Strategies to achieve systemic delivery of therapeutic cells and microbes to tumors

Silk fibroin microgels as a platform for cell microencapsulation

Cell microencapsulation has been utilized for years as a means of cell shielding from the external environment while facilitating the transport of gases, general metabolites, and secretory bioactive molecules at once. In this light, hydrogels may support the structural integrity and functionality of encapsulated biologics whereas ensuring cell viability and function and releasing potential therapeutic factors once in situ. In this work, we describe a straightforward strategy to fabricate silk fibroin (SF) microgels (µgels) and encapsulate cells into them. SF µgels (size ≈ 200 µm) were obtained through ultrasonication-induced gelation of SF in a water-oil emulsion phase. A thorough physicochemical (SEM analysis, and FT-IR) and mechanical (microindentation tests) characterization of SF µgels were carried out to assess their nanostructure, porosity, and stiffness. SF µgels were used to encapsulate and culture L929 and primary myoblasts. Interestingly, SF µgels showed a selective release of relatively small proteins (e.g., VEGF, molecular weight, M_W = 40 kDa) by the encapsulated primary myoblasts, while bigger (macro)molecules (M_W = 160 kDa) were hampered to diffusing through the µgels. This article provided the groundwork to expand the use of SF hydrogels into a versatile platform for encapsulating relevant cells able to release paracrine factors potentially regulating tissue and/or organ functions, thus promoting their regeneration.

Development of oncolytic viruses for cancer therapy

Oncolytic virotherapy is a therapeutic approach that uses replication-competent viruses to kill cancers. The ability of oncolytic viruses to selectively replicate in cancer cells leads to direct cell lysis and induction of anticancer immune response. Like other anticancer therapies, oncolytic virotherapy has several limitations such as viral delivery to the target, penetration into the tumor mass, and antiviral immune responses. This review provides an insight into the different characteristics of oncolytic viruses (natural and genetically modified) that contribute to effective applications of oncolytic virotherapy in preclinical and clinical trials, and strategies to overcome the limitations. The potential of oncolytic virotherapy combining with other conventional treatments or cancer immunotherapies involving immune checkpoint inhibitors and CAR-T therapy could form part of future multimodality treatment strategies.

A bibliometric review of oncolytic virus research as a novel approach for cancer therapy

Background

In recent years, oncolytic viruses (OVs) have drawn attention as a novel therapy to various types of cancers, both in clinical and preclinical cancer studies all around the world. Consequently, researchers have been actively working on enhancing cancer therapy since the early twentieth century. This study presents a systematic review of the literature on OVs, discusses underlying research clusters and, presents future directions of OVs research.

Methods

A total of 1626 published articles related to OVs as cancer therapy were obtained from the Web of Science (WoS) database published between January 2000 and March 2020. Various aspects of OVs research, including the countries/territories, institutions, journals, authors, citations, research areas, and content analysis to find trending and emerging topics, were analysed using the bibliometrix package in the R-software.

Results

In terms of the number of publications, the USA based researchers were the most productive (n = 611) followed by Chinese (n = 197), and Canadian (n = 153) researchers. The Molecular Therapy journal ranked first both in terms of the number of publications (n = 133) and local citations (n = 1384). The most prominent institution was Mayo Clinic from the USA (n = 117) followed by the University of Ottawa from Canada (n = 72), and the University of Helsinki from Finland (n = 63). The most impactful author was Bell J.C with the highest number of articles (n = 67) and total local citations (n = 885). The most impactful article was published in the Cell journal. In addition, the latest OVs research mainly builds on four research clusters.

Conclusion

The domain of OVs research has increased at a rapid rate from 2000 to 2020. Based on the synthesis of reviewed studies, adenovirus, herpes simplex virus, reovirus, and Newcastle disease virus have shown potent anti-cancer activity. Developed countries such as the USA, Canada, the UK, and Finland were the most productive, hence, contributed most to this field. Further collaboration will help improve the clinical research translation of this therapy and bring benefits to cancer patients worldwide.

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.

Updates to the antitumor mechanism of oncolytic virus

Oncolytic viruses (OVs) are promising new therapeutic agents in the field of malignant tumor treatment. OVs can achieve the goal of targeted therapy by selectively killing tumor cells and inducing specific antitumor immunity. The key roles of OVs are tumor targeting and tumor killing mechanisms. Recently, molecular biotechnology has been used to optimize the transformation of wild virus strains in order to ensure a stronger oncolytic effect and lower adverse reactions, to enable testing in clinical trials as an antitumor drug. The main purpose of this review is to provide a description of oncolytic mechanisms, clinical studies, combination therapies, current challenges, and future prospects of OVs.

White paper on microbial anti-cancer therapy and prevention

In this White Paper, we discuss the current state of microbial cancer therapy. This paper resulted from a meeting ('Microbial Based Cancer Therapy') at the US National Cancer Institute in the summer of 2017. Here, we define 'Microbial Therapy' to include both oncolytic viral therapy and bacterial anticancer therapy. Both of these fields exploit tumor-specific infectious microbes to treat cancer, have similar mechanisms of action, and are facing similar challenges to commercialization. We designed this paper to nucleate this growing field of microbial therapeutics and increase interactions between researchers in it and related fields. The authors of this paper include many primary researchers in this field. In this paper, we discuss the potential, status and opportunities for microbial therapy as well as strategies attempted to date and important questions that need to be addressed. The main areas that we think will have the greatest impact are immune stimulation, control of efficacy, control of delivery, and safety. There is much excitement about the potential of this field to treat currently intractable cancer. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other biological or small molecule drugs. By better understanding and controlling these mechanisms, we will create new therapies that will become integral components of cancer care.

Oncolytic virotherapy

Oncolytic virotherapy is an emerging technology that uses engineered viruses to treat malignancies. Viruses can be designed with biological specificity to infect cancerous cells preferentially, and to replicate in these cells exclusively. Malignant cells may be killed directly by overwhelming viral infection and lysis, which releases additional viral particles to infect neighboring cells and distant metastases. Viral infections may also activate the immune system, unmask stealthy tumor antigens, and aid the immune system to recognize and attack neoplasms. Delivery of live virus particles is potentially complex, and may require the expertise of the interventional community.

Crosstalk between immune cell and oncolytic vaccinia therapy enhances tumor trafficking and antitumor effects

The combination of an oncolytic virus, that directly destroys tumor cells and mediates an acute immune response, with an immune cell therapy, capable of further enlisting and enhancing the host immune response, has the potential to create a potent therapeutic effect. We have previously developed several strategies for optimizing the delivery of oncolytic vaccinia virus vectors to their tumor targets, including the use of immune cell-based carrier vehicles and the incorporation of mutations that increase production of the enveloped form of vaccinia (extracellular enveloped viral (EEV)) that is better adapted to spread within a host. Here, we initially combine these approaches to create a novel therapeutic, consisting of an immune cell (cytokine-induced killer, CIK) preloaded with an oncolytic virus that is EEV enhanced. This resulted in direct interaction between the viral and immune cell components with each assisting the other in directing the therapy to the tumor and so enhancing the antitumor effects. This effect could be further improved through CCL5 expression from the virus. The resulting multicomponent therapy displays the ability for synergistic crosstalk between components, so significantly enhancing tumor trafficking and antitumor effects.

Intravenous injection of irradiated tumor cell vaccine carrying oncolytic adenovirus suppressed the growth of multiple lung tumors in a mouse squamous cell carcinoma model

BACKGROUND

Although cancer therapy using replication-selective oncolytic adenoviruses has been available for many years, its anti-tumor efficacy is suboptimal as a result of low and nonspecific infectivity that depends on coxsackie adenovirus receptor expression of the target cancer and normal cells, and generation of an anti-adenovirus neutralizing antibody. In addition, concerns of triggering a severe innate immune response against the adenovirus limit the systemic administration. We developed the carrier cell-based oncolytic virus system (CBOVS) using irradiated tumor cells as carrier cells and concealing the adenovirus (Ad-IAI.3B) inside to improve the specific infectivity. We investigated the anti-tumor effect of CBOVS in a multiple lung tumor mouse model.

METHODS

The ability of CBOVS to infect Ad-IAI.3B to the target cancer cells was examined in vitro in the presence of anti-adenovirus antibodies. To evaluate the systemic effect of CBOVS, we intravenously injected CBOVS into mice with lung tumors (KLN205 cell lines).

RESULTS

CBOVS enhanced the infectivity of Ad-IAI.3B to tumor cells in the presence of anti-adenovirus antibodies in vitro. Intravenous injections of CBOVS produced an accumulation of the adenovirus in the lung-bearing tumors and produced a strong anti-tumor effect in vivo. Furthermore, lymphocytes collected from the CBOVS-treated mice induced an increase in cytokines related to the Th1 response (interferon-γ, interleukin-12) by pulsing with KLN205.

CONCLUSIONS

These findings suggest that CBOVS could protect adenoviruses from neutralizing antibodies and systemically deliver them to lung tumors. Furthermore, CBOVS appears to have potential as a tumor cell vaccine that activates cytotoxic immunity against cancer cells.

Non-invasive cell tracking in cancer and cancer therapy

Cell-based therapy holds great promise for cancer treatment. The ability to non-invasively track the delivery of various therapeutic cells (e.g. T cells and stem cells) to the tumor site, and/or subsequent differentiation/proliferation of these cells, would allow better understanding of the mechanisms of cancer development and intervention. This brief review will summarize the various methods for non-invasive cell tracking in cancer and cancer therapy. In general, there are two approaches for cell tracking: direct (cells are labeled with certain tags that can be detected directly with suitable imaging equipment) and indirect cell labeling (which typically uses reporter genes approach). The techniques for tracking various cell types (e.g. immune cells, stem cells, and cancer cells) in cancer are described, which include fluorescence, bioluminescence, positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI). Non-invasive tracking of immune and stem cells were primarily intended for (potential) cancer therapy applications while tracking of cancer cells could further our understanding of cancer development and tumor metastasis. Safety is a major concern for future clinical applications and the ideal imaging modality for tracking therapeutic cells in cancer patients requires the imaging tags to be non-toxic, biocompatible, and highly specific. Each imaging modality has its advantages and disadvantages and they are more complementary than competitive. MRI, radionuclide-based imaging techniques, and reporter gene-based approaches will each have their own niches towards the same ultimate goal: personalized medicine for cancer patients.

Cell carriers for oncolytic viruses: Fed Ex for cancer therapy

Oncolytic viruses delivered directly into the circulation face many hazards that impede their localization to, and infection of, metastatic tumors. Such barriers to systemic delivery could be overcome if couriers, which confer both protection, and tumor localization, to their viral cargoes, could be found. Several preclincal studies have shown that viruses can be loaded into, or onto, different types of cells without losing the biological activity of either virus or cell carrier. Importantly, such loading can significantly protect the viruses from immune-mediated virus-neutralizing activities, including antiviral antibody. Moreover, an impressive portfolio of cellular vehicles, which have some degree of tropism for tumor cells themselves, or for the biological properties associated with the tumor stroma, is already available. Therefore, it will soon be possible to initiate clinical protocols to test the hypopthesis that cell-mediated delivery can permit efficient shipping of oncolytic viruses from the loading bay (the production laboratory) directly to the tumor in immune-competent patients with metastatic disease.

CNOB/ChrR6, a new prodrug enzyme cancer chemotherapy

We report the discovery of a new prodrug, 6-chloro-9-nitro-5-oxo-5H-benzo(a)phenoxazine (CNOB). This prodrug is efficiently activated by ChrR6, the highly active prodrug activating bacterial enzyme we have previously developed. The CNOB/ChrR6 therapy was effective in killing several cancer cell lines in vitro. It also efficiently treated tumors in mice with up to 40% complete remission. 9-Amino-6-chloro-5H-benzo(a)phenoxazine-5-one (MCHB) was the only product of CNOB reduction by ChrR6. MCHB binds DNA; at nonlethal concentration, it causes cell accumulation in the S phase, and at lethal dose, it induces cell surface Annexin V and caspase-3 and caspase-9 activities. Further, MCHB colocalizes with mitochondria and disrupts their electrochemical potential. Thus, killing by CNOB involves MCHB, which likely induces apoptosis through the mitochondrial pathway. An attractive feature of the CNOB/ChrR6 regimen is that its toxic product, MCHB, is fluorescent. This feature proved helpful in in vitro studies because simple fluorescence measurements provided information on the kinetics of CNOB activation within the cells, MCHB killing mechanism, its generally efficient bystander effect in cells and cell spheroids, and its biodistribution. The emission wavelength of MCHB also permitted its visualization in live animals, allowing noninvasive qualitative imaging of MCHB in mice and the tumor microenvironment. This feature may simplify exploration of barriers to the penetration of MCHB in tumors and their amelioration.

Integrating the biological characteristics of oncolytic viruses and immune cells can optimize therapeutic benefits of cell-based delivery

Despite significant advances in the development of tumor-selective agents, strategies for effective delivery of these agents across biological barriers to cells within the tumor microenvironment has been limiting. One tactical approach to overcoming biological barriers is to use cells as delivery vehicles, and a variety of different cell types have been investigated with a range of agents. In addition to transporting agents with targeted delivery, cells can also produce their own tumoricidal effect, conceal a payload from an immune response, amplify a selective agent at the target site and facilitate an antitumor immune response. We have reported a therapeutic combination consisting of cytokine induced killer cells and an oncolytic vaccinia virus with many of these features that led to therapeutic synergy in animal models of human cancer. The synergy was due to the interaction of the two agents to enhance the antitumor benefits of each individual component. As both of these agents display broad tumor-targeting potential and possess unique tumor killing mechanisms, together they were able to recognize and destroy a far greater number of malignant cells within the heterogeneous tumor than either agent alone. Effective cancer therapy will require recognition and elimination of the root of the disease, the cancer stem cell, and the combination of CIK cells and oncolytic vaccinia viruses has this potential. To create effective tumor-selective agents the viruses are modified to take advantage of the unique biology of the cancer cell. Similarly, if we are to develop targeted therapies that are sufficiently multifaceted to eliminate cancer cells at all stages of disease, we should integrate the virus into the unique biology of the cell delivery vehicle.

Oncolytic virotherapy: molecular targets in tumor-selective replication and carrier cell-mediated delivery of oncolytic viruses

Tremendous advances have been made in developing oncolytic viruses (OVs) in the last few years. By taking advantage of current knowledge in cancer biology and virology, specific OVs have been genetically engineered to target specific molecules or signal transduction pathways in cancer cells in order to achieve efficient and selective replication. The viral infection and amplification eventually induce cancer cells into cell death pathways and elicit host antitumor immune responses to further help eliminate cancer cells. Specifically targeted molecules or signaling pathways (such as RB/E2F/p16, p53, IFN, PKR, EGFR, Ras, Wnt, anti-apoptosis or hypoxia) in cancer cells or tumor microenvironment have been studied and dissected with a variety of OVs such as adenovirus, herpes simplex virus, poxvirus, vesicular stomatitis virus, measles virus, Newcastle disease virus, influenza virus and reovirus, setting the molecular basis for further improvements in the near future. Another exciting new area of research has been the harnessing of naturally tumor-homing cells as carrier cells (or cellular vehicles) to deliver OVs to tumors. The trafficking of these tumor-homing cells (stem cells, immune cells and cancer cells), which support proliferation of the viruses, is mediated by specific chemokines and cell adhesion molecules and we are just beginning to understand the roles of these molecules. Finally, we will highlight some avenues deserving further study in order to achieve the ultimate goals of utilizing various OVs for effective cancer treatment.

Targeting of interferon-beta to produce a specific, multi-mechanistic oncolytic vaccinia virus

BACKGROUND

Oncolytic viruses hold much promise for clinical treatment of many cancers, but a lack of systemic delivery and insufficient tumor cell killing have limited their usefulness. We have previously demonstrated that vaccinia virus strains are capable of systemic delivery to tumors in mouse models, but infection of normal tissues remains an issue. We hypothesized that interferon-beta (IFN-beta) expression from an oncolytic vaccinia strain incapable of responding to this cytokine would have dual benefits as a cancer therapeutic: increased anticancer effects and enhanced virus inactivation in normal tissues. We report the construction and preclinical testing of this virus.

METHODS AND FINDINGS

In vitro screening of viral strains by cytotoxicity and replication assay was coupled to cellular characterization by phospho-flow cytometry in order to select a novel oncolytic vaccinia virus. This virus was then examined in vivo in mouse models by non-invasive imaging techniques. A vaccinia B18R deletion mutant was selected as the backbone for IFN-beta expression, because the B18R gene product neutralizes secreted type-I IFNs. The oncolytic B18R deletion mutant demonstrated IFN-dependent cancer selectivity and efficacy in vitro, and tumor targeting and efficacy in mouse models in vivo. Both tumor cells and tumor-associated vascular endothelial cells were targeted. Complete tumor responses in preclinical models were accompanied by immune-mediated protection against tumor rechallenge. Cancer selectivity was also demonstrated in primary human tumor explant tissues and adjacent normal tissues. The IFN-beta gene was then cloned into the thymidine kinase (TK) region of this virus to create JX-795 (TK-/B18R-/IFN-beta+). JX-795 had superior tumor selectivity and systemic intravenous efficacy when compared with the TK-/B18R- control or wild-type vaccinia in preclinical models.

CONCLUSIONS

By combining IFN-dependent cancer selectivity with IFN-beta expression to optimize both anticancer effects and normal tissue antiviral effects, we were able to achieve, to our knowledge for the first time, tumor-specific replication, IFN-beta gene expression, and efficacy following systemic delivery in preclinical models.

Myxoma virus and oncolytic virotherapy: a new biologic weapon in the war against cancer

Oncolytic virotherapy is an innovative alternative to more conventional cancer therapies. The ability of some viruses to specifically target and kill malignant cancerous cells while leaving normal tissue unscathed has opened a large repertoire of new and selective cancer killing therapeutic candidates. Poxviruses, such as vaccinia virus, have a long history of use in humans as live vaccines and have more recently been studied as potential platforms for delivery of immunotherapeutics and attenuated variants of vaccinia have been explored as oncolytic candidates. In contrast, the poxvirus myxoma virus is a novel oncolytic candidate that has no history of use in humans directly, as it has a distinct and absolute host species tropism to lagomorphs (rabbits). Myxoma virus has been recently shown to be able to also selectively infect and kill human tumor cells, a unique tropism that is linked to dysregulated intracellular signalling pathways found in the majority of human cancers. This review outlines the existing knowledge on the tropism of myxoma virus for human cancer cells, as well as preclinical data exhibiting its ability to infect and clear tumors in animal models of cancer. This is an exciting new therapeutic option for treating cancer, and myxoma virus joins a growing group of oncolytic virus candidates that are being developed as a new class of cancer therapies in man.

Endothelial progenitor cells as cellular vehicles to deliver oncolytic virus therapies to metastatic tumors: the "Trojan horse" approach

In view of the limited success of available treatment modalities for metastatic tumor, alternative and complementary strategies need to be developed. Oncolytic viruses are capable of selective replication in malignant cells and therefore offer levels of potency and specificity that are potentially far higher than conventional treatments for tumor. However, lack of systemic delivery technique for therapeutic viruses impacts their application in treating patients with multiple disseminated metastases. Recent studies have demonstrated that when being transplanted, endothelial progenitor cells can migrate via peripheral blood and home exclusively to the site of tumor neovasculature. We hypothesized that endothelial progenitor cells can act as "Trojan horse" to systemically deliver oncolytic virus to metastases in order to inhibit tumor neovascularization formation and eventually eradicate the metastatic tumor.

Recent advances on the molecular mechanisms involved in the drug resistance of cancer cells and novel targeting therapies

This review summarizes the recent knowledge obtained on the molecular mechanisms involved in the intrinsic and acquired resistance of cancer cells to current cancer therapies. We describe the cascades that are often altered in cancer cells during cancer progression that may contribute in a crucial manner to drug resistance and disease relapse. The emphasis is on the implication of ATP-binding cassette (ABC) multidrug efflux transporters in drug disposition and antiapoptotic factors, including epidermal growth factor receptor cascades and deregulated enzymes in ceramide metabolic pathways. The altered expression and activity of these signaling elements may have a critical role in the resistance of cancer cells to cytotoxic effects induced by diverse chemotherapeutic drugs and cancer recurrence. Of therapeutic interest, new strategies for reversing the multidrug resistance and developing more effective clinical treatments against the highly aggressive, metastatic, and recurrent cancers, based on the molecular targeting of the cancer progenitor cells and their further differentiated progeny, are also described.