A structural investigation into the compaction behavior of pharmaceutical composites using powder X-ray diffraction and total scattering analysis.

PURPOSE: To use advanced powder X-ray diffraction (PXRD) to characterize the structure of anhydrous theophylline following compaction, alone, and as part of a binary mixture with either alpha-lactose monohydrate or microcrystalline cellulose. MATERIALS AND METHODS: Compacts formed from (1) pure theophylline and (2) each type of binary mixture were analyzed intact using PXRD. A novel mathematical technique was used to accurately separate multi-component diffraction patterns. The pair distribution function (PDF) of isolated theophylline diffraction data was employed to assess structural differences induced by consolidation and evaluated by principal components analysis (PCA). RESULTS: Changes induced in PXRD patterns by increasing compaction pressure were amplified by the PDF. Simulated data suggest PDF dampening is attributable to molecular deviations from average crystalline position. Samples compacted at different pressures were identified and differentiated using PCA. Samples compacted at common pressures exhibited similar inter-atomic correlations, where excipient concentration factored in the analyses involving lactose. CONCLUSIONS: Practical real-space structural analysis of PXRD data by PDF was accomplished for intact, compacted crystalline drug with and without excipient. PCA was used to compare multiple PDFs and successfully differentiated pattern changes consistent with compaction-induced disordering of theophylline as a single component and in the presence of another material.

A peptide-based material platform for displaying antibodies to engage T cells.

This study investigated a strategy by which antibodies are displayed to engage T cells. A peptide composite containing binding sites was characterized in vitro and explored as an injectable system in vivo. The composite consists of two amphiphilic peptides, AEAEAKAKAEAEAKAK (referred to as "EAK") and EAK appended with six consecutive histidines at the C-terminus ("EAKH6"). Spectroscopic analysis showed the two peptides integrated into a single structure. Prior to combination, conformational analysis revealed that EAKH6 adopts a mixed α-helix/ß-strand conformation. In the presence of EAK, EAKH6 exists predominately in ß-strand conformation. The composite of EAK-EAKH6 was found to display His-tags, using nickel-bound horseradish peroxidase as a probe. T cell-specific antibodies were found stably displayed on the EAK-EAKH6 assembly using recombinant protein A/G and anti-histidines antibody as an adaptor. When mounted with anti-CD4 antibody, the system was shown to capture CD4T cells in a mixed population of lymphocytes. Antibodies were concentrated in the subcutaneous space in mice when co-administered with EAK and EAKH6 along with protein A/G and anti-histidines antibody as a solution. We report here the use of amphiphilic peptides to display Ab in vivo, the results indicating that the design can be used as a platform for engaging specific subsets of leukocytes for the purpose of immune modulation.