Circular dichroism of biopharmaceutical proteins in a quality-regulated environment

With growing regulatory interest in ensuring the integrity and consistency of the higher order structure of biopharmaceutical and vaccine products, validated methods will be required that operate in quality-regulated environments and in compliance with guidelines such as those published by the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use [ICH]. Circular dichroism [CD] is a widely available, rapid and sensitive method to compare the secondary and tertiary structures of samples. For use in quality-regulated analyses multiple factors need to be considered. Firstly, a thorough understanding of the sources of experimental error is required, alongside protocols and reference standards for sample preparation, instrument calibration and performance monitoring. Secondly, validated algorithms to objectively compare spectra are required, with statistical evaluation to assess when values are significantly different and to define compliance criteria. Thirdly, regulatory authorities mandate the process of method assessment and validation to be acceptable for use in regulated environments. In this review I discuss regulatory expectation, the sources and magnitudes of instrument- and sample-derived uncertainties, the use of reference standards to define and correct instrument performance, and the algorithms used to objectively compare spectra. The ideas discussed here support the use of CD not only in quality-regulated environments but also best practice when used in a research environment.