Abstract
ABSTRACTProlonged signaling at the parathyroid hormone receptor 1 (PTHR1) correlates with the capacity of a ligand to bind to a G protein‐independent receptor conformation (R0). As long‐acting PTH (LA‐PTH) ligands hold interest as potential treatments for hypoparathyroidism (HP), we explored the structural basis in the ligand for stable R0 binding and prolonged cAMP signaling. A series of PTH/PTHrP hybrid analogs were synthesized and tested for actions in vitro and in vivo. Of the series, [Ala1,3,12,Gln10,Arg11,Trp14]‐PTH(1‐14)/PTHrP(15–36) (M‐PTH/PTHrP) bound with high affinity to R0, induced prolonged cAMP responses in UMR106 rat osteoblast‐derived cells, and induced the most prolonged increases in serum calcium (sCa) in normal rats. Daily s.c. injection of M‐PTH/PTHrP into thyroparathyroidectomized (TPTX) rats, a model of HP, normalized sCa without raising urine Ca. In contrast, oral alfacalcidol, a widely used treatment for HP, normalized sCa, but induced frank hypercalciuria. M‐PTH/PTHrP exhibited low solubility in aqueous solutions of neutral pH; however, replacement of Leu18, Phe22, and His26 with the less hydrophobic residues, Ala, Ala, and Lys, at those respective positions markedly improved solubility while maintaining bioactivity. Indeed, we recently showed that the resultant analog [Ala18,22,Lys26]‐M‐PTH/PTHrP or LA‐PTH, effectively normalizes sCa in TPTX rats and mediates prolonged actions in monkeys. These studies provide useful information for optimizing PTH and PTHrP ligand analogs for therapeutic development. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.
Highlights
We tested these different hybrid compounds for parathyroid hormone receptor 1 (PTHR1) binding affinity in vitro, assessing both the G protein-coupled and uncoupled receptor conformations, RG and R0, respectively.[13]. Our previous studies revealed that relative affinity for the R0 conformation correlates with duration of cAMP signaling.[14,15] Most importantly, we evaluated the analogs in vivo and assessed their capacities to stimulate a calcemic response in normal rats after a single i.v. administration
Affinities at the RG PTHR1 conformation were similar for all analogs tested, whereas each hybrid peptide bound to the R0 conformation with an affinity several-fold higher than that of PTH[1–34], and only slight differences in affinity were detected between any of the hybrid analogs (Tables 1 and 2)
We systematically explored a series of hybrid molecules composed of PTH and PTHrP
Summary
Hypoparathyroidism (HP) is a rare disorder of calcium (Ca) and phosphate metabolism that most often arises as a result of parathyroid gland damage or removal during surgery of the thyroid gland, but is associated with hereditary or acquired abnormalities, such as certain autoimmunity disorders, DiGeorge syndrome, mitochondrial dysfunction, and activating mutations of the Ca-sensing receptor.[1–4] Traditional therapy for HP is a regimen of oral vitamin D (typically, 1,25(OH)2-vitamin D3) and Ca supplementation, but this treatment, often effective, can be associated with marked variations in blood Ca, hypercalciuria, renal deterioration, and even nephrocalcinosis.[5,6] Recent clinical investigations on PTH-based modes of hormone-replacement therapy, including a double-blind, placebo-controlled randomized phase 3 study in which PTH [1–84] was given daily by s.c. injection,(7) have demonstrated sufficient effectiveness, such that PTH[1–84] has been approved by the US Food and Drug Administration as a treatment option. Recent clinical investigations on PTH-based modes of hormone-replacement therapy, including a double-blind, placebo-controlled randomized phase 3 study in which PTH [1–84] was given daily by s.c. injection,(7) have demonstrated sufficient effectiveness, such that PTH[1–84] has been approved by the US Food and Drug Administration as a treatment option. This represents an important advance in the treatment of the disease, challenges persist, in the capacity to maintain a steady-state level of blood Ca without excessive urinary Ca (uCa) excretion. We present key findings that led to the selection of LA-PTH as the optimum ligand in the series, and provide further data that compare the Ca-mobilizing actions of this type of hybrid PTH/PTHrP analog with those of a vitamin D analog in TXPTX rats
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
