Ho H T, Hitchcock M J
Pharmaceutical Research and Development Division, Bristol-Myers Company, Wallingford, Connecticut 06492-7660.
Antimicrob Agents Chemother. 1989 Jun;33(6):844-9. doi: 10.1128/AAC.33.6.844.
2',3'-Dideoxy-2',3'-didehydrothymidine (D4T) is a thymidine nucleoside analog which has potent anti-human immunodeficiency virus activity in vitro. We have studied its metabolism in cells to assist in determining its mechanism of action. D4T is metabolized in cells to the mono-, di-, and triphosphate nucleotides. Our data suggest that the initial conversion to the monophosphate is catalyzed by thymidine kinase. This enzyme has an affinity for D4T 600-fold lower than for thymidine and catalyzes the rate-limiting step in production of the triphosphate. Nevertheless, intracellular concentrations of the triphosphate approximately equal to the reported Ki for human immunodeficiency virus reverse transcriptase are attained with extracellular concentrations of free drug as low as 0.05 microM. The pattern of phosphorylation is different from that of 3'-azido-3'-deoxythymidine (AZT), which has an affinity for thymidine kinase equivalent to that of thymidine and is easily phosphorylated. The rate-limiting step in formation of AZT triphosphate is conversion of mono- to diphosphate, and thus the monophosphate accumulates. On removal of D4T or AZT from the media, both triphosphates have an intracellular half-life of about 200 min, and this rate ultimately controls the rate of elimination of the drugs from cells. The differences in metabolism of D4T and AZT observed in vitro may be responsible for the differences in toxicity seen in vitro and in vivo and support the exploration of the clinical utility of D4T as an anti-human immunodeficiency virus agent.
2',3'-二脱氧-2',3'-二脱氢胸苷（D4T）是一种胸苷核苷类似物，在体外具有强大的抗人类免疫缺陷病毒活性。我们研究了其在细胞中的代谢情况，以协助确定其作用机制。D4T在细胞中代谢为单磷酸、二磷酸和三磷酸核苷酸。我们的数据表明，最初转化为单磷酸是由胸苷激酶催化的。该酶对D4T的亲和力比对胸苷低600倍，并催化三磷酸生成中的限速步骤。然而，当细胞外游离药物浓度低至0.05微摩尔时，三磷酸的细胞内浓度约等于报道的人类免疫缺陷病毒逆转录酶的Ki值。磷酸化模式与3'-叠氮-3'-脱氧胸苷（AZT）不同，AZT对胸苷激酶的亲和力与胸苷相当，且易于磷酸化。AZT三磷酸形成中的限速步骤是单磷酸向二磷酸的转化，因此单磷酸会积累。从培养基中去除D4T或AZT后，两种三磷酸的细胞内半衰期约为200分钟，该速率最终控制药物从细胞中消除的速率。体外观察到的D4T和AZT代谢差异可能是体外和体内毒性差异的原因，并支持探索D4T作为抗人类免疫缺陷病毒药物的临床应用。
