In recent years, monoclonal antibody treatment in the form of subcutaneous injections has grown significantly due to its many advantages over other parenteral routes of administration. The volume of the solution is limited to a maximum of 2 ml in subcutaneous administration, which leads to the need for high concentrations of monoclonal antibodies (above 100 mg/ml). High concentrations of monoclonal antibodies (mAbs) can lead to high viscosity and poorer stability of the biological macromolecules, which, in addition to the optimisation of the production process, e.g., filtering, mixing, also requires forceful injection of the solution into the subcutaneous tissue, which can be painful for the patient.
In the master's thesis we wanted to find out which excipients effectively lower the viscosity of a solution of a selected mAb with a concentration of 150 mg/ml. We tested solutions of 20 different compounds at a concentration of 25 mM, including amino acids, amino acid mimetics, and di- and tripeptides. The concentration of monoclonal antibodies was determined spectrophotometrically, and the viscosity was determined using an on-chip viscometer. We found that all tested compounds lowered the viscosity of the monoclonal antibody solutions to some extent, but only 14 compounds lowered the viscosity below an acceptable value for subcutaneous administration (20 mPas). The most effective viscosity lowering was achieved by compounds acting on both electrostatic and hydrophobic interactions. Of the functional groups present, the carboxyl group had the greatest effect on lowering the viscosity of the mAb solution, while the hydroxyl group had the least effect. The position of the functional groups on the aromatic ring is also important, with the most promising compounds containing a functional group at the para position of the ring. For di- and tripeptides, we found that compounds containing two pyrrolidine rings had the greatest influence, while compounds containing a glycine residue had the least. We also measured the size distribution of the mAb particle for all solutions and found that there was no correlation between the efficacy of the compounds in lowering the viscosity of the mAb solutions and the stability of the mAb.
To further ensure the stability of monoclonal antibodies, it would be useful to add stabilisers such as sucrose to the solutions. We have found that the viscosity of the solution increases exponentially with sucrose concentration, which should be taken into account when developing monoclonal antibody formulations. We also added arginine and histidine to the sucrose solution and found that they had no effect on the viscosity of the sucrose solution.
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