Overcoming the Impact of Hypoxia in Driving Radiotherapy Resistance in Head and Neck Squamous Cell Carcinoma

Phytochemicals and their Nanoformulations for Overcoming Drug Resistance in Head and Neck Squamous Cell Carcinoma

BACKGROUND

Drug resistance remains a significant challenge in the treatment of head and neck squamous cell carcinoma (HNSCC), leading to therapeutic failure and poor patient prognosis. Numerous mechanisms, including drug efflux pumps, altered tumor microenvironment (TME), and dysregulated cell death pathways, contribute to the development of resistance against conventional chemotherapeutic agents, immunotherapy, and targeted therapies. As resistance to traditional treatments continues to emerge, there is an urgent need for innovative therapeutic strategies to overcome these challenges. Phytochemicals are naturally occurring bioactive compounds and have demonstrated remarkable potential in targeting multiple resistance mechanisms simultaneously.

METHOD

This review comprehensively overviews the current understanding of drug resistance mechanisms in HNSCC and explores innovative strategies utilizing phytochemicals and their nanoformulations to overcome these resistance mechanisms, with a particular focus on recent developments and future perspectives in this field.

RESULTS AND DISCUSSION

Phytochemicals with anticancer properties include a wide range of herbal-derived molecules such as flavonoids, stilbenes, curcuminoids, alkaloids, traditional Chinese medicine, and others. These compounds can modulate ATP-binding cassette transporters, reverse epithelial-to-mesenchymal transition (EMT), target cancer stem cells (CSCs), and regulate various signaling pathways involved in drug resistance. The integration of phytochemicals into advanced nanoformulation systems has also shown a remarkable improvement in enhancing their bioavailability, stability, and targeted delivery to the TME, potentially improving their therapeutic efficacy. Furthermore, the combination of phytochemicals with conventional chemotherapeutic agents, targeted molecular therapy, and immune checkpoint inhibitors (ICIs) has exhibited synergistic effects, offering a promising approach to restoring drug sensitivity in resistant HNSCC cells.

CONCLUSION

Phytochemicals and their nanoformulations may improve response of HNSCC to therapy by alleviating drug resistance.

Differential cell architecture and microenvironmental responses of pretumoral and tumoral cellular models exposed to coverslip-induced hypoxia

The tumor microenvironment is an altered milieu that imposes multiple selective pressures leading to the survival and dissemination of aggressive and fit tumor cell subpopulations. How pre-tumoral and tumoral cells respond to changes in their microenvironment will determine the subsequent evolution of the tumor. In this study, we have subjected pre-tumoral and tumoral cells to coverslip-induced hypoxia, which recapitulates the intracellular hypoxia and extracellular acidification characteristic of the early tumor microenvironment, and we have used a combination of quantitative phase microscopy and epifluorescence to analyze diverse cellular responses to this altered environment. In normoxia, tumor cells showed differences in nuclear organization, as evidenced by decreased numbers of HP1 foci, and in hypoxia major changes in nuclear architecture were observed, with tumor cells significantly increasing the number of high dry mass density foci in the nucleus compared to pre-tumoral and non-tumoral cells. Conversely, compared to pre-tumoral and normal cells, mitochondrial ATP levels decayed markedly in tumor cells in hypoxia, whereas the activation of executioner caspases increased only in tumor cells in this condition. Therefore, in terms of cellular organization, metabolic changes and activation of cell death processes, tumor cells showed more dramatic responses to an altered microenvironment than their pre-tumoral and normal counterparts, responses which in turn could play fundamental roles in shaping future tumor development.

HDAC Inhibitors Can Enhance Radiosensitivity of Head and Neck Cancer Cells Through Suppressing DNA Repair

Background/Objectives: The incidence of head and neck squamous cell carcinoma (HNSCC), currently ~800,000 cases per year worldwide, is rising. Radiotherapy remains a mainstay for the treatment of HNSCC, although inherent radioresistance, particularly in human papillomavirus (HPV)-negative disease subtypes, remains a significant barrier to effective treatment. Therefore, combinatorial strategies using drugs or inhibitors against specific cellular targets are necessary to enhance HNSCC radiosensitivity to lead to an improvement in patient outcomes. Given that radiotherapy acts through targeting and damaging DNA, a common strategy is to focus on enzymes within DNA-dependent cellular pathways, such as DNA damage repair. Methods: Here, we have employed a 3D spheroid model of HNSCC (FaDu) in combination with a targeted drug screen to identify novel radiosensitisers that suppress tumour growth. Results: We identified that histone deacetylases (HDACs) were prominent candidates, and subsequently identified that the HDAC inhibitors mocetinostat and pracinostat, as well as the combined HDAC-epidermal growth factor receptor inhibitor CUDC-101, were effective at radiosensitising cell models of HNSCC (FaDu, A253, UMSCC11b) through their impact on both spheroid growth and clonogenic survival assays. We also demonstrated that this combinatorial strategy leads to inhibition of the repair of DNA double-strand breaks through the neutral comet assay and γH2AX foci analysis using immunofluorescence microscopy, providing a mechanism of action through which HDAC inhibition functions in HNSCC radiosensitisation. Conclusions: We believe that this approach should be further investigated in preclinical models, in order to realise the full therapeutic potential of HDAC inhibition for the radiosensitisation of HNSCC, eventually leading to improved patient treatment efficacy and outcomes.

Transcriptomic and epigenetic landscape of nimorazole-enhanced radiochemotherapy in head and neck cancer

BACKGROUND

Hypoxia remains a challenge for the therapeutic management of head and neck squamous cell carcinoma (HNSCC). The combination of radiotherapy with nimorazole has shown treatment benefit in HNSCC, but the precise underlying molecular mechanisms remain unclear.

PURPOSE

To assess and to characterize the transcriptomic/epigenetic landscape of HNSCC tumor models showing differential therapeutic response to fractionated radiochemotherapy (RCTx) combined with nimorazole.

MATERIALS/METHODS

Bulk RNA-sequencing and DNA methylation experiments were conducted using untreated and treated HNSCC xenografts after 10 fractions of RCTx with and without nimorazole. These tumor models (FaDu, SAS, Cal33, SAT and UT-SCC-45) previously showed a heterogeneous response to RCTx with nimorazole. The prognostic impact of candidate genes was assessed using clinical and gene expression data from HNSCC patients treated with primary RCTx within the DKTK-ROG.

RESULTS

Nimorazole responder and non-responder tumor models showed no differences in hypoxia gene signatures However, non-responder models showed upregulation of metabolic pathways. From that, a subset of 15 differentially expressed genes stratified HNSCC patients into low and high-risk groups with distinct outcome.

CONCLUSION

In the present study, we found that nimorazole non-responder models were characterized by upregulation of genes involved in Retinol metabolism and xenobiotic metabolic process pathways, which might contribute to identify mechanisms of resistance to nitroimidazole compounds and potentially expand the repertoire of therapeutic options to treat HNSCC.

Digital Spatial Profiling identifies distinct patterns of immuno-oncology-related gene expression within oropharyngeal tumours in relation to HPV and p16 status

Background

The incidence of oropharyngeal cancer (OPC) is increasing, due mainly to a rise in Human Papilloma Virus (HPV)-mediated disease. HPV-mediated OPC has significantly better prognosis compared with HPV-negative OPC, stimulating interest in treatment de-intensification approaches to reduce long-term sequelae. Routine clinical testing frequently utilises immunohistochemistry to detect upregulation of p16 as a surrogate marker of HPV-mediation. However, this does not detect discordant p16-/HPV+ cases and incorrectly assigns p16+/HPV- cases, which, given their inferior prognosis compared to p16+/HPV+, may have important clinical implications. The biology underlying poorer prognosis of p16/HPV discordant OPC requires exploration.

Methods

GeoMx digital spatial profiling was used to compare the expression patterns of selected immuno-oncology-related genes/gene families (n=73) within the tumour and stromal compartments of formalin-fixed, paraffin-embedded OPC tumour tissues (n=12) representing the three subgroups, p16+/HPV+, p16+/HPV- and p16-/HPV-.

Results

Keratin (multi KRT) and HIF1A, a key regulator of hypoxia adaptation, were upregulated in both p16+/HPV- and p16-/HPV- tumours relative to p16+/HPV+. Several genes associated with tumour cell proliferation and survival (CCND1, AKT1 and CD44) were more highly expressed in p16-/HPV- tumours relative to p16+/HPV+. Conversely, multiple genes with potential roles in anti-tumour immune responses (immune cell recruitment/trafficking, antigen processing and presentation), such as CXCL9, CXCL10, ITGB2, PSMB10, CD74, HLA-DRB and B2M, were more highly expressed in the tumour and stromal compartments of p16+/HPV+ OPC versus p16-/HPV- and p16+/HPV-. CXCL9 was the only gene showing significant differential expression between p16+/HPV- and p16-/HPV- tumours being upregulated within the stromal compartment of the former.

Conclusions

In terms of immune-oncology-related gene expression, discordant p16+/HPV- OPCs are much more closely aligned with p16-/HPV-OPCs and quite distinct from p16+/HPV+ tumours. This is consistent with previously described prognostic patterns (p16+/HPV+ >> p16+/HPV- > p16-/HPV-) and underlines the need for dual p16 and HPV testing to guide clinical decision making.

Establishment of a prognostic model for hypoxia-associated genes in OPSCC and revelation of intercellular crosstalk

Hypoxia exerts a profound influence on the tumor microenvironment and immune response, shaping treatment outcomes and prognosis. Utilizing consistency clustering, we discerned two hypoxia subtypes in OPSCC bulk sequencing data from GEO. Key modules within OPSCC were identified through weighted gene correlation network analysis (WGCNA). Core modules underwent CIBERSORT immune infiltration analysis and GSEA functional enrichment. Univariate Cox and LASSO analyses were employed to construct prognostic models for seven hypoxia-related genes. Further investigation into clinical characteristics, the immune microenvironment, and TIDE algorithm prediction for immunotherapy response was conducted in high- and low-risk groups. scRNA-seq data were visually represented through TSNE clustering, employing the scissors algorithm to map hypoxia phenotypes. Interactions among cellular subpopulations were explored using the Cellchat package, with additional assessments of metabolic and transcriptional activities. Integration with clinical data unveiled a prevalence of HPV-positive patients in the low hypoxia and low-risk groups. Immunohistochemical validation demonstrated low TDO2 expression in HPV-positive (P16-positive) patients. Our prediction suggested that HPV16 E7 promotes HIF-1α inhibition, leading to reduced glycolytic activity, ultimately contributing to better prognosis and treatment sensitivity. The scissors algorithm effectively segregated epithelial cells and fibroblasts into distinct clusters based on hypoxia characteristics. Cellular communication analysis illuminated significant crosstalk among hypoxia-associated epithelial, fibroblast, and endothelial cells, potentially fostering tumor proliferation and metastasis.

Autophagy is the main driver of radioresistance of HNSCC cells in mild hypoxia

Hypoxia poses a significant challenge to the effectiveness of radiotherapy in head and neck squamous cell carcinoma (HNSCC) patients, and it is imperative to discover novel approaches to overcome this. In this study, we investigated the underlying mechanisms contributing to x-ray radioresistance in HPV-negative HNSCC cells under mild hypoxic conditions (1% oxygen) and explored the potential for autophagy modulation as a promising therapeutic strategy. Our findings show that HNSCC cells exposed to mild hypoxic conditions exhibit increased radioresistance, which is largely mediated by the hypoxia-inducible factor (HIF) pathway. We demonstrate that siRNA knockdown of HIF-1α and HIF-1β leads to increased radiosensitivity in HNSCC cells under hypoxia. Hypoxia-induced radioresistance was not attributed to differences in DNA double strand break repair kinetics, as these remain largely unchanged under normoxic and hypoxic conditions. Rather, we identify autophagy as a critical protective mechanism in HNSCC cells following irradiation under mild hypoxia conditions. Targeting key autophagy genes, such as BECLIN1 and BNIP3/3L, using siRNA sensitizes these cells to irradiation. Whilst autophagy's role in hypoxic radioresistance remains controversial, this study highlights the importance of autophagy modulation as a potential therapeutic approach to enhance the effectiveness of radiotherapy in HNSCC.

Enhanced perfusion following exposure to radiotherapy: A theoretical investigation

Tumour angiogenesis leads to the formation of blood vessels that are structurally and spatially heterogeneous. Poor blood perfusion, in conjunction with increased hypoxia and oxygen heterogeneity, impairs a tumour's response to radiotherapy. The optimal strategy for enhancing tumour perfusion remains unclear, preventing its regular deployment in combination therapies. In this work, we first identify vascular architectural features that correlate with enhanced perfusion following radiotherapy, using in vivo imaging data from vascular tumours. Then, we present a novel computational model to determine the relationship between these architectural features and blood perfusion in silico. If perfusion is defined to be the proportion of vessels that support blood flow, we find that vascular networks with small mean diameters and large numbers of angiogenic sprouts show the largest increases in perfusion post-irradiation for both biological and synthetic tumours. We also identify cases where perfusion increases due to the pruning of hypoperfused vessels, rather than blood being rerouted. These results indicate the importance of considering network composition when determining the optimal irradiation strategy. In the future, we aim to use our findings to identify tumours that are good candidates for perfusion enhancement and to improve the efficacy of combination therapies.

Enhancing radiotherapy outcomes in rectal cancer: A systematic review of targeting hypoxia-induced radioresistance

Introduction

Neoadjuvant radiotherapy is successfully used in rectal cancer to improve overall survival. However, treatment response is both unpredictable and variable. There is strong evidence to show that the phenomenon of tumour hypoxia is associated with radioresistance, however the mechanism(s) behind this are poorly understood. Consequently, there have only been a small number of studies evaluating methods targeting hypoxia-induced radioresistance. The purpose of this systematic review is to evaluate the potential effectiveness of targeting hypoxia-induced radioresistance in rectal cancer and provide recommendations for future research in this area.

Methods

A comprehensive literature search was performed following the PRISMA guidelines. This study was registered on the Prospero database (CRD42023441983).

Results

Eight articles met the inclusion criteria. All studies identified were in vitro or in vivo studies, there were no clinical trials. Of the 8 studies identified, 5 assessed the efficacy of drugs which directly or indirectly targeted hypoxia and three that identified potential targets. There was conflicting in vivo evidence for the use of metformin to overcome hypoxia induced radioresistance. Vorinostat, atovaquone, and evofosfamide showed promising preclinical evidence that they can overcome hypoxia-induced radioresistance.

Discussion

The importance of investigating hypoxia-induced radioresistance in rectal cancer is crucial. However, to date, only a small number of preclinical studies exist evaluating this phenomenon. This systematic review highlights the importance of further research to fully understand the mechanism behind this radioresistance. There are promising targets identified in this systematic review however, substantially more pre-clinical and clinical research as a priority for future research is needed.

The role of autophagy in hypoxia-induced radioresistance

Radiotherapy is a widely used treatment modality against cancer, and although survival rates are increasing, radioresistant properties of tumours remain a significant barrier for curative treatment. Tumour hypoxia is one of the main contributors to radioresistance and is common in most solid tumours. Hypoxia is responsible for many molecular changes within the cell which helps tumours to survive under such challenging conditions. These hypoxia-induced molecular changes are predominantly coordinated by the hypoxia inducible factor (HIF) and have been linked with the ability to confer resistance to radiation-induced cell death. To overcome this obstacle research has been directed towards autophagy, a cellular process involved in self degradation and recycling of macromolecules, as HIF plays a large role in its coordination under hypoxic conditions. The role that autophagy has following radiotherapy treatment is conflicted with evidence of both cytoprotective and cytotoxic effects. This literature review aims to explore the intricate relationship between radiotherapy, hypoxia, and autophagy in the context of cancer treatment. It provides valuable insights into the potential of targeting autophagy as a therapeutic strategy to improve the response of hypoxic tumours to radiotherapy.

Role of Microenvironmental Components in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell cancer (HNSCC) is one of the ten most common malignant neoplasms, characterized by an aggressive course, high recurrence rate, poor response to treatment, and low survival rate. This creates the need for a deeper understanding of the mechanisms of the pathogenesis of this cancer. The tumor microenvironment (TME) of HNSCC consists of stromal and immune cells, blood and lymphatic vessels, and extracellular matrix. It is known that HNSCC is characterized by complex relationships between cancer cells and TME components. TME components and their dynamic interactions with cancer cells enhance tumor adaptation to the environment, which provides the highly aggressive potential of HNSCC and resistance to antitumor therapy. Basic research aimed at studying the role of TME components in HNSCC carcinogenesis may serve as a key to the discovery of both new biomarkers-predictors of prognosis and targets for new antitumor drugs. This review article focuses on the role and interaction with cancer of TME components such as newly formed vessels, cancer-associated fibroblasts, and extracellular matrix.

Remodeling the tumor microenvironment to overcome treatment resistance in HPV-negative head and neck cancer

Despite intensive efforts and refined techniques, overall survival in HPV-negative head and neck cancer remains poor. Robust immune priming is required to elicit a strong and durable antitumor immune response in immunologically cold and excluded tumors like HPV-negative head and neck cancer. This review highlights how the tumor microenvironment could be affected by different immune and stromal cell types, weighs the need to integrate metabolic regulation of the tumor microenvironment into cancer treatment strategies and summarizes the emerging clinical applicability of personalized immunotherapeutic strategies in HPV-negative head and neck cancer.