This has prompted their potential applications in cytoplasmic drug delivery,. Vinyl poly(α-alkylacrylic acid) polymers can be manipulated by controlling the hydrophobicity of pendant alkyl groups to disrupt lipid bilayer membranes at endosomal pH values, whilst being essentially non-lytic at physiological pH,. The hydrophobicity of polymers is one of the factors that influences their membrane-disruptive behaviour, , and the balance between their hydrophobic and hydrophilic components is required to be manipulated. Hydrophobic interactions between the resulting hydrophobic domains and lipid bilayer membranes, and/or hydrogen bonding involving protonated carboxyl groups and lipid phosphodiester groups, lead to increased membrane binding of polymers and subsequent membrane disruption, ,, , through pore formation, or membrane solubilisation. The biomimetic polymers containing hydrophobic side chains and ionisable carboxyl groups undergo a change of conformation from extended charged chains to globular hydrophobic structures upon reduction of pH below their p K a ranges. Anionic pH-responsive polymers are of interest as drug carriers because they can mimic the structure and pH-dependent membrane-lytic behaviour of endosomolytic viral peptides. Cationic polyethyleneimine, poly(2-(dimethylamino)ethyl methacrylate) and polyamidoamine dendrimers mediate gene delivery through the ‘proton sponge’ effect, but suffer from cytotoxicity and relatively low transduction efficiencies. A variety of synthetic polymers have therefore been developed as non-viral vectors. Recombinant viruses and fusogenic viral peptides have been used to mediate gene transfection, ,, but their clinical use is potentially limited by safety issues and difficulties in large-scale production. In order to achieve efficient intracellular delivery of such drugs, delivery systems are required that facilitate their release into the cytoplasm by destabilising endosomal membranes under mildly acidic conditions (pH 5.0–6.8).
![hydrophobic amino acids in membran hydrophobic amino acids in membran](https://images.slideplayer.com/26/8299147/slides/slide_4.jpg)
Amongst other problems, their clinical applications may be impaired by degradation by lysosomal enzymes during uptake into cells. nucleic acids and proteins) with potential for the treatment of a wide variety of diseases. It has been demonstrated by confocal microscopy that the grafted polymers can induce a significant release of endocytosed materials into the cytoplasm of HeLa cells, which is a feature critical for drug delivery applications.Īdvances in genomics and proteomics have enabled the development of biomacromolecular drugs (e.g. The in-vitro cytotoxicity of the grafted polymers has been assessed using a propidium iodide fluorescence assay. The mechanism of the polymer-mediated membrane destabilisation has been investigated. With increasing concentration, the grafted polymers showed an increased ability to lyse cell membranes and caused noticeable membrane disruption at physiological pH.
![hydrophobic amino acids in membran hydrophobic amino acids in membran](http://www.cryst.bbk.ac.uk/PPS95/course/7_tertiary/7_memb1.gif)
PP-75 was 35-fold more lytic on a molar basis than the membrane-lytic peptide melittin. At 0.025 mg mL −1, the grafted polymers were almost non-haemolytic at pH 7.4, but mediated considerable membrane lysis after 60 min in the pH range characteristic of early endosomes, which ranked in the order: PP-75 > PL-75 > PV-75 > poly( l-lysine iso-phthalamide). The effect of such modification on the pH-, concentration- and time-dependent cell membrane-disruptive activity of the grafted polymers has been investigated using a haemolysis model.
![hydrophobic amino acids in membran hydrophobic amino acids in membran](https://cdn.numerade.com/ask_images/918dc3d44adb4b14b4fa3ad1e85d716a.jpg)
PH-responsive polymers have been synthesised by grafting l-valine (PV-75), l-leucine (PL-75) and l-phenylalanine (PP-75) onto the pendant carboxylic acid moieties of a pseudo-peptide, poly( l-lysine iso-phthalamide), at a stoichiometric degree of substitution of 75 mol%.