Identity, therapeutic proteins

When such investigation is technically possible, as shown in the examples of MAbs and CD40L, MS analysis of complete molecules is fast, powerful, and the method of choice to obtain detailed characterization information. Such a technique should be among the first to be applied for the study of a therapeutic protein. Limitations of the technique include lack of resolution of heterogeneous mixtures and lack of interpretation of isobaric structures, identical in mass but molecularly distinct. The first point can be overcome by reduction of heterogeneity... 

The successful application of CE technology has resulted in dramatic growth of CE as an essential tool for protein characterization, R D, and QC of therapeutic biomolecules. CE methods have clearly been shown to be superior over traditional slab-gel methods. Many biopharmaceutical companies have adopted CE techniques in QC environments for determination of product purity, identity and consistency needed for the release of protein products. The success of validation per ICH guidelines has moved CE technology to a position of greater prominence and ensures the quality release of therapeutic proteins and antibodies. 

The genetic manipulation of animal cells allows the production of therapeutic proteins in animal cell culture systems. Mammalian cells such as Chinese hamster ovarian cells and baby hamster kidney cells are commonly used. These mammalian hosts produce recombinant proteins that have almost identical properties to those made by human cells. However, the use of mammalian cells does have disadvantages. As noted earlier, they are expensive to use. This is influenced by their more complex nutritional requirements, their slower growth, and their increased susceptibility to physical damage (Walsh, 2003). 

As with small molecules, the key analytical parameters to be addressed for therapeutic proteins on a lot-to-lot basis are identity, purity, and potency. In addition, a rigorous proof of structure is required for the reference standard lot to be used for routine analysis of production batches. 

Another possible system for the production of therapeutic proteins consists of transgenic animals. Although there is controversy regarding safety and reproducibility, many reports on this subject have been published and some proteins derived from these systems are currently under clinical trials. Parker et al. (2004) purified and characterized human fetoprotein a secreted in transgenic goat milk. This protein, used in the treatment of autoimmune diseases, proved to be identical to the native form by mass spectrometry, circular dichroism, and pharmacokinetic tests. 

As has been the case with conventional drugs, therapeutic proteins produced by biotechnology are also open to misuse as in the cases of the use of human growth hormone and erythropoietin by athletes to enhance their athletic performance. Their being identical to their counterparts produced in the body makes their detection in routine tests nearly impossible (Spalding, 1991). These concerns are also being addressed by the manufacturers of such drugs. 

A biosimilar is dehned as any therapeutic protein by its own manufacturing process that may influence the characteristics of the product itself but also introduce specihc process-related impurities. The producers of biosimilars therefore need to demonstrate consistency and robustness of their production process. They need to do formulation studies showing stability and compatibility, even if the formulation is identical to the reference product. 

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