Therapeutic brain cancer targeting by gene therapy and immunomodulation : a translational study

The hypothesis pertinent to this thesis is that glioma tumours can be therapeutically targeted by gene and/or immunotherapy in order to eliminate or delay tumour recurrence leading to significant morbidity and mortality. In our gene therapeutic approach, described in Chapter 2, we observed that chronic expression of the C-terminal fusion of IsK with EGFP (enhanced green fluorescent protein) led to cell death of more than 50% of transfected U87-MG human astrocytoma cells as early as 2 days after transfection. Our results are consistent with activation of apoptotic pathways following IsK-mediated increase in K+ efflux. However, we abandoned the gene therapy approach because of the more attractive immunotherapeutic intervention strategies for of brain tumours, which is currently emerging as a highly potential clinical option as reviewed in Chapter 3. Interestingly, as described in Chapter 4, we found a strong therapeutic antitumour efficacy for the innate immune response modifier Resiquimod, even as a stand-alone treatment, eventually leading to immunological memory against secondary tumour challenges. In parallel, we observed that cyclophosphamide treatment, although effective as chemotherapeutic agent, may be deleterious to maintenance of long-term antitumour immune memory. Our data also demonstrates that immunotherapeutic parenteral treatment of established glioma tumours by Resiquimod, as defined in the protocol, significantly improves anti-brain tumour immunity in a way that leads to immune memory, which is superior to cyclophosphamide treatment alone. Our studies have thereby identified a promising novel antitumour immunotherapy which may lead to clinical benefit. In Chapter 5, we describe our finding that, in multiple rat glioma models, a certain composition of antigens derived from syngeneic tumour cells and their lysates when therapeutically co-administered with allogeneic cells and their lysates is able to confer anti-tumour immune responses and tumour regression. For the syngeneic C6 model in SD rats therapeutic injections of allogeneic cells alone were sufficient to trigger tumour regression. This immunization approach may prove useful as a postsurgery adjuvant therapy in future cancer treatment protocols, or even as a stand-alone therapeutic tumour vaccination. In another syngeneic rat glioma model, described in Chapter 6, we found that for regression of CNS-1 glioma tumours in Lewis rats specific innate immune response stimulating substances were required as immunological adjuvants. In our hands BCG and IL-2, the Toll-Like receptor (TLR) 7/8 activator Resiquimod, and the cytokine granulocyte-macrophage colony stimulating factor (GM-CSF), showed potent activity. Finally, as described in Chapter 7, we demonstrate that our prototype therapeutic vaccine, when co-delivered in a specific regimen together with the cytokine GM-CSF as immunological adjuvant, is able to arrest progression of glioma tumour growth, when therapeutically administered following low-dose cyclophosphamide. GM-CSF is an attractive vaccine adjuvant because of its proven immune modulatory effects and low toxicity profile. The safe pharmacological use of GM-CSF in patients is well-established, which makes it feasible for clinical use. The use of GM-CSF has been included in the first clinical studies that have been approved for an Investigational New Drug application (IND) for Single patient use in the U.S.