Site-selective template-directed synthesis of antibody Fc conjugates with concomitant ligand release

Template-directed methods are emerging as some of the most effective means to conjugate payloads at selective sites of monoclonal antibodies (mAbs). We have previously reported a method based on an engineered Fc-III reactive peptide to conjugate a radionuclide chelator to K317 of antibodies with the concomitant release of the Fc-III peptide ligand. Here, our method was redesigned to target two lysines proximal to the Fc-III binding site, K248 and K439. Using energy minimization predictions and a semi-combinatorial synthesis approach, we sampled multiple Fc-III amino acid substituents of A3, H5, L6 and E8, which were then converted into Fc-III reactive conjugates. Middle-down MS/MS subunit analysis of the resulting trastuzumab conjugates revealed that K248 and K439 can be selectively targeted using the Fc-III reactive variants L6Dap, L6Orn, L6Y and A3K or A3hK, respectively. Across all variants tested, L6Orn-carbonate appeared to be the best candidate, yielding a degree and yield of conjugation of almost 2 and 100% for a broad array of payloads including radionuclide chelators, fluorescent dyes, click-chemistry reagents, pre-targeted imaging reagents, and some cytotoxic small molecules. Furthermore, L6Orn carbonate appeared to yield similar conjugation results across multiple IgG subtypes. In vivo proof of concept was achieved by conjugation of NODAGA to the PD1/PD-L1 immune checkpoint inhibitor antibody atezolizumab, followed by PET imaging of PD-L1 expression in mice bearing PD-L1 expressing tumor xenograft using radiolabeled [64Cu]Cu-atezolizumab.

Abstract 1760: The antibody-drug conjugate GENA-111 conjugated to auristatin F shows therapeutic potency in BCAM positive epithelial cancer

Antibody-drug conjugates (ADCs) are considered as promising cancer treatment modalities that combine the selectivity of antibodies and the cytotoxic properties of payloads using chemical linkers. However, despite their success, ADCs still suffer from drawbacks, e.g., systemic toxicity, which limit their potential clinical applications. The systemic toxicity of an ADC is mainly related to the stability of its linker, and to the selectivity of its antibody towards the targeted antigen expressed on cancer cells. Lu/BCAM (Lutheran/basal cell adhesion molecule) is a member of the immunoglobulin superfamily and is a receptor for laminin, a protein that facilitates cell adhesion, migration, and invasion. A growing number of studies show that BCAM plays an essential role in tumor progression and is overexpressed on epithelial cancers e.g., skin cancer. Here we describe GENA-111, a human monoclonal anti-BCAM IgG4 (S228P) antibody that binds to human BCAM with high affinity, and that is significantly internalized by BCAM-positive tumor cells. We also describe the GENA-111-auristatin F ADC, wherein the GENA-111 antibody has been armed with an auristatin F derivative using a new linker technology and a stabilized thiol maleimide conjugation. This new linker technology comprises a cleavable peptidic sequence that facilitates multidrug attachment and the production of ADCs with tailored drug-to-antibody ratios (DARs). Cytotoxic drugs are rapidly and selectively released from the linker by the carboxypeptidase activity of Cathepsin B. In vitro cytotoxicity examination showed the potent cytotoxic effects of this GENA-111-auristatin F ADC on BCAM-expressing tumor cells, with a positive correlation between cytotoxicity and BCAM expression. Moreover, this ADC was also shown to significantly reduce the growth of tumor cells, including A431, T47D, and Huh7. The GENA-111-auristatin F ADC was evaluated in a xenograft mouse model established by subcutaneous injection of A431 cells, a BCAM positive human skin cancer cell line. The results of this study will be presented and discussed. Taken together, our data suggest that an ADC targeting BCAM e.g., GENA-111-auristatin F, might be a promising treatment strategy for BCAM positive epithelial cancer patients.

Citation Format: Hyunkyung Yu, Nathalie Bellocq, Youngeun Ha, Hyunuk Kim, Yunyeon Kim, Bu-Nam Jeon, Léo Marx, Mathilde Pantin, Hyunjin Yoo, Seungmin Byun, Joo-Yeon Chung, Mi Young Cha, Patrick Garrouste, Frédéric Lévy. The antibody-drug conjugate GENA-111 conjugated to auristatin F shows therapeutic potency in BCAM positive epithelial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1760.

Template directed synthesis of antibody Fc conjugates with concomitant ligand release

Antibodies are an attractive therapeutic modality for cancer treatment as they allow the increase of the treatment response rate and avoid the severe side effects of chemotherapy. Notwithstanding the strong benefit of antibodies, the efficacy of anti-cancer antibodies can dramatically vary among patients and ultimately result in no response to the treatment. Here, we have developed a novel means to regioselectively label the Fc domain of any therapeutic antibody with a radionuclide chelator in a single step chemistry, with the aim to study by SPECT/CT imaging if the radiolabeled antibody is capable of targeting cancer cells in vivo. A Fc-III peptide was used as bait to bring a carbonate electrophilic site linked to a metal chelator and to a carboxyphenyl leaving group in close proximity with an antibody Fc nucleophile amino acid (K317), thereby triggering the covalent linkage of the chelator to the antibody lysine, with the concomitant release of the carboxyphenyl Fc-III ligand. Using CHX-A′′-DTPA, we radiolabeled trastuzumab with indium-111 and showed in biodistribution and imaging experiments that the antibody accumulated successfully in the SK-OV-3 xenograft tumour implanted in mice. We found that our methodology leads to homogeneous conjugation of CHX-A′′-DTPA to the antibody, and confirmed that the Fc domain can be selectively labeled at K317, with a minor level of unspecific labeling on the Fab domain. The present method can be developed as a clinical diagnostic tool to predict the success of the therapy. Furthermore, our Fc-III one step chemistry concept paves the way to a broad array of other applications in antibody bioengineering.

A method is reported to attach a radionuclide chelator in a single step chemistry to the Fc domain of any therapeutic antibody.

Abstract 1304: AbYlinkTM: A site-selective labeling method for preclinical imaging of therapeutic antibodies

Clinical development of therapeutic antibodies relies on robust and thorough preclinical evaluation of multiple pharmacodynamic and pharmacokinetic parameters of antibody candidates. While current methods are available for in vitro characterization of antibodies, in vivo determination of tissue distribution, tumor accumulation and retention and potential off-target effects cannot be performed non-invasively in vivo over a prolonged period of time.

Here, we used AbYlinkTM, a novel site-selective labeling method of native antibodies, enabling the single-step covalent conjugation of a radionuclide chelator to the Fc domain of any IgG antibody isotype. Given the selectivity of this reaction for the Fc region of the immunoglobulin, labeling of the antibody at this location should not compromise binding to the antigen. Chelators that are covalently attached to the antibody allows for the labeling with radioisotopes such as 68Ga, 177Lu, 111In and 89Zr, and for the sensitive and quantitative molecular in vivo measurement by Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT). AbYlinkTM also permits the conjugation of fluorescent dyes to antibodies with the aim to measure antibody pharmacodynamic parameters by intravital microscopy. In this work, we have validated the technology by labeling several antibodies and ADCs with different payloads. Importantly, antibodies conjugated with AbYlinkTM retained the same affinity to the antigen as the original, unconjugated antibodies, contrary to the randomly labelled antibodies. We will also present data on the specific radiolabeling of commercially available trastuzumab with 111Indium and the SPECT images obtained after injection of mice bearing HER2-positive tumors with 111In-trastuzumab.

The present data suggest that AbYlinkTM can be used to support preclinical drug discovery tools to assist in the selection of therapeutic antibody candidates and/or for pharmacodynamic assessment of commercial antibodies. Furthermore, the specificity of the chemical conjugation suggests that AbYlinkTM can help to control the chelator distribution on the antibody drug conjugates.

Citation Format: Viktoriia Postupalenko, Léo Marx, David Viertl, Natalia Gasilova, Mathilde Plantin, Nadège Gsponer, Alexandre Johanssen, Thibaut Denoel, Gerrit Hagens, Jean-Manuel Segura, Frédéric Levy, Patrick Garrouste, John Prior, Margret Schottelius, Niklaus Schaefer, Origene Nyanguile. AbYlinkTM: A site-selective labeling method for preclinical imaging of therapeutic antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1304.

Chemoselectively addressable HCan building blocks in peptide synthesis: L-homocanaline derivatives

(S-2-amino-5-(aminooxy)pentanoic acid (L-homocanaline, HCan), a structural analogue of lysine, contains a reactive alkyloxyamine side chain and is therefore considered to react chemoselectively with carbonyl compounds by forming a kinetically stable oxime bond. The chemical synthesis of L-homocanaline starting from protected glutamic acid derivatives is described. Two orthogonally protected homocanaline derivatives were synthesized and their use in standard SPPS procedures was exemplified for the synthesis of a chemoselectively addressable cyclic peptide for use in TASP design. Moreover, the wide range of applications of this unique building block was demonstrated for the chemoselective ligation of an unprotected disaccharide to a HCan containing model peptide resulting in a chimeric glycopeptide structure.