Preclinical studies on promising combinations of radiochemotherapy and cytoprotective agents: The role of gemcitabine and amifostine

Gemcitabine is a pyrimidine nucleoside analogue with radiosensitising properties observed both in preclinical and clinical studies. The mechanism of radiosensitisation has not been completely clarified yet. Although combined-modality treatment may lead to an improved therapeutic outcome, it also results in a marked increase in toxic effects in clinical studies. Therefore, the aim of this thesis was to investigate the radiosensitising effect of gemcitabine and to optimise the clinical application of the combination of gemcitabine and radiotherapy.; The first part of our study focused on the development of an alternative survival assay to the very laborious clonogenic assay (CA). When sufficient time is allowed for delayed radiation-induced cell death and exponential growth is guaranteed during the assay, the sulforhodamine B (SRB) test was shown to be as useful as the CA for research on chemotherapy/radiotherapy interactions in cell lines with moderate radiosensitivity.; The SRB test gave us the opportunity for more extensive research to the radiosensitising effect of gemcitabine. A clear radiosensitising effect was observed in 8 different human tumour cell lines. This sensitising effect was found to be concentration-, cell line- and schedule dependent.; Now that we had a sound grasp on the radiosensitising effects of gemcitabine the research was extended to studies focusing at the radiosensitising mechanism of gemcitabine. For that reason, the role of gemcitabine on the cell cycle, the role of p53 protein within this context, the role of apoptosis and the radiosensitising potential of the main metabolite of gemcitabine (dFdU) have been investigated.; In order to facilitate the clinical application of the combination gemcitabine and radiotherapy, considering its cytotoxic effects on normal tissues, we showed that amifostine was able to reduce the increased radiation-induced toxicity. This observation might lead to further improvements of the in vivo application of this promising combination.; The above mentioned studies form a firm basis for further in depth investigation of the molecular mechanism of the radiosensitising effect of gemcitabine and could result in a better application of the combination of gemcitabine and radiotherapy in the treatment of different tumour types.