Synthetic control of living cells by intracellular polymerization

Tracking host-guest recognition in cells by a BODIPY·CB[7] complex

Interested in host·guest binding events in cellular environments, intracellular recognition between fluorescent BODIPY+ and cucurbit[7]uril was explored for lysosome tracking in living cancer cells. Sequential deaggregation from spontaneously dimerized BODIPY+ was unusually discovered upon complexation with CB[7].

Bacteria-Mediated Intracellular Radical Polymerizations

Intracellular radical polymerizations allow for the direct bioorthogonal synthesis of various synthetic polymers within living cells, thereby providing a pathway to polymer-modified cells or the fermentative production of polymers. Here, we show that Escherichia coli cells can initiate the polymerization of various acrylamide, acrylic, and methacrylic monomers through an atom transfer radical reaction triggered by the activity of naturally occurring biomolecules within the bacterial cells. Intracellular radical polymerizations were confirmed by nuclear magnetic resonance spectroscopy, gel permeation chromatography of polymers extracted from the cells, and fluorescence labeling of the polymer directly inside the cells. The effect of polymerization on cell behavior and the response of the cells to polymerization was investigated through fluorescence microscopy and flow cytometry techniques, as well as metabolic and membrane integrity assays. The polymer synthesis and resulting products are cell-compatible, as indicated by the high viability of the polymerized cells. In cellulo synthesis of synthetic polymers containing fluorescent dyes was also achieved. These results not only enhance our understanding of the untapped potential of bacterial cells as living catalysts for polymer production but also reveal intracellular polymerization based on atom transfer radical polymerization initiators as a bioorthogonal tool for cell engineering and synthetic biology.

Hypoxia-Initiated Supramolecular Free Radicals Induce Intracellular Polymerization for Precision Tumor Therapy

Despite the development of various controlled release systems for antitumor therapies, off-target side effects remain a persistent challenge. In situ therapeutic synthesis from biocompatible substances offers a safer and more precise alternative. This study presents a hypoxia-initiated supramolecular free radical system capable of inducing intracellular polymerization, thereby disrupting the cytoskeleton and organelles within 4T1 cells. The system utilizes a 2:1 supramolecular host-guest complex of cucurbit[7]uril (CB[7]) and perylene diimide derivative (PDI), termed PDI+2CB[7], which is selectively reduced by the tumor's hypoxic and reducing environment to generate delocalized free radical anions. CB[7] effectively stabilizes these anions, enabling the PDI+2CB[7] complex to initiate free radical polymerization with 2-hydroxyethyl methacrylate (HEMA) inside the 4T1 cells. The resulting in situ polymerization significantly disrupts tumor metabolism, leading to a strong antitumor response without systemic toxicity. This study demonstrates that stable, endogenous stimulus-induced supramolecular free radicals can trigger intracellular polymerization reactions, achieving a selective and effective antitumor therapy without conventional chemotherapeutic agents.

Living Cell-Mediated Self-Assembly: From Monomer Design and Morphology Regulation to Biomedical Applications

The self-assembly of molecules into highly ordered architectures is a ubiquitous and natural process, wherein molecules spontaneously organize into large structures to perform diverse functions. Drawing inspiration from the formation of natural nanostructures, cell-mediated self-assembly has been developed to create functional assemblies both inside and outside living cells. These techniques have been employed to regulate the cellular world by leveraging the dynamic intracellular and extracellular microenvironment. This review highlights the recent advances and future trends in living cell-mediated self-assembly, ranging from their cytocompatible monomer designs, synthetic strategies, and morphological control to functional applications. The assembly behaviors are also discussed based on the dimensionality of the self-assembled morphologies from zero to three dimensions. Finally, this review explores its promising potential for biomedical applications, clarifying the relationship between initial morphological regulation and the therapeutic effects of subsequent artificial assemblies. Through rationally designing molecular structures and precisely controlling assembly morphologies, living cell mediated self-assembly would provide an innovative platform for executing biological functions.

Light-Controlled Intracellular Synthesis of Poly(luciferin) Polymers Induces Cell Paraptosis

Accumulation of misfolded proteins challenges cellular proteostasis and is implicated in aging and chronic disorders. Cancer cells, moreover, face an elevated level of basal proteotoxic stress; hence, exacerbating endoplasmic reticulum (ER) stress has been shown to induce programmed cell death while enhancing anticancer immunogenicity. We hypothesize that hydrophobic abiotic macromolecules can trigger a similar stress response. Most polymers and nanoparticles, however, are sequestered in endo/lysosomes after endocytosis, which prevents their interaction with the proteostasis machinery. We adopted an in situ polymerization approach to synthesize polymers in cells with cell-permeable monomers. Specifically, we developed a biocompatible polycondensation between l-cysteine and 2-cyanobenzothiazole (CBT) with photochemical control to form insoluble poly(luciferin) aggregates. We identified that in situ polymerization activates the BiP-PERK-CHOP pathway of the unfolded protein response and that the unresolved ER stress initiates a form of regulated cell death consistent with paraptosis. In addition, the dying cells emit damage-associated molecular patterns (DAMPs), indicating an immunogenic cell death that could potentiate antitumor immunity. Our results show that in situ polymerization mimics misfolded protein aggregates to induce proteotoxic stress and cancer cell death, offering a novel therapeutic strategy to exploit cancer vulnerability.

Fabrication of cyborg bacterial cells as living cell-material hybrids using intracellular hydrogelation

The production of living therapeutics, cell-based delivery of drugs and gene-editing tools and the manufacturing of bio-commodities all share a common concept: they use either a synthetic or a living cell chassis to achieve their primary engineering or therapeutic goal. Live-cell chassis face limitations inherent to their auto-replicative nature and the complexity of the cellular context. This limitation highlights the need for a new chassis combining the engineering simplicity of synthetic materials and the functionalities of natural cells. Here, we describe a protocol to assemble a synthetic polymeric network inside bacterial cells, rendering them incapable of cell division and allowing them to resist environmental stressors such as high pH, hydrogen peroxide and cell-wall-targeting antibiotics that would otherwise kill unmodified bacteria. This cellular bioengineering protocol details how bacteria can be transformed into single-lifespan devices that are resistant to environmental stressors and possess programable functionality. We designate the modified bacteria as cyborg bacterial cells. This protocol expands the synthetic biology toolset, conferring precise control over living cells and creating a versatile cell chassis for biotechnology, biomedical engineering and living therapeutics. The protocol, including the preparation of gelation reagents and chassis strain, can be completed in 4 d. The implementation of the protocol requires expertise in microbiology techniques, hydrogel chemistry, fluorescence microscopy and flow cytometry. Further functionalization of the cyborg bacterial cells and adaptation of the protocol requires skills ranging from synthetic genetic circuit engineering to hydrogel polymerization chemistries.

Precise Regulations at the Subcellular Level through Intracellular Polymerization, Assembly, and Transformation

A living cell is an intricate machine that creates subregions to operate cell functions effectively. Subcellular dysfunction has been identified as a potential druggable target for successful drug design and therapy. The treatments based on intracellular polymerization, self-assembly, or transformation offer various advantages, including enhanced blood circulation of monomers, long-term drug delivery pharmacokinetics, low drug resistance, and the ability to target deep tissues and organelles. In this review, we discuss the latest developments of intracellular synthesis applied to precisely control cellular functions. First, we discuss the design and applications of endogenous and exogenous stimuli-triggered intracellular polymerization, self-assembly, and dynamic morphology transformation of biomolecules at the subcellular level. Second, we highlight the benefits of these strategies applied in cancer diagnosis and treatment and modulating cellular states or cell metabolism of living systems. Finally, we conclude the recent progress in this field, discuss future perspectives, analyze the challenges of the intracellular functional reactions for regulation, and find future opportunities.

Engineering Cyborg Pathogens through Intracellular Hydrogelation

Synthetic biology primarily focuses on two kinds of cell chassis: living cells and nonliving systems. Living cells are autoreplicating systems that have active metabolism. Nonliving systems, including artificial cells and nanoparticles, are nonreplicating systems typically lacking active metabolism. In recent work, Cyborg bacteria that are nonreplicating-but-metabolically active have been engineered through intracellular hydrogelation. Intracellular hydrogelation is conducted by infusing gel monomers and photoactivators into cells, followed by the activation of polymerization of the gel monomers inside the cells. However, the previous work investigated only Escherichia coli cells. Extending the Cyborg-Cell method to pathogenic bacteria could enable the exploitation of their pathogenic properties in biomedical applications. Here, we focus on different strains of Pseudomonas aeruginosa, Staphylococcus aureus, and Klebsiella pneumoniae. To synthesize the Cyborg pathogens, we first reveal the impact of different hydrogel concentrations on the metabolism, replication, and intracellular gelation of Cyborg pathogens. Next, we demonstrate that the Cyborg pathogens are taken up by macrophages in a similar magnitude as wild-type pathogens through confocal microscopy and real-time PCR. Finally, we show that the macrophage that takes up the Cyborg pathogen exhibits a similar phenotypic response to the wild-type pathogen. Our work generalizes the intracellular hydrogelation approach from lab strains of E. coli to bacterial pathogens. The new Cyborg pathogens could be applied in biomedical applications ranging from drug delivery to immunotherapy.

Artificial Polymerizations in Living Organisms for Biomedical Applications

Within living organisms, numerous nanomachines are constantly involved in complex polymerization processes, generating a diverse array of biomacromolecules for maintaining biological activities. Transporting artificial polymerizations from lab settings into biological contexts has expanded opportunities for understanding and managing biological events, creating novel cellular compartments, and introducing new functionalities. This review summarizes the recent advancements in artificial polymerizations, including those responding to external stimuli, internal environmental factors, and those that polymerize spontaneously. More importantly, the cutting-edge biomedical application scenarios of artificial polymerization, notably in safeguarding cells, modulating biological events, improving diagnostic performance, and facilitating therapeutic efficacy are highlighted. Finally, this review outlines the key challenges and technological obstacles that remain for polymerizations in biological organisms, as well as offers insights into potential directions for advancing their practical applications and clinical trials.

Architectural engineering of Cyborg Bacteria with intracellular hydrogel

Synthetic biology primarily uses genetic engineering to control living cells. In contrast, recent work has ushered in the architectural engineering of living cells through intracellular materials. Specifically, Cyborg Bacteria are created by incorporating synthetic PEG-based hydrogel inside cells. Cyborg Bacteria do not replicate but maintain essential cellular functions, including metabolism and protein synthesis. Thus far, Cyborg Bacteria have been engineered using one primary composition of intracellular hydrogel components. Here, we demonstrate the versatility of controlling the physical and biochemical aspects of Cyborg Bacteria using different structures of hydrogels. The intracellular cell-gel architecture is modulated using a different photoinitiator, PEG-diacrylate (PEG-DA) of different molecular weights, 4arm PEG-DA, and dsDNA-PEG. We show that the molecular weight of the PEG-DA affects the generation and metabolism of Cyborg Bacteria. In addition, we show that the hybrid dsDNA-PEG intracellular hydrogel controls protein expression levels of the Cyborg Bacteria through post-transcriptional regulation and polymerase sequestration. Our work creates a new frontier of modulating intracellular gel components to control Cyborg Bacteria function and architecture.

Intracellular Gelation-Mediated Living Bacteria for Advanced Biotherapeutics in Mouse Models

Despite its significant potential in various disease treatments and diagnostics, microbiotherapy is consistently plagued by multiple limitations ranging from manufacturing challenges to in vivo functionality. Inspired by the strategy involving nonproliferating yet metabolically active microorganisms, we report an intracellular gelation approach that can generate a synthetic polymer network within bacterial cells to solve these challenges. Specifically, poly(ethylene glycol dimethacrylate) (PEGDA, 700 Da) monomers are introduced into the bacterial cytosol through a single cycle of freeze-thawing followed by the initiation of intracellular free radical polymerization by UV light to create a macromolecular PEGDA gel within the bacterial cytosol. The molecular crowding resulting from intracytoplasmic gelation prohibits bacterial division and confers robust resistance to simulated gastrointestinal fluids and bile acids while retaining the ability to secrete functional proteins. Biocompatibility assessments demonstrate that the nondividing gelatinized bacteria are effective in alleviating systemic inflammation triggered by intravenous Escherichia coli injection. Furthermore, the therapeutic efficacy of gelatinized Lactobacillus rhamnosus in colitis mice provides additional support for this approach. Collectively, intracellular gelation indicates a universal strategy to manufacture next-generation live biotherapeutics for advanced microbiotherapy.

Reversible Intracellular Gelation of MCF10A Cells Enables Programmable Control Over 3D Spheroid Growth

In nature, some organisms survive extreme environments by inducing a biostatic state wherein cellular contents are effectively vitrified. Recently, a synthetic biostatic state in mammalian cells is achieved via intracellular network formation using bio-orthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) reactions between functionalized poly(ethylene glycol) (PEG) macromers. In this work, the effects of intracellular network formation on a 3D epithelial MCF10A spheroid model are explored. Macromer-transfected cells are encapsulated in Matrigel, and spheroid area is reduced by ≈50% compared to controls. The intracellular hydrogel network increases the quiescent cell population, as indicated by increased p21 expression. Additionally, bioenergetics (ATP/ADP ratio) and functional metabolic rates are reduced. To enable reversibility of the biostasis effect, a photosensitive nitrobenzyl-containing macromer is incorporated into the PEG network, allowing for light-induced degradation. Following light exposure, cell state, and proliferation return to control levels, while SPAAC-treated spheroids without light exposure (i.e., containing intact intracellular networks) remain smaller and less proliferative through this same period. These results demonstrate that photodegradable intracellular hydrogels can induce a reversible slow-growing state in 3D spheroid culture.

Rapid plasma membrane isolation via intracellular polymerization-mediated biomolecular confinement

Plasma membrane isolation is a foundational process in membrane proteomic research, cellular vesicle studies, and biomimetic nanocarrier development, yet separation processes for this outermost layer are cumbersome and susceptible to impurities and low yield. Herein, we demonstrate that cellular cytosol can be chemically polymerized for decoupling and isolation of plasma membrane within minutes. A rapid, non-disruptive in situ polymerization technique is developed with cell membrane-permeable polyethyleneglycol-diacrylate (PEG-DA) and a blue-light-sensitive photoinitiator, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). The photopolymerization chemistry allows for precise control of intracellular polymerization and tunable confinement of cytosolic molecules. Upon cytosol solidification, plasma membrane proteins and vesicles are rapidly derived and purified as nucleic acids and intracellular proteins as small as 15 kDa are stably entrapped for removal. The polymerization chemistry and membrane derivation technique are broadly applicable to primary and fragile cell types, enabling facile membrane vesicle extraction from shorted-lived neutrophils and human primary CD8 T cells. The study demonstrates tunable intracellular polymerization via optimized live cell chemistry, offers a robust membrane isolation methodology with broad biomedical utility, and reveals insights on molecular crowding and confinement in polymerized cells. STATEMENT OF SIGNIFICANCE: Isolating the minute fraction of plasma membrane proteins and vesicles requires extended density gradient ultracentrifugation processes, which are susceptible to low yield and impurities. The present work demonstrates that the membrane isolation process can be vastly accelerated via a rapid, non-disruptive intracellular polymerization approach that decouples cellular cytosols from the plasma membrane. Following intracellular polymerization, high-yield plasma membrane proteins and vesicles can be derived from lysis buffer and sonication treatment, respectively. And the intracellular content entrapped within the polymerized hydrogel is readily removed within minutes. The technique has broad utility in membrane proteomic research, cellular vesicle studies, and biomimetic materials development, and the work offers insights on intracellular hydrogel-mediated molecular confinement.

Macrophage-Based Microrobots for Anticancer Therapy: Recent Progress and Future Perspectives

Macrophages, which are part of the mononuclear phagocytic system, possess sensory receptors that enable them to target cancer cells. In addition, they are able to engulf large amounts of particles through phagocytosis, suggesting a potential "Trojan horse" drug delivery approach to tumors by facilitating the engulfment of drug-hidden particles by macrophages. Recent research has focused on the development of macrophage-based microrobots for anticancer therapy, showing promising results and potential for clinical applications. In this review, we summarize the recent development of macrophage-based microrobot research for anticancer therapy. First, we discuss the types of macrophage cells used in the development of these microrobots, the common payloads they carry, and various targeting strategies utilized to guide the microrobots to cancer sites, such as biological, chemical, acoustic, and magnetic actuations. Subsequently, we analyze the applications of these microrobots in different cancer treatment modalities, including photothermal therapy, chemotherapy, immunotherapy, and various synergistic combination therapies. Finally, we present future outlooks for the development of macrophage-based microrobots.