Immunological and biological characteristics of recombinant human thyrotropin

Thyrotropin isoforms: implications for thyrotropin analysis and clinical practice

Serum thyrotropin (TSH) is considered the single most sensitive and specific measure of thyroid function in the general population owing to its negative logarithmic association with free triiodothyronine and free thyroxine concentrations. It is therefore often the test of choice for screening, diagnosis, and monitoring of primary hypothyroidism. Serum TSH concentrations can be analyzed quantitatively using third-generation immunoassays, whereas its bioactivity can be measured by TSH activity assays in cell culture. Theoretically, if serum TSH concentrations are directly related to TSH activity, the two tests should yield comparable results. However, on occasion, the results are discordant, with serum concentrations being higher than TSH biological activity. This review focuses on the dissociation between the clinical state and serum TSH concentrations and addresses clinically important aspects of TSH analysis.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

Diagnostic and therapeutic use of recombinant human TSH (rhTSH) in differentiated thyroid cancer

Traditionally, withdrawal of thyroid hormone to increase serum levels of thyroid-stimulating hormone (TSH) has been used in patients with differentiated thyroid carcinoma (DTC) to optimize radio-iodine uptake and serum thyroglobulin (Tg) stimulation during follow-up and in preparation for radio-iodine therapy. However, this procedure is associated with signs and symptoms of hypothyroidism which negatively affect the patient's quality of life. Recombinant human thyrotropin (rhTSH) has provided an effective alternative to thyroid hormone withdrawal. After favourable experimental trials in humans, rhTSH obtained regulatory approval in North America and in Europe as a diagnostic tool, and more recently as a preparation for radio-iodine thyroid remnant ablation. Since then, rhTSH has radically changed the diagnostic and therapeutic management of DTC patients. This review will focus on the clinical application of rhTSH in the management of DTC, highlighting current indications and future perspectives.

Feasibility Study of New Calibrators for Thyroid-Stimulating Hormone (TSH) Immunoprocedures Based on Remodeling of Recombinant TSH to Mimic Glycoforms Circulating in Patients with Thyroid Disorders

Background: Differences between the glycosylation patterns of a pituitary thyroid-stimulating hormone calibrator (pitTSH) and serum samples have been shown to be responsible for nonidentical epitope expression and for introducing discrepancies in TSH measurements. We studied the feasibility of developing new candidate reference materials by remodeling recombinant TSH (recTSH) to generate potential mimics of serum TSH.

Methods: Terminal sialylation and/or inner fucosylation of recTSH were remodeled by a combination of enzyme treatments followed (or not) by lentil lectin-Sepharose affinity chromatography. The resulting TSH preparations were screened for epitope similarity in 23 immunoassays mapping 3 antigenic clusters common to the pitTSH 2nd International Reference Preparation (IRP) and the recTSH 1st IRP and then challenged against a pool of 63 patients with increased serum TSH (>60 mIU/L).

Results: pitTSH was poorly correlated with serum TSH, with a mean (SD) slope of 2.124 (0.001), in contrast to recTSH [slope, 1.178 (0.056)]. Comparison of variably sialylated preparations with recTSH gave slopes of 0.860 (0.057) for desialylated TSH, 1.064 (0.057) for α2,3/6-oversialylated recTSH, and 0.953 (0.033) for α2,6-resialylated recTSH, indicating that TSH forms enriched in sialic acid closely resemble serum TSH. Further testing against serum TSH showed satisfactory agreement with both TSH preparations containing α2,6-sialic acid [slopes, 1.064 (0.057) and 0.953 (0.033)], particularly in the absence of nonfucosylated forms [0.985 (0.044)].

Conclusions: Glyco-engineered recTSH preparations enriched in sialic acid and inner fucose are promising candidates for future reference materials. These preparations may have advantages over existing preparations used for standardizing TSH measurements.

Compassionate use of recombinant human thyrotropin to facilitate radioiodine therapy: case report and review of literature

OBJECTIVE

To describe the use of recombinant human thyrotropin (thyroid-stimulating hormone) (rhTSH) to assist in radioiodine therapy in a patient with thyroid carcinoma who was unable to produce sufficient endogenous thyrotropin when hypothyroid and to review the related literature.

METHODS

The study patient underwent formal dosimetric analysis and received radioiodine in conjunction with rhTSH. Follow-up scanning studies were performed.

RESULTS

We found good localization of radioiodine on the posttherapy scans after administration of (131)I while the patient continued to receive thyroxine replacement after two intramuscularly administered injections of rhTSH. Some of his metastatic lesions disappeared and his serum thyroglobulin level decreased after the first rhTSH-assisted dose of (131)I was administered. His blood radioiodine clearance rate was unexpectedly more rapid in the hypothyroid state than when he was euthyroid (taking thyroxine) after administration of rhTSH. His whole-body clearance rate was more delayed when he was hypothyroid. Swelling of some of the metastatic thyroid cancer lesions developed when the patient was hypothyroid and after rhTSH was administered, the latter being much more rapid in onset.

CONCLUSION

Therapeutic doses of radioiodine can be delivered with the assistance of rhTSH administration while patients continue to take suppressive doses of thyroxine. Metastatic thyroid carcinoma lesions can swell rapidly after administration of rhTSH. The commercially available form of rhTSH is approved only for diagnostic use. Its safety and efficacy in assisting radioiodine therapy have not been fully determined.

Radioiodine Treatment of Thyroid Cancer with the Aid of Recombinant Human Thyrotropin

OBJECTIVE

To update endocrinologists on the use of recombinant human thyrotropin (thyroid-stimulating hormone or TSH) (rhTSH) in thyroid diseases, with an emphasis on thyroid cancer.

METHODS

We reviewed the available literature on potential uses of rhTSH, including published studies and case reports.

RESULTS

Clinical trials have shown that rhTSH injections stimulate radioiodine uptake into normal and malignant thyroid tissue almost as well as that found in the hypothyroid state. The benefit to the athyreotic patient is the avoidance of the disability of hypothyroidism. When rhTSH is used in the doses currently recommended for scanning, few negative side effects occur. The more rapid clearance of iodine in the euthyroid state, however, may necessitate the use of more radioiodine to achieve the same amount of irradiation to metastatic lesions. We have used rhTSH for both dosimetric studies and therapy. This approach is essential in patients who cannot make sufficient endogenous TSH (because of hypothalamic-pituitary disease or medications that suppress TSH). Other patients with widespread metastatic lesions who have serious complications when allowed to become hypothyroid also benefit from rhTSH. Finally, we have found that rhTSH may provide new insights into the biologic features of thyroid cancer when used in combination with positron emission tomographic scanning. Use in the treatment of nonmalignant thyroid conditions such as toxic multinodular goiter is also feasible.

CONCLUSION

Overall, rhTSH provides a new and clinically important advance for patients with thyroid disease, especially thyroid cancer.

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 reproducible process, for the expression and purification of biologically active recombinant human thyroid stimulating hormone (rhTSH).rhTSH was expressed 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 selected, and subsequently cultured on microcarrier beads. The rhTSH-containing media, produced under serum-free conditions, was clarified and purified by a combination of ion exchange, dye and gel filtration chromatographies. Individual step recoveries were greater than 90% with the exception of a very conservative pooling of the final gel filtration step (78% recovery) that resulted in a cumulative yield of 54% for the purification process. Purity of the final bulk material was judged to be > 99% by SDS polyacrylamide gel electrophoresis (SDS-PAGE), reverse phase HPLC, and size exclusion chromatography. Initial characterization of the oligosaccharide composition indicated the presence of partially sialylated bi- and triantenary complex oligosaccharides. Purified rhTSH 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 monkeys 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 half life was approximately 9.8 hours. Furthermore, the monkeys showed cumulative increases in minimum plasma rhTSH levels when given three daily intramuscular (IM) rhTSH injections; a phenomenon not observed when 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 bTSH doses of 0.143 IU/kg (10 IU/70kg) previously administered to humans.

The use of recombinant human growth hormone for radioiodination and standard preparation in radioimmunoassay

Recombinant human growth hormone (rec-hGH) obtained by cloning hGH precursor gene, bacterial expression and periplasmic secretion of the authentic, mature form of the hormone was used, after purification and characterization, for the preparation of radioimmunoassay (RIA) reagents. 125I-rec-hGH was prepared by the classical chloramine-T iodination technique, while an internal standard of the same rec-hGH was used and calibrated against pituitary hGH reference preparation (NIDDK-hGH-RP-1) with the use of a reference antiserum (NIDDK-anti-hGH-2). In both cases the behavior of the recombinant preparation was identical to that of the pituitary hormone. This confirms previous data on bacterial correct processing and folding of the protein, as far as its immunological behavior is concerned and indicates its suitability for the preparation of immunoassay reagents.