How to store peptides: storage and transit of lyophilized powder

Transit and storage are questions about a solid. A lyophilized vial holds the peptide as a dry, porous cake with very little water. Chemical change generally needs molecular mobility, and water acts as a plasticizer that supplies it. A dry cake offers little of either.

What degrades a dry peptide

The routes most often reported for dry peptides are deamidation (mainly at asparagine), oxidation (at methionine, cysteine and tryptophan) and backbone cleavage at aspartic acid; aggregation is also reported. Mobility helps all of them, and deamidation and cleavage need water itself. Residual moisture in the cake and humidity in the surrounding air supply it.

Heat accelerates each of them. In the usual Arrhenius range, a reaction rate rises roughly two- to four-fold for each 10 °C, a rule of thumb and not a measurement on any particular peptide. Light is a separate route to oxidation, covered in the companion article Light and peptides.

Why the solid state is forgiving

In an amorphous cake held below its glass transition temperature, molecular motion is very slow. Accelerated testing rests on the Arrhenius relationship: stress a product with heat, measure the change and extrapolate to milder conditions. The extrapolation holds only while the degradation mechanism stays the same, and for an amorphous solid it can fail as the stress temperature nears the glass transition. ICH Q1A(R2) is the stability guideline such studies follow; its conditions are the guideline's, not Solara's test results.

What transit does to a vial

A parcel moves between a warm truck and a cold depot, so it sees swings rather than a steady temperature. ICH Q1A(R2) sets no accelerated condition for material labelled for freezer storage; it asks for a separate study at 5 °C or 25 °C to cover shipping excursions. Where a cold pack is used, it buffers heat peaks; it does not hold −20 °C. Arrival at room temperature therefore shows neither that a vial has changed nor that it has not. Solara ships from Canada within one to two business days, packed to protect the powder in transit, and has published no stability data for its lots.

Storage once the vial arrives

Solara's site guidance is to store the lyophilized powder at −20 °C, sealed, protected from light and moisture. Each condition maps to one of the routes above:

• Cold: rates fall with temperature, so −20 °C slows every route above.
• Sealed: the closure is the barrier against humid air.
• Dark: excluding light removes photo-initiated oxidation.
• Dry: moisture is the input most routes depend on.

Solara's guidance is that a sealed vial reach room temperature before it is opened, so that water does not condense onto the cake.