One consideration that does need to be borne in mind is the spectroscopic profile of the drug conjugated to the mAb. Depending on the drug, it may have absorption characteristics in the spectral range of some of the instrumentation (CD in particular). A spectroscopic profile of the native drug is therefore absolutely necessary when assessing HOS data from an ADC to help assess any impact the drug is having on the overall ADC profile. Again, the use of orthogonal techniques means that any interferences from the drug in a particular analysis can be circumvented by data from other procedures and a clearer understanding of the ADC HOS is obtained.
The chemical processes used to produce ADCs could result in enhanced aggregation as a result of structural disruption of the mAb and this needs to be investigated. Again, a sample of the native mAb should be analyzed alongside the ADCs to provide baseline aggregate levels. As with HOS analysis, aggregation of non-conjugated proteins has been discussed in a separate blog.
Just as with other HOS analyses, orthogonality is very important in aggregation studies. This comes out of the general principle of the value of orthogonal investigations, as recognized by the regulatory agencies, stemming from the fact that different aggregation techniques will give different values for the level of aggregation due to the nature of the techniques themselves. At BioPharmaSpec, we use a combination of sedimentation velocity ultra-centrifugation (SV-AUC) and size exclusion chromatography with multi-angle laserlight scattering (SEC-MALS) for aggregation studies and these have been shown to be applicable to ADCs.