pH and excipient profiles during formulation of highly concentrated biotherapeutics using bufferless media.

Several models have been developed to describe the shifts in pH and excipient concentrations seen during diafiltration of monoclonal antibody (mAb) products accounting for both Donnan equilibrium and electroneutrality constraints. However, these models have assumed that the mAb charge is either constant or only a function of pH, assumptions that will not be valid when formulating highly concentrated mAbs using bufferless or low-buffered media due to the change in local H+ concentration at the protein surface. The objective of this study was to incorporate the effects of both pH and ionic strength on the mAb charge, through the use of a charge regulation model based on the amino acid sequence of the mAb, into an appropriate mass balance model to describe the pH and excipient profiles during diafiltration. The model involves no adjustable parameters, with the protein charge evaluated directly from the protonation/deprotonation of the ionizable amino acids accounting for the electrostatic interactions between the charged mAb and the H+ ions. Model predictions are in excellent agreement with experimental data for the pH and ion concentrations during diafiltration of a mAb and fusion protein with different isoelectric points and different formulation conditions. Model simulations are then used to obtain fundamental insights into the factors controlling the diafiltration behavior as well as guidelines for development of diafiltration processes to achieve target bufferless formulation conditions.

CT2108A and B: New fatty acid synthase inhibitors as antifungal agents.

A systematic screen for new natural products that displayed antifungal activity by inhibition of fungal fatty acid synthase (FAS) led to the discovery of two new fungal metabolites, designated CT2108A (1) and CT2108B (2). The metabolites were produced by Penicillium solitum (Westling) strain CT2108 and were classified as azaphilones. The structures of these new metabolites were determined using a variety of 1D and 2D NMR experiments, including COSY, HMQC, and HMBC. The chemical conversion of CT2108A to CT2108B was effected using WCl(6). The related metabolite, patulodin (3), was also isolated from the fermentation culture of this P. solitum isolate. Both new compounds inhibited fungal FAS, and neither was found to significantly inhibit human FAS activity.