Alkyl ester prodrugs are well known to be bioconverted by carboxylesterases, particularly in rodents’ by first-pass metabolism in the systemic circulation and liver. However, the bioconversion of structurally more complex esters with polar functional groups is less well understood, especially in humans. Therefore, it is not clear if ester prodrugs can be utilized for targeted drug delivery. In the present study a brain-targeted ester prodrug (1) of ketoprofen, utilizing the l-type amino acid transporter 1 (LAT1) was prepared and the enzymes involved in its metabolism in human plasma and liver S9 subcellular fraction as well as rat brain S9 fraction were identified. Furthermore, species differences among mouse, rat and human plasma and liver S9 fraction were compared. The results showed that bioconversion of the ester prodrug was much faster in mouse plasma compared to human, while it’s half-life in rat plasma was closer to the one of human. Moreover, both rodent species showed more efficient bioconversion in the liver S9 fractions compared to human and relatively efficient bioconversion in the brain S9 fractions. More specifically, butyrylcholinesterase (BChE) and paraoxygenase 1 (PON1) were the main hydrolyzing enzymes of the prodrug 1 in human plasma, while carboxylesterases 1 and 2 (CES1 and CES2) as well as PONs were the main bioconverting enzymes in human liver S9 fractions. In rat brain S9 fraction, acetylcholinesterase (AChE) was hydrolyzing the prodrug 1, although also other unidentified metal-and pH-dependent enzyme(s) were recognized to be participating to the total bioconversion of the compound 1 in the brain.

众所周知，烷基酯前药可通过羧酸酯酶进行生物转化，尤其是在啮齿类动物中，通过体循环和肝脏中的首过代谢进行生物转化。然而，对具有极性官能团的结构更复杂的酯的生物转化知之甚少，尤其是在人类中。因此，尚不清楚酯前药是否可用于靶向药物递送。在本研究中脑靶向酯前药（1酮洛芬），利用升制备了氨基酸型转运蛋白1（LAT1），并鉴定了其在人血浆和肝脏S9亚细胞级分以及大鼠脑S9级分中代谢的酶。此外，比较了小鼠，大鼠和人血浆与肝脏S9组分之间的物种差异。结果表明，与人类相比，小鼠血浆中酯类前药的生物转化要快得多，而在大鼠血浆中的半衰期则接近于人类。此外，与人类相比，两种啮齿动物物种在肝脏S9组分中均显示出更有效的生物转化，而在大脑S9组分中则显示出相对有效的生物转化。更具体地，丁酰胆碱酯酶（BChE）和对氧合酶1（PON1）是前药1的主要水解酶。在人血浆中，羧酸酯酶1和2（CES1和CES2）以及PON是人肝S9组分中的主要生物转化酶。在大鼠大脑S9组分中，乙酰胆碱酯酶（AChE）正在水解前药1，尽管还认识到其他未确定的金属和pH依赖性酶也参与了化合物1在脑中的全部生物转化。