After a nuclear disaster like the one in Fukushima, Japan, in 2011, first responders need to quickly measure radiation exposure en masse and decide who requires urgent treatment. Existing tests are fast and accurate—but they rely on sophisticated laboratories, expensive machinery and meticulous work, says Dipanjan Chowdhury, a radiation oncologist at the Dana-Farber Cancer Institute. “We don't have copious amounts of radiation drugs available” in such a situation, he adds. “So how do we decide who gets them?”
To address this question, Chowdhury and his colleagues are developing a simple assay that responders could deploy in the field with limited expertise or equipment. The test, described in March in Science Translational Medicine, detects levels of molecules called microRNAs (miRNAs) in blood and other bodily fluids. The same researchers had previously identified certain miRNAs whose levels rise or fall in mice exposed to radiation.
Chowdhury's team members found that this radiation signature also exists in monkeys (which are the best lab proxies for humans). Their study identifies seven miRNAs that fluctuate in both mice and macaques exposed to radiation. The monkeys were given lethal doses of 5.8, 6.5 or 7.2 grays of whole-body radiation, similar to levels inhaled by Fukushima workers (all the animals received “lethal” doses, but only some resulted in death). Together three of these miRNAs—miR-133b, miR-215 and miR-375—can indicate with 100 percent accuracy whether a macaque has encountered radiation, and two—miR-30a and miR-126—can predict whether the exposure will be fatal. The signature appears within 24 hours of exposure and can be measured using polymerase chain reaction (PCR), a common technique. “Based on the ingredients and the complexity, the miRNA test should be significantly cheaper than any existing test,” Chowdhury says.
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The findings in nonhuman primates are encouraging, says Nicholas Dainiak, director of the Radiation Emergency Assistance Center/Training Site at the Oak Ridge Institute for Science and Education, who was not involved in the study. Dainiak is skeptical, however, that the test will outperform the gold standard metric for radiation exposure: the dicentric chromosome assay (DCA), which requires technical expertise and carefully calibrated equipment. “Every time a new test comes along, and you compare it with the DCA, it typically fails,” Dainiak says.
Chowdhury has held informal talks with companies that are interested in creating a rapid diagnostic kit for radiation. “When we did this in mice, people said, 'We've seen a lot of stuff in mice that never pans out in primates,'” Chowdhury says. “Well, this seems to be panning out in primates.”
