Self-Propelled and Near-Infrared-Phototaxic Photosynthetic Bacteria as Photothermal Agents for Hypoxia-Targeted Cancer Therapy

Path to bacteriotherapy: From bacterial engineering to therapeutic perspectives

The major reason for the failure of conventional therapies is the heterogeneity and complexity of tumor microenvironments (TMEs). Many malignant tumors reprogram their surface antigens to evade the immune surveillance, leading to reduced antigen-presenting cells and hindered T-cell activation. Bacteria-mediated cancer immunotherapy has been extensively investigated in recent years. Scientists have ingeniously modified bacteria using synthetic biology and nanotechnology to enhance their biosafety with high tumor specificity, resulting in robust anticancer immune responses. To enhance the antitumor efficacy, therapeutic proteins, cytokines, nanoparticles, and chemotherapeutic drugs have been efficiently delivered using engineered bacteria. This review provides a comprehensive understanding of oncolytic bacterial therapies, covering bacterial design and the intricate interactions within TMEs. Additionally, it offers an in-depth comparison of the current techniques used for bacterial modification, both internally and externally, to maximize their therapeutic effectiveness. Finally, we outlined the challenges and opportunities ahead in the clinical application of oncolytic bacterial therapies.

Microbe-material hybrids for therapeutic applications

As natural living substances, microorganisms have emerged as useful resources in medicine for creating microbe-material hybrids ranging from nano to macro dimensions. The engineering of microbe-involved nanomedicine capitalizes on the distinctive physiological attributes of microbes, particularly their intrinsic "living" properties such as hypoxia tendency and oxygen production capabilities. Exploiting these remarkable characteristics in combination with other functional materials or molecules enables synergistic enhancements that hold tremendous promise for improved drug delivery, site-specific therapy, and enhanced monitoring of treatment outcomes, presenting substantial opportunities for amplifying the efficacy of disease treatments. This comprehensive review outlines the microorganisms and microbial derivatives used in biomedicine and their specific advantages for therapeutic application. In addition, we delineate the fundamental strategies and mechanisms employed for constructing microbe-material hybrids. The diverse biomedical applications of the constructed microbe-material hybrids, encompassing bioimaging, anti-tumor, anti-bacteria, anti-inflammation and other diseases therapy are exhaustively illustrated. We also discuss the current challenges and prospects associated with the clinical translation of microbe-material hybrid platforms. Therefore, the unique versatility and potential exhibited by microbe-material hybrids position them as promising candidates for the development of next-generation nanomedicine and biomaterials with unique theranostic properties and functionalities.

Intratumoral Microbiota as a Target for Advanced Cancer Therapeutics

In recent years, advancements in microbial sequencing technology have sparked an increasing interest in the bacteria residing within solid tumors and its distribution and functions in various tumors. Intratumoral bacteria critically modulate tumor oncogenesis and development through DNA damage induction, chronic inflammation, epigenetic alterations, and metabolic and immune regulation, while also influencing cancer treatment efficacy by affecting drug metabolism. In response to these discoveries, a variety of anti-cancer therapies targeting these microorganisms have emerged. These approaches encompass oncolytic therapy utilizing tumor-associated bacteria, the design of biomaterials based on intratumoral bacteria, the use of intratumoral bacterial components for drug delivery systems, and comprehensive strategies aimed at the eradication of tumor-promoting bacteria. Herein, this review article summarizes the distribution patterns of bacteria in different solid tumors, examines their impact on tumors, and evaluates current therapeutic strategies centered on tumor-associated bacteria. Furthermore, the challenges and prospects for developing drugs that target these bacterial communities are also explored, promising new directions for cancer treatment.

The Rational Engineered Bacteria Based Biohybrid Living System for Tumor Therapy

Living therapy based on bacterial cells has gained increasing attention for their applications in tumor treatments. Bacterial cells can naturally target to tumor sites and active the innate immunological responses. The intrinsic advantages of bacteria attribute to the development of biohybrid living carriers for targeting delivery toward hypoxic environments. The rationally engineered bacterial cells integrate various functions to enhance the tumor therapy and reduce toxic side effects. In this review, the antitumor effects of bacteria and their application are discussed as living therapeutic agents across multiple antitumor platforms. The various kinds of bacteria used for cancer therapy are first introduced and demonstrated the mechanism of antitumor effects as well as the immunological effects. Additionally, this study focused on the genetically modified bacteria for the production of antitumor agents as living delivery system to treat cancer. The combination of living bacterial cells with functional nanomaterials is then discussed in the cancer treatments. In brief, the rational design of living therapy based on bacterial cells highlighted a rapid development in tumor therapy and pointed out the potentials in clinical applications.

Photosynthetic Bacteria-Hitchhiking 2D iMXene-mRNA Vaccine to Enable Photo-Immunogene Cancer Therapy

Therapeutic mRNA vaccines have become powerful therapeutic tools for severe diseases, including infectious diseases and malignant neoplasms. mRNA vaccines encoding tumor-associated antigens provide unprecedented hope for many immunotherapies that have hit the bottleneck. However, the application of mRNA vaccines is limited because of biological instability, innate immunogenicity, and ineffective delivery in vivo. This study aims to construct a novel mRNA vaccine delivery nanosystem to successfully co-deliver a tumor-associated antigen (TAA) encoded by the Wilms' tumor 1 (WT1) mRNA. In this system, named PSB@Nb1.33C/mRNA, photosynthetic bacteria (PSB) efficiently delivers the iMXene-WT1 mRNA to the core tumor region using photo-driven and hypoxia-driven properties. The excellent photothermal therapeutic (PTT) properties of PSB and 2D iMxene (Nb1.33C) trigger tumor immunogenic cell death, which boosts the release of the WT1 mRNA. The released WT1 mRNA is translated, presenting the TAA and amplifying immune effect in vivo. The designed therapeutic strategy demonstrates an excellent ability to inhibit distant tumors and counteract postsurgical lung metastasis. Thus, this study provides an innovative and effective paradigm for tumor immunotherapy, i.e., photo-immunogene cancer therapy, and establishes an efficient delivery platform for mRNA vaccines, thereby opening a new path for the wide application of mRNA vaccines.

High-Lactate-Metabolizing Photosynthetic Bacteria Reprogram Tumor Immune Microenvironment

The elevated levels of lactate in tumor tissue play a pivotal role in fostering an immunosuppressive microenvironment. Therefore, efficiently reducing lactate levels to reprogram tumor immune microenvironment (TIM) is considered a crucial step for boosted immunotherapy. Here, a high-lactate-metabolizing photosynthetic bacteria (LAB-1) is selectively screened for TIM reprogramming, which then improves the efficacy of tumor immunotherapy. The culture medium for LAB-1 screening is initially developed through an orthogonal experiment, simulating the tumor microenvironment (TME) and utilizing lactate as the sole organic carbon source. As demonstrated in a murine 4T1 model, LAB-1 colonizes the TME selectively, resulting in a significant reduction in lactate levels and a subsequent increase in pH values within the tumor tissue. Furthermore, single-cell RNA sequencing analysis reveals that LAB-1 effectively reprograms the TIM, thereby enhancing the effectiveness of antitumor immune therapy. This approach of utilizing lactate-consuming bacteria represents a potent tool for augmenting tumor immunotherapy efficiency.

Engineered Microorganisms for Advancing Tumor Therapy

Engineered microorganisms have attracted significant interest as a unique therapeutic platform in tumor treatment. Compared with conventional cancer treatment strategies, engineering microorganism-based systems provide various distinct advantages, such as the intrinsic capability in targeting tumors, their inherent immunogenicity, in situ production of antitumor agents, and multiple synergistic functions to fight against tumors. Herein, the design, preparation, and application of the engineered microorganisms for advanced tumor therapy are thoroughly reviewed. This review presents a comprehensive survey of innovative tumor therapeutic strategies based on a series of representative engineered microorganisms, including bacteria, viruses, microalgae, and fungi. Specifically, it offers extensive analyses of the design principles, engineering strategies, and tumor therapeutic mechanisms, as well as the advantages and limitations of different engineered microorganism-based systems. Finally, the current challenges and future research prospects in this field, which can inspire new ideas for the design of creative tumor therapy paradigms utilizing engineered microorganisms and facilitate their clinical applications, are discussed.

Tailoring therapeutics via a systematic beneficial elements comparison between photosynthetic bacteria-derived OMVs and extruded nanovesicles

Photosynthetic bacteria (PSB) has shown significant potential as a drug or drug delivery system owing to their photothermal capabilities and antioxidant properties. Nevertheless, the actualization of their potential is impeded by inherent constraints, including their considerable size, heightened immunogenicity and compromised biosafety. Conquering these obstacles and pursuing more effective solutions remains a top priority. Similar to extracellular vesicles, bacterial outer membrane vesicles (OMVs) have demonstrated a great potential in biomedical applications. OMVs from PSB encapsulate a rich array of bioactive constituents, including proteins, nucleic acids, and lipids inherited from their parent cells. Consequently, they emerge as a promising and practical alternative. Unfortunately, OMVs have suffered from low yield and inconsistent particle sizes. In response, bacteria-derived nanovesicles (BNVs), created through controlled extrusion, adeptly overcome the challenges associated with OMVs. However, the differences, both in composition and subsequent biological effects, between OMVs and BNVs remain enigmatic. In a groundbreaking endeavor, our study meticulously cultivates PSB-derived OMVs and BNVs, dissecting their nuances. Despite minimal differences in morphology and size between PSB-derived OMVs and BNVs, the latter contains a higher concentration of active ingredients and metabolites. Particularly noteworthy is the elevated levels of lysophosphatidylcholine (LPC) found in BNVs, known for its ability to enhance cell proliferation and initiate downstream signaling pathways that promote angiogenesis and epithelialization. Importantly, our results indicate that BNVs can accelerate wound closure more effectively by orchestrating a harmonious balance of cell proliferation and migration within NIH-3T3 cells, while also activating the EGFR/AKT/PI3K pathway. In contrast, OMVs have a pronounced aptitude in anti-cancer efforts, driving macrophages toward the M1 phenotype and promoting the release of inflammatory cytokines. Thus, our findings not only provide a promising methodological framework but also establish a definitive criterion for discerning the optimal application of OMVs and BNVs in addressing a wide range of medical conditions.

Advances in Nanomaterials for Immunotherapeutic Improvement of Cancer Chemotherapy

Immuno-stimulative effect of chemotherapy (ISECT) is recognized as a potential alternative to conventional immunotherapies, however, the clinical application is constrained by its inefficiency. Metronomic chemotherapy, though designed to overcome these limitations, offers inconsistent results, with effectiveness varying based on cancer types, stages, and patient-specific factors. In parallel, a wealth of preclinical nanomaterials holds considerable promise for ISECT improvement by modulating the cancer-immunity cycle. In the area of biomedical nanomaterials, current literature reviews mainly concentrate on a specific category of nanomaterials and nanotechnological perspectives, while two essential issues are still lacking, i.e., a comprehensive analysis addressing the causes for ISECT inefficiency and a thorough summary elaborating the nanomaterials for ISECT improvement. This review thus aims to fill these gaps and catalyze further development in this field. For the first time, this review comprehensively discusses the causes of ISECT inefficiency. It then meticulously categorizes six types of nanomaterials for improving ISECT. Subsequently, practical strategies are further proposed for addressing inefficient ISECT, along with a detailed discussion on exemplary nanomedicines. Finally, this review provides insights into the challenges and perspectives for improving chemo-immunotherapy by innovations in nanomaterials.

Synergistic Brilliance: Engineered Bacteria and Nanomedicine Unite in Cancer Therapy

Engineered bacteria are widely used in cancer treatment because live facultative/obligate anaerobes can selectively proliferate at tumor sites and reach hypoxic regions, thereby causing nutritional competition, enhancing immune responses, and producing anticancer microbial agents in situ to suppress tumor growth. Despite the unique advantages of bacteria-based cancer biotherapy, the insufficient treatment efficiency limits its application in the complete ablation of malignant tumors. The combination of nanomedicine and engineered bacteria has attracted increasing attention owing to their striking synergistic effects in cancer treatment. Engineered bacteria that function as natural vehicles can effectively deliver nanomedicines to tumor sites. Moreover, bacteria provide an opportunity to enhance nanomedicines by modulating the TME and producing substrates to support nanomedicine-mediated anticancer reactions. Nanomedicine exhibits excellent optical, magnetic, acoustic, and catalytic properties, and plays an important role in promoting bacteria-mediated biotherapies. The synergistic anticancer effects of engineered bacteria and nanomedicines in cancer therapy are comprehensively summarized in this review. Attention is paid not only to the fabrication of nanobiohybrid composites, but also to the interpromotion mechanism between engineered bacteria and nanomedicine in cancer therapy. Additionally, recent advances in engineered bacteria-synergized multimodal cancer therapies are highlighted.

The emerging tumor microbe microenvironment: From delineation to multidisciplinary approach-based interventions

Intratumoral microbiota has become research hotspots, and emerges as a non-negligent new component of tumor microenvironments (TME), due to its powerful influence on tumor initiation, metastasis, immunosurveillance and prognosis despite in low-biomass. The accumulations of microbes, and their related components and metabolites within tumor tissues, endow TME with additional pluralistic features which are distinct from the conventional one. Therefore, it's definitely necessary to comprehensively delineate the sophisticated landscapes of tumor microbe microenvironment, as well as their functions and related underlying mechanisms. Herein, in this review, we focused on the fields of tumor microbe microenvironment, including the heterogeneity of intratumor microbiota in different types of tumors, the controversial roles of intratumoral microbiota, the basic features of tumor microbe microenvironment (i.e., pathogen-associated molecular patterns (PAMPs), typical microbial metabolites, autophagy, inflammation, multi-faceted immunomodulation and chemoresistance), as well as the multidisciplinary approach-based intervention of tumor microbiome for cancer therapy by applying wild-type or engineered live microbes, microbiota metabolites, antibiotics, synthetic biology and rationally designed biomaterials. We hope our work will provide valuable insight to deeply understand the interplay of cancer-immune-microbial, and facilitate the development of microbes-based tumor-specific treatments.

pH-Responsive Amphiphilic Triblock Fluoropolymers as Assemble Oxygen Nanoshuttles for Enhancing PDT against Hypoxic Tumor

Photodynamic therapy (PDT) is a cancer treatment strategy that utilizes photosensitizers to convert oxygen within tumors into reactive singlet oxygen (1O2) to lyse tumor cells. Nevertheless, pre-existing tumor hypoxia and oxygen consumption during PDT can lead to an insufficient oxygen supply, potentially reducing the photodynamic efficacy. In response to this issue, we have devised a pH-responsive amphiphilic triblock fluorinated polymer (PDP) using copper-mediated RDRP. This polymer, composed of poly(ethylene glycol) methyl ether acrylate, 2-(diethylamino)ethyl methacrylate, and (perfluorooctyl)ethyl acrylate, self-assembles in an aqueous environment. Oxygen, chlorine e6 (Ce6), and doxorubicin (DOX) can be codelivered efficiently by PDP. The incorporation of perfluorocarbon into the formulation enhances the oxygen-carrying capacity of PDP, consequently extending the lifetime of 1O2. This increased lifetime, in turn, amplifies the PDT effect and escalates the cellular cytotoxicity. Compared with PDT alone, PDP@Ce6-DOX-O2 NPs demonstrated significant inhibition of tumor growth. This study proposes a novel strategy for enhancing the efficacy of PDT.

Redirecting Antigens by Engineered Photosynthetic Bacteria and Derived Outer Membrane Vesicles for Enhanced Cancer Immunotherapy

Significant strides have been made in the development of cancer vaccines to combat malignant tumors. However, the natural immunosuppressive environment within tumors, known as the tumor microenvironment (TME), hampers the uptake and presentation of antigens by antigen-presenting cells (APCs) within the tumor itself. This limitation results in inadequate activation of immune responses against cancer. In contrast, immune cells in peritumoral tissue maintain their normal functions. In this context, we present an interesting approach to enhance cancer immunotherapy by utilizing engineered photosynthetic bacteria (PSB) and their outer membrane vesicles (OMVPSB) to capture and transport antigens to the outer regions of the tumor. We modified PSB with maleimide (PSB-MAL), which, when exposed to near-infrared (NIR) laser-mediated photothermal therapy (PTT), induced extensive cancer cell death and the release of tumor antigens. Subsequently, the NIR-phototactic PSB-MAL transported these tumor antigens to the peripheral regions of the tumor under NIR laser exposure. Even more intriguingly, PSB-MAL-derived OMVPSB-MAL effectively captured and delivered antigens to tumor-draining lymph nodes (TDLNs). This facilitated enhanced antigen presentation by mature and fully functional APCs in the TDLNs. This intricate communication network between PSB-MAL, the OMVPSB-MAL, and APCs promoted the efficient presentation of tumor antigens in the tumor periphery and TDLNs. Consequently, there was a notable increase in the infiltration of cytotoxic T lymphocytes (CTLs) into the tumor, triggering potent antitumor immune responses in both melanoma and breast cancer models. This cascade of events resulted in enhanced suppression of tumor metastasis and recurrence, underscoring the robust efficacy of our approach. Our interesting study, harnessing the potential of bacteria and OMVs to redirect tumor antigens for enhanced cancer immunotherapy, provides a promising path toward the development of personalized cancer vaccination strategies.

Deep Tumor Penetration of CRISPR-Cas System for Photothermal-Sensitized Immunotherapy via Probiotics

Since central cells are more malignant and aggressive in solid tumors, improving penetration of therapeutic agents and activating immunity in tumor centers exhibit great potential in cancer therapies. Here, polydopamine-coated Escherichia coli Nissle 1917 (EcN) bearing CRISPR-Cas9 plasmid-loaded liposomes (Lipo-P) are applied for enhanced immunotherapy in deep tumors through activation of innate and adaptive immunity simultaneously. After accumulation in the tumor center through hypoxia targeting, Lipo-P could be detached under the reduction of reactive oxygen species (ROS)-responsive linkers, lowering the thermal resistance of cancer cells via Hsp90α depletion. Owing to that, heating induced by polydopamine upon near-infrared irradiation could achieve effective tumor ablation. Furthermore, mild photothermal therapy induces immunogenic cell death, as bacterial infections in tumor tissues trigger innate immunity. This bacteria-assisted approach provides a promising photothermal-sensitized immunotherapy in deep tumors.

Revolutionizing cancer treatment: The power of cell-based drug delivery systems

Intravenous administration of drugs is a widely used cancer therapy approach. However, the efficacy of these drugs is often hindered by various biological barriers, including circulation, accumulation, and penetration, resulting in poor delivery to solid tumors. Recently, cell-based drug delivery platforms have emerged as promising solutions to overcome these limitations. These platforms offer several advantages, including prolonged circulation time, active targeting, controlled release, and excellent biocompatibility. Cell-based delivery systems encompass cell membrane coating, intracellular loading, and extracellular backpacking. These innovative platforms hold the potential to revolutionize cancer diagnosis, monitoring, and treatment, presenting a plethora of opportunities for the advancement and integration of pharmaceuticals, medicine, and materials science. Nevertheless, several technological, ethical, and financial barriers must be addressed to facilitate the translation of these platforms into clinical practice. In this review, we explore the emerging strategies to overcome these challenges, focusing specifically on the functions and advantages of cell-mediated drug delivery in cancer treatment.

Bacteria-based immunotherapy for cancer: a systematic review of preclinical studies

Immunotherapy has been emerging as a powerful strategy for cancer management. Recently, accumulating evidence has demonstrated that bacteria-based immunotherapy including naive bacteria, bacterial components, and bacterial derivatives, can modulate immune response via various cellular and molecular pathways. The key mechanisms of bacterial antitumor immunity include inducing immune cells to kill tumor cells directly or reverse the immunosuppressive microenvironment. Currently, bacterial antigens synthesized as vaccine candidates by bioengineering technology are novel antitumor immunotherapy. Especially the combination therapy of bacterial vaccine with conventional therapies may further achieve enhanced therapeutic benefits against cancers. However, the clinical translation of bacteria-based immunotherapy is limited for biosafety concerns and non-uniform production standards. In this review, we aim to summarize immunotherapy strategies based on advanced bacterial therapeutics and discuss their potential for cancer management, we will also propose approaches for optimizing bacteria-based immunotherapy for facilitating clinical translation.

Modulation of tumour hypoxia by ultrasound-responsive microbubbles to enhance the sono-photodynamic therapy effect on triple-negative breast cancer

Sono-photodynamic therapy (SPDT) is an oxidative stress-dependent antitumour treatment modality. Due to the hypoxic tumour microenvironment, the antitumour effect of SPDT is limited. In this study, we developed lipid vesicles to transport a photosensitizer (chlorin e6, Ce6) and oxygen into tumours to promote SPDT efficiency on triple-negative breast cancer in vitro and in vivo. The results showed that compared with the same concentration of free Ce6, Lipo-Ce6 produced a higher singlet oxygen level under light irradiation. Cellular Lipo-Ce6 accumulation was 4-fold higher than that of free Ce6. The cytotoxicity on 4T1 cells caused by Lipo-Ce6-SPDT was significantly stronger than that caused by free Ce6-SPDT, and oxygen microbubbles (O₂MB) further enhanced the cytotoxicity of Lipo-Ce6-SPDT under hypoxic conditions. Cellular ROS production in the Lipo-Ce6-SPDT+O₂MB group was approximately 2.5-fold higher than that in the Lipo-Ce6-SPDT+C₃F₈MB group. Furthermore, O₂MB rapidly relieved 4T1 subcutaneous xenograft hypoxia conditions under ultrasound exposure and significantly improved the antitumour activity of SPDT in vivo. These results indicate that the combination of O₂MB and a high-activity liposome photosensitizer can significantly enhance the antitumour efficiency of SPDT for hypoxic tumours.

Biogenic Copper Selenide Nanoparticles for Near-Infrared Photothermal Therapy Application

Near-infrared (NIR) photothermal therapy (PTT) is attractive for cancer treatment but is currently restricted by limited availability and insufficient NIR-II photoactivity of photothermal agents, for which artificial nanomaterials are usually used. Here, we report the first use of biogenic nanomaterials for PTT application. A fine-controlled extracellular biosynthesis of copper selenide nanoparticles (bio-Cu_2-xSe) by Shewanella oneidensis MR-1 was realized. The resulting bio-Cu_2-xSe, with fine sizes (∼35.5 nm) and high product purity, exhibited 76.9% photothermal conversion efficiency under 1064 nm laser irradiation, outperforming almost all the existing counterparts. The protein capping also imparted good biocompatibility to bio-Cu_2-xSe to favor a safe PTT application. The in vivo PTT with injected bio-Cu_2-xSe in mice (without extraction nor further modification) showed 87% tumor ablation without impairing the normal organisms. Our work not only opens a green route to synthesize the NIR-II photothermal nanomaterial but may also lay a basis for the development of bacteria-nanomaterial hybrid therapy technologies.

Probiotic Escherichia coli Nissle 1917 propelled micro-robot with pH sensitivity for hypoxia targeted intestinal tumor therapy

Poor drug penetration in hypoxia area of solid tumor is a big challenge for intestinal tumor therapy and thus it is crucial to develop an effective strategy to overcome this challenge. Compared with other bacteria used for construction of hypoxia targeted bacteria micro-robot, the Escherichia coli Nissle 1917 (EcN) bacteria are nonpathogenic Gram-negative probiotic and can especially target and identify the signal molecules in the hypoxic region of tumor, and thus, in this study, we choose EcN to construct a bacteria propelled micro-robot for targeting intestinal tumor therapy. Firstly, the MSNs@DOX with average diameter of 200 nm were synthesized and conjugated with EcN bacteria using EDC/NHS chemical crosslinking method to construct a EcN propelled micro-robot. The motility of micro-robot was then evaluated and the motion velocity of EcN-pMSNs@DOX was 3.78 µm/s. Compared with pMSNs@DOX without EcN driven, EcN bacteria propelled micro-robot transported much more pMSNs@DOX into the inner of HCT-116 3D multicellular tumor spheroids. However, the EcN bacteria are non-intracelluar bacteria which lead to the micro-robot can not directly enter into tumor cells. Therefore, we utilized acid-labile linkers of cis-aconitic amido bone to link EcN with MSNs@DOX nanoparticles to achieve the pH sensitive separation of EcN with MSNs@DOX from the micro-robot. At 4 h of incubation, the isolated MSNs@DOX began to enter into the tumor cells through CLSM observation. In vitro live/dead staining results show that EcN-pMSNs@DOX induced much more cell death than pMSNs@DOX at 24 and 48 h of incubation with HCT-116 tumor cells in acid culture media (pH 5.3). For the validation of the therapeutic efficacy of the micro-robot for intestinal tumor, we established the HCT-116 subcutaneous transplantation tumor model. After 28 days of treatment, EcN-pMSNs@DOX dramatically inhibit tumor growth with tumor volume was around 689 mm³, induce much more tumor tissues necrosis and apoptosis. Finally, the toxicity of this micro-robot was investigated by pathological analysis the liver and heart tissues. We expect that the pH sensitive EcN propelled micro-robot here we constructed may be a safe and feasible strategy for intestinal tumor therapy.

Bacteria-based multiplex system eradicates recurrent infections with drug-resistant bacteria via photothermal killing and protective immunity elicitation

BACKGROUND

The high mortality associated with drug-resistant bacterial infections is an intractable clinical problem resulting from the low susceptibility of these bacteria to antibiotics and the high incidence of recurrent infections.

METHODS

Herein, a photosynthetic bacteria-based multiplex system (Rp@Al) composed of natural Rhodopseudomonas palustris (Rp) and Food and Drug Administration-approved aluminum (Al) adjuvant, was developed to combat drug-resistant bacterial infections and prevent their recurrence. We examined its photothermal performance and in vitro and in vivo antibacterial ability; revealed its protective immunomodulatory effect; verified its preventative effect on recurrent infections; and demonstrated the system's safety.

RESULTS

Rp@Al exhibits excellent photothermal properties with an effective elimination of methicillin-resistant Staphylococcus aureus (MRSA). In addition, Rp@Al enhances dendritic cell activation and further triggers a T helper 1 (T_H1)/T_H2 immune response, resulting in pathogen-specific immunological memory against recurrent MRSA infection. Upon second infection, Rp@Al-treated mice show significantly lower bacterial burden, faster abscess recovery, and higher survival under near-lethal infection doses than control mice.

CONCLUSIONS

This innovative multiplex system, with superior photothermal and immunomodulatory effects, presents great potential for the treatment and prevention of drug-resistant bacterial infections.

Bacterial-Mediated Tumor Therapy: Old Treatment in a New Context

Targeted therapy and immunotherapy have brought hopes for precision cancer treatment. However, complex physiological barriers and tumor immunosuppression result in poor efficacy, side effects, and resistance to antitumor therapies. Bacteria-mediated antitumor therapy provides new options to address these challenges. Thanks to their special characteristics, bacteria have excellent ability to destroy tumor cells from the inside and induce innate and adaptive antitumor immune responses. Furthermore, bacterial components, including bacterial vesicles, spores, toxins, metabolites, and other active substances, similarly inherit their unique targeting properties and antitumor capabilities. Bacteria and their accessory products can even be reprogrammed to produce and deliver antitumor agents according to clinical needs. This review first discusses the role of different bacteria in the development of tumorigenesis and the latest advances in bacteria-based delivery platforms and the existing obstacles for application. Moreover, the prospect and challenges of clinical transformation of engineered bacteria are also summarized.

Integrating Bacteria with a Ternary Combination of Photosensitizers for Monochromatic Irradiation-Mediated Photoacoustic Imaging-Guided Synergistic Photothermal Therapy

Photosensitizer-based therapy often suffers from unitary and easily attenuated photosensitive effects, limited tumor penetration and retention, and requirement of multiple irradiation for combination therapy, which largely restrict its application. Here, bacteria are integrated with a monochromatic irradiation-mediated ternary combination of photosensitizers for photoacoustic imaging-guided synergistic photothermal therapy. Bacteria that are bioengineered to express natural melanin are decorated with dual synthetic photosensitizers by nanodeposition with indocyanine green and polydopamine under a cytocompatible condition. The combined photosensitizers, which share an adequate excitation at 808 nm, endow integrated bacteria with a stable triple photoacoustic and photothermal effect under a monochromatic irradiation. Due to their living characteristics, these bacteria preferentially colonize hypoxic tumor tissue with homogeneous distribution and durable retention and generate uniform imaging signals and a sufficient heating of tumor upon laser irradiation. Supported by significantly inhibited tumor growth and extended survival of animals in different tumor-bearing murine models, our work proposes the development of bacteria-based innovative photosensitizers for imaging-guided therapy.

Living Gut Bacteria Functionalized with Gold Nanoclusters and Drug for Facile Cancer Theranostics

Bacbots are potent self-propelling vehicles for targeted therapy that can be guided by chemical and biochemical stimuli of the host. In addition, they can be guided externally by the use of magnetic field or other physical forces. The challenge is to incorporate drugs and diagnostic tools in living bacteria with retention of theranostic activity until reaching the targets and easy clearance of the remainder following the treatment. We report that living Lactobacillus rhamnosus, when functionalized with photoluminescent Au nanoclusters and the anticancer drug methotrexate, was cytotoxic to monolayer and spheroids of cancer cells (HeLa and HT29) even at a low dose of bacteria used (10⁷ cfu/mL). The observed cell death was nearly 90% in HeLa spheroids and 70% in HT29 spheroids. Further, functionalization of the bacterial surface with the nanoclusters helped incorporate the drug onto their cell surfaces. The drug and nanocluster-loaded bacteria annihilated the cells and the spheroids in a rather short time (6 h) that revealed the specificity and effectiveness of the bacbots. The bacbots exhibited synergistic toxicity on the cells as their effect was more than the drug and the bacteria individually. This higher toxicity could be associated with elevated levels of reactive oxygen species generated in the bacbot-treated cells. The multifunctional bacbots reported here provide an option for guided therapy with the natural variant of the human gut-friendly living bacteria without the need for attenuation or genetic modification.

Hypoxia signaling in cancer: Implications for therapeutic interventions

Hypoxia is a persistent physiological feature of many different solid tumors and a key driver of malignancy, and in recent years, it has been recognized as an important target for cancer therapy. Hypoxia occurs in the majority of solid tumors due to a poor vascular oxygen supply that is not sufficient to meet the needs of rapidly proliferating cancer cells. A hypoxic tumor microenvironment (TME) can reduce the effectiveness of other tumor therapies, such as radiotherapy, chemotherapy, and immunotherapy. In this review, we discuss the critical role of hypoxia in tumor development, including tumor metabolism, tumor immunity, and tumor angiogenesis. The treatment methods for hypoxic TME are summarized, including hypoxia-targeted therapy and improving oxygenation by alleviating tumor hypoxia itself. Hyperoxia therapy can be used to improve tissue oxygen partial pressure and relieve tumor hypoxia. We focus on the underlying mechanisms of hyperoxia and their impact on current cancer therapies and discuss the prospects of hyperoxia therapy in cancer treatment.

Prospects for hypoxia-based drug delivery platforms for the elimination of advanced metastatic tumors: From 3D modeling to clinical concepts

Hypoxia is a unique characteristic of the solid tumor microenvironment. Hypoxia contributes to multi-drug resistance, metastasis and cancer relapse through numerous molecular pathways, but at the same time provides an opportunity for the development of novel drugs or modalities specifically targeting hypoxic tumor regions. Given the high significance of tumor hypoxia in therapeutic results, we here discuss a variety of hypoxia-adopted strategies, and their potential and utility in the treatment of deep-seated hypoxic tumor cells. We discuss the merits and demerits of these approaches, as well as their combination with other approaches such as photodynamic therapy. We also survey the currently available 3D hypoxia modeling systems, in particular organoid-based microfluidics. Finally, we discuss the potential and the current status of preclinical tumor hypoxia approaches in clinical trials for advanced cancer. We believe that multi-modal imaging and therapeutic hypoxia adopted drug delivery platforms could provide better efficacy and safety profiles, and more importantly personalized therapy. Determining the hypoxia status of tumors could offer a second chance for the clinical translation of hypoxia-based agents, such as hypoxia activated prodrugs (HAPs) from bench to bedside.

Bacteria-Driven Tumor Microenvironment-Sensitive Nanoparticles Targeting Hypoxic Regions Enhances the Chemotherapy Outcome of Lung Cancer

Background

Chemotherapy still plays a dominant role in cancer treatment. However, the inability of conventional chemotherapeutic drugs to reach the hypoxic zone of solid tumors significantly weakens their efficacy. Bacteria-mediated drug delivery systems can be an effective targeting strategy for improving the therapeutic outcomes in cancer. Anaerobic bacteria have the unique ability to selectively transport drug loads to the hypoxic regions of tumors.

Methods

We designed a Bifidobacterium infantis (Bif)-based biohybrid (Bif@PDA-PTX-NPs) to deliver polydopamine (PDA)-coated paclitaxel nanoparticles (PTX-NPs) to tumor tissues.

Results

The self-driven Bif@PDA-PTX-NPs maintained the toxicity of PTX as well as the hypoxic homing tendency of Bif. Furthermore, Bif@PDA-PTX-NPs significantly inhibited the growth of A549 xenografts in nude mice, and prolonged the survival of the tumor-bearing mice compared to the other PTX formulations without any systemic or localized toxicity.

Conclusion

The Bif@PDA-PTX-NPs biohybrids provide a new therapeutic strategy for targeted chemotherapy to solid tumors.

Alternative Strategy to Optimize Cerium Oxide for Enhanced X-ray-Induced Photodynamic Therapy

The emergence of X-ray-induced photodynamic therapy (X-PDT) holds tremendous promise for clinical deep-penetrating cancer therapy. However, the clinical application of X-PDT in cancer treatment is still limited due to the hypoxic property of cancerous tissue, the inherent antioxidant system of tumor cells, and the difficulty in matching the absorption spectra of photosensitizers. Herein, a versatile core-shell radiosensitizer (SCNPs@DMSN@CeO_x-PEG, denoted as SSCP) was elaborately designed and constructed to enhance X-PDT by coating tunable mesoporous silica on nanoscintillators, followed by embedding the cerium oxide nanoparticles in situ. The obtained SSCP radiosensitizer demonstrated a distinct blue-shift in the ultraviolet light region, so that it could perfectly absorb the ultraviolet light converted by the SCNPs core, resulting in the formation of photoinduced electron-hole (e^--h⁺) pairs separation to generate reactive oxygen species (ROS). In addition, the cerium oxide exhibits high glutathione consumption to heighten ROS accumulation, and catalase-like activity to alleviate the hypoxia, which further enhances the efficiency of radiotherapy. Benefiting from the abundant Lu and Ce elements, the computed tomography imaging performance of SSCP is about 3.79-fold that of the clinical contrast agent (iohexol), which has great potential in both preclinical imaging and clinical translation.

The development of live microorganism-based oxygen shuttles for enhanced hypoxic tumor therapy

Hypoxia is a prominent feature of malignant tumors and contributes to tumor proliferation, metastasis, and drug resistance in various solid tumors. Therefore, improving tumor oxygenation is crucial for curing tumors. To date, multiple strategies, including oxygen delivering and producing materials, have been designed to increase the oxygen concentration in hypoxic tumors. However, the unsustainable supply of oxygen is still the main obstacle, resulting in a suboptimal outcome in treating oxygen-deprived tumors. Thus, a sufficient oxygen supply is highly desirable in the treatment of hypoxic tumors. Photosynthesis, as the main source of oxygen in nature through the conversion of light energy into chemical energy and oxygen, has been widely studied in scientific research. Moreover, photosynthetic microorganisms have been increasingly applied in cancer therapy by increasing oxygenation, which improves the therapeutic effect of oxygen-consuming tumor therapeutic tools such as radiotherapy and photodynamic therapy. In this review, we summarize recent advances in the design and manufacture of live bacteria as oxygen shuttles for a new generation of hypoxic tumor treatment strategies. Finally, current challenges and future directions are also discussed for successfully addressing hypoxic tumor issues.

Recent advances in bacteria-mediated cancer therapy

Cancer is among the leading cause of deaths worldwide. Although conventional therapies have been applied in the fight against the cancer, the poor oxygen, low extracellular pH, and high interstitial fluid pressure of the tumor microenvironment mean that these treatments fail to completely eradicate cancer cells. Recently, bacteria have increasingly been considered to be a promising platform for cancer therapy thanks to their many unique properties, such as specific tumor-targeting ability, high motility, immunogenicity, and their use as gene or drug carriers. Several types of bacteria have already been used for solid and metastatic tumor therapies, with promising results. With the development of synthetic biology, engineered bacteria have been endowed with the controllable expression of therapeutic proteins. Meanwhile, nanomaterials have been widely used to modify bacteria for targeted drug delivery, photothermal therapy, magnetothermal therapy, and photodynamic therapy, while promoting the antitumor efficiency of synergistic cancer therapies. This review will provide a brief introduction to the foundation of bacterial biotherapy. We begin by summarizing the recent advances in the use of many different types of bacteria in multiple targeted tumor therapies. We will then discuss the future prospects of bacteria-mediated cancer therapies.

Microbial hydrogen "manufactory" for enhanced gas therapy and self-activated immunotherapy via reduced immune escape

BACKGROUND

As an antioxidant, hydrogen (H₂) can selectively react with the highly toxic hydroxyl radical (·OH) in tumor cells to break the balance of reactive oxygen species (ROS) and cause oxidative stress. However, due to the high diffusibility and storage difficulty of hydrogen, it is impossible to achieve long-term release at the tumor site, which highly limited their therapeutic effect.

RESULTS

Photosynthetic bacteria (PSB) release a large amount of hydrogen to break the balance of oxidative stress. In addition, as a nontoxic bacterium, PSB could stimulate the immune response and increase the infiltration of CD4+ and CD8+ T cells. More interestingly, we found that hydrogen therapy induced by our live PSB did not lead to the up-regulation of PD-L1 after stimulating the immune response, which could avoid the tumor immune escape.

CONCLUSION

Hydrogen-immunotherapy significantly kills tumor cells. We believe that our live microbial hydrogen production system provides a new strategy for cancer hydrogen treatment combining with enhanced immunotherapy without up-regulating PD-L1.

Photosynthetic microorganisms for the oxygenation of advanced 3D bioprinted tissues

3D bioprinting technology has emerged as a tool that promises to revolutionize the biomedical field, including tissue engineering and regeneration. Despite major technological advancements, several challenges remain to be solved before 3D bioprinted tissues could be fully translated from the bench to the bedside. As oxygen plays a key role in aerobic metabolism, which allows energy production in the mitochondria; as a consequence, the lack of tissue oxygenation is one of the main limitations of current bioprinted tissues and organs. In order to improve tissue oxygenation, recent approaches have been established for a broad range of clinical applications, with some already applied using 3D bioprinting technologies. Among them, the incorporation of photosynthetic microorganisms, such as microalgae and cyanobacteria, is a promising approach that has been recently explored to generate chimerical plant-animal tissues where, upon light exposure, oxygen can be produced and released in a localized and controlled manner. This review will briefly summarize the state-of-the-art approaches to improve tissue oxygenation, as well as studies describing the use of photosynthetic microorganisms in 3D bioprinting technologies. STATEMENT OF SIGNIFICANCE: 3D bioprinting technology has emerged as a tool for the generation of viable and functional tissues for direct in vitro and in vivo applications, including disease modeling, drug discovery and regenerative medicine. Despite the latest advancements in this field, suboptimal oxygen delivery to cells before, during and after the bioprinting process limits their viability within 3D bioprinted tissues. This review article first highlights state-of-the-art approaches used to improve oxygen delivery in bioengineered tissues to overcome this challenge. Then, it focuses on the emerging roles played by photosynthetic organisms as novel biomaterials for bioink generation. Finally, it provides considerations around current challenges and novel potential opportunities for their use in bioinks, by comparing latest published studies using algae for 3D bioprinting.

Nanotechnology-based combinatorial phototherapy for enhanced cancer treatment

Nanotechnology-based phototherapy has attracted enormous attention to cancer treatment owning to its non-invasiveness, high controllability and accuracy. Given the fast development of anti-tumor strategies, we summarize various examples of multifunctional nanosystems to highlight the recent advances in nanotechnology-based combinatorial phototherapy towards improving cancer treatment. The limitations of the monotherapeutic approach and the superiority of the photo-involved combinatorial strategies are discussed in each part. The future breakthroughs and clinical perspectives of combinatorial phototherapy are also outlooked. Our perspectives may inspire researchers to develop more effective phototherapy-based cancer-treating approaches.

Engineering a photosynthetic bacteria-incorporated hydrogel for infected wound healing

Treating wounds with multidrug-resistant bacterial infections remains a huge and arduous challenge. In this work, we prepared a "live-drug"-encapsulated hydrogel dressing for the treatment of multidrug-resistant bacterial infections and full-thickness skin incision repair. Our live dressing was comprised of photosynthetic bacteria (PSB) and extracellular matrix (ECM) gel with photothermal, antibacterial and antioxidant properties, as well as good cytocompatibility and blood compatibility. More interestingly, live PSB could be regarded as not only photothermal agents but also as anti-inflammatory agents to promote wound healing owing to their antioxidant metabolites. In vitro and in vivo studies showed that the PSB hydrogel not only had a high killing rate against methicillin-resistant Staphylococcus aureus (MRSA) but it also accelerated collagen deposition and granulation tissue formation by promoting cell proliferation and migration, which significantly promoted skin tissue regeneration and wound healing. We believe that the large-scale production of PSB Gel-based therapeutic dressings has the advantages of easy use and promising clinical applications. STATEMENT OF SIGNIFICANCE: Rapid wound healing and the treatment of bacterial infections have always been the two biggest challenges in the field of wound care. We prepared a "live drug" dressing by encapsulating photosynthetic bacteria into an extracellular matrix hydrogel to sterilize the wound and promote wound healing. First, photosynthetic bacteria are not only a photothermal agent for photothermal wound sterilization, but also possess the anti-inflammatory capacity to enhance wound healing due to their antioxidant metabolites. Second, the extracellular matrix hydrogel is rich in a variety of growth factors and nutrients to promote cell migration and accelerate wound healing. Third, photosynthetic bacteria are not only green and non-toxic, but also can be obtained on a large scale, which facilitates manufacturing and clinical transformation.

Photosynthetic Oxygenation-Augmented Sonodynamic Nanotherapy of Hypoxic Tumors

Reactive oxygen species (ROS) has been employed as a powerful therapeutic agent for eradicating tumor via oxidative stress. As an emerging ROS-involving noninvasive anticancer therapeutic modality, sonodynamic therapy (SDT) with high tissue penetration depth and benign remote spatiotemporal selectivity has been progressively utilized as the distinct alternative for ROS-based tumor treatment. However, the hypoxic tumor microenvironment substantially restricts the sonodynamic effect. In this work, an oxygen self-sufficient hybrid sonosensitizer on the basis of photosynthetic microorganisms cyanobacteria (Cyan) integrated with ultrasmall oxygen-deficient bimetallic oxide Mn_1.4 WO_x nanosonosensitizers, termed as M@C, is designed and engineered to overcome the critical issue of hypoxia-induced tumor resistance and strengthen the SDT effect. The sustained photosynthetic oxygen production by Cyan under light illumination can promote Mn_1.4 WO_x nanosonosensitizers to produce more ROS against cancer cells both in vitro and in vivo under ultrasound (US) irradiation. Especially, the sustained oxygen evolution for suppressing the gene expression of hypoxia-inducible factor 1alpha (HIF-1α) further boosts and augments the SDT efficiency. Thus, this work provides the paradigm that the rationally engineered biohybrid microorganism-based multifunctional sonosensitizers can serve as an effective bioplatform for augmenting the therapeutic efficiency of SDT, particularly for the treatment of hypoxic tumors.

A novel targeted multifunctional nanoplatform for visual chemo-hyperthermia synergy therapy on metastatic lymph nodes via lymphatic delivery

Background

Distant metastasis to vital organs is the major contributor to breast cancer mortality, and regional lymph node metastasis is an important facilitator of distant metastasis and recurrence in this cancer. The early diagnosis and precise treatment of lymph node metastasis are crucial for staging and prognosis in breast cancer. Herein, we report a visualized precision medicine nanoplatform of metastatic lymph nodes for ultrasonic/photoacoustic (US/PA) dual modal imaging-guided in situ targeted hyperthermia-combined chemotherapy.

Results

Carbon nanoparticles (CNs), approved by the China Food and Drug Administration, were loaded with docetaxel and rationally combined with anti-hypoxia-inducible factor 1α antibody-modified poly (lactic-co-glycolic acid) (PLGA) nanoparticles to achieve the combination of passive targeting at the lymph nodes and intracellular targeting at HIF 1α factor. The accumulation and retention of nanoparticles in metastatic lymph nodes via lymphatic delivery were enhanced. Docetaxel could be effectively offloaded by CNs that have active carbon nanoparticles, and the PLGA membrane prevented drug leakage. The nanoparticles exhibited excellent photothermal performance with a photothermal conversion efficiency of 28.9%, killing tumor cells in metastatic lymph nodes through hyperthermia. In vitro and in vivo systematic evaluations revealed that hyperpyrexia triggered the rupture of nanoparticles caused by the phase transition of perfluorohexane, resulting in docetaxel release for achieving in situ hyperthermia-combined chemotherapy.

Conclusions

The laser-triggered highly efficient in situ chemotherapy nanosystem achieves targeted synergistic chemo-hyperthermia treatment of metastatic lymph nodes, and lymphatic delivery represents a strategy to avoid additional injury caused by drugs entering the blood circulation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01186-8.

Customized materials-assisted microorganisms in tumor therapeutics

Microorganisms have been extensively applied as active biotherapeutic agents or drug delivery vehicles for antitumor treatment because of their unparalleled bio-functionalities. Taking advantage of the living attributes of microorganisms, a new avenue has been opened in anticancer research. The integration of customized functional materials with living microorganisms has demonstrated unprecedented potential in solving existing questions and even conferring microorganisms with updated antitumor abilities and has also provided an innovative train of thought for enhancing the efficacy of microorganism-based tumor therapy. In this review, we have summarized the emerging development of customized materials-assisted microorganisms (MAMO) (including bacteria, viruses, fungi, microalgae, as well as their components) in tumor therapeutics with an emphasis on the rational utilization of chosen microorganisms and tailored materials, the ingenious design of biohybrid systems, and the efficacious antitumor mechanisms. The future perspectives and challenges in this field are also discussed.