Extranodal extension in oral cancer: A role for the nodal microenvironment?

Oral squamous cell carcinoma (OSCC) is a significant cause of morbidity and mortality worldwide and accounts for the majority of head and neck cancers. Metastasis of primary tumours, primarily to cervical lymph nodes in the neck, is associated with worsening prognosis. Furthermore, the prognosis of patients with extranodal extension of metastatic tumour from the lymph nodes into the neck tissues is particularly poor. The factors affecting this process are poorly understood, and detection is difficult pre-surgery. Mounting evidence shows that components of the tumour microenvironment including cancer-associated fibroblasts, vascular and lymphatic endothelial cells, the extracellular matrix and inflammatory immune cells, are important modulators of tumour behaviour in primary OSCC and other cancers. However, little is known about the lymph node microenvironment, its response to tumour presence and role in extranodal extension. In addition, there are many lymph node-specific cell types and structures, such as fibroblast reticular cells and high endothelial venules, making the lymph node microenvironment distinct from that found at primary tumour sites, and which contribute to the nodal response to tumour presence. This review details the current knowledge regarding the lymph node tumour microenvironment in OSCC and its role in lymph node metastasis and extranodal extension and relates this to features of the primary tumour. Understanding the role that the lymph node microenvironment plays in promoting tumour development and extranodal extension may aid the identification of novel biomarkers and alternative treatment strategies to improve the prognosis of patients with advanced OSCC.

Epigenetic changes in histone acetylation underpin resistance to the topoisomerase I inhibitor irinotecan.

The topoisomerase I (TOP1) inhibitor irinotecan triggers cell death by trapping TOP1 on DNA, generating cytotoxic protein-linked DNA breaks (PDBs). Despite its wide application in a variety of solid tumors, the mechanisms of cancer cell resistance to irinotecan remains poorly understood. Here, we generated colorectal cancer (CRC) cell models for irinotecan resistance and report that resistance is neither due to downregulation of the main cellular target of irinotecan TOP1 nor upregulation of the key TOP1 PDB repair factor TDP1. Instead, the faster repair of PDBs underlies resistance, which is associated with perturbed histone H4K16 acetylation. Subsequent treatment of irinotecan-resistant, but not parental, CRC cells with histone deacetylase (HDAC) inhibitors can effectively overcome resistance. Immunohistochemical analyses of CRC tissues further corroborate the importance of histone H4K16 acetylation in CRC. Finally, the resistant clones exhibit cross-resistance with oxaliplatin but not with ionising radiation or 5-fluoruracil, suggesting that the latter two could be employed following loss of irinotecan response. These findings identify perturbed chromatin acetylation in irinotecan resistance and establish HDAC inhibitors as potential therapeutic means to overcome resistance.