Improved potency assay for recombinant bovine somatotropin by high-performance size-exclusion chromatography.

A high-performance size-exclusion chromatographic method was developed for the determination of potency of recombinant bovine somatotropin (rbST) monomer and the estimation of dimer and soluble aggregates in bulk drug substances. These proteins can be completely extracted from bulk drug substances with sodium borate-ethylenediamine-tetraacetic acid disodium salt (EDTA) at pH 9.5 and separated on TSK G3000SW column with a mobile phase of pH 7.3 sodium borate-EDTA. The results demonstrated that this method was a non-denaturing assay for the determination of potency of rbST monomer and the data obtained in this study correlated well with data of the hypophysectomized rat body weight gain bioassay. The rbST monomer and dimer in the separation were verified by liquid chromatography-electrospray mass spectrometry. This method was optimized and validated.