PROMOTIVE EFFECTS OF HYPERTHERMIA ON THE INHIBITION OF DNA SYNTHESIS IN EHRLICH ASCITES TUMOR CELLS BY EICOSAPENTAENOIC AND DOCOSAHEXAENOIC ACIDS

Tanaka H., Kageyama K., Kimura M., Iwamoto S.-I., Ueno Y., Asagi K., Asada R., Miwa N.

Aim: To evaluate inhibitory effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on DNA synthesis in combination with hyperthermia in vitro. Methods: A suspension of Ehrlich ascites tumor cells (EAT) was mixed with DHA or EPA in a glass tube, heated at 37 °C, 40 °C, or 42 °C for 1 h in a water bath, and cultured at 37 °C for 19 or 96 h. DNA synthesis was assayed by monitoring of the incorporation of [³H]-thymidine into the acid-insoluble fraction. DHA or EPA incorporated into EAT cells was extracted and measured by thin-layer chromatography and gas-liquid chromatography. Results: The inhibition of DNA synthesis by EPA or DHA increased markedly upon the treatment at 42 °C and 40 °C compared to that at 37 °C. At 37 °C, inhibitory action of EPA was more potent than that of DHA at low concentrations (at 50 µM — DNA synthesis level: EPA, 63.1%; DHA, 87.9%), whereas inhibitory action of DHA was higher at 150 µM (16.7%, 4.4%, ibid.). The effect of DHA compared to EPA was more marked at 40 °C (29.0%, 19.2% at 100 µM) or 42 °C (19.7%, 10.6% at 100 µM). Evaluation of DNA synthesis rate in the cells treated for 1 h by EPA or DHA with the next culturing of EAT cells for 19 h resulted in the enhanced inhibitory activity of EPA even at concentrations as low as 50 µM at either 37 °C (0.5%, 11.3%) or 42 °C (0.6%, 4.5%), which in these conditions was higher than that of DHA. At the same time the rate of incorporation of EPA in EAT cells at 37 °C or 42 °C was lower than that of DHA. Conclusion: Administration of DHA or EPA in vitro significantly inhibit DNA synthesis, and such effect is enhanced by combination of PUFAs with hyperthermia.