Abstract 574: Mechanism of radiation-induced bystander effect: Role of NFκß pathway

Abstract

Abstract Evidence from our lab and others clearly delineated that the transcriptional regulator NFκB plays a key role in induced responses in non-targeted bystander cells. We further reported curcumin impedes radiation (IR)-induced NFκB. However, full potential of curcumin is yet to be realized because of its poor bioavailability. This prompted us to investigate the efficacy of a more potent synthetic analogue of curcumin, EF24 in this setting. In this study, we investigated the orchestration of NFκB signaling after IR in an organ (lung) distant from the exposure field and elucidated the effect of EF24 in reverting the induced response. C57/BL6 mice either mock irradiated, exposed to single dose IR (SDR: 2 or 10Gy) or fractionated IR (FIR, 2 Gy/day for 5d) with or without EF24 (i.p. 200μg/Kg, 3h prior to IR) treatment were sacrificed after 24h. All IR exposures were limited to the lower abdomen area (1cm diameter), while the rest of the animal was protected by a specially designed cerrobend shield. EMSA analysis was used to examine the changes in NFκB DNA binding activity in lungs. Transcriptional activation of 88 NFκB pathway molecules was assessed using QPCR profiling. Phosphorylation of ERK1/2 and p38 that play a key role in NFκB signal transduction were examined using immunoblotting. DNA fragmentation was measured using TdT nick end labeling. A known NFκB dependent oxidative stress response SOD2 localization was examined using immunohistochemistry. IR significantly induced NFκB DNA binding activity in lungs. On the other hand, EF24 markedly suppressed IR-bystander effect (BSE)-induced NFκB DNA binding activity. QPCR profiling showed a significant and differential modulation in NFκB pathway transcriptome. To that end, of the 88 genes analyzed, 86, 86 and 70 genes were upregulated after 2Gy, 10Gy and FIR, respectively. Of these, 85, 80 and 63 genes were significantly (≫ 2 fold) upregulated. Conversely, EF24 completely suppressed 51, 52 and 43 SDR (2Gy, 10Gy) and FIR upregulated genes respectively in the non-targeted lungs. While IR profoundly phosphorylated ERK1/2 and p38 in distant lungs, EF24 treatment completely inhibited the phosphorylation of these kinases. Furthermore, IR-induced SOD2 levels in distant lung after all three IR-dose regimens were notably conferred by EF24 treatment. In addition, IR-enhanced DNA fragmentations in the lung tissue were significantly reduced with EF24. Taken together, these data clearly indicated that (i) an induced non-targeted effect occurs in mice lungs after clinically relevant doses of IR exposure; (ii) the orchestration of NFκB signal transduction may play a key role in induced abscopal responses; and (iii) EF24 treatment may attenuate NFκB and thereby alleviate radiation-induced abscopal effect at the distant organ. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 574. doi:10.1158/1538-7445.AM2011-574