Scaffold-drug Conjugates Development

Studies have emerged suggesting that traditional IgG scaffolds may not be the optimal format for targeted payload delivery. Besides utilizing antibody fragments as targeting moieties, the protein engineering community has begun to explore alternative high-binding protein scaffolds as antibody mimics. Armed with rich experience in scaffold design and synthesis, Creative Biolabs provides comprehensive scaffold-drug conjugates (SDCs) development services for our clients. We are capable of developing different kinds of engineered scaffolds targeting various targets to meet your conjugation needs.

Scaffold-drug Conjugates

The non-antibody binding scaffold field is emerging commercially after many years of R&D. These scaffolds tend to be smaller than antibody fragments ranging from 6-21 kDa, can be expressed at high yield in E. coli, selected by in vitro display, and have higher stability. Currently, the majority of applications are for imaging (due to excellent contrast ratios) and receptor/ligand inhibition. A recent commercial analysis of this space identified 84 unique alternative scaffold products in development with 82% in the preclinical/discovery stage and 40% aimed at oncology. Different kinds of scaffolds have been reported to generate SDCs in recently years.

A diagrammatical representation of various antibody fragments and binding scaffolds. Fig.1 A diagrammatical representation of various antibody fragments and binding scaffolds. (Richards, 2018)

Affibody-drug Conjugates

Affibodies are small (∼7 kDa) three-helix proteins derived from the Z-domain of Staphylococcus protein-A. Affibodies are readily expressed in E. coli and can be selected for using ligand-display technologies such as phage display and cell display. Furthermore, the simplicity of the scaffold allows for solid-phase peptide synthesis. Chemical conjugation to Affibodies is achieved primarily through site-specific incorporation of cysteine residues into regions of the scaffold which tolerate modification. This has been achieved using site-directed mutagenesis and solid-phase peptide synthesis.

Centyrin-drug Conjugates

Centyrins are small (∼10 kDa) cysteine-free scaffolds based on the 10th type-III fibronectin domain of human fibronectin. These scaffolds contain multiple loops that are structurally analogous to the complementarity-determining (CDR) regions of IgGs and impart target specificity. Containing only one domain and no disulfide bonds, they can be readily expressed in various expression systems. Currently, site-specific introduction of cysteine residues followed by maleimide chemistry remains the most employed conjugation strategy for this kind of scaffold.

Cystine Knot-drug Conjugates

Cystine knots (Knottins) are 30-50 amino acid residue polypeptides in length (∼3-6 kDa) that have remarkable chemical-, protease-, and thermal- stability properties, due to their highly-compact structure. These scaffolds form a compact three-dimensional (3D) structure that is stabilized by at least three disulfide bonds and can be engineered to bind to multiple targets. The most common method for the generation of cystine knots is solid-phase peptide synthesis, followed by oxidative folding. Though Knottins contain multiple disulfide bonds, disulfide bridging chemistries have not been explored. Effective conjugation to Knottins could be achieved through site-specific incorporation of an azide residue into the Knottin backbone by copper-free click chemistry.

DARPin-drug Conjugates

Designed ankyrin repeat proteins (DARPins) are scaffolds based on Akyrin repeats. Typical DARPins consist of 4-6 repeat units, and each repeat unit is around 33 aa in length. These scaffolds can be selected by phage display or ribosomal display and can be easily expressed in large quantities using E. coli. Site-selective conjugation to DARPins can be achieved through site-specific incorporation of cysteine residues to the scaffold followed by reaction with maleimide linkers. Incorporation of azido-homoalanine onto the N-terminus of a DARPin can be easily exploited for chemical conjugation using strain-promoted alkyne-azide cycloaddition click chemistry.

Scaffold-drug Conjugates Development

Creative Biolabs has been involved in the development of antibody-drug conjugates (ADCs) for many years. Now we provide personalized SDC development services including but not limited to the following:

  1. Production of functional scaffold using cell-free protein synthesis or cell-based expression systems
  2. One-to-one custom drug conjugation
  3. Characterization of the resulting conjugates in tumor cell culture and animal models.

If you are interested in developing SDCs, please don’t hesitate to contact us for more information. For antibody fragment based drug conjugates, please refer to antibody fragment-drug conjugates development.

Reference

  1. Richards, D. A. Exploring alternative antibody scaffolds: Antibody fragments and antibody mimics for targeted drug delivery. Drug Discovery Today: Technologies. 2018, 30: 35-46.

For lab research use only, not for any in vivo human use.


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