Ligand Accessibility and Bioactivity of a Hormone鈥揇endrimer Conjugate Depend on pH and pH History

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• 作者：Sung Hoon Kim ; Zeynep Madak-Erdogan ; Sung Chul Bae ; Kathryn E. Carlson ; Christopher G. Mayne ; Steve Granick ; Benita S. Katzenellenbogen ; John A. Katzenellenbogen
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：August 19, 2015
• 年：2015
• 卷：137
• 期：32
• 页码：10326-10335
• 全文大小：776K
• ISSN：1520-5126

文摘

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鈥揹endrimer 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 (17伪-ethynylestradiol and diphenolic acid). Collisional quenching and time-resolved fluorescence anisotropy experiments with TMR鈥揚AMAM 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鈥揚AMAM conjugation) to 4.5 (e.g., endosome/lysosome) and through 6.5 (e.g., hypoxic environment) back to pH 8.5, the 17伪-ethynylestradiol鈥?and diphenolic acid鈥揚AMAM 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鈥揹endrimer 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.