Characterization and suitability of therapeutic antibody dense phases for subcutaneous delivery.

Subcutaneous antibody dosing formulations comprising solid suspensions have the potential to reduce dosage viscosity and injection volume. Gel beads of three therapeutic antibodies were prepared to determine the feasibility of such formulations. The beads were formed directly from aqueous solution within 0.1-4 days upon addition of biocompatible precipitating agents under conditions compatible with the use of stabilizing excipients. The phase behavior of antibody gel beads and their mechanical characteristics were measured. Gel beads were characterized by reduced elastic moduli of 0.4-1.0 MPa, as measured by atomic force microscopy, and completely redissolved within 10-20 min under physiologic conditions, in vitro. Crystalline particles could also be prepared in some cases and were found to have reduced elastic moduli 3 orders of magnitude greater than those for the gel beads. Both crystalline and gel particles had protein concentrations of 100-180 mg/mL within the dense phase. Protein stored within the dense phase was recoverable after 40 days of incubation at room temperature or 4 °C.

Solubilization and stabilization of bacteriophage MS2 in organic solvents.

Several techniques were examined for the solubilization of bacteriophage MS2 in organic solvents. Direct extraction of the MS2 from an aqueous phase into isooctane containing 2 mM AOT, a proven approach for the organic solubilization of many proteins, was not successful. However, predried samples of MS2 were solubilized through the direct addition of organic solvents containing 500 mM AOT. As an alternative procedure, reverse micelles containing aqueous solutions of MS2 were prepared in isooctane using AOT, dehydrated through solvent evaporation and azeotropic drying, and resolubilized in a solvent of choice. The structure and microenvironment of organic-solubilized MS2 were investigated by UV absorbance, the fluorescence emission of an attached solvatochromatic dye, tryptophan fluorescence, and atomic force microscopy, all of which contributed evidence for a fully assembled capsid in the organic solvent. The solubilized MS2 was derivatized with stearic acid in chloroform, illustrating that bioconjugation reactions can be performed on organic-solubilized capsids using reagents that are completely insoluble in water. Furthermore, the organic-solubilized phage remained infectious after heating at 90 degrees C for 20 min, whereas phage in aqueous buffer or dried with nitrogen were nonviable following the heat treatment protocol. The extended range of available chemical modifications and the enhanced thermal stability of the organic-solubilized capsids bodes well for the formulation of storage-stable vaccines predicated on reactions in or exposure to organic media.

Direct solubilization of enzyme aggregates with enhanced activity in nonaqueous media.

A protein solubilization method has been developed to directly solubilize protein clusters into organic solvents containing small quantities of surfactant and trace amounts of water. Termed "direct solubilization," this technique was shown to solubilize three distinct proteins - subtilisin Carlsberg, lipase B from Candida antarctica, and soybean peroxidase - with much greater efficiencies than extraction of the protein from aqueous solution into surfactant-containing organic solvents (referred to as extraction). More significant, however, was the dramatic increase in directly solubilized enzyme activity relative to extracted enzyme activity, particularly for subtilisin and lipase in polar organic solvents. For example, in THF the initial rate towards bergenin transesterification was ca. 70 times higher for directly solubilized subtilisin than for the extracted enzyme. Furthermore, unlike their extracted counterparts, the directly solubilized enzymes yielded high product conversions across a spectrum of non-polar and polar solvents. Structural characterization of the solubilized enzymes via light scattering and atomic force microscopy revealed soluble proteins consisting of active enzyme aggregates containing approximately 60 and 100 protein molecules, respectively, for subtilisin and lipase. Formation of such clusters appears to provide a microenvironment conducive to catalysis and, in polar organic solvents at least, may protect the enzyme from solvent-induced inactivation.

Predictive crystallization of ribonuclease A via rapid screening of osmotic second virial coefficients.

Important progress has been made in recent years toward developing a molecular-level understanding of protein phase behavior in terms of the osmotic second virial coefficient, a thermodynamic parameter that characterizes pairwise protein interactions. Yet there has been little practical application of this knowledge to the field of protein crystallization, largely because of the difficult and time-consuming nature of traditional techniques for characterizing protein interactions. Self-interaction chromatography has recently been proposed as a highly efficient method for measuring the osmotic second virial coefficient. The utility of the technique is examined in this work by characterizing virial coefficients for ribonuclease A under 59 solution conditions using several crystallization additives, including PEG, sodium chloride, ammonium sulfate, and propanol. The virial coefficient measurements show some counterintuitive trends and shed light on the previous difficulties in crystallizing ribonuclease A. Crystallization experiments at the corresponding solution conditions were conducted by using ultracentrifugal crystallization. Using this methodology, ribonuclease A crystals were obtained under conditions for which the virial coefficients fell within the "crystallization slot." Crystallographic characterization showed that the crystals diffract to high resolution. Metastable crystals were also obtained for conditions outside, but near, the "crystallization slot," and they could also be frozen and used to collect structural information.