Characterization of protein particles: Challenges and future trends
Protein therapy has revolutionized the way we treat disease, from cancer to autoimmune disorders. Market Data Forecast reports the market size exceeded $170 billion last year. Monoclonal antibodies are predicted to dominate the best selling drugs in 2023 by Evaluate Pharma.
Subcutaneous injection and intravenous infusion remain the main routes of administration of protein drugs.
However, protein therapy is susceptible to various forms of instability such as aggregation, degradation and particle formation. Particles can be a significant concern, as they can compromise the safety and efficacy of the injection. According to the FDA, since 2017, 40% of injectable drug recalls are due to particulate contamination. Therefore, the ability to monitor particle formation is essential for developing control strategies and ensuring the quality, safety and efficacy of injectable drugs.
What are particles?
Any injectable drug may contain various types of particles, which may originate from external sources such as biological materials, building materials or personnel. Intrinsic particles originate within the drug product, and can originate from processing, packaging materials, or product interactions.
Compared to non-biological injections, therapeutic proteins will contain protein aggregates, some of which are large enough to be quantified and characterized with nano and microparticle counters. And excipient-associated degradation products, such as fatty acid particles, may also be formed due to drug-product interactions. They are considered congenital particles if measured and form part of the clinical profile.
“Some of the main culprits of (protein) particles are interfaces. And one of the biggest problems that we have in this industry is the damage that protein products cause due to the filling process (where the protein formulation encounters a lot of different interfaces),” said John Carpenter, Emeritus Professor at the University of Colorado Anschutz Medical College, in a keynote address at the meeting. annual American Association of Pharmaceutical Scientists (AAPS).
Carpenter highlights how some of the main causes of protein particle formation is the adsorption of protein molecules onto interfaces, such as the walls of a syringe or processing tube. He stressed that mechanical stress, agitation, compression, dilation, instability of active pharmaceutical ingredients, and product-package interactions are all factors that can contribute to particle formation.
These inherent particles can pose a significant risk to patients, causing adverse immune reactions or reducing product efficacy. Therefore, it is very important to detect and measure protein particles accurately and reliably. The size range can be from a few nanometers to hundreds of micrometers. This is especially important for invisible particles, called subvisible particles (SvPs), which require specialized analytical methods.
Analytical methods for detecting and analyzing subvisible particles are used throughout the drug development process, from formulation development to stability testing to release testing and post-market surveillance.
What is a universal method capable of measuring particles across all size ranges throughout the drug development process?
There is no state-of-the-art technology to provide data across the particle size range.
One established and widely accepted method for measuring SvP analysis is light obscuration (LO), which meets regulatory requirements and is recognized as the official compendial method in many pharmacopoeias. Although LO has historical data available, it has limitations when it comes to the detection of protein particles. LO only provides number and size information, and does not distinguish between protein particles and other particles. In addition, LO may underestimate the translucence of particles, due to the low index of refraction between the solution and the particles. These are particles that often form due to interfacial pressure. The protein molecules form a film at the interface, which can break for various reasons, releasing translucent particles that are difficult for LO to detect.
To overcome these limitations, experts in the field use complementary methods, such as light microscopy, size exclusion chromatography, nanoparticle tracking analysis (NTA), flow imaging microscopy (FIM) and other techniques to gain a more comprehensive understanding of the characteristics of protein particles. It should be noted that each technique measures particles using different properties, and the inherent miscorrelation between the different methods must be accepted.
Rosch et al. notes that differences in results do not necessarily mean that one technique is more “right” or “wrong” than another, but instead can be used to gain better insight into the particle content of a sample.
What new solutions will we see in the future?
Prospects for the characterization of protein particles are bright, with several emerging trends in the field.
One trend that has been developing for more than a decade, is the use of multi-technique approaches to produce a more complete picture of particle characteristics. Many studies on this topic have concluded in the same way that no single analytical technique can provide a complete understanding of particle properties and behavior. Therefore, efforts should be made to align method choices across industries to increase the comparability of results.
Machine learning algorithms are also being used more frequently to support identifying patterns in particle morphology that may be difficult for humans to detect, leading to more informative results. We also look at the integration and combination of techniques within a single instrument, such as the LO and FIM systems directly coupled by FlowCam or the integration of Raman spectroscopy with imaging technology. This type of instrument can further improve the characterization of protein particles. In addition, the development of new analytical methods such as sensing of tunable resistive pulses, was reported by Wu et al.will continue to contribute in the field.
While there are still limitations in current techniques, such as LO for detecting protein aggregates, startup Bionter is focused on optimizing LO. The company has developed a non-destructive and automated way to utilize sufficient samples for comprehensive complementary analysis to enable a multi-technique approach. Further optimization of LO could include rethinking the light source to increase sensitivity to protein aggregates, as Tobias Werk, founder and CEO of Bionter, explained in his recent talk at AAPS.
Finally, with the increasing development of new protein drugs and other biologics (e.g. cell and gene therapies and lipid nanoparticle based vaccines), there will be a need for faster and more efficient methods of particle analysis that can be implemented in real-time during the manufacturing process. This will require the development of in-line and online monitoring techniques that can detect particle formation and growth in real time during the production process.
Overall, the prospects for the characterization of protein particles are promising, with ongoing efforts to innovate and ensure the safety and efficacy of protein therapies for the benefit of public health.
To learn more about Bionter AG and the company’s offerings, please visit their website.
Author: Angelika Schrems
Image courtesy of Bionter AG and Shutterstock