OVERCOMING ALKYLTRANSFERASE-RELATED DRUG RESISTANCE

肿瘤细胞耐药机制降低了化疗的有效性， 化疗药物DNA修复酶的活性是 耐药性的原因，特别是对亚硝基脲（如BCNU）， 相关的烷基化剂。BCNU在O 6位形成加合物， 鸟嘌呤，加合物随后与胞嘧啶残基反应， 相反的链引起对细胞有细胞毒性的交联。 这些加合物由DNA修复酶06-烷基鸟嘌呤DNA修复 烷基转移酶（AGT），在反应中不可逆地失活 酵素酶的恢复需要合成新的 分子。在临床前研究中， 与BCNU的细胞毒性以及BCNU的消耗相关。 酶增强了药物的有效性。AGT的特异性抑制剂， O 6-苄基鸟嘌呤（BG），已被证明消耗AGT活性，在- 体外和体内临床前研究，迄今已被证明， 相对无毒。该补助金提出了一系列第一阶段和 II期临床试验旨在确定AGT耗竭是否 BG在肿瘤组织中的应用是可行和安全的， BG和BCNU的组合可以增强已知具有 AGT水平高，但对BCNU反应差。一个关键特征 这些研究的一个重要方面是结合了新的技术， 直接测量肿瘤组织中的AGT活性， 这些水平与BG的动力学。最初的I期试验是 专门设计来确定生化调节剂量 (BMD)消耗肿瘤组织AGT所需的BG， BG的药代动力学，以评估外周血单个核细胞 AGT水平作为肿瘤组织AGT的可能替代物，以及 评估BCNU联合BMD的最大耐受剂量 的BG。该试验之后将进行两项转移性II期试验， 恶性黑色素瘤患者，多发性骨髓瘤患者， BG + BCNU联合治疗的临床疗效 测试.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 和临床前研究预测的BCNU组合。这 在细胞水平监测药效学事件的方法 有望成为未来细胞毒性药物开发的原型。

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.