Radioresistance in cells with high content of metallothionein

Summary An endogenous cytoplasmic protein, metallothionein (MT) apparently gave rise to radioresistance in 2 different cell lines. A dose reduction factor of 1.9 was achieved in MT-containing cells. MT accounted for a 3–4-fold increase of total sulfhydryl groups in the resistant cell strains, compared to the non-resistant lines from which they were derived. The protein is rich in cysteine (30%), an amino acid known to give radioprotection when administered exogeneously. Glutathione levels and cell-cycle phase distribution showed no marked difference between resistant and corresponding non-resistant cells.We thank Dr F. Devik, Dr L. Eldjarn and Dr E. Jellum for stimulating discussions, and Miss A. K. Syversen and Mrs T. Nysted for skillful technical assistance. This work was partly supported by the Norgwegian Council for Science and the Humanitites. LE is a fellow of the Norwegian Society for Fighting Cancer.