Charge Detection Mass Spectrometry Reveals Conformational Heterogeneity in Megadalton-Sized Monoclonal Antibody Aggregates.

Aggregation of protein-based therapeutics can occur during development, production, or storage and can lead to loss of efficacy and potential toxicity. Native mass spectrometry of a covalently linked pentameric monoclonal antibody complex with a mass of ∼800 kDa reveals several distinct conformations, smaller complexes, and abundant higher-order aggregates of the pentameric species. Charge detection mass spectrometry (CDMS) reveals individual oligomers up to the pentamer mAb trimer (15 individual mAb molecules; ∼2.4 MDa) whereas intermediate aggregates composed of 6-9 mAb molecules and aggregates larger than the pentameric dimer (1.6 MDa) were not detected/resolved by standard mass spectrometry, size exclusion chromatography (SEC), capillary electrophoresis (CE-SDS), or by mass photometry. Conventional quadrupole time-of-flight mass spectrometry (QTOF MS), mass photometry, SEC, and CE-SDS did not resolve partially or more fully unfolded conformations of each oligomer that were readily identified using CDMS by their significantly higher extents of charging. Trends in the charge-state distributions of individual oligomers provides detailed insight into how the structures of compact and elongated mAb aggregates change as a function of aggregate size. These results demonstrate the advantages of CDMS for obtaining accurate masses and information about the conformations of large antibody aggregates despite extensive overlapping m/z values. These results open up the ability to investigate structural changes that occur in small, soluble oligomers during the earliest stages of aggregation for antibodies or other proteins.

Discovery and Evaluation of TLR-Targeted Immune Agonists.

Toll-like receptor (TLR) activation converts immunologically inactive tumors into immunologically active tumors by activating tumor residing antigen-presenting cells and recruitment of cytotoxic T lymphocytes. Targeted immune agonists (TIAs) are antibody drug conjugates with small-molecule TLR agonist payloads. The mechanism of action of TIAs involves tumor antigen recognition, Fcγ-receptor-dependent phagocytosis, and TLR-mediated activation to drive tumor killing by myeloid cells. Several new low DAR anti-HER2 TIAs conjugated with novel TLR7 or dual-TLR7/8 agonists with cleavable and noncleavable linkers were synthesized and profiled. In vitro studies demonstrated that these TIAs activate myeloid cells only in the presence of antigen-expressing cancer cells. Evaluation in ELISpot-based assays confirmed the low immunogenicity of these constructs. Systemic administration of the novel TIAs in tumor-bearing mice resulted in tumor reduction at low doses. These results provide a strong rationale for further development of the TIAs as a novel class of immunotherapeutics.

Design and Optimization of Selectivity-Tunable Toll-like Receptor 7/8 Agonists as Novel Antibody-Drug Conjugate Payloads.

Toll-like receptors 7 and 8 are involved in modulating the adaptive and innate immune responses, and their activation has shown promise as a therapeutic strategy in the field of immuno-oncology. While systemic exposure to TLR7/8 agonists can result in poor tolerance, combination therapies and targeted delivery through antibody-drug conjugates (ADCs) can help mitigate adverse effects. Described herein is the identification of a novel and potent series of pyrazolopyrimidine-based TLR7/8 agonists with tunable receptor selectivity. Representative agonists from this series were successfully able to induce the production of various proinflammatory cytokines and chemokines from human peripheral blood mononuclear cells. Anti-HER2-25 and anti-HER2-26 ADCs made from this class of payloads demonstrated mechanism-based activation of TLR7/8 in a THP1/N87 coculture system.

Development and application of an in vitro assay to assess target-independent B-cell activation by targeted TLR7 immune agonists.

Targeted immune agonist (TIA) comprising a TLR7 agonist conjugated to tumor-targeting antibodies have been shown to induce potent anti-tumor responses in various preclinical models. However, the clinical proof-of-concept of a TIA has been hampered by systemic dose-limiting immune-related toxicities, including rapid induction of anti-drug antibodies in patients. We have developed ELISPOT-based assay to measure activation of antibody-secreting cells (ASCs), intended to simulate the interaction between TIA and peripheral B cells as a tool to pre-clinically de-risk tumor target-independent peripheral B-cell activation by TIA. This method has proven to be robust and has fast turn-around time to evaluate the induction of spontaneous B-cell activation by TIA in a tumor target- and FcγR-independent manner. This novel ASC assay platform may serve as a preclinical tool to de-risk TIAs that can potentially induce immune-related adverse effects in the clinic.

Cryo-EM structures of inhibitory antibodies complexed with arginase 1 provide insight into mechanism of action.

Human Arginase 1 (hArg1) is a metalloenzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea, and modulates T-cell-mediated immune response. Arginase-targeted therapies have been pursued across several disease areas including immunology, oncology, nervous system dysfunction, and cardiovascular dysfunction and diseases. Currently, all published hArg1 inhibitors are small molecules usually less than 350 Da in size. Here we report the cryo-electron microscopy structures of potent and inhibitory anti-hArg antibodies bound to hArg1 which form distinct macromolecular complexes that are greater than 650 kDa. With local resolutions of 3.5 Å or better we unambiguously mapped epitopes and paratopes for all five antibodies and determined that the antibodies act through orthosteric and allosteric mechanisms. These hArg1:antibody complexes present an alternative mechanism to inhibit hArg1 activity and highlight the ability to utilize antibodies as probes in the discovery and development of peptide and small molecule inhibitors for enzymes in general.