The role of the chemokine receptor CXCR4 in oral squamous cell carcinoma metastasis

Abstract

Oral Squamous Cell Carcinoma (OSCC) is the sixth most common cancer worldwide. The greatest cause of mortality and surgical morbidity is due to the common spread of tumour cells from the primary lesion to the lymph nodes of the neck. This pathway is not unique to cancer: under physiological conditions, specific chemokine receptors on the surface of leukocytes mediate cell “homing” to tissues defined by gradients of complimentary chemotactic cytokines (chemokines). The chemokine receptors CXCR4 and CCR7 mediate leukocyte “homing” to secondary lymphoid tissue and have been demonstrated on the surface of a number of carcinomas of the aero-digestive tract. The aim of this project was to determine the role of chemokine receptor expression and function in OSCC metastasis. CXCR4 mRNA expression (microarrays and semi-quantitative RT-PCR) and surface protein production (flow cytometry and immunocytochemistry) was significantly increased in some (but not all) established OSCC cell lines compared with primary oral keratinocytes grown in culture. Examination of clinical samples using a novel, quantitative immunohistochemistry methodology demonstrated a positive association between CXCR4 staining of the cell membrane in primary OSCC lesions and histological evidence of lymph node metastases. CXCR4 over-expression in a constitutively low expressing OSCC cell line (H357) was produced using stable transfection with the CXCR4 insert. Stimulation of CXCR4-bearing OSCC cells with the ligand SDF was shown to mediate statistically significant increases in OSCC cell proliferation in-vitro using a number of complimentary techniques. No effect on apoptosis was demonstrated. The SDF/CXCR4 axis also mediated significant increases in tumour cell chemokinesis, chemotaxis and invasion as measured by a range of in-vitro assays. These results demonstrate a potential role for CXCR4 as part of a panel of prognostic markers for OSCC. Therapeutic strategies aimed at the SDF/CXCR4 axis may be clinically beneficial if the problems of systemic toxicity can be overcome.