γ-Glutamyl PAMAM Dendrimer as Versatile Precursor for Dendrimer-Based Targeting Devices

Abstract

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.

Designing Dendrimers for Drug Delivery and Imaging: Pharmacokinetic Considerations

“…Recently, Kaminskas et al studied the biodistribution of anionic arylsulfonate or succinate-modified lysine dendrimers G3-4 (95). The anionic arylsulfonate-lysine dendrimers (MW 10-14 kDa) were highly retained in the blood circulation with a five-fold increase in half-life more than succinate-lysine dendrimers (MW 7.4 kDa), which were predominately eliminated by urinary excretion similar to succinate-PAMAM G4 dendrimers (111). As expected, the more anionic charge and greater size of the arylsulfonate-lysine dendrimers, the higher their uptake in the RES, which might be due to the scavenger receptor-mediated process as previously described (89,95).…”

Synthesis of efficient gene delivery systems by grafting pegylated alkylcarboxylate chains to PAMAM dendrimers: Evaluation of transfection efficiency and cytotoxicity in cancerous and mesenchymal stem cells

“…Multifunctional dendrimers were prepared by other researchers in order to target specific cells, 11,12 reduce cytotoxicity, 8,13,14 enhance cellular uptake, and modify carrier pharmacokinetics. 9,15 Previously, it was shown that the alkylcarboxylate substitution of primary amines of polyethyleneimine (PEI) and polypropyleneimine (PPI) would enhance transfection efficiency while maintaining low toxicity.…”

Covalent Immobilization of Trypsin on a Novel Aldehyde-Terminated PAMAM Dendrimer

“…In most cases of the applications of dendrimers, molecules are covalently linked to dendrimer surface or coupled with the functional components in the branched structure of dendrimer. [13][14][15][16][17] The essential element in designing a dendrimer-protein conjugate is the functional end groups present on the surface of dendrimer, and the functional groups on the proteins to be coupled. PAMAM dendrimers have different functional groups including amine, carboxylate, hydroxyl, ester and other possible moieties.…”