SYNTHESIS OF NOVEL POLYAMPHOLYTE COMB-TYPE COPOLYMERS CONSISTING OF APOLY(L-LYSINE) BACKBONE AND HYALURONIC-ACID SIDE-CHAINS FOR A DNA CARRIER

The polyampholyte comb-type copolymers consisting of a poly(L-lysine) (PLL) main chain, a DNA binding site, and hyaluronic acid (HA) side ch ains, cell-specific ligands, have been prepared as the DNA carrier tar geting sinusoidal endothelial cells of liver. The reducing end of HA a nd E-amino groups of PLL were covalently coupled by reductive aminatio n to obtain the resulting comb-type copolymers (PLL-graft-HA). The cha in length of HA was controlled by the enzymatic hydrolysis of high-mol ecular weight HA. Since HA formed polyion complexes with PLL, the coup ling reaction was carried out with high-ionic strength media to suppre ss polyion complex formation. The reaction proceeded in a homogeneous system, leading to a high efficiency of coupling (>70%) of HA onto the PLL backbone. By using the enzymatic hydrolysis of HA and the reducti ve amination reaction between HA and PLL with high-ionic strength medi a, it is possible to prepare the various comb-type copolymers with a d efined density and a defined length of HA side chains. Furthermore, we also find that these polyampholyte comb-type copolymers vary their as sembling structure in water in response to two kinds of environmental factors, i.e., ionic strength and pH. Finally, a H-1 NMR study reveals that the PLL backbone efficiently interacts with DNA molecules despit e the presence of HA side chains having negative charges.