How many freeze-thaw cycles will survodutide at 2 mg/mL tolerate?

The case in front of me: survodutide · 2 mg/mL.

I have done this once and I suspect I got away with it rather than got it right.

For context: I keep records of every batch, every lot number and every result, so an answer that requires me to track something is fine.

What would you do, and what would you check afterwards?

Nobody has published a cycle count, and at 2 mg/mL the concentration tells you what a wrong guess costs: a 0.1 mL aliquot holds 0.2 mg and every microlitre is 2 µg. Damage from freezing is not gradual attrition — it is concentrated at the phase transitions, where ice excludes solute and the unfrozen fraction climbs well above 2 mg/mL for as long as the transition lasts. Two slow cycles can therefore do more than four fast ones, which is why a cycle count is the wrong unit in the first place. The way to make the number one is to make it one: split at reconstitution into single-draw aliquots, label each with 2 mg/mL and the date, and never thaw a container you will refreeze.

Start with how many cycles are actually planned, because one or two are immaterial and ten are not.

Buffer salts crystallise at different points during freezing. Sodium phosphate is the classic example: the dibasic form crystallises first and the pH of the residual liquid falls by several units. That pH excursion is the real damage in many cases.

Reported and extrapolated stability by condition

Windows for the solid state are chemical; windows for solution are microbiological and usually shorter than the chemical limit.

It helps to be literal here: let a frozen vial reach room temperature before opening it. Opening a cold vial in humid air condenses water into the cake, which raises residual moisture and undoes what lyophilisation achieved.

Selective crystallisation of sodium phosphate buffer components producing large pH shifts on freezing is a classical result in the lyophilisation literature.

Count cycles, not degrees. The cycle is the damaging event.

This is one of the few handling questions with a genuinely quantitative literature behind it.

Thaw slowly at room temperature or in the refrigerator rather than in warm water. Rapid warming creates local thermal and concentration gradients that promote aggregation.

During freezing, solutes are excluded from the ice lattice and concentrate into the residual liquid. Local concentrations can rise many-fold, which promotes aggregation independently of temperature.

Cryoconcentration of solutes at the ice front is a well-documented mechanism in freeze-thaw damage to proteins and peptides.

Aliquoting itself is a handling step and introduces its own contamination opportunity.

Aliquot before the first freeze. That is the whole answer.

edited 17 Nov 2024 by greta_holzmann — added the placebo-arm figures

Answer first: each freeze-thaw cycle costs something through aggregation and pH shift, so the mitigation is aliquoting rather than choosing a better freezer.

The mitigation is aliquoting. Divide the reconstituted solution into single-use volumes before the first freeze, and each aliquot then experiences exactly one cycle.

Count cycles rather than worrying about degrees. Minus twenty and minus eighty differ far less than one cycle and five do.

Condensation onto cold lyophilised material on opening is a recognised handling error and is the basis for the equilibrate-before-opening rule.

The number of tolerable cycles is sequence- and formulation-dependent and no general number is honest.

Let a frozen vial reach room temperature before opening, or you condense water into it.

The short version: aliquot before freezing, thaw slowly, never refreeze a thawed aliquot, and count your cycles.

A dry lyophilised powder is much less affected by a temperature cycle because there is no liquid phase for anything to concentrate into. Condensation on a cold vial opened warm is the real risk there.

Aliquoting to eliminate repeated cycles is standard laboratory practice for exactly this reason.

Thaw slowly and never refreeze an aliquot.

Answering this needs to know whether the material is dry or in solution, since a dry powder is largely indifferent to a temperature cycle.

Never refreeze a thawed aliquot. The whole point of aliquoting is that the aliquot is single-use, and refreezing it discards the benefit.

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

Dry powder tolerates cycles far better than solution does.

edited 15 Jan 2025 by forty_two_c — added the method parameters