Wang, R. and Coderre, J. A. A Bystander Effect in Alpha-Particle Irradiations of Human Prostate Tumor Cells. Radiat. Res. 164, 711–722 (2005).
Alpha-particle exposures were used to determine whether cells of the human prostate carcinoma cell line DU-145 can produce and respond to a bystander effect signal. An apparatus for α-particle irradiation of cells growing as a monolayer on a 1.4-μm-thick Mylar membrane directly above an 241Am α-particle source was constructed and calibrated. At the cell irradiation position, the α-particle fluence was 998 counts/mm2 s−1, the average α-particle energy was 3.14 MeV, and the average linear energy transfer was 128 keV/μm. The average dose rate to the cells growing on the Mylar surface was 1.2 Gy/min. A co-culture system was used to examine bystander effects transmitted through the medium from the directly targeted cells to tumor cells growing on an insert well beyond the range of the α particles. Alpha-particle doses from 0.1 to 6.0 Gy to the targeted cells on the Mylar membrane, followed by a 2-h co-incubation of the cells on the insert in the irradiated medium above the irradiated cells, all caused an ∼50% increase in micronucleus formation in the nontargeted co-cultured cells. Addition of the radical scavenger DMSO to the medium during the irradiation and the 2-h postirradiation incubation period completely blocked the bystander effect, whereas addition of a nitric oxide scavenger had no effect. Irradiation of medium containing serum, followed by a 2-h incubation, caused no bystander effect in the co-cultured cells. When the co-cultured cells on the insert were placed into the irradiated medium above the directly targeted cells immediately (∼1 min) after the irradiation and co-incubated for 2 h, there was no bystander effect. These data indicate that the observed bystander effect requires that the co-cultured cells be present in the medium during the irradiation of the directly targeted cells and suggest the involvement of a short-lived radical species.