Reducing the antigen-independent toxicity of antibody-drug conjugates by minimizing their non-specific clearance through PEGylation

Recently, we described a family of non-targeting monomethylauristatin E (MMAE) antibody-drug conjugates (ADCs) whose pharmacokinetics could be tuned through incorporation of a short polyethylene glycol (PEG) moiety of up to twelve units into a drug-linker to render the ADC surface more hydrophilic. That work demonstrated that more hydrophilic ADCs were simultaneously more effective and better tolerated in mouse models, suggesting an improvement in therapeutic index via this strategy. Here, we describe the biodistribution and toxicology assessments in Sprague-Dawley rats after intravenous dosing with the aim of elucidating the relationships between these biological outcomes and the underlying physicochemical properties of non-targeted ADCs. Dosing a non-PEGylated ADC exhibited rapid nonspecific cellular uptake, leading to ADC catabolism and rapid release of the cytotoxic payload which reached peak plasma and tissue concentrations within the first day. Introduction of a PEG chain of four, eight, or twelve units resulted in increasingly slower uptake and decreases in peak payload concentrations in all tissues. These ADCs with minimal non-specific uptake also exhibited substantially less hematologic toxicity, with reduced histologic depletion of bone marrow and less dramatic decreases and/or more rapid recovery in peripheral hematologic cell counts (neutrophils, platelets, and reticulocytes). These results support a strong correlation between ADC hydrophobicity, rate of non-specific uptake, peak tissue concentration of released payload, and resulting toxicology parameters. Should these correlations be translatable to the clinic, this would provide a more general and highly tractable strategy for reducing the antigen-independent toxicity of ADCs through drug-linker design to modulate non-specific biodistribution.