Effect of Pendant Group Structure on the Hydrolytic Stability of Polyaspartamide Polymers under Physiological Conditions

Abstract

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.

Supermacroporous chemically cross-linked poly(aspartic acid) hydrogels

“…PASP is biocompatible because of its chemical structure [1,2]. It is proved to be biodegradable, but its degradation rate depends on the type and degree of substitution [3]. Its precursor anhydride, polysuccinimide (PSI), reacts with primary amines under mild reaction conditions even without catalyst [1,4].…”

A High-Sensitivity Lanthanide Nanoparticle Reporter for Mass Cytometry: Tests on Microgels as a Proxy for Cells

“…In our model system, SAv serves as the model biomarker; thus, we need an MCP with biotin end-functionality as the recognition element. As an MCP, we employ a biotin-end-capped polyaspartamide synthesized as described previously, 41 with diethylenetriaminepentaacetic acid (DTPA) groups attached to each of its 50 pendant groups. Details are provided in the Supporting Information.…”

“…41 Details are provided in the Supporting Information. The synthesis and characterization of biotinylated NaHoF 4 nanoparticles are also described in the Supporting Information.…”

Trilayer micelles for combination delivery of rapamycin and siRNA targeting Y-box binding protein-1 (siYB-1)

“…The next day, 10 µl of micelle formulations containing either: empty NP, siYB-1/NP, RAP formulated with DMSO (RAP/DMSO), RAP/NP, or siYB-1/RAP/NP were added to wells at a final concentration of 0.01–1 nM RAP. The cells were incubated for another 24 or 48 h before measuring cell viability with the resazurin assay [36]. …”