Oncolytic reovirus induces ovarian cancer cell apoptosis in a TLR3-dependent manner

Highlights

• Different levels of cathepsins B/L expression confer different oncolytic effect of reovirus.

• Reovirus dsRNA induced the apoptosis of reovirus-resistant tumor cells.

• Reovirus dsRNA induced reovirus-resistant tumor cell apoptosis through the TLR3 signaling pathway.

Abstract

Globally, ovarian cancer is the seventh most common cancer and the eighth-most common cause of cancer death among women with a five-year survival rate of less than 45%. Although reovirus is known to be effective for treating ovarian cancer, some types of tumor cells still exhibit resistance to reovirus. In order to solve this resistance problem in the treatment of ovarian cancer, we selected the reovirus-resistant OV-90 ovarian cancer cells to study reovirus oncolytic effects. We found that the viability of OV-90 cells decreased after reovirus double-stranded RNA (dsRNA) genome transfection. Interestingly, we observed that chemical blockage of the Toll-like receptor 3 (TLR3)-dsRNA binding complex in OV-90 cells and the inhibition of downstream TLR3 signaling disrupted OV-90 apoptosis triggered by reovirus dsRNA. Together, these results demonstrate that reovirus dsRNA induces reovirus-resistant tumor cell apoptosis through the TLR3 signaling pathway.

Introduction

Ovarian cancer is one of the three major malignant cancers of the female reproductive system with a high fatality rate (Da et al., 2020). In recent years, the incidence of ovarian cancer has increased annually. The standard therapy for ovarian cancer includes debulking surgery followed by chemotherapy with a platinum or a taxane agent (Kuroki and Guntupalli, 2020). Although most ovarian cancer patients are sensitive to initial chemotherapy, most chemotherapeutic drugs lack a tumor-targeting ability and have strong toxic side effects on patients, thus greatly limiting the application of chemotherapy in ovarian tumor therapy (Tian et al., 2020). The early symptoms of ovarian cancer are hidden and abdominal metastasis often occurs before the symptom appearance (Murakami et al., 2020). Therefore, surgical treatment is not recommended. Conservative treatment led by chemotherapy is chosen to prolong the survival in patients. However, patients often experience tumor recurrence due to chemotherapeutic resistance within 2 years after the initial treatment (Chen et al., 2020). Thus, more effective treatment strategies are needed for the treatment of ovarian cancer.

Oncolytic virus (OV) is a type of virus that can specifically replicate in tumor cells without presenting harm to normal cells, thus resulting in tumor cell destruction during release (Cao et al., 2020; Rahman and McFadden, 2020). Reovirus has a double-stranded (ds) RNA genome and is approximately 85 nm in diameter (Abad and Danthi, 2020). The tumor antigens released from reovirus can induce potent and specific anti-tumor immunity, which not only directly mediates the local anti-tumor response but also leads to tumor regression and triggers the innate and adaptive immune responses to prevent tumor recurrence (Mondal et al., 2020; Pidelaserra-Marti and Engeland, 2020). As a leader in the research and application of oncolytic virus, Oncolytics Biotech of Canada has conducted more than 30 clinical trials using Reolysin® (reovirus) worldwide, among which treatment of squamous cell carcinoma of the head and neck via reovirus has entered a phase III clinical trial (Mahalingam et al., 2020a). The results of clinical trials of direct intratumoral injection have confirmed the safety and efficacy of reovirus (Groeneveldt et al., 2020a; Mahalingam et al., 2020b; Trager et al., 2020). Thus, reovirus can directly kill tumor and exert immunological effects, representing a promising therapeutic prospect in anti-tumor therapy.

Despite the current use and promising future of reovirus, some types of tumor cells show resistance to reovirus (IstIflI et al., 2020; Padmanabhan et al., 2020). In this study, we used reovirus dsRNA to transfect ovarian cancer cell lines, especially those exhibiting resistance to reovirus with low cathepsin B/L expression, to explore the molecular mechanism of apoptosis induced by reovirus. Our goal is to further understand the anti-tumor mechanism of reovirus and to explore its clinical application.