Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Anatomy and Cell Biology

Supervisor

Dr. Trevor Shepherd

Abstract

The management of patients with epithelial ovarian cancer (EOC) faces two major challenges which standard treatments fail to effectively address: 1) Diffuse metastasis as a consequence of late stage diagnosis and 2) intra-tumoral heterogeneity, which fuels tumor evolution and drives the acquisition of chemotherapeutic resistance. In this thesis, we tested new therapeutic strategies using a 3-dimensional in vitro spheroid culture model that mimics key steps of epithelial ovarian cancer metastasis; and another model that mimics both temporal and cellular heterogeneity by establishing multiple cell lines from a single patient over the course of disease progression. Using these models, we investigated the therapeutic efficacy of three oncolytic viruses for treatment of ovarian cancer: Myxoma virus (MYXV), a modified Vaccinia virus (vvDD), and Maraba virus (MRBV). We determined that all three viruses were capable of inducing some level of oncolysis, but that spheroid formation limited the replication efficiency of poxviruses (MYXV and vvDD), which heavily rely on cell proliferation. However, upon spheroid reattachment, poxvirus oncolysis was restored and prevented cell dispersion. MRBV was least affected by spheroid formation, although there was a capacity for some cell lines to develop resistance to MRBV upon spheroid formation. We discovered MRBV uses the low-density lipoprotein receptor (LDLR) to gain entry to host cells and that entry into spheroids was affected by dynamic changes in LDLR expression. However, we observed that this was only a partial mediator of MRBV tropism. In our in vitro assays of tumor heterogeneity, we observed temporal changes that directly impact MRBV oncolysis and we identified two major groups of subclones in our patient derived cell lines: one that was highly susceptible to MRBV, and another set which exhibited 1000-fold reduced susceptibility to MRBV- iii mediated oncolysis. Differential susceptibility to MRBV virus oncolysis did not strictly depend on LDLR expression. Furthermore, co-culture of virus-sensitive and virus-resistant cells conferred sensitization of virus-resistant cells to MRBV oncolysis. We therefore sought other mechanisms which could impact MRBV tropism and found that oncolysis could be significantly increased through the induction of TGFβ signaling and epithelial-to-mesenchymal transition, commonly activated pathways found during ovarian cancer metastasis. Taken together, these findings not only define the differential therapeutic efficacies between oncolytic viruses for metastatic EOC, but also identify key trophic factors which impact MRBV oncolysis that can be exploited to enhance MRBV-mediated oncolysis for EOC in future therapeutic strategies.

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