and Neck Squamous Cell Carcinomas In Vitro

Cidofovir (CDV) is an antiviral agent with antiproliferative properties. The aim of our study was to investigate the efficacy of CDV in HPV-positive and -negative head and neck squamous cell carcinoma (HNSCC) cell lines and whether it is caused by a difference in response to DNA damage. Upon CDV treatment of HNSCC and normal oral keratinocyte cell lines, we carried out MTT analysis (cell viability), flow cytometry (cell cycle analysis), (immuno) fluorescence and western blotting (DNA double strand breaks, DNA damage response, apoptosis and mitotic catastrophe). The growth of the cell lines was inhibited by CDV treatment and resulted in γ-H2AX accumulation and upregulation of DNA repair proteins. CDV did not activate apoptosis but induced S- and G2/M phase arrest. Phospho-Aurora Kinase immunostaining showed a decrease in the amount of mitoses but an increase in aberrant mitoses suggesting mitotic catastrophe. In conclusion, CDV inhibits cell growth in HPV-positive and -negative HNSCC cell lines and was more profound in the HPV-positive cell lines. CDV treated cells show accumulation of DNA DSBs and DNA damage response activation, but apoptosis does not seem to occur. Rather our data indicate the occurrence of mitotic catastrophe.

Phase II Evaluation of Aggressive Dose De-Escalation for Adjuvant Chemoradiotherapy in Human Papillomavirus-Associated Oropharynx Squamous Cell Carcinoma

PURPOSE

The purpose of this study was to determine if dose de-escalation from 60 to 66 Gy to 30 to 36 Gy of adjuvant radiotherapy (RT) for selected patients with human papillomavirus-associated oropharyngeal squamous cell carcinoma could maintain historical rates for disease control while reducing toxicity and preserving swallow function and quality of life (QOL).

PATIENTS AND METHODS

MC1273 was a single-arm phase II trial testing an aggressive course of RT de-escalation after surgery. Eligibility criteria included patients with p16-positive oropharyngeal squamous cell carcinoma, smoking history of 10 pack-years or less, and negative margins. Cohort A (intermediate risk) received 30 Gy delivered in 1.5-Gy fractions twice per day over 2 weeks along with 15 mg/m² docetaxel once per week. Cohort B included patients with extranodal extension who received the same treatment plus a simultaneous integrated boost to nodal levels with extranodal extension to 36 Gy in 1.8-Gy fractions twice per day. The primary end point was locoregional tumor control at 2 years. Secondary end points included 2-year progression-free survival, overall survival, toxicity, swallow function, and patient-reported QOL.

RESULTS

Accrual was from September 2013 to June 2016 (N = 80; cohort A, n = 37; cohort B, n = 43). Median follow-up was 36 months, with a minimum follow-up of 25 months. The 2-year locoregional tumor control rate was 96.2%, with progression-free survival of 91.1% and overall survival of 98.7%. Rates of grade 3 or worse toxicity at pre-RT and 1 and 2 years post-RT were 2.5%, 0%, and 0%. Swallowing function improved slightly between pre-RT and 12 months post-RT, with one patient requiring temporary feeding tube placement.

CONCLUSION

Aggressive RT de-escalation resulted in locoregional tumor control rates comparable to historical controls, low toxicity, and little decrement in swallowing function or QOL.

HPV, hypoxia and radiation response in head and neck cancer

Over the last decades, the incidence of human papilloma virus (HPV) positive head and neck squamous-cell carcinoma (HNSCC) has significantly increased. Infection with high-risk HPV types drives tumourigenesis through expression of the oncoproteins E6 and E7. Currently, the primary treatment of HNSCC consists of radiotherapy, often combined with platinum-based chemotherapeutics. One of the common features of HNSCC is the occurrence of tumour hypoxia, which impairs the efficacy of radiotherapy and is a negative prognostic factor. Therefore, it is important to detect and quantify the severity of hypoxia, as well as develop strategies to specifically target hypoxic tumours. HPV-positive tumours are remarkably radiosensitive compared to HPV-negative tumours and consequently the HPV-positive patients have a better prognosis. This provides an opportunity to elucidate mechanisms of radiation sensitivity, which may reveal targets for improved therapy for HPV-negative head and neck cancers. In this review, we will discuss the differences between HPV-positive and HPV-negative head and neck tumours and methods of hypoxia detection and targeting in these disease types. Particular emphasis will be placed on the mechanisms by which HPV infection impacts radiosensitivity.

Human papillomavirus type 16 E6 and E7 oncoproteins interact with the nuclear p53-binding protein 1 in an in vitro reconstructed 3D epithelium: new insights for the virus-induced DNA damage response

Background

Despite vaccination and screening measures, anogenital cancer, mainly promoted by HPV16 oncoproteins, still represents the fourth tumor and the second cause of death among women.

Cell replication fidelity is the result of the host DNA damage response (DDR). Unlike many DNA viruses that promote their life cycle through the DDR inactivation, HR-HPVs encourage cells proliferation despite the DDR turned on. Why and how it occurs has been only partially elucidated.

During HPV16 infection, E6 links and degrades p53 via the binding to the E6AP LXXLL sequence; unfortunately, E6 direct role in the DDR response has not clearly identified yet.

Similarly, E7 increases DDR by competing with E2F1-pRb interaction, thus leading to the inactivation of pRb, and promotion, E2F1 mediated, of DDR genes translation, by binding to the pRb-like proteins CBP/p300 and p107, that also harbour LXXLL sequence, and via the interaction and activation of several DDR proteins.

Methods

To gain information regarding E6 and E7 contribution in DDR activation, we produced an in vitro 3D HPV16-E6E7 infected epithelium, already consolidated study model for HPVs, and validated it by assessing H&E staining and BrdU, HPV16 DNA, E6E7 proteins and γH2A.X/53BP1 double-strand break (DSBs) sensors expression; then we made an immuno-colocalization of E6 and E7 with cyclin E2 and B1.

Since 53BP1, like E6 and E7, also binds p53 and pRb, we supposed their possible direct binding. To explore this hypothesis, we performed a double immunofluorescence of E6 and E7 with 53BP1, a sequence analysis of 53BP1 within its BRCT2 domain and then an in situ PLA within CaSki, E6E7HPV16 NHEKs and the 3D model.

Results

The in vitro epithelium resembled the histology and the events typical of in vivo infected tissues. E6E7HPV16 were both expressed in basal and differentiated strata and induced H2A.X phosphorylation and 53BP1 increment into nuclear foci.

After highlighting E6 and E7 co-expression with 53BP1 and a LKVLL sequence within the 53BP1 BRCT2 domain, we demonstrated the bindings via the PLA technique.

Conclusions

Our results reinforce E6 and E7 role in cellular function control providing potentially new insights into the activity of this tumor virus.

Human papillomavirus and genome instability: from productive infection to cancer

Infection with high oncogenic risk human papillomavirus types is the etiological factor of cervical cancer and a major cause of other epithelial malignancies, including vulvar, vaginal, anal, penile and head and neck carcinomas. These agents affect epithelial homeostasis through the expression of specific proteins that deregulate important cellular signaling pathways to achieve efficient viral replication. Among the major targets of viral proteins are components of the DNA damage detection and repair machinery. The activation of many of these cellular factors is critical to process viral genome replication intermediates and, consequently, to sustain faithful viral progeny production. In addition to the important role of cellular DNA repair machinery in the infective human papillomavirus cycle, alterations in the expression and activity of many of its components are observed in human papillomavirus-related tumors. Several studies from different laboratories have reported the impact of the expression of human papillomavirus oncogenes, mainly E6 and E7, on proteins in almost all the main cellular DNA repair mechanisms. This has direct consequences on cellular transformation since it causes the accumulation of point mutations, insertions and deletions of short nucleotide stretches, as well as numerical and structural chromosomal alterations characteristic of tumor cells. On the other hand, it is clear that human papillomavirus-transformed cells depend on the preservation of a basal cellular DNA repair activity level to maintain tumor cell viability. In this review, we summarize the data concerning the effect of human papillomavirus infection on DNA repair mechanisms. In addition, we discuss the potential of exploiting human papillomavirus-transformed cell dependency on DNA repair pathways as effective antitumoral therapies.

Dose-Modifying Factor of Radiation Therapy with Concurrent Cisplatin Treatment in HPV-Positive Squamous Cell Carcinoma: A Preclinical Study

Human papillomavirus (HPV) is an important etiological factor in oropharyngeal squamous cell carcinoma (SCC). Compared to HPV-negative tumors, HPV-positive oropharyngeal SCC has shown a better response to nonsurgical treatments. In this study, we determined the dose-modifying factors for HPV-positive tumors with single-dose irradiation, with or without low radiosensitizing doses of cisplatin. In vitro, we determined an increased radiosensitivity of HPV-positive SCC, which might be a consequence of HPV-induced changes in the cell cycle regulation and DNA damage response, leading to increased cell death. Additionally, compared to HPV-negative tumors, 30% higher radiosensitivity of HPV-positive tumors was determined by tumor growth delay monitoring in immunodeficient mice in vivo. Concurrent cisplatin treatment had an additive effect in both HPV-negative and HPV-positive tumors, resulting in 20% better response in HPV-positive tumors than in HPV-negative tumors.

Novel insights into epigenetic drivers of oropharyngeal squamous cell carcinoma: role of HPV and lifestyle factors

In the last years, the explosion of high throughput sequencing technologies has enabled epigenome-wide analyses, allowing a more comprehensive overview of the oropharyngeal squamous cell carcinoma (OPSCC) epigenetic landscape. In this setting, the cellular pathways contributing to the neoplastic phenotype, including cell cycle regulation, cell signaling, DNA repair, and apoptosis have been demonstrated to be potential targets of epigenetic alterations in OPSCC. Of note, it has becoming increasingly clear that HPV infection and OPSCC lifestyle risk factors differently drive the epigenetic machinery in cancer cells. Epigenetic changes, including DNA methylation, histone modifications, and non-coding RNA expression, can be used as powerful and reliable tools for early diagnosis of OPSCC patients and improve prognostication. Since epigenetic changes are dynamic and reversible, epigenetic enzymes may also represent suitable targets for the development of more effective OPSCC therapeutic strategies. Thus, this review will focus on the main known epigenetic modifications that can occur in OPSCC and their exploitation as potential biomarkers and therapeutic targets. Furthermore, we will address epigenetic alterations to OPSCC risk factors, with a particular focus on HPV infection, tobacco exposure, and heavy alcohol consumption.

The interplay of UV and cutaneous papillomavirus infection in skin cancer development

Cutaneous human papillomaviruses (HPVs) are considered as cofactors for non-melanoma skin cancer (NMSC) development, especially in association with UVB. Extensively studied transgenic mouse models failed to mimic all aspects of virus-host interactions starting from primary infection to the appearance of a tumor. Using the natural model Mastomys coucha, which reflects the human situation in many aspects, we provide the first evidence that only UVB and Mastomys natalensis papillomavirus (MnPV) infection strongly promote NMSC formation. Using UVB exposures that correspond to UV indices of different geographical regions, irradiated animals developed either well-differentiated keratinizing squamous cell carcinomas (SCCs), still supporting productive infections with high viral loads and transcriptional activity, or poorly differentiated non-keratinizing SCCs almost lacking MnPV DNA and in turn, early and late viral transcription. Intriguingly, animals with the latter phenotype, however, still showed strong seropositivity, clearly verifying a preceding MnPV infection. Of note, the mere presence of MnPV could induce γH2AX foci, indicating that viral infection without prior UVB exposure can already perturb genome stability of the host cell. Moreover, as shown both under in vitro and in vivo conditions, MnPV E6/E7 expression also attenuates the excision repair of cyclobutane pyrimidine dimers upon UVB irradiation, suggesting a viral impact on the DNA damage response. While mutations of Ras family members (e.g. Hras, Kras, and Nras) were absent, the majority of SCCs harbored-like in humans-Trp53 mutations especially at two hot-spots in the DNA-binding domain, resulting in a loss of function that favored tumor dedifferentiation, counter-selective for viral maintenance. Such a constellation provides a reasonable explanation for making continuous viral presence dispensable during skin carcinogenesis as observed in patients with NMSC.