What are Process-Related Residuals? | Which is the Best Method for Analyzing Process Impurities?

During development and manufacturing of biologics process-related impurities must be analyzed to ensure safety and efficacy of the final product.
Without an analysis, the impurities may affect the final biologic by:
Increasing toxicity,
inducing immunogenicity
or decreasing drug stability.
There are 3 types of process-related impurities:
Cell substrate-derived - like Host Cell Proteins (HCPs),
cell culture-derived - like antibiotics,
and downstream process-derived - like enzymes.
We will focus on the downstream process-derived, also termed process-related residuals.
Various residuals are added to the host cell to facilitate protein expression. Common residuals include:
Benzonase nuclease
Protein A
Aminopeptidase
PEG
Triton-X
and several other solvents and enzymes.
FDA requires that the residuals clearance is documented
through the development and manufacturing of biologics.
This is typically done by ELISA or mass spectrometry.
These methods have different pros and cons.
For ELISA, the pros include
fast concentration determination
and the possibility to run many samples in a short time.
Some of the cons are that
the accuracy depends on the antibody specificity
and it takes a long time
to develop process-specific assays.
With mass spec, the pros include:
A high accuracy down to less than 50 ppm
and it can be applied to all known host species.
The cons are that it is at first
more expensive than a generic ELISA kit,
and if you do not have prior
mass spec knowledge and equipment
it is very difficult to develop an approach.
When you must choose between the methods, it depends on your setup and desire to obtain detailed information about the residuals.
A suitable method should ensure and include:
Regulatory documentation
and intelligent process development.
Mass spec offers several advantages for both, especially if you need absolute quantification of enzymes & other proteins.