Mechanisms of mammalian orthoreovirus-induced cell death and NF-kB activation in ER+ breast cancer.

Abstract

e13171 Background: Estrogen receptor positive (ER+) breast cancer is one of the most commonly diagnosed types of breast cancer in the United States. Although the five-year survival rate of ER+ breast cancer is 90% or higher, ER+ breast cancer can recur and metastasize 10-20+ years after initial diagnosis. Novel therapeutic strategies are needed to prevent and treat breast cancer recurrence and metastasis. A possible solution is mammalian orthoreovirus (MRV), a replication-competent natural oncolytic virus. The strain T3D (Reolysin) is in current clinical trials to treat metastatic breast cancer; however, the mechanisms of MRV-induced death are not well elucidated. Furthermore, other MRV strains have not been well studied for their oncolytic potential in ER+ breast cancer. Our studies aim to explore the different cell death pathways elicited by MRV. Prior studies have reported that MRV induces cell death in L929 cells (murine fibroblasts, permissive to MRV infection) by activating apoptosis, necroptosis, and inhibiting the NFκB pathway to enhance viral replication. Methods: Our goal is to compare the effects of MRV in L929 cells and ER+ breast cancer cell line MCF7 using chemical inhibitors of necroptosis, apoptosis, and the NFκB pathway. Results: Our results indicate that necroptosis inhibitors do not impact cell viability in response to MRV infection, but apoptosis inhibitors increase cell viability, suggesting that MRV-induces apoptotic cell death in ER+ breast cancer cells. Previous work has shown that the NFκB pathway may be activated or inhibited by MRV. Our cell viability studies in MCF7 cells with the IKK inhibitor BAY-11-7082 indicate that several MRV strains likely activate the NFκB pathway to potentially enhance viral replication. Conclusions: Future studies are aimed at further defining mechanisms of MRV-induced cell death in ER+ breast cancer. We anticipate future studies will lead to an improved MRV virotherapeutic that may be combined with clinically relevant treatments, such as CDK4/6 inhibitors and anti-estrogens, to prevent and treat therapy-resistant ER+ breast cancer.