A decision-support model for evaluating changes in biopharmaceutical manufacturing processes.

A simulation is described that evaluates the impacts of altering bio-manufacturing processes. Modifications designed to improve production levels, times and costs were assessed, including increasing feed volumes/titres, replacing initial downstream stages with packed or expanded bed affinity steps and removing ion exchange steps. Options were evaluated for manufactured product mass, COG, batch times and development costs and timescales. Metrics were combined using multi-attribute-decision-making techniques generating a single assessment metric for each option. The utility of this approach was illustrated by application to an FDA-approved process manufacturing rattlesnake anti-venom (Protherics U.K.). Currently, ovine serum containing anti-venom IgG is purified by precipitation/centrifugation, prior to antibody proteolysis by papain. An ion exchanger removes F(C), before affinity chromatography yields the final anti-venom. An expanded bed affinity column operating with an 80% higher IgG titre, 66% higher feed volume and without the ion exchanger delivered the best multi-attribute-decision-making value, potentially providing the most desirable alternative.

The interaction between rac1 and its guanine nucleotide dissociation inhibitor (GDI), monitored by a single fluorescent coumarin attached to GDI.

The interaction of rac with guanine nucleotide dissociation inhibitor protein (rhoGDI) is described, using GDI fluorescently labeled on its single cysteine with N-[2-(1-maleimidyl)ethyl]-7-diethylaminocoumarin-3-carboxamide (MDCC). The labeled GDI shows a 70% decrease in fluorescence emission on binding geranylgeranylated rac1.GDP and has an affinity for rac1 within a factor of 2 of the unlabeled GDI. The labeled GDI was used to determine the kinetic mechanism of the interaction by measuring the association and dissociation in real time. The kinetics are interpreted in terms of a two-step mechanism: binding of rac to GDI and then a conformational change of the complex with an overall dissociation constant of 0.4 nM. The conformational change has a rate constant of 7.3 s-1 (pH 7.5, 30 degrees C), and the reverse has a rate constant of 1.4 x 10(-)3 s-1. To overcome difficulties inherent in using and manipulating lipid-modified rac, we also used a combination of unmodified rac1, expressed in Escherichia coli and produced with C-terminal truncation (thus lacking the cysteine that is the site of lipid attachment), and farnesylated C-terminal peptide. This combination can mimic geranylgeranylated rac1, producing a complex with the coumarin-labeled GDI, and was used to examine the relative importance of different regions of rac1 in interaction with GDI.