Regular article AATEX 2(3):115-126
As a contribution to the MEIC project, we determined the in vitro toxicities of MEIC chemicals on human lung squamous carcinoma cells by lactate dehydrogenase (LDH) release assay. The LDH activities in the culture supernatant and the cell layer, corresponding to those of Iysed dead cells and surviving cells, respectively, were measured simultaneously after 48-hour treatment with the MEIC chemicals. In terms of the ED50, the dose for 50% survival of cells, the most toxic chemical was digoxin (0.38 ƒÊM), followed by arsenic trioxide (3.24 ƒÊM) and mercuric chloride (13 ƒÊM), and the least toxic was ethylene glycol (1,220 mM). The ED50, values correlated closely with the known toxicities to laboratory animals, especially with LD50, values for dogs determined by intravenous administration (r=0.914). A new index of cell killing was defined as the ratio of the LDH activity in the culture supernatant after 48 hour treatment to that of the cells at the beginning of treatment. The dose-response curve of this index was almost the mirror image of that of surviving cells within the same dose range around the ED50 in the case of chloroquine diphosphate. However, in the case of caffeine, the curve of the killing index was shifted to a higher dose range than that of the curve of surviving cells. These results suggest that chloroquine diphosphate is mainly cytocidal, whereas caffeine mainly inhibits cell proliferation. Thus the modes of toxic action of chemicals could be partially assessed by this single LDH release assay.