Fairlamb A H, Carter N S, Cunningham M, Smith K
Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, UK.
Mol Biochem Parasitol. 1992 Jul;53(1-2):213-22. doi: 10.1016/0166-6851(92)90023-d.
An arsenical resistant cloned line of Trypanosoma brucei brucei was derived from a parent sensitive clone by repeated selection in vivo with the pentavalent melaminophenyl arsenical, sodium melarsen. The melarsen-resistant line was tested in vivo in mice against a range of trypanocidal compounds and found to be cross-resistant to the trivalent arsenicals, melarsen oxide, melarsoprol and trimelarsen (33, 67 and 122-fold, respectively). A similar pattern of cross-resistance was found in vitro using a spectrophotometric lysis assay (greater than 200-fold resistance to melarsen oxide and greater than 20-fold resistance to both trimelarsen and melarsoprol). Both lines were equally sensitive to lysis by the lipophilic analogue phenylarsine oxide in vitro, suggesting that the melamine moiety is involved in the resistance mechanism. Although trypanothione has been reported to be the primary target for trivalent arsenical drugs [1], levels of trypanothione and glutathione were not significantly different between the resistant and sensitive lines. Statistically significant differences were found in the levels of trypanothione reductase (50% lower in the resistant clone) and dihydrolipoamide dehydrogenase (38% higher in the resistant clone). However, the Km for trypanothione disulphide, the Ki for the competitive inhibitor Mel T (the melarsen oxide adduct with trypanothione) and the pseudo-first order inactivation rates with melarsen oxide were the same for trypanothione reductase purified from both clones. The melarsen-resistant line also showed varying degrees of cross-resistance to the diamidines: stilbamidine (38-fold), berenil (31.5-fold), propamidine (5.7-fold) and pentamidine (1.5-fold). Cross-resistance correlates with the maximum interatomic distance between the amidine groups of these drugs and suggests that the diamidines and melaminophenyl arsenicals are recognised by the same transport system.
用五价的三聚氰胺基苯胂制剂美拉胂醇钠在体内对布氏布氏锥虫的一个亲本敏感克隆进行反复筛选，从而获得了一个耐胂克隆株。对该耐美拉胂株在小鼠体内进行了一系列杀锥虫化合物的测试，发现其对三价胂制剂氧化美拉胂、美拉胂醇和三美拉胂具有交叉抗性（分别为33倍、67倍和122倍）。使用分光光度法裂解试验在体外也发现了类似的交叉抗性模式（对氧化美拉胂的抗性大于200倍，对三美拉胂和美拉胂醇的抗性大于20倍）。两株在体外对亲脂性类似物氧化苯胂的裂解同样敏感，这表明三聚氰胺部分参与了抗性机制。尽管有报道称锥虫硫醇是三价胂药物的主要靶点[1]，但耐胂株和敏感株之间的锥虫硫醇和谷胱甘肽水平并无显著差异。在锥虫硫醇还原酶水平（耐胂克隆株中低50%）和二氢硫辛酰胺脱氢酶水平（耐胂克隆株中高38%）上发现了统计学上的显著差异。然而，从两个克隆株中纯化得到的锥虫硫醇还原酶对锥虫硫醇二硫化物的Km值、对竞争性抑制剂Mel T（氧化美拉胂与锥虫硫醇的加合物）的Ki值以及对氧化美拉胂的假一级失活速率是相同的。耐美拉胂株对双脒类药物也表现出不同程度的交叉抗性：对司替巴脒（38倍）、贝尼尔（31.5倍）、丙脒（5.7倍）和喷他脒（1.5倍）。交叉抗性与这些药物双脒基团之间的最大原子间距离相关，这表明双脒类药物和美拉明苯胂制剂被相同的转运系统识别。
