A major instigator of radiation-induced pathology is cellular damage caused by reactive oxygen species formed in the first moments after exposure. Most therapeutic agents are free radical scavengers which must be present in high concentrations as exposure occurs, making their use as treatments problematic. In addition, the normal cell already has scavenger molecules present, such as glutathione. Glutathione accepts electrons from reactive electrophiles as part of the normal cellular defenses, but the resultant electrophilic glutathione conjugates still pose a threat to cellular integrity. Final elimination of risk then requires the transport and elimination of these reactive glutathione S-conjugates - a key function of RLIP76, a membrane-associated transport protein. Terapio has been testing RLIP76 as a systemic therapy for high-dose radiation poisoning. Preliminary studies in mice show that increasing cellular content of RLIP76 by systemic administration significantly increases survival even if the protein is administered AFTER radiation exposure, with a clear dose-response relationship between amount of RLIP76 administered and survival that extends to all but the highest exposure levels. Further, RLIP76 can be orally administered, increasing its ease of treatment. In order to move forward with clinical development, additional work regarding protein storage, stability, optimal dosing and schedule of administration is necessary. Further, although much is known about the protein's mechanism of action on a cellular level, organ-specific effects have yet to be determined. Therefore, this proposal will focus on three main areas.
Specific Aim 1 will look at the stability of the protein under a variety of storage conditions to determine loss of activity and how that may affect recommended dosing in the field. Expanded studies of in vivo stability of the protein will be performed by following tissue levels of administered protein over time.
Specific Aim 2 will enlarge understanding of the relationship between dose level, timing and schedule of administration and length of treatment in a mouse model.
Specific Aim 3 will look at how RLIP76 affects specific organ toxicity from radiation and examine potential long term effects, again in a mouse model. The information obtained is necessary to plan an optimal treatment regimen for RLIP76 under different radiation release scenarios.
RLIP76 is a naturally-occurring protein that can be given orally and counteract the effects of radiation poisoning even if given AFTER exposure occurs. This project will investigate the most effective dosing of the protein and how to optimize packaging for long term storage.