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Lactam Formation Increases Receptor Binding, Adenylyl Cyclase Stimulation and Bone Growth Stimulation by Human Parathyroid Hormone (hPTH)(1–28)NH 2
Author(s) -
Whitfield J. F.,
Morley P.,
Willick G. E.,
Isaacs R. J.,
MacLean S.,
Ross V.,
Barbier J.R.,
Divieti P.,
Bringhurst F. R.
Publication year - 2000
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.2000.15.5.964
Subject(s) - adenylyl cyclase , parathyroid hormone , endocrinology , medicine , stimulation , chemistry , receptor , forskolin , agonist , parathyroid hormone receptor , biology , hormone receptor , calcium , cancer , breast cancer
Abstract Human parathyroid hormone (1–28)NH 2 [hPTH(1–28)NH 2 ] 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 IC 50 of 110 nM for displacing 125 I‐[Nle 8,18 , Tyr 34 ]bovine PTH(1–34)NH 2 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 EC 50 of 23.9 nM for stimulating adenylyl cyclase in ROS 17/2 cells. Increasing the amphiphilicity of the α‐helix in the residue 17–28 region by replacing Lys27 with Leu and stabilizing the helix by forming a lactam between Glu 22 and Lys 26 to produce the [Leu 27 ]cyclo(Glu 22 ‐Lys 26 )hPTH(1–28)NH 2 analog dramatically reduced the IC 50 for displacing 125 I‐[Nle 8,18 , Tyr 34 ]bPTH(1–34)NH 2 from hPTHIRs from 110 to 6 nM and dropped the EC 50 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)NH 2 . Thus, hPTH(1–28)NH 2 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 [Leu 27 ]cyclo(Glu 22 ‐Lys 26 )hPTH(1–28)NH 2 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)NH 2 considerably closer to the potencies of the larger PTH peptides and analogs. (J Bone Miner Res 2000;15:964–970)