Preformulation studies of Clostridium difficile toxoids A and B.

To enhance the physical stability of Clostridium difficile toxoids A and B, screening for stabilizing compounds was performed. The screening of 30 GRAS compounds at various concentrations and in several combinations was performed in two parts. First, a high-throughput aggregation assay was used to screen for compounds which delayed or prevented aggregation of toxoids under stress conditions (toxoids at pH 5-5.5 were incubated at 55 degrees C for 55 or 75 min). Compounds which stabilized both proteins were further studied for their ability to delay unfolding under conditions leading to a presumably native-like folded state (pH 6.5). The thermal stability of the toxoids on the surface of Alhydrogel was monitored with DSC and also showed significant improvement in the presence of certain excipients. This study has generated information concerning the free and adjuvant bound toxoids behavior under a range of conditions (temperature, solutes) that can be used to design pharmaceutical formulations of enhanced physical stability.