Please stand by: how oncolytic viruses impact bystander cells

Oncolytic viruses (OVs) do more than simply infect and kill host cells. The accepted mechanism of action for OVs consists of a primary lytic phase and a subsequent antitumor and antiviral immune response. However, not all cells are subject to the direct effects of OV therapy, and it is becoming clear that OVs can also impact uninfected cells in the periphery. This review discusses the effects of OVs on uninfected neighboring cells, so-called bystander effects, and implications for OV therapies alone or in combination with other standard of care chemotherapy.

High Mobility Group Box 1 Influences HSV1716 Spread and Acts as an Adjuvant to Chemotherapy

High Mobility Group Box 1 (HMGB1) is a multifunctional protein that plays various roles in the processes of inflammation, cancer, and other diseases. Many reports document abundant HMGB1 release following infection with oncolytic viruses (OVs). Further, other groups including previous reports from our laboratory highlight the synergistic effects of OVs with chemotherapy drugs. Here, we show that virus-free supernatants have varying cytotoxic potential, and HMGB1 is actively secreted by two established fibroblast cell lines (NIH 3T3 and 3T6-Swiss albino) following HSV1716 infection in vitro. Further, pharmacologic inhibition or genetic knock-down of HMGB1 reveals a role for HMGB1 in viral restriction, the ability to modulate bystander cell proliferation, and drug sensitivity in 3T6 cells. These data further support the multifactorial role of HMGB1, and suggest it could be a target for modulating the efficacy of oncolytic virus therapies alone or in combination with other frontline cancer treatments.

Abstract B033: Cytokine responses following intrapleural administration of oncolytic HSV SEPREHVIR® in patients with malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) remains a major challenge, with limited therapeutic options. Multifocal intrapleural disease can cause disabling symptoms of pain and breathlessness, in the absence of distant metastases, so an intrapleural treatment approach is attractive. SEPREHVIR (HSV1716) is a mutant oncolytic herpes simplex virus type 1 deleted in the RL1 gene which encodes the protein ICP34.5, a specific determinant of virulence. Mutants lacking the RL1 gene are capable of specific replication in cancer cells and inducing anti-tumour immune responses. Clinical studies with SEPREHVIR have been completed in adult glioma, melanoma, squamous cell head and neck cancer, and studies are ongoing in both pediatric CNS and non-CNS solid tumors and MPM. In total, 92 patients have received SEPREHVIR and the virus is well-tolerated with no spread to surrounding normal tissue or no shedding in patients. SEPREHVIR selectivity for replication only in tumour cells and intimations of efficacy and immuno-stimulatory potential have been demonstrated.

We are currently conducting a phase I/IIa trial to determine the safety and potential for efficacy of SEPREHVIR given intrapleurally to patients with MPM. Patients receive 1x107iu SEPREHVIR through their pleural catheter on one, two or four occasions a week apart, in three separate patient cohorts. To date 9 patients have been treated, 3 in each cohort and SEPREHVIR has been well-tolerated with few adverse events in any patients. Pleural fluid and plasma samples have been collected pre- and post treatment and analysed to assess patient responses to SEPREHVIR administration.

HSV DNA was detected in the pleural fluids of most patients and in some persisted for at least two weeks post-administration. Analysis of pleural fluid cytokines/chemokines by ELISA indicated that they were rich in IL-6, MIG and VEGF. Post SEPREHVIR administration there were increased levels of IFNγ, IP-10, MIG, TNFα and IL-6 in most patients. There were variable responses of VEGF, IL-2, IL-10 and IL-12 after SEPREHVIR administration with IL-2, IL-10 and IL-12 increases most notable in patients receiving 4 doses of SEPREHVIR. IL-1α, IL-4, IL-21, and IFNα were not detected pre-treatment and showed little or no response to SEPREHVIR administration.

Analysis of plasma samples indicated strong anti-HSV IgG responses post SEPREHVIR administration, particularly after 2 and 4 doses. Interestingly, in most patients, these were accompanied by the appearance of a novel anti-tumour IgG response as detected by immunoblotting against extracts from MPM cell lines. Thus, oncolytic SEPREHVIR has immunotherapeutic potential capable of inducing novel anti-tumour immune responses in patients.

Citation Format: Kirsty Learmonth, Lynne Braidwood, Penella Woll, Joe Conner. Cytokine responses following intrapleural administration of oncolytic HSV SEPREHVIR® in patients with malignant pleural mesothelioma. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B033.

8th international conference on oncolytic virus therapeutics

The 8th International Conference on Oncolytic Virus Therapeutics meeting was held from April 10-13, 2014, in Oxford, United Kingdom. It brought together experts in the field of oncolytics from Europe, Asia, Australasia, and the Americas and provided a unique opportunity to hear the latest research findings in oncolytic virotherapy. Presentations of recent work were delivered in an informal and intimate setting afforded by a small group of attendees and an exquisitely focused conference topic. Here we describe the oral presentations and enable the reader to share in the benefits of bringing together experts to share their findings.

Potent efficacy signals from systemically administered oncolytic herpes simplex virus (HSV1716) in hepatocellular carcinoma xenograft models

Oncolytic herpes simplex virus (HSV1716), lacking the neurovirulence factor ICP34.5, has highly selective replication competence for cancer cells and has been used in clinical studies of glioma, melanoma, head and neck squamous cell carcinoma, pediatric non-central nervous system solid tumors, and malignant pleural mesothelioma. To date, 88 patients have received HSV1716 and the virus is well tolerated, with selective replication in tumor cells and no spread to surrounding normal tissue. We assessed the potential value of HSV1716 in preclinical studies with two human hepatocellular carcinoma cell lines, HuH7 and HepG2-luc. HSV1716 displayed excellent replication kinetics in vitro in HepG2-luc cells, a cell line engineered to express luciferase, and virus-mediated cell killing correlated with loss of light emissions from the cells. In vivo, the HepG2-luc cells readily formed light-emitting xenografts that were easily visualized by an in vivo imaging system and efficiently eliminated by HSV1716 oncolysis after intratumoral injection. HSV1716 also demonstrated strong efficacy signals in subcutaneous HuH7 xenografts in nude mice after intravenous administration of virus. In the HuH7 model, the intravenously injected virus replicated prolifically immediately after efficient tumor localization, resulting in highly significant reductions in tumor growth and enhanced survival. Our preclinical results demonstrate excellent tumor uptake of HSV1716, with prolific replication and potent oncolysis. These observations warrant a clinical study of HSV1716 in hepatocellular carcinoma.

Oncolytic herpes viruses, chemotherapeutics, and other cancer drugs

Oncolytic viruses are emerging as a potential new way of treating cancers. They are selectively replication-competent viruses that propagate only in actively dividing tumor cells but not in normal cells and, as a result, destroy the tumor cells by consequence of lytic infection. At least six different oncolytic herpes simplex viruses (oHSVs) have undergone clinical trials worldwide to date, and they have demonstrated an excellent safety profile and intimations of efficacy. The first pivotal Phase III trial with an oHSV, talimogene laherparepvec (T-Vec [OncoVex(GM-CSF)]), is almost complete, with extremely positive early results reported. Intuitively, therapeutically beneficial interactions between oHSV and chemotherapeutic and targeted therapeutic drugs would be limited as the virus requires actively dividing cells for maximum replication efficiency and most anticancer agents are cytotoxic or cytostatic. However, combinations of such agents display a range of responses, with antagonistic, additive, or, perhaps most surprisingly, synergistic enhancement of antitumor activity. When synergistic interactions in cancer cell killing are observed, chemotherapy dose reductions that achieve the same overall efficacy may be possible, resulting in a valuable reduction of adverse side effects. Therefore, the combination of an oHSV with "standard-of-care" drugs makes a logical and reasonable approach to improved therapy, and the addition of a targeted oncolytic therapy with "standard-of-care" drugs merits further investigation, both preclinically and in the clinic. Numerous publications report such studies of oncolytic HSV in combination with other drugs, and we review their findings here. Viral interactions with cellular hosts are complex and frequently involve intracellular signaling networks, thus creating diverse opportunities for synergistic or additive combinations with many anticancer drugs. We discuss potential mechanisms that may lead to synergistic interactions.

In vivo evaluation of a cancer therapy strategy combining HSV1716-mediated oncolysis with gene transfer and targeted radiotherapy

Oncolytic herpes viruses show promise for cancer treatment. However, it is unlikely that they will fulfill their therapeutic potential when used as monotherapies. An alternative strategy is to use these viruses not only as oncolytic agents but also as a delivery mechanism of therapeutic transgenes to enhance tumor cell killing. The herpes simplex virus 1 deletion mutant HSV1716 is a conditionally replicating oncolytic virus that selectively replicates in and lyses dividing tumor cells. It has a proven safety profile in clinical trials and has demonstrated efficacy as a gene-delivery vehicle. To enhance its therapeutic potential, we have engineered HSV1716 to convey the noradrenaline transporter (NAT) gene (HSV1716/NAT), whose expression endows infected cells with the capacity to accumulate the noradrenaline analog metaiodobenzylguanidine (MIBG). Thus, the NAT gene-infected cells are susceptible to targeted radiotherapy using radiolabeled (131)I-MIBG, a strategy that has already shown promise for combined targeted radiotherapy-gene therapy in cancer cells after plasmid-mediated transfection.

METHODS

We used HSV1716/NAT as a dual cell lysis-gene delivery vehicle for targeting the NAT transgene to human tumor xenografts in vivo.

RESULTS

In tumor xenografts that did not express NAT, intratumoral or intravenous injection of HSV1716/NAT induced the capacity for active uptake of (131)I-MIBG. Administration of HSV1716/NAT and (131)I-MIBG resulted in decreased tumor growth and enhanced survival relative to injection of either agent alone. Efficacy was dependent on the scheduling of delivery of the 2 agents.

CONCLUSION

These findings support a role for combination radiotherapy-gene therapy for cancer using HSV1716 expressing the NAT transgene and targeted radionuclide therapy.

Antitumor activity of a selectively replication competent herpes simplex virus (HSV) with enzyme prodrug therapy

BACKGROUND

HSV1790 is an oncolytic virus generated by inserting the enzyme nitroreductase (NTR) into the virus HSV1716. NTR converts the prodrug CB1954 into an active alkylating agent.

MATERIALS AND METHODS

In vitro, 3T6 cells (non permissive to HSV) were used in order to distinguish between virus-induced cytopathic effect and cell death due to activated prodrug. In vivo, xenograft models were injected with HSV1790 (10(5)-10(9) PFU) with or without CB1954 (max 80mg/kg) and tumor volume recorded regularly. Biodistribution of HSV1790 was determined immunohistochemically and by PCR.

RESULTS

HSV1790 + CB1954 in vitro was more effective at killing tumor cells than the virus or the prodrug alone. In vivo, the combination reduced tumor volume and increased survival compared to treatment with HSV1790 or CB1954 alone. Following systemic administration of HSV1790, viral replication was detected in tumors, but not organs.

CONCLUSION

HSV1790 + prodrug enhances tumor cell killing in vitro and reduces tumor volume and increases survival in vivo.

A strategy for systemic delivery of the oncolytic herpes virus HSV1716: redirected tropism by antibody-binding sites incorporated on the virion surface as a glycoprotein D fusion protein

We report on the ability of single-chain variable fragment (scFv) incorporated into the viral envelope to alter the tropism of herpes simplex virus (HSV) 1716. Using recombinant viruses expressing fusion proteins comprising cell-surface antigen-specific scFvs N terminus linked to amino acids 274-393 of gD, we demonstrated that the tropism of these HSV1716 variants was modified such that infection was mediated by the cognate antigen. Thus, an HSV1716 variant that expressed an anti-CD55 scFv targeting moiety linked to these gD residues was able to infect non-permissive Chinese hamster ovary cells expressing CD55 and this infection was specifically blocked by an anti-CD55 monoclonal antibody. Similarly, the infection efficiency of an HSV1716 variant for semi-permissive human leukaemic, CD38-positive cell lines was greatly improved by an anti-CD38 scFv targeting moiety linked to gD residues 274-393, and this enhanced infectivity was abrogated specifically by an anti-CD38 monoclonal antibody. Finally, intravenous/intraperitoneal injection of an HSV1716 variant displaying an anti-epidermal growth factor receptor (EGFR) scFv linked to residues 274-393 of gD enhanced destruction of subcutaneous EGFR-positive tumours in nude mice compared to unmodified HSV1716. Therefore, targeting of HSV1716 oncolysis to specific cell types through the display of entry mediating scFv/gD fusion proteins represents an efficient route for systemic delivery.

Bidirectional tachycardia in a child. A study using His bundle electrography

This is a report of a case of bidirectional tachycardia in a 6-year-old girl with no evidence of any structural abnormality of the heart. The patient had never received digitalis. The arrhythmia appeared to be precipitated by effort and emotional stress, and could be induced by increasing the heart rate by atrial pacing or isoprenaline administration. His bundle electrography showed that the arrhythmia was ventricular in origin. This emphasizes the importance of recording an effort electrocardiogram in all children with unexplained syncopal episodes, even when the resting electrocardiogram is normal.