Technology

Bioconjugation to proteins is most commonly achieved by exploiting the reactivity of lysine and cysteine residues.  Specifically, bioconjugation to antibodies is typically accomplished via modification of lysine residues, which are numerous on the antibody surface, or via free cysteine residues following the reduction of native disulfide bonds. In both cases, subsequent conjugates are afforded as mixtures of products and those formed following disulfide reduction will also have reduced structural stability.

Technology that will allow modification of antibodies to yield homogeneous products is highly desirable. In particular, it has been demonstrated that homogeneous antibody drug conjugates (ADCs) have a greatly improved therapeutic index over analogous heterogeneous formulations. Introducing greater homogeneity into antibody conjugates will also greatly simplify process and development issues, thereby reducing costs. 

We have developed a groundbreaking conjugation technology that allows the selective bridging and functionalisation of disulfide bonds in antibodies, proteins and peptides.

1) Disulfide Bridging Chemistry:

Conjugation across native disulfide bonds to generate a single point of functionalisation per rebridged disulfide bond.   This chemistry offers significant advantages over existing approaches to bioconjugation:

• High efficiency – Fast reaction times.
• In situ protocol – Simultaneous addition of bridging and reducing agents ensures rapid functionalisation of sensitive disulfides.
• Works across a range of protein complexities – full antibodies, antibody fragments, proteins and peptides.
• Conjugates retain biological activity and are well tolerated in vivo.
• Full Antibodies – Fully tuneable conjugation to give drug to antibody ratios of 1, 2, 3, or 4.

2) Cysteine Modification Chemistry:

Conjugation at a thiol group of a free cysteine.  It is widely reported that traditional maleimide conjugates suffer from a lack of stability over prolonged periods in vivo.  This is caused by an elimination reaction of the thiosuccinimide conjugates, which releases the drug from the antibody. Notably, conjugates generated using our next generation maleimide chemistries have been specifically designed so as to not suffer from this mechanism of cleavage.  Our recent data supports the complete stability of next generation maleimide protein conjugates in blood plasma, which is in stark contrast to the traditional maleimide variants.  In the ADC setting, this high stability will maximise the amount of toxin that reaches the target cell – addressing an established limitation of current chemical approaches.

3) Acid Cleavable Linker Chemistry:

Compatible with our Disulfide Bridging and Cysteine Modification Chemistries we have developed a novel acid-cleavable linker strategy for antibody-drug conjugation. This linker is stable at physiological pH and temperature, but quantitatively cleaves at lysosomal pH to release the drug payload.

4) Dual Functionalisation Disulfide Bridging Chemistry:

Conjugation across native disulfide bonds to generate two points of functionalisation per rebridged disulfide bond.  This latest generation chemistry allows multi-labelling of protein conjugates via disulfide modification.  It works across a range of protein complexities – full antibodies, antibody fragments, proteins and peptides.  This technology is being used to create fragment-based ADCs via the introduction of half-life extension and linker/drug and theranostic ADCs via the introduction of a diagnostic label and linker/drug.  This chemistry can also be used to generate two points of functionalisation at a thiol group of a free cysteine.