Macrophage delivery of an oncolytic virus abolishes tumor regrowth and metastasis after chemotherapy or irradiation

An oncolytic adenovirus targeting SLAMF7 demonstrates anti-myeloma efficacy

We investigated a novel SLAMF7-promoter driven oncolytic adenovirus (Ad[CE1A]) as a potential therapeutic for multiple myeloma, an incurable hematological malignancy. Ad[CE1A] infection, replication, and oncolysis were assessed in a panel of myeloma cell lines (n = 8) and ex vivo samples from myeloma patients (n = 17) and healthy donors (HDs) (n = 14). Ad[CE1A] efficiently infected, replicated, and induced oncolysis in myeloma cells, but not in control cell lines or HDs, demonstrating selective cytotoxicity. Mechanistic studies revealed Ad[CE1A]-induced cell death is caspase-independent, with a potential involvement of necroptosis. Ad[CE1A] also altered immunogenic cell death markers (calreticulin, CD47, extracellular ATP), enhanced antigen presentation via increased MHC class I and II receptor expression (HLA-ABC and HLA-DR), and stimulated bystander cytokine killing, indicating potential for direct and immune-mediated anti-myeloma responses. In vivo experiments with 5TGM1 syngeneic and U266 xenograft models showed Ad[CE1A] significantly reduced myeloma tumor burden compared to vehicle control. Combination therapy with anti-myeloma drugs, bortezomib, melphalan, panobinostat and pomalidomide, enhanced Ad[CE1A] efficacy, with melphalan upregulating SLAMF7, resulting in increased viral replication. In summary, these findings support Ad[CE1A] as a promising myeloma therapy.

Synergistic effects of immunotherapy and adjunctive therapies in prostate cancer management

In recent years, cancer immunotherapy has received widespread attention due to significant tumor clearance in some malignancies. Various immunotherapy approaches, including vaccines, immune checkpoint inhibitors, oncolytic virotherapy, bispecific T cell engagers, and adoptive T cell transfer, have completed or are undergoing clinical trials for prostate cancer. Despite immune checkpoint blockade's extraordinary effectiveness in treating a variety of cancers, targeted prostate cancer treatment using the immune system is still in its infancy. Multiple factors including the heterogeneity of prostate cancer, the cold tumor microenvironment, and a low level of neoantigens, contribute to the poor immunotherapy response. Significant effort is being devoted to improving immune-based prostate cancer therapy. Recently, several key discoveries demonstrate that prostate cancer immunotherapy agents may be used to promise better prognosis for patients as part of combination strategies with other agents targeting tumor-associated immune mechanism of resistance. Here, this review comprehensively examines the recent advancements in immunotherapy for prostate cancer, exploring its potential synergistic effects when combined with other treatment modalities to enhance clinical efficacy.

Harnessing macrophage-drug conjugates for allogeneic cell-based therapy of solid tumors via the TRAIN mechanism

Treatment of solid tumors remains challenging and therapeutic strategies require continuous development. Tumor-infiltrating macrophages play a pivotal role in tumor dynamics. Here, we present a Macrophage-Drug Conjugate (MDC) platform technology that enables loading macrophages with ferritin-drug complexes. We first show that macrophages actively take up human heavy chain ferritin (HFt) in vitro via macrophage scavenger receptor 1 (MSR1). We further manifest that drug-loaded macrophages transfer ferritin to adjacent cancer cells through a process termed 'TRAnsfer of Iron-binding protein' (TRAIN). The TRAIN process requires direct cell-to-cell contact and an immune synapse-like structure. At last, MDCs with various anti-cancer drugs are formulated with their safety and anti-tumor efficacy validated in multiple syngeneic mice and orthotopic human tumor models via different routes of administration. Importantly, MDCs can be prepared in advance and used as thawed products, supporting their clinical applicability. This MDC approach thus represents a promising advancement in the therapeutic landscape for solid tumors.

Oncolytic senecavirus A in tumor immunotherapy: Mechanisms, progress, and future directions

Oncolytic virotherapy has emerged as a promising immunotherapy strategy against cancer. As the first picornavirus tested in humans for its oncolytic potential, Senecavirus A (SVA) possesses several advantageous features, including its small size, rapid replication, and ability to penetrate the vascular system of solid tumors, allowing for the specific targeting and lysis of tumor cells. Additionally, SVA does not integrate into the host genome, thus avoiding potential genomic damage, and it lacks oncogenes or other virulence genes. Importantly, no significant pathogenic effects have been observed in humans or companion animals. Due to its simple genetic structure, SVA is amenable to various genetic modifications, allowing it to carry exogenous genes to further enhance tumor therapy. This review summarizes current knowledge of SVA's mechanisms of action and its progress in oncolytic therapy research, while also addressing the challenges and future directions.

Bioorthogonal oncolytic-virus nanovesicles combined bio-immunotherapy with CAR-T cells for solid tumors

Various oncolytic viruses (OVs) have been adopted as therapeutic tools to increase the efficacy of chimeric antigen receptor (CAR)-T cells against solid tumors. However, the therapeutic effect of OVs has been limited by pre-existing neutralizing antibodies and poor targeting delivery for systemic administration. Herein, we propose using bioorthogonal OV nanovesicles to boost the antitumor effects of CAR-T cells in solid tumors by reshaping the tumor microenvironment. Using a cell-membrane nanomimetic technique, we embedded artificial chemical ligands on cancer cell surfaces and then encapsulated lysoviral particles to obtain dual-targeted OV nanovesicles with bioorthogonal targeting and homologous recognition. OVs can be directly encapsulated into cancer cell nanovesicles and exhibit a liposome-like nanostructure, efficient loading, and excellent tumor-targeting capability. Encouragingly, OV nanovesicles efficiently induced tumor-cell apoptosis while sparing normal tissues and cells, thereby inhibiting tumor growth. Administration of viral nanovesicles effectively increased the secretion of anti-tumor cytokines such as IL-2, TNF-α and IFN-γ, and significantly promoted the infiltration and activation of CD8+CAR-T cells in tumors. Our data suggest that bioorthogonal OV nanovesicles hold great potential to overcome the limitations of CAR-T cells as monotherapies against solid tumors and, thus, drive the clinical application of combination therapy.

Nanotherapeutics for Macrophage Network Modulation in Tumor Microenvironments: Targets and Tools

Macrophage is an important component in the tumor immune microenvironment, which exerts significant influence on tumor development and metastasis. Due to their dual nature of promoting and suppressing inflammation, macrophages can serve as both targets for tumor immunotherapy and tools for treating malignancies. However, the abundant infiltration of tumor-associated macrophages dominated by an immunosuppressive phenotype maintains a pro-tumor microenvironment, and engineering macrophages using nanotechnology to manipulate the tumor immune microenvironment represent a feasible approach for cancer immunotherapy. Additionally, considering the phagocytic and specifically tumor-targeting capabilities of M1 macrophages, macrophages manipulated through cellular engineering and nanotechnology, as well as macrophage-derived exosomes and macrophage membranes, can also become effective tools for cancer treatment. In conclusion, nanotherapeutics targeting macrophages remains immense potential for the development of macrophage-mediated tumor treatment methods and will further enhance our understanding, diagnosis, and treatment of various malignants.

Beyond the Gut: The intratumoral microbiome's influence on tumorigenesis and treatment response

The intratumoral microbiome (TM) refers to the microorganisms in the tumor tissues, including bacteria, fungi, viruses, and so on, and is distinct from the gut microbiome and circulating microbiota. TM is strongly associated with tumorigenesis, progression, metastasis, and response to therapy. This paper highlights the current status of TM. Tract sources, adjacent normal tissue, circulatory system, and concomitant tumor co-metastasis are the main origin of TM. The advanced techniques in TM analysis are comprehensively summarized. Besides, TM is involved in tumor progression through several mechanisms, including DNA damage, activation of oncogenic signaling pathways (phosphoinositide 3-kinase [PI3K], signal transducer and activator of transcription [STAT], WNT/β-catenin, and extracellular regulated protein kinases [ERK]), influence of cytokines and induce inflammatory responses, and interaction with the tumor microenvironment (anti-tumor immunity, pro-tumor immunity, and microbial-derived metabolites). Moreover, promising directions of TM in tumor therapy include immunotherapy, chemotherapy, radiotherapy, the application of probiotics/prebiotics/synbiotics, fecal microbiome transplantation, engineered microbiota, phage therapy, and oncolytic virus therapy. The inherent challenges of clinical application are also summarized. This review provides a comprehensive landscape for analyzing TM, especially the TM-related mechanisms and TM-based treatment in cancer.

Oncolytic virus and tumor-associated macrophage interactions in cancer immunotherapy

Oncolytic viruses (OV) are a promising strategy in cancer immunotherapy. Their capacity to promote anti-tumoral immunity locally raises hope that cancers unresponsive to current immunotherapy approaches could be tackled more efficiently. In this context, tumor-associated macrophages (TAM) must be considered because of their pivotal role in cancer immunity. Even though TAM tend to inhibit anti-tumoral responses, their ability to secrete pro-inflammatory cytokines and phagocytose cancer cells can be harnessed to promote therapeutic cancer immunity. OVs have the potential to promote TAM pro-inflammatory functions that favor anti-tumoral immunity. But in parallel, TAM pro-inflammatory functions induce OV clearance in the tumor, thereby limiting OV efficacy and highlighting that the interaction between OV and TAM is a double edge sword. Moreover, engineered OVs were recently developed to modulate specific TAM functions such as phagocytic activity. The potential of circulating monocytes to deliver OV into the tumor after intravenous administration is also emerging. In this review, we will present the interaction between OV and TAM, the potential of engineered OV to modulate specific TAM functions, and the promising role of circulating monocytes in OV delivery to the tumor.

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

Erythrocyte-Leveraged Oncolytic Virotherapy (ELeOVt): Oncolytic Virus Assembly on Erythrocyte Surface to Combat Pulmonary Metastasis and Alleviate Side Effects

Despite being a new promising tool for cancer therapy, intravenous delivery of oncolytic viruses (OVs) is greatly limited by poor tumor targeting, rapid clearance in the blood, severe organ toxicity, and cytokine release syndrome. Herein, a simple and efficient strategy of erythrocyte-leveraged oncolytic virotherapy (ELeOVt) is reported, which for the first time assembled OVs on the surface of erythrocytes with up to near 100% efficiency and allowed targeted delivery of OVs to the lung after intravenous injection to achieve excellent treatment of pulmonary metastases while greatly improving the biocompatibility of OVs as a drug. Polyethyleneimine (PEI) as a bridge to assemble OVs on erythrocytes also played an important role in promoting the transfection of OVs. It is found that ELeOVt approach significantly prolonged the circulation time of OVs and increased the OVs distribution in the lung by more than tenfold, thereby significantly improving the treatment of lung metastases while reducing organ and systemic toxicity. Taken together, these findings suggest that the ELeOVt provides a biocompatible, efficient, and widely available approach to empower OVs to combat lung metastasis.

Breaking down the tumor immune infiltration within pediatric sarcomas

Immunotherapies are a promising therapeutic option, yet for a variety of reasons, these treatments have achieved limited success against sarcomas. The immunosuppressive tumor microenvironment (TME) of sarcomas as well as lack of predictive biomarkers, decreased T-cell clonal frequency, and high expression of immunosuppressive infiltrating cells has thus far prevented major success using immunotherapies. By breaking down the TME into its individual components and understanding how the various cell types interact with each other as well as in the context of the complex immune microenvironment, can lead to effective therapeutic immunotherapy treatments, potentially improving outcomes for those with metastatic disease.

Therapy with oncolytic viruses: progress and challenges

Oncolytic viruses (OVs) are an emerging class of cancer therapeutics that offer the benefits of selective replication in tumour cells, delivery of multiple eukaryotic transgene payloads, induction of immunogenic cell death and promotion of antitumour immunity, and a tolerable safety profile that largely does not overlap with that of other cancer therapeutics. To date, four OVs and one non-oncolytic virus have been approved for the treatment of cancer globally although talimogene laherparepvec (T-VEC) remains the only widely approved therapy. T-VEC is indicated for the treatment of patients with recurrent melanoma after initial surgery and was initially approved in 2015. An expanding body of data on the clinical experience of patients receiving T-VEC is now becoming available as are data from clinical trials of various other OVs in a range of other cancers. Despite increasing research interest, a better understanding of the underlying biology and pharmacology of OVs is needed to enable the full therapeutic potential of these agents in patients with cancer. In this Review, we summarize the available data and provide guidance on optimizing the use of OVs in clinical practice, with a focus on the clinical experience with T-VEC. We describe data on selected novel OVs that are currently in clinical development, either as monotherapies or as part of combination regimens. We also discuss some of the preclinical, clinical and regulatory hurdles that have thus far limited the development of OVs.

Managing the immune microenvironment of osteosarcoma: the outlook for osteosarcoma treatment

Osteosarcoma, with poor survival after metastasis, is considered the most common primary bone cancer in adolescents. Notwithstanding the efforts of researchers, its five-year survival rate has only shown limited improvement, suggesting that existing therapeutic strategies are insufficient to meet clinical needs. Notably, immunotherapy has shown certain advantages over traditional tumor treatments in inhibiting metastasis. Therefore, managing the immune microenvironment in osteosarcoma can provide novel and valuable insight into the multifaceted mechanisms underlying the heterogeneity and progression of the disease. Additionally, given the advances in nanomedicine, there exist many advanced nanoplatforms for enhanced osteosarcoma immunotherapy with satisfactory physiochemical characteristics. Here, we review the classification, characteristics, and functions of the key components of the immune microenvironment in osteosarcoma. This review also emphasizes the application, progress, and prospects of osteosarcoma immunotherapy and discusses several nanomedicine-based options to enhance the efficiency of osteosarcoma treatment. Furthermore, we examine the disadvantages of standard treatments and present future perspectives for osteosarcoma immunotherapy.

HSV1716 Prevents Myeloma Cell Regrowth When Combined with Bortezomib In Vitro and Significantly Reduces Systemic Tumor Growth in Mouse Models

Multiple myeloma remains largely incurable due to refractory disease; therefore, novel treatment strategies that are safe and well-tolerated are required. Here, we studied the modified herpes simplex virus HSV1716 (SEPREHVIR®), which only replicates in transformed cells. Myeloma cell lines and primary patient cells were infected with HSV1716 and assessed for cell death using propidium iodide (PI) and Annexin-V staining and markers of apoptosis and autophagy by qPCR. Myeloma cell death was associated with dual PI and Annexin-V positivity and increased expression of apoptotic genes, including CASP1, CASP8, CASP9, BAX, BID, and FASL. The combination of HSV1716 and bortezomib treatments prevented myeloma cell regrowth for up to 25 days compared to only transient cell growth suppression with bortezomib treatment. The viral efficacy was tested in a xenograft (JJN-3 cells in NSG mice) and syngeneic (murine 5TGM1 cells in C57BL/KaLwRijHsd mice) systemic models of myeloma. After 6 or 7 days, the post-tumor implantation mice were treated intravenously with the vehicle or HSV1716 (1 × 107 plaque forming units/1 or 2 times per week). Both murine models treated with HSV1716 had significantly lower tumor burden rates compared to the controls. In conclusion, HSV1716 has potent anti-myeloma effects and may represent a novel therapy for multiple myeloma.

The emerging field of oncolytic virus-based cancer immunotherapy

Oncolytic viruses (OVs) provide novel and promising therapeutic options for patients with cancers resistant to traditional therapies. Natural or genetically modified OVs are multifaceted tumor killers. They directly lyse tumor cells while sparing normal cells, and indirectly potentiate antitumor immunity by releasing antigens and activating inflammatory responses in the tumor microenvironment. However, some limitations, such as limited penetration of OVs into tumors, short persistence, and the host antiviral immune response, are impeding the broad translation of oncolytic virotherapy into the clinic. If these challenges can be overcome, combination therapies, such as OVs plus immune checkpoint blockade (ICB), chimeric antigen receptor (CAR) T cells, or CAR natural killer (NK) cells, may provide powerful therapeutic platforms in the clinic.

Harnessing Engineered Immune Cells and Bacteria as Drug Carriers for Cancer Immunotherapy

Immunotherapy continues to be in the spotlight of oncology therapy research in the past few years and has been proven to be a promising option to modulate one's innate and adaptive immune systems for cancer treatment. However, the poor delivery efficiency of immune agents, potential off-target toxicity, and nonimmunogenic tumors significantly limit its effectiveness and extensive application. Recently, emerging biomaterial-based drug carriers, including but not limited to immune cells and bacteria, are expected to be potential candidates to break the dilemma of immunotherapy, with their excellent natures of intrinsic tumor tropism and immunomodulatory activity. More than that, the tiny vesicles and physiological components derived from them have similar functions with their source cells due to the inheritance of various surface signal molecules and proteins. Herein, we presented representative examples about the latest advances of biomaterial-based delivery systems employed in cancer immunotherapy, including immune cells, bacteria, and their derivatives. Simultaneously, opportunities and challenges of immune cells and bacteria-based carriers are discussed to provide reference for their future application in cancer immunotherapy.

Repeated dosing improves oncolytic rhabdovirus therapy in mice via interactions with intravascular monocytes

There is debate in the field of oncolytic virus (OV) therapy, whether a single viral dose, or multiple administrations, is better for tumor control. Using intravital microscopy, we describe the fate of vesicular stomatitis virus (VSV) delivered systemically as a first or a second dose. Following primary administration, VSV binds to the endothelium, initiates tumor infection and activates a proinflammatory response. This initial OV dose induces neutrophil migration into the tumor and limits viral replication. OV administered as a second dose fails to infect the tumor and is captured by intravascular monocytes. Despite a lack of direct infection, this second viral dose, in a monocyte-dependent fashion, enhances and sustains infection by the first viral dose, promotes CD8 T cell recruitment, delays tumor growth and improves survival in multi-dosing OV therapy. Thus, repeated VSV dosing engages monocytes to post-condition the tumor microenvironment for improved infection and anticancer T cell responses. Understanding the complex interactions between the subsequent viral doses is crucial for improving the efficiency of OV therapy and virus-based vaccines.

Near-Infrared Bioluminescence Imaging of Macrophage Sensors for Cancer Detection In Vivo

Melanoma is an aggressive type of skin cancer with a poor prognosis after it gets metastasized. The early detection of malignant melanoma is critical for effective therapy. Because melanoma often resembles moles, routine skin check-up may help for timely identification of suspicious areas. Recently, it has been shown that the interplay of melanoma cells with the immune system can help develop efficient therapeutic strategies. Here, we leveraged engineered macrophages (BMC2) as cell-based sensors for metastatic melanoma. To perform dual-color bioluminescence imaging (BLI) in vivo, macrophages were engineered to express a green click beetle luciferase (CBG2) and a near-infrared fluorescent dye (DiR), and B16F10 melanoma cells were instead engineered to express a near-infrared click beetle luciferase (CBR2). Using real-time in vivo dual-color BLI and near-infrared fluorescence (FL) imaging, we could demonstrate that macrophages were able to sense and substantially accumulate in subcutaneous and metastatic melanoma tissues at 72 h after systemic injections. Together, we showed the potentiality to use optical imaging technologies to track circulating macrophages for the non-invasive detection of metastatic melanoma.

Novel Immunotherapies for Osteosarcoma

Osteosarcoma (OS) is the most common primary malignant bone sarcoma mainly affecting adolescents and young adults, which often progresses to pulmonary metastasis and leads to the death of OS patients. OS is characterized as a highly heterogeneous cancer type and the underlying pathologic mechanisms triggering tumor progress and metastasis are incompletely recognized. Surgery combined with neoadjuvant and postoperative chemotherapy has elevated 5-year survival to over 70% for patients with localized OS tumors, as opposed to only 20% of patients with recurrence and/or metastasis. Therefore, novel therapeutic strategies are needed to overcome the drawbacks of conventional treatments. Immunotherapy is gaining momentum for the treatment of OS with an increasing number of FDA-approved therapies for malignancies resistant to conventional therapies. Here, we review the OS tumor microenvironment and appraise the promising immunotherapies available in the management of OS.

Targeting circulating monocytes with CCL2-loaded liposomes armed with an oncolytic adenovirus

Oncolytic viruses (OVs) selectively replicate in and destroy cancer cells resulting in anti-tumor immunity. However, clinical use remains a challenge because of virus clearance upon intravenous delivery. OV packaging using a nanomedicine approach could overcome this. Here we encapsulate an oncolytic adenovirus (Ad[I/PPT-E1A]) into CCL2-coated liposomes in order to exploit recruitment of CCR2-expressing circulating monocytes into tumors. We demonstrate successful encapsulation of Ad[I/PPT-E1A] into CCL2-coated liposomes that were preferentially taken up by CCR2-expressing monocytes. No complex-related toxicities were observed following incubation with prostate tumor cells and the encapsulation did not affect virus oncolytic activity in vitro. Furthermore, intravenous administration of our nanomedicine resulted in a significant reduction in tumor size and pulmonary metastasis in prostate cancer-bearing mice whereby a 1000-fold less virus was needed compared to Ad[I/PPT-E1A] alone. Taken together our data provide an opportunity to target OVs via circulation to inaccessible tumors using liposome-assisted drug delivery.

Machine Learning: A New Prospect in Multi-Omics Data Analysis of Cancer

Cancer is defined as a large group of diseases that is associated with abnormal cell growth, uncontrollable cell division, and may tend to impinge on other tissues of the body by different mechanisms through metastasis. What makes cancer so important is that the cancer incidence rate is growing worldwide which can have major health, economic, and even social impacts on both patients and the governments. Thereby, the early cancer prognosis, diagnosis, and treatment can play a crucial role at the front line of combating cancer. The onset and progression of cancer can occur under the influence of complicated mechanisms and some alterations in the level of genome, proteome, transcriptome, metabolome etc. Consequently, the advent of omics science and its broad research branches (such as genomics, proteomics, transcriptomics, metabolomics, and so forth) as revolutionary biological approaches have opened new doors to the comprehensive perception of the cancer landscape. Due to the complexities of the formation and development of cancer, the study of mechanisms underlying cancer has gone beyond just one field of the omics arena. Therefore, making a connection between the resultant data from different branches of omics science and examining them in a multi-omics field can pave the way for facilitating the discovery of novel prognostic, diagnostic, and therapeutic approaches. As the volume and complexity of data from the omics studies in cancer are increasing dramatically, the use of leading-edge technologies such as machine learning can have a promising role in the assessments of cancer research resultant data. Machine learning is categorized as a subset of artificial intelligence which aims to data parsing, classification, and data pattern identification by applying statistical methods and algorithms. This acquired knowledge subsequently allows computers to learn and improve accurate predictions through experiences from data processing. In this context, the application of machine learning, as a novel computational technology offers new opportunities for achieving in-depth knowledge of cancer by analysis of resultant data from multi-omics studies. Therefore, it can be concluded that the use of artificial intelligence technologies such as machine learning can have revolutionary roles in the fight against cancer.

The Multifaceted Role of Macrophages in Oncolytic Virotherapy

One of the cancer hallmarks is immune evasion mediated by the tumour microenvironment (TME). Oncolytic virotherapy is a form of immunotherapy based on the application of oncolytic viruses (OVs) that selectively replicate in and induce the death of tumour cells. Virotherapy confers reciprocal interaction with the host’s immune system. The aim of this review is to explore the role of macrophage-mediated responses in oncolytic virotherapy efficacy. The approach was to study current scientific literature in this field in order to give a comprehensive overview of the interactions of OVs and macrophages and their effects on the TME. The innate immune system has a central influence on the TME; tumour-associated macrophages (TAMs) generally have immunosuppressive, tumour-supportive properties. In the context of oncolytic virotherapy, macrophages were initially thought to predominantly contribute to anti-viral responses, impeding viral spread. However, macrophages have now also been found to mediate transport of OV particles and, after TME infiltration, to be subjected to a phenotypic shift that renders them pro-inflammatory and tumour-suppressive. These TAMs can present tumour antigens leading to a systemic, durable, adaptive anti-tumour immune response. After phagocytosis, they can recirculate carrying tissue-derived proteins, which potentially enables the monitoring of OV replication in the TME. Their role in therapeutic efficacy is therefore multifaceted, but based on research applying relevant, immunocompetent tumour models, macrophages are considered to have a central function in anti-cancer activity. These novel insights hold important clinical implications. When optimised, oncolytic virotherapy, mediating multifactorial inhibition of cancer immune evasion, could contribute to improved patient survival.

Pouring petrol on the flames: Using oncolytic virotherapies to enhance tumour immunogenicity

Oncolytic viruses possess the ability to infect, replicate and lyse malignantly transformed tumour cells. This oncolytic activity amplifies the therapeutic advantage and induces a form of immunogenic cell death, characterized by increased CD8 + T-cell infiltration into the tumour microenvironment. This important feature of oncolytic viruses can result in the warming up of immunologically 'cold' tumour types, presenting the enticing possibility that oncolytic virus treatment combined with immunotherapies may enhance efficacy. In this review, we assess some of the most promising candidates that might be used for oncolytic virotherapy: immunotherapy combinations. We assess their potential as separate agents or as agents combined into a single therapy, where the immunotherapy is encoded within the genome of the oncolytic virus. The development of such advanced agents will require increasingly sophisticated model systems for their preclinical assessment and evaluation. In vivo rodent model systems are fraught with limitations in this regard. Oncolytic viruses replicate selectively within human cells and therefore require human xenografts in immune-deficient mice for their evaluation. However, the use of immune-deficient rodent models hinders the ability to study immune responses against any immunomodulatory transgenes engineered within the viral genome and expressed within the tumour microenvironment. There has therefore been a shift towards the use of more sophisticated ex vivo patient-derived model systems based on organoids and explant co-cultures with immune cells, which may be more predictive of efficacy than contrived and artificial animal models. We review the best of those model systems here.

Oncolytic viruses as a promising therapeutic strategy for hematological malignancies

The incidence of hematological malignancies such as multiple myeloma, leukemia, and lymphoma has increased over time. Although bone marrow transplantation, immunotherapy and chemotherapy have led to significant improvements in efficacy, poor prognosis in elderly patients, recurrence and high mortality among hematological malignancies remain major challenges, and innovative therapeutic strategies should be explored. Besides directly lyse tumor cells, oncolytic viruses can activate immune responses or be engineered to express therapeutic factors to increase antitumor efficacy, and have gradually been recognized as an appealing approach for fighting cancers. An increasing number of studies have applied oncolytic viruses in hematological malignancies and made progress. In particular, strategies combining immunotherapy and oncolytic virotherapy are emerging. Various phase I clinical trials of oncolytic reovirus with lenalidomide or programmed death 1(PD-1) immune checkpoint inhibitors in multiple myeloma are ongoing. Moreover, preclinical studies of combinations with chimeric antigen receptor T (CAR-T) cells are underway. Thus, oncolytic virotherapy is expected to be a promising approach to cure hematological malignancies. This review summarizes progress in oncolytic virus research in hematological malignancies. After briefly reviewing the development and oncolytic mechanism of oncolytic viruses, we focus on delivery methods of oncolytic viruses, especially systemic delivery that is suitable for hematological tumors. We then discuss the main types of oncolytic viruses applied for hematological malignancies and related clinical trials. In addition, we present several ways to improve the antitumor efficacy of oncolytic viruses. Finally, we discuss current challenges and provide suggestions for future studies.

Macrophages Mediate the Antitumor Effects of the Oncolytic Virus HSV1716 in Mammary Tumors

Oncolytic viruses (OV) have been shown to activate the antitumor functions of specific immune cells like T cells. Here, we show OV can also reprogram tumor-associated macrophage (TAM) to a less immunosuppressive phenotype. Syngeneic, immunocompetent mouse models of primary breast cancer were established using PyMT-TS1, 4T1, and E0771 cell lines, and a metastatic model of breast cancer was established using the 4T1 cell line. Tumor growth and overall survival was assessed following intravenous administration of the OV, HSV1716 (a modified herpes simplex virus). Infiltration and function of various immune effector cells was assessed by NanoString, flow cytometry of dispersed tumors, and immunofluorescence analysis of tumor sections. HSV1716 administration led to marked tumor shrinkage in primary mammary tumors and a decrease in metastases. This was associated with a significant increase in the recruitment/activation of cytotoxic T cells, a reduction in the presence of regulatory T cells and the reprograming of TAMs towards a pro-inflammatory, less immunosuppressive phenotype. These findings were supported by in vitro data demonstrating that human monocyte-derived macrophages host HSV1716 replication, and that this led to immunogenic macrophage lysis. These events were dependent on macrophage expression of proliferating cell nuclear antigen (PCNA). Finally, the antitumor effect of OV was markedly diminished when TAMs were depleted using clodronate liposomes. Together, our results show that TAMs play an essential role in support of the tumoricidal effect of the OV, HSV1716-they both host viral replication via a novel, PCNA-dependent mechanism and are reprogramed to express a less immunosuppressive phenotype.

Oncolytic Virotherapy in Solid Tumors: The Challenges and Achievements

Oncolytic virotherapy (OVT) is a promising approach in cancer immunotherapy. Oncolytic viruses (OVs) could be applied in cancer immunotherapy without in-depth knowledge of tumor antigens. The capability of genetic modification makes OVs exciting therapeutic tools with a high potential for manipulation. Improving efficacy, employing immunostimulatory elements, changing the immunosuppressive tumor microenvironment (TME) to inflammatory TME, optimizing their delivery system, and increasing the safety are the main areas of OVs manipulations. Recently, the reciprocal interaction of OVs and TME has become a hot topic for investigators to enhance the efficacy of OVT with less off-target adverse events. Current investigations suggest that the main application of OVT is to provoke the antitumor immune response in the TME, which synergize the effects of other immunotherapies such as immune-checkpoint blockers and adoptive cell therapy. In this review, we focused on the effects of OVs on the TME and antitumor immune responses. Furthermore, OVT challenges, including its moderate efficiency, safety concerns, and delivery strategies, along with recent achievements to overcome challenges, are thoroughly discussed.

Abraxane-induced bone marrow CD11b+ myeloid cell depletion in tumor-bearing mice is visualized by μPET-CT with 64Cu-labeled anti-CD11b and prevented by anti-CSF-1

To investigate the utility of noninvasive µPET-CT with 64Cu-DOTA-anti-CD11b (64Cu-αCD11b) in assessing bone marrow status after anticancer therapies, and the protective role of anti-CSF-1 (αCSF-1) against bone marrow suppression induced by Abraxane. Methods: MDA-MB-435 tumor-bearing mice were treated with Abraxane, αCSF-1, or αCSF-1 plus Abraxane. µPET-CT and biodistribution of 64Cu-αCD11b were performed after intravenous injection of the radiotracer. Cells from mouse bone marrow and MDA-MB-435 tumor were analyzed by flow cytometry. A humanized αCSF-1 was investigated for its role in protecting bone marrow cells, using a transgenic mouse model that expresses functional human CSF-1. Results: μPET-CT showed that 64Cu-αCD11b had high uptake in the bone marrow and spleen of both normal and tumor-bearing mice. Abraxane significantly reduced 64Cu-αCD11b uptake in the bone marrow and spleen of treated mice compared to untreated mice. Interestingly, 64Cu-αCD11b μPET-CT revealed that αCSF-1 alleviated the depletion of bone marrow cells by Abraxane. These changes in the bone marrow population of CD11b+ myeloid cells were confirmed by flow cytometry. Moreover, αCSF-1 potently enhanced tolerance of bone marrow granulocytic myeloid cells to Abraxane, decreased cell migration, and suppressed recruitment of myeloid cells to the tumor microenvironment. The humanized αCSF-1 also alleviated the effects of Abraxane on bone marrow cells in transgenic mice expressing human CSF-1, suggesting clinical relevance of αCSF-1 in prevention of bone marrow suppression in addition to its role in reducing tumor-infiltrating myeloid cells. Conclusions: Abraxane-induced bone marrow CD11b+ myeloid cell depletion in tumor-bearing mice could be noninvasively assessed by μPET-CT with 64Cu-αCD11b and prevented by αCSF-1.

Cell-Based Tracers as Trojan Horses for Image-Guided Surgery

Surgeons rely almost completely on their own vision and palpation to recognize affected tissues during surgery. Consequently, they are often unable to distinguish between different cells and tissue types. This makes accurate and complete resection cumbersome. Targeted image-guided surgery (IGS) provides a solution by enabling real-time tissue recognition. Most current targeting agents (tracers) consist of antibodies or peptides equipped with a radiolabel for Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), magnetic resonance imaging (MRI) labels, or a near-infrared fluorescent (NIRF) dye. These tracers are preoperatively administered to patients, home in on targeted cells or tissues, and are visualized in the operating room via dedicated imaging systems. Instead of using these 'passive' tracers, there are other, more 'active' approaches of probe delivery conceivable by using living cells (macrophages/monocytes, neutrophils, T cells, mesenchymal stromal cells), cell(-derived) fragments (platelets, extracellular vesicles (exosomes)), and microorganisms (bacteria, viruses) or, alternatively, 'humanized' nanoparticles. Compared with current tracers, these active contrast agents might be more efficient for the specific targeting of tumors or other pathological tissues (e.g., atherosclerotic plaques). This review provides an overview of the arsenal of possibilities applicable for the concept of cell-based tracers for IGS.

Development of a New Hyaluronic Acid Based Redox-Responsive Nanohydrogel for the Encapsulation of Oncolytic Viruses for Cancer Immunotherapy

Oncolytic viruses (OVs) are emerging as promising and potential anti-cancer therapeutic agents, not only able to kill cancer cells directly by selective intracellular viral replication, but also to promote an immune response against tumor. Unfortunately, the bioavailability under systemic administration of OVs is limited because of undesired inactivation caused by host immune system and neutralizing antibodies in the bloodstream. To address this issue, a novel hyaluronic acid based redox responsive nanohydrogel was developed in this study as delivery system for OVs, with the aim to protect the OVs following systemic administration. The nanohydrogel was formulated by water in oil (W/O) nanoemulsion method and cross-linked by disulfide bonds derived from the thiol groups of synthesized thiolated hyaluronic acid. One DNA OV Ad[I/PPT-E1A] and one RNA OV Rigvir^® ECHO-7 were encapsulated into the developed nanohydrogel, respectively, in view of their potential of immunovirotherapy to treat cancers. The nanohydrogels showed particle size of approximately 300–400 nm and negative zeta potential of around −13 mV by dynamic light scattering (DLS). A uniform spherical shape of the nanohydrogel was observed under the scanning electron microscope (SEM) and transmission electron microscope (TEM), especially, the successfully loading of OV into nanohydrogel was revealed by TEM. The crosslinking between the hyaluronic acid chains was confirmed by the appearance of new peak assigned to disulfide bond in Raman spectrum. Furthermore, the redox responsive ability of the nanohydrogel was determined by incubating the nanohydrogel into phosphate buffered saline (PBS) pH 7.4 with 10 μM or 10 mM glutathione at 37 °C which stimulate the normal physiological environment (extracellular) or reductive environment (intracellular or tumoral). The relative turbidity of the sample was real time monitored by DLS which indicated that the nanohydrogel could rapidly degrade within 10 h in the reductive environment due to the cleavage of disulfide bonds, while maintaining the stability in the normal physiological environment after 5 days. Additionally, in vitro cytotoxicity assays demonstrated a good oncolytic activity of OVs-loaded nanohydrogel against the specific cancer cell lines. Overall, the results indicated that the developed nanohydrogel is a delivery system appropriate for viral drugs, due to its hydrophilic and porous nature, and also thanks to its capacity to maintain the stability and activity of encapsulated viruses. Thus, nanohydrogel can be considered as a promising candidate carrier for systemic administration of oncolytic immunovirotherapy.

The twin cytokines interleukin-34 and CSF-1: masterful conductors of macrophage homeostasis

Macrophages are specialized cells that control tissue homeostasis. They include non-resident and tissue-resident macrophage populations which are characterized by the expression of particular cell surface markers and the secretion of molecules with a wide range of biological functions. The differentiation and polarization of macrophages relies on specific growth factors and their receptors. Macrophage-colony stimulating factor (CSF-1) and interleukine-34 (IL-34), also known as "twin" cytokines, are part of this regluatory landscape. CSF-1 and IL-34 share a common receptor, the macrophage-colony stimulating factor receptor (CSF-1R), which is activated in a similar way by both factors and turns on identical signaling pathways. However, there is some discrete differential activation leading to specific activities. In this review, we disscuss recent progress in understanding of the role of the twin cytokines in macrophage differentiation, from their interaction with CSF-1R and the activation of signaling pathways, to their implication in macrophage polarization of non-resident and tissue-resident macrophages. A special focus on IL-34, its involvement in pathophsyiological contexts, and its potential as a theranostic target for macrophage therapy will be proposed.

Improving antitumor efficacy via combinatorial regimens of oncolytic virotherapy

As a promising therapeutic strategy, oncolytic virotherapy has shown potent anticancer efficacy in numerous pre-clinical and clinical trials. Oncolytic viruses have the capacity for conditional-replication within carcinoma cells leading to cell death via multiple mechanisms, including direct lysis of neoplasms, induction of immunogenic cell death, and elicitation of innate and adaptive immunity. In addition, these viruses can be engineered to express cytokines or chemokines to alter tumor microenvironments. Combination of oncolytic virotherapy with other antitumor therapeutic modalities, such as chemotherapy and radiation therapy as well as cancer immunotherapy can be used to target a wider range of tumors and promote therapeutic efficacy. In this review, we outline the basic biological characteristics of oncolytic viruses and the underlying mechanisms that support their use as promising antitumor drugs. We also describe the enhanced efficacy attributed to virotherapy combined with other drugs for the treatment of cancer.

Engineering Macrophages for Cancer Immunotherapy and Drug Delivery

Macrophages play an important role in cancer development and metastasis. Proinflammatory M1 macrophages can phagocytose tumor cells, while anti-inflammatory M2 macrophages such as tumor-associated macrophages (TAMs) promote tumor growth and invasion. Modulating the tumor immune microenvironment through engineering macrophages is efficacious in tumor therapy. M1 macrophages target cancerous cells and, therefore, can be used as drug carriers for tumor therapy. Herein, the strategies to engineer macrophages for cancer immunotherapy, such as inhibition of macrophage recruitment, depletion of TAMs, reprograming of TAMs, and blocking of the CD47-SIRPα pathway, are discussed. Further, the recent advances in drug delivery using M1 macrophages, macrophage-derived exosomes, and macrophage-membrane-coated nanoparticles are elaborated. Overall, there is still significant room for development in macrophage-mediated immune modulation and macrophage-mediated drug delivery, which will further enhance current tumor therapies against various malignant solid tumors, including drug-resistant tumors and metastatic tumors.

Multidirectional Strategies for Targeted Delivery of Oncolytic Viruses by Tumor Infiltrating Immune Cells

Oncolytic virus (OV) immunotherapy has demonstrated to be a promising approach in cancer treatment due to tumor-specific oncolysis. However, their clinical use so far has been largely limited due to the lack of suitable delivery strategies with high efficacy. Direct 'intratumoral' injection is the way to cross the hurdles of systemic toxicity, while providing local effects. Progress in this field has enabled the development of alternative way using 'systemic' oncolytic virotherapy for producing better results. One major potential roadblock to systemic OV delivery is the low virus persistence in the face of hostile immune system. The delivery challenge is even greater when attempting to target the oncolytic viruses into the entire tumor mass, where not all tumor cells are equally exposed to exactly the same microenvironment. The microenvironment of many tumors is known to be massively infiltrated with various types of leucocytes in both primary and metastatic sites. Interestingly, this intratumoral immune cell heterogeneity exhibits a degree of organized distribution inside the tumor bed as evidenced, for example, by the hypoxic tumor microenviroment where predominantly recruits tumor-associated macrophages. Although in vivo OV delivery seems complicated and challenging, recent results are encouraging for decreasing the limitations of systemically administered oncolytic viruses and an improved efficiency of oncolytic viral therapy in targeting cancerous tissues in vitro. Here, we review the latest developments of carrier cell-based oncolytic virus delivery using tumor-infiltrating immune cells with a focus on the main features of each cellular vehicle.

Oxygen sensing; a stunningly elegant molecular machinery highjacked in cancer

Oxygen is of fundamental importance for most living organisms, and the maintenance of oxygen homeostasis is a key physiological challenge for all large animals. Oxygen deprivation, hypoxia, is a critical component of many human diseases including cancer, heart disease, stroke, vascular disease, and anaemia. The discovery of oxygen sensing provides fundamental knowledge of a stunningly elegant molecular machinery; it also promises development of new therapeutics for serious diseases such as cancer. As a result of their impressive contributions to our understanding of the mechanisms by which cells sense oxygen and signal in hypoxia, Gregg Semenza, Peter Ratcliffe, and William Kaelin were awarded the Nobel Prize in 2019.

Transient Chimeric Ad5/37 Fiber Enhances NK-92 Carrier Cell-Mediated Delivery of Oncolytic Adenovirus Type 5 to Tumor Cells

Methods for customizing and improving virus vector tropism are limited. In this study, we introduce a microRNA (miRNA)-regulated molecular method to enhance vector transduction without genome alteration. Based on the importance of adenovirus (Ad) vectors for cancer and gene treatment, we exemplified this technology for an Ad type 5 (Ad5) vector temporally carrying a knob from Ad37. We constructed a producer cell line stably expressing a fused Ad5/37 chimeric fiber comprising the Ad5 shaft-tail and the Ad37 knob and a miRNA inhibiting Ad5 knob expression (HEK293-Ad5/37-miRNA). The chimeric Ad5/37 vector resulted in enhanced transduction rates in Ad37 adequately and Ad5 poorly transduced cells. Particularly, encapsidation of the oncolytic Ad5-human telomerase reverse transcriptase (hTERT) vector genome into the chimeric Ad5/37 capsid showed efficient transduction of NK-92 carrier cells. These infected carrier cells then delivered the oncolytic vector to tumor cells, which resulted in enhanced Ad5-hTERT-mediated tumor cell killing. We show that this transiently capsid-modified chimeric vector carrying an Ad5 genome displayed higher transduction efficiencies of natural killer cell-derived NK-92 cells utilized as carriers in cancer immune therapy. In summary, transiently modified adenoviral vectors will have important implications for cancer and gene therapy.

Expanding the Spectrum of Adenoviral Vectors for Cancer Therapy

Adenoviral vectors (AdVs) have attracted much attention in the fields of vaccine development and treatment for diseases such as genetic disorders and cancer. In this review, we discuss the utility of AdVs in cancer therapies. In recent years, AdVs were modified as oncolytic AdVs (OAs) that possess the characteristics of cancer cell-specific replication and killing. Different carriers such as diverse cells and extracellular vesicles are being explored for delivering OAs into cancer sites after systemic administration. In addition, there are also various strategies to improve cancer-specific replication of OAs, mainly through modifying the early region 1 (E1) of the virus genome. It has been documented that oncolytic viruses (OVs) function through stimulating the immune system, resulting in the inhibition of cancer progression and, in combination with classical immune modulators, the anti-cancer effect of OAs can be even further enforced. To enhance the cancer treatment efficacy, OAs are also combined with other standard treatments, including surgery, chemotherapy and radiotherapy. Adenovirus type 5 (Ad5) has mainly been explored to develop vectors for cancer treatment with different modulations. Only a limited number of the more than 100 identified AdV types were converted into OAs and, therefore, the construction of an adenovirus library for the screening of potential novel OA candidates is essential. Here, we provide a state-of-the-art overview of currently performed and completed clinic trials with OAs and an adenovirus library, providing novel possibilities for developing innovative adenoviral vectors for cancer treatment.

Bone sarcomas in the immunotherapy era

Bone sarcomas are primary bone tumours found mainly in children and adolescents, as osteosarcoma and Ewing's sarcoma, and in adults in their 40s as chondrosarcoma. The last four decades the development of therapeutic approaches was based on drug combinations have shown no real improvement in overall survival. Recently oncoimmunology has allowed a better understand of the crucial role played by the immune system in the oncologic process. This led to clinical trials with the aim of reprogramming the immune system to facilitate cancer cell recognition. Immune infiltrates of bone sarcomas have been characterized and their molecular profiling identified as immune therapeutic targets. Unfortunately, the clinical responses in trials remain anecdotal but highlight the necessity to improve the characterization of tumour micro-environment to unlock the immunotherapeutic response, especially in their paediatric forms. Bone sarcomas have entered the immunotherapy era and here we overview the recent developments in immunotherapies in these sarcomas. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Key genes with prognostic values in suppression of osteosarcoma metastasis using comprehensive analysis

BACKGROUND

Osteosarcoma is a primary malignant tumor originating from mesenchymal tissue, with a poor distant metastasis prognosis. The molecular mechanisms of osteosarcoma metastasis are extremely complicated.

METHODS

A public data series (GSE21257) was used to identify differentially expressed genes (DEGs) in osteosarcoma patients that did, or did not, develop metastases. Functional enrichment analysis, a protein-protein interaction network, and survival analysis of DEGs were performed. DEGs with a prognostic value were considered as candidate genes and their functional predictions, different expression in normal and malignant tissues, and immune infiltration were analyzed.

RESULTS

The DEGs were mainly enriched in the immune response. Three candidate genes (ALOX5AP, CD74, and FCGR2A) were found, all of which were expressed at higher levels in lungs and lymph nodes than in matched cancer tissues and were probably expressed in the microenvironment.

CONCLUSIONS

Candidate genes can help us understand the molecular mechanisms underlying osteosarcoma metastasis and provide targets for future research.

Harnessing tumor-associated macrophages as aids for cancer immunotherapy

Cancer immunotherapies that engage immune cells to fight against tumors are proving to be powerful weapons in combating cancer and are becoming increasingly utilized in the clinics. However, for the majority of patients with solid tumors, little or no progress has been seen, presumably due to lack of adequate approaches that can reprogram the local immunosuppressive tumor milieu and thus reinvigorate antitumor immunity. Tumor-associated macrophages (TAMs), which abundantly infiltrate most solid tumors, could contribute to tumor progression by stimulating proliferation, angiogenesis, metastasis, and by providing a barrier against antitumor immunity. Initial TAMs-targeting strategies have shown efficacy across therapeutic modalities and tumor types in both preclinical and clinical studies. TAMs-targeted therapeutic approaches can be roughly divided into those that deplete TAMs and those that modulate TAMs activities. We here reviewed the mechanisms by which macrophages become immunosuppressive and compromise antitumor immunity. TAMs-focused therapeutic strategies are also summarized.

Virus oncolíticos: un arma contra el cáncer

Introducción. Los virus oncolíticos son virus atenuados, mutados o que por naturaleza se dirigen y matan específicamente células tumorales, sin afectar a las células normales. La administración intratumoral del virus ofrece la oportunidad de tratar el tumor primario pero no focos metastásicos, los cuales pueden ser alcanzados mediante la administración intravenosa. Sin embargo, su eficiencia puede disminuir por la presencia de una respuesta inmunológica preexistente en los sujetos tratados.Objetivo. Exponer las técnicas utilizadas para envolver y transportar los virus con el fin de eludir el sistema inmunológico antes de que el virus llegue al tumor.Materiales y métodos. Se realizó una búsqueda narrativa de la literatura original y de revisión en las bases de datos PubMed, JSTOR y EBSCO sobre métodos o técnicas utilizadas para el tratamiento del cáncer mediante el uso de virus oncolíticos.Resultados. La formación de nanocomplejos entre los virus oncolíticos y biopolímeros —ya sea mediante la unión química o mediante la unión a través de interacciones electrostáticas o el uso de micropartículas, células transportadoras, liposomas, ultrasonido o terapias combinadas– es eficaz para evitar la respuesta inmunológica del huésped contra el virus.Conclusión. Para evitar la respuesta inmunológica del huésped contra los virus oncolíticos se han desarrollo diversos métodos que permiten la liberación controlada y especifica de los mismos. Sin embargo, debido a la diversidad de los virus, se debe tener en cuenta que la eficacia de los métodos de protección y transporte depende de las características bioquímicas tanto del biomaterial como del virus.

Oncolytic viruses: overcoming translational challenges

Oncolytic virotherapy (OVT) is a promising approach in which WT or engineered viruses selectively replicate and destroy tumor cells while sparing normal ones. In the last two decades, different oncolytic viruses (OVs) have been modified and tested in a number of preclinical studies, some of which have led to clinical trials in cancer patients. These clinical trials have revealed several critical limitations with regard to viral delivery, spread, resistance, and antiviral immunity. Here, we focus on promising research strategies that have been developed to overcome the aforementioned obstacles. Such strategies include engineering OVs to target a broad spectrum of tumor cells while evading the immune system, developing unique delivery mechanisms, combining other immunotherapeutic agents with OVT, and using clinically translatable mouse tumor models to potentially translate OVT more readily into clinical settings.

Calcium Bisphosphonate Nanoparticles with Chelator-Free Radiolabeling to Deplete Tumor-Associated Macrophages for Enhanced Cancer Radioisotope Therapy

Tumor-associated macrophages (TAMs) are often related with poor prognosis after radiotherapy. Depleting TAMs may thus be a promising method to improve the radio-therapeutic efficacy. Herein, we report a biocompatible and biodegradable nanoplatform based on calcium bisphosphonate (CaBP-PEG) nanoparticles for chelator-free radiolabeling chemistry, effective in vivo depletion of TAMs, and imaging-guided enhanced cancer radioisotope therapy (RIT). It is found that CaBP-PEG nanoparticles prepared via a mineralization method with poly(ethylene glycol) (PEG) coating could be labeled with various radioisotopes upon simple mixing, including gamma-emitting ^99mTc for single-photon-emission computed tomography (SPECT) imaging, as well as beta-emitting ³²P as a therapeutic radioisotope for RIT. Upon intravenous injection, CaBP(^99mTc)-PEG nanoparticles exhibit efficient tumor homing, as evidenced by SPECT imaging. Owning to the function of bisphosphonates as clinical drugs to deplete TAMs, suppressed angiogenesis, normalized tumor vasculatures, enhanced intratumoral perfusion, and relieved tumor hypoxia are observed after TAM depletion induced by CaBP-PEG. Such modulated tumor microenvironment appears to be highly favorable for cancer RIT using CaBP(³²P)-PEG as the radio-therapeutic agent, which offers excellent synergistic therapeutic effect in inhibiting the tumor growth. With great biocompatibility and multifunctionalities, such CaBP-PEG nanoparticles constituted by Ca²⁺ and a clinical drug would be rather attractive for clinical translation.

Mathematical modelling of a hypoxia-regulated oncolytic virus delivered by tumour-associated macrophages

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A continuum model of macrophages releasing an oncolytic virus within a tumour spheroid.

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Predictive modelling of this treatment given in combination with radiotherapy.

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Investigation into how radiotherapy and oncolytic virotherapy should be scheduled.

Tumour hypoxia has long presented a challenge for cancer therapy: Poor vascularisation in hypoxic regions hinders both the delivery of chemotherapeutic agents and the response to radiotherapy, and hypoxic cancer cells that survive treatment can trigger tumour regrowth after treatment has ended. Tumour-associated macrophages are attractive vehicles for drug delivery because they localise in hypoxic areas of the tumour. In this paper, we derive a mathematical model for the infiltration of an in vitro tumour spheroid by macrophages that have been engineered to release an oncolytic adenovirus under hypoxic conditions. We use this model to predict the efficacy of treatment schedules in which radiotherapy and the engineered macrophages are given in combination. Our work suggests that engineered macrophages should be introduced immediately after radiotherapy for maximum treatment efficacy. Our model provides a framework that may guide future experiments to determine how multiple rounds of radiotherapy and macrophage virotherapy should be coordinated to maximise therapeutic responses.

Harnessing Biology to Deliver Therapeutic and Imaging Entities via Cell-Based Methods

The accumulation of therapeutic and imaging agents at sites of interest is critical to their efficacy. Similarly, off-target effects (especially toxicity) are a major liability for these entities. For this reason, the use of delivery vehicles to improve the distribution characteristics of bio-active agents has become ubiquitous in the field. However, the majority of traditionally employed, cargo-bearing platforms rely on passive accumulation. Even in cases where "targeting" functionalities are used, the agents must first reach the site in order for the ligand-receptor interaction to occur. The next stage of vehicle development is the use of "recruited" entities, which respond to biological signals produced in the tissues to be targeted, resulting in improved specificities. Recently, many advances have been made in the utilization of cells as delivery agents. They are biocompatible, exhibit excellent circulation lifetimes and tissue penetration capabilities, and respond to chemotactic signals. In this Minireview, we will explore various cell types, modifications, and applications where cell-based delivery agents are used.

Potentiating prostate cancer immunotherapy with oncolytic viruses

The clinical effectiveness of immunotherapies for prostate cancer remains subpar compared with that for other cancers. The goal of most immunotherapies is the activation of immune effectors, such as T cells and natural killer cells, as the presence of these activated mediators positively correlates with patient outcomes. Clinical evidence shows that prostate cancer is immunogenic, accessible to the immune system, and can be targeted by antitumour immune responses. However, owing to the detrimental effects of prostate-cancer-associated immunosuppression, even the newest immunotherapeutic approaches fail to initiate the clinically desired antitumour immune reaction. Oncolytic viruses, originally used for their preferential cancer-killing activity, are now being recognized for their ability to overturn cancer-associated immune evasion and promote otherwise absent antitumour immunity. This oncolytic-virus-induced subversion of tumour-associated immunosuppression can potentiate the effectiveness of current immunotherapeutics, including immune checkpoint inhibitors (for example, antibodies against programmed cell death protein 1 (PD1), programmed cell death 1 ligand 1 (PDL1), and cytotoxic T lymphocyte antigen 4 (CTLA4)) and chemotherapeutics that induce immunogenic cell death (for example, doxorubicin and oxaliplatin). Importantly, oncolytic-virus-induced antitumour immunity targets existing prostate cancer cells and also establishes long-term protection against future relapse. Hence, the strategic use of oncolytic viruses as monotherapies or in combination with current immunotherapies might result in the next breakthrough in prostate cancer immunotherapy.

Oncolytic virus delivery: from nano-pharmacodynamics to enhanced oncolytic effect

With the advancement of a growing number of oncolytic viruses (OVs) to clinical development, drug delivery is becoming an important barrier to overcome for optimal therapeutic benefits. Host immunity, tumor microenvironment and abnormal vascularity contribute to inefficient vector delivery. A number of novel approaches for enhanced OV delivery are under evaluation, including use of nanoparticles, immunomodulatory agents and complex viral–particle ligands along with manipulations of the tumor microenvironment. This field of OV delivery has quickly evolved to bioengineering of complex nanoparticles that could be deposited within the tumor using minimal invasive image-guided delivery. Some of the strategies include ultrasound (US)-mediated cavitation-enhanced extravasation, magnetic viral complexes delivery, image-guided infusions with focused US and targeting photodynamic virotherapy. In addition, strategies that modulate tumor microenvironment to decrease extracellular matrix deposition and increase viral propagation are being used to improve tumor penetration by OVs. Some involve modification of the viral genome to enhance their tumoral penetration potential. Here, we highlight the barriers to oncolytic viral delivery, and discuss the challenges to improving it and the perspectives of establishing new modes of active delivery to achieve enhanced oncolytic effects.

Quantitative Temporal in Vivo Proteomics Deciphers the Transition of Virus-Driven Myeloid Cells into M2 Macrophages

Myeloid cells play a central role in the context of viral eradication, yet precisely how these cells differentiate throughout the course of acute infections is poorly understood. In this study, we have developed a novel quantitative temporal in vivo proteomics (QTiPs) platform to capture proteomic signatures of temporally transitioning virus-driven myeloid cells directly in situ, thus taking into consideration host–virus interactions throughout the course of an infection. QTiPs, in combination with phenotypic, functional, and metabolic analyses, elucidated a pivotal role for inflammatory CD11b⁺, Ly6G^–, Ly6C^high-low cells in antiviral immune response and viral clearance. Most importantly, the time-resolved QTiPs data set showed the transition of CD11b⁺, Ly6G^–, Ly6C^high-low cells into M2-like macrophages, which displayed increased antigen-presentation capacities and bioenergetic demands late in infection. We elucidated the pivotal role of myeloid cells in virus clearance and show how these cells phenotypically, functionally, and metabolically undergo a timely transition from inflammatory to M2-like macrophages in vivo. With respect to the growing appreciation for in vivo examination of viral–host interactions and for the role of myeloid cells, this study elucidates the use of quantitative proteomics to reveal the role and response of distinct immune cell populations throughout the course of virus infection.