How to think about HCP impurity testing
Getting a meaningful result
Many good points were raised when it comes to impurity testing at the latest Gyrolab User Seminar, held in Milan in June. This included a roundtable discussion on a subject that has been a stumbling block for many – how to measure Host Cell Protein (HCP) levels in a meaningful way.
HCPs are major process-related impurities in the production of biologics that can affect product safety, stability and efficacy. For example, some HCPs can be proteases that degrade the drug substance, while others can be immunogenic, result in off-target effects, or reduce the efficacy. The level of residual HCPs in drug product is generally considered a critical quality attribute (CQA) and monitoring the removal of HCPs in drug product during bioprocess development is a regulatory requirement. Finding these HCPs early on in process development can therefore be critical to long-term success in drug development, regulatory submission, and onto the market.
The difficulty of identifying a problematic HCP and determining its critical concentration necessitates a risk control strategy involving robust downstream bioprocessing to successively remove HCPs to as low a level as possible. Specific HCPs that are co-purified with the final drug product are then identified using process specific reagents. It is generally accepted that a sensitive, validated method involving, for example, ELISA is required to monitor residual HCPs in accordance with regulatory guidelines. Based on risk assessments, clinical experience and manufacturing capability typically accepted levels are < 100 ppm (100 ng HCP/mg product).
The discussion at the Gyrolab User Seminar started with the subject of bridging from ELISA to Gyrolab assays, including HCP analysis and can be summarized as follows:
The gold standard has been ELISA, backed by high quality antibody reagents. Transferring the method to Gyrolab system offers the possibility of increasing throughput with less hands-on time, but the question is, will this system give a better result that can be passed on to process development? And what exactly does ‘better’ mean? Do I actually want to ‘rock the boat’ by changing (= improving) my methods and discovering a problem (= high HCP level) where there was none before?
This reminded me of a commentary article I recently read that highlighted the need for improved methods in HCP analysis by Ken Hoffman, CEO of Cygnus Technologies (1). As he writes, there is an inbuilt resistance in the industry to change when it comes to HCP analysis that is based on the perception that regulatory authorities are reluctant to address new methods. Certainly the gold standard has been ELISA, and guidelines still accept older methods with the philosophy that it is incorrect to hold new drugs to higher standards than old ones that have passed the ‘HCP test’ and have a proven track record. But regulatory authorities welcome new and more effective methods. Added to that, improving HCP analysis can be a cost-effective way of shortening development time and reducing the risk of releasing drugs that have hidden problems, such as the presence of trace proteases that affect stability.
Getting back to the roundtable discussion on bridging:
A Field Application Specialist from Gyros Protein Technologies offered some advice: “If you are aiming to transfer to Gyrolab system, then start by comparing results from ELISA and your Gyrolab assay, both with the same reagents and also, where possible, by testing the relevant Gyrolab kit. A critical point is to test dilutional linearity. If there are large differences between the ELISA and Gyrolab assay then you will need to investigate with an orthogonal method, such as mass spectrometry.”
So, yes, it is possible to get meaningful data from your HCP analysis, and generic Gyrolab HCP assays can make this work a lot easier providing you use high quality reagents such as those in Gyrolab kits. Above all, take a long hard look at the way you are analyzing HCPs to ensure that you use the best method to ensure cost-effective development and production of a final product with the purity needed to ensure high stability, safety, and efficacy. This might mean enlisting orthogonal methods to determine the nature of specific HCPs that, despite your best efforts, are being co-purified with your drug substance. Or it might mean using a Gyrolab assay based on process-specific reagents to measure the levels of these key HCP impurities.
Learn more about how scientists at Sanofi have successfully implemented the Gyrolab immunoassay system as a reliable platform for high-throughput HCP analysis, in combination with a robotic liquid handling system. The results were comparable to their gold-standard ELISA method.
- Commentary: Moving beyond regulatory analytical requirements for better biotherapeutics. Hoffman, K. DDNews, May 2019.