Abstract
The degree of stability of antibody-drug linkers in systemic circulation, and the rate of their intracellular processing within target cancer cells are among the key factors determining the efficacy of antibody-drug conjugates (ADC) in vivo Previous studies demonstrated the susceptibility of cleavable linkers, as well as auristatin-based payloads, to enzymatic cleavage in rodent plasma. Here, we identify Carboxylesterase 1C as the enzyme responsible for the extracellular hydrolysis of valine-citrulline-p-aminocarbamate (VC-PABC)-based linkers in mouse plasma. We further show that the activity of Carboxylesterase 1C towards VC-PABC-based linkers, and consequently the stability of ADCs in mouse plasma, can be effectively modulated by small chemical modifications to the linker. While the introduced modifications can protect the VC-PABC-based linkers from extracellular cleavage, they do not significantly alter the intracellular linker processing by the lysosomal protease Cathepsin B. The distinct substrate preference of the serum Carboxylesterase 1C offers the opportunity to modulate the extracellular stability of cleavable ADCs without diminishing the intracellular payload release required for ADC efficacy. Mol Cancer Ther; 15(5); 958-70. ©2016 AACR.
Highlights
Antibody–drug conjugates (ADC) are a growing class of cancer therapeutics with promising clinical outcomes
We show that mouse Carboxylesterase 1C (Ces1C) in its purified form, as well as in the context of mouse plasma, is sensitive to chemical derivatization of the linker which can modulate its VC-PABC hydrolysis activity
We further demonstrate that modifications of the VC-PABC linkers that are resistant to mouse Ces1C cleavage do not have the same effect on the human Cathepsin B (CatB), the lysosomal protease responsible for intracellular linker processing and release of the drug moiety
Summary
Antibody–drug conjugates (ADC) are a growing class of cancer therapeutics with promising clinical outcomes. Cynomolgus monkey and human species appear to have negligible levels of both cleavable and noncleavable linkerpayload degradation in plasma stability assays, either type of conjugate must undergo rodent studies where the described linker-payload instability can have significant effects on efficacy This differential ADC stability between rodent and primate species can lead to difficulties in evaluating the efficacy of a drug candidate, largely performed in mouse models, relative to its safety, typically tested in non-human primate models. We further demonstrate that modifications of the VC-PABC linkers that are resistant to mouse Ces1C cleavage do not have the same effect on the human Cathepsin B (CatB), the lysosomal protease responsible for intracellular linker processing and release of the drug moiety This distinct linker substrate preference of the two enzymes offers the ability to modulate the extracellular stability of the VC-PABC–linked conjugates in rodent circulation without interfering with the intracellular linker processing in the lysosomal degradation pathway of the target cell. Comparison between the structures of the human liver carboxylesterase homolog and human lysosomal CatB offers a possible explanation for the differential substrate selectivity of the two enzymes
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call