Esterase inhibitors diminish the modulation of gene expression by butyric acid derivative, pivaloyloxymethyl butyrate (AN-9).

Pivaloyloxymethyl butyrate (AN-9) belongs to the family of acyloxyalkyl ester prodrugs of carboxylic acids which undergo intracellular hydrolysis to yield butyric acid (BA). We have previously shown that AN-9 and BA reduce the level of c-myc and enhance c-jun transcripts in HL-60 cells, and that the differentiation of these cells, induced by AN-9, is dependent on the presence of intracellular esterases. In this study we show that esterase inhibitors abolish the changes induced by AN-9 on c-myc and c-jun expression. In contrast, esterase inhibitors do not change the effects of BA on c-myc or c-jun. Interestingly, these inhibitors affect the modulation induced by both AN-9 and BA on the retinoblastoma tumor suppressor gene. These data suggest that AN-9 is indeed a prodrug of BA and that prior intracellular hydrolysis by esterases is material for AN-9 activity.