Hemolytic activity of pH-responsive polymer-streptavidin bioconjugates

Drug delivery systems that increase the rate and/or quantity of drug releas e to the cytoplasm are needed to enhance cytosolic delivery and to circumve nt nonproductive cell trafficking routes. We have previously demonstrated t hat poly(2-ethylacrylic acid) (PEAAc) has pH-dependent hemolytic properties , and more recently, we have found that poly(2-propylacrylic acid) (PPAAc) displays even greater pH-responsive hemolytic activity than PEAAc at the ac idic pHs of the early endosome. Thus, these polymers could potentially serv e as endosomal releasing agents in immunotoxin therapies. In this paper, we have investigated whether the pH-dependent membrane disruptive activity of PPAAc is retained after binding to a protein. We did this by measuring the hemolytic activity of PPAAc-streptavidin model complexes with different pr otein to polymer stoichiometries. Biotin was conjugated to amine-terminated PPAAc, which was subsequently bound to streptavidin by biotin complexation . The ability of these samples to disrupt red blood cell membranes was inve stigated for a range of polymer concentrations, a range of pH values, and t wo polymer-to-streptavidin ratios of 3:1 and 1:1. The results demonstrate t hat (a) the PPAAc-streptavidin complex retains the ability to lyse the RBC lipid bilayers at low pHs, such as those existing in endosomes, and (b) the hemolytic ability of the PPAAc-streptavidin complex is similar to that of the free PPAAc.