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Pro-Electrophiles A Previously Overlooked Class of Protein-reactive Extractables?

Extractable and leachable studies on primary packaging systems are well-established in the pharmaceutical industry. For extraction studies, guidelines and best practice guides mandate a worst-case approach, taking the active, the formulation and the container closure system into account. The data from the extraction study should enable a meaningful risk assessment about the possible occurrence of impurities leaching from packaging components during the product’s shelf-life. The guidelines and best practice guides recognise packaging materials as a potential source of impurities and assess their direct toxic or genotoxic effect on the patient. However, an assessment of the protein-reactivity of extractives is not in the scope of standard extraction procedures. Changes to the protein structure caused by compounds acting as a catalyst or by direct covalent reactions may render the Biopharmaceutical inefficacious or even immunogenic. Previously, we have described a screening assay for packaging material extracts, to identify possible protein-reactive extractable, enabling an assessment including the risk of possible leachable having a direct or indirect effect on the protein structure. However useful this proposed assay is, it only allows an evaluation of the reactivity of extractable during the extraction process. It does not consider extractable, which is not reactive per se but may be converted to a protein-reactive derivative caused by ageing processes, which might occur over the shelf-life of the product. In this article, we propose a modification of the protein-reactivity screening, by adding an electrochemical oxidation step, to not only evaluate extractable, which are reactive during the extraction process but to also see, if there is a subset of extractable, that oxidised derivatives have protein-reactive properties. This modified assay does not only evaluate the reactivity of extractable during the extraction process but also takes into account, that leaching processes are time-dependent and therefore, potential leachable is like the drug product prone to ageing-dependent degradation or modification, which may have an impact on the reactivity of the compound.

Biopharmaceuticals, drug products with protein- or peptide-based active ingredients, are mainly administered as parenteral solutions. These solutions are prepared either prior to application by reconstitution of a lyophilized product with a suitable diluent or are formulated directly as a liquid for injection. Parenteral drug products are mainly stored in glass container closure systems sealed with a rubber stopper/septum; the standard vial-stopper configuration. In some cases, the product may be filled directly into the syringe, a so-called pre-filled syringe. These consist of a glass barrel, which may be lubricated, a rubber-based plunger and a syringe needle held in place by an adhesive and a capping device. All these components and adhesives are potential sources of leachable, which may migrate into the product over its shelf life. To evaluate the risk of leachable migrating into the product, extraction studies are performed. Extraction studies should be designed in a way, that they represent a worst-case scenario in terms of the extractive properties of the extraction media and extraction conditions, mainly temperature and time. Here it is important to note, that a forensic-style evaluation of the primary packaging, e.g. by completely dissolving each component under the harshest of conditions, does not give rise to a representative extraction profile. The USP chapters <1663>and <1664>offer guidance on the design, justification and evaluation of data from extractable and leachable studies, but do not propose exact experimental conditions for extraction studies.1,2 The Product Quality Research Institute (PQRI), however, published widely accepted best practice guides for Orally Inhaled and Nasal (OINDP) as well as for Parenteral and Ophthalmic Drug Products (PODP).3,4 The guideline covering parenteral formulations, proposes three different extraction media considering aqueous buffered formulations at basic and acidic pH, as well as water with an organic solvent to simulate the extractive properties of often highly concentrated protein-based actives and excipients like polysorbates, aiding protein solubility. The guideline also proposes a Safety Concern Threshold (SCT) considering the parenteral and ophthalmic route of administration, under which a daily exposure to an unknown compound is considered to likely have no adverse effect on the patient. The SCT is an extrapolation of no observed effect levels (NOEL) obtained for different substance classes in animal models.5 For the evaluation of the extraction profiles, the SCT is translated into an analytical evaluation threshold (AET), which takes into account the maximum daily delivered dose of the drug and the extraction volume. Any extractable, which falls short of the concentration limit defined in the AET, is not further evaluated, since they are unlikely to either leach in the product over its shelf life or at least are very likely to stay under defined SCT. Compounds in the extract, that are detected above the AET need to be identified and toxicologically assessed to evaluate whether the compound needs to the monitored during a leachable study. The analytical techniques applied must be capable of detecting a single compound, in the case of a leachable study, or multiple compounds from an extraction study at the defined AET level. Furthermore, for the evaluation of extracts, the analytical techniques must be suitable to detect an array of extractable from inorganic compounds, e.g. metals from glass components, to organic compounds with diverse Physico-chemical properties, e.g. from rubber components or adhesives.