ARA-290 (Cibinetide): An EPO-Derived Peptide

ARA-290, also called cibinetide, is a synthetic 11-residue peptide whose sequence is pGlu-Glu-Gln-Leu-Glu-Arg-Ala-Leu-Asn-Ser-Ser. It was designed to reproduce the solvent-facing surface of helix B of erythropoietin (EPO), the part of the hormone that engages the EPOR/CD131 heteroreceptor rather than the EPO receptor homodimer that drives red cell production. It is investigational: no drug containing it is approved by the FDA or any other regulator, and the published human work stops at Phase 2.

This profile covers where the sequence came from and why it is not a straightforward fragment of EPO, the receptor distinction it was built on, the models it has been studied in, the trials that were registered, its regulatory position, and the handling points that follow from a peptide beginning in pyroglutamate.

Identity at a glance

Values below are from the PubChem record for cibinetide (CID 91810664).

Counting charges: two glutamate side chains and the free C-terminal carboxylate give three negative charges at neutral pH against a single arginine, so the peptide is acidic overall, with a net charge near −2. There is no cysteine, tryptophan or tyrosine, so there are no disulfides and essentially no absorbance at 280 nm.

Where the sequence came from

The design is set out in a 2008 PNAS paper by Brines and colleagues. Their starting point was a receptor distinction. EPO's hormonal role, stimulating erythrocyte production, is mediated by the EPO receptor as a homodimer. The tissue-protective actions reported for locally produced EPO are attributed instead to a heterocomplex of the EPO receptor with CD131, the cytokine receptor common beta subunit shared by the interleukin-3, interleukin-5 and GM-CSF receptors (UniProt P32927). The developers of ARA-290 refer to that heterocomplex as the tissue-protective receptor.

Working from the crystal structure, the authors identified helix B of EPO, residues 58 to 82 of the mature protein, as a region that faces the aqueous medium when EPO is bound to the receptor homodimer. The aqueous face of that helix consists of the residues QEQLERAL, and three further residues from the adjacent BC loop were added, giving QEQLERALNSS. In their words, the residues are spatially, but not linearly, adjacent in the folded protein.

That detail is easy to check and worth checking, because ARA-290 is often described loosely as an EPO fragment. The mature human EPO sequence in UniProt P01588 contains no QEQLERAL stretch: reading along the chain through the helix B region gives ...EVGQQAVEVWQGLALLSEAVLRGQALLVNSS... ARA-290 is therefore a surface mimic assembled from residues that sit next to each other in three dimensions, not a contiguous piece of the hormone. UniProt's own secondary-structure annotation places a long helix over mature residues 56 to 82, consistent with the helix B assignment used in the design.

One more piece of chemistry completes the molecule. The peptide's N-terminal glutamine cyclizes spontaneously to pyroglutamate, and Brines and colleagues reported that early preparations were mixtures in which roughly 90 percent still had a free N-terminal glutamine. The cyclized form was then made deliberately and named pHBSP, the pyroglutamate helix B surface peptide. ARA-290 and cibinetide refer to this form.

The parent peptide is short-lived. The 2008 paper reports a plasma half-life of about 2 minutes in rats and rabbits, which is shorter than the interval over which tissue effects were observed in those experiments.

Reported mechanism

The mechanistic claim for ARA-290 is that it engages the EPOR/CD131 heteroreceptor without activating the EPOR homodimer. Brines and colleagues reported that neither helix B itself nor the 11-residue surface peptide was erythropoietic in vitro or in vivo, while both were protective in their injury models. Later work from other groups has used the peptide as a tool to probe that receptor: Nairz and colleagues (2017) reported effects on innate immune cell function in an experimental colitis model, and Awida and colleagues (2021) reported inhibition of osteoclast formation in vitro along with changes in bone mineral density in mice.

Because the receptor complex itself is defined largely by pharmacological evidence rather than by a solved structure of the ternary complex, the mechanism should be treated as a working model. What is well supported is the negative half of it: the peptide does not stimulate erythropoiesis in the assays where EPO does.

Research models

The models in the published literature cluster around nerve, immune and transplantation biology:

• Nerve injury and neuropathic models. The 2008 paper used sciatic nerve crush in rodents. Swartjes and colleagues (2014) reported long-term relief of neuropathic pain in a rat model together with suppression of the spinal microglial response.
• Ischemia models. Middle cerebral artery occlusion in rodents and renal ischemia-reperfusion were among the systems used to characterize the helix B peptides.
• Eye. Diabetes-induced retinal edema in rodents, and corneal nerve fiber measurements in later human work.
• Inflammation. Experimental colitis, where cibinetide was reported to dampen innate immune cell functions.
• Islet transplantation. Work by Yao and colleagues examined cibinetide with isolated human islets and in islet allograft models.
• Bone. In-vitro osteoclastogenesis assays plus bone density measurements in mice.

These are animal and cell models. For a different peptide that is also studied across ischemia models, but whose target is a mitochondrial lipid rather than a receptor, see the profile of SS-31.

Human trials and regulatory status

Human work with ARA-290 is limited and all of it is Phase 1 or Phase 2. Registered studies on ClinicalTrials.gov include a Phase 2 study of ARA 290 on corneal nerve fiber density and neuropathic symptoms in sarcoidosis (NCT02039687), a Phase 2 study in prediabetes and type 2 diabetes (NCT01933529), a Phase 1/2 study of cognitive and neural effects (NCT02070783), and a Phase 2 study in diabetic macular edema (NCT06626971), which the registry lists as terminated.

The 28-day Phase 2b trial in sarcoidosis-associated small nerve fiber loss was published by Culver and colleagues in 2017. Its primary endpoint was the change in corneal nerve fiber area measured by corneal confocal microscopy, with regenerating intraepidermal fibers, pain severity and a 6-minute walk test as further measures. Naming the endpoints is the appropriate level of detail here; the trial report itself gives the numbers.

On regulatory status, the facts are these. ARA-290 is not approved by the FDA or, as far as published records show, by any other regulator, for any indication. No Phase 3 trial appears in the registry. The sponsor, Araim, announced on July 5, 2016 that FDA had granted orphan drug designation for ARA 290 for the treatment of sarcoidosis. An orphan designation is a development incentive, awarded before efficacy is established, and it is not an approval.

Handling ARA-290 in the lab

The sequence dictates most of the practical points.

• Pyroglutamate at the N-terminus. The cyclized residue blocks the free alpha-amine. That makes the peptide resistant to aminopeptidases and to classical Edman sequencing, and it means the pyroglutamate form is 17 Da lighter than the corresponding glutamine form. A mass spectrum showing both species indicates incomplete cyclization, which is exactly the heterogeneity the developers set out to remove.
• Solubility. ARA-290 is an acidic, hydrophilic peptide and dissolves readily in water; a neutral to slightly basic buffer helps if dissolution is slow. The general method is in the guide on how to reconstitute peptides.
• Deamidation. The asparagine followed by serine (Asn9-Ser10) is a classic deamidation motif. Deamidation adds about 1 Da and a negative charge, and it is accelerated at higher pH and temperature, so keep stock solutions cold and prepare them fresh.
• Analytics. With an average mass of 1257.3 Da, identity is straightforward to confirm by mass spectrometry. HPLC purity is reported as the area of the principal peak against the total signal; the post on peptide purity explains how that figure is produced and what it does and does not cover. An 11-mer of this kind is made by solid-phase synthesis, described in the post on how peptides are made.
• Storage. Keep the lyophilized powder sealed, cold, dry and away from light, and aliquot solutions for single use.

Anhydrolabs supplies ARA-290 as a lyophilized powder in vacuum-sealed vials, and also as 10-vial kits.