Myxoma virus therapy for human embryonal rhabdomyosarcoma in a nude mouse model

Oncolytic Myxoma virus Increases Autophagy in Multiple Myeloma

Objective

Multiple myeloma, which affects plasma cells, is the second most common hematological malignancy. Despite the development of new drugs and treatment protocols, patient survival has not reached the desired level. In this study, we investigated the effects of Myxoma virus (MYXV), an oncolytic virus, on autophagy in myeloma cells.

Materials and Methods

We analyzed protein expressions of ATG-5, p62, Beclin-1, LC3B, and the apoptosis marker Bcl-2 as autophagy markers in human U-266 and mouse MOPC-315 myeloma cell lines subjected to different doses of MYXV. In addition, autophagic images of myeloma cells were investigated using transmission electron microscopy (TEM).

Results

In the first 24 h, which is the early stage of autophagy, ATG-5 and Beclin-1 expression levels were increased in the U-266 and MOPC-315 cell lines in the groups that had received MYXV at a multiplicity of infection of 15. At 48 h, a significant increase was detected in the expression of LC3B, which is a late indicator. Autophagosomes were observed in myeloma cells by TEM.

Conclusion

MYXV shows an antimyeloma effect by increasing autophagy in myeloma cells.

Myxoma Virus Combination Therapy Enhances Lenalidomide and Bortezomib Treatments for Multiple Myeloma

This study aimed to explore the effectiveness and safety of Myxoma virus (MYXV) in MM cell lines and primary myeloma cells obtained from patients with multiple myeloma. Myeloma cells were isolated from MM patients and cultured. MYXV, lenalidomide, and bortezomib were used in MM cells. The cytotoxicity assay was investigated using WST-1. Apoptosis was assessed through flow cytometry with Annexin V/PI staining and caspase-9 concentrations using ELISA. To explore MYXV entry into MM cells, monoclonal antibodies were used. Moreover, to explore the mechanisms of MYXV entry into MM cells, we examined the level of GFP-labeled MYXV within the cells after blocking with monoclonal antibodies targeting BCMA, CD20, CD28, CD33, CD38, CD56, CD86, CD117, CD138, CD200, and CD307 in MM cells. The study demonstrated the effects of treating Myxoma virus with lenalidomide and bortezomib. The treatment resulted in reduced cell viability and increased caspase-9 expression. Only low-dose CD86 blockade showed a significant difference in MYXV entry into MM cells. The virus caused an increase in the rate of apoptosis in the cells, regardless of whether it was administered alone or in combination with drugs. The groups with the presence of the virus showed higher rates of early apoptosis. The Virus, Virus + Bortezomib, and Virus + Lenalidomide groups had significantly higher rates of early apoptosis (p < 0.001). However, the measurements of late apoptosis and necrosis showed variability. The addition of MYXV resulted in a statistically significant increase in early apoptosis in both newly diagnosed and refractory MM patients. Our results highlight that patient-based therapy should also be considered for the effective management of MM.

Oclacitinib and Myxoma Virus Therapy in Dogs with High-Grade Soft Tissue Sarcoma

Human rhabdomyosarcomas are rarely cured by surgical resection alone. This is also true for high-grade soft tissue sarcomas in dogs. Dogs with spontaneous sarcoma are good models for clinical responses to new cancer therapies. Strategic combinations of immunotherapy and oncolytic virotherapy (OV) could improve treatment responses in canine and human cancer patients. To develop an appropriate combination of immunotherapy and OV for dogs with soft tissue sarcoma (STS), canine cancer cells were inoculated with myxoma viruses (MYXVs) and gene transcripts were quantified. Next, the cytokine concentrations in the canine cancer cells were altered to evaluate their effect on MYXV replication. These studies indicated that, as in murine and human cells, type I interferons (IFN) play an important role in limiting MYXV replication in canine cancer cells. To reduce type I IFN production during OV, oclacitinib (a JAK1 inhibitor) was administered twice daily to dogs for 14 days starting ~7 days prior to surgery. STS tumors were excised, and MYXV deleted for serp2 (MYXV∆SERP2) was administered at the surgical site at two time points post-operatively to treat any remaining microscopic tumor cells. Tumor regrowth in dogs treated with OV was decreased relative to historical controls. However, regrowth was not further inhibited in patients given combination therapy.

Treatment of an Alveolar Rhabdomyosarcoma Allograft with Recombinant Myxoma Virus and Oclacitinib

Purpose

Rhabdomyosarcomas (RMS) are difficult tumors to treat with conventional therapies. Publications indicate that oncolytic virotherapy (OV) could benefit cancer patients with tumors that are refractory to conventional treatments. It is believed that the efficacy of OV can be enhanced when used in combination with other treatments. This study evaluated the response of mice with aggressive alveolar RMS (ARMS) allografts to treatment with an OV [recombinant myxoma virus (MYXVΔserp2)] in combination with a Janus kinase (JAK) inhibitor (oclacitinib). Oclacitinib is known to inhibit JAK1 and JAK2 cell signaling pathways, which should limit the antiviral Type I interferon response. However, oclacitinib does not inhibit immune pathways that promote antigen presentation, which help stimulate an anti-cancer immune response.

Materials and Methods

To determine if MYXVΔserp2 and oclacitinib could improve outcomes in animals with ARMS, nude mice were inoculated subcutaneously with murine ARMS cells to establish tumors. Immune responses, tumor growth, and clinical signs in mice treated with combination therapy were compared to mice given placebo therapy and mice treated with OV alone.

Results

Combination therapy was safe; no viral DNA was detected in off-target organs, only within tumors. As predicted, viral DNA was detected in tumors of mice given oclacitinib and MYXVΔserp2 for a longer time period than mice treated with OV alone. Although tumor growth rates and median survival times were not significantly different between groups, clinical signs were less severe in mice treated with OV.

Conclusion

Our data indicate that MYXVΔserp2 treatment benefits mice with ARMS by reducing clinical signs of disease and improving quality of life.

Recombinant Myxoma Virus Expressing Walleye Dermal Sarcoma Virus orfC Is Attenuated in Rabbits

The poxvirus, myxoma virus (MYXV) has shown efficacy as an oncolytic virus (OV) in some cancer models. However, MYXV replication within murine cancer models and spontaneous canine sarcomas is short-lived. In mice, successful treatment of tumors requires frequent injections with MYXV. We hypothesize that treatment of cancer with a recombinant MYXV that promotes apoptosis could improve the efficacy of MYXV. The orfC gene of walleye dermal sarcoma virus (WDSV), which induces apoptosis, was recombined into the MYXV genome (MYXVorfC). A marked increase in apoptosis was observed in cells infected with MYXVorfC. To ensure that expression of WDSV orfC by MYXV does not potentiate the pathogenesis of MYXV, we evaluated the effects of MYXVorfC inoculation in the only known host of MYXV, New Zealand white rabbits. Virus dissemination in rabbit tissues was similar for MYXVorfC and MYXV. Virus titers recovered from tissues were lower in MYXVorfC-infected rabbits as compared to MYXV-infected rabbits. Importantly, rabbits infected with MYXVorfC had a delayed onset of clinical signs and a longer median survival time than rabbits infected with MYXV. This study indicates that MYXVorfC is attenuated and suggests that MYXVorfC will be safe to use as an OV therapy in future studies.

The potential of the combined use of targeted type I interferon pathway inhibitors and oncolytic viruses to treat sarcomas

Replicating oncolytic viruses (OVs) are appealing, new, FDA-approved, therapeutic options for humans with head and neck cancers and melanomas. These treatments are not yet available for veterinary patients, but recent clinical trials have shown several OVs to be safe in dogs and cats. Specific viruses being used to treat sarcomas in dogs include modified canine adenovirus 2, myxoma virus, vesicular stomatitis virus and reovirus. In cats with vaccine-associated sarcomas, poxviruses have been injected postoperatively and a reduced rate of tumour recurrence was documented. To date, the response rates of canine and feline patients to OV therapy have been variable (as they are in people). Optimal methods of OV administration and dosing schedules continue to be evaluated. One way to improve outcomes of OV therapy in veterinary patients may be to use OVs in combination with other immunomodulatory therapies. This review discusses the potential utility of concurrent therapy with an OV and an inhibitor of the type I interferon pathway.

Focal adhesion kinase (FAK) phosphorylation is a key regulator of embryonal rhabdomyosarcoma (ERMS) cell viability and migration

BACKGROUND

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in children. Pathogenesis of RMS is associated with aggressive growth pattern and increased risk of morbidity and mortality. There are two main subtypes or RMS: embryonal and alveolar. The embryonal type is characterized by distinct molecular aberrations, including alterations in the activity of certain protein kinases. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that plays a vital role in focal adhesion (FA) assembly to promote cytoskeleton dynamics and regulation of cell motility. It is regulated by multiple phosphorylation sites: tyrosine 397, Tyr 576/577, and Tyr 925. Tyrosine 397 is the autophosphorylation site that regulates FAK localization at the cell periphery to facilitate the assembly and formation of the FA complex. The kinase activity of FAK is mediated by the phosphorylation of Tyr 576/577 within the kinase domain activation loop. Aberrations of FAK phosphorylation have been linked to the pathogenesis of different types of cancers. In this regard, pY397 upregulation is linked to increase ERMS cell motility, invasion, and tumorigenesis.

METHODS

In this study, we have used an established human embryonal muscle rhabdomyosarcoma cell line RD as a model to examine FAK phosphorylation profiles to characterize its role in the pathogenies of RMS.

RESULTS

Our findings revealed a significant increase of FAK phosphorylation at pY397 in RD cells compared to control cells (hTERT). On the other hand, Tyr 576/577 phosphorylation levels in RD cells displayed a pronounced reduction. Our data showed that Y925 residue exhibited no detectable change. The in vitro analysis showed that the FAK inhibitor, PF-562271 led to G1 cell-cycle arrest induced cell death (IC₅₀, ~ 12 µM) compared to controls. Importantly, immunostaining analyses displayed a noticeable reduction of Y397 phosphorylation following PF-562271 treatment. Our data also showed that PF-562271 suppressed RD cell migration in a dose-dependent manner associated with a reduction in Y397 phosphorylation.

CONCLUSIONS

The data presented herein indicate that targeting FAK phosphorylation at distinct sites is a promising strategy in future treatment approaches for defined subgroups of rhabdomyosarcoma.

Poxvirus oncolytic virotherapy

INTRODUCTION

Over the last decade, advances in biological therapies have resulted in remarkable clinical responses for the treatment of some previously incurable cancers. Oncolytic virotherapy is one of these promising novel strategies for cancer therapy. A successful oncolytic virus promotes tumor cell oncolysis and elicits a robust long-term anti-tumor immunity.

AREAS COVERED

Oncolytic poxviruses (Vaccinia virus and Myxoma virus) demonstrated encouraging results in multiple pre-clinical tumor models and some clinical trials for the treatment of various cancers. This review summarizes the advances made on poxvirus oncolytic virotherapy in the last five years.

EXPERT OPINION

Many challenges remain in poxvirus oncolytic virotherapy. Two key goals to achieve are enhancing the efficiency of viral delivery to tumor sites and overcoming local tumor immune-evasion. Additional efforts are necessary to explore the best combination of virotherapy with standard available treatments, particularly immunotherapies. By addressing these issues, this new modality will continue to improve as an adjunct biotherapy to treat malignant diseases.

Oncolytic Virus-Mediated RAS Targeting in Rhabdomyosarcoma

Aberrant activation of the receptor tyrosine kinase-mediated RAS signaling cascade is the primary driver of embryonal rhabdomyosarcoma (ERMS), a pediatric cancer characterized by a block in myogenic differentiation. To investigate the cellular function of activated RAS signaling in regulating the growth and differentiation of ERMS cells, we genetically ablated activated RAS oncogenes with high-efficiency genome-editing technology. Knockout of NRAS in CRISPR-inducible ERMS xenograft models resulted in near-complete tumor regression through a combination of cell death and myogenic differentiation. Utilizing this strategy for therapeutic RAS targeting in ERMS, we developed a recombinant oncolytic myxoma virus (MYXV) engineered with CRISPR/Cas9 gene-editing capability. Treatment of pre-clinical human ERMS tumor xenografts with an NRAS-targeting version of this MYXV significantly reduced tumor growth and increased overall survival. Our data suggest that targeted gene-editing cancer therapies have promising translational applications, especially with improvements to gene-targeting specificity and oncolytic vector technology.

Safety of an Oncolytic Myxoma Virus in Dogs with Soft Tissue Sarcoma

Many oncolytic viruses that are efficacious in murine cancer models are ineffective in humans. The outcomes of oncolytic virus treatment in dogs with spontaneous tumors may better predict human cancer response and improve treatment options for dogs with cancer. The objectives of this study were to evaluate the safety of treatment with myxoma virus lacking the serp2 gene (MYXVΔserp2) and determine its immunogenicity in dogs. To achieve these objectives, dogs with spontaneous soft tissue sarcomas were treated with MYXVΔserp2 intratumorally (n = 5) or post-operatively (n = 5). In dogs treated intratumorally, clinical scores were recorded and tumor biopsies and swabs (from the mouth and virus injection site) were analyzed for viral DNA at multiple time-points. In all dogs, blood, urine, and feces were frequently collected to evaluate organ function, virus distribution, and immune response. No detrimental effects of MYXVΔserp2 treatment were observed in any canine cancer patients. No clinically significant changes in complete blood profiles, serum chemistry analyses, or urinalyses were measured. Viral DNA was isolated from one tumor swab, but viral dissemination was not observed. Anti-MYXV antibodies were occasionally detected. These findings provide needed safety information to advance clinical trials using MYXVΔserp2 to treat patients with cancer.

Refinement and Successful Implementation of a Scoring System for Myxomatosis in a Susceptible Rabbit (Oryctolagus cuniculus) Model

Myxoma virus is a member of Leporipoxviridae whose tropism is tightly restricted to lagomorphs. In susceptible Oryctolagus rabbits, the virus causes a highly lethal disease known as myxomatosis, which begins as a localized infection but rapidly disseminates throughout the animal, leading to immune compromise, mucosal infections, multiorgan failure, and death. In a research setting, myxoma infection of susceptible Oryctolagus cuniculus rabbits is used as a model of poxviral disease progression and represents one of only a few means to study the pathogenesis of this viral family in a native host species. However, the rapid progression of myxomatosis makes accurate prediction of humane endpoints critical to limiting animal pain and distress and preventing death as an endpoint. Here we present case studies of myxomatosis at 2 institutions and offer a refined scoring system to reliably track the course of disease in susceptible rabbits infected with myxoma virus.

Potential of oncolytic viruses in the treatment of multiple myeloma

Multiple myeloma (MM) is a clonal malignancy of plasma cells that is newly diagnosed in ~30,000 patients in the US each year. While recently developed therapies have improved the prognosis for MM patients, relapse rates remain unacceptably high. To overcome this challenge, researchers have begun to investigate the therapeutic potential of oncolytic viruses as a novel treatment option for MM. Preclinical work with these viruses has demonstrated that their infection can be highly specific for MM cells and results in impressive therapeutic efficacy in a variety of preclinical models. This has led to the recent initiation of several human trials. This review summarizes the current state of oncolytic therapy as a therapeutic option for MM and highlights a variety of areas that need to be addressed as the field moves forward.