Limits...
Identification of an orally active small-molecule PTHR1 agonist for the treatment of hypoparathyroidism

View Article: PubMed Central - PubMed

ABSTRACT

Parathyroid hormone (PTH) is essential for calcium homeostasis and its action is mediated by the PTH type 1 receptor (PTHR1), a class B G-protein-coupled receptor. Hypoparathyroidism and osteoporosis can be treated with PTH injections; however, no orally effective PTH analogue is available. Here we show that PCO371 is a novel, orally active small molecule that acts as a full agonist of PTHR1. PCO371 does not affect the PTH type 2 receptor (PTHR2), and analysis using PTHR1–PTHR2 chimeric receptors indicated that Proline 415 of PTHR1 is critical for PCO371-mediated PTHR1 activation. Oral administration of PCO371 to osteopenic rats provokes a significant increase in bone turnover with limited increase in bone mass. In hypocalcemic rats, PCO371 restores serum calcium levels without increasing urinary calcium, and with stronger and longer-lasting effects than PTH injections. These results strongly suggest that PCO371 can provide a new treatment option for PTH-related disorders, including hypoparathyroidism.

No MeSH data available.


Effects of PCO371 on serum parameters in TPTX rats.(a,b) Calcemic (a) and hypophosphatemic (b) effects of oral PCO371 or subcutaneous hPTH(1–84) in single administration. (c–e) Changes in serum Ca level (c), urinary Ca excretion (d), and serum 1,25(OH)2D3 level (e) from twice-daily repeated oral dosing of PCO371 (arrows in c) for 4 weeks. (f,g) Changes in serum Ca level (f), urinary Ca excretion (g) in once-daily repeated oral dosing of PCO371 (arrows) as an add-on to oral alfacalcidol treatment for 4 weeks. The shaded area shows the target therapeutic range (7.6–11.2 mg dl−1) of serum Ca level. Data are represented as the mean+or±s.e.m. of one experiment (n=6 in a,b,f and g, n=5 in c–e). Student's t test was used to compare the sham and TPTX vehicle-treated groups (#P<0.05 in g) and the alfacalcidol 75 ng ml−1 and TPTX control groups (§P<0.05 in g.) Parametric Dunnett's test was used to compare each treated group with the TPTX control group; *P<0.05, ***P<0.001 in e and g.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5120204&req=5

f6: Effects of PCO371 on serum parameters in TPTX rats.(a,b) Calcemic (a) and hypophosphatemic (b) effects of oral PCO371 or subcutaneous hPTH(1–84) in single administration. (c–e) Changes in serum Ca level (c), urinary Ca excretion (d), and serum 1,25(OH)2D3 level (e) from twice-daily repeated oral dosing of PCO371 (arrows in c) for 4 weeks. (f,g) Changes in serum Ca level (f), urinary Ca excretion (g) in once-daily repeated oral dosing of PCO371 (arrows) as an add-on to oral alfacalcidol treatment for 4 weeks. The shaded area shows the target therapeutic range (7.6–11.2 mg dl−1) of serum Ca level. Data are represented as the mean+or±s.e.m. of one experiment (n=6 in a,b,f and g, n=5 in c–e). Student's t test was used to compare the sham and TPTX vehicle-treated groups (#P<0.05 in g) and the alfacalcidol 75 ng ml−1 and TPTX control groups (§P<0.05 in g.) Parametric Dunnett's test was used to compare each treated group with the TPTX control group; *P<0.05, ***P<0.001 in e and g.

Mentions: We next examined the effect of PCO371 on serum Ca and inorganic phosphate (Pi) in TPTX rats. After a single oral administration, PCO371 dose-dependently increased serum Ca and decreased Pi, with greater efficacy and longer-lasting effects than those of hPTH(1–84) (Fig. 6a,b) or hPTH(1–34) (Supplementary Fig. 4a,b). Pharmacokinetics profiles of PCO371 and hPTH(1–84) were determined in TPTX rats. PCO371 had longer serum T1/2 and Tmax than hPTH(1–84) (Supplementary Table 4). We then examined the efficacy of PCO371 in 4-week multiple oral dosing studies in TPTX rats. In this model, subcutaneous treatment with hPTH(1–84) or hPTH(1–34) transiently increased serum Ca to within the target therapeutic range (7.6–11.2 mg dl−1)1011, but the serum Ca level dropped quickly to the basal level following each injection (Supplementary Fig. 4c,d). No increase in urinary Ca excretion was observed after 4-week treatment of hPTH(1–84) (Supplementary Fig. 4e). Twice-daily oral PCO371 at 3 mg kg−1 or more dose-dependently increased serum Ca to within the target therapeutic range, and maintained the Ca level within this range for at least 6 h after each administration from the first administration until the end of the study (Fig. 6c). In this experiment, no hypercalcemia (>11.2 mg dl−1) was observed at 0, 6 and 10 h after administrations of PCO371 on days 1, 7, 14, 22 and 29. Urinary Ca excretion after 4-week treatment was not increased by treatment with PCO371 up to 9 mg kg−1, even when the serum Ca had reached the target therapeutic range (Fig. 6d), possibly because renal Ca reabsorption was stimulated. Serum 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels increased significantly in rats treated with 9 mg kg−1 PCO371 (Fig. 6e), similarly to animals treated with hPTH(1–34) (Supplementary Fig. 4f). There was no significant difference in body weight or general condition between vehicle-treated rats and PCO371-treated rats (Supplementary Fig. 4g).


Identification of an orally active small-molecule PTHR1 agonist for the treatment of hypoparathyroidism
Effects of PCO371 on serum parameters in TPTX rats.(a,b) Calcemic (a) and hypophosphatemic (b) effects of oral PCO371 or subcutaneous hPTH(1–84) in single administration. (c–e) Changes in serum Ca level (c), urinary Ca excretion (d), and serum 1,25(OH)2D3 level (e) from twice-daily repeated oral dosing of PCO371 (arrows in c) for 4 weeks. (f,g) Changes in serum Ca level (f), urinary Ca excretion (g) in once-daily repeated oral dosing of PCO371 (arrows) as an add-on to oral alfacalcidol treatment for 4 weeks. The shaded area shows the target therapeutic range (7.6–11.2 mg dl−1) of serum Ca level. Data are represented as the mean+or±s.e.m. of one experiment (n=6 in a,b,f and g, n=5 in c–e). Student's t test was used to compare the sham and TPTX vehicle-treated groups (#P<0.05 in g) and the alfacalcidol 75 ng ml−1 and TPTX control groups (§P<0.05 in g.) Parametric Dunnett's test was used to compare each treated group with the TPTX control group; *P<0.05, ***P<0.001 in e and g.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120204&req=5

f6: Effects of PCO371 on serum parameters in TPTX rats.(a,b) Calcemic (a) and hypophosphatemic (b) effects of oral PCO371 or subcutaneous hPTH(1–84) in single administration. (c–e) Changes in serum Ca level (c), urinary Ca excretion (d), and serum 1,25(OH)2D3 level (e) from twice-daily repeated oral dosing of PCO371 (arrows in c) for 4 weeks. (f,g) Changes in serum Ca level (f), urinary Ca excretion (g) in once-daily repeated oral dosing of PCO371 (arrows) as an add-on to oral alfacalcidol treatment for 4 weeks. The shaded area shows the target therapeutic range (7.6–11.2 mg dl−1) of serum Ca level. Data are represented as the mean+or±s.e.m. of one experiment (n=6 in a,b,f and g, n=5 in c–e). Student's t test was used to compare the sham and TPTX vehicle-treated groups (#P<0.05 in g) and the alfacalcidol 75 ng ml−1 and TPTX control groups (§P<0.05 in g.) Parametric Dunnett's test was used to compare each treated group with the TPTX control group; *P<0.05, ***P<0.001 in e and g.
Mentions: We next examined the effect of PCO371 on serum Ca and inorganic phosphate (Pi) in TPTX rats. After a single oral administration, PCO371 dose-dependently increased serum Ca and decreased Pi, with greater efficacy and longer-lasting effects than those of hPTH(1–84) (Fig. 6a,b) or hPTH(1–34) (Supplementary Fig. 4a,b). Pharmacokinetics profiles of PCO371 and hPTH(1–84) were determined in TPTX rats. PCO371 had longer serum T1/2 and Tmax than hPTH(1–84) (Supplementary Table 4). We then examined the efficacy of PCO371 in 4-week multiple oral dosing studies in TPTX rats. In this model, subcutaneous treatment with hPTH(1–84) or hPTH(1–34) transiently increased serum Ca to within the target therapeutic range (7.6–11.2 mg dl−1)1011, but the serum Ca level dropped quickly to the basal level following each injection (Supplementary Fig. 4c,d). No increase in urinary Ca excretion was observed after 4-week treatment of hPTH(1–84) (Supplementary Fig. 4e). Twice-daily oral PCO371 at 3 mg kg−1 or more dose-dependently increased serum Ca to within the target therapeutic range, and maintained the Ca level within this range for at least 6 h after each administration from the first administration until the end of the study (Fig. 6c). In this experiment, no hypercalcemia (>11.2 mg dl−1) was observed at 0, 6 and 10 h after administrations of PCO371 on days 1, 7, 14, 22 and 29. Urinary Ca excretion after 4-week treatment was not increased by treatment with PCO371 up to 9 mg kg−1, even when the serum Ca had reached the target therapeutic range (Fig. 6d), possibly because renal Ca reabsorption was stimulated. Serum 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels increased significantly in rats treated with 9 mg kg−1 PCO371 (Fig. 6e), similarly to animals treated with hPTH(1–34) (Supplementary Fig. 4f). There was no significant difference in body weight or general condition between vehicle-treated rats and PCO371-treated rats (Supplementary Fig. 4g).

View Article: PubMed Central - PubMed

ABSTRACT

Parathyroid hormone (PTH) is essential for calcium homeostasis and its action is mediated by the PTH type 1 receptor (PTHR1), a class B G-protein-coupled receptor. Hypoparathyroidism and osteoporosis can be treated with PTH injections; however, no orally effective PTH analogue is available. Here we show that PCO371 is a novel, orally active small molecule that acts as a full agonist of PTHR1. PCO371 does not affect the PTH type 2 receptor (PTHR2), and analysis using PTHR1&ndash;PTHR2 chimeric receptors indicated that Proline 415 of PTHR1 is critical for PCO371-mediated PTHR1 activation. Oral administration of PCO371 to osteopenic rats provokes a significant increase in bone turnover with limited increase in bone mass. In hypocalcemic rats, PCO371 restores serum calcium levels without increasing urinary calcium, and with stronger and longer-lasting effects than PTH injections. These results strongly suggest that PCO371 can provide a new treatment option for PTH-related disorders, including hypoparathyroidism.

No MeSH data available.