Treatment of tumour cell with 5-aza-2-deoxycytidine (DAC) for immune tumour therapy of Glioma in Fischer-344 rats

Fisher 344 rats with implanted N29 glioma tumours were treated with Pulsed Electric Fields (PEF) in combination with immunization using either IFN-gamma-gene-transfected syngeneic tumour cells or IFN-gamma transfected N29 cells treated with 10 micro-M 5-aza-2-deoxycytidine (DAC). Tumours (N29) were inoculated subcutaneously on both thighs of female F- 344 syngeneic rats. The left tumour was treated once with 16 exponential pulses with an electric field strength of 1400 V/cm, and 1.0 ms duration (time constant). No anticancer drugs were given at any time. The following day and then once weekly for three weeks, the animals were given intra-peritoneal injections of irradiated, modified N29 tumour cells. The results were evaluated by daily measuring the size of tumour on both sides of the animals. Treatment with solely PEF in 32 animals resulted in a specific growth rate decrease of 20±6 % on the PEF exposed tumour. The effect at the non targeted tumour was negligible (0±4 %). Treatment with IFN-gamma secreting tumour cells resulted in a significant decrease of tumour growth rate on the right tumour of 20± 2 % (p< 0.05) and no significant effect (3±0.3% ) was observed on the left tumour. Immunization with DAC treated IFN-gamma secreting cells in 12 animals showed no significant decreased growth rate, on neither the left nor the right tumours. By combining PEF+IFN-gamma no significant decrease in growth rate was achieved. But in the combination of PEF and IFN-gamma secreting cells grown in DAC medium the tumour growth rate decreased by about 50 % at the PEF treated tumour and there was a decrease of about 20% in tumour growth at the non-PEF treated tumour rate which is about the same as for PEF treatment alone. Immune therapy of rats with intracranial N32 tumours by immunization with IFN-gamma secreting syngeneic cells treated with DAC resulted in a slight (3%) but not significant increase in survival time. With a single RT fraction of 15 Gy there was, however, a significant increase of 32% in the length of survival time of the rats with N32 tumours (p<0.02). Radiation therapy with a single fraction of 15 Gy combined with immunization with IFN-gamma secreting syngeneic cells treated with DAC resulted in significant (p