Abstract P196: Novel hydrophilic drug linkers enable exatecan-based antibody-drug conjugates with promising physiochemical properties and in vivo activity

Abstract The physiochemical properties of an antibody-drug conjugate (ADC) can impact its stability and pharmacokinetics/pharmacodynamics and are one of the key design attributes. Typically, ADCs with better hydrophilicity are less prone to aggregation and have lower systemic clearance and greater anti-tumor activities. However, the need of incorporating lipophilic payloads with enhanced bystander activity has posed significant challenges to ADC and linker design, especially at higher drug-antibody ratios (DAR). Here we present novel hydrophilic linkers that can greatly improve the hydrophilicity of ADCs conjugated to lipophilic payloads such as exatecan. Exatecan is camptothecin analogue that has failed as a small molecule drug in clinical trials due to lack of therapeutic window but retains considerable promise as an ADC payload because of its high potency and resistance to Pgp efflux. By introducing highly polar PEG, polyhydroxyl and/or polycarboxyl groups, we generated hydrophilic linkers that enable site specific, highly homogeneous conjugation of exatecan to multiple prototypical monoclonal antibodies at DAR8. The linkers may also allow for other DARs such as DAR4 and DAR16. These exatecan-based ADCs with novel hydrophilic linkers were evaluated for their binding affinity and stability and compared with corresponding naked antibodies and deruxtecan-based and conventional vedotin-based ADCs for hydrophilicity, pharmacokinetics, in vitro and in vivo anti-tumor activities. Safety assessments in cynomolgus monkeys have also been planned. ADCs conjugated with the novel hydrophilic linkers were stable at 37oC for 15 days, after 5 cycles of freeze-thaw, and at concentrations as high as 100 mg/mL, as assessed by visual inspection, hydrophobic interaction chromatography, and size-exclusion chromatography. Binding affinity to target-positive cell lines was similar to corresponding naked antibodies. At DAR8, these ADCs were more hydrophilic than deruxtecan-based ADCs and DAR2 species of conventional vedotin-based ADCs. These ADCs also demonstrated potent in vitro cell growth inhibition and induced comparable or stronger tumor regression with single or multiple dosing in multiple mouse xenograft models. The pharmacokinetics profiles of these ADCs are similar to those of the naked antibodies. In summary, our novel hydrophilic linkers can enable conjugation of exatecan-based ADCs at high DARs with favorable physiochemical properties, which result in robust stability, pharmacokinetics, potency, and the potential for a meaningful therapeutic window. Citation Format: Haidong Liu, Lei Wang, Julia Gavrilyuk, Tae Han, Baiteng Zhao, Xiao Shang. Novel hydrophilic drug linkers enable exatecan-based antibody-drug conjugates with promising physiochemical properties and in vivo activity [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P196.