Our Scalable Biochemical Protein Synthesis Platform: Designing and Manufacturing a New Generation of Biotherapeutics

Conventional methods for expressing proteins utilize cell lines originating from bacteria, yeast, insects, plants, or mammals. Because these methods require intact, functioning cells, the biochemical and biophysical parameters under which proteins are produced using these methods are inherently limited, often failing to produce many proteins and biologics. Using cell-based expression systems to produce protein variants is also a cumbersome way to enable selection of the best therapeutic candidates.

Our technology is different. Sutro’s technology platform is made possible by the separation, into an extract, of the cellular components required to produce proteins from the process of protein generation itself. The extract includes all the necessary biochemical components for energy production, transcription and translation and can be used to support cell-free biochemical protein synthesis by the addition of the specific DNA sequence for the desired protein. The process produces single proteins at g/L yields in 8-10 hours at any scale.

Sutro designs, discovers, characterizes, and manufactures therapeutic proteins for the treatment or prevention of diseases for itself and for its partners using its proprietary XpressCF™ and Xpress CF+™ platform technologies.  Our XpressCF™ technology allows us to provide customized manufacture, design and development of therapeutic proteins and to discover drugs that feature therapeutic proteins that contain only amino acids all for the treatment and prevention of diseases.  XpressCF+™ is used to design, discover, characterize, and manufacture therapeutic proteins that contain one or more non-natural amino acids in addition to natural amino acids and to discover drugs that feature such proteins.
In addition, Sutro uses ProteinSAR™ to conduct research to identify and characterize the structure, function and the relationship of the therapeutic proteins.  Sutro’s advanced technology allows a rapid and deep analysis of structure-function relationship that is not practical with traditional cell-based methods for protein expression.
A wide variety of protein products have been produced using Sutro’s platform. These range from small peptides to multimeric complex mammalian proteins such as monoclonal antibodies.Uniquely, production of proteins in our cell free system can be scaled rapidly from sub-1mL scale to manufacturing scale; the platform is effectively a liquid handling solution to protein synthesis. The advantages of such a flexible platform over conventional cell-based expression systems are enormous:
  • Proteins can be rapidly engineered and optimized by producing many variants in parallel in 96-well plates from DNA libraries
  • Producing large quantities of a particular protein can be accomplished days from first DNA synthesis, allowing large animal pharmacology and safety assessments to be performed during the design and discovery phase of development
  • Linearly scalable candidate production is assured with predictable performance from bench to GMP production
  • A single master cell bank used for extract generation is capable of providing the manufacturing format for many different proteins, leading to accelerated development times
  • Extract stockpiling provides a means for flexible and fast deployment of surge protein production in the event of unexpected demand for product
  • The synthesis of many novel therapeutic proteins and families of proteins that are challenging by cell-based expression systems is now feasible, for example: Difficult-to-fold proteinsCytotoxic molecules, and Non-natural amino-acid containing proteins

Sutro’s cell-free expression technology provides a rapid and powerful platform for the discovery and development of next generation antibody-drug conjugates (ADCs). Current ADCs in development have immense promise, but they are limited by the fact that they are structurally heterogeneous populations in which the position and number of conjugated linkers and warheads vary significantly. Such heterogeneity prevents the definition of structure-activity relationships (SARs). Consequently, using traditional ADC technologies prevents researchers from discovering and developing candidates with optimal therapeutic indices and can result in products with unpredictable and sub-optimal pharmacokinetic properties, stability and efficacy.
Sutro can incorporate non-natural amino acids (nnAA) at any site in an antibody structure, thereby allowing for single-species ADCs with site-specific conjugation of linker and warhead. Of vital importance in this process is Sutro’s ability to perform rapid and parallel synthesis of numerous variants taking advantage of a substantial number of different sites, enabling analyses early in discovery to define SARs and locate the best positions for nnAA incorporation based on:

  • Protein expression levels
  • Efficiency of incorporation of the nnAA
  • Linker / warhead conjugation efficiency
  • Target binding efficiency
  • Cell killing efficiency
  • Internalization characteristics
It has been well documented that the cell-killing effects of ADCs are highly dependent on the location of the warhead as well as the drug to antibody ratio. Sutro can control both of these variables with exquisite specificity, resulting in truly optimized product candidates. Sutro has also addressed the challenge of manufacturing nnAA-containing ADCs by engineering additional versions of cell-free extract that achieve high rates of incorporation of nnAAs and by developing chemistries that allow for efficient conjugation of linkers and warheads to antibodies.


Sutro’s cell-free expression technology provides a rapid and powerful platform for the discovery and development of antibodies that bind simultaneously to two separate antigens (bispecific antibodies). Bispecific antibodies can be designed to achieve different purposes:
  • To bring an antigen-expressing cell in close proximity to a killing cell, e.g. bispecifics that comprise a tumor cell antigen-binding site and a T-cell or NK cell antigen-binding domain
  • To increase the apparent affinity of binding to an antigen, using avidity, e.g. by binding two separate proteins or two epitopes of a single protein on a cell’s surface
  • To increase the relative selectivity of binding of an antibody to a particular antigen on disease tissue over normal tissue by using a similar avidity approach, e.g. two antigens expressed on the same diseased cell
  • To increase the internalization rates of particular antigens on a cell’s surface by cross-linking two cell surface proteins or by binding to two different epitopes on a given antigen. This emerging approach could also be used to more efficiently deliver warhead payloads to tumor cells using a bispecific antibody-drug conjugate
While many different bispecific antibody formats have been exemplified using cell-based expression systems, and some have been successful enough to show promise as new classes of therapeutics, the precise geometry and spatial orientation of binding domains, linkers and functional domains can be a challenge to optimize. Additionally, the use of cell-based systems has revealed immense difficulties in their expression efficiency, particular at larger scale, often resulting in poorly folded and aggregated material. Consequently, using traditional cell-based technologies prevents researchers from discovering and developing bispecific candidates with optimal therapeutic indices and can result in products with unpredictable pharmacokinetic properties, stability and efficacy.

Sutro’s technology has the ability to perform rapid expression and characterization of many variants early in discovery to define structure-activity relationships and thereby optimize:
  • Binding efficiency to each target
  • Spatial orientation and linker design
  • Target killing efficiency
  • Protein expression and folding efficiency
  • Stability
Sutro can optimize rapidly for all of these variables with exquisite specificity, resulting in optimized product candidates.
Sutro has the ability to manufacture our own cell extract and protein on a large scale. Our manufacturing facility is located in San Carlos, CA and is GMP compliant. The facility was designed to produce extract in batch mode. However, as Sutro’s production needs have expanded, we have found that the method of growing cells continuously increases our capacity significantly. We are now in the process of redesigning our facility to accommodate the continuous cell growth method. Once the modifications have been made, Sutro will be able to produce extract and protein more quickly and efficiently than before, while also producing greater amounts.