[Synchronization of tumor cells with 5-fluorouracil plus uracil and with vinblastine and irradiation of the synchronized cultures. A contribution to combined radio-chemotherapy].

In this article, some arguments are put forward which support the conception of a combined radio-chemotherapy acting by a reversible inhibition of tumor cells with cytostatic drugs in a not cytocidal dose and the following selective killing by irradiation of the cells blocked in a radiosensitive phase. The two cytostatic drugs 5-fluorouracil (FU) and vinblastine (VLB), as inhibitors of DNA synthesis and mitosis, respectively, are tested in vitro both separately and combined in two tumor cell lines of the mouse, i.e. the Ehrlich ascites tumor and the sarcoma S 180. A cell-proliferative and, as far as possible, not cytocidal dose is used because of the inevitable side effects exerted by these drugs on normal tissues. A reversible synchronization of the ascites tumor is achieved even in the young mouse by FU in a dose of 15 ng to 500 ng (applied seven times every two hours), if the synchronization is controlled by applying the antimetabolite together with uracil in an equimolar concentration and then stimulating the growth of the cells inhibited during DNA synthesis by the administration of thymidine. The statistical analysis of dose-effect curves after X-ray irradiation shows an increased radiosensitivity of the synchronized cell population, provided that the optimum moment had been chosen for the irradiation.