The Future for Biosensors in Biopharmaceutical Production

Pharmaceutical Commentary BRACEWELL & POLIZZI The future for biosensors in biopharmaceutical production 2 Commentary The future for biosensors in biopharmaceutical production Pharm. Bioprocess. Keywords: bioprocess monitoring • bioprocess control • in-vivo biosensor • PAT Daniel G Bracewell*,1 • synthetic biology & Karen M Polizzi2 1The Advanced Centre for Biochemical Engineering, Department of Biochemical A defining feature of bioprocesses is the need straightforward. This is not to say there have Engineering, University College London, for measurement, monitoring and control; in not been significant successes: Torrington Place, London, WC1E 7JE, UK the context of biopharmaceuticals this need 2Department of Life Sciences & Centre • The world’s diabetic population depends is further heightened by the absolute require- for Synthetic Biology & Innovation, on blood glucose measurements to admin- Imperial College London, London, UK ment to ensure the quality of the product [1] . ister insulin based on an amperometric *Author for correspondence: This is evidenced by the size of bioanalytical based biosensor technology (enzyme elec- [email protected] endeavor found within the R&D programs trodes). This represents the largest single of the major biopharmaceutical companies biosensor application in terms of numbers and the supplier industry that caters for this of devices and market size; instrumentation need. It is a need that grows at a pace reflected in the initiatives involv- • Optical biosensors, largely surface plas- ing the regulatory authorities such as PAT mon resonance (BIAcore) has become central to the larger vision of QbD. At the the default method to directly mea- core of these attempts to improve biophar- sure protein–protein interactions in the maceutical production is the need for rapid, laboratory. 10.2217/PBP.14.4 ideally online, measurement [2]. This would open up a whole range of opportunities for Both of these technologies have been improved control of such processes [3]. In this adapted for the bioprocess sector, enzyme article we will highlight the relatively small electrodes are used to measure metabolites but significant roles biosensors currently play such as lactate and glutamine in mammalian in biopharmaceutical process development cell culture (e.g., Nova Biomedical). Equally 2 and operation and debate the reasons for this optical transduction technology is now in the face of the great potential offered by available in a parallel probe type configura- biosensors. The article will then progress to tion (Fortebio) for use in a microtiter plate examine new biosensor concepts deriving format to enable higher throughput protein 2014 from synthetic biology – that of in vivo bio- quantitation (e.g., for product molecules such sensors which may deliver the online infor- as antibodies, this technology is directed at mation we desire and see biosensors play a process development activities). much more significant role in the future of The interesting question is why then in bioprocessing. the face of such successes is the approach not A biosensor is often defined as ‘a device for much more widespread. The fact is that bio- the detection of an analyte that combines a sensors must be designed for their application biological component with a physicochemi- to have: the correct selectivity and dynamic cal detector component’. In many senses, the range, and the capacity to cope with impuri- concept of the biosensor is the magic bullet ties/interfering compounds likely to be pres- for the bioanalytical sector; it is perhaps not ent; this represents a significant challenge. surprising therefore that to achieve this is not It is in contrast to traditional bioanalytical part of 10.2217/PBP.14.4 © 2014 Future Science Ltd Pharm. Bioprocess. (2014) 2(2), 121–124 ISSN 2048-9145 121 Commentary Bracewell & Polizzi methods we might employ such as HPLC, MS or tion element traditionally referred to when describing immunoassays where as much as possible the analyte a biosensor is transposed to features designed within fits within known methodological approaches. Biosen- the cellular components which could then be measured sors conceptually are most closely related to immuno- remotely by fluorescence for example. This would assays, where the creation of an antibody with the right enable non-invasive measurement of the process alle- selectivity is the critical step in assay development, viating concerns associated with the often conflicting from which point somewhat generic procedures can needs of GMP, for example. be adopted. To progress to what could be described This concept of organism design in the field of as a biosensor requires the direct transduction of the analytical technology is now starting to produce find- analyte–antibody interaction to create a signal. This ings of direct relevance to bioprocessing. It has been investment is often difficult to justify unless the sensor shown possible to design dedicated organisms for the can used multiple times requiring a very stable system. purposes of biosensing and to include genetic circuits This has meant researchers in the area have looked for designed to report on the internal state of the cell ways to tackle this problem from applying methods to within the design of strains for manufacturing [10] . stabilize antibodies or using antibodies from species The latter enable the rapid, non-invasive analysis of cell which are intrinsically stronger molecules (e.g., cam- metabolism, including information on nutrient utili- elid), to small so called biomimetic molecules (e.g., zation, product formation, and the detection of stress triazine dyes), which may offer the stability and life- responses. These new types of in vivo biosensors could time required, through to evolving methods to create a be applied to bioprocess design, used in manufacturing process called molecular imprinting [4]. for online processing monitoring and control or both. Despite such challenges, the match between the Since they are derived from or contained within living immediacy of measurement offered by biosensors and organisms, they are self-renewing and also avoid the the growing need for in-process measurement of mul- challenges associated with engineering bio-compatible tiple biochemical and biological species indicates the surfaces and interfaces to mediate detection. need [5]. The potential offered can be seen when using In direct analogy to other types of biosensors, biosensors to monitor fermentation [6] and chroma- in vivo biosensors can be thought of as consisting of tography operations [7]. The challenge that remains is three components: a sensor, a transducer and an output making the technology robust and accessible. There are [11] . The sensor will be responsible for signal recogni- some clear issues if such a sensor is to be placed in a pro- tion and the choice of this element confers the specific- cess for online sensing. How will the risk of contami- ity of the biosensor. The transducer (also sometimes nation or leaching of sensor components be avoided? called an actuator or a signal processor) converts the And how will calibration be achieved? Such issues are a signal into a measurable output such as fluorescence, strong argument for spectroscopic methods that allow luminescence, a colour change or an electrical current for online and non-invasive measurement but the issues [10] . Most of the examples of in vivo biosensors to date here surround the data analysis required to deconvo- rely on an output that can be measured spectroscopi- lute specific biological data from the signals, an area cally, although steps towards the biological production of continuing research for in-process modeling for the of an electrical current are underway [12] . biopharmaceutical sector [8]. The use of such methods One of the engineering principles that synthetic to fingerprint raw materials has already become com- biology has adopted is modularity [9]. When applied mon. This means the relatively basic needs of product, to the design of in vivo biosensors, this means that the key metabolites and critical impurities measurement individual components can be designed and character- remain off-line, usually laboratory-based at present. ized separately and then linked together in new com- If biosensors are to address this unmet need there binations to create biosensors for different purposes. is a need to see a step change in the biosensor concept Hence, for example, determining the link between which as noted can frequently be complicated by the arbitrary fluorescence units and the number of mole- need to construct complex surfaces and interfaces to cules of green fluorescent protein in a particular exper- mediate the sensing, the longevity of such sensors is as imental set up allows direct quantification of output a result often limiting for this application. The poten- from a circuit regardless of the method of sensing and tial to remove the need for this surface is therefore an transduction or characterization of the specificity and exciting possibility. The advent of synthetic biology binding affinity of a particular protein domain allows may present such an opportunity; it is an emerging it reuse in many biosensor designs in different contexts discipline that seeks to apply engineering principles to (e.g., [13–15] all use variants of the same binding protein the design and construction of biological organisms for to sense, respectively, glutamine in mammalian cells, user-defined purposes [9]. It could

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