Biosynthetic labeling with 32P: radiation damage to mammalian cells

Theoretical calculations showed that biosynthetic radiolabeling of cells using typical concentrations of 32P (1 mCi/ml) resulted in high radiation doses (200-500 rad/h) being absorbed by the cells. Subsequent investigations with a mouse myelomonocytic leukemia cell line (WEHI-3B(D+)) showed significant loss of replicative ability during brief (less than 1 h) exposures to 1 mCi/ml of 32P. Complete loss of cell replicative ability was found with isotopic doses less than 100 rad (i.e., 100 muCi/ml for 5 h). Experiments employing a less radiosensitive pre-B-cell line (18.81) revealed that significant loss of viability occurred during incubation with 32P under identical conditions to those employed for the WEHI-3B(D+) cell line. Control experiments utilizing decayed batches of 32P and physical separation of the isotope solution from the cells confirmed that the cytotoxicity was caused by radiation emission rather than the presence of toxic components in the isotopic solution. The radiation doses absorbed by cells biosynthetically labeled with 59Fe, 33P, 35S, and 14C were calculated. Although significant levels of radiation can be absorbed 32P was considerably more radiotoxic than the other isotopes. The results of calculations indicated that the judicious choice of container geometry could reduce the absorbed radiation dose from 32P solutions. In particular the biosynthetic radiolabeling of cells in capillary tubes (diameter less than 1 mm) can reduce the absorbed rate to less than one-tenth of the dose received by cells suspended in Petri dishes or centrifuge tubes.