The design and synthesis of polymers for eukaryotic membrane disruption

The intracellular trafficking of drugs is critical to the efficacy of drugs that are susceptible to attack by lysosomal enzymes. It is therefore an im portant goal to design and synthesize molecules which can enhance the trans port of endocytosed drugs from the endosomal compartments to the cytoplasm. The pH of an endosome is lower than that of the cytosol by one to two pH u nits, depending on the stage of endosomal development. This pH gradient is a key factor in the design of membrane-disruptive polymers which could enha nce the endosomal release of drugs. Such polymers should disrupt lipid bila yer membranes at pH 6.5 and below, but should be non-lytic at pH 7.4. We ha ve designed and synthesized pH-sensitive synthetic polymers which efficient ly disrupt red blood cells within a sharply defined pH range. One of these polymers, poly(ethyl acrylic acid) (PEAAc) has been previously shown to dis rupt synthetic vesicles in a pH-dependent fashion [6]. PEAAc hemolyzes red blood cells with an activity of 10(7) molecules per red blood cell, which i s as efficient on a molar basis as the peptide melittin. The mechanism of R BC hemolysis by PEAAc is consistent with the colloid osmotic mechanism. PEA Ac's hemolytic activity rises rapidly as the pH decreases from 6.3 to 5.0, and there is no hemolytic activity at pH 7.4. A related polymer, poly(propy l acrylic acid) (PPAAc), was synthesized to test whether making the pendant alkyl group more hydrophobic by adding one methylene group would increase the hemolytic activity. PPAAc was found to disrupt red blood cells 15 times more efficiently than PEAAc at pH 6.1. PPAAc was also not active at pH 7.4 and displayed a pH-dependent hemolysis that was shifted toward higher pH's . Random 1:1 copolymers of ethyl acrylate (EA) and acrylic acid (AAc) (whic h contain random -COOH and -C2H5 groups that are present and regularly repe at in PEAAc) also displayed significant hemolytic activity, with an efficie ncy close to PEAAc. These results demonstrate that pH-sensitive synthetic p olymers can be molecularly engineered to efficiently disrupt eukaryotic mem branes within defined and narrow pH ranges. Thus, these polymers might serv e as endosomal disruptive agents with specificities for early or late endos omes. (C) 1999 Elsevier Science B.V. All rights reserved.