Endocrine Abstracts

Human GH is a member of a family of closely related hormones that include prolactin and placental lactogen. GH regulates a wide variety of physiological processes, including growth and differentiation of muscle, bone and cartilage cells. The use of GH for the treatment of children with impaired linear growth has been accepted as an important therapeutic modality for many years. In addition, beneficial effects of GH replacement therapy in hypopituitary adults are well established. One major issue regarding the clinical use of GH is its relatively short half-life due to its rapid clearance by glomerular filtration. Thus the therapeutic protocol used in the treatment of patient required frequent injections of GH. To address this issue, we constructed five chimeric genes by fusing hGH cDNA to one, two or three cassettes of the carboxyl-terminal peptide (CTP) of human chorionic gonadotropin β (hCGβ) subunit. Chimeric genes, were inserted into the pCI – DHFR plasmid, a eukaryotic expression vector, transfected into DG44 cells and stable clones which secreted hGH variants were selected. For pharmacological evaluation of hGH variants, hypophysectomized Sprague–Dawley male rats were used. The results indicated that s.c. injection of GH-CTPs once a week for 2 weeks resulted in a dramatic increase in weight gain comparing to GH wild-type. Similar effect was achieved by daily injection of GH wild-type. Pharmacokinetic studies indicated that a higher level of the chimera is still detectable in serum after 50 h where the level of biotropin (a commercial GH) after 24 h was undetectable. The half-life of GH-CTPs is increased 4–5 folds comparing to biotropin. These data suggest that the mechanism of GH metabolic clearance is affected by the presence of CTP. This may establish a rationale for using this chimera as a long-acting GH analog.