Fusogenic activity of various water-soluble polymers.

The fusogenic activity of seven water-soluble polymers was investigated using L929 cells in a monolayer state. Among these polymers, only two, poly(ethylene glycol) (PEG) and EPAN 680 were capable of inducing the membrane fusion of L929 cells. EPAN 680 is an ABA type block copolymer composed of 80% ethylene oxide(A) and 20% propylene oxide(B) sequences with a total molecular weight of 8800. Evaluation of the polymer hydrophobicity indicated that there was no clear correlation between it and the fusogenic activity of the polymer, although highly hydrophobic polymers caused cell shrinkage without membrane fusion. Differential scanning calorimetry on these polymers strongly suggested that hydration of the polymers in culture medium had a large effect on their fusogenic activity. It was concluded that the assembly of cell membranes, stabilized by water molecules, was disturbed by strong interaction with the polymer molecules having a strong hydration power, resulting in membrane fusion.