Stereotactic microdialysis for metabolic assessment and experimental treatment of malignant glioma

Abstract: Glioblastoma multiforme, the most common primary brain tumor, has a dire prognosis despite multimodal treatments that include surgery and radio-chemotherapy. To improve the outcome of this destructive disease, we need to improve our understanding of its tumor biology. Furthermore, the development of new treatment strategies will improve with a better understanding of the interplay between malignant cells and their direct surrounding microenvironment.This thesis aims to increase the understanding of the processes within high-grade glioma and its microenvironment during normal conditions as well as during the distress associated with treatment. Specifically, we have investigated the metabolic response to radiotherapy (study I and II), the immunologic response to radiotherapy (study II), and the metabolic response pattern to loco-regional treatment with cisplatin (study III and IV). Using microdialysis, we collected samples from the extracellular space in both normal brain and tumor tissue during radiotherapy (study I and II) and loco-regional cisplatin treatment (study III and IV). Theses samples were analyzed for glucose metabolites, glycerol, and glutamate (study I, II, and III) and for cytokines (study II). In addition, we analyzed the global metabolism with mass spectrometry to identify and assess the response pattern of malignant glioma cells to loco-regional cisplatin treatment (study IV).In study I and II, we found that malignant glioma cells used glucose at a higher rate than normal cells and preferred glycolysis for glucose metabolism. The given radiation dose (2 Gray (Gy) daily for five days) did not significantly affect glucose metabolism, glycerol levels, or glutamate levels in tumor tissue or the microenvironment. However, in study II, we observed an induced inflammatory effect due to the given radiation dose as several of the cytokines investigated showed significantly increased levels during radiotherapy. In study IV, we observed a complex and strong metabolic response to the loco-regional cisplatin therapy. At baseline, we found a metabolic pattern corresponding well with highly proliferating tumor tissue–i.e., high levels of amino acids, their metabolites, and other metabolic end products and low levels of sugar derivatives, antioxidants, and nucleotides. During the loco-regional therapy, we observed a clearly localized cytotoxic effect within the tumor and a metabolic response pattern corresponding with cisplatin’s complex mechanism of action, affecting several metabolic pathways within the malignant cell. Glutamate and glycerol also increased in tumor tissue following loco-regional treatment, a finding that further supported the observation of local toxicity.In study III, we investigated microdialysis as a method to assess the microenvironment in high-grade glioma and as a method for drug delivery (retrograde microdialysis). All studies demonstrated the usefulness of microdialysis as a tool for in vivo real-time assessment of molecular events in malignant glioma tissue. Although the method is invasive, no complications related to the surgical procedure or assessment were noted. In study III, we also demonstrated that retrograde microdialysis is a feasible method for locally delivering clinically significant doses of drugs such as cisplatin to tumor tissue in the brain. However, in addition to having a cytotoxic effect on tumor cells, cisplatin may induce clinically significant edema.