Synergistic effects of nuclear factor-kappa B inhibitor on^131I induced apoptosis in differentiated thy-roid cancer cells

Abstract

Objective To study pro-apoptotic effects of a nuclear factor-kappa B （NF-κB） inhibi- tor （ Bay 11-7082） and ^131Ⅰ on DTC cells and investigate the synergistic effects of the combined treatments. Methods Western blot was used to detect relative protein expression changes of NF-κB regulated to anti- apoptotic factors （ X-chromosome-linked inhibitor of apoptosis （XIAP） and survivin） as well as key apoptot- ic factors （caspase 3 and poly-adenosine diphosphate-ribose polymerase （PAP, P）） after either mono-treat- ment and combined treatment for 24 h. β-actin was used as control and semi-quantitative analysis was per- formed. Flow cytnmetry with Annexin V-fluoreseein isothiocyanate/propidium iodide double staining wasused to analyze the induction of apoptosis after different treatments as well. One-way analysis of variance and q test were used for statistical analysis. Results Basic expressive levels of XIAP and survivin were （ 16.62 ± 0.73） % and （ 15.20 ± 0.53 ） % , respectively. The levels increased to （95.22 ± 3.27） % and （71.80 ±2.76）% after ^131Ⅰ treatment, respectively. In the combined treatment group with ^131Ⅰ and Bay 11- 7082, XIAP and survivin expressions were （ 8.29 ± 0.35 ） % and （6.87 ± 0.28 ） %, respectively. The differences of XIAP and survivin with different treatments were statistically significant （ F = 1823.47 and 1406.12, both P 〈 0.01 ）. The expression levels in the combined treatment group showed significant differ- ences compared with that in ^131Ⅰ mono-treatment or the control group （ q = 13.37 - 45.38, all P 〈 0.01 ）. Basic levels of caspase 3 subunits p19 and p17, as well as degraded PARP protein p89 were （4.93 ± 0. 49） %, （4.67 ± 0.34） % and （4.87 ± 0.64） %, respectively. After 131i treatment they displayed ex- pressive enhancement as （25.07 ±1.26）%, （18.29 ± 1.14）% and （34.97 ± 1.90）%, and after Bay 11-7082 treatment their levels increased to （60.32 ±3.59）%, （41.29 ±3.23）% and （66.49 ± 2. 96 ） %, respectively. In the combination treatment group the above parameters were （ 104.62 ± 5.02） %, （94.72 ± 4.28 ） % and （ 101.59 ± 4.04） % and the differences were statistically significant （ F = 575.13, 625.95 and 712.87, all P 〈 0.01 ）. Compared with the mono-treatment group, the combined treatment group showed significantly higher levels of p19, p17 and p89 （q = 15.95 - 86.01, all P 〈0.01 ）. Flow cy- tometry also showed significantly higher percentage of apoptotic cells in the combined treatment group （47.02± 4.53 ）% than that in ^131Ⅰ treatment group （9.44 ± 0.66）% or Bay 11-7082 treatment group （18.92±1.84）% （F=201.12, q =13. 86 and17.13, allP〈0.01）. Conclusions 131Imayinduceen- hancement of anti-apoptotic factor expressions by activation of NF-κB pathway in DTC cells. This enhance- ment may be inhibited by combination with NF-κB inhibitor Bay 11-7082. Thus NF-κB inhibitor may exert synergistic effects on^131Ⅰ induced apoptosis in DTC cells. Key words: Thyroid neoplasms ; Cell apoptosis; Iodine radioisotopes ; Drug synergism; Bay 11-7082