Thermal stability of adenovirus type 2 as a function of pH.

Although several recent studies have focused on the characterization and formulation of adenovirus type 5, similar efforts focusing on adenovirus type 2 (Ad2) have been lacking. To this end, multiple biophysical techniques were employed to investigate the thermal stability of Ad2 as a function of pH. Highly cooperative thermally induced changes in capsid conformation were detected near 45 and 65 degrees C under neutral conditions. The first transition is attributed to the loss of the penton bases and their associated fibers followed by more complete physical degradation at higher temperatures. Data in this work as well as previous studies suggest that a common mechanism of icosahedral virus thermal degradation exists. Conformational changes detected in these studies occurred at increasingly higher temperatures with decreasing pH from 8 to 5 suggesting that the physical stability of Ad2 is enhanced under mildly acidic conditions. To consolidate the data generated in these studies, a multi-dimensional Eigenvector approach was employed to generate an empirical phase diagram (EPD) of Ad2. The EPD identifies conditions, or "phase boundaries," where structural integrity is altered, in addition to providing a tool that can be used to identify conditions under which forced degradation and excipient-screening studies can be conducted.