New Agent Protects from Radioactivity Even After Exposure

Radiation is truly the invisible killer. Coming in the form of waves or moving subatomic particles, it's unheard and unseen and can only be felt after some time, when it's usually too late for a treatment.

Currently, there is no effective treatment for radiation poisoning (also called radiation sickness), a form of damage to organ tissue due to excessive exposure to ionizing radiation, that can induce cancer as cell-cycle genes are mutated and even a relatively quick, though painful, death.

Within weeks after exposure, but often even less, the radiation kills blood cells vital to clotting and fighting infection, along with the stem cells needed to replenish their supply.

The only available treatments are limited to drugs that boost the production of blood cells and platelets, but this approach is futile if underlying stem cells are also killed off. Moreover, there are no available treatments that can be given after exposure to limit damage to cells.

Fortunately, a team of researchers at Washington University School of Medicine in St. Louis seem to have created an effective agent for preventing the death of young cells, instead of supplementing the already dying ones.

"We are using an entirely different approach," says Clayton Hunt, Ph.D., of the Department of Radiation Oncology. "Rather than ramp up the production of blood cells, we are trying to prevent radiation-induced cell death from occurring in the first place."

They explained that they developed the agent by attaching a portion of the Bcl-xL protein, already known to prevent cell death - a snippet called BH4 - to the HIV protein TAT, which can deftly carry other molecules into cells.

The applications used mice that were exposed to 5 Grays of radiation, a level of exposure that would cause a sharp drop in blood cells in humans, leaving individuals with an increased risk of infection and bleeding.

They intravenously injected the mice with the treatment and found that it helped protect rapidly dividing T cells and B cells in the spleen - immune system cells that are prone to radiation damage - regardless of the timetable, 30 minutes before radiation exposure or 30 minutes afterward.

"This gives us a window of opportunity to treat patients and still prevent cells from undergoing programmed cell death," said Richard Hotchkiss, M.D., professor of anesthesiology, medicine and surgery. "We have a lot more work to do, but we are encouraged by these early findings."

"TAT-BH4 may one day be a viable candidate because theoretically it could be given after radiation exposure, administered in pill form, and synthesized and stored in large quantities - all properties that would be desirable for treating large groups of individuals exposed to high levels of radiation," Hotchkiss said.