David A. Keire, Ph.D., Director, Division of Pharmaceutical Analysis, Office of Testing and Research, Office of Pharmaceutical Quality, CDER
When scientists in the Office of Testing and Research (OTR) in CDER’s Office of Pharmaceutical Quality (OPQ) need to demonstrate the quality and performance of a drug product, they use a variety of novel analytical techniques. These techniques help to assess specific information about a drug or drug product, such as its chemical structure, purity, and quantity of active ingredient. For commonly used drugs like aspirin, “classical” analytical methods to measure these properties work well to spot problems in the drug that could impair its safety or effectiveness.
Increasingly, the drugs that are approved for use in people are becoming more complex. Some drugs are complex because they are mixtures of closely related molecules that together result in drug action. Some drugs are considered complex because they are designed to function in the patient over long periods of time or to be delivered to certain areas within the body. Some complex drugs are manufactured and purified from living cells, and at the molecular level, such drugs are typically larger than traditional drugs. Because of this complexity, OTR scientists often need to use advanced analytical methods to provide assurance of drug safety and effectiveness.
Advanced Methods for Characterizing Complex Drugs
Two analytical techniques that OTR scientists use to characterize therapeutic proteins and other complex drugs are nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). These methods were first developed for the analysis of simple chemicals, but over the past few decades they have evolved significantly. Today, OTR experts use these advanced methods to ensure that samples of a given therapeutic protein or complex drug product, even when produced by different manufacturers, are highly similar or equivalent to one another at the molecular level.
One example of a complex drug that OTR scientists have analyzed with NMR and MS methods is heparin. Heparin is a complex mixture of sugar-based molecules and is used in patients to prevent blood clots. Since the 1930s, heparin has been prepared from animal sources and was monitored by classical analysis methods. In 2007, however, heparin products that later proved to be contaminated were associated with a number of patient deaths. The crisis revealed the need for better analysis methods to monitor this essential drug.1
In response, OTR scientists developed new NMR and MS methods to pick out and measure the active components or key characteristics from within complex heparin mixtures and to provide better assurance of consistency and safety in heparin products. Methods were also developed for the analysis of modified heparin products like enoxaparin, ultimately leading to approval of the first generic version of this complex drug.
Another example of modernizing drug analysis methods relates to the drug filgrastim, which is used to treat side effects associated with chemotherapy. Compared to the small-molecule drug acetaminophen (a pain medication), filgrastim (a therapeutic protein) is a hundred times greater in size. The molecular structure of filgrastim thus depends on the proper placement of thousands of atoms in three-dimensional space. The large “backbone” of linked atoms in the filgrastim molecule must twist and fold in specific ways to ensure filgrastim functions as a protein. Scientists call this twisting and folding in three-dimensional space the “higher-order” structure of the protein.
Verifying proper higher-order structure within protein therapeutics poses many challenges. Scientists around the world who investigate protein product similarity have to find methods that, on the one hand, can allow for harmless variations in higher-order structure but, on the other hand, ensure that those structural elements necessary for protein function are preserved. When an FDA-approved protein product is marketed by multiple manufacturers, as is the case for filgrastim, FDA scientists are challenged to ensure structural consistency across diverse manufacturing locations and facilities.
For OTR chemists, the reliability of NMR techniques to test for the higher-order levels of structure of filgrastim biosimilar products is an important concern. NMR techniques are so sensitive that results may sometimes vary in response to differences in temperature, laboratory handling, and salts and buffers to which proteins are exposed during manufacture or analysis. Moreover, NMR machines themselves differ from laboratory to laboratory. To ensure structural similarity across multiple geographic areas and regulatory jurisdictions, FDA regulatory scientists therefore need to rely on NMR-based structural analyses whenever and wherever a filgrastim biosimilar is tested.
To test the variability and reliability of NMR methods, OTR scientists have collaborated with scientists in the United States and abroad in a series of experiments to study the structure of distinct filgrastim biosimilar products at four independent NMR laboratories. 2 The group of scientists found that by calibrating their NMR instruments properly, they could generate uniform results across the four independent laboratory settings, even though the samples were handled by different individual investigators from different countries, using NMR instruments of varying magnetic power. The NMR data were so precise and reproducible that the structural information can be securely used for years to come, providing a cost-effective basis for the development of additional filgrastim biosimilar products in the future.
To help the FDA review complex drugs in a timely manner and provide patients with safe and effective drug products, the use of robust, highly sensitive and high-resolution analytical technologies like NMR and MS provides better information. Ultimately, such modern analytical methods reduce the risk to the American public of getting drugs that don’t work as they should.
1 The US regulatory and pharmacopeia response to the global heparin contamination crisis. Szajek AY, Chess E, Johansen K, Gratzl G, Gray E, Keire D, Linhardt RJ, Liu J, Morris T, Mulloy B, Nasr M, Shriver Z, Torralba P, Viskov C, Williams R, Woodcock J, Workman W, Al-Hakim A. Nat Biotechnol. 2016 Jun;34(6):625-30.
2 Precision and robustness of 2D-NMR for structure assessment of filgrastim biosimilars. Ghasriani H, Hodgson DJ, Brinson RG, McEwen I, Buhse LF, Kozlowski S, Marino JP, Aubin Y, Keire DA. Nat Biotechnol. 2016 Feb;34(2):139-41.
The Spotlight series presents generalized perspectives on ongoing research- and science-based activities within CDER. Spotlight articles should not be construed to represent FDA’s views or policies.