Absolute Quantification of Oligonucleotides by ICP-MS/MS

Arnaud Delobel
Juliusz Bianga
Magali Perez
Damien Mouvet
Caroline Cajot

As for all therapeutic products, oligonucleotide concentration in drug substances and drug products is considered a critical quality attribute, as it impacts both safety and efficacy of the drug. UV spectroscopy is the most widely used technique for this purpose, but it requires either a well-characterised reference material or the prior knowledge of the extinction coefficient of the oligonucleotide. In both cases, an analytical method for the absolute quantification of oligonucleotides is a prerequisite. In this application note, we describe a method based on phosphorus determination by triple quadrupole ICP-MS for the quantification of oligonucleotides in drug substances and drug products. The performance of the method was studied in terms of precision and accuracy.

Oligonucleotides are a promising class of therapeutics, that have been under clinical development for more than 30 years. As of December 2020, 11 oligonucleotide therapeutics have been approved by the US FDA, and many more are still under development. They have a potential to be used in the treatment of a wide range of diseases, including cancer, cardiovascular and metabolic conditions, ophthalmic diseases, and neurological disorders.

In order to make oligonucleotides amenable to therapeutic use, many modifications were developed. Their aim is to stabilise the molecule and increase its resistance to enzymatic degradation.

As with all therapeutic products, a reliable determination of the concentration is required, to ensure both efficacy and safety of the drug. Quantification of oligonucleotides is routinely performed by UV spectroscopy. But this approach requires the use of a well-characterised reference standard, or the prior knowledge of the extinction coefficient.

A method was developed for the absolute quantification of purified therapeutic oligonucleotides, based on phosphorus determination by
This method can be used for the characterisation of oligonucleotide samples, but also for the determination of the extinction
coefficient, that could further be used for UV spectroscopy analysis during routine testing (batch release and stability studies).

Even without the availability of certified oligonucleotide material, we were able to demonstrate the excellent performance of the method,
both in terms of precision and accuracy.

This method is now proposed as a GMP service at Quality Assistance.