[Role of NF-κB in the anti-tumor effect of thymoquinone on bladder cancer]

To explore the effects and mechanism of thymoquinone in the growth inhibition of bladder cancer both in vitro and in vivo.

After the treatment of thymoquinone, the cellular proliferation of human bladder cancer cell line BIU-87 was detected by the method of methyl thiazolyl tetrazolium (MTT). Flow cytometry (FCM) was used to determine the cellular apoptosis. And the location of nuclear factor (NF)-κB was identified by the method of immunofluorescent histochemistry. Western blotting was employed to detect the cellular expressions of NF-κB, survivin and XIAP. BIU-87 cells were injected subcutaneously into nude mice to establish a xenograft model. After 2 weeks of implantation, the mice were randomized into 2 groups (n = 8): (a) vehicle alone (control), (b) thymoquinone (5 mg/kg daily by intragastric intubation). All treatments lasted for 2 weeks. At Week 7 post-implantation, the mice were sacrificed and their tumor weights and inhibition rates evaluated. Immunohistochemistry was used to detect the positive expressions of Ki-67, NF-κB and XIAP in tumors.

The proliferation of bladder cancer cells was inhibited significantly by thymoquinone at 20, 40, 80 µmol/L (81.2% ± 4.6%, 72.5% ± 6.5%, 58.4% ± 8.9% vs 100%, all P < 0.05). Apoptosis rate induced by thymoquinone was more significant than that of the control (7.6% ± 1.6%, 11.2% ± 2.1%, 14.3% ± 2.8%vs 1.6% ± 0.5%, all P < 0.05). Immunofluorescent histochemistry showed that thymoquinone could significantly lower the nuclear expression of NF-κB. The expressions of NF-κB and XIAP were down-regulated in BIU-87 cells after the treatment of thymoquinone. But thymoquinone had no effect on the expression of survivin. The final tumor weight showed significant decrease in the test group versus the control group ((0.41 ± 0.12) vs (0.89 ± 0.23) g, P < 0.05). Furthermore, the positive expressions of Ki-67, NF-κB and XIAP decreased in tumors after the administration of thymoquinone.

Thymoquinone exerts anti-tumor effects on bladder cancer both in vitro and in vivo through the down-regulations of NF-κB and its regulated molecules such as XIAP.