An Albumin-Holliday Junction Biomolecular Modular Design for Programmable Multifunctionality and Prolonged Circulation.

Combinatorial properties such as long-circulation and site- and cell-specific engagement need to be built into the design of advanced drug delivery systems to maximize drug payload efficacy. This work introduces a four-stranded oligonucleotide Holliday Junction (HJ) motif bearing functional moieties covalently conjugated to recombinant human albumin (rHA) to give a "plug-and-play" rHA-HJ multifunctional biomolecular assembly with extended circulation. Electrophoretic gel-shift assays show successful functionalization and purity of the individual high-performance liquid chromatography-purified modules as well as efficient assembly of the rHA-HJ construct. Inclusion of an epidermal growth factor receptor (EGFR)-targeting nanobody module facilitates specific binding to EGFR-expressing cells resulting in approximately 150-fold increased fluorescence intensity determined by flow cytometric analysis compared to assemblies absent of nanobody inclusion. A cellular recycling assay demonstrated retained albumin-neonatal Fc receptor (FcRn) binding affinity and accompanying FcRn-driven cellular recycling. This translated to a 4-fold circulatory half-life extension (2.2 and 0.55 h, for the rHA-HJ and HJ, respectively) in a double transgenic humanized FcRn/albumin mouse. This work introduces a novel biomolecular albumin-nucleic acid construct with extended circulatory half-life and programmable multifunctionality due to its modular design.

An albumin-angiotensin converting enzyme 2-based SARS-CoV-2 decoy with FcRn-driven half-life extension.

The emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants and breakthrough infections despite available coronavirus disease 2019 (COVID-19) vaccines calls for antiviral therapeutics. The application of soluble angiotensin converting enzyme 2 (ACE2) as a SARS-CoV-2 decoy that reduces cell bound ACE2-mediated virus entry is limited by a short plasma half-life. This work presents a recombinant human albumin ACE2 genetic fusion (rHA-ACE2) to increase the plasma half-life by an FcRn-driven cellular recycling mechanism, investigated using a wild type (WT) albumin sequence and sequence engineered with null FcRn binding (NB). Binding of rHA-ACE2 fusions to SARS-CoV-2 spike protein subdomain 1 (S1) was demonstrated (WT-ACE2 KD = 32.8 nM and NB-ACE2 KD = 31.7 nM) using Bio-Layer Interferometry and dose-dependent in vitro inhibition of host cell infection of pseudotyped viruses displaying surface SARS-CoV-2 spike (S) protein. FcRn-mediated in vitro recycling was translated to a five times greater plasma half-life of WT-ACE2 (t½ ß = 13.5 h) than soluble ACE2 (t½ ß = 2.8 h) in humanised FcRn/albumin double transgenic mice. The rHA-ACE2-based SARS-CoV-2 decoy system exhibiting FcRn-driven circulatory half-life extension introduced in this work offers the potential to expand and improve the anti-COVID-19 anti-viral drug armoury. STATEMENT OF SIGNIFICANCE: The COVID-19 pandemic has highlighted the need for rapid development of efficient antiviral therapeutics to combat SARS-CoV-2 and new mutants to lower morbidity and mortality in severe cases, and for people that are unable to receive a vaccine. Here we report a therapeutic albumin ACE2 fusion protein (rHA-ACE2), that can bind SARS-CoV-2 S protein decorated virus-like particles to inhibit viral infection, and exhibits extended in vivo half-life compared to ACE2 alone. Employing ACE2 as a binding decoy for the virus is expected to efficiently inhibit all SARS-CoV-2 mutants as they all rely on binding with endogenous ACE2 for viral cell entry and, therefore, rHA-ACE2 constitutes a versatile addition to the therapeutic arsenal for combatting COVID-19.

Tumor targeted 4-1BB agonist antibody-albumin fusions with high affinity to FcRn induce anti-tumor immunity without toxicity.

Costimulation of tumor-infiltrating T lymphocytes by anti-4-1BB monoclonal antibodies (mAbs) has shown anti-tumor activity in human trials, but can be associated with significant off-tumor toxicities involving FcγR interactions. Here, we introduce albumin-fused mouse and human bispecific antibodies with clinically favorable pharmacokinetics designed to confine 4-1BB costimulation to the tumor microenvironment. These Fc-free 4-1BB agonists consist of an EGFR-specific VHH antibody, a 4-1BB-specific scFv, and a human albumin sequence engineered for high FcRn binding connected in tandem (LiTCo-Albu). We demonstrate in vitro cognate target engagement, EGFR-specific costimulatory activity, and FcRn-driven cellular recycling similar to non-fused FcRn high-binding albumin. The mouse LiTCo-Albu exhibited a prolonged circulatory half-life and in vivo tumor inhibition, with no indication of 4-1BB mAb-associated toxicity. Furthermore, we show a greater therapeutic effect when used in combination with PD-1-blocking mAbs. These findings demonstrate the feasibility of tumor-specific LiTCo-Albu antibodies for safe and effective costimulatory strategies in cancer immunotherapy.

Albumin Biomolecular Drug Designs Stabilized through Improved Thiol Conjugation and a Modular Locked Nucleic Acid Functionalized Assembly.

Albumin-nucleic acid biomolecular drug designs offer modular multifunctionalization and extended circulatory half-life. However, stability issues associated with conventional DNA nucleotides and maleimide bioconjugation chemistries limit the clinical potential. This work aims to improve the stability of this thiol conjugation and nucleic acid assembly by employing a fast-hydrolyzing monobromomaleimide (MBM) linker and nuclease-resistant nucleotide analogues, respectively. The biomolecular constructs were formed by site-selective conjugation of a 12-mer oligonucleotide to cysteine 34 (Cys34) of recombinant human albumin (rHA), followed by annealing of functionalized complementary strands bearing either a fluorophore or the cytotoxic drug monomethyl auristatin E (MMAE). Formation of conjugates and assemblies was confirmed by gel shift analysis and mass spectrometry, followed by investigation of serum stability, neonatal Fc receptor (FcRn)-mediated cellular recycling, and cancer cell killing. The MBM linker afforded rapid conjugation to rHA and remained stable during hydrolysis. The albumin-nucleic acid biomolecular assembly composed of stabilized oligonucleotides exhibited high serum stability and retained FcRn engagement mediating FcRn-mediated cellular recycling. The MMAE-containing assembly exhibited cytotoxicity in the human MIA PaCa-2 pancreatic cancer cell line with an IC50 of 342 nM, triggered by drug release from breakdown of an acid-labile linker. In summary, this work presents rHA-nucleic acid module-based assemblies with improved stability and retained module functionality that further promotes the drug delivery potential of this biomolecular platform.

The impact of atmospheric oxidation on hygroscopicity and cloud droplet activation of inorganic sea spray aerosol.

Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.

Programmable half-life and anti-tumour effects of bispecific T-cell engager-albumin fusions with tuned FcRn affinity.

Fc-less bispecific T-cell engagers have reached the immuno-oncology market but necessitate continual infusion due to rapid clearance from the circulation. This work introduces a programmable serum half-life extension platform based on fusion of human albumin sequences engineered with either null (NB), wild type (WT) or high binding (HB) FcRn affinity combined with a bispecific T-cell engager. We demonstrate in a humanised FcRn/albumin double transgenic mouse model (AlbuMus) the ability to tune half-life based on the albumin sequence fused with a BiTE-like bispecific (anti-EGFR nanobody x anti-CD3 scFv) light T-cell engager (LiTE) construct [(t½ 0.6 h (Fc-less LiTE), t½ 19 hours (Albu-LiTE-NB), t½ 26 hours (Albu-LiTE-WT), t½ 37 hours (Albu-LiTE-HB)]. We show in vitro cognate target engagement, T-cell activation and discrimination in cellular cytotoxicity dependent on EGFR expression levels. Furthermore, greater growth inhibition of EGFR-positive BRAF mutated tumours was measured following a single dose of Albu-LiTE-HB construct compared to the Fc-less LiTE format and a full-length anti-EGFR monoclonal antibody in a new AlbuMus RAG1 knockout model introduced in this work. Programmable half-life extension facilitated by this albumin platform potentially offers long-lasting effects, better patient compliance and a method to tailor pharmacokinetics to maximise therapeutic efficacy and safety of immuno-oncology targeted biologics.