A rapid assay for measuring the metabolism of [H-3]-retinoic acid in cell cultures

A simple method was developed to detect the metabolism of [H-3]-retinoic acid to polar products using intact tumor cells in culture. Unaltered [H-3]-retinoic acid was separated from more polar metabolites using C-18-bonded solid phase extraction cartridges. Separation of unaltered retinoic acid and polar metabolites was confirmed by HPLC. The murine mammary carcinoma cell line TA3 Ha used in these studies converted 40% to 50% of added radioactive retinoic acid to polar metabolites released into the culture medium during a 4-hr incubation period. Metabolism of [H-3]-retinoic acid by TA3 Ha cells was inhibited by the cytochrome P-450 inhibitors ketoconazole, clotrimazole, and liarozole. The simplicity and rapidity of this assay should make it useful for evaluating compounds as inhibitors of retinoic acid metabolism.