Frederick Abbie M, Davis Marguerite L, Rice Kevin P
Department of Chemistry, Colby College, 5763 Mayflower Hill Road, Waterville, ME 04901, USA.
Biochem Biophys Res Commun. 2009 Jan 16;378(3):419-23. doi: 10.1016/j.bbrc.2008.11.042. Epub 2008 Nov 21.
The antineoplastic prodrug Cloretazine exerts its cytotoxicity via a synergism between 2-chloroethylating and carbamoylating activities that are cogenerated upon activation in situ. Cloretazine is reported here to inhibit the nucleotidyl-transferase activity of purified human DNA polymerase beta (Pol beta), a principal enzyme of DNA base excision repair (BER). The 2-chloroethylating activity of Cloretazine alkylates DNA at the O(6) position of guanine bases resulting in 2-chloroethoxyguanine monoadducts, which further react to form cytotoxic interstrand DNA crosslinks. Alkylated DNA is often repaired via BER in vivo. Inhibition of the polymerase activity of Pol beta may account for some of the synergism between Cloretazine's two reactive subspecies in cytotoxicity assays. This inhibition was only observed using agents with carbamoylating activity. Furthermore, while therapeutically relevant concentrations of Cloretazine inhibited the polymerase activity of Pol beta, the enzyme's lyase activity, which may also participate in BER, was not significantly inhibited.
抗肿瘤前药氯雷他嗪通过原位激活时共同产生的2-氯乙基化和氨基甲酰化活性之间的协同作用发挥其细胞毒性。本文报道氯雷他嗪可抑制纯化的人DNA聚合酶β（Polβ）的核苷酸转移酶活性，Polβ是DNA碱基切除修复（BER）的一种主要酶。氯雷他嗪的2-氯乙基化活性使鸟嘌呤碱基的O(6)位发生DNA烷基化，生成2-氯乙氧基鸟嘌呤单加合物，该单加合物进一步反应形成细胞毒性的链间DNA交联。烷基化的DNA在体内通常通过BER进行修复。在细胞毒性试验中，Polβ聚合酶活性的抑制可能是氯雷他嗪两个反应性亚类之间协同作用的部分原因。这种抑制仅在使用具有氨基甲酰化活性的试剂时观察到。此外，虽然具有治疗相关性的氯雷他嗪浓度抑制了Polβ的聚合酶活性，但该酶的裂合酶活性（也可能参与BER）并未受到显著抑制。
