Parathyroid Hormone-Related Protein 1-36

Summary

Parathyroid hormone‑related protein 1‑36 (PTHrP (1‑36)) is a synthetic peptide that mimics the N‑terminal region of the endogenous hormone‑like factor PTHrP. It binds the same type‑1 parathyroid hormone receptor (PTH1R) as parathyroid hormone, activating cAMP signaling. Early human studies have examined intermittent subcutaneous dosing as an anabolic stimulus for bone in postmenopausal osteoporosis and as a diagnostic probe for calcium‑phosphate disorders. The compound remains investigational and is not approved for therapeutic use.

Mechanism of Action

PTHrP (1‑36) engages the PTH1R on osteoblasts, osteocytes, renal tubular cells and other target tissues. Receptor activation stimulates G‑protein–mediated adenylate cyclase activity, raising intracellular cAMP and activating protein kinase A pathways that promote osteoblastic activity and increase renal 1α‑hydroxylase, elevating 1,25‑dihydroxyvitamin D. Intermittent exposure favors bone formation, whereas continuous exposure drives osteoclast recruitment and suppresses osteoblast maturation, mirroring the dual anabolic/catabolic actions described for PTH.

What the Research Shows

Human studies have explored both intermittent and continuous administration of PTHrP (1‑36). A 3‑month randomized trial in postmenopausal women compared daily subcutaneous PTHrP (1‑36) (400 µg or 600 µg) with daily PTH (1‑34) (20 µg). All groups showed similar increases in lumbar spine BMD; the 400 µg dose also raised hip BMD, while bone turnover markers rose less markedly than with PTH (1‑34). Mild, transient hyper‑calcemia occurred at higher PTHrP doses. A separate 7‑day continuous infusion study in healthy volunteers demonstrated rapid elevation of serum calcium, increased bone resorption, and a 30‑40 % suppression of bone‑formation markers that rebounded after infusion stopped, indicating that continuous exposure mimics catabolic states. Earlier dose‑finding work confirmed that subcutaneous PTHrP (1‑36) elicits expected changes in phosphate handling, urinary cAMP and 1,25‑(OH)₂ D without altering serum calcium at low doses. Animal and in‑vitro data show comparable receptor binding and adenylate cyclase activation to PTH, supporting its mechanistic plausibility as an anabolic agent.

Reported Benefits

Intermittent subcutaneous PTHrP (1‑36) increased lumbar spine bone density to a similar extent as the approved anabolic agent PTH (1‑34) and also produced modest gains in hip bone density, suggesting potential utility for osteoporosis treatment. The peptide demonstrated biologic activity at low subcutaneous doses, influencing calcium‑phosphate homeostasis and vitamin D metabolism, which could be advantageous for diagnostic differentiation of humoral hypercalcemia of malignancy from primary hyperparathyroidism. Its ability to activate the same receptor pathways as PTH supports its theoretical efficacy as a bone‑building therapy.

Limitations of the Evidence

Evidence is limited to short‑term human trials (up to three months) and modest sample sizes, with no data on long‑term fracture outcomes or optimal dosing regimens. The comparative study showed less pronounced stimulation of bone turnover markers than PTH (1‑34), and higher doses produced transient hyper‑calcemia, indicating a narrow therapeutic window. Continuous infusion studies revealed suppression of bone formation, underscoring the importance of dosing schedule. No regulatory approval exists, and the peptide’s efficacy in diverse populations or in combination with other osteoporosis treatments remains untested.

Safety Considerations

In the 3‑month trial, mild, transient hyper‑calcemia occurred in participants receiving 400 µg and required dose reduction at 600 µg; overall adverse‑event rates were similar across groups. Continuous low‑dose infusions produced mild hyper‑calcemia and hyper‑calciuria without altering vitamin D or phosphate handling, but bone‑formation markers were suppressed during infusion. Subcutaneous doses up to 3.28 µg/kg in healthy women altered phosphate and calcium excretion but did not raise serum calcium. Reported side effects are limited to these metabolic changes; no serious safety signals have emerged, but longer‑term safety data are lacking.

How It Is Administered

PTHrP (1‑36) has been studied as a sterile peptide solution administered by subcutaneous injection once daily for intermittent regimens, and as an intravenous infusion for continuous exposure. Doses in trials ranged from 0.8–3.3 µg/kg subcutaneously to 400–600 µg daily, and 2–4 pmol/kg/h intravenously for up to seven days. Formulations are typically aqueous solutions prepared for injection.

Routes of Administration

Goals & Uses

• Osteoporosis treatmentBone MetabolismModerate
• Anabolic bone therapyMusculoskeletalModerate
• Research tool for PTH1R signalingResearchHigh
• HypoparathyroidismCalcium DeficiencyLow
• Hypercalcemia of malignancy researchOncology / Calcium MetabolismLow
• Reduction of fracture riskOsteoporosisLow
• Increase bone mineral densityBone HealthModerate

Contraindications

• Active malignancy with bone metastasesOncologyModerate
• HypercalcemiaMetabolic DisorderHigh
• Severe renal impairmentOrganModerateKidney function concerns
• PregnancyPopulationModeratePotential fetal risk or insufficient safety data
• Paget's disease of boneBone DisorderModerate
• History of skeletal malignancy or bone metastasesOncologyHigh
• Severe hypercalcemiaElectrolyte DisorderHigh

Adverse Effects

• Elevated bone turnover markersLaboratoryCommon
• Hypercalcemia / hypercalciuriaMetabolicCommon
• HypercalcemiaMetabolicCommon
• Injection site reactionsLocalCommon
• Injection site painLocalCommonPain at the injection site
• HypotensionCardiovascularUncommonLow blood pressure
• NauseaGastrointestinalCommonFeeling of sickness or urge to vomit
• Dizziness / orthostatic hypotensionCardiovascularUncommon

Drug Interactions

• Loop diureticsModerate
• BisphosphonatesLow
• DigoxinHigh
• Calcium and Vitamin D supplementsLow
• Thiazide diureticsModerate

Population Constraints

• Pediatric patientsAgeRelative
• ElderlyAgeRelative
• Elderly patients (>75 years)AgeRelative
• Pregnant womenReproductiveRelative
• Patients with nephrolithiasis historyRenalRelative
• ChildrenPediatricRelative

Regulatory Status

• European UnionInvestigationalUnder clinical evaluation; not authorized.
• United StatesInvestigationalInvestigational New Drug (IND) application filed; not FDA‑approved.
• United KingdomInvestigationalNo MHRA approval; research compound

Not approved for clinical use; investigated in early‑phase trials for osteoporosis and hypoparathyroidism.

Evidence & Sources

• A comparison of parathyroid hormone-related protein (1-36) and parathyroid hormone (1-34) on markers of bone turnover and bone density in postmenopausal women: the PrOP study
  Journal ArticleModerateHorwitz MJ, et al.2013-01-01T00:00:00.000000Z
• A 7-day continuous infusion of PTH or PTHrP suppresses bone formation and uncouples bone turnover
  Journal ArticleModerateHorwitz MJ, et al.2011-01-01T00:00:00.000000Z
• Parathyroid hormone-related protein-(1-36) is biologically active when administered subcutaneously to humans
  Journal ArticleLowHenry JG, et al.1997-01-01T00:00:00.000000Z
• Spatial and temporal expression of parathyroid hormone-related protein during wound healing
  Journal ArticleLowBlomme EA, et al.1999-01-01T00:00:00.000000Z
• Functional properties of a synthetic chicken parathyroid hormone-related protein 1-36 fragment
  Journal ArticleLowSchermer DT, et al.1994-01-01T00:00:00.000000Z
• PTHrP(1-36) as a skeletal anabolic agent for the treatment of osteoporosis
  Journal ArticleModerateStewart AF1996-01-01T00:00:00.000000Z

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