Lactam formation increases receptor binding, adenylyl cyclase stimulation and bone growth stimulation by human parathyroid hormone (hPTH)(1-28)NH2.
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.
Whitfield
J F
JF
Institute for Biological Sciences, National Research Council of Canada, Ottawa, Ontario.
Morley
P
P
Willick
G E
GE
Isaacs
R J
RJ
MacLean
S
S
Ross
V
V
Barbier
J R
JR
Divieti
P
P
Bringhurst
F R
FR
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001846:Bone Development / Q000187:drug effects*; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D007769:Lactams / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism*; D013552:Swine; D019379:Teriparatide / Q000031:analogs & derivatives* / Q000494:pharmacology
D007769:Lactams; D010446:Peptide Fragments; D018016:Receptors, Parathyroid Hormone; D019379:Teriparatide; D000262:Adenylyl Cyclases; C035748:parathyroid hormone (1-34)amide