Development of gene expression signatures for practical radiation biodosimetry

Abstract

Purpose: In a large-scale radiologic emergency, estimates of exposure doses and radiation injury would be required for individuals without physical dosimeters. Current methods are inadequate for the task, so we are developing gene expression profiles for radiation biodosimetry. This approach could provide both an estimate of physical radiation dose and an indication of the extent of individual injury or future risk.

Methods and materials: We used whole genome microarray expression profiling as a discovery platform to identify genes with the potential to predict radiation dose across an exposure range relevant for medical decision making in a radiologic emergency. Human peripheral blood from 10 healthy donors was irradiated ex vivo, and global gene expression was measured both 6 and 24 h after exposure.

Results: A 74-gene signature was identified that distinguishes between four radiation doses (0.5, 2, 5, and 8 Gy) and controls. More than one third of these genes are regulated by TP53. A nearest centroid classifier using these same 74 genes correctly predicted 98% of samples taken either 6 h or 24 h after treatment as unexposed, exposed to 0.5, 2, or > or =5 Gy. Expression patterns of five genes (CDKN1A, FDXR, SESN1, BBC3, and PHPT1) from this signature were also confirmed by real-time polymerase chain reaction.

Conclusion: The ability of a single gene set to predict radiation dose throughout a window of time without need for individual pre-exposure controls represents an important advance in the development of gene expression for biodosimetry.

Figure 1

Relative induction of CDKN1A by irradiation. White bars: quantitative hybridization data from (6)(n=4), black bars: current real-time PCR data (n=5). The measurements made using the two techniques are not significantly different from each other (p>0.05) at any dose or time. Dashed line indicates unirradiated control ratio.

Figure 2

Average linkage clustering of genes in the radiation consensus signature. Dose in Gray is shown across the top. Genes used for qRT-PCR are indicated along the right edge, and annotation of all genes in clustered order is presented in Table 1.

Figure 3

The 74-gene consensus signature visualized by MDS. Open symbols: 6 hour samples, Filled symbols: 24 hour samples. Axes represent the first three principal components of gene expression. Each point represents the relative gene expression of all 74 array features for an individual sample. The distance between any two points reflects their overall similarity of expression levels of all 74 genes. The points are colored according to dose: 0 Gy (purple), 0.5 Gy (blue), 2 Gy (green), 5 Gy (orange) and 8 Gy (red).

Figure 4

Relative expression of FDXR (■), CDKN1A (●), PHPT1 (□), BBC3 (▲) and SESN1 (○) at A) 6 and B) 24 hours after irradiation as measured by qRT-PCR. Points are the mean of responses in 5 independent donors, error bars are standard errors.