Obtaining control of cell surface functionalizations via Pre-targeting and Supramolecular host guest interactions

Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Chemically augmented malaria sporozoites display an altered immunogenic profile

Despite promising results in malaria-naïve individuals, whole sporozoite (SPZ) vaccine efficacy in malaria-endemic settings has been suboptimal. Vaccine hypo-responsiveness due to previous malaria exposure has been posited as responsible, indicating the need for SPZ vaccines of increased immunogenicity. To this end, we here demonstrate a proof-of-concept for altering SPZ immunogenicity, where supramolecular chemistry enables chemical augmentation of the parasite surface with a TLR7 agonist-based adjuvant (SPZ-SAS(CL307)). In vitro, SPZ-SAS(CL307) remained well recognized by immune cells and induced a 35-fold increase in the production of pro-inflammatory IL-6 (p < 0.001). More promisingly, immunization of mice with SPZ-SAS(CL307) yielded improved SPZ-specific IFN-γ production in liver-derived NK cells (percentage IFN-γ+ cells 11.1 ± 1.8 vs. 9.4 ± 1.5%, p < 0.05), CD4+ T cells (4.7 ± 4.3 vs. 1.8 ± 0.7%, p < 0.05) and CD8+ T cells (3.6 ± 1.4 vs. 2.5 ± 0.9%, p < 0.05). These findings demonstrate the potential of using chemical augmentation strategies to enhance the immunogenicity of SPZ-based malaria vaccines.

Cell-based Relay Delivery Strategy in Biomedical Applications

The relay delivery strategy is a two-step targeting approach based on two distinct modules in which the first step with an initiator is to artificially create a target/environment which can be targeted by the follow-up effector. This relay delivery concept creates opportunities to amplify existing or create new targeted signals through deploying initiators to enhance the accumulation efficiency of the following effector at the disease site. As the "live" medicines, cell-based therapeutics possess inherent tissue/cell homing abilities and favorable feasibility of biological and chemical modifications, endowing them the great potential in specifically interacting with diverse biological environments. All these unique capabilities make cellular products great candidates that can serve as either initiators or effectors for relay delivery strategies. In this review, we survey recent advances in relay delivery strategies with a specific focus on the roles of various cells in developing relay delivery systems.

Chemically Enhanced Immunogenicity of Bacteria by Supramolecular Functionalization with an Adjuvant

Many pathogens blunt immune responses because they lack immunogenic structural features, which typically results in disease. Here, we show evidence suggesting that pathogen immunogenicity can be chemically enhanced. Using supramolecular host-guest chemistry, we complexed onto the surface of a poorly immunogenic bacterium (Staphylococcus aureus) a TLR7 agonist-based adjuvant. "Adjuvanted" bacteria were readily recognized by macrophages and induced a more pro-inflammatory immunophenotype. Future applications of this concept could yield treatment modalities that bolster the immune system's response to pathogenic microbes.

Cell-surface Labeling via Bioorthogonal Host-Guest Chemistry

The widespread adoption of the bioorthogonal chemical reporter strategy revolutionized chemical biology. However, its translation to living mammals has been challenging, due to the size/stability properties of the chemical reporter group and/or the reaction kinetics of the labeling step. While developing new bioorthogonal reactions has been the traditional approach to optimizing the bioorthogonal chemical reporter strategy, here we present a different avenue, leveraging intermolecular interactions, to create bioorthogonal host-guest pairs. This approach, deemed "bioorthogonal complexation, does not rely on activated functional groups or second-order rate constants. We utilize the cucurbit[7]uril (CB[7]) scaffold to showcase bioorthogonal complexation and determine that medium-affinity (K_a ≈ 10⁸-10⁹ M^-1) guests efficiently label cell surfaces and outperform the strain-promoted azide-alkyne cycloaddition. Finally, we implement bioorthogonal complexation in the chemical reporter strategy through the metabolic incorporation of ortho-carborane into cell-surface glycans and detection with a CB[7]-fluorescein conjugate.

Targeted Delivery and Site-Specific Activation of β-Cyclodextrin-Conjugated Photosensitizers for Photodynamic Therapy through a Supramolecular Bio-orthogonal Approach

Targeted delivery of photosensitizers using hydrophilic and tumor-directing carriers and site-specific activation of their photocytotoxicity are two common strategies to enhance the specificity of anticancer photodynamic therapy. We report herein a novel supramolecular bio-orthogonal approach to integrate these two functions. A β-cyclodextrin-substituted aza-boron-dipyrromethene-based photosensitizer was first complexed with a ferrocene-substituted black-hole quencher to inhibit its photosensitizing ability. Upon encountering the adamantane moieties that had been delivered to target cancer cells through specific binding of the conjugated peptide to the overexpressed epidermal growth factor receptor, the ferrocene-based guest species were displaced due to the stronger binding interactions between β-cyclodextrin and adamantane, thereby restoring the photodynamic activity of the photosensitizer. Hence, this two-step process enabled targeted delivery and site-specific activation of the photosensitizer, as demonstrated through a series of experiments in aqueous media, in a range of cancer cell lines and in tumor-bearing nude mice.

Cyclodextrin/Adamantane-Mediated Targeting of Inoculated Bacteria in Mice

Cyclodextrin (CD)-based host–guest interactions with adamantane (Ad) have demonstrated use for functionalizing living cells in vitro. The next step in this supramolecular functionalization approach is to explore the concept to deliver chemical cargo to living cells in vivo, e.g., inoculated bacteria, in order to study their dissemination. We validated this concept in two rodent Staphylococcus aureus models. Bacteria (1 × 10⁸ viable S. aureus) were inoculated by (1) intramuscular injection or (2) intrasplenic injection followed by dissemination throughout the liver. The bacteria were prefunctionalized with ^99mTc-UBI_29–41-Ad₂ (primary vector), which allowed us to both determine the bacterial load and create an in vivo target for the secondary host-vector (24 h post-inoculation). The secondary vector, i.e., chemical cargo delivery system, made use of a ¹¹¹In-Cy5_0.5CD₉PIBMA₃₉ polymer that was administered intravenously. Bacteria-specific cargo delivery as a result of vector complexation was evaluated by dual-isotope SPECT imaging and biodistribution studies (¹¹¹In), and by fluorescence (Cy5); these evaluations were performed 4 h post-injection of the secondary vector. Mice inoculated with nonfunctionalized S. aureus and mice without an infection served as controls. Dual-isotope SPECT imaging demonstrated that ¹¹¹In-Cy5_0.5CD₉PIBMA₃₉ colocalized with ^99mTc-UBI_29–41-Ad₂-labeled bacteria in both muscle and liver. In inoculated muscle, a 2-fold higher uptake level (3.2 ± 1.0%ID/g) was noted compared to inoculation with nonfunctionalized bacteria (1.9 ± 0.4%ID/g), and a 16-fold higher uptake level compared to noninfected muscle (0.2 ± 0.1%ID/g). The hepatic accumulation of the host-vector was nearly 10-fold higher (27.1 ± 11.1%ID/g) compared to the noninfected control (2.7 ± 0.3%ID/g; p < 0.05). Fluorescence imaging of the secondary vector corroborated SPECT-imaging and biodistribution findings. We have demonstrated that supramolecular host–guest complexation can be harnessed to achieve an in vivo cargo delivery strategy, using two different bacterial models in soft tissue and liver. This proof-of-principle study paves a path toward developing innovative drug delivery concepts via cell functionalization techniques.

Fluorescence background quenching as a means to increase Signal to Background ratio - a proof of concept during Nerve Imaging

Introduction: Adequate signal to background ratios are critical for the implementation of fluorescence-guided surgery technologies. While local tracer administrations help to reduce the chance of systemic side effects, reduced spatial migration and non-specific tracer diffusion can impair the discrimination between the tissue of interest and the background. To combat background signals associated with local tracer administration, we explored a pretargeting concept aimed at quenching non-specific fluorescence signals. The efficacy of this concept was evaluated in an in vivo neuronal tracing set-up.

Methods: Neuronal tracing was achieved using a wheat germ agglutinin (WGA) lectin^. functionalized with an azide-containing Cy5 dye (N₃-Cy5-WGA). A Cy7 quencher dye (Cy7-DBCO) was subsequently used to yield Cy7-Cy5-WGA, a compound wherein the Cy5 emission is quenched by Förster resonance energy transfer to Cy7. The photophysical properties of N₃-Cy5-WGA and Cy7-Cy5-WGA were evaluated together with deactivation kinetics in situ, in vitro (Schwannoma cell culture), ex vivo (muscle tissue from mice; used for dose optimization), and in vivo (nervus ischiadicus in THY-1 YFP mice).

Results:In situ, conjugation of Cy7-DBCO to N₃-Cy5-WGA resulted in >90% reduction of the Cy5 fluorescence signal intensity at 30 minutes after addition of the quencher. In cells, pretargeting with the N₃-Cy5-WGA lectin yielded membranous staining, which could efficiently be deactivated by Cy7-DBCO over the course of 30 minutes (91% Cy5 signal decrease). In ex vivo muscle tissue, administration of Cy7-DBCO at the site where N₃-Cy5-WGA was injected induced 80-90% quenching of the Cy5-related signal after 10-20 minutes, while the Cy7-related signal remained stable over time. In vivo,Cy7-DBCO effectively quenched the non-specific background signal up to 73% within 5 minutes, resulting in a 50% increase in the signal-to-background ratio between the nerve and injection site.

Conclusion: The presented pretargeted fluorescence-quenching technology allowed fast and effective reduction of the background signal at the injection site, while preserving in vivo nerve visualization. While this proof-of-principle study was focused on imaging of nerves using a fluorescent WGA-lectin, the same concept could in the future also apply to applications such as sentinel node imaging.

A Supramolecular Platform Technology for Bacterial Cell Surface Modification

In an era of antimicrobial resistance, a better understanding of the interaction between bacteria and the sentinel immune system is needed to discover new therapeutic targets for combating bacterial infectious disease. Sentinel immune cells such as macrophages phagocytose intact bacteria and thereby initiate ensuing immune responses. The bacterial surface composition is a key element that determines the macrophage signaling. To study the role of the bacterial cell surface composition in immune recognition, we developed a platform technology for altering bacterial surfaces in a controlled manner with versatile chemical scaffolds. We show that these scaffolds are efficiently loaded onto both Gram-positive and -negative bacteria and that their presence does not impair the capacity of monocyte-derived macrophages to phagocytose bacteria and subsequently signal to other components of the immune system. We believe this technology thus presents a useful tool to study the role of bacterial cell surface composition in disease etiology and potentially in novel interventions utilizing intact bacteria for vaccination.

COvalent monolayer patterns in Microfluidics by PLasma etching Open Technology – COMPLOT

Plasma microcontact patterning (PμCP) and replica molding were combined to make PDMS/glass microfluidic devices with β-cyclodextrin (β-CD) patterns attached covalently on the glass surface inside microchannels.

On-Flow Immobilization of Polystyrene Microspheres on β-Cyclodextrin-Patterned Silica Surfaces through Supramolecular Host-Guest Interactions

Species-specific isolation of microsized entities such as microplastics and resistant bacteria from waste streams is becoming a growing environmental challenge. By studying the on-flow immobilization of micron-sized polystyrene particles onto functionalized silica surfaces, we ascertain if supramolecular host-guest chemistry in aqueous solutions can provide an alternative technology for water purification. Polystyrene particles were modified with different degrees of adamantane (guest) molecules, and silica surfaces were patterned with β-cyclodextrin (β-CD, host) through microcontact printing (μCP). The latter was exposed to solutions of these particles flowing at different speeds, allowing us to study the effect of flow rate and multivalency on particle binding to the surface. The obtained binding profile was correlated with Comsol simulations. We also observed that particle binding is directly aligned with particle's ability to form host-guest interactions with the β-CD-patterned surface, as particle binding to the functionalized glass surface increased with higher adamantane load on the polystyrene particle surface. Because of the noncovalent character of these interactions, immobilization is reversible and modified β-CD surfaces can be recycled, which provides a positive outlook for their incorporation in water purification systems.

Covalently bound monolayer patterns obtained by plasma etching on glass surfaces

Micropatterns of β-cyclodextrin (β-CD) monolayers on glass are obtained by using a plasma etching approach with polydimethylsiloxane (PDMS) stamps. This simple and versatile approach provides a promising alternative to current techniques for creating patterns of covalently bound molecules. It is also possible to fabricate sub-10 μm sized features.

Molecular conjugation using non-covalent click chemistry

Molecular conjugation refers to methods used in biomedicine, advanced materials and nanotechnology to link two partners - from small molecules to large and sometimes functionally complex biopolymers. The methods ideally have a broad structural scope, proceed under very mild conditions (including in H₂O), occur at a rapid rate and in quantitative yield with no by-products, enable bioorthogonal reactivity and have zero toxicity. Over the past two decades, the field of click chemistry has emerged to afford us new and efficient methods of molecular conjugation. These methods are based on chemical reactions that produce permanently linked conjugates, and we refer to this field here as covalent click chemistry. Alternatively, if molecular conjugation is undertaken using a pair of complementary molecular recognition partners that associate strongly and selectively to form a thermodynamically stable non-covalent complex, then we refer to this strategy as non-covalent click chemistry. This Perspective is concerned with this latter approach and highlights two distinct applications of non-covalent click chemistry in molecular conjugation: the pre-assembly of molecular conjugates or surface-coated nanoparticles and the in situ capture of tagged biomolecular targets for imaging or analysis.

In vivo stability of supramolecular host-guest complexes monitored by dual-isotope multiplexing in a pre-targeting model of experimental liver radioembolization

INTRODUCTION

Cyclodextrin (CD)-based supramolecular interactions have been proposed as nanocarriers for drug delivery. We previously explored the use of these supramolecular interactions to perform targeted hepatic radioembolization. In a two-step procedure the appropriate location of the diagnostic pre-targeting vector can first be confirmed, after which the therapeutic vector will be targeted through multivalent host-guest interactions. Such a procedure would prevent therapeutic errors that come from a mismatch between diagnostic and therapeutic procedures. In the current study we explored the use of dual-isotope imaging to assess the in vivo stability of the formed complex and individual components.

METHODS

Dual-isotope imaging of the host and guest vectors was performed after labeling of the pre-targeted guest vector, being adamantane (Ad) functionalized macro-aggregated albumin (MAA) particles, with technetium-99 m (^99mTc-MAA-Ad). The host vector, Cy5_0.5CD₉PIBMA₃₉, was labeled with indium-111 (¹¹¹In-Cy5_0.5CD₉PIBMA₃₉). The in situ stability of both the individual vectors and the resulting [MAA-Ad-¹¹¹In-Cy5_0.5CD₉PIBMA₃₉] complexes was studied over 44 h at 37 °C in a serum protein-containing buffer. In vivo, the host vector ¹¹¹In-Cy5_0.5CD₉PIBMA₃₉ was administered two hours after local deposition of ^99mTc-MAA-Ad in mice. Dual-isotope SPECT imaging and quantitative biodistribution studies were performed between 2 and 44 h post intravenous host vector administration.

RESULTS

The individual vectors portrayed <5% dissociation of the radioisotope over the course of 20 h. Dissociation of [MAA-Ad-¹¹¹In-Cy5_0.5CD₉PIBMA₃₉] complexes remained within a 10-20% range after incubation in serum. In vivo dual-isotope SPECT imaging of host-guest interactions revealed co-localization of the tracer components. Quantitative assessment of the biodistribution revealed that the hepatic accumulation of the host vector nearly doubled between 2 h and 44 h post-injection (from 14.9 ± 6.1%ID/g to 26.2 ± 2.1%ID/g).

CONCLUSIONS

Assessment of intra-hepatic host-guest complexation was successfully achieved using dual isotope multiplexing, underlining the complex stability that was found in situ (up to 44 h in serum). Overall, the results obtained in this study highlight the potential of supramolecular chemistry as a versatile platform that could advance the field of nanomedicine.

Fabrication of Supramolecular Bioactive Surfaces via β-Cyclodextrin-Based Host-Guest Interactions

Supramolecular host-guest interactions provide a facile and versatile basis for the construction of sophisticated structures and functional assemblies through specific molecular recognition of host and guest molecules to form inclusion complexes. In recent years, these interactions have been exploited as a means of attaching bioactive molecules and polymers to solid substrates for the fabrication of bioactive surfaces. Using a common host molecule, β-cyclodextrin (β-CD), and various guest molecules as molecular building blocks, we fabricated several types of bioactive surfaces with multifunctionality and/or function switchability via host-guest interactions. Other groups have also taken this approach, and several intelligent designs have been developed. The results of these investigations indicate that, compared to the more common covalent bonding-based methods for attachment of bioactive ligands, host-guest based methods are simple, more broadly ("universally") applicable, and allow convenient renewal of bioactivity. In this Spotlight on Applications, we review and summarize recent developments in the fabrication of supramolecular bioactive surfaces via β-CD-based host-guest interactions. The main focus is on the work from our laboratory, but highlights on work from other groups are included. Applications of the materials are also emphasized. These surfaces can be categorized into three types based on: (i) self-assembled monolayers, (ii) polymer brushes, and (iii) multilayered films. The host-guest strategy can be extended from material surfaces to living cell surfaces, and work along these lines is also reviewed. Finally, a brief perspective on the developments of supramolecular bioactive surfaces in the future is presented.

Phosphorescent cationic iridium(iii) complexes dynamically bound to cyclodextrin vesicles: applications in live cell imaging

We report cationic Ir(iii) complexes functionalized with adamantyl groups designed to bind to β-cyclodextrin vesicles (CDV) with high affinity (K a = 1 × 106 M-1). The emission of the complexes is tuned by changing the nature of the cyclometalating ligands. The host-guest adduct of CDV and Ir(iii) complexes shows increased and significantly blue-shifted emission due to the lower mobility of the Ir(iii)-complexes residing in the less polar environment of the vesicle surface. Ir(iii)-decorated CDV are efficiently taken up by cells and can be used in live cell imaging. The CDV act as carriers to transport the phosphorescent complexes into cells where they selectively stain mitochondria.

A Supramolecular Approach for Liver Radioembolization

Hepatic radioembolization therapies can suffer from discrepancies between diagnostic planning (scout-scan) and the therapeutic delivery itself, resulting in unwanted side-effects such as pulmonary shunting. We reasoned that a nanotechnology-based pre-targeting strategy could help overcome this shortcoming by directly linking pre-interventional diagnostics to the local delivery of therapy.

Methods: The host-guest interaction between adamantane and cyclodextrin was employed in an in vivo pre-targeting set-up. Adamantane (guest)-functionalized macro albumin aggregates (MAA-Ad; d = 18 μm) and (radiolabeled) Cy5 and β-cyclodextrin (host)-containing PIBMA polymers (^99mTc-Cy5_0.5CD₁₀PIBMA₃₉; MW ~ 18.8 kDa) functioned as the reactive pair. Following liver or lung embolization with (^99mTc)-MAA-Ad or (^99mTc)-MAA (control), the utility of the pre-targeting concept was evaluated after intravenous administration of ^99mTc-Cy5_0.5CD₁₀PIBMA₃₉.

Results: Interactions between MAA-Ad and Cy5_0.5CD₁₀PIBMA₃₉ could be monitored in solution using confocal microscopy and were quantified by radioisotope-based binding experiments. In vivo the accumulation of the MAA-Ad particles in the liver or lungs yielded an approximate ten-fold increase in accumulation of ^99mTc-Cy5_0.5CD₁₀PIBMA₃₉ in these organs (16.2 %ID/g and 10.5 %ID/g, respectively) compared to the control. Pre-targeting with MAA alone was shown to be only half as efficient. Uniquely, for the first time, this data demonstrates that the formation of supramolecular interactions between cyclodextrin and adamantane can be used to drive complex formation in the chemically challenging in vivo environment.

Conclusion: The in vivo distribution pattern of the cyclodextrin host could be guided by the pre-administration of the adamantane guest, thereby creating a direct link between the scout-scan (MAA-Ad) and delivery of therapy.

Surface Hydrophilicity of Poly(l-Lactide) Acid Polymer Film Changes the Human Adult Adipose Stem Cell Architecture

Current knowledge indicates that the molecular cross-talk between stem cells and biomaterials guides the stem cells’ fate within a tissue engineering system. In this work, we have explored the effects of the interaction between the poly(l-lactide) acid (PLLA) polymer film and human adult adipose stem cells (hASCs), focusing on the events correlating the materials’ surface characteristics and the cells’ plasma membrane. hASCs were seeded on films of pristine PLLA polymer and on a PLLA surface modified by the radiofrequency plasma method under oxygen flow (PLLA+O₂). Comparative experiments were performed using human bone-marrow mesenchymal stem cells (hBM-MSCs) and human umbilical matrix stem cells (hUCMSCs). After treatment with oxygen-plasma, the surface of PLLA films became hydrophilic, whereas the bulk properties were not affected. hASCs cultured on pristine PLLA polymer films acquired a spheroid conformation. On the contrary, hASCs seeded on PLLA+O₂ film surface maintained the fibroblast-like morphology typically observed on tissue culture polystyrene. This suggests that the surface hydrophilicity is involved in the acquisition of the spheroid conformation. Noteworthy, the oxygen treatment had no effects on hBM-MSC and hUCMSC cultures and both stem cells maintained the same shape observed on PLLA films. This different behavior suggests that the biomaterial-interaction is stem cell specific.