Mono- and bicyclic analogs of parathyroid hormone-related protein. 1. Synthesis and biological studies.
The bioactive conformation of parathyroid hormone-related protein (PTHrP), a single-chain linear peptide structurally similar to parathyroid hormone (PTH), is of considerable interest because PTH and PTHrP both recognize and bind to a shared G-protein-coupled receptor. Both hormones are thought to present a bioactive conformation to the receptor which is substantially alpha-helical in nature. To better characterize this putative biologically relevant conformation, we prepared a series of conformationally constrained analogs of PTHrP with enhanced alpha-helical stability. A combination of structural constraint and helix stabilization was achieved through side chain-to-side chain lactam ring formation between Lys(i) and Asp(i+4) residues (13-to-17 and 26-to-30) along the PTHrP sequence. Mono- and bicyclic analogs derived from the agonist PTHrP-(1-34)NH2 and the antagonist PTHrP-(7-34)NH2 were prepared and characterized in terms of receptor binding and stimulation (or antagonism) of PTH-stimulated adenylyl cyclase activity in osteoblast-like cells. The binding affinity of monocyclic [Lys13,Asp17]-(I) and bicyclic [Lys13,Asp17,Lys26,Asp30]PTHrP-(1-34)NH2 (III) agonists was in the low nanomolar range and similar to that of the parent linear peptide. Furthermore, their efficacy was in the sub-nanomolar range and about 10-fold higher than that of the corresponding linear parent peptide. Analogs I and III are the first cyclic PTH/PTHrP receptor agonists and amongst the most potent PTHrP analogs yet designed. The rank-order of potency in the cyclic antagonist series does not correlate with the binding affinities. In light of the positional dependence and the differential effects of lactam bridge formation on the biological activities of agonist vs antagonists, these analogs may provide insight regarding the biologically relevant conformations of PTHrP-derived ligands [Maretto et al. (1997) Biochemistry 36, 3300-3307].
Bisello
A
A
Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Nakamoto
C
C
Rosenblatt
M
M
Chorev
M
M
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002460:Cell Line; D006801:Humans; D007202:Indicators and Reagents; D007700:Kinetics; D007769:Lactams; D008969:Molecular Sequence Data; D012516:Osteosarcoma; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D011506:Proteins / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D044168:Receptor, Parathyroid Hormone, Type 1; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism*; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013329:Structure-Activity Relationship
D007202:Indicators and Reagents; D007769:Lactams; C470121:PTHLH protein, human; D010281:Parathyroid Hormone; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D011506:Proteins; D044168:Receptor, Parathyroid Hormone, Type 1; D018016:Receptors, Parathyroid Hormone; D000262:Adenylyl Cyclases