Oncolytic viral anti-cancer therapy: a magic bullet?

Viral expression of NE/PPE enhances anti-colorectal cancer efficacy of oncolytic adenovirus by promoting TAM M1 polarization to reverse insufficient effector memory/effector CD8+ T cell infiltration

BACKGROUND

Oncolytic adenoviruses are among the most widely utilized oncolytic viruses due to their notable anti-tumor and gene expression capabilities, and modification of ADVs to create armed adenoviruses remains a popular research direction. Nonetheless, immune suppression triggered by ADV and targeted enhancements based on this limitation have been relatively unexplored.

METHODS

Flow cytometry was employed to assess immune infiltration in the tumor microenvironment following ADV therapy. Targeted novel recombinant oncolytic viruses, ADVNE and ADVPPE, were designed, and their antitumor efficacy, safety, and ability to reshape immune infiltration were evaluated in both subcutaneous tumor models in mice and in vitro experiments. Immune cell depletion assays confirmed the critical role of macrophages. The impact of HMGB1 on macrophage polarization was investigated using shRNA, qRT-PCR, ELISA, and flow cytometry. Furthermore, the importance of TLR4 and its downstream pathways was validated through immunoprecipitation, Western blotting, homozygous knockout mice, and TLR4 inhibitors.

RESULTS

We demonstrated that ADV limits the infiltration of effector memory/effector CD8 + T cells (TEM/TE) within the tumor microenvironment. To address this, we leveraged the strong capacity of NE or PPE to recruit TEM/TE by constructing novel recombinant oncolytic adenoviruses, ADVNE or ADVPPE, armed with NE or PPE. These recombinant viruses induce pyroptosis in colorectal cancer cells accompanied by the release of HMGB1. HMGB1 binds to TLR4 on the surface of macrophages, activating the MyD88-NFκB-NLRP3 (ASC) pathway and promoting M1 polarization of TAMs, thereby increasing TEM/TE cell infiltration and enhancing antitumor efficacy.

CONCLUSIONS

In summary, this study presents the development of the novel oncolytic adenoviruses ADVNE and ADVPPE with enhanced anti-tumor efficacy and provides an in-depth exploration of their specific anti-tumor mechanisms. These findings indicate promising clinical therapeutic prospects and offer new insights for advancing oncolytic adenovirus therapies.

Polymeric oncolytic adenovirus for cancer gene therapy

Oncolytic adenovirus (Ad) vectors present a promising modality to treat cancer. Many clinical trials have been done with either naked oncolytic Ad or combination with chemotherapies. However, the systemic injection of oncolytic Ad in clinical applications is restricted due to significant liver toxicity and immunogenicity. To overcome these issues, Ad has been engineered physically or chemically with numerous polymers for shielding the Ad surface, accomplishing extended blood circulation time and reduced immunogenicity as well as hepatotoxicity. In this review, we describe and classify the characteristics of polymer modified oncolytic Ad following each strategy for cancer treatment. Furthermore, this review concludes with the highlights of various polymer-coated Ads and their prospects, and directions for future research.

Mechanism of tumor remission by cytomegalovirus in a murine lymphoma model: evidence for involvement of virally induced cellular interleukin-15

A murine model of B and T cell lymphomas in recipients after hematoablative conditioning for hematopoietic cell transplantation (HCT) has previously revealed a tumor-repressive, metastasis-inhibiting function of murine cytomegalovirus (mCMV). More recently, this prediction from the experimental model was put on trial in several clinical studies that indeed gave evidence for a lower incidence of tumor relapse associated with early reactivation of latent human cytomegalovirus (hCMV) after allogeneic HCT in patients treated against different types of hematopoietic malignancies, including lymphoma and acute as well as chronic leukemias. Due to the limitations inherent to clinical studies, the tumor-repressive role of hCMV remained observational with no approach to clarify mechanisms. Although the tumor-repressive mechanisms of mCMV and hCMV may differ and depend on the type of tumor, experimental approaches in the murine model might give valuable hints for concepts to follow in clinical research. We have previously shown for the liver-adapted A20-derived B cell lymphoma E12E that mCMV does not infect the lymphoma cells for causing cell death by viral cytopathogenicity but triggers tumor-selective apoptosis at a tissue site of tumor metastasis distant from a local site of infection. This finding suggested involvement of a cytokine that triggers apoptosis, directly or indirectly. Here we used a series of differential high-density microarray analyses to identify cellular genes whose expression is specifically upregulated at the site of virus entry only by viruses capable of triggering lymphoma cell apoptosis. This strategy identified interleukin-15 (IL-15) as most promising candidate, eventually confirmed by lymphoma repression with recombinant IL-15.

Prospective therapies for high-grade glial tumours: A literature review

After three decades of intensive research, cytoreductive surgery remains the gold standard of treatment of malignant gliomas. Survivorship at both 1-year and 5-years has not drastically changed in the UK. Concomitant chemo- and radiotherapy has enhanced the efficiency of surgery, enabling more aggressive tumour resection whilst also preserving the surrounding healthy brain parenchyma. More accurate imaging techniques have also played a role in tumour identification, key to this has been pre- and intra-operative contrast enhancement and compounds that have a high affinity in binding to glioma cells. Intra-operative imaging has heralded the ability to give the operating surgeon continuous feedback to assess the completeness of resection. Research is shifting into investigating the complex cellular and molecular glial tumour-genesis, and has led to the development of efficacious chemotherapy agents and trial novel therapies. Oncolytic virotherapy has shown promise in clinical trials and gene therapy in-vitro studies. Surgery however remains the primary therapeutic option for the management of malignant gliomas removing the mass of proliferating malignant tumour cells and decompression of the space-occupying lesion.

Trial watch: Oncolytic viruses for cancer therapy

Oncolytic virotherapy is emerging as a promising approach for the treatment of several neoplasms. The term "oncolytic viruses" is generally employed to indicate naturally occurring or genetically engineered attenuated viral particles that cause the demise of malignant cells while sparing their non-transformed counterparts. From a conceptual standpoint, oncolytic viruses differ from so-called "oncotropic viruses" in that only the former are able to kill cancer cells, even though both display a preferential tropism for malignant tissues. Of note, such a specificity can originate at several different steps of the viral cycle, including the entry of virions (transductional specificity) as well as their intracellular survival and replication (post-transcriptional and transcriptional specificity). During the past two decades, a large array of replication-competent and replication-incompetent oncolytic viruses has been developed and engineered to express gene products that would specifically promote the death of infected (cancer) cells. However, contrarily to long-standing beliefs, the antineoplastic activity of oncolytic viruses is not a mere consequence of the cytopathic effect, i.e., the lethal outcome of an intense, productive viral infection, but rather involves the elicitation of an antitumor immune response. In line with this notion, oncolytic viruses genetically modified to drive the local production of immunostimulatory cytokines exert more robust therapeutic effects than their non-engineered counterparts. Moreover, the efficacy of oncolytic virotherapy is significantly improved by some extent of initial immunosuppression (facilitating viral replication and spread) followed by the administration of immunostimulatory molecules (boosting antitumor immune responses). In this Trial Watch, we will discuss the results of recent clinical trials that have evaluated/are evaluating the safety and antineoplastic potential of oncolytic virotherapy.

Imaging in gene therapy of patients with glioma

Over 10 years ago, the first successful gene therapy paradigms for experimental brain tumors models have been conducted, and they were thought to revolutionize the treatment of patients with gliomas. Application of gene therapy has been quickly forced into clinical trials, the first patients being enrolled in 1994, with overall results being disappointing. However, single patients seemed to benefit from gene therapy showing long-term treatment response, and most of these patients bearing small glioblastomas. Whereas the gene therapy itself has been performed with high sophistication, limited attention has been paid on technologies, which (i) allow an identification of viable target tissue in heterogenous glioma tissue and which (ii) enable an assessment of successful vector administration and vector-mediated gene expression in vivo. However, these measures are a prerequisite for the development of successful gene therapy in the clinical application. As biological treatment strategies such as gene and cell-based therapies hold promise to selectively correct disease pathogenesis, successful clinical implementation of these treatment strategies rely on the establishment of molecular imaging technology allowing the non-invasive assessment of endogenous and exogenous gene expression in vivo. Imaging endogenous gene expression will allow the characterization and identification of target tissue for gene therapy. Imaging exogenously introduced cells and genes will allow the determination of the 'tissue dose' of transduced cell function and vector-mediated gene expression, which in turn can be correlated to the induced therapeutic effect. Only these combined strategies of non-invasive imaging of gene expression in vivo will enable the establishment of safe and efficient vector administration and gene therapy protocols for clinical application. Here, we review some aspects of imaging in gene therapy trials for glioblastoma, and we present a 'proof-of-principle' 2nd-generation gene therapy protocol integrating molecular imaging technology for the establishment of efficient gene therapy in clinical application.

Molecular Imaging of Gliomas

Gliomas are the most common types of brain tumors. Although sophisticated regimens of conventional therapies are being carried out to treat patients with gliomas, the disease invariably leads to death over months or years. Before new and potentially more effective treatment strategies, such as gene- and cell-based therapies, can be effectively implemented in the clinical application, certain prerequisites have to be established. First of all, the exact localization, extent, and metabolic activity of the glioma must be determined to identify the biologically active target tissue for a biological treatment regimen; this is usually performed by imaging the expression of up-regulated endogenous genes coding for glucose or amino acid transporters and cellular hexokinase and thymidine kinase genes, respectively. Second, neuronal function and functional changes within the surrounding brain tissue have to be assessed in order to save this tissue from therapy-induced damage. Third, pathognomonic genetic changes leading to disease have to be explored on the molecular level to serve as specific targets for patient-tailored therapies. Last, a concerted noninvasive analysis of both endogenous and exogenous gene expression in animal models as well as the clinical setting is desirable to effectively translate new treatment strategies from experimental into clinical application. All of these issues can be addressed by multimodal radionuclide and magnetic resonance imaging techniques and fall into the exciting and fast growing field of molecular and functional imaging. Noninvasive imaging of endogenous gene expression by means of positron emission tomography (PET) may reveal insight into the molecular basis of pathogenesis and metabolic activity of the glioma and the extent of treatment response. When exogenous genes are introduced to serve for a therapeutic function, PET imaging may reveal the assessment of the “location,” “magnitude,” and “duration” of therapeutic gene expression and its relation to the therapeutic effect. Detailed reviews on molecular imaging have been published from the perspective of radionuclide imaging (Gambhir et al., 2000; Blasberg and Tjuvajev, 2002) as well as magnetic resonance and optical imaging (Weissleder, 2002). The present review focuses on molecular imaging of gliomas with special reference on the status and perspectives of imaging of endogenous and exogenously introduced gene expression in order to develop improved diagnostics and more effective treatment strategies of gliomas and, in that, to eventually improve the grim prognosis of this devastating disease.

Tumor control in a model of bone marrow transplantation and acute liver-infiltrating B-cell lymphoma: an unpredicted novel function of cytomegalovirus

Tumor relapse and cytomegalovirus (CMV) infection are major concerns in the therapy of hematopoietic malignancies by bone marrow transplantation (BMT). Little attention so far has been given to a possible pathogenetic interplay between CMV and lymphomas. CMV inhibits stem cell engraftment and hematopoietic reconstitution. Thus, by causing maintenance of bone marrow aplasia and immunodeficiency, CMV could promote tumor relapse. Alternatively, CMV could aid tumor remission. One might think of cytopathogenic infection of tumor cells, induction of apoptosis or inhibitory cytokines, interference with tumor cell extravasation or tumor vascularization, or bystander stimulation of an antitumoral immune response. To approach these questions, the established model of experimental BMT and murine CMV infection was extended by the introduction of liver-infiltrating, highly tumorigenic variant clone E12E of BALB/c-derived B-cell lymphoma A20. We document a remarkable retardation of lymphoma progression. First-guess explanations were ruled out: (i) lymphoma cells were not infected; (ii) lymphoma cells located next to infected hepatocytes did not express executioner caspase 3 but were viable and proliferated; (iii) an inhibitory effect of virus on the formation of tumor nodules in the liver became apparent by day 7 after BMT, long before the reconstitution of immune cells; and (iv) recombinant tumor necrosis factor alpha (TNF-alpha) did not substitute for virus; accordingly anti-TNF-alpha did not prevent the inhibition. Notably, while the antitumoral effect required replicative virus, prevention of cytopathogenic infection of the liver by antiviral CD8 T cells did not abolish lymphoma control. These findings are paradigmatic for a novel virus-associated antitumoral mechanism distinct from oncolysis.