Abaloparatide binds the PTH receptor in a way that produces shorter-lived signaling, which may explain why it stimulates bone formation with less bone resorption and fewer calcium spikes than teriparatide.
RG-selective bindingAbaloparatide preferentially binds the RG receptor conformation, producing shorter signaling bursts that favor bone building over bone breakdown
What the researchers found
Abaloparatide (a synthetic analog of PTHrP) binds more selectively to the RG conformation of the PTH type 1 receptor (PTHR1) compared to the R0 conformation, while PTH(1-34) (teriparatide) binds both conformations more equally.
This RG-selective binding produces more transient cAMP signaling responses in PTHR1-expressing cells. Because transient (intermittent-like) receptor activation favors bone formation over bone resorption, this receptor selectivity provides a molecular explanation for why abaloparatide may build bone with less accompanying bone loss and fewer hypercalcemic side effects than teriparatide.
Why it matters
Osteoporosis treatments that stimulate bone formation are powerful but come with trade-offs — teriparatide (PTH 1-34) can also increase bone resorption and raise calcium levels. This study reveals the molecular reason why abaloparatide may have a better safety profile: it activates the receptor in a more transient way that preferentially drives bone building. Understanding this mechanism helps explain clinical differences between the two drugs and could guide the design of even better bone-building peptides in the future.
The numbers in context
RG vs R0 conformation selectivity · more transient cAMP responses · in vitro HEK293 cells
How the study worked
The researchers used HEK293 cells engineered to express the PTH type 1 receptor (PTHR1) and performed binding assays to measure how abaloparatide and PTH(1-34) interact with two different receptor conformations (R0 and RG). They then measured downstream cAMP signaling responses to determine whether each peptide produced sustained or transient cellular activation.
Who was studied
In vitro study using HEK293 cells expressing PTHR1
What this study cannot tell us
This is an in vitro study using engineered cell lines, not human bone tissue or animal models. The receptor binding and signaling results may not directly translate to the complexity of bone biology in living organisms. The study does not include clinical outcomes or patient data.
How to read the evidence
This is rated Preliminary because it is an in vitro mechanistic study using engineered cell lines. While it provides an important molecular explanation, it does not include animal or human clinical data to confirm these receptor-level findings translate to actual bone outcomes.
When this study was published
Published in 2016, this foundational mechanistic study preceded abaloparatide's FDA approval in 2017 and remains relevant as the key explanation for its receptor pharmacology.
The bigger picture
This study contributes to the growing understanding of how different peptides can activate the same receptor in fundamentally different ways — a concept called biased signaling. For osteoporosis, this means drugs can be designed to favor bone formation while minimizing the bone resorption that limits older therapies. Abaloparatide (marketed as Tymlos) was approved by the FDA in 2017 for osteoporosis, and this receptor-level mechanism is part of the scientific foundation supporting its development.
Questions still open
- Could even more RG-selective peptide analogs be designed to further improve the bone formation-to-resorption ratio?
- Does this receptor binding difference fully explain the clinical differences between abaloparatide and teriparatide, or are other mechanisms involved?
- How does this RG-selective binding pattern translate to bone cell responses in living tissue rather than engineered cell lines?
Common questions
What is the difference between the R0 and RG receptor conformations?
Does this mean abaloparatide is better than teriparatide for osteoporosis?
Read the original research
Binding Selectivity of Abaloparatide for PTH-Type-1-Receptor Conformations and Effects on Downstream Signaling.
Endocrinology, 157(1), 141-9
Citation
Hattersley, Gary; Dean, Thomas; Corbin, Braden A; Bahar, Hila; Gardella, Thomas J. (2016). Binding Selectivity of Abaloparatide for PTH-Type-1-Receptor Conformations and Effects on Downstream Signaling.. Endocrinology, 157(1), 141-9. https://doi.org/10.1210/en.2015-1726