Newman R A, Farquhar D, Lu K, Meyn R, Moore E C, Massia S, Korp J D, Wright J A, McKinney M
Biochem Pharmacol. 1986 Aug 15;35(16):2781-7. doi: 10.1016/0006-2952(86)90190-5.
Preclinical pharmacologic studies of caracemide [N-acetyl-N-(methylcarbamoyloxy)-N'-methylurea; CAR] have demonstrated a marked instability of this compound in the presence of either phosphate buffer (pH 7.4) or human plasma. Using [1-14C-acetyl]CAR and [3H-methylcarbamoyloxy]CAR, three CAR degradation products were identified: product A, N-(methylcarbamoyloxy)acetamide; product B: N-(methylcarbamoyloxy)-N'-methylurea; and product C: N-hydroxy-N'-methylurea. CAR degradation in human plasma was demonstrated by high-performance liquid chromatography (HPLC) to occur in a time- and temperature-dependent manner. A 30-min incubation (37 degrees) of CAR (10(-4) M) with human plasma resulted in degradation of more than 55% of parent compound; at 1 hr, more than 75% of original CAR was degraded. Incubation of [1-14C-acetyl]CAR with rat brain homogenate resulted in the formation of 14CO2. This reaction was partially inhibited by coincubation with physostigmine (10(-3) M). CAR inhibited acetylcholinesterase activity in neuroblastoma cells with an IC50 of 14 microM. In mechanism of action studies, CAR was found to inhibit ribonucleotide reductase activity but only at nine times the IC50 of hydroxyurea. In contrast to hydroxyurea, CAR was found to be non-cell-cycle phase-specific and non-cross-resistant with two CHO cell lines resistant to hydroxyurea. These data demonstrate the instability of CAR; moreover, they suggest that its mechanism of cytotoxicity is distinctly different from that of hydroxyurea and that the neurotoxicity associated with CAR administration may be caused in part by inhibition of acetylcholinesterase activity.
卡醋胺[N-乙酰基-N-(甲基氨甲酰氧基)-N'-甲基脲；CAR]的临床前药理研究表明，该化合物在磷酸盐缓冲液（pH 7.4）或人血浆存在的情况下具有明显的不稳定性。使用[1-14C-乙酰基]CAR和[3H-甲基氨甲酰氧基]CAR，鉴定出三种CAR降解产物：产物A，N-(甲基氨甲酰氧基)乙酰胺；产物B：N-(甲基氨甲酰氧基)-N'-甲基脲；产物C：N-羟基-N'-甲基脲。高效液相色谱法（HPLC）证明，CAR在人血浆中的降解呈时间和温度依赖性。将CAR（10(-4) M）与人血浆在37℃孵育30分钟，导致超过55%的母体化合物降解；1小时后，超过75%的原始CAR被降解。[1-14C-乙酰基]CAR与大鼠脑匀浆孵育导致14CO2的形成。与毒扁豆碱（10(-3) M）共同孵育可部分抑制该反应。CAR抑制神经母细胞瘤细胞中的乙酰胆碱酯酶活性，IC50为14 microM。在作用机制研究中，发现CAR仅在羟基脲IC50的九倍浓度时抑制核糖核苷酸还原酶活性。与羟基脲不同，CAR是非细胞周期阶段特异性的，并且与两种对羟基脲耐药的CHO细胞系无交叉耐药性。这些数据证明了CAR的不稳定性；此外，它们表明其细胞毒性机制与羟基脲明显不同，并且与CAR给药相关的神经毒性可能部分是由乙酰胆碱酯酶活性的抑制引起的。
