Optimization of a PEGylated glucuronide-monomethylauristatin E linker for antibody–drug conjugates

PJ Burke, JZ Hamilton, SC Jeffrey, JH Hunter… - Molecular Cancer …, 2017 - AACR
PJ Burke, JZ Hamilton, SC Jeffrey, JH Hunter, SO Doronina, NM Okeley, JB Miyamoto…
Molecular Cancer Therapeutics, 2017AACR
The emergence of antibody–drug conjugates (ADC), such as brentuximab vedotin and ado-
trastuzumab emtansine, has led to increased efforts to identify new payloads and develop
improved drug-linker technologies. Most antibody payloads impart significant hydrophobicity
to the ADC, resulting in accelerated plasma clearance and suboptimal in vivo activity,
particularly for conjugates with high drug-to-antibody ratios (DAR). We recently reported on
the incorporation of a discrete PEG24 polymer as a side chain in a β-glucuronidase …
Abstract
The emergence of antibody–drug conjugates (ADC), such as brentuximab vedotin and ado-trastuzumab emtansine, has led to increased efforts to identify new payloads and develop improved drug-linker technologies. Most antibody payloads impart significant hydrophobicity to the ADC, resulting in accelerated plasma clearance and suboptimal in vivo activity, particularly for conjugates with high drug-to-antibody ratios (DAR). We recently reported on the incorporation of a discrete PEG24 polymer as a side chain in a β-glucuronidase-cleavable monomethylauristatin E (MMAE) linker to provide homogeneous DAR 8 conjugates with decreased plasma clearance and increased antitumor activity in xenograft models relative to a non-PEGylated control. In this work, we optimized the drug-linker by minimizing the size of the PEG side chain and incorporating a self-stabilizing maleimide to prevent payload de-conjugation in vivo. Multiple PEG-glucuronide-MMAE linkers were prepared with PEG size up to 24 ethylene oxide units, and homogeneous DAR 8 ADCs were evaluated. A clear relationship was observed between PEG length and conjugate pharmacology when tested in vivo. Longer PEG chains resulted in slower clearance, with a threshold length of PEG8 beyond which clearance was not impacted. Conjugates bearing PEG of sufficient length to minimize plasma clearance provided a wider therapeutic window relative to faster clearing conjugates bearing shorter PEGs. A lead PEGylated glucuronide-MMAE linker was identified incorporating a self-stabilizing maleimide and a PEG12 side chain emerged from these efforts, enabling highly potent, homogeneous DAR 8 conjugates and is under consideration for future ADC programs. Mol Cancer Ther; 16(1); 116–23. ©2016 AACR.
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