Cell detachment and cloning efficiency as parameters for cytotoxicity

Cell detachment and cloning efficiency of Baby Hamster Kidney cells (BHK-21 C13) were used as parameters to quantify cytotoxicity in vitro of 3 endogenous chemicals (glutathione, L-methionine, L-cysteine HCl) and 4 organotin compounds (tributyltinoxide, tributylchloride, tetrabutyltin, tetraphenyltin). IC₅₀ values (inhibitory concentration at which the cloning efficiency was reduced to 50%) were estimated to be larger than 10^?3 M for all 3 endogenous substances, which served as a calibration of the cell culture system for non-toxic chemicals. For the 2 tributyltin salts the IC₅₀ values were estimated to be near 10^?6 M and for the 2 tetraalkyltin compounds near 10^?5 M.The estimated CD₅₀ values (concentration at whicb 50% of the cells detach) were at least twice as large as the corresponding IC₅₀ values for all 7 chemicals tested. For the toxic tributyltin salts the cell detachment assay was 30–60 times less sensitive than the cloning efficiency assay. However, both assays rank all compounds tested in the same sequence of toxicity as that known from in vivo studies.