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Sep 1, 2010 (Vol. 30, No. 15)

Process Monitoring Realm Expanding

Traditional Sensor Approaches Evolve to Include Measurements that Enable PAT

  • Building on the Scientific Foundation

    With increasing numbers of bioprocessors taking PAT and QbD seriously, the future appears bright for bioprocess monitoring and advanced technologies for measuring quality attributes in real- or near-real time.

    One hurdle to adoption of new process-monitoring technologies is the risk aversion of many biopharmaceutical companies, particularly with respect to highly regulated operations like cleaning and fermentation. But the FDA has made an effort, says Bader, to evaluate new techniques and technologies scientifically.

    Regulators and companies alike, he says, are looking for favorable, substantiated precedents, preferably in already approved manufacturing processes. “Once they see a few case studies, see that people are doing it, and the technique has gone through regulatory approval, everyone is much more open.”

  • Sidebar: Applying PAT to Vaccine Manufacturing

    The complexity and heterogeneity of vaccines makes them much more difficult to characterize than therapeutic proteins, and even more so in real time. For example, mAbs of molecular weights up to about 150 kDa range are easily analyzed for sequence, isoforms, and glycosylation.

    “By contrast, virus-like particles can be more than 1,000-fold greater in size than proteins and hold much more complex structures,” notes Gerard Powell, Ph.D., analytical development scientist at Eden Biodesign. Vaccines are also held to a higher safety standard than other biologicals, which makes safety an even higher priority, both during manufacture and after release.

    The question, given the complexity of vaccine formulations and relevant analytics, is which techniques lend themselves to in-process monitoring, and how many such orthogonal methods will provide manufacturers and regulators with a reasonable level of safety assurance?

    Electrophoresis, immunoblotting, PCR, amino acid sequencing, quaternary structure analysis, and electron microscopy are all quite slow. And given the heterogeneity of vaccines, real-time platform analytics are unlikely to emerge.

    “But where it is impossible to identify every attribute of the whole vaccine, well-chosen assays can ensure an overall quality picture is achieved,” Dr. Powell says. For example process engineers can monitor total protein and quantify sub-visible particles; purity may be established using ion-exchange HPLC using novel monolithic columns and size-exclusion chromatography with multi-angle laser light scattering analysis; biological activity is assessed through serological assaying and, in the case of adenoviruses, measuring infectious titer.

    However, classical analytics such as HPLC/ uHPLC and spectroscopy, while useful, lack the resolving power and sensitivity to detect small changes that may result in production of an effective vaccine, or even a safe product, in real time.

    Yet, says Dr. Powell, applying PAT to vaccine manufacturing and process development is essential “if we are to fully understand, and ultimately be able to control, the manufacturing process.”

    First, vaccine-makers must establish critical quality attributes whose real-time measurements may be used to control the process. Applicable techniques may include on-line liquid chromatography approaches such as size-exclusion chromatography coupled with multi-angle light scattering detection, and ion-exchange chromatography using monolithic columns. These techniques, he says, can estimate quality during process development as well as production in much the same way that analytical protein A chromatography allows with mAbs.

    “These on-line PAT techniques allow much more flexibility in rapid decision making during vaccine process development, which is critical to building optimal platform processes for vaccine manufacturing.”

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