Wirtszellprotein

Wirtszellproteine (Host Cell Proteins, HCP) sind Rückstände aus genetisch veränderten Wirtszellen, die bei der Herstellung von Biologika oder Peptiden anfallen. Diese Proteine stammen von den verwendeten Produktionsorganismen wie Bakterien oder Hefen und gehören nicht zum eigentlichen Arzneistoff. Da sie die Reinheit und Sicherheit des Endprodukts beeinflussen, müssen sie im Labor präzise überwacht werden.

Messung der HCP-Konzentration für Produktsicherheit und Haltbarkeit

Labore bestimmen den HCP-Wert, um die Effizienz des Aufreinigungsprozesses zu bewerten und klinische Risiken zu minimieren. Der Standardnachweis erfolgt meist über einen ELISA-Assay, der die Gesamtmenge an Wirtszellproteinen in Nanogramm pro Milligramm (ng/mg) oder Parts per million (ppm) angibt. Ergänzend wird oft die Massenspektrometrie (LC-MS/MS) genutzt, um spezifische Einzelproteine zu identifizieren, die der ELISA-Test eventuell übersieht.

Ein niedriger HCP-Wert ist ein Qualitätsmerkmal für die Reinheit und Stabilität des Produkts. Verbleibende Fremdproteine können das Immunsystem der Patienten reizen oder den Wirkstoff vorzeitig abbauen, was die Haltbarkeit und Wirksamkeit des Medikaments gefährdet.

• Ein numerischer HCP-Wert als Messergebnis
• Die angewendete Assay-Methode (z. B. ELISA)
• Die angegebene Wirtszelllinie der Produktion
• Ein relevanter Richtwert als Vergleichsgröße, etwa weniger als 100 ng/mg für bestimmte Biologika

Unterschied zwischen HCP und anderen Verunreinigungen

Wirtszellproteine müssen klar von anderen prozessbedingten Rückständen unterschieden werden, um die Analysedaten korrekt zu interpretieren. Während HCPs fremde Proteine der Produktionszelle sind, handelt es sich bei Wirtszell-DNA um genetisches Restmaterial. Endotoxine wiederum sind spezifische Giftstoffe aus bakteriellen Zellwänden, und produktbezogene Verunreinigungen bezeichnen Abbauprodukte des Wirkstoffs selbst.

Quellen

1. INTRODUCTION Biotechnology products, in many cases recombinant proteins, are derived from a complex expression/production system involving a genetically modified host cell (bacteria, yeast or mammalian cell). Among impurities to be eliminated during the downstream purification process, two components which are of major interest for safety and tolerance reasons are residual host cell DNA and residual host cell proteins (HCP). Since submission of the first marketing applications for recombinant proteins, depending mainly on the type of production cell system, the European regulatory authorities have adopted different approaches to deal with these impurities. In summary, for HCP, whatever the product and production system, residual HCP have to be tested for on a routine basis, whereas residual DNA is tested for on a routine basis only for products derived from continuous mammalian cells. It is necessary to guarantee that such impurities are reduced to an acceptable level in the medicinal product to be administered to the patient. For that, two approaches can be envisaged : • a “validation approach”: to validate the production process to establish that, at given steps of the purification scheme, those impurities are removed in a consistent and reproducible manner to an acceptable level. Based on the reduction factors it may be possible to predict and guarantee the residual level of impurity in the final product. • a “routine approach”: to develop analytical tools that allow monitoring, as closely as possible, of the level of those impurities at various steps of the process and set fixed limits to be met, so that the impurities are well monitored in the final product. A combination of these two approaches is also possible, i.e. routine testing at an earlier step of the purification process and demonstrated reduction by validation in order to ensure a limit at the final product level, if tested. In the context of the world-wide use of recombinant proteins, it is necessary to harmonise the evaluation criteria between the three regions of USA, EC and Japan, so that manufacturers can develop their products on the same lines whatever the intended regions for submission and marketing. RESIDUAL HOST CELL DNA Regarding residual DNA, it is already accepted for bacteria- and yeast- derived products that there is no need for routine testing provided that acceptable levels in the final product are achieved and, adequate validation data are submitted in the dossier. As far as DNA from continuous mammalian cell lines (CCLs) is concerned, this impurity was considered, in the past, as a risk factor because of concerns that residual host DNA may be tumorigenic. Further information, however, now suggests that CCL DNA poses much less of a risk than previously thought and accordingly should be considered as a general impurity (WHO Expert Committee on Biological Standardisation: Highlights of the 46th meeting, October 1996, in WHO Weekly Epidemiological Record, 1997, 72, 141-145). Validation studies (e.g. spiking experiments using an adequate size distribution of DNA) should be performed in an attempt to identify the major steps capable of reducing the DNA burden and to document the capacity of those steps in reducing residual cellular DNA content in the final
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