Comparison of two cytotoxicity assays--tetrazolium derivative reduction (MTT) and tritiated thymidine uptake--on three malignant mouse cell lines using chemotherapeutic agents and investigational drugs.

Two different techniques [reduction of a tetrazolium derivative (MTT) and 3HTdR uptake assays] were compared in order to evaluate the cytotoxic effects of different chemotherapeutic agents in vitro. The cytotoxicities of Melphalan, hexamethylmelamine and seven derivatives, and daunorubicin were measured on P388D1 mouse macrophage-like cell line, RC mouse renal carcinoma cell line, and B16 mouse melanoma cell lines. Growth inhibition was determined after one hour as well as after continuous (48 hours) exposure to drugs. The IC50 was calculated using an appropriate algorithm (FADHA) which allowed within and between run variabilities to be taken into account. Optimal conditions had to be elucidated for culture conditions before assay: number of cells/well and assay duration for each line. The MTT and 3HTdR uptake assays were found to be similar in terms of sensitivity and reproducibility, both for adherent and floating cell lines. However, the MTT assay has the advantages of low cost and time saving. It also avoids problems related to radioactivity manipulation and counting. Both techniques rank the same chemicals as active or inactive. The algorithm Fadha was found to be a very powerful mathematical tool for comparing the IC50 values obtained by both assays.