Abaloparatide Injection

Abaloparatide Injection is an artificially synthesized 34 amino acid peptide that is an analog of parathyroid hormone related protein (PTHrP). It works by selectively activating parathyroid hormone type 1 receptor (PTH1R). PTH1R belongs to the G protein coupled receptor family, mainly expressed in bones and kidneys, and is an important target for the treatment of osteoporosis. After binding to PTH1R, Abaparatide activates the intracellular cyclic adenosine monophosphate (cAMP) - protein kinase A (PKA) signaling pathway, promoting osteoblast proliferation and differentiation. Compared with teriparatide (PTH1-34), Abaparatide has a bias towards activating PTH1R, more inclined to promote osteogenic activity rather than osteoclast activity, thereby improving bone remodeling imbalance.

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Abaloparatide\Abaloparatide Acetate COA

Certificate of Analysis
Compound name	Abaloparatide
Grade	Pharmaceutical grade
CAS No.	247062-33-5
Quantity	10g
Packaging standard	PE bag+Al foil bag
Manufacturer	Shaanxi BLOOM TECH Co., Ltd
Lot No.	202601090058
MFG	Jan 9th 2026
EXP	Jan 8th 2029
Structure
Item	Enterprise standard	Analysis result
Appearance	White or almost white powder	Conformed
Water content	≤5.0%	0.48%
Loss on drying	≤1.0%	0.35%
Heavy Metals	Pb≤0.5ppm	N.D.
	As≤0.5ppm	N.D.
	Hg≤0.5ppm	N.D.
	Cd≤0.5ppm	N.D.
Purity (HPLC)	≥99.0%	99.90%
Single impurity	<0.8%	0.57%
Total microbial count	≤750cfu/g	170
E. Coli	≤2MPN/g	N.D.
Salmonella	N.D.	N.D.
Ethanol (by GC)	≤5000ppm	500ppm
Storage	Store in a sealed, dark, and dry place below 2-8°C

Abaloparatide Injection, as a 34 peptide analogue of parathyroid hormone related peptide (PTHrP), has the core pharmacological essence of precise manipulation of the PTH1R receptor's "dual personality" - by selectively stabilizing the receptor's specific conformation, driving the spatiotemporal game between cAMP PKA signal and β - arrestin signal, achieving precise uncoupling of bone formation and resorption.

PTH1R belongs to the B-class G protein coupled receptor (GPCR), and its core biological feature is the existence of two mutually exclusive conformations, R0 (G protein uncoupled high affinity conformation) and RG (G protein coupled high affinity conformation), which respectively dominate the completely different signal spectra of sustained intracellular cAMP signal+strong β - arrestin activation and transient cell membrane cAMP signal+weak β - arrestin binding, forming the molecular basis of the receptor's "dual personality".
 

The R0 conformation is not dependent on G protein coupling, and the receptor's intracellular third ring (ICL3) is highly phosphorylated with the C-terminus. The extracellular domain (ECD) and transmembrane domain (TMD) are in a "closed" conformation, with extremely high affinity for ligands (Kd<1nM).
Signal characteristics: After ligand binding, the R0 conformation rapidly recruits β - arrestin1/2, mediating uptake into the early endosome by the receptor and continuously activating G α s-adenylate cyclase (AC) on the endosome membrane, producing a sustained cAMP signal for 60-90 minutes; Simultaneously, strong coupling with G α q activates the PLC-IP3-Ca ² ⁺ pathway, significantly promoting the expression of bone resorption related genes.

Functional bias: Mainly focused on osteoclast activation and calcium homeostasis regulation, with osteogenic effects accompanied by strong bone resorption, it is the core driving conformation for hypercalcemia and bone turnover imbalance.
Ligand preference: Teriparatide (PTH 1-34) has a 3.2-fold affinity for R0 conformation compared to RG, making it a typical R0 biased ligand.

RG conformation: Short term synthetic personality of transient signals
Conformational features: RG conformation strictly depends on G α s protein coupling, with low phosphorylation levels at the C-terminus of receptor ICL3. ECD-TMD exhibits an "open" conformation, and upon ligand binding, it rapidly triggers G protein GDP-GTP exchange with moderate affinity (Kd 1-5nM).

Signal characteristics: Ligand binding only activates G α s-AC on the surface of the cell membrane, generating an instantaneous cAMP signal for 15-30 minutes, which rapidly decays after the signal peak; Almost uncoupling of G α q, extremely weak recruitment of β - arrestin, delayed endocytosis of receptors, and negligible intracellular cAMP signaling.
Functional preference: It is mainly characterized by proliferation and differentiation of osteoblasts, synthesis of bone matrix, weak activation of bone resorption, and extremely low high calcium effect, making it an ideal conformation for bone synthesis metabolism.
Ligand preference: Abalotide has an affinity for RG conformation 8.7 times that of R0, making it the only highly RG biased clinical drug currently available.

The molecular switch of "dual personality": the obscure key site of PTH1R conformational transition

 

The conformational transition of PTH1R is regulated by three obscure key residues, which determine the ligand signal bias:
His223 (ICL2): Highly binds to β - arrestin in the R0 conformation, and is blocked by G α s in the RG conformation, blocking β - arrestin recruitment.
Ser489/Ser493 (C-terminus): Phosphorylated by GRK4/6 in the R0 conformation, serving as a β - arrestin binding site; Phosphorylation is inhibited in the RG conformation, and β - arrestin cannot bind stably.
Phe334 (TMD6): TMD6 shifts outward in the RG conformation, opening the G α s binding pocket; TMD6 invagination in R0 conformation, G α s dissociation, and enhanced β - arrestin binding.

Reference information source:

1. Vilardaga J P, et al. Molecular basis of parathyroid hormone receptor signaling and trafficking: a family B GPCR paradigm. Trends Pharmacol Sci. 2012
2. Dean T, et al. Binding Selectivity of Abaloparatide for PTH-Type-1-Receptor Conformations and Effects on Downstream Signaling. Endocrinology. 2016.
3. White A D, et al. Endosomal parathyroid hormone receptor signaling. Am J Physiol Cell Physiol. 2022.
4. Sutkeviciute I, et al. Spatial bias in cAMP generation determines biological responses to PTH type 1 receptor activation. J Biol Chem. 2022.
5. Chinese Journal of Pharmacology Progress in the development of conformational dynamics and biased agonists for B-class GPCRs two thousand and twenty-four

Abaloparatide Injection has 76% homology with natural PTHrP (1-34) and only 41% homology with PTH (1-34). Three non conservative amino acid substitutions are the key to its precise locking of RG conformation and breaking the balance of PTH1R "dual personality", completely distinguishing it from the R0 bias of teriparatide.

22nd place: Asp → Glu-Selective enhancement of Gαs

 

Structural niche effect: The 22nd Asp side chain of natural PTHrP is short and has weak hydrogen bonding, which can easily lead to receptor conformational shift towards R0; Abalotide is replaced with Glu, the side chain is extended by 1 CH ₂, and the carboxyl group forms a double hydrogen bond with Arg231 in the RG conformation, significantly enhancing the coupling stability of G α s.
The impact of signal obscurity: the G α s binding constant increased by 2.8 times, the cAMP signal EC50 decreased by 2.3 times (0.8nM vs 1.8nM), and the transient activation efficiency of cell membrane cAMP was significantly improved.
Conformal locking: Glu22 steric hindrance prevents TMD6 invagination, inhibits receptor conformational transition to R0, and continuously shields β - arrestin binding sites (His223, Ser489).

28th position: Glutamine (Gln)→ Leucine (Leu) - hydrophobic interaction reconstruction

 

Structural niche effect: The 28th Gln of natural PTHrP is a polar residue with poor compatibility with the hydrophobic pocket of the receptor ECD; Abalotide is replaced with hydrophobic Leu, forming strong hydrophobic clusters with Phe108 and Val129 of the receptor ECD, accurately adapting to the open interface of ECD-TMD in RG conformation.
Signal niche impact: RG conformation affinity increased by 4.1 times, R0 conformation affinity decreased by 52%, and conformational selectivity ratio (RG/R0) increased from 1.2 to 8.7.
Inhibition of endocytosis: Leu28 disrupts the hydrophobic binding interface between the ligand and β - arrestin, resulting in a 61% decrease in β - arrestin recruitment efficiency. Receptor endocytosis is delayed until 60 minutes (compared to 15 minutes for teriparatide).

34th position: Glutamine (Gln)→ 2-methylanine (Aib) - C-terminal steric hindrance regulation

 

Structural effect: The 34th Gln of natural PTHrP is a flexible residue that easily induces conformational changes in the C-terminus of the receptor and promotes phosphorylation of GRK; Abalotide is replaced with the non natural amino acid Aib, forming a rigid steric hindrance at the C-terminus to prevent the receptor from approaching ICL3.
Signal influence: The phosphorylation level of Ser489/Ser493 mediated by GRK4/6 decreased by 73%, the stable binding of β - arrestin was completely blocked, and the intracellular cAMP signal almost disappeared.
Signal termination acceleration: Aib34 reduces the stability of ligand receptor complexes, shortens the ligand dissociation half-life (τ off) to 30 seconds (180 seconds for teriparatide), and rapidly terminates cAMP signals.

Reference information source:

1. Hattersley G, et al. Molecular recognition of two endogenous hormones by the human parathyroid hormone receptor-1. J Biol Chem. 2022.
2. Peptide-DB. Abaloparatide: Molecular Modification & Conformational Selectivity. 2026.
3. Leder B Z, et al. Differential Signaling and Anabolic Actions of Abaloparatide and Teriparatide in Human Osteoblasts. J Bone Miner Res. 2021.
4. MCE. Abaloparatide (BA 058) Structural & Pharmacological Properties. 2026.
5. Journal of Medicinal Chemistry. Application of non natural amino acid modifications in GPCR biased agonists two thousand and twenty-five

Cell membrane: the absolute home field of cAMP signaling

 

92% of the cAMP signal of Abaloparatide Injection is concentrated on the cell membrane, and the RG conformation is highly expressed on the surface of osteoblast membrane PTH1R. The signal is directly transmitted to the osteogenic effector without spatial loss.
Cell membrane cAMP preferentially activates membrane-bound PKA, targeting the regulation of osteoblast membrane receptors and ion channels (such as Ca ² ⁺ - ATPase), promoting calcium and phosphorus deposition and bone matrix mineralization.

Internal body: Inhibition of β - arrestin signal away from home

 

The endocytosis rate of receptors mediated by Abalotide is only 24% (78% for Teriparatide), and there is almost no G α s coupling of receptors in the endosome. The cAMP signal in the endosome is less than 5% of the cell membrane.
Endosomal β - arrestin cannot form signal complexes, does not activate the endoplasmic reticulum ERK and JNK pathways, and blocks the transcription of sustained bone resorption genes (such as RANKL and CTSK).

Efficient entry of osteogenic signals into the nucleus and interception of osteoclast signals

 

CAMP PKA phosphorylated Runx2/Osterix rapidly enters the nucleus (10 minutes) and binds to the osteogenic gene promoter, resulting in a 3.7-fold increase in transcriptional activity.
Due to its weak intensity and short duration, the β - arrestin-ERK signal cannot effectively enter the nucleus, and the activation of osteoclast related transcription factors (NFATc1, c-Fos) is inhibited. The RANKL/OPG ratio only increases by 38% (teriparatide is 112%).

Reference information source:

1. Vilardaga J P, et al. PTH receptor-1 signalling-mechanistic insights and therapeutic prospects. Nat Rev Endocrinol. 2023.
2. Whalen E P, et al. Comparable Initial Engagement of Intracellular Signaling Pathways by Parathyroid Hormone Receptor Ligands. J Bone Miner Res. 2021.
3. Frolik W, et al. Abaloparatide exhibits greater osteoanabolic response and higher cAMP stimulation and β-arrestin recruitment than teriparatide. J Pharmacol Exp Ther. 2020.

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