Oligonucleotides are unique in nature, somewhere between a small molecules and biologics, they present a novel set of challenges. They are chemically synthesized molecules with complex impurity profiles. The impurities stem from synthesis reactions, degradation and storage.
“Something in between small molecules and biologics but are usually chemically manufactured using phosphormidite building blocks and solid phase synthesis approach.”
Regulatory interest around oligonucleotides has grown in recent years. Ulrike Reider, Scientific lead at Novartis explained that existing ICH guidelines are applicable to oligonucleotides with a few modifications. Reider notes that: “Acceptance criteria based on the performance characteristics based on the performance characteristics of the method might be a bit different when having oligonucleotides compared to small molecules.”
To address gaps in current guidelines specifically around product related impurities, the EMA draft and Chinese CDE are developing new guidelines. Reider also highlighted the importance of impurity classification, informed by structure and safety thresholds, as outlined in white papers like those from the Oligonucleotide Safety Working Group.
Analytical methods such as LC-UV, MS, and chromatography play critical roles in identifying and quantifying impurities, with tailored approaches required for siRNA. siRNA requires additional considerations, such as the quantification of single-strand impurities through size-exclusion chromatography. Alignment of methodologies across drug substances and products ensures consistency in impurity profiles.
Reider stated: “The grouping of impurities is dependent on the applied methodology but also the development stage.”Morevover, impurities can either be grouped based on their structure particularly when using MS based methods or based on retention time or the retention time window.
Looking ahead, there is a growing need for innovative analytical tools to address increasingly complicated oligonucleotide conjugates and modifications. Furthermore, developing efficient data processing tools will address evolving manufacturing complexities, ensure regulatory compliance and product quality.
