Hapten/Myristoyl Functionalized Poly(propyleneimine) Dendrimers as Potent Cell Surface Recruiters of Antibodies for Mediating Innate Immune Killing.

Recruiting endogenous antibodies to the surface of cancer cells using antibody-recruiting molecules has the potential to unleash innate immune effector killing mechanisms against antibody-bound cancer cells. The affinity of endogenous antibodies is relatively low, and many currently explored antibody-recruiting strategies rely on targeting over-expressed receptors, which have not yet been identified in most solid tumors. Here, both challenges are addressed by functionalizing poly(propyleneimine) (PPI) dendrimers with both multiple dinitrophenyl (DNP) motifs, as anti-hapten antibody-recruiting motifs, and myristoyl motifs, as universal phospholipid cell membrane anchoring motifs, to recruit anti-hapten antibodies to cell surfaces. By exploiting the multivalency of the ligand exposure on the dendrimer scaffold, it is demonstrated that dendrimers featuring ten myristoyl and six DNP motifs exhibit the highest antibody-recruiting capacity in vitro. Furthermore, it is shown that treating cancer cells with these dendrimers in vitro marks them for phagocytosis by macrophages in the presence of anti-hapten antibodies. As a proof-of-concept, it is shown that intratumoral injection of these dendrimers in vivo in tumor-bearing mice results in the recruitment of anti-DNP antibodies to the cell surface in the tumor microenvironment. These findings highlight the potential of dendrimers as a promising class of novel antibody-recruiting molecules for use in cancer immunotherapy.

Sequence-defined antibody-recruiting macromolecules.

Antibody-recruiting molecules represent a novel class of therapeutic agents that mediate the recruitment of endogenous antibodies to target cells, leading to their elimination by the immune system. Compared to single-ligand copies, macromolecular scaffolds presenting multiple copies of an antibody-binding ligand offer advantages in terms of increased complex avidity. In this study, we describe the synthesis of sequence-defined macromolecules designed for antibody recruitment, utilising dinitrophenol (DNP) as a model antibody-recruiting motif. The use of discrete macromolecules gives access to varying the spacing between DNP motifs while maintaining the same chain length. This characteristic enables the investigation of structure-dependent binding interactions with anti-DNP antibodies. Through solid-phase thiolactone chemistry, we synthesised a series of oligomers with precisely localised DNP motifs along the backbone and a terminal biotin motif for surface immobilisation. Utilising biolayer interferometry analysis, we observed that oligomers with adjacent DNP motifs exhibited enhanced avidity for anti-DNP antibodies. Molecular modelling provided insights into the structures and dynamics of the various macromolecules, shedding light on the accessibility of the ligands to the antibodies. Overall, our findings highlight that the use of sequence-defined macromolecules can contribute to our understanding of structure-activity relationships and provide insights for the design of novel antibody-recruiting therapeutic agents.

Towards a Rational Design of Antibody-Recruiting Molecules through a Computational Microscopy View of their Interactions with the Target Antibody.

Antibody recruiting molecules (ARMs) are an innovative class of chimeric molecules, consisting of an antibody-binding ligand (ABL) and a target-binding ligand (TBL). ARMs mediate ternary complex formation between a target cell of interest for elimination and endogenous antibodies that are present in human serum. Clustering of fragment crystallizable (Fc) domains on the surface of antibody-bound cells mediate destruction of the target cell by innate immune effector mechanisms. ARMs are typically designed by conjugating small molecule haptens to a (macro)molecular scaffold, without considering the structure of the respective anti-hapten antibody. Here we report on a computational molecular modeling methodology that allows for studying the close contacts between ARMs and the anti-hapten antibody, considering (1) the spacer length between ABL and TBL; (2) the number of ABL and TBL, and (3) the molecular scaffold onto which these are positioned. Our model predicts the difference in binding modes of the ternary complex and predicts which ARMs are optimal recruiters. Avidity measurements of the ARM-antibody complex and ARM-mediated antibody recruitment to cell surfaces in vitro confirmed these computational modeling predictions. This kind of multiscale molecular modelling holds potential for design of drug molecules that rely on antibody binding for their mechanism of action.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Lipid Amphiphile Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine*.

The search for vaccines that protect from severe morbidity and mortality because of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Here we describe an amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile. It is water-soluble and exhibits massive translocation to lymph nodes upon local administration through binding to albumin, affording localized innate immune activation and reduction in systemic inflammation. The adjuvanticity of IMDQ-PEG-CHOL was validated in a licensed vaccine setting (quadrivalent influenza vaccine) and an experimental trimeric recombinant SARS-CoV-2 spike protein vaccine, showing robust IgG2a and IgG1 antibody titers in mice that could neutralize viral infection in vitro and in vivo in a mouse model.

Covalent Cell Surface Conjugation of Nanoparticles by a Combination of Metabolic Labeling and Click Chemistry.

Conjugation of nanoparticles (NP) to the surface of living cells is of interest in the context of exploiting the tissue homing properties of ex vivo engineered T cells for tumor-targeted delivery of drugs loaded into NP. Cell surface conjugation requires either a covalent or non-covalent reaction. Non-covalent conjugation with ligand-decorated NP (LNP) is challenging and involves a dynamic equilibrium between the bound and unbound state. Covalent NP conjugation results in a permanently bound state of NP, but the current routes for cell surface conjugation face slow reaction kinetics and random conjugation to proteins in the glycocalyx. To address the unmet need for alternative bioorthogonal strategies that allow for efficient covalent cell surface conjugation, we developed a 2-step click conjugation sequence in which cells are first metabolically labeled with azides followed by reaction with sulfo-6-methyl-tetrazine-dibenzyl cyclooctyne (Tz-DBCO) by SPAAC, and subsequent IEDDA with trans-cyclooctene (TCO) functionalized NP. In contrast to using only metabolic azide labeling and subsequent conjugation of DBCO-NP, our 2-step method yields a highly specific cell surface conjugation of LNP, with very low non-specific background binding.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Modified Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine.

The search for vaccines that protect from severe morbidity and mortality as a result of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Several vaccine candidates are currently being tested in the clinic. Inactivated virus and recombinant protein vaccines can be safe options but may require adjuvants to induce robust immune responses efficiently. In this work we describe the use of a novel amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile). This amphiphile is water soluble and exhibits massive translocation to lymph nodes upon local administration, likely through binding to albumin. IMDQ-PEG-CHOL is used to induce a protective immune response against SARS-CoV-2 after single vaccination with trimeric recombinant SARS-CoV-2 spike protein in the BALB/c mouse model. Inclusion of amphiphilic IMDQ-PEG-CHOL in the SARS-CoV-2 spike vaccine formulation resulted in enhanced immune cell recruitment and activation in the draining lymph node. IMDQ-PEG-CHOL has a better safety profile compared to native soluble IMDQ as the former induces a more localized immune response upon local injection, preventing systemic inflammation. Moreover, IMDQ-PEG-CHOL adjuvanted vaccine induced enhanced ELISA and in vitro microneutralization titers, and a more balanced IgG2a/IgG1 response. To correlate vaccine responses with control of virus replication in vivo, vaccinated mice were challenged with SARS-CoV-2 virus after being sensitized by intranasal adenovirus-mediated expression of the human angiotensin converting enzyme 2 (ACE2) gene. Animals vaccinated with trimeric recombinant spike protein vaccine without adjuvant had lung virus titers comparable to non-vaccinated control mice, whereas animals vaccinated with IMDQ-PEG-CHOL-adjuvanted vaccine controlled viral replication and infectious viruses could not be recovered from their lungs at day 4 post infection. In order to test whether IMDQ-PEG-CHOL could also be used to adjuvant vaccines currently licensed for use in humans, proof of concept was also provided by using the same IMDQ-PEG-CHOL to adjuvant human quadrivalent inactivated influenza virus split vaccine, which resulted in enhanced hemagglutination inhibition titers and a more balanced IgG2a/IgG1 antibody response. Enhanced influenza vaccine responses correlated with better virus control when mice were given a lethal influenza virus challenge. Our results underscore the potential use of IMDQ-PEG-CHOL as an adjuvant to achieve protection after single immunization with recombinant protein and inactivated virus vaccines against respiratory viruses, such as SARS-CoV-2 and influenza viruses.

Poly(2-methyl-2-oxazoline) conjugates with doxorubicin: From synthesis of high drug loading water-soluble constructs to in vitro anti-cancer properties.

Poly(2-oxazoline)s represent an emerging class of polymers with increasing potential in biomedical sciences. To date, most of the work on poly(2-oxazoline)-drug conjugates focused on poly(2-ethyl-2-oxazoline) (PEtOx), a biocompatible water-soluble polymer with biological properties similar to polyethylene glycol. However, the more hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) shows better anti-fouling properties than PEtOx and thus indicates greater potential for the construction of polymer therapeutics. Herein, we synthesized for the first time a drug delivery system based on a linear PMeOx with a molar mass that is high enough (40 kDa) to exploit passive accumulation in the tumor by the enhanced permeation and retention effect. The anti-cancer drug doxorubicin is attached to the polymer carrier via an acid-sensitive hydrazone bond, which allows its pH-triggered release in the tumor. The in vitro study demonstrates successful cellular uptake of the PMeOx-doxorubicin conjugate via clathrin-mediated endocytosis, pH-sensitive drug release and high cytotoxicity against B16 melanoma cells. Finally, these properties were critically compared to the analogous systems based on the established PEtOx revealing that the more hydrophilic PMeOx carrier outperforms PEtOx in most of the parameters, showing higher maximal drug loading, superior cellular uptake, better anti-fouling properties, as well as improved in vitro anti-cancer efficiency. The study demonstrates the potential of PMeOx as a versatile platform for synthesis of new drug delivery systems.

Multivalent Antibody-Recruiting Macromolecules: Linking Increased Binding Affinity with Enhanced Innate Immune Killing.

Antibody-recruiting molecules (ARMs) are a novel class of immunotherapeutics. They are capable of introducing antibodies onto disease-relevant targets such as cancer cells, bacterial cells or viruses. This can induce antibody-mediated immune responses such as antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and antibody-dependent phagocytosis (ADCP), which can kill the pathogen. In contrast to the classic ARMs, multivalent ARMs could offer the advantage of increasing the efficiency of antibody recruitment and subsequent innate immune killing. Such compounds consist of multiple target-binding termini (TBT) and/or antibody-binding termini (ABT). Those multivalent interactions are able to convert low binding affinities into increased binding avidities. This minireview summarizes the current status of multivalent ARMs and gives insight into possible benefits, hurdles still to be overcome and future perspectives.

Cell surface clicking of antibody-recruiting polymers to metabolically azide-labeled cancer cells.

Triggering antibody-mediated innate immune mechanisms to kill cancer cells is an attractive therapeutic avenue. In this context, recruitment of endogenous antibodies to the cancer cell surface could be a viable alternative to the use of monoclonal antibodies. We report on antibody-recruiting polymers containing multiple antibody-binding hapten motifs and cyclooctynes that can covalently conjugate to azides introduced onto the glycocalyx of cancer cells by metabolic labeling with azido sugars.

Efficient Innate Immune Killing of Cancer Cells Triggered by Cell-Surface Anchoring of Multivalent Antibody-Recruiting Polymers.

Binding of monoclonal antibodies (mAbs) onto a cell surface triggers antibody-mediated effector killing by innate immune cells through complement activation. As an alternative to mAbs, synthetic systems that can recruit endogenous antibodies from the blood stream to a cancer cell surface could be of great relevance. Herein, we explore antibody-recruiting polymers (ARPs) as a novel class of immunotherapy. ARPs consist of a cell-binding motif linked to a polymer that contains multiple small molecule antibody-binding motifs along its backbone. As a proof of concept, we employ a lipid anchor that inserts into the phospholipid cell membrane and make use of a polymeric activated ester scaffold onto which we substitute dinitrophenol as an antibody-binding motif. We demonstrate that ARPs allow for high avidity antibody binding and drive antibody recruitment to treated cells for several days. Furthermore, we show that ARP-treated cancer cells are prone to antibody-mediated killing through phagocytosis by macrophages.