Differential effect of cycloheximide on normal tissue tolerance and tumor control in irradiated rats.

The effect of the protein synthesis inhibitor cycloheximide (CHM) on normal tissue tolerance and tumor control in the rat following single doses of radiation has been studied. We have previously shown that the drug protects against skin damage when administered prior to irradiation of the hind limbs. It does not protect against six-month lethality when given prior to irradiation of the kidneys. In the present studies protection of rat bone marrow as evidenced by 30-day lethality was observed when CHM was given prior to whole-body irradiation. When CHM was given to rats bearing the BA1112 tumor, it had no protective effect on radiocurability. Therapeutically favorable differential protection of rapidly proliferating normal tissue over tumor can be achieved when CHM is administered prior to single radiation doses in the rat. This effect is most likely due to inhibition of protein synthesis and resultant interruption of the cell cycle in proliferating normal tissue. Further studies are required to determine the clinical applicability of CHM.