Effects of retinoids, β‐carotene, and canthaxanthin on UV‐ and x‐ray‐induced transformation of C3H10t1/2 cellsin vitro

We observed that various retinoids (including all-trans-retinoic acid, 13-cis-retinoic acid, and the synthetic retinoid Ro-11-1430) have approximately the same ability to suppress ultraviolet light-induced transformation of C3H10T1/2 cells in vitro. Retinoids also suppress X-ray induced transformation in vitro. Ro-11-1430 has no effect when present for only 1 day after the X-ray exposure but does have a suppressive effect on radiation transformation when present for 5 or 10 days after irradiation. Ro-11-1430 has its major suppressive effect on X-ray transformation when present in irradiated cultures in the confluent stationary phase of growth. Natural beta-carotene (type IV) from carrots, but not synthetic beta-carotene, has the ability to suppress radiation (X-ray)-induced transformation when present for the entire transformation assay period. Natural beta-carotene is without effect on the transformation process when present in irradiated cultures only during confluence. For these retinoids, as well as beta-carotene and canthaxanthin, there is a highly significant suppressive effect on radiation transformation and radiation transformation enhanced by 12-O-tetradecanoylphorbol-13-acetate when the compounds are present at toxic levels; when nontoxic levels are utilized, these compounds have the ability to suppress the yield of transformed cells to approximately one-half of that observed in irradiated cultures in the absence of these compounds. A selective toxicity for transformed cells appeared to exist for the beta-carotene-treated F-17 cells. This apparent selective toxicity was not observed in another line of transformed cells. Cl 16 cells, or in human cells. We observed different uptake patterns of beta-carotene by nontransformed C3H10T1/2 cells, F-17 cells, and Cl 16 cells that may account for the observed apparent selective toxicity of one line of transformed cells (F-17 cells) to beta-carotene.