The effluent was monitored by measuring the absorbance at 675 nm. The reaction was stirred overnight at room temperature in the dark and was purified by size exclusion chromatography (SEC)-HPLC with an analytical Zorbax GF-250 column (250 × 4.6 mm) that was eluted with 20 mM Na 2HPO 4 and 130 mM NaCl (pH 7.2) containing 20% (v/v) of ACN at a flow rate of 0.3 mL/min. PEG–NH 2 (4.37 mg, 0.874 μmol) was solubilized in 300 μL of 0.1 M Na 2HPO 4, 0.15 M NaCl, pH 8.0, and 1 equiv of dye, previously dissolved in anhydrous DMSO at a concentration of 10 mg/mL. The synthesis and characterization of the novel PEG–Cy5.5 conjugate was carried out as follows. (10) By using an actual drug, we, therefore, confer a clinical meaning to the proposed strategy. Finally, we validate the hypothesis by measuring the placental uptake of PEG–drug conjugates that contain two different molecular weights of PEG, and a drug (haloperidol) that can freely penetrate the placental barrier and reach the fetus when administered in the nonconjugated form.
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Then, using a fluorescently tagged PEG conjugate (PEG–cyanine-5.5 (Cy5.5)), we probe the ability of conjugation to prevent cellular uptake of the free Cy5.5 dye by the placenta. First, we evaluate the biocompatibility of PEG with the placental tissue by measuring changes in the proliferation, apoptosis, necrosis, and the secretory function in human term placental explants after exposure to PEG. This hypothesis is assessed at three levels.
In this Communication, we propose and validate the concept of PEG–drug conjugation via a nondegradable linker as a means to restrict drugs to the maternal bloodstream, thus preventing fetal transfer ( Figure 1).
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