See also “smart polymers” and “partitioning” right hang panel.

Polyelectrolytes are water-soluble polymers comprised of charged monomer units. The electrolyte (charged functionality) group undergoes protein dissociation (ionization) in aqueous solutions according to acidity (pH). Negatively charged, anionic polyelectrolytes and positively charged, cationic polyelectrolytes may be used in a precipitation reaction to purfiy antibodies.

When the solution pH is less that the pI of a particular antibody, the antibody is positively charged. Under these conditions, a cationic polyelectrolyte may precipitate impurities and leave the antibody of interest in solution. Conversely, an anionic polyelectrolyte may precipitate the antibody forming a protein-polyelectrolyte precipitate, leaving impurities in solution (WO2008/091740A2). 

Polyelectrolyte Precipitation Methods In General

Jaber, Moya, etc. (US 8,691,918; see also WO 2011/146394) disclose separating a target molecule by providing a sample containing the target molecule, contacting the sample with a soluble stimulate responisve polymer comprising a polyelectrolyte backbone comprising one or mroe hydrophobic groups attached to the backbone to form a complex of the polymer and one or more impurities, adding a stimulus to the sample to precipitate the complex out of solution to thereby separate the target molecule from one or more impurities. The resulting clarified cell culture fluid may be subsequently passed through a capture step using a chromatography media to bind the desired target molecule. The selection of the particular stimulus responsive polymer to sue is based on what the polymer is intended to bind. For example, in case of a biomolecule that has a net hegative charge at a pH above its pI (e.e.g, whole cells, cellular debris, DNA, endotoxins and proteins), a stimulus responsive polymer having a polyelectrolyte backbone that is cationic (i.e., positively charge) is desirable to use. On the other hand, in case of a biomolcule which has a net positive charge at a pH below its pI (.e.g. certain proteins), a stimulus responsive polymer compirsing a polyeletrolyte backbone which is anionic (i.e., negatively charged) is desirable to use.

Moya (US 8,362,217 and and WO2008/079280A1) (See also Moya, US2008/0255027 and US 13/747495) discloses a Ph dependent polymer such as poly(4-vinylpyridine-co-styrene) which has an affinity for a desired biomolecule such as an antibody in the insoluble state. In a first step, a mixture is harvested from cell broth, then the mixture is conditioned to the correct pH (e.g., below 5) to maintain the polymer in solution, then the mixture conditions are changed to cause the polymer to precipitate out of solution by altering the pH (e.g., 7.0) and the antibody recovered such as by elution. Moya discloses that preferred pH sensitive soluble polymers include cationic polyelectrolytes such as chitosan, polyvinylpyridines, primary amino containing polymers, secondary amine containing polymers and teriary amino containing polymers and anionic polyelectrolytes such as acrylic acid, methacrylic acid and methyl methacrylate. The polymers have the capability even when precipitated to selectively and reversible bind to one of more biomolecules of interest. Preferred polymers have electrostatic and hydrophobic ability. As some of these polymers may not have the ability to selectively bind or elute the desired molecules, they need to be modified with ligands of chemical groups that will complex with the desired molecule and hold it in complex and then release it under appropriate elution conditions. Such chemical groups can include carboxylated and pyridine groups formed as part of or attached to the polymer.

Anionic polyelectrolytes (polyanion polyelectrolytes): See outline

Cationic polyelectrolytes (polycation polyelectrolytes): See outline