Innervation of the Oral Cancer Microenvironment: A Novel Therapeutic Target?

Objectives: Nerves have recently been implicated in breast, pancreatic and prostate cancer progression, but the molecular mechanisms underlying this are poorly understood. Little is known regarding the contribution of nerves to disease progression in oral cancer. This study’s objective was to investigate neuronal –tumour interactions in oral squamous cell carcinoma (OSCC).
Methods: Quantitative polymerase chain reaction (qPCR) and immunocytochemistry were used to identify the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), and their receptors in normal oral keratinocytes (NOKs) and cell-lines derived from oral dysplasias, primary and metastatic OSCC, and neurones. Co-culture systems were used to identify functional cross-talk mediated by neuronal, cancer cell and fibroblast (the predominant cell type of the tumour microenvironment) secretions. ELISA and qPCR were employed to identify secreted factors playing roles in neural-tumour interactions.
Results: CGRP and SP receptor transcripts were detected by qPCR in most cell lines. Immunocytochemistry localised receptor components within OSCC cells. CGRP and SP were detected in cultured trigeminal ganglion neurones used for co-culture systems. Significant chemoattractant and proliferative effects of both neuropeptides were identified in OSCC cells (H357) in a dose- and time-dependent manner. Nerve growth factor (NGF) transcripts were elevated in most cancer-derived cell lines relative to NOKs and NGF protein secretion was detected from H357 cells. NGF secretion from cancer-associated fibroblasts was significantly increased compared to normal oral fibroblasts; this was associated with increased neuronal outgrowth in indirect co-culture. H357-derived conditioned medium also caused significant increases in neuronal outgrowth.
Conclusions: The results indicate the existence of significant cross-talk between nerves and the OSCC tumour microenvironment. This suggests neuronal factors may have potential as therapeutic targets.