Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada.
Biomacromolecules. 2012 May 14;13(5):1296-306. doi: 10.1021/bm2018239. Epub 2012 Apr 3.
We describe the synthesis of metal chelating polymers based on polyaspartamide and polyglutamide backbones as carriers for (111)In in radioimmunoconjugates. These polymers [PAsp(DTPA), PGlu(DTPA)] have a biotin end group and diethylenetriaminepentaacetic acid (DTPA) chelators attached to the primary amines of the diethylenetriamine (DET) pendant groups of biotin-poly{N'-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} [PAsp(DET)] and of biotin-poly{N'-[N-(2-aminoethyl)-2-aminoethyl]glutamide} [PGlu(DET)]. Like Asn-containing proteins and polypeptides, polyaspartamides undergo uncatalyzed degradation under model physiological conditions (10 mM phosphate buffer, pH 7.4, 150 mM NaCl). We studied the uncatalyzed degradation of the polyaspartamide polymers by size exclusion chromatography and found that the degradation rate was sensitive to the nature of the pendant groups. The metal-free polymer underwent somewhat slower degradation than the corresponding polymers in which the DTPA groups were saturated with Eu(3+) or In(3+), but even after 14 days, substantial fractions of the polymers survived. We conclude that these polymers undergo negligible degradation on the time scale (24-48 h) of radioimmunotherapy treatment of tumors with (111)In. From a mechanistic perspective, we note that these degradation rates are on the order of the deamidation rates reported [J. Peptide Res. 2004, 63, 426] for Asn-containing pentapeptides, with half-times on the order of 10 days, but much slower than the rapid decay (hours) reported recently [Biomaterials 2010, 31, 3707] for poly{N'-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} itself. This variation in degradation rate can be explained in terms of the influence of positive charges on the pendant group enhancing the acidity of the side-chain amide nitrogen of the aspartamide repeat unit. The DET pendant group is positively charged at pH 7, but in indium-loaded PAsp(DTPA) this charge is offset by the net negative charge of the DTPA-In complex.
我们描述了基于聚天冬酰胺和聚谷氨酸骨架的金属螯合聚合物的合成，这些聚合物作为放射性免疫偶联物中的（111）In 的载体。这些聚合物 [PAsp(DTPA)，PGlu(DTPA)] 具有生物素末端基团和二乙三胺五乙酸 (DTPA) 螯合剂，连接到生物素-聚{N'-[N-(2-氨基乙基)-2-氨基乙基]天冬酰胺}[PAsp(DET)]和生物素-聚{N'-[N-(2-氨基乙基)-2-氨基乙基]谷氨酸}[PGlu(DET)]的二乙三胺 (DET) 侧链氨基上。与含有 Asn 的蛋白质和多肽一样，聚天冬酰胺在模型生理条件下（10 mM 磷酸盐缓冲液，pH 值 7.4，150 mM NaCl）下会发生无催化降解。我们通过尺寸排阻色谱法研究了聚天冬酰胺聚合物的无催化降解，发现降解速率对侧链基团的性质敏感。金属自由聚合物的降解速度比相应的聚合物稍慢，其中 DTPA 基团被 Eu(3+)或 In(3+)饱和，但即使经过 14 天，聚合物的大部分仍得以存活。我们得出的结论是，在使用（111）In 进行肿瘤放射性免疫治疗的时间范围内（24-48 小时），这些聚合物的降解微不足道。从机制的角度来看，我们注意到这些降解速率与含有 Asn 的五肽的报道脱酰胺速率相当[J. Peptide Res. 2004, 63, 426]，半衰期在 10 天左右，但比最近报道的聚[N'-[N-(2-氨基乙基)-2-氨基乙基]天冬酰胺]本身的快速衰减（小时）慢得多[Biomaterials 2010, 31, 3707]。这种降解速率的变化可以用侧链酰胺氮的正电荷对侧链酰胺氮的影响来解释天冬酰胺重复单元。在 pH 值为 7 时，DET 侧链带正电荷，但在负载铟的 PAsp(DTPA)中，这种电荷被 DTPA-In 配合物的净负电荷抵消。
