News & Events
Potential Need for Measurement Standards to Facilitate R&D of Biologic Drugs
Steven Kozlowski, M.D.
Director, Office of Biotechnology Products
Office of Pharmaceutical Science
Center for Drug Evaluation and Research
Food and Drug Administration
the Committee on Science and Technology
Subcommittee on Technology and Innovation
U.S. House of Representatives
Mr. Chairman and Members of the Subcommittee, I am Dr. Steven Kozlowski, Director of Biotechnology Products in the Center for Drug Evaluation and Research at the Food and Drug Administration (FDA or the Agency). I very much appreciate this opportunity to discuss how the development of measurement science, standards, and related technologies might make it easier to characterize FDA-regulated biological products.
I will begin with a general description of one type of biological product—therapeutic proteins—and explain some of the difficulties we face in characterizing these products. I will then discuss potential benefits that could follow from improved analytical methods and measurement standards. Finally, I would like to describe three specific properties of biological products that we cannot sufficiently measure, but that are very important for understanding the behavior of biological protein products. Better analytical methods to measure these three properties would be extremely helpful in determining the similarity of similar biological protein products.
Congress has charged FDA with ensuring the safety and effectiveness of drug and biological products sold in the United States. As part of fulfilling this responsibility, it is important that FDA be able to understand, or characterize, the composition of these products. We want to know:
- what materials they are made up of, and
- how the materials are arranged (i.e., the structure) at a molecular level.
For some medical products, characterization is relatively straightforward. Non-biological, often called small-molecule, drugs are typically of low molecular size and are manufactured in chemical reactors rather than biological systems. The structure of small-molecule drugs can be verified through established analytical testing. However, we are now in the era of molecular biology where many new therapies are manufactured by inserting novel genes into living cells so as to produce therapeutic proteins by biologic processes. For example, many therapeutic monoclonal antibodies are produced using cell lines with manipulated DNA.
Size and Complexity of Biologics: Protein Therapeutics
Compared to assessing the structure of small-molecule drugs, which generally have fewer than 100 atoms, assessing the structure of biologics is a formidable task. Therapeutic proteins are much larger than typical small-molecule drugs. Using molecular weight as a measure of size, human growth hormone is more than 150 times larger than aspirin and a monoclonal antibody is more than five times larger still than human growth hormone. Therapeutic proteins are also much more complex than typical small-molecule drugs. Attached is a graphic depiction of human growth hormone and aspirin, which illustrates the differences in size and complexity.
The manufacture of biologics is also quite complex. Most biologics are composed of many thousands of atoms linked together in a precise arrangement (called the primary structure). This organization of atoms is further organized into a three-dimensional higher order structure by the folding of the linked atoms into a specific pattern that is held together by relatively unstable connections. A protein molecule consists of a long chain of building blocks called amino acids, of which there are 20 types—a single protein chain can be made up of hundreds of amino acids. The sequential order of these building blocks in the chain can be critical for medicinal activity. Protein chains with the same sequence of amino acids can fold in different ways—much like a single piece of rope can be tied into a variety of different knots. The specific folding of these chains is also very important in carrying out their therapeutic functions.
In addition, many of the linked amino acids can have modifications attached. These attachments can be small (only a few atoms) or very large (similar in size to the rest of the protein). One commonly observed attachment is the addition of complex groups of sugar molecules, called oligosaccharides. Attachments occur at very specific locations on the protein and, like folding, can have great impact on the therapeutic function of the protein. A protein can thus be represented as a long chain with 20 different types of links with different possible attachments on the links.
To further complicate matters, biologics are not composed of structurally identical units. Instead, they are a mixture of products with slightly different features. This is referred to as micro heterogeneity and can be represented as a mixture of very similar chains that differ in a few links or in a few of the attachments. The protein chains themselves can then be linked together or aggregated (i.e., clumped). It is a challenge to analyze and characterize the composition of such a mixture. Even with currently available analytical technologies, some uncertainty regarding the actual structure of a biologic usually remains. Simple measurements of biological activity, such as enzyme activity, may provide additional information about a product. But there is currently no way to, a priori, understand how the product will perform in patients (e.g. distribution in the body, immune responses against the product). As a result, nonclinical or clinical studies are necessary to assess the safety and effectiveness of the product.
Potential Benefits of Improved Analytical Methods
Advances in analytical tests during the last two decades have driven progress in biopharmaceutical manufacturing, but there is still room for significant improvement. New or enhanced analytical technologies and measurement systems and standards that can more accurately and precisely assess the higher order structure and attachments of biologics would provide additional assurance of the quality of biologics in at least three specific ways:
- Improved analytical methods would enable quicker and more confident assessments of the potential effects of changes in the manufacturing process, equipment, or raw materials.
At present, manufacturers and FDA are hampered by the inability to fully measure structural differences that could be caused by changes in the manufacturing process. Since these unknown structural differences could change the properties of the product, FDA might only approve a manufacturing change after seeing the results of studies of the product in animals or humans. This can significantly slow the implementation of innovative process improvements and impede the manufacturer’s ability to react to changes in raw material supplies, which could reduce the availability of the drug to patients who need it. Improved analytical methods could reduce the requirements for animal and/or human studies for evaluation of manufacturing changes. In addition, for products that have abbreviated pathways for approval, improved analytical methods could facilitate comparison of products and detection of differences between manufacturers.
- The development of analytical methods that can evaluate the quality of the biologic throughout the manufacturing process would provide a superior system for ensuring product quality.
This would enable increased productivity and improved quality control during the manufacturing process.
- Improved analytical methods would increase general knowledge in the field of biopharmaceuticals.
FDA can use knowledge from improved analytical methods to inform our regulatory decisions, and industry can use this knowledge to design better products. Experience to date with certain monoclonal antibodies, a type of therapeutic protein, illustrates how this increased knowledge can inform both regulatory decisionmaking and product design. Some monoclonal antibodies better direct a patient’s immune system to kill tumor cells, and some do not. One reason for this difference was only discovered after the development of an analytical technique that enabled scientists to characterize the structure of the sugar chains attached to the antibodies. It was discovered that antibodies with certain sugar chains were more consistently able to direct an immune system to kill tumor cells than antibodies with different sugar chains. FDA initially used this knowledge to require monitoring and control of these sugar chains to ensure consistent clinical benefit to patients. But this knowledge has also enabled industry to design new monoclonal antibody products with enhanced tumor-killing activity.
Potential Benefits of New Measurement Standards
With the development of new analytical methods comes the need for new standards to evaluate them. The term standard can apply to measurements or to processes, and although process standards are valuable in ensuring effective manufacturing process operation and validation, today, I will focus on measurement standards. A measurement standard can be standardized test materials used to evaluate the performance of a measurement method, or it can be a specific analytical procedure used to take a measurement. Standardized test materials can be used to evaluate the precision and accuracy of many different analytical technologies and are, thus, more likely to foster competition and development of new and improved analytical methods by industry and academia. Standard test materials could be used to test the ability of an analytical method to detect differences between product batches from a single manufacturer or products from different manufacturers. For example, if a method is being developed to assess the sugars attached to a protein, the analytical method could be used to test a set of related standard test materials in order to determine the precision and accuracy of the method. In this way, a given technology can be optimized or a variety of different technologies can be compared for their ability to accurately and quantitatively assess the quality of a product. The development of such measurement standards would also be extremely valuable for ensuring that current and future analytical methods are working properly and are providing consistent results from assay to assay and from lab to lab.
Three Specific Properties Needing Improved Measurement
FDA has identified three properties of therapeutic proteins that cannot be sufficiently measured at this time but that are very important for understanding the behavior of protein drugs. Improved analytical methods to measure these three properties would be particularly useful in determining the extent of similarity of biological protein products intended to be similar.
1. Post-translation Modifications
As indicated previously, proteins contain added structural features, such as attached sugar chains, that may be critical for their clinical activity. These attached modifications can be complex and heterogeneous, and we currently lack standardized analytical methods to qualitatively and quantitatively assess the structure as it relates to the intact protein and understand the relationship of the modifications to potency and clinical performance. We are particularly interested in better methods for analyzing the sugars (glycosylation) and other modifications known to affect the medicinal activity of these products.
2. Three-dimensional Structure
As described previously, proteins must be folded into a three-dimensional structure to become functional (sometimes a three-dimensional structure can be misfolded). The proteins within a biologic will have one major three-dimensional structure along with a distribution of other variants differing in three-dimensional structure. Our current ability to predict the potency of biologics would be enhanced if we had improved ability to measure and quantify the correct (major) three-dimensional structure, aberrant three-dimensional structures (misfolding), and the distribution of different three-dimensional structures.
3. Protein Aggregation
Some biological products can stick to one another. When many protein molecules stick together, they are referred to as aggregates and have the potential to cause adverse immune responses in patients. There are many forms and sizes of aggregates and many current methodologies have gaps in their ability to detect different types of aggregates. Our ability to minimize adverse immune reactions would be enhanced if we had improved ability to measure and quantify different types of aggregates.
The field of biopharmaceuticals is advancing rapidly—in many ways more rapidly than analytical technologies. New measurement tools and standards would be of value in all the areas I have discussed. In particular, reliable and discriminating material standards would enhance use of current methodologies and encourage new technologies to fill current gaps. Moreover, as the field of biopharmaceuticals continues to advance, there is the potential for greater research and development in the evolving area of follow-on biologics, which could provide significant savings for consumers and the federal government over time.
Thank you again for the opportunity to testify today. I am happy to address any questions you may have.