Radiation Measurements 42 (2007) 1152 – 1157 www.elsevier.com/locate/radmeas Short communication Genistein-induced alterations of radiation-responsive gene expression M.B. Grace ∗ , W.F. Blakely, M.R. Landauer Armed Forces Radiobiology Research Institute, 8901 Wisconsin Avenue, Bethesda, MD 20889-5603, USA Abstract In order to clarify the molecular mechanism of radioprotection and understand biological dosimetry in the presence of medical countermeasure- radioprotectants, their effects on ionizing radiation (IR)-responsive molecular biomarkers must be examined. We used genistein in a radiation model system and measured gene expression by multiplex QRT-PCR assay in drug-treated healthy human blood cultures. Genistein has been demonstrated to be a radiosensitizer of malignant cells and a radioprotector against IR-induced lethality in a mouse model. Whole-blood cultures were supplemented with 50, 100, and 200 M concentrations of genistein, 16 h prior to receiving a 2-Gy ( 60 Co- rays, 10 cGy/min) dose of IR. Total RNA was isolated from whole blood 24h postirradiation for assessments. Combination treatments of genistein and IR resulted in no significant genistein effects on ddb2 and bax downstream transcripts to p53, or proliferating cell-nuclear antigen, pcna, necessary for DNA synthesis and cell-cycle progression. Use of these radiation-responsive targets would be recommended for dose-assessment applications. We also observed decreased expression of pro-survival transcript, bcl-2. Genistein and IR-increased expression of cdkn1a and gadd45a, showing that genistein also stimulates p53 transcriptional activity. These results confirm published molecular signatures for genistein in numerous in vitro models. Evaluation of gene biomarkers may be further exploited for devising novel radiation countermeasure and/or therapeutic strategies. Published by Elsevier Ltd. Keywords: Transcription; QRT-PCR; Biomarkers; Genistein; Apoptosis; Cell cycle 1. Introduction The analysis of molecular biomarker responses to doses of ionizing radiation (IR) is a novel and rapid approach that can complement chromosome-aberration assays and other dose assessment methodologies (Blakely et al., 2001). Recent technological advances in genomics and proteomics lend them- selves to the potential discovery and application of a plethora of radiation-responsive biomarkers (Amundson et al., 2000; 2001; 2004; Menard et al., 2006). The gene expression bioassay is an early-response (< 3 days) radiation biomarker sensitive over a broad dose range (1–3 Gy) (Blakely et al., 2002; Grace et al., 2002, 2003) including low doses < 25 cGy (Amundson et al., 1999). We have demonstrated utility of the quantitative reverse transcription-polymerase chain reaction (QRT-PCR) assay for dose assessment of multiple gene targets from different ∗ Corresponding author. Tel./fax: +1 301 295 0369. E-mail address: grace@afrri.usuhs.mil (M.B. Grace). 1350-4487/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.radmeas.2007.05.011 cellular pathways in a human whole blood ex vivo irradia- tion model (Grace et al., 2002, 2003). Several issues need to be addressed before a gene expression bioassay can be used for biodosimetry applications, including the choice of sentinel biomarkers, inter-individual variation of radiation re- sponse and basal expression, and potential effects of medical countermeasure-radioprotectants on expression of responsive biomarkers from different cellular pathways. Naturally occurring dietary components offer opportunities for development as effective chemopreventive and radiopro- tective agents because of their potential low toxicity (Coleman et al., 2004; Sarkar and Li, 2004; Weiss and Landauer, 2003). Genistein (4 ′ ,5,7-trihydroxyflavone), a naturally occurring isoflavone derived from soybeans, has gained increasing at- tention because of its association with beneficial effects for treatment of cardiovascular disease, high blood pressure, os- teoporosis, breast cancer, and prostate cancer (McCue and Shetty, 2004; Valachovicova et al., 2004). Genistein has been demonstrated to be nontoxic and an effective radioprotectant in animal studies. A single subcutaneous dose of genistein (25–200 mg kg -1 ) administered 24 h before cobalt-60 gamma