Yao Shijie, Petluru Pavankumar, Parker Aulma, Ding Daoyuan, Chen Xinghai, Huang Qiuli, Kochat Harry, Hausheer Frederick
BioNumerik Pharmaceuticals, Inc., 8122 Datapoint Drive, Suite 1250, San Antonio, TX, 78229, USA.
Cancer Chemother Pharmacol. 2015 Apr;75(4):719-28. doi: 10.1007/s00280-015-2686-y. Epub 2015 Jan 30.
Camptothecins contain a lactone ring that is necessary for antitumor activity, and hydrolysis of the lactone ring yields an inactive carboxylate species. Human serum albumin (HSA) and alpha-1 acid glycoprotein (AGP) are clinically significant plasma proteins thought to have important roles in camptothecin lactone stability. Herein, we examined the effect(s) of HSA and AGP on the lactone stability of Karenitecin, a novel, highly lipophilic camptothecin analog, currently at the phase 3 clinical testing stage.
An AGP-immobilized protein column was used to develop HPLC methods to evaluate the effect(s) of physiologically relevant HSA and AGP concentrations on the lactone/carboxylate ratio and hydrolysis kinetics of Karenitecin, camptothecin (CPT), and topotecan (TPT).
Physiologically relevant concentrations of HSA and AGP substantially slowed Karenitecin lactone hydrolysis. AGP was notably more effective at protecting the Karenitecin lactone from hydrolysis than HSA was in promoting hydrolysis. Additionally, AGP reversed the hydrolysis of partially hydrolyzed Karenitecin lactone. In contrast, HSA and AGP had minimal effects on hydrolysis of the TPT lactone, while the AGP/HSA solutions dramatically accelerated hydrolysis of the CPT lactone.
AGP strongly enhances the lactone stability of Karenitecin. Since Karenitecin is highly protein-bound in human plasma and exhibits greater lactone stability, relative to other camptothecins, in patient plasma samples, this newly identified role of AGP in promoting lactone stability may have important implications for the design of more effective anticancer agents within the Karentecin™ and camptothecin classes.
喜树碱类药物含有一个内酯环，该内酯环是抗肿瘤活性所必需的，内酯环水解会产生无活性的羧酸盐形式。人血清白蛋白（HSA）和α-1酸性糖蛋白（AGP）是具有临床意义的血浆蛋白，被认为在喜树碱内酯稳定性中起重要作用。在此，我们研究了HSA和AGP对卡瑞立辛内酯稳定性的影响，卡瑞立辛是一种新型的、高度亲脂性的喜树碱类似物，目前处于3期临床试验阶段。
使用AGP固定化蛋白柱开发HPLC方法，以评估生理相关浓度的HSA和AGP对卡瑞立辛、喜树碱（CPT）和拓扑替康（TPT）的内酯/羧酸盐比率及水解动力学的影响。
生理相关浓度的HSA和AGP显著减缓了卡瑞立辛内酯的水解。AGP在保护卡瑞立辛内酯不被水解方面比HSA在促进水解方面明显更有效。此外，AGP使部分水解的卡瑞立辛内酯发生逆水解。相比之下，HSA和AGP对TPT内酯的水解影响极小，而AGP/HSA溶液显著加速了CPT内酯的水解。
AGP强烈增强了卡瑞立辛的内酯稳定性。由于卡瑞立辛在人血浆中高度与蛋白结合，并且相对于其他喜树碱类药物，在患者血浆样本中表现出更高的内酯稳定性，AGP在促进内酯稳定性方面这一新发现的作用可能对设计更有效的卡瑞立辛类和喜树碱类抗癌药物具有重要意义。
