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Abstract

Over the past decade, cancer therapy has witnessed significant advancements, particularly in the field of oncolytic virotherapy. Oncolytic viruses specifically target cancer cells and trigger an immune response through immunogenic cell death. H-1 Parvovirus (H-1PV) is an oncolytic virus which has shown extensive potential in various cancer models. Phase I and IIa clinical evaluation of H-1PV in pancreatic cancer and glioblastoma has demonstrated a safe and non-toxic pro- file of the virus. The virus treatment showed initial signs of effectiveness, such as a shift in the tumour microenvironment towards improved immune response, ef- fective distribution of the virus within the tumour bed, and overall better patient survival. However, it was also observed that monotherapy alone is insufficient for complete tumour eradication. Thus, there is a need for improving H-1PV virotherapy. A promising approach involves the utilization of H-1PV in combination with other drugs. H-1PV has already shown promising results when combined with different drugs, espe- cially HDAC inhibitor VPA and pro-apoptotic drug ABT-737. In this regard, this study aims to investigate the effects of combining clinically tested oncolytic H-1PV with two different classes of therapeutics- HDAC inhibitors and BH3 mimetics- in prostate cancer. In order to identify an effective combination treatment, I adapted an assay to test the efficacy of the combination using a cell viability assay. My findings reveal that the combination of H-1PV with BH3 mimetic, pro-apoptotic drug ABT-737 is synergistic in killing PC3 prostate cancer cells. The combination of H-1PV and ABT-737 was able to induce upregulation of ac- tivated caspase 3/7 and mitochondrial outer membrane permeabilization (MoMP) in PC3 cells, which are both markers of apoptosis. After rescuing the cells by us- ing an apoptosis inhibitor, Z-VAD-FMK, I was able to confirm that H-1PV/ABT-737 combination was inducing an apoptotic cell death in PC3 cells. The dying cells were also expressing cell surface calreticulin, Hsp70 and Hsp90, which are all Danger associated molecular patterns (DAMPs) associated with an immunogenic cell death. Moreover, I was able to show that the immunogenic cell death of PC3 cells trig- gered by the H-1PV/ABT-737 co-treatment was able to induce the maturation and activation of dendritic cells (DCs). These DCs were further capable of phagocyto- sis and T-cell priming, thus indicating that H-1PV/ABT-737 combination treatment triggers the DC/T-cell axis in engaging the adaptive immune system for tumour clearance. I could show that H-1PV and ABT-737 co-treated PC3 cells displayed an up- regulated cell surface expression of pro-cytotoxicity natural killer cell associated ligands, MICA/MICB, CD155 and ULBP 2/5/6. Furthermore, this was capable of inducing NK cell activation, engaging the respective cell cytotoxicity receptors, NKG2D and DNAM-1 on NK cells. Thus, accelerating NK cell mediated clearance of PC3 cells. This impact was notably higher in the combination treated cells as compared to the individual therapies alone. This emphasizes the potential of the combina- tion in enhancing immune cell-mediated clearance of the tumour. Furthermore, the combination of H-1PV and ABT-737 was able to synergize in killing patient derived LuCaP 136 and LuCaP 147 cells, further cementing the potential of this combination across multiple cell types. Overall, this study highlights the potential benefits of combining H-1PV with BH3 mimetic ABT-737 in improving the immune response against prostate cancer, thereby suggesting its potential as a valuable treatment strategy.