Ligand Accessibility and Bioactivity of a Hormone-Dendrimer Conjugate Depend on pH and pH History.

Abstract

Estrogen conjugates with a polyamidoamine (PAMAM) dendrimer have shown remarkably selective regulation of the nongenomic actions of estrogens in target cells. In response to pH changes, however, these estrogen-dendrimer conjugates (EDCs) display a major morphological transition that alters the accessibility of the estrogen ligands that compromises the bioactivity of the EDC. A sharp break in dynamic behavior near pH 7 occurs for three different ligands on the surface of a PAMAM-G6 dendrimer: a fluorophore (tetramethylrhodamine [TMR]) and two estrogens (17α-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR-PAMAM revealed high ligand shielding above pH 7 and low shielding below pH 7. Furthermore, when the pH was cycled from 8.5 (conditions of ligand-PAMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17α-ethynylestradiol- and diphenolic acid-PAMAM conjugates experienced a dramatic, irreversible loss in cell stimulatory activity; dynamic NMR studies indicated that the hormonal ligands had become occluded within the more hydrophobic core of the PAMAM dendrimer. Thus, the active state of these estrogen-dendrimer conjugates appears to be metastable. This pH-dependent irreversible masking of activity is of considerable relevance to the design of drug conjugates with amine-bearing PAMAM dendrimers.

DOI: 10.1021/jacs.5b05952

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Cite this paper

@article{Kim2015LigandAA, title={Ligand Accessibility and Bioactivity of a Hormone-Dendrimer Conjugate Depend on pH and pH History.}, author={Sung Hoon Kim and Zeynep Madak-Erdogan and Sung Chul Bae and Kathryn E. Carlson and Christopher G. Mayne and Steve Granick and Benita S Katzenellenbogen and John A. Katzenellenbogen}, journal={Journal of the American Chemical Society}, year={2015}, volume={137 32}, pages={10326-35} }