Human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase that plays an oncogenic role in breast, gastric and other solid tumors. However, anti-HER2 therapies are only currently approved for the treatment of breast and gastric/gastric esophageal junction cancers and treatment resistance remains a problem. Here, we engineer an anti-HER2 IgG1 bispecific, biparatopic antibody (Ab), zanidatamab, with unique and enhanced functionalities compared to both trastuzumab and the combination of trastuzumab plus pertuzumab (tras + pert). Zanidatamab binds adjacent HER2 molecules in trans and initiates distinct HER2 reorganization, as shown by polarized cell surface HER2 caps and large HER2 clusters, not observed with trastuzumab or tras + pert. Moreover, zanidatamab, but not trastuzumab nor tras + pert, elicit potent complement-dependent cytotoxicity (CDC) against high HER2-expressing tumor cells in vitro. Zanidatamab also mediates HER2 internalization and downregulation, inhibition of both cell signaling and tumor growth, antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP), and also shows superior in vivo antitumor activity compared to tras + pert in a HER2-expressing xenograft model. Collectively, we show that zanidatamab has multiple and distinct mechanisms of action derived from the structural effects of biparatopic HER2 engagement.

l‐2‐Haloacid dehalogenases, industrially and environmentally important enzymes that catalyse cleavage of the carbon‐halogen bond in S‐2‐halocarboxylic acids, were known to hydrolyse chlorinated, brominated and iodinated substrates but no activity towards fluorinated compounds had been reported. A screen for novel dehalogenase activities revealed four l‐2‐haloacid dehalogenases capable of defluorination. We now report crystal structures for two of these enzymes, Bpro0530 and Rha0230, as well as for the related proteins PA0810 and RSc1362, which hydrolyse chloroacetate but not fluoroacetate, all at ∼2.2 Å resolution. Overall structure and active sites of these enzymes are highly similar. In molecular dynamics (MD) calculations, only the defluorinating enzymes sample more compact conformations, which in turn allow more effective interactions with the small fluorine atom. Structural constraints, based on X‐ray structures and MD calculations, correctly predict the defluorination activity of the homologous enzyme ST2570.

Antibody drug conjugate (ADC) therapies such as Kadcyla® and Adcetris® have significantly improved outcomes for patients. Despite these early advances, many ADCs have failed due to tolerability and efficacy concerns; therefore, there is a need to develop ADCs with a greater therapeutic window. We have previously reported the increased tolerability of a novel N-acyl sulfonamide auristatin payload conjugated to trastuzumab via a protease cleavable linker. In non-human primates (NHPs), the HNSTD for this ADC was 18 mg/kg compared to 3 mg/kg for the MMAE conjugate control. Separately, we have also reported that a biparatopic antibody targeting a tumor associated antigen (e.g. anti-HER2 bispecific antibody ZW25) can lead to enhanced receptor clustering and improved internalization, thereby increasing the efficiency of payload delivery. Our aim is to develop a series of novel biparatopic ADCs with expanded therapeutic windows against multiple targets. Here we present the proof-of-concept in vitro and in vivo characterization of benchmark ADCs against 3 different targets with improved tolerability and equivalent efficacy. Benchmark antibodies against 3 known clinical targets were conjugated to our N-acyl sulfonamide auristatin (mAb-ADCs) or to MMAE or DM4 controls (mAb-control ADCs) via cleavable linkers and were assessed for in vitro binding affinity and cytotoxicity. The therapeutic windows of mAb-ADCs and mAb-control ADCs were compared by assessing efficacy in mouse xenograft models and tolerability and pharmacokinetics in NHPs. mAb-ADCs had similar binding affinities to recombinant targets and/or to cancer cells expressing low to high levels of target antigen compared to the mAb-control ADCs. mAb-ADCs demonstrated similar in vitro cytotoxicity compared to mAb-control ADCs and this was recapitulated in vivo with similar tumor growth inhibition in mouse xenograft models. In a NHP tolerability/PK study, mAb-ADCs for all 3 targets were tolerated at doses up to 18 mg/kg (single dose IV infusion) compared to the mAb-control ADCs that showed severe to life-threatening neutropenia at lower doses. The increase in maximum tolerated dose for the mAb-ADCs over the mAb-control ADCs, together with comparable efficacy across 3 different targets, demonstrates the broad applicability of the novel N-acyl sulfonamide auristatin payload to expand the therapeutic window. This strategy, together with ongoing efforts to identify synergistic antibody paratopes that more efficiently deliver payload, could lead to next-generation biparatopic ADCs with improved activity. Citation Format: Rupert H. Davies, Stuart D. Barnscher, Peter W. Chan, Laurence Madera, Jamie R. Rich, Marylou Vallejo, Grant R. Wickman, Kevin Yin, Vincent Fung, Kevin J. Hamblett, Patrick G. Kaminker, John S. Babcook. Towards development of next-generation biparatopic ADCs using a novel linker-toxin with expanded therapeutic window [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3912.

Dynamic behavior of proteins is critical to their function. X-ray crystallography, a powerful yet mostly static technique, faces inherent challenges in acquiring dynamic information despite decades of effort. Dynamic `structural changes' are often indirectly inferred from `structural differences' by comparing related static structures. In contrast, the direct observation of dynamic structural changes requires the initiation of a biochemical reaction or process in a crystal. Both the direct and the indirect approaches share a common challenge in analysis: how to interpret the structural heterogeneity intrinsic to all dynamic processes. This paper presents a real-space approach to this challenge, in which a suite of analytical methods and tools to identify and refine the mixed structural species present in multiple crystallographic data sets have been developed. These methods have been applied to representative scenarios in dynamic crystallography, and reveal structural information that is otherwise difficult to interpret or inaccessible using conventional methods.

The carbon-fluorine bond is the strongest covalent bond in organic chemistry, yet fluoroacetate dehalogenases can readily hydrolyze this bond under mild physiological conditions. Elucidating the molecular basis of this rare biocatalytic activity will provide the fundamental chemical insights into how this formidable feat is achieved. Here, we present a series of high-resolution (1.15-1.80 Å) crystal structures of a fluoroacetate dehalogenase, capturing snapshots along the defluorination reaction: the free enzyme, enzyme-fluoroacetate Michaelis complex, glycolyl-enzyme covalent intermediate, and enzyme-product complex. We demonstrate that enzymatic defluorination requires a halide pocket that not only supplies three hydrogen bonds to stabilize the fluoride ion but also is finely tailored for the smaller fluorine halogen atom to establish selectivity toward fluorinated substrates. We have further uncovered dynamics near the active site which may play pivotal roles in enzymatic defluorination. These findings may ultimately lead to the development of novel defluorinases that will enable the biotransformation of more complex fluorinated organic compounds, which in turn will assist the synthesis, detoxification, biodegradation, disposal, recycling, and regulatory strategies for the growing markets of organofluorines across major industrial sectors.