Targeting JAK/STAT Signaling Antagonizes Resistance to Oncolytic Reovirus Therapy Driven by Prior Infection with HTLV-1 in Models of T-Cell Lymphoma.

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus that infects at least 10 million people worldwide and is associated with the development of T-cell lymphoma (TCL). The treatment of TCL remains challenging and new treatment options are urgently needed. With the goal of developing a novel therapeutic approach for TCL, we investigated the activity of the clinical formulation of oncolytic reovirus (Reolysin, Pelareorep) in TCL models. Our studies revealed that HTLV-1-negative TCL cells were highly sensitive to Reolysin-induced cell death, but HTLV-1-positive TCL cells were resistant. Consistent with these data, reovirus displayed significant viral accumulation in HTLV-1-negative cells, but failed to efficiently replicate in HTLV-1-positive cells. Transcriptome analyses of HTLV-1-positive vs. negative cells revealed a significant increase in genes associated with retroviral infection including interleukin-13 and signal transducer and activator of transcription 5 (STAT5). To investigate the relationship between HTLV-1 status and sensitivity to Reolysin, we infected HTLV-1-negative cells with HTLV-1. The presence of HTLV-1 resulted in significantly decreased sensitivity to Reolysin. Treatment with the JAK inhibitor ruxolitinib suppressed STAT5 phosphorylation and expression of the key anti-viral response protein MX1 and enhanced the anti-TCL activity of Reolysin in both HTLV-1-positive and negative cells. Our data demonstrate that the inhibition of the JAK/STAT pathway can be used as a novel approach to antagonize the resistance of HTLV-1-positive cells to oncolytic virus therapy.

The PERK Inhibitor GSK2606414 Enhances Reovirus Infection in Head and Neck Squamous Cell Carcinoma via an ATF4-Dependent Mechanism.

Reovirus type 3 Dearing (reovirus) is a tumor-selective oncolytic virus currently under evaluation in clinical trials. Here, we report that the therapeutic efficacy of reovirus in head and neck squamous cell cancer can be enhanced by targeting the unfolded protein response (UPR) kinase, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). PERK inhibition by GSK2606414 increased reovirus efficacy in both 2D and 3D models in vitro, while perturbing the normal host cell response to reovirus-induced endoplasmic reticulum (ER) stress. UPR reporter constructs were used for live-cell 3D spheroid imaging. Profiling of eIF2a-ATF4, IRE1a-XBP1, and ATF6 pathway activity revealed a context-dependent increase in eIF2a-ATF4 signaling due to GSK2606414. GSK2606414 blocked eIF2a-ATF4 signaling because of the canonical ER stress agent thapsigargin. In the context of reovirus infection, GSK2606414 induced eIF2a-ATF4 signaling. Knockdown of eIF2a kinases PERK, GCN2, and PKR revealed eIF2a-ATF4 reporter activity was dependent on either PERK or GCN2. Knockdown of ATF4 abrogated the GSK2606414-induced increase in reovirus protein levels, confirming eIF2a-ATF signaling as key to the observed phenotype. Our work identifies a novel approach to enhance the efficacy and replication of reovirus in a therapeutic setting.

Trial Watch: Oncolytic viro-immunotherapy of hematologic and solid tumors.

Oncolytic viruses selectively target and kill cancer cells in an immunogenic fashion, thus supporting the establishment of therapeutically relevant tumor-specific immune responses. In 2015, the US Food and Drug Administration (FDA) approved the oncolytic herpes simplex virus T-VEC for use in advanced melanoma patients. Since then, a plethora of trials has been initiated to assess the safety and efficacy of multiple oncolytic viruses in patients affected with various malignancies. Here, we summarize recent preclinical and clinical progress in the field of oncolytic virotherapy.

A Phase II Study of Pelareorep (REOLYSIN®) in Combination with Gemcitabine for Patients with Advanced Pancreatic Adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis, with 1 and 5-year survival rates of ~18% and 7% respectively. FOLFIRINOX or gemcitabine in combination with nab-paclitaxel are standard treatment options for metastatic disease. However, both regimens are more toxic than gemcitabine alone. Pelareorep (REOLYSIN®), a proprietary isolate of reovirus Type 3 Dearing, has shown antitumor activity in clinical and preclinical models. In addition to direct cytotoxic effects, pelareorep can trigger antitumor immune responses. Due to the high frequency of RAS mutations in PDAC, we hypothesized that pelareorep would promote selective reovirus replication in pancreatic tumors and enhance the anticancer activity of gemcitabine. Chemotherapy-naïve patients with advanced PDAC were eligible for the study. The primary objective was Clinical Benefit Rate (complete response (CR) + partial response (PR) + stable disease (SD) ≥ 12 weeks) and secondary objectives include overall survival (OS), toxicity, and pharmacodynamics (PD) analysis. The study enrolled 34 patients; results included one partial response, 23 stable disease, and 5 progressive disease. The median OS was 10.2 months, with a 1- and 2-year survival rate of 45% and 24%, respectively. The treatment was well tolerated with manageable nonhematological toxicities. PD analysis revealed reovirus replication within pancreatic tumor and associated apoptosis. Upregulation of immune checkpoint marker PD-L1 suggests future consideration of combining oncolytic virus therapy with anti-PD-L1 inhibitors. We conclude that pelareorep complements single agent gemcitabine in PDAC.

A Randomized Phase II Study of FOLFOX6/Bevacizumab With or Without Pelareorep in Patients With Metastatic Colorectal Cancer: IND.210, a Canadian Cancer Trials Group Trial.

BACKGROUND: Oncolytic reovirus pelareorep might preferentially infect and destroy rat sarcoma (RAS)-activated cells, and has preclinical and early clinical activity against colorectal cancer (CRC). PATIENTS AND METHODS: After a 6-patient safety run-in, 103 patients with metastatic CRC were randomly assigned to standard first-line leucovorin/5-FU/oxaliplatin (FOLFOX6)/bevacizumab (FOLFOX/BEV) every 2 weeks with (n = 51) or without (n = 52) pelareorep 3 × 1010 tissue culture infective dose 50 on days 1 to 5 (cycles 1, 2, 4, and alternate cycles thereafter). The primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS), objective response rate (ORR), quality of life, and correlative analyses. RESULTS: At 13 months' median follow-up, PFS was inferior in the pelareorep arm (median 7 vs. 9 months; hazard ratio [HR], 1.59 [80% confidence interval (CI), 1.18-2.15]; P = .046). There was no statistical difference in OS (median, 19.2 vs. 20.1 months; HR, 1.22; P = .38). An increased ORR was observed with pelareorep (adjusted odds ratio, 2.52 [80% CI, 1.44-4.41]; P = .03), but with a shorter median duration of response (5 vs. 9 months; P = .028). Pelareorep patients experienced more hypertension and proteinuria, and were more likely to omit bevacizumab before progression. A trend to lower dose intensity and shorter oxaliplatin and bevacizumab treatment duration was observed with pelareorep. CONCLUSION: Combination pelareorep with FOLFOX/BEV was tolerable with an increased ORR, but PFS was inferior. Subgroup analysis of baseline variables including Kirsten rat sarcoma oncogene did not identify subgroups with PFS benefit. Decreased treatment intensity with standard agents likely contributed to the lack of benefit with pelareorep. Future studies might consider alternate pelareorep/chemotherapy strategies or combination therapy with novel agents.

Oncolytic reovirus inhibits angiogenesis through induction of CXCL10/IP-10 and abrogation of HIF activity in soft tissue sarcomas.

The tumor-selective viral replication capacity and pro-apoptotic effects of oncolytic reovirus have been reported to be dependent on the presence of an activated RAS pathway in several solid tumor types. However, the mechanisms of selective anticancer efficacy of the reovirus-based formulation for cancer therapy (Reolysin, pelareorep) have not been rigorously studied in soft tissue sarcomas (STS). Here we report that Reolysin triggered a striking induction of the anti-angiogenic chemokine interferon-γ-inducible protein 10 (IP-10)/CXCL10 (CXC chemokine ligand 10) in both wild type and RAS mutant STS cells. Further analysis determined that Reolysin treatment possessed significant anti-angiogenic activity irrespective of RAS status. In addition to CXCL10 induction, Reolysin dramatically downregulated the expression of hypoxia inducible factor (HIF)-1α, HIF-2α and inhibited vascular endothelial growth factor (VEGF) secretion. CXCL10 antagonism significantly diminished the anti-angiogenic effects of Reolysin indicating that it is a key driver of this phenomenon. Xenograft studies demonstrated that Reolysin significantly improved the anticancer activity of the anti-angiogenic agents sunitinib, temsirolimus, and bevacizumab in a manner that was associated with increased CXCL10 levels. This effect was most pronounced following treatment with Reolysin in combination with temsirolimus. Further analysis in additional sarcoma xenograft models confirmed the significant increase in CXCL10 and increased anticancer activity of this combination. Our collective results demonstrate that Reolysin possesses CXCL10-driven anti-angiogenic activity in sarcoma models, which can be harnessed to enhance the anticancer activity of temsirolimus and other agents that target the tumor vasculature.

A phase II study of REOLYSIN® (pelareorep) in combination with carboplatin and paclitaxel for patients with advanced malignant melanoma.

REOLYSIN® (pelareorep) is an investigational new drug, consisting of a live, replication-competent, Reovirus Type 3 Dearing strain in a proprietary formulation. Several preclinical and clinical trials with REOLYSIN® on a wide range of cancer indications have demonstrated antineoplastic activity on cells with activated RAS-signaling pathway. Furthermore, long-term survival benefits were evident in post-treatment patients indicating a potential antitumor immune response triggered by REOLYSIN®. Numerous mono and/or combination therapy studies with the agent showed a consistent safety profile. The current study is a phase II, single-arm, open label trial of REOLYSIN® in combination with carboplatin and paclitaxel for patients with advanced melanoma. Results from the 14 patients enrolled in the study exhibited no grade 4 adverse events or deaths but manageable grade-3 toxicities commonly attributed to REOLYSIN®, including pyrexia, chills, myalgia, pain, fatigue, and nausea. The number of treatment cycles ranged from 2 to 20 with a median of 6 cycles. The study met its treatment and efficacy goal for the first stage with three partial responses (ORR was 21%). No complete responses were noted. The median PFS and OS were 5.2 and 10.9 months, respectively. The 1-year OS was 43% with a disease control rate of 85%. In conclusion, REOLYSIN® combined with carboplatin and paclitaxel is a safe and potentially efficacious therapy for patients with advanced malignant melanoma. Additional combination studies using REOLYSIN® with chemo/immunotherapy drugs may support more favorable outcomes for patients in this indication.

Trial Watch-Oncolytic viruses and cancer therapy.

Oncolytic virotherapy relies on the administration of non-pathogenic viral strains that selectively infect and kill malignant cells while favoring the elicitation of a therapeutically relevant tumor-targeting immune response. During the past few years, great efforts have been dedicated to the development of oncolytic viruses with improved specificity and potency. Such an intense wave of investigation has culminated this year in the regulatory approval by the US Food and Drug Administration (FDA) of a genetically engineered oncolytic viral strain for use in melanoma patients. Here, we summarize recent preclinical and clinical advances in oncolytic virotherapy.

Oncolytics Biotech® Inc.: REOLYSIN® for melanoma therapy.

Oncolytics Biotech® Inc. is focused on the development of oncolytic viruses for use as cancer therapeutics. The Company's lead product, REOLYSIN®, a proprietary formulation of the human reovirus, is in late-stage clinical testing in a range of cancers. REOLYSIN has been utilized in nearly 30 clinical trials including translational, Phase I, Phase II (single arm and randomized) and Phase III studies in a broad range of cancer indications. To date, Oncolytics has been issued more than 370 patents worldwide and has more than 230 pending applications. Issued patent claims pertaining to the reovirus cover: compositions of matter comprising reovirus; pharmaceutical use of reoviruses to treat neoplasia and cellular proliferative diseases and combination therapy with radiation, chemotherapy and/or immune suppressants.

Trial Watch:: Oncolytic viruses for cancer therapy.

Oncolytic viruses are natural or genetically modified viral species that selectively infect and kill neoplastic cells. Such an innate or exogenously conferred specificity has generated considerable interest around the possibility to employ oncolytic viruses as highly targeted agents that would mediate cancer cell-autonomous anticancer effects. Accumulating evidence, however, suggests that the therapeutic potential of oncolytic virotherapy is not a simple consequence of the cytopathic effect, but strongly relies on the induction of an endogenous immune response against transformed cells. In line with this notion, superior anticancer effects are being observed when oncolytic viruses are engineered to express (or co-administered with) immunostimulatory molecules. Although multiple studies have shown that oncolytic viruses are well tolerated by cancer patients, the full-blown therapeutic potential of oncolytic virotherapy, especially when implemented in the absence of immunostimulatory interventions, remains unclear. Here, we cover the latest advances in this active area of translational investigation, summarizing high-impact studies that have been published during the last 12 months and discussing clinical trials that have been initiated in the same period to assess the therapeutic potential of oncolytic virotherapy in oncological indications.

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.