Delivery of PAMAM dendrimers and dendriplexes across natural barriers (blood–brain barrier and placental barrier) in healthy pregnant mice

Gene therapy is an important tool for treating fetal diseases that allows for the delivery and integration of therapeutic genes into the genome of cells carrying mutations. Nanomolecules, like PAMAM dendrimers, have recently come into wider use for carrying vectors as they have several advantages over viral vectors. Namely, (1) tunable size and surface chemistry, (2) uniform size, (3) the ability to target specific tissues, and (4) the ability to carry large biomolecules and drugs. Recently, we demonstrated that 4th generation (G4) PAMAM dendrimer with a cystamine core and a non-toxic surface having 90% –OH and 10% –NH₂ groups (D-Cys) could cross the blood–brain barrier following injection into the bloodstream. In the current study, as a proof of concept, we delivered the dendrimers alone (D-Cys) tagged with Cy5.5 (D-Cys-cy5.5) to healthy pregnant C57BL/6J mice to determine the fate of these dendrimers in the pregnant mice as well as in the fetus. Systematic diffusion of the D-Cys-cy5.5 was evaluated on gestational day 17 (3 days after injection) using in vivo imaging. This revealed that the dendrimer was taken up into circulation and away from the injection site. Analysis of sections by fluorescence microscopy showed that D-Cys-cy5.5 was able to successfully cross the maternal blood–brain barrier. However, analysis of the fetal brains failed to detect dendrimers in the central nervous system (CNS). Instead, they appeared to be retained in the placenta. This is one of the first studies to analyze the distribution of surface-modified PAMAM dendrimer in the pregnant mouse and fetus following systemic injection.