Transcriptional response in normal mouse tissues after i.v. ²¹¹At administration - response related to absorbed dose, dose rate, and time

Background: In cancer radiotherapy, knowledge of normal tissue responses and toxicity risks is essential in order to deliver the highest possible absorbed dose to the tumor while maintaining normal tissue exposure at non-critical levels. However, few studies have investigated normal tissue responses in vivo after ²¹¹At administration. In order to identify molecular biomarkers of ionizing radiation exposure, we investigated genome-wide transcriptional responses to (very) low mean absorbed doses from ²¹¹At in normal mouse tissues. Methods: Female BALB/c nude mice were intravenously injected with 1.7 kBq ²¹¹At and killed after 1 h, 6 h, or 7 days or injected with 105 or 7.5 kBq and killed after 1 and 6 h, respectively. Controls were mock-treated. Total RNA was extracted from tissue samples of kidney cortex and medulla, liver, lungs, and spleen and subjected to microarray analysis. Enriched biological processes were categorized after cellular function based on Gene Ontology terms. Results: Responses were tissue-specific with regard to the number of significantly regulated transcripts and associated cellular function. Dose rate effects on transcript regulation were observed with both direct and inverse trends. In several tissues, Angptl4, Per1 and Per2, and Tsc22d3 showed consistent transcript regulation at all exposure conditions. Conclusions: This study demonstrated tissue-specific transcriptional responses and distinct dose rate effects after ²¹¹At administration. Transcript regulation of individual genes, as well as cellular responses inferred from enriched transcript data, may serve as biomarkers in vivo. These findings expand the knowledge base on normal tissue responses and may help to evaluate and limit side effects of radionuclide therapy.