Gene Therapy - Kathrine Ryman, Ph.D.

Key Member

Kate Ryman, Ph.D.
Associate Professor
Dept. of Microbiology and Immunology

See the Curriculum Vitae
Ryman Lab

     The resistance of cancers to conventional therapies has inspired the search for novel therapeutic strategies. Recently, the use of replicating "oncolytic" viruses for cancer therapy (virotherapy) has gained favor. We have constructed a series of propagation-competent and incompetent virus vectors based on the alphavirus, Sindbis virus (SB). SB vectors offer several features advantageous to oncolytic virotherapy: i) efficient and targeted cell-type specific delivery; ii) high-level expression of a transgene; and iii) cytolytic activity in the targeted cell with minimal side-effects. As our understanding of the molecular events leading to the generation and evolution of malignancies increases, we are able to tailor and/or select virus vectors for their ability to replicate preferentially in tumor cells by altering virus tropism with modifications in viral surface antigens to refine cell targeting, by conditionally expressing toxic gene products with tissue-specific gene promoter elements, or by utilizing the ability of a virus to selectively kill tumor cells as a result of cancer-specific defects in the innate antiviral response.

     Project One: The interferons (IFNs) are circulating factors that trigger antiviral responses and induce growth inhibitory and/or apoptotic signals in cells. However, attempts to exploit the ability of IFNs to limit the growth of tumor cells in patients have met with limited success because of cancer-specific mutations of gene products in the IFN pathway. Although IFN-non-responsive cancer cells may have acquired a growth/survival advantage over their normal counterparts, their antiviral response has simultaneously been compromised. SB replicates to high titers and triggers apoptosis in many immortalized and transformed cell lines. In collaboration with Dr. Michael Mathis (Dept. of Cell Biology and Anatomy, LSUHSC-S), we are testing the premise that compromised IFN-signaling in tumor cells creates a cellular environment that supports SB infection and replication, whereas normal cells. We believe that tumor-specific targeting of SB vectors can be achieved by taking advantage of the natural sensitivity of this virus to IFN-mediated antiviral pathways. We have demonstrated that SB virus vectors efficiently infect and induce the cytolysis of a panel of human and murine tumor cell lines in vitro. We will determine whether cell death is apoptotic and by what pathway apoptosis is triggered. In addition, we will determine whether enhanced susceptibility of tumor cell lines (compared with normal) corresponds to a defect in IFNaß activity in these cells. This information is applied to an in vivo ovarian cancer model to assess the efficacy of SB vectors in achieving tumor regression.

     Project Two: SB virus can be readily adapted to bind ubiquitously-expressed, cell-surface glycosaminoglycan (GAG), heparan sulfate (HS), facilitated by the accumulation of positively-charged amino acid substitutions in the SB envelope glycoprotein, E2. The use of HS-binding SB vectors offers several advantages for cancer gene therapy applications. When inoculated intratumorally, the infectivity of HS-binding particles for cells in the local area will be optimized, while at the same time the particles will be less likely to spread and replicate beyond the site of inoculation, providing additional safety. In collaboration with Dr. William Klimstra (Dept. of Microbiology and Immunology, LSUHSC-S), we are attempting to select tumor-specific HS-binding mutations in the E2 protein.

     Project Three: SB vectors are readily engineered to express a transgene and we are investigating several possibilities for optimizing the vectors for use in cancer virotherapy. We are genetically-engineering the vectors to express three categories of heterologous protein: i) tumor suppressor proteins; and ii) cell suicide proteins to accentuate the oncolytic nature of the virus vector itself; or iii) cytokines to augment the immune response against the tumor tissue. Consequently, the ability to modify alphavirus vectors through genetic engineering affords the opportunity to develop new generations of custom-made alphavirus vectors that contain immunomodulatory and/or suicide cassettes designed to increase their anti-tumor activity.

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