Therapeutic potential of mammalian orthoreovirus in HER2+ breast cancer

Abstract

Mammalian orthoreovirus (MRV) is a clinically benign cancer killing virus which has been investigated in over 30 clinical trials. However, specific tumor environments most susceptible to MRV therapy remain unknown. Based on evidence from prior literature epidermal growth factor receptor (EGFR/HER1) and activated RAS pathway aid in tumor susceptibility to MRV. This dissertation investigates a closely related receptor and binding partner of EGFR/HER1, human epidermal growth factor receptor 2 (HER2) breast cancer (BC). Within this work, we examine HER2+ BC as a tumor environment to target for MRV therapy. HER2+ BC is one of the most aggressive subtypes and is characterized by increased tumor growth, metastasis, and increased likelihood of recurrence. While MRV infection does not directly alter the HER2 pathway, we confirmed that MRV infects, replicates, and induces apoptosis in HER2 expressing cells. The five-year survival rate of HER2+ BC significantly increased with FDA approval of trastuzumab, a humanized antibody that reduces HER2 signaling and induces antibody dependent cell cytotoxicity. However, patients with HER2+ BC that also have accumulation of hypoxia inducible factor-1 alpha (HIF-1a) are likely to develop trastuzumab resistance with long term use. Based on prior investigation of MRV infection in colon, lung carcinoma, and prostate cells, we hypothesized that MRV infection would lead to the reduction of HIF-1a accumulation in HER2+ BC cells. Indeed, we confirmed that under hypoxic, or low oxygen conditions, MRV infected cells have significantly lower accumulation of HIF-1a compared to mock-infected cells. With the identification of HER2+ BC as a suitable tumor environment to target with MRV therapy, we sought to design a recombinant MRV that could induce a robust anti-tumor immune response against HER2. Currently, peptide vaccines that prevent recurrence in patients with HER2+ BC are being investigated in clinical trials. Three peptides include E75, found in the extracellular domain of HER2, GP2, found in the transmembrane domain of HER2, and AE36, found in the intracellular domain of HER2. E75 and GP2 induce production of HER2 specific CD8+ T cells when injected in patients in combination with granulocyte macrophage colony stimulating factor (GM-CSF), and AE36 induces production of CD4+ T cells. We hypothesized creation of an MRV that expresses HER2 peptides, could potentially lead to a large HER2 specific immune response, since MRV infection induces an anti-viral and anti-tumor immune response. We designed and recovered a recombinant MRV, S1/HER2nhd, that expresses E75, GP2, and AE36 as a fusion added to s1 protein on MRV. S1/HER2nhd is stable for up to six passages and expresses both viral protein and the s1/HER2 peptide fusion protein on the virion surface and inside infected cells. S1/HER2nhd also infects, replicates, and reduces cell survival in HER2 expressing BC cells. Overall, this work has identified HER2 expressing tumor environments with an accumulation of HIF-1a as a suitable target for MRV treatment. Therefore, we propose combination of MRV therapy and trastuzumab in HER2+ tumors with high levels of HIF-1a has the potential to reduce patient resistance to trastuzumab treatment. Additionally, characterization of S1/HER2nhd provides evidence for future investigations into the immune response elicited during infection in vivo and evidence for S1/HER2nhd use as a potential HER2 peptide vaccine.