Does aggregation of cagrilintide at 25 °C show up as a loss of content or of purity?

Question

Setup, so nobody has to ask: aggregation · cagrilintide · 25 °C. The empirical answer seems settled. The explanation does not. If the honest answer is that nobody knows, I would rather hear that than a plausible story. Why does this happen, and what would falsify the usual explanation?

tare_weight · Accepted Answer

At 25 °C it can show up as either, and which one depends entirely on whether the product still elutes under the main peak. Purity is a ratio of areas, so a degradant only costs purity if the method resolves it. Content is a mass against a standard, so a degradant costs content whenever the parent is consumed — resolved or not. Molecules associate without any covalent change, so the mass is unchanged and a reversed-phase run — which is performed in organic solvent — mostly dissolves the evidence before it can be measured. That is why the two measurements are not interchangeable and why an unchanged purity figure after an excursion to 25 °C is weak evidence: the method may simply be integrating the degradant along with the parent and reporting the sum as one peak. The relevant point is that a mass shift of plus one dalton is deamidation and plus sixteen is oxidation, so degradation is often visible in a mass spectrum if anyone looks. Light exposure matters for tryptophan-containing sequences and for anything with a chromophore. Amber vials and a closed box are free mitigations. Reported and extrapolated stability by condition State Condition Usable window Basis Lyophilised solid −20 °C, sealed, dry 24–36 months Supplier guidance Lyophilised solid 2–8 °C, sealed 12–24 months Supplier guidance Lyophilised solid 25 °C, sealed 4–8 weeks Extrapolated (Arrhenius) Lyophilised solid 40 °C, sealed 1–2 weeks Extrapolated Solution, preserved 2–8 °C 28 days USP microbiological convention Solution, preserved 25 °C 3–7 days Extrapolated Solution, unpreserved 2–8 °C 24 hours USP microbiological convention Windows for the solid state are chemical; windows for solution are microbiological and usually shorter than the chemical limit. Aggregation is physical: peptides unfold at air-liquid interfaces and associate. Shaking maximises that interface, which is why swirling and shaking produce visibly different outcomes on the same vial. Aggregation at air-liquid interfaces is established from surface-tension and particle-count studies and is the basis for anti-agitation handling guidance. Sequence decides which pathways are even available. Check the residues.

Dr_Ingrid_Baumgartner · Answer

Answering this needs the physical state, since a dry powder is protected from most of these and a solution is protected from none.

Deamidation converts asparagine or glutamine to the corresponding acid via a succinimide intermediate, adding one dalton. It is base-catalysed, accelerates above neutral pH and is the dominant aqueous pathway for many peptides.

The part that matters: freeze-thaw cycling drives aggregation through concentration at the ice interface and pH shifts as buffer components crystallise out at different rates. Each cycle costs something.

Nothing here is medical advice, and research-use compounds are not approved for human use.

A mass spectrum names the pathway. Plus one, plus sixteen, minus eighteen.

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answeredDr_Ingrid_Baumgartner73k589 Dec 2024

h_pergande · Answer

The part that matters: asparagine and glutamine are the deamidation risk, and methionine is the oxidation risk.

Adsorption onto glass and plastic is significant at low concentrations — micrograms per millilitre — and negligible at milligrams per millilitre. It is the usual explanation for an apparent loss in a dilute preparation.

A mass spectrum resolves most of this: minus eighteen is dehydration or succinimide, plus one is deamidation, plus sixteen is oxidation, and an unchanged mass with a shifted retention time is an isomer.

Adsorption losses at low concentrations are quantified in formulation studies and are the reason carrier proteins are used in dilute preparations.

The caveat is that none of these pathways can be seen by looking at a vial, and a clear solution can be substantially degraded.

At dilute concentrations, suspect adsorption before you suspect chemistry.

edited 8 Jan 2025 by h_pergande — clarified the distinction between purity and content

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answeredh_pergande71k15820 Dec 2024

Same experience here, different supplier. – dead_volume 10 months ago

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fibre_or_fragment · Answer

Aggregation is a physical process and is the one most often caused by handling rather than by time.

Oxidation targets methionine, cysteine and tryptophan, adding sixteen daltons per oxygen. It is catalysed by trace metals and promoted by dissolved oxygen and by light.

Metal-catalysed oxidation of methionine is documented across peptide and protein formulations and is why chelators appear in some formulations.

Cold, dry, dark, still. Those four words cover most of the mitigation.

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answeredfibre_or_fragment13k3812 Jan 2025

6Is there a reason to prefer minus eighty here, or is minus twenty genuinely enough? – Dr_Priya_Raghunathan 5 months ago

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Dr_Ingrid_Baumgartner · Answer

The honest answer is that most reported "degradation" is adsorption and dilution error rather than chemistry. Hydrolysis cleaves the backbone, most readily at aspartate-proline and aspartate-glycine sequences, and is acid-catalysed. In a dry solid it barely proceeds at all. Deamidation via the succinimide intermediate is well characterised, with sequence-dependent rates highest for asparagine-glycine motifs. Swirl, never shake. Aggregation is a handling problem more than a time problem.

Does aggregation of cagrilintide at 25 °C show up as a loss of content or of purity?

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State	Condition	Usable window	Basis
Lyophilised solid	−20 °C, sealed, dry	24–36 months	Supplier guidance
Lyophilised solid	2–8 °C, sealed	12–24 months	Supplier guidance
Lyophilised solid	25 °C, sealed	4–8 weeks	Extrapolated (Arrhenius)
Lyophilised solid	40 °C, sealed	1–2 weeks	Extrapolated
Solution, preserved	2–8 °C	28 days	USP microbiological convention
Solution, preserved	25 °C	3–7 days	Extrapolated
Solution, unpreserved	2–8 °C	24 hours	USP microbiological convention