PARENT SESSION
1:30 PM to 3:30 PM
Wednesday, April 24, 2002
Poster Session 26 Apoptosis
Room: Nevada Exhibition Center

(P31-303) Increased radiosensitivity through inhibition of NFB activation.

Algan, Ozer^*,1, Stratton, Mimie¹, Sikorski, Ewa¹, Zhao, Bryan¹, Yen, David¹, Triehn, Hien, Bowden, Tim, ¹ Department of Radiation Oncology, Tucson, AZ

ABSTRACT-
The role of apoptosis in determining tumor radiosensitivity continues to be poorly understood. Various regulators of apoptosis have been identified in the literature. Of these, NFB appears to play a significant role in preventing cells from undergoing apoptosis, after various stimuli including ionizing radiation treatments. Similarly, there is growing clinical data suggesting that the extent of apoptosis may correlate with tumor aggressiveness and treatment outcome for various types of malignancies. In prostate cancer, there are data suggesting that poorly differentiated tumors, recurrent tumors, and hormone resistant tumors have a lower apoptotic index and worse treatment outcome. Similarly, there are data suggesting a direct relationship between the level of apoptosis within a tumor and the overall radiosensitivity of the tumor cells. We hypothesize that ionizing radiation induced NFB activation can be blocked in DU-145 human prostate carcinoma cells, and that this inhibition of NFB activation will result in increased levels of radiation induced apoptosis. Our data demonstrate that DU-145 cells will undergo apoptosis in a dose dependent fashion after ionizing radiation therapy. Similarly, using Western Gel analysis and reporter assays, we are able to demonstrate increased NFB activation, and increased intranuclear levels of the p65 component of NFB after radiation treatment. This activation and translocation of NFB could be abrogated by transfections with a plasmid construct encoding a dominant negative IB gene, or by pretreatment with either 1mM sulfasalazine or 18uM SN-50 (cell permeable inhibitor peptide for NFB) 4-6 hours prior to ionizing radiation treatments. By blocking NFB activation after ionizing radiation treatments, a 2-4 fold increase in radiation induced apoptosis was detected. The inhibition of NFB activation and the increased rates of radiation induced apoptosis correlated with a 10-15% reduction in the surviving fraction after a single dose of 2Gy as determined by clonogenic survival curves.

KEYWORDS: Radiation Induced Apoptosis, NFB, Radiosensitivity, Prostate Carcinoma