Figure 5.
Composition of the PAMAM delivery systems of siRNA. (a) Generation 4 PAMAM-OH dendrimer. (b) Internally quaternized PAMAM to form QPAMAM-OH dendrimer with inner cationic charges. PAMAM are frequently quaternized by methyl iodide (ICH3) and the terminal surface become very positive allowing the efficient electrostatic binding/loading of negatively charged backbone of siRNA. (c) QPAMAM with different surface modifications, including the addition of acetyl group by direct reaction with acetic anhydride (Ac2O) 112, poly(ethylene glycol) (PEG) and poly-L-lysine (PLL) 113, LHRH peptide 114. This addition of polymer structures such as PEG and PLL is reported to enhance the surface positive charge and circulation of PAMAM nanoparticles. While, the conjugation to LHRH peptides confers targeting ability in PAMAM based delivery applications.