Data from Optimization of a PEGylated Glucuronide-Monomethylauristatin E Linker for Antibody–Drug Conjugates

Abstract

<div>Abstract<p>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 <i>in vivo</i> activity, particularly for conjugates with high drug-to-antibody ratios (DAR). We recently reported on the incorporation of a discrete PEG<sub>24</sub> 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 <i>in vivo</i>. 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 <i>in vivo</i>. Longer PEG chains resulted in slower clearance, with a threshold length of PEG<sub>8</sub> 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 PEG<sub>12</sub> side chain emerged from these efforts, enabling highly potent, homogeneous DAR 8 conjugates and is under consideration for future ADC programs. <i>Mol Cancer Ther; 16(1); 116–23. ©2016 AACR</i>.</p></div>