The Importance of Exposure Period and Cell Type in <i>In Vitro</i> Cytotoxicity Tests

Abstract

The cytotoxicities of 50 coded chemicals from the FRAME blind trial set were estimated by the FRAME kenacid blue (KB) and Rockefeller neutral red (NR) assay methods after test periods of 24 hours and 72 hours with murine 3T3 fibroblasts. Results obtained after the two test periods were considered to be similar for 25 of the chemicals, but different for 25 others. Our results indicate that a test period of 72 hours is more suitable for the assessment of potential cytotoxicity by the KB and NR methods than the 24 hour test period, which is less likely to allow sufficient time for certain chemicals to exert their toxic effects, particularly those that inhibit cell division or affect cell viability through other long-term effects. A comparison of results obtained by the 72 hour KB method with 3T3 cells and with human BCL-D1 cells indicated that substantially different ID50 values were found for 8 of 48 chemicals. These results are discussed in terms of the importance of choice of test period, assay method and cell type used in in vitro cytotoxicity tests.