Therapeutic proteins preparation

As pharmaceutical scientists gain experience and tackle the primary challenges of developing stable parenteral formulations of proteins, the horizons continue to expand and novel delivery systems and alternative routes of administration are being sought. The interest in protein drug delivery is reflected by the wealth of literature that covers this topic [150-154]. Typically, protein therapeutics are prepared as sterile products for parenteral administration, but in the past several years, there has been increased interest in pulmonary, oral, transdermal, and controlled-release injectable formulations and many advances have been made. Some of the more promising recent developments are summarized in this section. 

Based on the above principles, it might be assumed that a therapeutic protein obtained by direct extraction from human sources (e.g. some antibody preparations) or produced via recombinant expression of a human gene/cDNA sequence (e.g. recombinant human hormones or cytokines) would be non-immunogenic in humans whereas foreign therapeutic proteins (e.g. non-engineered monoclonal antibodies) would stimulate a human immune response. This general principle holds in many cases, but not all. So why do therapeutic proteins of human amino acid sequences have the potential to trigger an immune response Potential reasons can include ... 

As mentioned in Section 11.2, a special class of proteinaceous targeting constructs are those in which a therapeutic protein is used as the active drug substance. In such a preparation, the protein is redirected to the target tissue by the attachment of site-directing ligands such as those discussed in Section 11.3. For instance, interferon beta (IFN- 3) can be redirected to the liver by enz5matic desialylation in a procedure similar to that described earlier for fetuin (Section 11.3.1). The resultant asialo-IFN- 3 was found to have an in vivo anti-viral effect when tested in a hepatitis B model in athymic nude mice [54]. 

Mammalian cells are commonly employed for the production of therapeutic and diagnostic proteins, since they are able to correctly synthetize the large and complex structures that the human body requires as medicine [1]. Nowadays, they are employed for the large-scale production of recombinant therapeutic proteins, monoclonal antibodies (MAbs) and viruses used in the preparation of vaccines (e.g. against rabies, hepathytis B, polio, etc) [2]. An overview of some licensed/approved products derived from mammalian cell culture is given in Table 1. 

A wide range of pharmaceutical substances are derived from animal sources (Table 1.10). Many are protein-based and detailed description of products such as insulin and other polypeptide hormones, antibody preparations, vaccines, enzymes, etc., have been deferred to subsequent chapters. (Many of the therapeutic proteins are now also produced by recombinant DNA technology. Considerable overlap would have been generated had a product obtained by direct extraction from native sources been discussed here, with further discussion of a version of the same product produced by recombinant DNA technology at a later stage.) Non-proteinaceous pharmaceuticals originally derived from animal sources include steroid (sex) hormones, corticosteroids and prostaglandins. A limited discussion of these substances is presented below, as they will not be discussed in subsequent chapters. Most of these substances are now prepared synthetically. 

Walsh (2003) defined biopharmaceuticals as therapeutic protein or nucleic acid preparations made by techniques involving recombinant deoxyribonucleic acid (DNA) technology. Therapeutic proteins include blood clotting factors and plasminogen activators, hemopoietic factors, hormones, interferons and interleukins, and monoclonal antibodies (LeVine, 2006). Over time, the term biopharmaceutical has broadened, and, in addition to proteins and nucleic acids, now includes bacteriophages, viral and bacterial vaccines, vectors for gene therapy, and cells for cell therapy (Primrose and Twyman, 2004). Attention here focuses on proteins, since the majority of approved biopharmaceuticals are proteins. 

The process of purification, also called downstream processing, depends on the product and the degree of purification required.74 Current strategies used for purification of therapeutic proteins generally involve these steps (1) sample preparation (clarification or extraction), (2) product capture (product concentration), (3) intermediate purification (removal of bulk impurities), and (4) polishing (removal of trace impurities) as shown in Figure 32.4. 

These impurities pose risks for the safety of proteins used as therapeutics and must be removed to a final concentration below their target limit. In addition, the product stream contacts materials such as filters and resins. Extractables, such as leachates from protein A resins, can pose an immunogenic risk to the patient and must be eliminated.75 Finally, adventitious agents such as viruses and bacterial pathogens or related contaminants such as endotoxins can lead to serious problems with the safety of the protein preparation and therefore must be minimized. Table 32.6 lists concentrations for the above impurities that are generally considered acceptable in a final protein product.76... 

Therapeutic proteins typically exist in a noncrystalline or amorphous form because their macro-molecular structures are not readily crystallized. These materials are commonly prepared in an amorphous dispersion with bulking and stabilizing excipients to ensure an adequate product shelf life and ease of administration. Examples of such therapeutic proteins include insulin and interferon. 

Therapeutic proteins are usually prepared in liquid formulations or as freeze-dried powders that are to be reconstituted immediately before use. A number of the proteins have been found to be unstable when dried... 

High temperatures can break native S—S bonds and form new S—S bonds that can lock the protein into a denatured configuration. Low pH, sodium dodecyl sulfate. Tween 80 , chaotropic salts, and exogenous proteins have been used to protect proteins from thermal inactivation.f Ethylene glycol at 30-50% was used as a protectant of antiviral activity of p-interferon preparations. Human serum albumin was used inrecombinant human interferon-pser-i7, which resulted in increased thermal stability. Water-soluble polysaccharides such as dextrans and amylose and point-specific (site-directed) mutagenesis have also been used to increase thermal stability of therapeutic proteins and peptides. 

With background information, assays, and sample preparation and extraction procedures in place the Three Phase Purification Strategy can be applied (Figure 3). This strategy is used as an aid to the development of purification processes for therapeutic proteins in the pharmaceutical industry and is equally efficient as an aid when developing purification schemes in the research laboratory. 

The term encapsulation has been used to distinguish entrapment preparations in which the biocatalyst environment is comparable to that of the bulk phase and where there is no covalent attachment of the protein to the containment medium (Fig. 6-1 D)[21J. Enzymes or whole cells may be encapsulated within the interior of a microscopic semi-permeable membranes (microencapsulation) or within the interior of macroscopic hollow-fiber membranes. Liposome encapsulation, a common microscopic encapsulation technique, involves the containment of an enzyme within the interior of a spherical surfactant bilayer, usually based on a phospholipid such as lecithin. The dimensions and shape of the liposome are variable and may consist of multiple amphiphile layers. Processes in which microscopic compart-mentalization (cf. living cells) such as multienzyme systems, charge transfer systems, or processes that require a gradient in concentration have employed liposome encapsulation. This method of immobilization is also commonly used for the delivery of therapeutic proteins. 

Case Study Reference Standard Compared with a Lyophilized Formulated Dose In this case study, calibrators for an immunoassay were prepared from a lyophilized formulated dosage material for a therapeutic protein, and compared with the corresponding liquid formulation reference standard. Spiked control samples were likewise prepared from both sources of material and run in the... 

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