| Abstract
| - Dendrimers have emerged as promising multifunctional nanomaterials for drug delivery due to theirwell-defined size and tailorability. We compare two schemes to obtain methylprednisolone (MP)−polyamidoamine dendrimer (PAMAM-G4-OH) conjugate. Glutaric acid (GA) was used as a spacer tofacilitate the conjugation. In scheme A, PAMAM-G4-OH was first coupled to GA and then furtherconjugated with MP to obtain PAMAM-G4−GA−MP conjugates. This scheme yields a lower conjugationratio of MP, presumably because of lower reactivity and steric hindrance for the steroid at the crowdeddendrimer periphery. In scheme B, this steric hindrance was overcome by first preparing the MP−GA conjugate, which was then coupled to the PAMAM-G4-OH dendrimer. The 1H NMR spectrum ofthe conjugate from scheme B indicates a conjugation of 12 molecules of MP with the dendrimer,corresponding to a payload of 32 wt %. In addition, conjugates were further fluorescent-labeled withfluoroisothiocynate (FITC) to evaluate the dynamics of cellular entry. Flow cytometry and UV/visiblespectroscopic analysis showed that the conjugate is rapidly taken up inside the cell. Fluorescenceand confocal microscopy images on A549 human lung epithelial carcinoma cells treated with conjugatesshow that the conjugate is mostly localized in cytosol. MP−GA−dendrimer conjugate showedcomparable pharmacological activity to free MP, as measured by inhibition of prostaglandin secretion.These conjugates can potentially be further conjugated with a targeting moiety to deliver the drugsto specific cells in vivo.
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