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STABILITY OF RETINOIDS IN CULTURE

The stability of all‐trans‐retinoic acid, 13‐cis‐retinoic acid and Ro10‐9359 (etretinate) in culture was analyzed by measuring the amount of each retinoid in culture medium with HPLC. In cultures of human keratinocytes and B16 mouse melanoma cells (K440B), all‐trans‐retinoic acid was fairly stable, but it disappeared rapidly in cultures of HeLa cells. In general, 13‐cis‐retinoic acid was more unstable. When all‐trans‐ or 13‐cis‐retinoic acid was used, the 13‐cis or all‐trans forms also appeared in the culture medium as a result of cis‐trans isomerization. Human epidermal keratinocytes were able to de‐esterify Ro10‐9359, and Ro10‐1670 was also detected in the culture medium. K440B cells had a strong capacity for de‐esterifying Ro10‐9359. When 10 nmole/ml Ro10‐9359 was added to the culture, about 1 nmole/ml of Ro10‐1670 was maintained from 24 to 96 h later. In the HeLa cells culture, no Ro10‐1670 was detected after the addition of 1 nmole/ml Ro10‐9359. These results indicate that, in the tissue culture system, the pharmacokinetics of each retinoid depended upon its concentration, the cell type and the cellular density.