RESUMO
<p><b>OBJECTIVE</b>To determine if proteasome inhibitor bortezomib leads to enhanced radiation sensitivity of Hep-2 human laryngeal cancer cells and the relative mechanisms.</p><p><b>METHODS</b>Hep-2 cells with or without bortezomib were irradiated at 0, 2, 4, 6, 8, and 10 Gy. Growth and clonogenic survival data were obtained to assess effects of treatment on radiosensitization. In vitro results were tested in vivo using a Hep-2 xenograft model. Nuclear factor-kappaB (NF-kappaB) activation was determined by Trans AM NF-kappaB P65 kit. The distribution of cell cycle and apoptosis were evaluated by flow cytometry. Morphological evidence of apoptotic cells were observed with Hochest 33342.</p><p><b>RESULTS</b>It decreased cell growth and clonogenic survival. A 34% increase in radiosensitivity was observed for cells treated with bortezomib and radiation. Enhancement factor (EF) was 1.46 in Hep-2 xenografts receiving radiation and bortezomib. NF-kappaB activation was induced by radiation and inhibited by pretreatment with bortezomib, and was in a dose-dependent manner (r = 0.989, P < 0.05). Hep-2 cells treated with 100 nmol/L Bortezomib were arrested at G2-M phase (t = 22.31, P = 0.000) and resulted in all increased apoptosis with and without irradiation (P < 0.01). Morphological evidence of apoptotic cells could be distinguished under the fluorescence microscope after staining with Hochest 33342. Many nuclear fragments were observed in Hep-2 cells with bortezomib.</p><p><b>CONCLUSION</b>Bortezomib could enhanced the radiosensitivity of Hep-2 laryngeal cancer cells by regulation of the distribution of cell cycle.</p>