Brain gene delivery using histidine and arginine-modified dendrimers for ischemic stroke therapy

Polyamidoamine dendrimer has been studied as an efficient gene carrier. Due to its anti-inflammatory properties, polyamidoamine is a useful gene carrier, especially for inflammatory diseases. However, the commonly used polyamidoamine generation 6 dendrimer (PG6) has higher cytotoxicity than low-molecular weight polyamidoamines, which limits its applications. Therefore, early-generation polyamidoamine dendrimers, such as generation 2 (PG2), have been investigated as an alternative to PG6, although PG2 has a lower transfection efficiency. In this study, to improve gene delivery efficiency, histidine and arginine were conjugated on the primary amines of PG2, synthesizing PG2HR. The gene delivery efficiency of PG2HR was higher than that of PG2 or of PG2 conjugated with only arginine (PG2R), which may be due to higher cellular uptake and endosomal escape of the plasmid DNA (pDNA)/PG2HR complex. In addition, PG2HR had lower cytotoxicity than polyethylenimine (25 kDa, PEI25k), PG2, and PG2R. Mechanism studies showed that PG2HR delivered pDNA into the cells mainly by clathrin-independent endocytosis and partly by macropinocytosis. The therapeutic potential of PG2HR-mediated gene delivery was evaluated in middle cerebral artery occlusion (MCAO)-reperfusion stroke animal models. Heme oxygenase-1 (HO-1) plasmid was delivered into the brain by local injection. The results showed that PG2HR had higher gene delivery efficiency in the brain than did PEI25k, PG2, or PG2R. Furthermore, compared to the pHO-1/PEI25k, pHO-1/PG2, and pHO-1/PG2R complexes, the pHO-1/PG2HR complex had reduced apoptosis levels and infarct sizes in ischemic brains. Therefore, because of its low cytotoxicity and high gene delivery efficiency, PG2HR may be useful for gene therapy of inflammatory diseases including ischemic stroke.