Mass spectrometry (MS) is increasingly popular among drug makers keen to ensure that process impurities do not impact the safety or efficacy of their products. The method is used to measure the mass-to-charge ratio of molecules in a sample. From a biopharmaceutical industry perspective, the major benefit of MS is the level of detail it can provide, said Alla Zilberman, PhD, from Cygnus Technologies, who cites host-cell-protein (HCP) analysis as an example.

“Complete characterization of downstream HCPs is not part of the current regulatory guidelines. However, the potential for such information to help biopharmaceutical companies ensure the safety and efficacy of their products makes it recognized as value-added data by proactive manufacturers and regulators,” noted Zilberman.

HCPs constitute a major group of process-related impurities in biological drugs. They are produced inadvertently during the expression of recombinant proteins and secreted from host cells in response to cell stress and/or cell lysis over the course of bioprocessing. Many HCPs are benign, but some are immunogenic. In addition, some may interact with a drug substance, and others can reduce effective product dosage through direct action on the drug or its stability by interfering with formulation buffers.

Analytical combinations

An increasingly common approach to HCP characterization is to combine the standard method—identification using an enzyme-linked immunosorbent assay (ELISA) with MS-based analytics, according to Zilberman.

“Identification and quantification of HCPs by MS provides a powerful complementary method to ELISA. While HCP ELISA reports ‘total’ value for HCPs in the final drug substance,” continued Zilberman. MS can actually identify and quantify what that “Total HCP Number” consists of: how many HCPs, and in what quantities.

“There is one caveat though: drug product often masks HCPs. Drug substance is typically in mg/mL concentration while HCPs in low ng/mg drug substance,” he said.

To help customers address this, Cygnus recommends using antibody affinity extraction for the preparation method—which is a type of immune-affinity chromatography that utilizes the corresponding HCP ELISA antibody to enrich HCPs and deplete drug substance prior to MS analysis.

And there are other, business-relevant potential benefits of MS, according to Zilberman.

“If we take into consideration all aspects of method development and validation, analyst training, equipment cost, method robustness, etc., a well-developed and validated ELISA is a less costly and more reliable method for routine manufacturing quality control and product lot release.

“However, MS is an important tool during process development, process scale-up, transfer from one CDMO to another, and as a troubleshooting tool should there be any changes in the downstream process resulting in changes in HCP values.”

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