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The Use Of Cell-Free Synthesis In The Future Of Modern Medicine

By Daniel G. Bracewell, Professor of Bioprocess Analysis, UCL Department of Biochemical Engineering

This article was created from the author's presentation at the 2018 Bioprocessing Asia conference, with GE Healthcare as principal sponsor. The BioProcessing Asia Conference series was created to provide a platform to advance the contribution of bioprocessing sciences towards the development and manufacture of affordable biopharmaceutical products in Asia.

Personalized medicine stands to be a revolutionary transformation to patient care. The traditional methods for drug development will no longer be applicable, as this new approach to modern medicine focuses on a more targeted form of patient treatment. However, the models used to produce large batches of drug product are not economical on a smaller, individualized scale. Therefore, as the industry explores the possibilities of precision care, it must consider alternative manufacturing platforms that can make these ideas a commercial reality. To ensure these medicines can be affordable, improved agility and productivity in process design is critical.1

One possibility for doing so is the use of cell-free synthesis (CFS) systems, which were first introduced over 50 years ago as a tool to investigate genetic code as well as for the synthesis of proteins for structural biology. Also known as in vitro transcription/translation (IVTT), CFS is a method for protein synthesis through translation performed with biological components but without the use of living cells. Instead, the preparation or the growth of the cells is separated from the reaction itself using centrifugation, preserving the ribosomes, and transcriptional machinery of the cell. The cell-free reaction is then combined with an energy source and the DNA of the protein to be expressed. It may be necessary to add other cofactors and supplements, such as tRNA synthetases, translation initiation, and elongation factors.

Separating the biological reagent preparation from the cell-free reaction makes CFS systems well suited to manufacture at the point of treatment, improving patient access, particularly to communities without established distribution networks. Yet, transitioning to a more efficient model for the future of medicine faces several challenges due to restrictions in today’s regulatory, development, and manufacturing environments.

Reducing Complexity, Costs, And Uncertainty With CFS

Traditional bioprocessing methods rely on a centralized facility to create drug products using live cell fermentations, leading to long lead times for development and validation of a stable cell line before manufacturing can begin. Because of the adaptable nature of live cells, they can be very sensitive to even minor changes in a manufacturing process. Monitoring them appropriately to avoid batch-to-batch variation requires extensive analytical support, significant infrastructure support, and a highly skilled workforce. Eliminating the use of live cells through CFS allows for the product synthesis step to be separated from the reagent (crude lysate) generation, which offers potential for increased process agility and consistency.

With a process more akin to a chemical reaction, CFS can allow for more precision in molecular design, increasing confidence in product efficacy and quality. For example, Sutro Biopharma, a clinical-stage biotechnology company, used E. coli (one of CFS’ most dominant platforms) to develop a proprietary CFS and conjugation platform to enable the precise design, rapid empirical optimization, and manufacture of site-specific antibody-drug conjugates (ADCs).2 The drug is comprised of a single molecular species as opposed to first-generation ADCs made up of a mixture of imprecisely conjugated antibodies. Examples of the E. coli cell extract reagent preparation process used in this type of CFS process are outlined in Figure 1 below.

Figure 1: E. coli cell extract preparation

The cells are grown, broken, and the subcellular components released, then a low-speed spin is used to remove cell debris. In the case of Sutro Biopharma, the cell extract is made up of a novel strain of E. coli that allows the incorporation of a non-natural amino acid due to its additional transfer ribonucleic acid (tRNA). This non-natural amino acid enables site-specific chemistry, giving scientists the ability to design a single site for conjugation and increase yield compared to the heterogeneity typically seen.

CFS could also change the manufacturing landscape in terms of manufacturing facilities. For example, highly toxic materials are sometimes used in biopharmaceutical manufacturing. The main challenge of using these dangerous substances is maintaining the safety of the company’s operators, which requires the use of safety cabinets to contain the toxins and prevent direct human contact. With CFS, fermentation is no longer needed to carry out the reaction, so the toxins are only synthesized when the cell-free reaction takes place. This reduces the risks to the operators, as fermentation no longer has to take place in an environment of high containment, increasing process flexibility and minimizing the need for specialized engineering equipment. This is an approach Ipsen, a manufacturer of botulinum toxin-based medicines, is actively exploring in collaboration with the National Biologics Manufacturing Centre (NBMC) in the U.K.

Using CFS For Personalized Medicine Manufacturing

Most notably, the benefits of CFS are critical as today’s industry begins to explore the possibilities of personalized medicine, which, for examples like autologous cell therapies, presents a unique two-way supply chain where cells must be safely shipped to a production facility and then back to the patient. While temperature management is already an important component for the safe delivery of effective biological drugs, it becomes essential when transporting personalized medicine to individual patients as it requires delicate transfer of one dose, which is not only risky but costly. Delivery becomes an even bigger challenge if multiple geographical locations are involved.

By negating the need for a complex infrastructure normally associated with a centralized live cell facility, CFS creates the possibility of a distributed manufacturing model where drugs can be made at the point of treatment at a potentially lower cost. The differences between a traditional manufacturing and supply model and a CFS model are detailed in Figure 2.

Figure 2: Current biopharma manufacture and supply versus CFS enabled manufacturing as outlined in Cell free protein synthesis: a viable option for stratified medicines manufacturing? by Ogonah, Olotu W. et al. (2017)1

However, while other scalability, manufacturability, and sustainability issues would need to be addressed for CFS to be successful,1 it is not possible as long as there is an expectation from regulators to execute complex release assays for every batch of drug substance. Executing a distributed manufacturing model for CFS would require “the use of newer online monitoring techniques combined with the repeatability resulting from automation” to reduce the need for on-site testing.Process parameters/setpoints with predefined parameter space data shown to deliver the required quality  using a relatively small and mobile automated unit, enabling distributed manufacture and remote monitoring, could help make the case to the FDA and other regulators to rationalize current regulatory constraints. Doing so could prepare the industry for changes to the manufacturing paradigms it has become used to as well as for biological products that are targeted to smaller populations. As debate is happening between industry and regulators, greater clarity will be necessary before significant investment in CFS as a manufacturing platform can be made beyond examples such as those described here, which capitalize on unique features of CFS.

  1. Ogonah, Olotu W. et al. (2017), Current Opinion in Chemical Engineering, Cell free protein synthesis: a viable option for stratified medicines manufacturing?, Volume 18, Pages 77-83, retrieved from https://www.sciencedirect.com/science/article/pii/S221133981730045X?via%3Dihub
  2. Sutro Biopharma, Sutro Announces IND Submission and Conclusion of 30-Day Review Period for STRO-002, an Antibody-Drug Conjugate (ADC) Targeting Anti-Folate Receptor-α for Treatment of Ovarian and Endometrial Cancerhttps://www.sutrobio.com/sutro-announces-ind-submission-and-conclusion-of-30-day-review-period-for-stro-002-an-antibody-drug-conjugate-adc-targeting-anti-folate-receptor-%CE%B1-for-treatment-of-ovarian-and-endometrial-canc/

Daniel G. Bracewell is Professor of Bioprocess Analysis at the UCL Department of Biochemical Engineering. He has made major contributions to the fundamental understanding of biopharmaceutical purification operations, including collaborations with Thailand, India and the USA. He has authored more than 90 peer reviewed journal articles in the area to date and currently supervises 15 doctoral and postdoctoral projects, many of these studies are in collaboration with industry. One such project was the basis from which the spinout Puridify, recently acquired by GE Healthcare was created.