Lactam formation increases receptor binding, adenylyl cyclase stimulation and bone growth stimulation by human parathyroid hormone (hPTH)(1-28)NH2.

Abstract

Human parathyroid hormone (1-28)NH2 [hPTH(1-28)NH2] is the smallest of the PTH fragments that can fully stimulate adenylyl cyclase in ROS 17/2 rat osteoblast-like osteosarcoma cells. This fragment has an IC50 of 110 nM for displacing 125I-[Nle8,18,Tyr34]bovine PTH(1-34)NH2 from HKRK B7 porcine kidney cells, which stably express 950,000 human type 1 PTH/PTH-related protein (PTHrP) receptors (PTH1Rs) per cell. It also has an EC50 of 23.9 nM for stimulating adenylyl cyclase in ROS 17/2 cells. Increasing the amphiphilicity of the alpha-helix in the residue 17-28 region by replacing Lys27 with Leu and stabilizing the helix by forming a lactam between Glu22 and Lys26 to produce the [Leu27]cyclo(Glu22-Lys26)hPTH(1-28)NH2 analog dramatically reduced the IC50 for displacing 125I-[Nle8,18,Tyr34]bPTH(1-34)NH2 from hPTH1Rs from 110 to 6 nM and dropped the EC50 for adenylyl cyclase stimulation in ROS 17/2 cells from 23.9 to 9.6 nM. These modifications also increased the osteogenic potency of hPTH(1-28)NH2. Thus, hPTH(1-28)NH2 did not significantly stimulate either femoral or vertebral trabecular bone growth in rats when injected daily at a dose of 5 nmol/100 g body weight for 6 weeks, beginning 2 weeks after ovariectomy (OVX), but it strongly stimulated the growth of trabeculae in the cancellous bone of the distal femurs and L5 vertebrae when injected at 25 nmol/100 g body weight. By contrast [Leu27]cyclo(Glu22-Lys26)hPTH(1-28)NH2 significantly stimulated trabecular bone growth when injected at 5 nmol/100 g of body weight. Thus, these modifications have brought the bone anabolic potency of hPTH(1-28)NH2 considerably closer to the potencies of the larger PTH peptides and analogs.

• Authors: J F Whitfield, P Morley, G E Willick, R J Isaacs, S MacLean, V Ross, J R Barbier, P Divieti, F R Bringhurst
• Journal: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research (J Bone Miner Res) Vol. 15 Issue 5 Pg. 964-70 (May 2000) ISSN: 0884-0431 [Print] United States
• PMID: 10804028 (Publication Type: Journal Article)

Chemical References

• Lactams
• Peptide Fragments
• Receptors, Parathyroid Hormone
• Teriparatide
• Adenylyl Cyclases
• parathyroid hormone (1-34)amide

Topics

• Adenylyl Cyclases (metabolism)
• Animals
• Bone Development (drug effects)
• Cell Line
• Enzyme Activation
• Humans
• Lactams (metabolism)
• Peptide Fragments (pharmacology)
• Protein Binding
• Rats
• Rats, Sprague-Dawley
• Receptors, Parathyroid Hormone (metabolism)
• Swine
• Teriparatide (analogs & derivatives, pharmacology)