Bacterially Synthesized Tellurium Nanorods For Elimination Of Malignant Tumor By Photothermal Immunotherapy

With the rapid development of cancer immunology and genetic engineering technology,bacteria-mediated tumor therapy with a long history has provided novel ideas for tumor treatment.Owing to their intrinsic tumor targeting ability and immunomodulatory functions,bacteria have shown unique advantages in tumor therapy.However,the extensive application of bacteria in tumor therapy has been limited by the insufficient therapeutic efficacy of bacteria-based monotherapy and the potential toxicity.Using nonpathogenic or inactivated bacteria is an effective strategy to improve the biosafety of bacteria-mediated tumor therapy.To improve the therapeutic effects,bacteria-mediated therapy has been widely combined with other antitumor treatments such as chemotherapy,radiotherapy,photothermal therapy,etc.With bacteria as tumor targeting carriers and immunoadjuvants,and drugs or functional inorganic nanomaterial as the inducer of immunogenic tumor cell death,the combination therapy could synergistically enhance antitumor immune responses and improve tumor therapeutic effects.Insufficient drug loading capacity has limited the usage of bacteria as drug carriers.By utilizing the natural intracellular metabolic process of bacteria,bacterial intracellular synthesis with facile operations and mild reaction conditions has been considered a new method for the synthesis of functional inorganic nanomaterials.The chaaracteristics of constructed bacteria-inorganic nano hybrid materials include high loading capacity,low leakage rate,and maintenance of the structural integrity and surface properties of bacteria.Combining the biological characteristics of bacteria and the functions of inorganic nanomaterials,the biohybrid materials may find great potential in improving bacteria-mediated tumor therapy with increased antitumor efficacy and reduced toxicity.Based on the background above,the probiotic Escherichia coli Nissle 1917(EcN)was used as a bioreactor to synthesize tellurium nanorods(Te NRs)intracellularly.The obtained hybrid bacteria(Te@EcN)were applied for tumor photothermal immunotherapy,and the antitumor efficacy,immunomodulatory effects,and biosafety were investigated in detail.The main research contents and results are as follows:(1)Preparation,characterization and photothermal properties of Te@EcN.Te@EcN with high loading of Te NRs intracellularly was obtained by incubating EcN with sodium tellurite after deoxygenation treatment.Te@EcN,which had no viability and good stability,kept a similar structure and composition to EcN.Te@EcN showed strong near-infrared(NIR)absorption capacity,outstanding photothermal heating performances,remarkable photothermal stability,and high photothermal conversion efficiency.(2)In vitro therapeutic efficacy and immunomodulatory effects of Te@EcN-triggered photothermal heating.Te@EcN displayed good cytocompatibility while inducing a dramatic temperature increase under NIR irradiation,leading to cancer cell damage.With the aid of Te@EcN as an immunoadjuvant,heating-induced immunogenic cancer cell death significantly promoted the maturation of dendritic cells(DCs).Te@EcN effectively transformed M2-like macrophages into M1-like macrophages in vitro.(3)In vivo therapeutic efficacy and immune responses of Te@EcN-mediated photothermal immunotherapy.After intratumoral injection,Te@EcN induced tumor heating upon NIR irradiation,efficiently triggered antitumor immune responses,rapidly eliminated advanced malignant tumors,inhibited tumor recurrences and pulmonary metastases,prolonged survival of tumor-bearing mice,and induced long-term immune memory effects which effectively resisted rechallenge of tumors.Te@EcN administered systemically could efficiently accumulate and retain in tumors,and be rapidly metabolized and eliminated in normal organs.Significant tumor heating and elimination of advanced malignant tumors were achieved by systemical injection of Te@EcN under NIR irradiation,without obvious side effects on treated mice.The combination of systemically-injected Te@EcN-based photothermal killing and immunomodulatory effects of Te@EcN could synergistically promote DC maturation and repolarize M2-like tumor-associated macrophages,in turn enhancing tumor infiltration of cytotoxic T lymphocytes and inducing local and systemic antitumor immune responses.Intravenous administration of Te@EcN could evoke mild acute responses in healthy mice,followed by rapid recovery,and the biosafety was prominently improved compared to living bacteria.In summary,Te@EcN was constructed by simple bacterial intracellular synthesis as a biohybrid therapeutic platform for photothermal immunotherapy of malignant tumors.Tumor accumulation properties and immunomodulatory functions of EcN were organically combined with photothermal properties of Te NRs,to enhance antitumor immune responses through three dimensions: photothermal therapy induced release of tumor-associated antigens and damage-associated molecular patterns,EcN promoted DCs maturation as an immunoadjuvant,and EcN reversed the immunosuppressive tumor microenvironment.Most importantly,Te@EcN ameliorated the biosafety of bacteria-mediated tumor therapy due to its non-proliferative and non-virulent characteristics.This work provides a potential combined tumor therapeutic strategy based on Te@EcN with low toxicity and high efficiency.