OVERCOMING ALKYLTRANSFERASE-RELATED DRUG RESISTANCE

肿瘤细胞耐药机制降低阿司匹林的疗效 化疗药物。DNA修复酶的活性是一个主要的 抗药性的原因，特别是对亚硝脲(如BCNU)和 相关烷基化剂。BCNU在O6位形成加合物 鸟嘌呤，加合物随后与胞嘧啶残基反应 相反的链，产生对细胞有细胞毒性的交联链。 这些加合物被DNA修复酶06-烷基鸟嘌呤DNA修复 烷基转移酶(AGT)，在一个反应中不可逆转地使 酵素。酶的恢复需要合成新的 分子。在临床前研究中，该酶的细胞内活性 与BCNU的细胞毒性和细胞耗竭密切相关 酶能增强药物的有效性。AGT的一种特异性抑制剂， 研究表明，O6-苄基鸟嘌呤(BG)可耗尽体内AGT活性。 体外和体内的临床前研究，到目前为止已经证明 相对无毒。这笔赠款提出了一系列第一阶段和 旨在确定AGT耗竭的II期临床试验 在肿瘤组织中应用BG是可行和安全的，以及是否 联合应用BG和BCNU可增强对已知有 AGT水平较高，但对BCNU的反应较差。一项关键功能 这些研究中的一项是结合了新的技术， 直接测定肿瘤组织中AGT活性，并进行相关分析 这些水平与血糖的动力学有关。最初的第一阶段试验是 专为确定生化调节剂量而设计 (BMD)耗尽肿瘤组织AGT所需的BG，以评估 评价外周血单核细胞的BG药代动力学 AGT水平作为肿瘤组织AGT的可能替代物 结合骨密度评估BCNU的最大耐受量 BG的。这项试验之后将有两个第二阶段的转移性试验 恶性黑色素瘤患者，在多发性骨髓瘤患者中， BG联合BCNU的临床疗效是什么？ 测试过。进一步的I期试验将评估BCNU的剂量递增 使用干细胞拯救作为避免BG骨髓毒性的手段 以及根据临床前研究预测的BCNU组合。这 在细胞水平监测药效事件的方法成立 有望成为未来细胞毒剂发展的原型。

Tumor cell resistance mechanisms reduce the effectiveness of chemotherapeutic drugs. The activity of DNA repair enzymes are a major cause of resistance, especially to the nitrosoureas (such as BCNU) and related alkylating agents. BCNU forms adducts at the O6 position of guanine, and the adducts subsequently react with cytosine residues on the opposite strand causing crosslinks that are cytotoxic to cells. These adducts are repaired by the DNA repair enzyme 06-alkylguanine DNA alkyltransferase (AGT), in a reaction that irreversibly inactivates the enzyme. Restoration of the enzyme requires the synthesis of new molecules. In preclinical studies, intracellular activity of the enzyme correlates well with the cytotoxicity of BCNU, and depletion of the enzyme enhances effectiveness of the drug. A specific inhibitor of AGT, O6-benzylguanine (BG), has been shown to deplete AGT activity in in- vitro and in-vivo preclinical studies, and to date has been shown to be relatively non-toxic. This grant proposes a series of Phase I and Phase II clinical trials designed to establish whether AGT depletion in tumor tissue with BG is feasible and safe, and whether the combination of BG and BCNU can enhance efficacy in tumors known to have high levels of AGT, but whose responses to BCNU are poor. A key feature of these studies is the incorporation of novel techniques with which to measure AGT activity directly in tumor tissue, and to correlate these levels with the kinetics of BG.The initial Phase I trial is designed specifically to determine the biochemical modulatory dose (BMD) of BG required to deplete tumor tissue AGT, to assess the pharmacokinetics of BG, to evaluate peripheral blood mononuclear cell levels of AGT as a possible surrogate of tumor tissue AGT, and to assess the maximum tolerated dose of BCNU in combination with the BMD of BG. This trial will be followed by two Phase II trials in metastatic malignant melanoma patients, and in patients with multiple myeloma, in which the clinical efficacy of the BG plus BCNU combination will be tested. A further Phase I trial will assess the dose escalation of BCNU using stem cell rescue as a means of avoiding myelotoxicity of the BG and BCNU combination which is predicted from preclinical studies. This approach of monitoring pharmacodynamic events at a cellular level holds promise as a prototype for the future development of cytotoxic agents.