Challenges in the official testing of monoclonal antibodies in patient-specific preparations

Patient-specific preparations are medicinal products that are manufactured on the basis of a doctor's prescription for immediate use for a specific patient. Typical dosage forms of such individual formulations, which can be produced in any public pharmacy, are ointments, creams, gels, capsules or suppositories. However, in specially equipped pharmacies and hospital pharmacies as well as certain manufacturing plants, parenteral preparations can also be manufactured individually for patients. In tumour therapy in particular, monoclonal antibodies (mAb) have been increasingly used successfully over the last two decades alongside the long-known classic ‘small molecule’ drugs, although they are characterised by significantly higher drug costs compared to classic cytostatics. A widely publicised pharmaceutical incident in a Bottrop pharmacy brought the monitoring of these expensive patient-specific preparations to the increased focus of official drug monitoring. For this reason, the Official Medicines Control Laboratory (OMCL) of the State Laboratory Berlin-Brandenburg (LLBB) was commissioned to establish the necessary analyses for testing patient-specific preparations with monoclonal antibodies. The analysis of the mAb preparations at the LLBB is based on two pillars: (a) identity determination and (b) content determination. (a) The identity of mAb is determined using two separate measurements on the LC-QTof mass spectrometer. The first measurement is the determination of intact mAb mass. For this purpose, after diluting, the sample is injected into the UHPLC and measured in SCAN mode on the QTof. mAb typically have an average molecular mass of around 150 kDa. The second measurement is the peptide mapping of the mAb by amino acid sequencing after tryptic digestion. The peptide fragments obtained after chromatographic separation in the UHPLC are analyzed in the mass spectrometer (De Novo Sequencing) and compared with the theoretical amino acid sequence. (b) The content of the respective monoclonal antibody is determined by measuring the total protein content according to Monograph 2.5.33 Method 1 of the European Pharmacopoeia (Ph. Eur.) using photometry. The method is based on the characteristic of dissolved proteins to absorb light at a wavelength of 280 nm. For quantification, the absorption of mAb containing solutions is measured at this specific wavelength. The presentation highlights the challenges of built up this analysis in an official laboratory and goes into details of the analytical procedures established at the LLBB.