Safety and Biodistribution Profile of Poly(styrenyl acetal trehalose) and Its Granulocyte Colony Stimulating Factor Conjugate.

Poly(styrenyl acetal trehalose) (pSAT), composed of trehalose side chains linked to a polystyrene backbone via acetals, stabilizes a variety of proteins and enzymes against fluctuations in temperature. A promising application of pSAT is conjugation of the polymer to therapeutic proteins to reduce renal clearance. To explore this possibility, the safety of the polymer was first studied. Investigation of acute toxicity of pSAT in mice showed that there were no adverse effects of the polymer at a high (10 mg/kg) concentration. The immune response (antipolymer antibody and cytokine production) in mice was also studied. No significant antipolymer IgG was detected for pSAT, and only a transient and low level of IgM was elicited. pSAT was also safe in terms of cytokine response. The polymer was then conjugated to a granulocyte colony stimulating factor (GCSF), a therapeutic protein that is approved by the Federal Drug Administration, in order to study the biodistribution of a pSAT conjugate. A site-selective, two-step synthesis approach was developed for efficient conjugate preparation for the biodistribution study resulting in 90% conjugation efficiency. The organ distribution of GCSF-pSAT was measured by positron emission tomography and compared to controls GCSF and GCSF-poly(ethylene glycol), which confirmed that the trehalose polymer conjugate improved the in vivo half-life of the protein by reducing renal clearance. These findings suggest that trehalose styrenyl polymers are promising for use in therapeutic protein-polymer conjugates for reduced renal clearance of the biomolecule.

PEG Analogs Synthesized by Ring-Opening Metathesis Polymerization for Reversible Bioconjugation.

Poly(ethylene glycols) (PEGs) with protein-reactive end-groups are widely utilized in bioconjugation reactions. Herein, we describe the use of ring-opening metathesis polymerization (ROMP) to synthesize unsaturated protein-reactive PEG analogs. These ROMP PEGs (rPEGs) contained terminal aldehyde functionality and ranged in molecular weight from 6 to 20 kDa. The polymers were readily conjugated to free amines on the protein hen egg-white lysozyme (Lyz). Biocompatibility of the unsaturated PEGs was assessed in vitro, revealing the polymers to be nontoxic up to concentrations of at least 1 mg/mL in human dermal fibroblasts (HDFs). The resulting unsaturated rPEG-lysozyme conjugates underwent metathesis-based depolymerization, resulting in decreased molecular weight of the conjugate.

Lactone Stabilization is Not a Necessary Feature for Antibody Conjugates of Camptothecins.

Camptothecins exist in a pH-dependent equilibrium between the active, closed lactone and the inactive open-carboxylate forms. Several previous reports underscore the need for lactone stabilization in generating improved camptothecins, and indeed, such designs have been incorporated into antibody-drug conjugates containing this drug. Here, we demonstrate that lactone stabilization is not necessary for camptothecin-based ADC efficacy. We synthesized and evaluated camptothecin SN-38 drug linkers that differed with respect to lactone stability and released SN-38 or the hydrolyzed open-lactone form upon cleavage from the antibody carrier. An α-hydroxy lactone-linked SN-38 drug linker preserved the closed-lactone ring structure, while the phenol-linked version allowed conversion between the closed-lactone and open-carboxylate structures. The in vitro cytotoxicity, pharmacokinetic properties, and in vivo efficacy in the L540cy Hodgkin's lymphoma model of the corresponding ADCs were found to be indistinguishable, leading us to conclude that camptothecin-based antibody-drug conjugates possess pronounced activity regardless of the lactone state of the bound drug. This is most likely a result of ADC processing within acidic intracellular vesicles, delivering camptothecin in its active closed-lactone form.

Synthesis and Biological Evaluation of a Degradable Trehalose Glycopolymer Prepared by RAFT Polymerization.

There is a significant need for new biodegradable protein stabilizing polymers. Herein, the synthesis of a polymer with trehalose side chains and hydrolytically degradable backbone esters and its evaluation for protein stabilization and cytotoxicity are described. Specifically, an alkene-containing parent polymer is synthesized by reversible addition-fragmentation chain transfer polymerization, and thiolated trehalose is installed using a radical-initiated thiol-ene reaction. The stabilizing properties of the polymer are investigated by thermally stressing granulocyte colony-stimulating factor (G-CSF), which is expressed and purified using a custom-designed G-CSF fusion protein with a polyhistidine-tagged maltose binding protein. The degradable polymer is shown to stabilize G-CSF to 66% after heating at 40 °C. Poly(5,6-benzo-2-methylene-1,3-dioxepane (BMDO)-co-butyl methacrylate-trehalose) is degraded and its cellular compatibility is investigated. While the polymer is noncytotoxic, cytotoxic effects are observed from the degraded products in fibroblasts and murine myeloblasts. These data provide important information for future use of BMDO-containing trehalose glycopolymers for biomedical applications.

Trehalose glycopolymers as excipients for protein stabilization.

Herein, the synthesis of four different trehalose glycopolymers and investigation of their ability to stabilize proteins to heat and lyophilization stress are described. The disaccharide, α,α-trehalose, was modified with a styrenyl acetal, methacrylate acetal, styrenyl ether, or methacrylate moiety resulting in four different monomers. These monomers were then separately polymerized using free radical polymerization with azobisisobutyronitrile (AIBN) as an initiator to synthesize the glycopolymers. Horseradish peroxidase and glucose oxidase were incubated at 70 and 50 °C, respectively, and ß-galactosidase was lyophilized multiple times in the presence of various ratios of the polymers or trehalose. The protein activities were subsequently tested and found to be significantly higher when the polymers were present during the stress compared to no additive and to equivalent amounts of trehalose. Different molecular weights (10 kDa, 20 kDa, and 40 kDa) were tested, and all were equivalent in their stabilization ability. However, some subtle differences were observed regarding stabilization ability between the different polymer samples, depending on the stress. Small molecules such as benzyl ether trehalose were not better stabilizers than trehalose, and the trehalose monomer decreased protein activity, suggesting that hydrophobized trehalose was not sufficient and that the polymeric structure was required. In addition, cytotoxicity studies with NIH 3T3 mouse embryonic fibroblast cells, RAW 264.7 murine macrophages, human dermal fibroblasts (HDFs), and human umbilical vein endothelial cells (HUVECs) were conducted with polymer concentrations up to 8 mg/mL. The data showed that all four polymers were noncytotoxic for all tested concentrations. The results together suggest that trehalose glycopolymers are promising as additives to protect proteins from a variety of stressors.

Development of Novel Antibody-Camptothecin Conjugates.

We have developed a highly active and well-tolerated camptothecin (CPT) drug-linker designed for antibody-mediated drug delivery in which the lead molecule consists of a 7-aminomethyl-10,11-methylenedioxy CPT (CPT1) derivative payload attached to a novel hydrophilic protease-cleavable valine-lysine-glycine tripeptide linker. A defined polyethylene glycol stretcher was included to improve the properties of the drug-linker, facilitating high antibody-drug conjugate (ADC) drug loading, while reducing the propensity for aggregation. A CPT1 ADC with 8 drug-linkers/mAb displayed a pharmacokinetic profile coincident with parental unconjugated antibody and had high serum stability. The ADCs were broadly active against cancer cells in vitro and in mouse xenograft models, giving tumor regressions and complete responses at low (≤3 mg/kg, single administration) doses. Pronounced activities were obtained in both solid and hematologic tumor models and in models of bystander killing activity and multidrug resistance. Payload release studies demonstrated that two CPTs, CPT1 and the corresponding glycine analog (CPT2), were released from a cAC10 ADC by tumor cells. An ADC containing this drug-linker was well tolerated in rats at 60 mg/kg, given weekly four times. Thus, ADCs comprised of this valine-lysine-glycine linker with CPT drug payloads have promise in targeted drug delivery.

De novo design of ACE2 protein decoys to neutralize SARS-CoV-2.

There is an urgent need for the ability to rapidly develop effective countermeasures for emerging biological threats, such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes the ongoing coronavirus disease 2019 (COVID-19) pandemic. We have developed a generalized computational design strategy to rapidly engineer de novo proteins that precisely recapitulate the protein surface targeted by biological agents, like viruses, to gain entry into cells. The designed proteins act as decoys that block cellular entry and aim to be resilient to viral mutational escape. Using our novel platform, in less than ten weeks, we engineered, validated, and optimized de novo protein decoys of human angiotensin-converting enzyme 2 (hACE2), the membrane-associated protein that SARS-CoV-2 exploits to infect cells. Our optimized designs are hyperstable de novo proteins (∼18-37 kDa), have high affinity for the SARS-CoV-2 receptor binding domain (RBD) and can potently inhibit the virus infection and replication in vitro. Future refinements to our strategy can enable the rapid development of other therapeutic de novo protein decoys, not limited to neutralizing viruses, but to combat any agent that explicitly interacts with cell surface proteins to cause disease.

De novo design of potent and resilient hACE2 decoys to neutralize SARS-CoV-2.

We developed a de novo protein design strategy to swiftly engineer decoys for neutralizing pathogens that exploit extracellular host proteins to infect the cell. Our pipeline allowed the design, validation, and optimization of de novo human angiotensin-converting enzyme 2 (hACE2) decoys to neutralize severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The best monovalent decoy, CTC-445.2, bound with low nanomolar affinity and high specificity to the receptor-binding domain (RBD) of the spike protein. Cryo-electron microscopy (cryo-EM) showed that the design is accurate and can simultaneously bind to all three RBDs of a single spike protein. Because the decoy replicates the spike protein target interface in hACE2, it is intrinsically resilient to viral mutational escape. A bivalent decoy, CTC-445.2d, showed ~10-fold improvement in binding. CTC-445.2d potently neutralized SARS-CoV-2 infection of cells in vitro, and a single intranasal prophylactic dose of decoy protected Syrian hamsters from a subsequent lethal SARS-CoV-2 challenge.

Direct Write Protein Patterns for Multiplexed Cytokine Detection from Live Cells Using Electron Beam Lithography.

Simultaneous detection of multiple biomarkers, such as extracellular signaling molecules, is a critical aspect in disease profiling and diagnostics. Precise positioning of antibodies on surfaces, especially at the micro- and nanoscale, is important for the improvement of assays, biosensors, and diagnostics on the molecular level, and therefore, the pursuit of device miniaturization for parallel, fast, low-volume assays is a continuing challenge. Here, we describe a multiplexed cytokine immunoassay utilizing electron beam lithography and a trehalose glycopolymer as a resist for the direct writing of antibodies on silicon substrates, allowing for micro- and nanoscale precision of protein immobilization. Specifically, anti-interleukin 6 (IL-6) and antitumor necrosis factor alpha (TNFα) antibodies were directly patterned. Retention of the specific binding properties of the patterned antibodies was shown by the capture of secreted cytokines from stimulated RAW 264.7 macrophages. A sandwich immunoassay was employed using gold nanoparticles and enhancement with silver for the detection and visualization of bound cytokines to the patterns by localized surface plasmon resonance detected with dark-field microscopy. Multiplexing with both IL-6 and TNFα on a single chip was also successfully demonstrated with high specificity and in relevant cell culture conditions and at different times after cell stimulation. The direct fabrication of capture antibody patterns for cytokine detection described here could be useful for biosensing applications.

Trehalose glycopolymer resists allow direct writing of protein patterns by electron-beam lithography.

Direct-write patterning of multiple proteins on surfaces is of tremendous interest for a myriad of applications. Precise arrangement of different proteins at increasingly smaller dimensions is a fundamental challenge to apply the materials in tissue engineering, diagnostics, proteomics and biosensors. Herein, we present a new resist that protects proteins during electron-beam exposure and its application in direct-write patterning of multiple proteins. Polymers with pendant trehalose units are shown to effectively crosslink to surfaces as negative resists, while at the same time providing stabilization to proteins during the vacuum and electron-beam irradiation steps. In this manner, arbitrary patterns of several different classes of proteins such as enzymes, growth factors and immunoglobulins are realized. Utilizing the high-precision alignment capability of electron-beam lithography, surfaces with complex patterns of multiple proteins are successfully generated at the micrometre and nanometre scale without requiring cleanroom conditions.