Chiba University, Chiba, Japan.
Bioconjug Chem. 2010 Jan;21(1):175-81. doi: 10.1021/bc900410q.
Poly(amidoamine) (PAMAM) dendrimers are highly branched spherical polymers that have a unique surface of primary amine groups and provide a versatile design for targeted delivery of pharmaceuticals and imaging agents. Acetylation or succinylation of surface amine groups of PAMAM dendrimer derivatives is frequently performed to reduce nonspecific uptake. However, since targeting molecules, drugs/imaging agents, and acylating reagents react with the amine groups on dendrimer, such modification may limit the number of targeting molecules and/or drugs or may result in insufficient charge reduction. In this study, a gamma-glutamyl PAMAM dendrimer was designed and synthesized as a new precursor for targeting device. The relationship between surface electrical properties of the PAMAM dendrimer derivatives and pharmacokinetics was also determined. A PAMAM dendrimer (generation 4.0) was modified with a small number of Bolton-Hunter reagent to prepare Phe-P (pI 9.2). The amine residues of Phe-P were gamma-glutamylated to prepare Glu-P (pI 7.1). The alpha-amine residues of Glu-P were then acetylated or succinylated to prepare Ac-Glu-P (pI 5.3) or Suc-Glu-P (pI 3.6). For comparison, Phe-P was acetylated or succinylated to prepare Ac-P (pI 6.0) or Suc-P (pI 5.1). All the PAMAM dendrimer derivatives exhibited similar molecular size (7.2 to 7.8 nm) except for Ac-P (5.1 nm). The biodistribution studies were performed after radioiodination of each PAMAM dendrimer derivative with Na[(125)I]I. When injected intravenously to mice, both [(125)I]Ac-P and [(125)I]Suc-P exhibited prolonged radioactivity levels in the blood and significantly lower hepatic and renal radioactivity levels than those of [(125)I]Phe-P. Both [(125)I]Glu-P and [(125)I]Ac-Glu-P showed residence times in the blood similar to those of [(125)I]Ac-P and [(125)I]Suc-P. However, [(125)I]Glu-P also registered higher radioactivity levels in the kidney. High hepatic and renal radioactivity levels were observed with highly anionic [(125)I]Suc-Glu-P. These results indicate that, while the manipulation of pI between 5 to 6 would be appropriate to enhance blood retention and reduce renal and hepatic uptake, the amount of primary amine residues on dendrimer surface may also play a crucial role in their renal uptake. The findings in this study show that gamma-glutamyl PAMAM dendrimers would constitute versatile precursors to prepare PAMAM dendrimer-based targeting devices due to their neutral molecular charge (pI 7.1) and the presence of a large number of alpha-amine residues available for conjugation of targeting molecules and drugs/imaging agents.
聚（酰胺-胺）（PAMAM）树状聚合物是高度支化的球形聚合物，具有独特的一级胺表面，为药物和成像剂的靶向递送提供了多功能的设计。PAMAM 树状聚合物衍生物的表面胺基的乙酰化或琥珀酰化经常被用来减少非特异性摄取。然而，由于靶向分子、药物/成像剂和酰化试剂与树状聚合物上的胺基反应，这种修饰可能会限制靶向分子和/或药物的数量，或者可能导致电荷减少不足。在这项研究中，设计并合成了一种γ-谷氨酰 PAMAM 树状聚合物作为新型靶向装置的前体。还确定了 PAMAM 树状聚合物衍生物的表面电特性与药代动力学之间的关系。用少量的 Bolton-Hunter 试剂对 PAMAM 树突状聚合物（第 4.0 代）进行修饰，制备出 Phe-P（pI9.2）。Phe-P 的胺残基被γ-谷氨酰化以制备 Glu-P（pI7.1）。然后，Glu-P 的α-胺残基被乙酰化或琥珀酰化，制备 Ac-Glu-P（pI5.3）或 Suc-Glu-P（pI3.6）。作为比较，Phe-P 被乙酰化或琥珀酰化，制备 Ac-P（pI6.0）或 Suc-P（pI5.1）。除了 Ac-P（5.1nm）之外，所有 PAMAM 树状聚合物衍生物都表现出相似的分子大小（7.2 至 7.8nm）。用 Na[（125）I]I 对每种 PAMAM 树状聚合物衍生物进行放射性碘标记后，进行了体内分布研究。当静脉注射到小鼠体内时，[（125）I]Ac-P 和 [（125）I]Suc-P 在血液中的放射性水平均延长，肝和肾的放射性水平明显低于 [（125）I]Phe-P。[（125）I]Glu-P 和 [（125）I]Ac-Glu-P 在血液中的停留时间与 [（125）I]Ac-P 和 [（125）I]Suc-P 相似。然而，[（125）I]Glu-P 在肾脏中的放射性水平也较高。高度阴离子[（125）I]Suc-Glu-P 观察到高肝和肾放射性水平。这些结果表明，虽然在 5 到 6 之间操纵 pI 将有助于增强血液保留并减少肾和肝摄取，但树突状聚合物表面的初级胺残基数量也可能在其肾摄取中起关键作用。本研究结果表明，由于γ-谷氨酰 PAMAM 树状聚合物的中性分子电荷（pI7.1）和大量α-胺残基的存在，可为靶向分子和药物/成像剂的连接提供条件，因此γ-谷氨酰 PAMAM 树状聚合物将成为制备基于 PAMAM 树状聚合物的靶向装置的多功能前体。
