Fourier Transform Near-Infrared Spectrometry Reveals Significant Inter-Lot Variability in Thyrotropin Alfa...

Thyrotropin alfa is a recombinant heterodimeric glycoprotein that serves as a highly purified form of human thyroid stimulating hormone (TSH). It is produced through recombinant DNA technology within a genetically modified Chinese hamster ovary (CHO) cell line. The molecule is structurally complex, consisting of two non-covalently linked subunits: an alpha subunit (92 amino acid residues) with two N-linked glycosylation sites, and a beta subunit (118 residues) containing one N-linked glycosylation site. The resulting amino acid sequence is identical to that of human pituitary TSH. Thyrotropin alfa is supplied as a sterile, non-pyrogenic, white to off-white lyophilized product, intended for intramuscular (IM) administration after reconstitution with Sterile Water for Injection, USP. Each vial of Thyrogen contains 1.1 mg thyrotropin alfa, 36 mg mannitol, 5.1 mg sodium phosphate, and 2.4 mg sodium chloride. The intralot analysis of the 12 vials sampled from lot EY0155 revealed significant differences in the drug product within the same manufacturing lot, as evidenced by both spectral plots and multivariate analysis. The visual differences were observed in the following wavenumber regions: 4000 to 5000 cm^-1, 5150 cm^-1, and the 6700 cm^-1 regions. The differences seen at 5150 cm^-1 are very likely a difference in moisture content. 25% of the vials were flagged as outliers, with vials appearing 3.3, 3.8, and 5.3 SDs from the center of the cluster of 12 vials. The interlot analysis of a spectral library containing 171 vials from 18 different lots of thyrotropin alfa demonstrated tremendous variability in the near-infrared absorption profiles across the samples. Obvious differences were observed in the spectra of the library at several wavenumber regions, including around 5900 and 6650 cm^-1. The ratio between two peak sizes between 5900 and 5950 cm^-1 was dramatically variable. Differences were also noted around 4250, 4400, and 4540 cm^-1, and from 4700 to 4800 cm^-1. Only one vial was an outlier, appearing 7.8 SDs away from the center of the library spectral cluster. Some literature suggests differences in the spectra of vials may reflect differences in the stability and efficacy of the drug.