Simplification of the CHO/HGPRT mutation assay through the growth of Chinese hamster ovary cells as unattached cultures.

A novel technique for the growth of Chinese hamster ovary (CHO) cells as unattached cells on the nontissue culture plates was applied to the CHO/HGPRT mutation assay, using EMS and MNNG as mutagens. The subculturing procedures for the unattached cultures involved less time and effort than those for the conventional attached cultures since trypsinization was not required for cell detachment. No significant difference in the maximum mutation frequency was observed for cells grown as unattached or attached cultures during the expression period. The optimum expression time was, however, shorter for the unattached cells (6 days) than for the attached cells (9 days). No selection for or against the mutant population was observed when mutant and wild-type cells were co-cultivated as unattached cultures, indicating that the procedure does not affect the quantitativeness of the mutation assay. The growth of CHO cells as unattached cells during the expression period thus could decrease the cost and effort involved in the use of the CHO/HGPRT mutation assay in the screening of potential mutagens/carcinogens.