BioPharm: Biologics are clearly more complex to develop and characterize than small-molecule drug products. What would you say are the key unique challenges associated with biopharmaceutical development and testing?
Immune reactions on the part of the model to human protein, cell, or gene-based treatments can be complex and are required not only to detect antibodies to drug, but also to interpret toxicology results. Occasionally, this comparison of kinetic, biomarker, and immune-reaction assessments reveal that a drug's toxicity is due to immune reactions. In such a case, the drug can be freed from an "alert" and continued through development without interruption. Without the bioanalytical assays and careful scientific review of assay results, however, a drug program might be terminated for the wrong reasons.
Another challenge is that the process, not just product, must be characterized and understood. Potential contaminants are not just synthetic chemicals like those found in small-molecule manufacturing. Testing for more complex organisms, such as adventitious viruses, bacteria, yeast, fungi and mycoplasma, along with a wide array of antibiotics, and other additives, may need to be performed.
Assay development for small molecules usually consists of test article analysis using components and instruments that are generally available, such as extraction cartridges, high-performance liquid chromatography (HPLC) columns, and liquid chromatography/mass spectrometry (LC/MS) systems. Because most biologics are analyzed by immunoassay methods, specific reagents must be developed for a particular biologic. This requires time to produce novel, well-characterized reagents, as well as assay development time, which can lengthen the time needed to complete the full analysis of the studies required to file for product registration. However, in preclinical species, it may be possible to use readily-available antibodies that bind to the constant region (Fc) on a humanized monoclonal antibody (mAb) candidate for immunoassay detection, thus eliminating the need for reagent development.
Ultimately, the sponsor and CRO must work together to define and fulfill the reagent requirements at the onset of a project to mutually understand the sequence of developmental activities required to meet project timeline expectations.
Finally, with rare exceptions, small molecules undergo absorption, metabolism, and excretion after administration, using well-defined enzymatic and physiological pathways. The development and regulatory paradigm to evaluate small molecule disposition has been well studied and characterized. The disposition of biologics, on the other hand, is typically not well characterized during development.
Biologics must be assessed for the potential to develop neutralizing antibodies. There is no appropriate surrogate to assess the clinical development of neutralizing antibodies, which can be critical for endogenous biologic replacement therapy. The development of neutralizing antibodies to an endogenous protein can produce auto-immunity against a key physiological process. The sponsor and CRO therefore must develop a well-designed plan to assess neutralizing antibodies in nonhuman primates and in the clinic, as this is an important component of biologics development, especially when the biologic is meant to serve as a replacement therapy for an endogenous compound.
Another challenge tied to biologics analytical testing is the development and validation of robust and reliable potency assays. Among potency assays, cell-based assays are probably the most adequate predictive as they allow the measurement of the drug's efficacy in an in-vitro model. However, due to the intrinsic biological variability of cell and the complexity of cellular signaling pathways, it can be difficult to define the correct read-out for an assay. The choice of the right cellular model, biomarker, or physiological activity are important parameters that require expertise and specific technologies, such as flow-cytometry or multiplexing capabilities.