Biomarkers


Figure 3


The diagram illustrates the concept of ‘fit-for-purpose’ antibody through use in various applications. For


instance the requirement for an ELISA is substantially


different from that of IHC or diagnostic assay vs laboratory assay


assay-developers, and between pharmaceutical and diagnostic experts will be needed in a hand-in- glove fashion. The stages of companion diagnostic biomarker development are diagramed in Figure 2. Importantly, biomarker R&D needs to be carried out in parallel with the discovery and development process of a new drug – all too often it still happens as an afterthought once the medicine has entered the stage of clinical trials. While a biomarker will ultimately have to be validated in the context of human pathobiology, there are important opportu- nities of using biomarkers, and of characterising their potential and attributes, already in the pre- clinical phase, principally in animal models. This raises additional challenges, as it requires affinity reagents useable in animals as well.


Protein biomarker technology platforms: hypothesis-driven vs hypothesis-free approaches Protein biomarker assay platforms: Two types of protein assay platforms are currently applied to dis- cover protein biomarkers and to measure them quantitatively and qualitatively (ie, to determine the isoform state of a protein such as phosphorylation). It is instructive to point out here that an antibody use is a ‘fit-for-purpose’ antibody. For example, the requirement for an ELISA is substantially different


22


from that of IHC or diagnostic assay vs laboratory assay. Figure 3 illustrates the concept of ‘fit-for-pur- pose’ antibody through use in various applications.


Immunoassays: direct use of antibodies Immunoaffinity-based assays are the mainstay of testing for proteins. They use antibodies directed against the protein or isoform of interest. Detection of the antibody-antigen (protein) complex provides the quantitative measurement of the amount of antigen present in the sample. A variety of methods are used that vary both by how the antibody and antigen come into proximity of each other to form a complex (based on what the antibody or antigen is fixed to) and by the detection method used to monitor the amount of complex. Western blots are the simplest and most widely used immunoassay method in biomedical research; ELISA (enzyme- linked immune-sorbent assay) is the method most often used in clinical settings (eg PSA test). A num- ber of platform technologies offer methods for mul- tiplexed and miniaturised immunoaffinity assays (eg Luminex, MesoScale Discovery and PerkinElmer). Development of antibody-based assays is a time-consuming, resource-intensive effort and frequently hampered by cross-reactivity to other antigens. Moreover, results from immunoassays often do not discriminate among


Drug Discovery World Winter 2010/11


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