Wendy L. Hulse, R obert T. Forbes

1. Biopharmaceutical Formulation Group Taylor Dispersion Analysis to Gain an Insight into Formulation Buffer Salts on the Stability and Aggregation Behaviour of Proteins Wendy L. Hulse, RobertT. Forbes Biopharmaceutical Formulation Group, School of Life Sciences, University of Bradford, Bradford UK. Email: w.l.hulse1@bradford.ac.uk Objectives Results To explore the use of Taylor Dispersion Analysis to size lysozyme in the presence of different formulation buffers and additives and to detect protein aggregation potential with time. To compare the results obtained with those from the conventional size measuring technique of dynamic light scattering (DLS) and thermal analysis. Figure 1 shows the TDA results for different Lysozyme concentrations in phosphate buffer (pH 4.5, 50 mM) which show that increasing lysozyme concentration results in an increased hydrodynamic radius. All TDA and most DLS data points show that the hydrodynamic radius had increased after storage. Figure 3 shows the two VP-DSC heating cycles for lysozyme (10mg/ml). No unfolding enthalpy is present in the re-heat cycle indicating that lysozyme may be irreversibly unfolded by the first heating cycle. Methods TDA analysis was carried out using 60nl of sample injected using a flow-rate of 2 mm s-1, capillary size was 75:360 ID:OD with a total length of 143cm. DLS analysis was carried out using a Malvern Nano-S system. Thermal analysis was carried out using a VP-DSC with a heating and cooling rate of 1°C/min. Figure 1. TDA results for Lysozyme hydrodynamic radius in phosphate buffer. Figure 2. DLS results for Lysozyme hydrodynamic radius in phosphate buffer. Figure 3. VP-DSC results for Lysozyme in phosphate buffer (black trace initial heating cycle, blue trace second heating cycle). Figures 4 and 5 show the TDA and DLS results for different lysozyme concentrations in acetate buffer (pH 4.5, 0.1M) which displays a narrower size range in hydrodynamic radius with increasing lysozyme concentration for TDA. The VP-DSC in Figure 6 does shows that unlike in the phosphate system, lysozyme shows an unfolding enthalpy in the second heating cycle. Actipix TDA 200 TDA200 Coupled to PrinCE CE system TDA200 Coupled to HP CE system The TDA200 instrument uses UV area imaging and Taylor dispersion analysis (TDA) for determining diffusion coefficients and hydrodynamic radii of proteins in solution. The detector monitors broadening of a band of a therapeutic protein or small molecule solution injected into a stream of buffer solution and driven through a fused-silica capillary. Figure 5. DLS results for Lysozyme hydrodynamic radius in acetate buffer. Figure 4. TDA results for Lysozyme hydrodynamic radius in acetate buffer. Figure 6. VP-DSC results for Lysozyme in acetate buffer (black trace initial heating cycle, blue trace second heating cycle). Figure 7 shows the TDA results of lysozyme (phosphate) with added sodium chloride in differing concentrations. The data indicates that addition of NaCl produces a more consistent average hydrodynamic radius with protein concentration than without. Secondly, the hydrodynamic radius by TDA was little influenced by salt level for this system over 2-100mg/ml. The band is imaged at two points, the first on entry to and the second on exit from a loop in the capillary. The hydrodynamic radius is calculated from the measured differences between peak times (first moments) and variances (second moments) at the two windows. The VP-DSC thermal profile of lysozyme in the presence of NaCL (fig. 8) is different to that obtained without NaCl present (fig. 3), reflecting the conformational size related changes observed using TDA. Figure 7. TDA results for Lysozyme hydrodynamic radius in phosphate buffer with and without added sodium chloride. Figure 8. VP-DSC results for Lysozyme in phosphate buffer with 2mg/ml sodium chloride added to buffer (black trace initial heating cycle, blue trace second heating cycle). Band broadening due to Taylor dispersion is calculated from absorbance versus time data using the peak centre times at the first and second window, t1 and t2 respectively, and the corresponding standard deviations, t1 and t2 (band broadening). Conclusions Acknowledgements The authors wish to thank the EPSRC and TSB for financial support Buffer salt selection is important and TDA demonstrates that it can notably alter the hydrodynamic radius of proteins. The TDA is a useful complement to DSC in buffer selection. The inherent, intricate behaviour of proteins in solution is complicated further by buffer systems. Both the ion and the ionic strength can affect the proteins behaviour in solution. Additional buffer systems of different salt and ionic strength are being investigated. For more information regarding this poster or any of our other services please visit us at www.biopharmaceutical.brad.ac.uk