Fig. 9.

Properties of a long-acting PTH analog. Shown is the capacity of the long-acting analog, LA-PTH, a hybrid peptide consisting of a modified M-PTH(1–14) segment joined to a modified PTHrP(15–36) segment, to bind with high affinity to the R⁰ PTHR1 conformation and thus mediate prolonged signaling responses in cells and in animals. The analog is compared with PTH(1–34) for (A) binding to the PTHR1 in the G protein–independent conformation, R⁰; (B) inducing dose-dependent cAMP signaling responses in HEK-293 cells expressing the rat PTHR1 and the luciferase-based glosensor cAMP reporter; (C) capacity to maintain cAMP responses in the same cells after an initial application of ligand (0.3 nM/15 minutes) and then a washout (at t = 0') of unbound ligand; and (D) stimulating blood ionized calcium responses in mice [after injections with either vehicle, PTH(1–34) at 50 nmol/kg or LA-PTH at 10 nmol/kg]. Not shown is that LA-PTH bound to the G protein–coupled PTHR1 conformation, RG, with an affinity only threefold higher than that of PTH(1–34); this similar affinity for RG likely explains the similar potencies observed in the cAMP dose-response assays, whereas the greater difference in binding to the R⁰ PTHR1 conformation likely explains the more prolonged cAMP responses in cells and calcemic responses in animals. Adapted from Maeda et al. (2013).