Virotherapy for Breast Cancer

• Author / Creator

  Chaurasiya, Shyambabu

• Breast cancer (BrCa) is the most common cancer and the leading cause of cancer-related deaths in women worldwide. Current therapies for BrCa are insufficient to cure metastatic disease and are often associated with debilitating side effects that severely deteriorate the quality of patients’ lives. Therefore, novel therapeutic approaches for the treatment of BrCa are being sought. Virotherapy, a strategy to use live viruses as therapeutics, is an emerging field that holds promise for better treatment of cancer. Cancer virotherapy could be broadly categorized into two sub-classes: (i) use of non-replicating viruses as vectors in cancer gene therapy, and (ii) use of replicating viruses as oncolytic agents. In this study, we have studied both aspects of virotherapy. First, we have determined the feasibility of using non-replicating adenovirus (Ad) encoding transcriptionally targeted interleukin-2 (IL-2) for the treatment of BrCa. Second, we have studied the oncolytic activities of genetically-engineered replication-competent vaccinia virus (VACV) in BrCa. IL-2 has been approved for the treatment of some malignancies, however severe toxicities related to systemically administered IL-2 limit the therapeutic usefulness of this cytokine. Based on previous findings that restricting the high concentrations of IL-2 within the tumor could both reduce the toxicities and enhance its anti-tumor activities, we aimed to study the safety and anti-tumor efficacy of human IL-2 expressed specifically from the tumor cells. We constructed Ad vectors encoding hIL-2 under the control of either the BrCa-specific mammaglobin promoter/enhancer sequence (Ad-MPE2-IL-2) or the constitutively active immediate early promoter of murine CMV (MCMV) (Ad-MCMV-IL-2). Our data show that the MPE2 promoter is highly efficient in restricting expression of a transgene (luciferase or hIL-2) to BrCa cells, and that while the Ad-MCMV-IL-2 is highly toxic, the Ad-MPE2-IL-2 is safe in mice. Furthermore, while both the vectors were able to significantly delay growth of breast tumors in a syngeneic mouse model, complete tumor regressions were seldom observed in the treated animals. Additionally, attempts to enhance the anti-tumor efficacy of the Ad-MPE2-IL-2 by combining with a pro-apoptotic drug, PAC1, were unsuccessful. Previous studies from our group have shown that deletion of the VACV F4L gene, homolog of cellular RRM2 which is a rate limiting factor in the synthesis of dNTPs, highly attenuates virus growth in normal cells and renders it avirulent in mice. In the study presented here, we determined the oncolytic properties of VACV lacking either the F4L alone (∆F4L) or lacking F4L together with J2R (∆F4L∆J2R). Our results show that replication of ∆F4L VACV is dependent on cellular RRM2; notably, BrCa cells with high levels of RRM2 supported high levels of replication of these viruses. Both ∆F4L and ∆F4L∆J2R VACVs showed better specificity for BrCa in vitro compared to the VACV with a deletion of J2R (∆J2R) only. All three mutant viruses were able to completely control tumor growth in a xenograft mouse model of BrCa. In a syngeneic mouse model, all mutant viruses significantly delayed tumor growth and increased the overall survival of treated mice, although the anti-tumor effect was less profound compared to that in the xenograft model. Furthermore, the oncolytic activity of ∆F4L VACV towards the stem-like (CD44+CD24-/low) population isolated from SUM-149 cells was similar to that towards the differentiated cell population in that triple-negative human BrCa cell line. Finally, all mutant viruses were found to grow to high titers in endothelial cells in vitro and they increased hypoxia in xenograft tumors in mice upon intra-tumoral injection. Taken together, this study shows that virotherapy is a promising strategy for the treatment of breast cancer but would likely require additional interventions to completely clear tumors.

• Subjects / Keywords

  • Virotherapy
  • Gene Therapy
  • Interleukin-2
  • Vaccinia virus
  • Oncolytic virus
  • Breast cancer
  • Adenovirus

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R30000D7M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.