Black raspberry extracts (RSE) have been shown to inhibit cancer cell growth and stimulate apoptosis. Also, studies have demonstrated that RSE inhibits transcriptional regulators including NFkappa B. Accordingly, we investigated the effect of RSE in inhibiting radiation (IR) induced NFkappa B mediated radioprotection in breast adenocarcinoma cells. MCF-7 cells were exposed to IR (2Gy), treated with RSE (0.5, 1.0, 2.0 micro g/ml) or treated with RSE (1.0 micro g/ml) followed by IR exposure, and harvested after 1, 3, 6, 24, 48, and 72 h. NFkappa B DNA-binding activity was measured by EMSA and phosphorylated Ikappa Balpha by immunoblotting. Expression of IAP1, IAP2, XIAP and survivin were measured by QPCR and immunoblotting. Cell survival was measured using MTT assay and cell death using Caspase-3/7 activity. Effect of RSE on IR induced MnSOD, TNFalpha, IL-1alpha and MnSOD activity was also determined. RSE inhibited NFkappa B activity in a dose-dependent manner. Also, RSE inhibited IR-induced sustained activation of NFkappa B, and NFkappa B regulated IAP1, IAP2, XIAP, and survivin. In addition, RSE inhibited IR-induced TNFalpha, IL-1alpha, and MnSOD levels and MnSOD activity. RSE suppressed cell survival and enhanced cell death. These results suggest that RSE may act as a potent radiosensitizer by overcoming the effects of NFkappa B mediated radioprotection in human breast cancer cells.