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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., (©2023 The Authors; Published by the American Association for Cancer Research.)

The recent success of antibody-drug conjugates (ADC), exemplified by seven new FDA-approvals within three years, has led to increased attention for antibody based targeted therapeutics and fueled efforts to develop new drug-linker technologies for improved next generation ADCs. We present a highly efficient phosphonamidate-based conjugation handle that combines a discrete hydrophilic PEG-substituent, an established linker-payload and a cysteine-selective electrophile in one compact building block. This reactive entity provides homogeneous ADCs with a high drug-to-antibody ratio (DAR) of 8 in a one-pot reduction and alkylation protocol from non-engineered antibodies. The compact branched PEG-architecture introduces hydrophilicity without increasing the distance between antibody and payload, allowing the generation of the first homogeneous DAR 8 ADC from VC-PAB-MMAE without increased in vivo clearance rates. This high DAR ADC exhibits excellent in vivo stability and increased antitumor activity in tumour xenograft models relative to the established FDA approved VC-PAB-MMAE ADC Adcetris, clearly showing the benefit of the phosphonamidate based building-blocks as a general tool for the efficient and stable antibody-based delivery of highly hydrophobic linker-payload systems., Competing Interests: The technology described in the manuscript is part of a pending patent application by P. O., J. J., P. M., I. M., D. S., H. L., J. H., and M.-A. K, C. P. R. H. P. O., P. M., I. M., D. S., J. H., and M.-A. K are employers of Tubulis., (This journal is © The Royal Society of Chemistry.)

A biocatalytic reduction of 2 H-1,4-benzoxazines using imine reductases is reported. This process enables a smooth and enantioselective synthesis of the resulting cyclic amines under mild conditions in aqueous media by means of a catalytic amount of the cofactor NADPH as hydride source as well as glucose as the reducing agent used in stoichiometric amounts for in situ cofactor recycling. Several substrates were studied, and the 3,4-dihydro-2 H-1,4-benzoxazines were obtained with up to 99% ee. In addition, the efficiency of this reduction process based on imine reductases as catalysts has been demonstrated for one 2 H-1,4-benzoxazine on an elevated laboratory scale running at a substrate loading of 10 g L -1 in the presence of a tailor-made whole-cell catalyst.