Identification and chemoresistance of cancer stem cells in HPV-negative oropharyngeal cancer

Targeting cancer stem cells as a strategy for reducing chemotherapy resistance in head and neck cancers

PURPOSE

Resistance to chemotherapy and radiotherapy is the primary cause of a poor prognosis in oncological patients. Researchers identified many possible mechanisms involved in gaining a therapy-resistant phenotype by cancer cells, including alterations in intracellular drug accumulation, detoxification, and enhanced DNA damage repair. All these features are characteristic of stem cells, making them the major culprit of chemoresistance. This paper reviews the most recent evidence regarding the association between the stemness phenotype and chemoresistance in head and neck cancers. It also investigates the impact of pharmacologically targeting cancer stem cell populations in this subset of malignancies.

METHODS

This narrative review was prepared based on the search of the PubMed database for relevant papers.

RESULTS

Head and neck cancer cells belonging to the stem cell population are distinguished by the high expression of certain surface proteins (e.g., CD10, CD44, CD133), pluripotency-related transcription factors (SOX2, OCT4, NANOG), and increased activity of aldehyde dehydrogenase (ALDH). Chemotherapy itself increases the percentage of stem-like cells. Importantly, the intratumor heterogeneity of stem cell subpopulations reflects cell plasticity which has great importance for chemoresistance induction.

CONCLUSIONS

Evidence points to the advantage of combining classical chemotherapeutics with stemness modulators thanks to the joint targeting of the bulk of proliferating tumor cells and chemoresistant cancer stem cells, which could cause recurrence.

Preclinical trial comparing radiotherapy alone versus standard radiochemotherapy in three human papilloma virus (HPV) negative and three HPV-positive head and neck squamous cell carcinoma (HNSCC) xenograft tumour models

PURPOSE

To perform a preclinical trial comparing the efficacy of fractionated radiotherapy versus radiochemotherapy with cisplatin in HPV-positive and negative human head and neck squamous cell carcinoma (HNSCC) xenografts.

MATERIAL AND METHODS

Three HPV-negative and three HPV-positive HNSCC xenografts in nude mice were randomized to radiotherapy (RT) alone or to radiochemotherapy (RCT) with weekly cisplatin. To evaluate tumour growth time, 20 Gy radiotherapy (±cisplatin) were administered in 10 fractions over 2 weeks. Dose-response curves for local tumour control were generated for RT with 30 fractions over 6 weeks to different dose levels given alone or combined with cisplatin (RCT).

RESULTS

One of three investigated HPV-negative and two out of three HPV-positive tumour models showed a significant increase in local tumour control after RCT compared to RT alone. Pooled analysis of the HPV-positive tumour models showed a statistically significant and substantial benefit of RCT versus RT alone, with an enhancement ratio of 1.34. Although heterogeneity in response to both RT and RCT was also observed between the different HPV-positive HNSCC, these overall were more RT and RCT sensitive than HPV-negative models.

CONCLUSION

The impact of adding chemotherapy to fractionated radiotherapy on local control was heterogenous, both in HPV-negative and in HPV-positive tumours, calling for predictive biomarkers. RCT substantially increased local tumour control in the pooled group of all HPV-positive tumours whereas this was not found in HPV-negative tumours. Omission of chemotherapy in HPV-positive HNSCC as part of a treatment de-escalation strategy is not supported by this preclinical trial.

Cancer Stem Cells in Oropharyngeal Cancer

Oropharyngeal cancer (OPC), which is a common type of head and neck squamous cell carcinoma (HNSCC), is associated with tobacco and alcohol use, and human papillomavirus (HPV) infection. Underlying mechanisms and as a result prognosis of the HPV-positive and HPV-negative OPC patients are different. Like stem cells, the ability of self-renewal and differentiate, cancer stem cells (CSCs) have roles in tumor invasion, metastasis, drug resistance, and recurrence after therapy. Research revealed their roles to some extent in all of these processes but there are still many unresolved points to connect to CSC-targeted therapy. In this review, we will focus on what we currently know about CSCs of OPC and limitations of our current knowledge. We will present perspectives that will broaden our understanding and recent literature which may connect to therapy.

Tumor microenvironment: an evil nexus promoting aggressive head and neck squamous cell carcinoma and avenue for targeted therapy

Head and neck squamous cell carcinoma (HNSCC) is a very aggressive disease with a poor prognosis for advanced-stage tumors. Recent clinical, genomic, and cellular studies have revealed the highly heterogeneous and immunosuppressive nature of HNSCC. Despite significant advances in multimodal therapeutic interventions, failure to cure and recurrence are common and account for most deaths. It is becoming increasingly apparent that tumor microenvironment (TME) plays a critical role in HNSCC tumorigenesis, promotes the evolution of aggressive tumors and resistance to therapy, and thereby adversely affects the prognosis. A complete understanding of the TME factors, together with the highly complex tumor-stromal interactions, can lead to new therapeutic interventions in HNSCC. Interestingly, different molecular and immune landscapes between HPV^+ve and HPV^-ve (human papillomavirus) HNSCC tumors offer new opportunities for developing individualized, targeted chemoimmunotherapy (CIT) regimen. This review highlights the current understanding of the complexity between HPV^+ve and HPV^-ve HNSCC TME and various tumor-stromal cross-talk modulating processes, including epithelial-mesenchymal transition (EMT), anoikis resistance, angiogenesis, immune surveillance, metastatic niche, therapeutic resistance, and development of an aggressive tumor phenotype. Furthermore, we summarize the recent developments and the rationale behind CIT strategies and their clinical applications in HPV^+ve and HPV^-ve HNSCC.

HPV+ve/-ve oral-tongue cancer stem cells: A potential target for relapse-free therapy

The tongue squamous cell carcinoma (TSCC) is a highly prevalent head and neck cancer often associated with tobacco and/or alcohol abuse or high-risk human papillomavirus (HR-HPV) infection. HPV positive TSCCs present a unique mechanism of tumorigenesis as compared to tobacco and alcohol-induced TSCCs and show a better prognosis when treated. The poor prognosis and/or recurrence of TSCC is due to presence of a small subpopulation of tumor-initiating tongue cancer stem cells (TCSCs) that are intrinsically resistant to conventional chemoradio-therapies enabling cancer to relapse. Therefore, targeting TCSCs may provide efficient therapeutic strategy for relapse-free survival of TSCC patients. Indeed, the development of new TCSC targeting therapeutic approaches for the successful elimination of HPV+ve/-ve TCSCs could be achieved either by targeting the self-renewal pathways, epithelial mesenchymal transition, vascular niche, nanoparticles-based therapy, induction of differentiation, chemoradio-sensitization of TCSCs or TCSC-derived exosome-based drug delivery and inhibition of HPV oncogenes or by regulating epigenetic pathways. In this review, we have discussed all these potential approaches and highlighted several important signaling pathways/networks involved in the formation and maintenance of TCSCs, which are targetable as novel therapeutic targets to sensitize/eliminate TCSCs and to improve survival of TSCC patients.