Human head and neck squamous cell carcinoma cell lines are differentially radiosensitised by the honeybee product Propolis.

Purpose: Propolis, a product of honeybees, has anti-tumoural, cytotoxic, anti-metastatic and anti-inflammatory properties. The aim of this study was the evaluation of the radiosensitising capacity of Propolis in human head and neck squamous cell carcinoma (HNSCC) cells. Materials and methods: HNSCC cell lines (FaDu, UT-SCC15, UT-SCC45), fibroblasts (HSF2) and keratinocytes (HaCaT) were treated with Propolis (0--250 μμg/ml; 1, 4, 24 h) without and in combination with X-rays (0--6 Gy, single dose). Clonogenic survival, proliferation, apoptosis, expression and phosphorylation of different signalling proteins were determined. Liquid chromatography-mass spectrometry (LC-MS) was performed on Propolis. Results: Propolis significantly ( P < 0.01) reduced cell growth and clonogenic survival in a time- and concentration-dependent manner. Propolis-induced apoptosis and Caspase 3 cleavage, increased phosphorylation of Extracellular signal Regulated Kinase 1/2 (ERK1/2), protein kinase B/Akt1 (Akt1) and Focal adhesion kinase (FAK). While a 1-h Propolis pretreatment was ineffective, a 3-h pretreatment significantly ( P < 0.05) radiosensitised FaDu cells. LC-MS analysis identified 14 compounds of Propolis. Conclusions: Our data show that Propolis exerts cytotoxicity in a concentration- and time-dependent manner. In one out of three HNSCC cell lines, Propolis also caused an enhancement of radiosensitivity. Future studies on Propolis will shed further light on its potential as an adjuvant to radiotherapy. [ABSTRACT FROM AUTHOR]