A green and facile approach for synthesis of guanidine-rich hyperbranched polymers and the preliminary studies on their bioactivities

• Guanidine-rich branched polymers are synthesized by a two-step procedure. • Guanidine-rich branched polymers are synthesized without using organic solvents. • Guanidine-rich branched polymers promote free drug uptake by cancer cells. • Guanidine-rich branched polymers promote free drug penetration into tumor tissues. • Co-administration of the branched polymers enhances anticancer effect of free drugs. Guanidine-rich macromolecules show diverse bioactivities, and guanidine group-rich dendritic macromolecules often exhibit superior biological properties compared to linear ones with the same or similar number of guanidine groups. However, guanidine-rich dendritic macromolecules were usually synthesized through tedious and expensive procedures, in which toxic organic solvents had to be used. In the present work, we developed a two-step method to synthesize hyperbranched polymers with periphery guanidine groups without using any organic solvents. Hyperbranched polylysines were first synthesized by thermal polymerization of L-lysine hydrochloride in the presence of KOH. The molecular weight of the hyperbranched polylysines increased with polymerization time. Guanidine-rich hyperbranched polymers were then prepared by treating the hyperbranched polylysines with 1H-pyrazole-1-carboxamidine hydrochloride in the presence of a base using water as the solvent, in which the free amino groups of the hyperbranched polylysines were transformed into guanidine groups. The guanidine-rich hyperbranched polymers showed lower cytotoxicity and hemolytic activity than the corresponding precursor hyperbranched polylysines. Co-incubation of the guanidine-rich hyperbranched polymers and doxorubicin with pancreatic cancer cells (PANC-1) showed enhanced cellular uptake of the drug. The polymers also showed the ability to promote penetration of doxorubicin deeply into multicellular PANC-1 spheroids upon co-incubation. Co-administration of the guanidine-rich hyperbranched polymers with doxorubicin and gemcitabine, respectively, greatly enhanced the anticancer activity of the drugs in PANC-1 xenograft mouse models.