Analysis of genetically engineered oncolytic herpes simplex viruses in human prostate cancer organotypic cultures

A phase I/II study of triple-mutated oncolytic herpes virus G47∆ in patients with progressive glioblastoma

Here, we report the results of a phase I/II, single-arm study (UMIN-CTR Clinical Trial Registry UMIN000002661) assessing the safety (primary endpoint) of G47∆, a triple-mutated oncolytic herpes simplex virus type 1, in Japanese adults with recurrent/progressive glioblastoma despite radiation and temozolomide therapies. G47Δ was administered intratumorally at 3 × 10⁸ pfu (low dose) or 1 × 10⁹ pfu (set dose), twice to identical coordinates within 5–14 days. Thirteen patients completed treatment (low dose, n = 3; set dose, n = 10). Adverse events occurred in 12/13 patients. The most common G47Δ-related adverse events were fever, headache and vomiting. Secondary endpoint was the efficacy. Median overall survival was 7.3 (95%CI 6.2–15.2) months and the 1-year survival rate was 38.5%, both from the last G47∆ administration. Median progression-free survival was 8 (95%CI 7–34) days from the last G47∆ administration, mainly due to immediate enlargement of the contrast-enhanced area of the target lesion on MRI. Three patients survived >46 months. One complete response (low dose) and one partial response (set dose) were seen at 2 years. Based on biopsies, post-administration MRI features (injection site contrast-enhancement clearing and entire tumor enlargement) likely reflected tumor cell destruction via viral replication and lymphocyte infiltration towards tumor cells, the latter suggesting the mechanism for “immunoprogression” characteristic to this therapy. This study shows that G47Δ is safe for treating recurrent/progressive glioblastoma and warrants further clinical development.

G47Δ is a third-generation, triple-mutated oncolytic HSV-1 that has demonstrated anti-tumor efficacy in preclinical studies. Here the authors report the results of a phase I/II study of G47Δ in patients with recurrent or progressive glioblastoma.

NK cell tumor therapy modulated by UV-inactivated oncolytic herpes simplex virus type 2 and checkpoint inhibitors

Oncolytic virotherapy is a new and safe therapeutic strategy for cancer treatment. In our previous study, a new type of oncolytic herpes simplex virus type 2 (oHSV2) was constructed. Following the completion of a preclinical study, oHSV2 has now entered into clinical trials for the treatment of melanoma and other solid tumors (NCT03866525). Oncolytic viruses (OVs) are generally able to directly destroy tumor cells and stimulate the immune system to fight tumors. Natural killer (NK) cells are important components of the innate immune system and critical players against tumor cells. But the detailed interactions between oncolytic viruses and NK cells and these interaction effects on the antitumor immune response remain to be elucidated. In particular, the functions of activating surface receptors and checkpoint inhibitors on oHSV2-treated NK cells and tumor cells are still unknown. In this study, we found that UV-oHSV2 potently activates human peripheral blood mononuclear cells, leading to increased antitumor activity in vitro and in vivo. Further investigation indicated that UV-oHSV2-stimulated NK cells release IFN-γ via Toll-like receptor 2 (TLR2)/NF-κB signaling pathway and exert antitumor activity via TLR2. We found for the first time that the expression of a pair of checkpoint molecules, NKG2A (on NK cells) and HLA-E (on tumor cells), is upregulated by UV-oHSV2 stimulation. Anti-NKG2A and anti-HLA-E treatment could further enhance the antitumor effects of UV-oHSV2-stimulated NK92 cells in vitro and in vivo. As our oHSV2 clinical trial is ongoing, we expect that the combination therapy of oncolytic virus oHSV2 and anti-NKG2A/anti-HLA-E antibodies may have synergistic antitumor effects in our future clinical trials.

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 virotherapy with human telomerase reverse transcriptase promoter regulation enhances cytotoxic effects against gastric cancer

Currently, gastric cancer is the third most common cause of cancer-associated mortality worldwide. Oncolytic virotherapy using herpes simplex virus (HSV) has emerged as a novel therapeutic strategy against cancer. Telomerase is activated in >90of malignant tumors, including gastric cancer, and human telomerase reverse transcriptase (hTERT) is one of the major components of telomerase enzyme. Therefore, in oncolytic HSV, placing the essential genes under the regulation of the hTERT promoter may enhance its antitumor efficacy. The present study examined the antitumor effect of fourth-generation oncolytic HSVs, which contain the ICP6 gene under the regulation of the hTERT promoter (T-hTERT). To examine the association between hTERT expression and prognosis in patients with gastric cancer, immunohistochemical analysis of resected tumor specimens was performed. The enhanced efficacy of T-hTERT was determined in human gastric cancer cell lines in vitro and in human gastric adenocarcinoma specimens in vivo. In in vitro experiments, enhanced cytotoxicity of T-hTERT was observed in MKN1, MKN28 and MKN45 cells compared with that of a third-generation oncolytic HSV, T-null. In particular, the cytotoxicity of T-hTERT was markedly enhanced in MKN45 cells. Furthermore, in vivo experiments demonstrated that 36.7 and 54.9% of cells were found to be lysed 48 h after infection with T-null or T-hTERT viruses at 0.01 pfu/cell, respectively. The T-hTERT-treated group exhibited considerably lower cell viability than the control [phosphate-buffered saline (-)] group. Therefore, employing oncolytic HSVs that contain the ICP6 gene under the regulation of the hTERT promoter may be an effective therapeutic strategy for gastric cancer. To the best of our knowledge, the present study was the first to describe the effect of an oncolytic HSV with ICP6 expression regulated by the hTERT promoter on gastric cancer cells.

Oncolytic virus therapy in Japan: progress in clinical trials and future perspectives

Oncolytic virus therapy is a promising new option for cancer. It utilizes genetically engineered or naturally occurring viruses that selectively replicate in and kill cancer cells without harming normal cells. T-VEC (talimogene laherparepvec), a second-generation oncolytic herpes simplex virus type 1, was approved by the US Food and Drug Administration for the treatment of inoperable melanoma in 2015 and subsequently approved in Europe in 2016. Other oncolytic viruses using different parental viruses have also been tested in Phase III clinical trials and are ready for drug approval: Pexa-Vec (pexastimogene devacirepvec), an oncolytic vaccinia virus, CG0070, an oncolytic adenovirus, and REOLYSIN (pelareorep), an oncolytic reovirus. In Japan, as of May 2018, several oncolytic viruses have been developed, and some have already proceeded to clinical trials. In this review, we summarize clinical trials assessing oncolytic virus therapy that were conducted or are currently ongoing in Japan, specifically, T-VEC, the abovementioned oncolytic herpes simplex virus type 1, G47Δ, a third-generation oncolytic herpes simplex virus type 1, HF10, a naturally attenuated oncolytic herpes simplex virus type 1, Telomelysin, an oncolytic adenovirus, Surv.m-CRA, another oncolytic adenovirus, and Sendai virus particle. In the near future, oncolytic virus therapy may become an important and major treatment option for cancer in Japan.

Oncolytic Herpes Simplex Virus and PI3K Inhibitor BKM120 Synergize to Promote Killing of Prostate Cancer Stem-like Cells

Novel therapies to override chemo-radiation resistance in prostate cancer (PCa) are needed. Prostate cancer sphere-forming cells (PCSCs) (also termed prostate cancer stem-like cells) likely participate in tumor progression and recurrence, and they are important therapeutic targets. We established PCSC-enriched spheres by culturing human (DU145) and murine (TRAMP-C2) PCa cells in growth factor-defined serum-free medium, and we characterized stem-like properties of clonogenicity and tumorigenicity. The efficacy of two different oncolytic herpes simplex viruses (oHSVs) (G47Δ and MG18L) in PCSCs was tested alone and in combination with radiation; chemotherapy; and inhibitors of phosphoinositide 3-kinase (PI3K), Wnt, and NOTCH in vitro; and, G47Δ was tested with the PI3K inhibitor BKM120 in a PCSC-derived tumor model in vivo. PCSCs were more tumorigenic than serum-cultured parental cells. Human and murine PCSCs were sensitive to oHSV and BKM120 killing in vitro, while the combination was synergistic. oHSV combined with radiation, docetaxel, Wnt, or NOTCH inhibitors was not. In athymic mice bearing DU145 PCSC-derived tumors, the combination of intra-tumoral G47Δ and systemic BKM120 induced complete regression of tumors in 2 of 7 animals, and it exhibited superior anti-tumor activity compared to either monotherapy alone, with no detectable toxicity. oHSV synergizes with BKM120 in killing PCSCs in vitro, and the combination markedly inhibits tumor growth, even inducing regression in vivo.

Oncolytic herpes simplex virus and immunotherapy

BACKGROUND

Oncolytic viruses have been proposed to be employed as a potential treatment of cancer. Well targeted, they will serve the purpose of cracking tumor cells without causing damage to normal cells. In this category of oncolytic viral drugs human pathogens herpes simplex virus (HSV) is especially suitable for the cause. Although most viral infection causes antiviral reaction in the host, HSV has multiple mechanisms to evade those responses. Powerful anti-tumor effect can thus be achieved via genetic manipulation of the HSV genes involved in this evading mechanism, namely deletions or mutations that adapt its function towards a tumor microenvironment. Currently, oncolytic HSV (oHSV) is widely use in clinical; moreover, there's hope that its curative effect will be further enhanced through the combination of oHSV with both traditional and emerging therapeutics.

RESULTS

In this review, we provide a summary of the HSV host antiviral response evasion mechanism, HSV expresses immune evasion genes such as ICP34.5, ICP0, Us3, which are involved in inducing and activating host responses, so that the virus can evade the immune system and establish effective long-term latent infection; we outlined details of the oHSV strains generated by removing genes critical to viral replication such as ICP34.5, ICP0, and inserting therapeutic genes such as LacZ, granulocyte macrophage colony-stimulating factor (GM-CSF); security and limitation of some oHSV such G207, 1716, OncoVEX, NV1020, HF10, G47 in clinical application; and the achievements of oHSV combined with immunotherapy and chemotherapy.

CONCLUSION

We reviewed the immunotherapy mechanism of the oHSV and provided a series of cases. We also pointed out that an in-depth study of the application of oHSV in cancer treatment will potentially benefits cancer patients more.

Three-dimensional tumor cell cultures employed in virotherapy research

Oncolytic virotherapy constitutes an upcoming alternative treatment option for a broad spectrum of cancer entities. However, despite great research efforts, there is still only a single US Food and Drug Administration/European Medicines Agency-approved oncolytic virus available for clinical use. One reason for that is the gap between promising preclinical data and limited clinical success. Since oncolytic viruses are biological agents, they might require more realistic in vitro tumor models than common monolayer tumor cell cultures to provide meaningful predictive preclinical evaluation results. For more realistic invitro tumor models, three-dimensional tumor cell-culture systems can be employed in preclinical virotherapy research. This review provides an overview of spheroid and hydrogel tumor cell cultures, organotypic tumor-tissue slices, organotypic raft cultures, and tumor organoids utilized in the context of oncolytic virotherapy. Furthermore, we also discuss advantages, disadvantages, techniques, and difficulties of these three-dimensional tumor cell-culture systems when applied specifically in virotherapy research.

Stability and anti-tumor effect of oncolytic herpes simplex virus type 2

Oncolytic virotherapy is a new therapeutic strategy based on the inherent cytotoxicity of viruses and their ability to replicate and spread in tumors in a selective manner. We constructed a new type of oncolytic herpes simplex virus type 2 (oHSV-2, named OH2) to treat human cancers, but a systematic evaluation of the stability and oncolytic ability of this virus is lacking. In this study, we evaluated its physical stability, gene modification stability and biological characteristics stability, including its anti-tumor activity in an animal model. The physical characteristics as well as genetic deletions and insertions in OH2 were stable, and the anti-tumor activity remained stable even after passage of the virus for more than 20 generations. In conclusion, OH2 is a virus that has stable structural and biological traits. Furthermore, OH2 is a potent oncolytic agent against tumor cells.

Current status of clinical trials assessing oncolytic virus therapy for urological cancers

Oncolytic virus therapy has recently been recognized as a promising new option for cancer treatment. Oncolytic viruses replicate selectively in cancer cells, thus killing them without harming normal cells. Notably, T-VEC (talimogene laherparepvec, formerly called OncoVEX^GM-CSF ), an oncolytic herpes simplex virus type 1, was approved by the US Food and Drug Administration for the treatment of inoperable melanoma in October 2015, and was subsequently approved in Europe and Australia in 2016. The efficacies of many types of oncolytic viruses against urological cancers have been investigated in preclinical studies during the past decade, and some have already been tested in clinical trials. For example, a phase I trial of the third-generation oncolytic Herpes simplex virus type 1, G47Δ, in patients with prostate cancer was completed in 2016. We summarize the current status of clinical trials of oncolytic virus therapy in patients with the three major urological cancers: prostate, bladder and renal cell cancers. In addition to Herpes simplex virus type 1, adenoviruses, reoviruses, vaccinia virus, Sendai virus and Newcastle disease virus have also been used as parental viruses in these trials. We believe that oncolytic virus therapy is likely to become an important and major treatment option for urological cancers in the near future.

The oncolytic herpes simplex virus vector, G47Δ, effectively targets tamoxifen-resistant breast cancer cells

The aim of the present study was to establish a tamoxifen-resistant cell line (MCF-7/TAM-R) and to investigate the therapeutic effect of G47Δ on this cell line both in vitro and in vivo. In the present study, the MCF-7/TAM-R monoclonal subline was established after exposing MCF-7 cells to tamoxifen for 21 days. Then, it was compared with a wild-type MCF-7 subline (MCF-7W), which was not treated with tamoxifen. Cell proliferation, viability, cell cycle and apoptosis analyses were carried out to examine the characteristics of the MCF-7/TAM-R cells. Both in vitro and in vivo toxicity studies were conducted to investigate the therapeutic effect of G47Δ on the MCF-7/TAM-R cells. Compared to the MCF-7W cells, we found that the MCF-7/TAM-R cells exhibited a higher proliferation ability (P<0.05) and a stronger resistance to the cytotoxic effects induced by 4-hydroxytamoxifen (4-OHT) (P<0.05). G47Δ demonstrated a high cytotoxic effect on both the MCF-7/TAM-R and MCF-7W cell lines. After being infected with G47Δ at an MOI of 0.01, >90% of the MCF-7/TAM-R and MCF-7W cells died on day 5. G47Δ induced cell cycle arrest in the G2/M phase. Furthermore, G47Δ inhibited tumor growth in subcutaneous tumor models of both MCF-7/TAM-R and MCF-7W. Thus, we conclude that G47Δ, a third generation oncolytic herpes simplex virus, is highly sensitive and safe in targeting tamoxifen-resistant breast cancer cells both in vitro and in vivo.

Advance in herpes simplex viruses for cancer therapy

Oncolytic virotherapy is an attractive approach that uses live viruses to selectively kill cancer cells. Oncolytic viruses can be genetically engineered to induce cell lyses through virus replication and cytotoxic protein expression. Herpes simplex virus (HSV) has become one of the most widely clinically used oncolytic agent. Various types of HSV have been studied in basic or clinical research. Combining oncolytic virotherapy with chemotherapy or radiotherapy generally produces synergic action with unclear molecular mechanisms. Arming HSV with therapeutic transgenes is a promising strategy and can be used to complement conventional therapies. As an efficient gene delivery system, HSV has been successfully used to deliver various immunomodulatory molecules. Arming HSV with therapeutic genes merits further investigation for potential clinical application.

Combination of vinblastine and oncolytic herpes simplex virus vector expressing IL-12 therapy increases antitumor and antiangiogenic effects in prostate cancer models

Oncolytic herpes simplex virus (oHSV)-1-based vectors selectively replicate in tumor cells causing direct killing, that is, oncolysis, while sparing normal cells. The oHSVs are promising anticancer agents, but their efficacy, when used as single agents, leaves room for improvement. We hypothesized that combining the direct oncolytic and antiangiogenic activities of the interleukin (IL)-12-secreting NV1042 oHSV with microtubule disrupting agents (MDAs) would be an effective means to enhance antitumor efficacy. Vinblastine (VB) was identified among several MDAs screened, which displayed consistent and potent cytotoxic killing of both prostate cancer and endothelial cell lines. In matrigel tube-forming assays, VB was found to be highly effective at inhibiting tube formation of human umbilical vein endothelial cells. The combination of VB with NV1023 (the parental virus lacking IL-12) or NV1042 showed additive or synergistic activity against prostate cancer cell lines, and was not due to increased oHSV replication by VB. In athymic mice bearing CWR22 prostate tumors, VB in combination with NV1042 was superior to the combination of VB plus NV1023 in reducing tumor burden, appeared to be nontoxic and resulted in a statistically significant diminution in the number of CD31(+) cells as compared with other treatment groups. In human organotypic cultures using surgical samples from radical prostatectomies, both NV1023 and NV1042 were localized specifically to the epithelial cells of prostatic glands but not to the surrounding stroma. These data highlight the therapeutic advantage of combining the dual-acting antitumor and antiangiogenic activities of oHSVs and MDAs.

Chromatin binding by the androgen receptor in prostate cancer

Alterations in transcriptional programs are fundamental to the development of cancers. The androgen receptor is central to the normal development of the prostate gland and to the development of prostate cancer. To a large extent this is believed to be due to the control of gene expression through the interaction of the androgen receptor with chromatin and subsequently with coregulators and the transcriptional machinery. Unbiased genome-wide studies have recently uncovered the recruitment sites that are gene-distal and intragenic rather than associated with proximal promoter regions. Whilst expression profiles from AR-positive primary prostate tumours and cell lines can directly relate to the AR cistrome in prostate cancer cells, this distribution raises significant challenges in making direct mechanistic connections. Furthermore, extrapolating from datasets assembled in one model to other model systems or clinical samples poses challenges if we are to use the AR-directed transcriptome to guide the development of novel biomarkers or treatment decisions. This review will provide an overview of the androgen receptor before addressing the challenges and opportunities created by whole-genome studies of the interplay between the androgen receptor and chromatin.

Frontiers in targeting glioma stem cells

Patients with glioblastoma multiforme (GBM - WHO grade IV) seldom recover. This is due to the infiltrative nature of these tumours and the presence of cellular populations with ability to escape therapies and drive tumour recurrence and progression. In some cases, these resistant cells exhibit stem properties [glioma stem cells (GSC)]. This article aims at discussing relevant issues on GSC resistance to current therapies and outlines possible and promising avenues in regard to novel therapeutic strategies, such as pharmacological, immunological and viral interventions.

Identification of the ENT1 antagonists dipyridamole and dilazep as amplifiers of oncolytic herpes simplex virus-1 replication

Oncolytic herpes simplex virus-1 (oHSV) vectors selectively replicate in tumor cells, where they kill through oncolysis while sparing normal cells. One of the drawbacks of oHSV vectors is their limited replication and spread to neighboring cancer cells. Here, we report the outcome of a high-throughput chemical library screen to identify small-molecule compounds that augment the replication of oHSV G47Delta. Of the 2,640-screened bioactives, 6 compounds were identified and subsequently validated for enhanced G47Delta replication. Two of these compounds, dipyridamole and dilazep, interfered with nucleotide metabolism by potently and directly inhibiting the equilibrative nucleoside transporter-1 (ENT1). Replicative amplification promoted by dipyridamole and dilazep were dependent on HSV mutations in ICP6, the large subunit of ribonucleotide reductase. Our results indicate that ENT1 antagonists augment oHSV replication in tumor cells by increasing cellular ribonucleoside activity.