pDMAEMA is internalised by endocytosis but does not physically disrupt endosomes

Earlier workers proposed that poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) facilitates cell transfection by being endocytosed, complexed with DNA, and subsequently acting as a "proton sponge" to burst endosomes/lysosomes and release DNA to the cytosol. It also seemed feasible that the cytotoxicity of pDMAEMA might result from lysosomal bursting, which can induce cell death. Experiments were performed to determine the extent of cytotoxicity of uncomplexed pDMAEMA, the mode of cell death it induces (i.e. apoptosis or necrosis), its mechanism of entry into cells, and its ability to disrupt endosomes/lysosomes and release molecules into the cell cytosol. The results indicate that (i). pDMAEMA is highly cytotoxic and induces rapid, primarily necrotic cell death, (ii). it is internalised into cells via fluid-phase endocytosis, and (iii). although pDMAEMA affected the morphology of late endosomes/lysosomes, it did not physically disrupt them to release their contents to the cytosol. The lack of endosomal disruptive activity suggests that this is not involved in the cytotoxicity of pDMAEMA or in its ability to transfect cells. Further work will be required to establish the molecular mechanism(s) by which pDMAEMA facilitates transfection.