Synergistic effects of Actinobacillus suis cells in combination with 5-fluorouracil on mice bearing murine L1210 leukemia cells

Abstract

 The mean survival rates of female BDF₁ mice transplanted intravenously (i.v.) with murine L1210 leukemia cells were significantly prolonged by intraperitoneal (i.p.) pretreatment (before i.v. transplantation) or by i.p. pre- and post-treatment (before and after the i.v. transplantation) with heat-killed Actinobacillus suis cells ATCC 15557 (AS 15557) alone, as compared with untreated L1210-leukemia-cell-bearing control mice. However, significant prolongation of the mean survival rates was not elicited by the i.p. post-treatment with AS 15557 alone. When 5-fluorouracil (5-FU) was applied i.p. to mice receiving post-treatment with AS 15557 alone, the mean survival rates of the L1210-leukemia-cell-bearing mice were significantly prolonged. The antileukemic action of AS 15557, alone or in combination with 5-FU, against L1210 leukemia was superior to that of a streptococcal preparation (OK-432) and was almost the same as of bacillus Calmette-Guérin with or without 5-FU. The results suggest the possibility that the synergism of AS 15557 in combination with 5-FU may be dependent on the relationship between the indirect immunological function of AS 15557 and the direct cytotoxic action of 5-FU on L1210 leukemia cells.