title: 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.
authors.forename: Sung Hoon
authors.initials: SH
authors.lastname: Kim
authors.forename: Zeynep
authors.initials: Z
authors.lastname: Madak-Erdogan
authors.affiliation: §IBS Center for Soft and Living Matter and UNIST, Ulsan 689-798, South Korea.
authors.forename: Sung Chul
authors.initials: SC
authors.lastname: Bae
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Carlson
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Mayne
authors.affiliation: §IBS Center for Soft and Living Matter and UNIST, Ulsan 689-798, South Korea.
authors.forename: Steve
authors.initials: S
authors.lastname: Granick
authors.forename: Benita S
authors.initials: BS
authors.lastname: Katzenellenbogen
authors.forename: John A
authors.initials: JA
authors.lastname: Katzenellenbogen
mesh_terms: D002232:Carbocyanines / Q000737:chemistry; D050091:Dendrimers / Q000737:chemistry* / Q000494:pharmacology; D004337:Drug Carriers / Q000737:chemistry*; D004997:Ethinyl Estradiol / Q000737:chemistry* / Q000494:pharmacology; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000737:chemistry; D015870:Gene Expression; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D061986:MCF-7 Cells / Q000187:drug effects; D009682:Magnetic Resonance Spectroscopy; D008856:Microscopy, Fluorescence; D010421:Pentanoic Acids / Q000737:chemistry; D010636:Phenols / Q000737:chemistry; D011960:Receptors, Estrogen / Q000378:metabolism; D012235:Rhodamines / Q000737:chemistry
chemical_list: D002232:Carbocyanines; D050091:Dendrimers; D004337:Drug Carriers; D005456:Fluorescent Dyes; D008024:Ligands; C104700:PAMAM Starburst; D010421:Pentanoic Acids; D010636:Phenols; D011960:Receptors, Estrogen; D012235:Rhodamines; C085321:cyanine dye 5; C000622346:diphenolic acid; D004997:Ethinyl Estradiol; C005358:tetramethylrhodamine