Time- and Concentration-Dependent Cytotoxicity of Ricin in

Ricin, a potent ribosome-inactivating hetero-dimeric protein toxin (66kDa) produced in the seeds of the castor bean plant (Ricinus communis), is a Category B Agent on the Centres for Disease Control (CDC) Select Agent List. Using human small airway epithelial cells, this is the first study to investigate the timeand dose-dependent cytotoxic effects of ricin in a human cell line. Ricin (1100pM) produced a timeand dose-dependent decrease in small airway epithelial cell survival. Ricin (10 and 100pM) reduced cell survival to 57% and 50% respectively, after 12 hours exposure and to 12% cell survival after 24 hours exposure to the toxin. Washing cells after 1-5 minutes exposure to ricin (0.01-100pM) prevented any significant ricin-induced SAE cell death. However, after washing cells exposed to ricin for 15 or 30 minutes, there was a significant reduction in SAE cell survival (84% and 71%, respectively, for 10pM and 45% and 31%, respectively, for 100pM). The results suggest that the binding of ricin to the cell surface and subsequent intracellular uptake and cell death appears to be irreversible by washing between 5 and 15 minutes following exposure to the toxin. There may be a window of opportunity for treatment, and therefore prevention, of some lung cell death up to 12 hours after aerosol exposure to ricin given that there was some survival of human lung cells after this time of exposure. Approved for public release RELEASE LIMITATION Published by Human Protection and Performance Division DSTO Defence Science and Technology Organisation 506 Lorimer St Fishermans Bend, Victoria 3207 Australia Telephone: (03) 9626 7000 Fax: (03) 9626 7999 © Commonwealth of Australia 2007 AR-013-806 July 2007 APPROVED FOR PUBLIC RELEASE Timeand Concentration-Dependent Cytotoxicity of Ricin in Human Lung Epithelial Cells