Hydrophobic interaction chromatography measurements. Comparison of trastuzumab, trastuzumab-LP3 DAR8, trastuzumab-LP5 DAR8, Adcetris and Enhertu. Shown are chromatograms of Adcetris in black (Homogenous ADC, brentuximab conjugated to MC-VC-PAB-MMAE in DAR0, DAR2, DAR4, DAR6 and DAR8). Enhertu in grey, trastuzumab in light orange, trastuzumab-LP5 in orange and brentuximab-LP3 in purple. Hydrophilicity of all shown DAR8 VC-PAB-Exatecan constructs are in the range of a DAR2 of Adcetris.
ARTICLE ABSTRACT
Topoisomerase I (TOP1) Inhibitors constitute an emerging payload class to engineer antibody–drug conjugates (ADC) as next-generation biopharmaceutical for cancer treatment. Existing ADCs are using camptothecin payloads with lower potency and suffer from limited stability in circulation. With this study, we introduce a novel camptothecin-based linker–payload platform based on the highly potent camptothecin derivative exatecan. First, we describe general challenges that arise from the hydrophobic combination of exatecan and established dipeptidyl p-aminobenzyl-carbamate (PAB) cleavage sites such as reduced antibody conjugation yields and ADC aggregation. After evaluating several linker–payload structures, we identified ethynyl-phosphonamidates in combination with a discrete PEG24 chain to compensate for the hydrophobic PAB–exatecan moiety. Furthermore, we demonstrate that the identified linker–payload structure enables the construction of highly loaded DAR8 ADCs with excellent solubility properties. Head-to-head comparison with Enhertu, an approved camptothecin-based ADC, revealed improved target-mediated killing of tumor cells, excellent bystander killing, drastically improved linker stability in vitro and in vivo and superior in vivo efficacy over four tested dose levels in a xenograft model. Moreover, we show that ADCs based on the novel exatecan linker–payload platform exhibit antibody-like pharmacokinetic properties, even when the ADCs are highly loaded with eight drug molecules per antibody. This ADC platform constitutes a new and general solution to deliver TOP1 inhibitors with highest efficiency to the site of the tumor, independent of the antibody and its target, and is thereby broadly applicable to various cancer indications.
