Prüfung der HIF-1alpha induzierten Strahlenresistenzerhöhung bei humanen Adenokarzinomzellen der Lunge im Xenograftmodell

This paper is concerned with the examination of a HIF-1alpha induced increase of resistance against radiation in a xenograft model with alveolar adeno-carcinoma in mice by testing the effects of an inhibition of the hypoxia-inducible factors HIF 1alpha or HIF-2alpha. In the chosen tumour model of a subcutaneous induced alveolar adeno- carcinoma in mice, human adenocarcinoma cells (A549) were used. In all experiments CD1 nu/nu nude mice were chosen for their existing and documented tolerance against allo- and xenografts. In the first part of this paper the therapeutical irradiation dose was tested. It was verified that fractional irradiation with 6 x 1.8 Gy produces a significant reduction of the tumour volume. There was no significant reduction after a single irradiation with 2.0 Gy. In further immunohistochemical investigations the behavior of the tumors to external radiation has been shown that there was a significant reduction of angiogenesis and proliferation. A significant effect in terms of apoptosis could not be detected MRT-perfusion measurements were taken to view the state of perfusion in the subcutaneous tumours. This demonstrated a hypoperfusion of the tumour centre with a good perfusion of the tumour outlines. This hypoperfusion suggested hypoxic conditions in the tumour centre. The suggestibility of the hypoxia induced radiation resistance was tested in the second part of this paper in concluding experiments with the selected A549 xenograft model. The usage of specific siRNA against the increasingly expressed factors under hypoxia factors, HIF-1alpha and HIF-2alpha were investigated. After specific inhibition of the factors HIF-1alpha and HIF-2alpha and after specific inhibition of these factors in combination with external photon irradiation an induced growth delay was measured. It was shown that the sole inhibition with specific siRNA against the factors HIF-1alpha and HIF-2alpha significant delayed the growth of subcutaneous tumours. It was verified that the characteristics of the growth delays after inhibition of these two factors in each case were comparably strong (absolute growth delay: HIF-1alpha 8.7 days, HIF2 alpha 6.3 days). Moreover, it was shown, that the inhibition with specific siRNA against the factors HIF-1alpha or HIF-2alpha combined with photon irradiation exhibited subsequent differences in growth delay effects. It could be demonstrated that the delaying effects after inhibition of HIF-1alpha with subsequent radiotherapy were significantly more distinctive than after inhibition of HIF-2alpha with subsequent radiotherapy (absolute growth delay: HIF-1alpha 15.95 days, HIF 2alpha 8.9 days). From this the conclusion can be drawn that the inhibition of hypoxia inducible factor HIF 1alpha has influence on the hypoxia-mediated radiation resistance. Tumor growth can be influenced by inhibitating of HIF-1alpha.