Janowski B, Fischer G
Max-Planck-Society, Research Unit Enzymology of the Peptide Bond, Halle, Germany.
Bioorg Med Chem. 1997 Jan;5(1):179-86. doi: 10.1016/s0968-0896(96)00198-8.
Cyclosporin A (CsA) is a tight-binding inhibitor of the peptidyl-prolyl cis/trans isomerase (PPIase) activity of human cytosolic cyclophilin (Cyp18), the putative receptor for immunosuppressive effects of the drug. We examined the influence of cremophor EL (CEL), a surfactant that has found wide use for CsA formulation, on the kinetics of inhibition of the enzyme by CsA. Stock solutions of CsA in CEL administered into aqueous PPIase assays led to inhibition kinetics reminiscent to those of CsA dissolved in tetrahydrofurane, but caused an increase in the final Ki value of about sevenfold at 0.33% (v/v) CEL. The diminished drug affinity to Cyp18 obtained in experiments using CEL could also be established for analogues of cyclosporin A such as [Ala2]-Cs,[Thr2]-Cs, and [MeAla6]-Cs, exhibiting Ki values 13-16-fold higher than in the absence of CEL. In addition, the time-dependent pattern of inhibition indicate only a minor population of bioactive conformation of CsA in bulky CEL. Conformational reshuffling of the bioinactive [cis-MeLeu9-MeLeu10]-Cs to create an inhibitory fraction of the drug was delayed in the presence of CEL micelles, despite potential ability of micelles exists to catalyze cis/trans isomerizations of N-alkyl peptide bonds. The pattern of inhibition when using cyclophilins distinct in their amino acid sequences to the human enzyme can be rationalized in terms of exceptional high structural requirements of human Cyp18 for the drug conformation.
环孢素A（CsA）是一种紧密结合的人胞质亲环蛋白（Cyp18）肽基脯氨酰顺/反异构酶（PPIase）活性抑制剂，Cyp18被认为是该药物免疫抑制作用的受体。我们研究了聚氧乙烯蓖麻油（CEL）（一种在CsA制剂中广泛使用的表面活性剂）对CsA抑制该酶动力学的影响。将CsA在CEL中的储备溶液加入到水性PPIase测定中，其抑制动力学让人联想到溶解在四氢呋喃中的CsA，但在0.33%（v/v）的CEL存在下，最终的Ki值增加了约7倍。在使用CEL的实验中获得的药物对Cyp18亲和力的降低，对于环孢素A的类似物如[Ala2]-Cs、[Thr2]-Cs和[MeAla6]-Cs也同样成立，这些类似物的Ki值比不存在CEL时高13 - 16倍。此外，时间依赖性抑制模式表明，在大量的CEL中，只有少量的CsA具有生物活性构象。尽管胶束具有催化N - 烷基肽键顺/反异构化的潜在能力，但在CEL胶束存在下，无生物活性的[顺式 - MeLeu9 - MeLeu10]-Cs构象重排以产生药物抑制部分的过程被延迟。当使用氨基酸序列与人酶不同的亲环蛋白时，抑制模式可以根据人Cyp18对药物构象极高的结构要求来解释。
