RECOMBINANT HUMAN THYROID-STIMULATING HORMONE - DEVELOPMENT OF A BIOTECHNOLOGY PRODUCT FOR DETECTION OF METASTATIC LESIONS OF THYROID-CARCINOMA

We have genetically engineered a cell line, and developed a reproducib le process, for the expression and purification of biologically active recombinant human thyroid stimulating hormone (rhTSH). rhTSH was expr essed by co-transfecting a human alpha-subunit cDNA with a human beta- subunit partial genomic clone into Chinese Hamster Ovary (CHO) cells. Stable transfectants which expressed high levels of rhTSH were selecte d, and subsequently cultured on microcarrier beads. The rhTSH-containi ng media, produced under serum-free conditions, was clarified and puri fied by a combination of ion exchange, dye and gel filtration chromato graphies. Individual step recoveries were greater than 90% with the ex ception of a very conservative pooling of the final gel filtration ste p (78% recovery) that resulted in a cumulative yield of 54% for the pu rification process. Purity of the final bulk material was judged to be > 99% by SDS polyacrylamide gel electrophoresis (SDS-PAGE), reverse p hase HPLC, and size exclusion chromatography. Initial characterization of the oligosaccharide composition indicated the presence of partiall y sialylated bi- and triantenary complex oligosaccharides. Purified rh TSH was active in a thyroid membrane bioactivity assay with a specific activity of 8.2 IU/mg. The in vivo activity of rhTSH in cynomolgus mo nkeys appeared to be equal to or greater than that reported for bovine TSH (bTSH) in human subjects. The rapid clearance phase half-life of rhTSH was approximately 35 minutes while the post-distribution phase h alf life was approximately 9.8 hours. Furthermore, the monkeys showed cumulative increases in minimum plasma rhTSH levels when given three d aily intramuscular (IM) rhTNH injections; a phenomenon not observed wh en bTSH had been administered to humans. The rhTSH showed no evidence of toxic or adverse effects when administered at doses up to 7.2 IU/kg and 0.52 IU/kg in rat and monkey, respectively. These are 50X and 4X multiples of the bTNH doses of 0.143 IU/kg (10 IU/70kg) previously adm inistered to humans.