The antitumor effect of extracts obtained from the fruit body of Agaricus blazei Murill was examined in a double-grafted
tumor system, in which BALB/c mice received simultaneous
intradermal injections of Meth-A
tumor cells in both the right (10(6) cells) and left flank (2 x 10(5) cells), and were then injected with 5 mg of extracts of A. blazei in the right
tumor on days 3, 4 and 5. Intratumoral administration of
ethanol-soluble (Fraction 1), water-
ethanol-soluble (Fraction 2),
ammonium oxalate-soluble (Fraction 3) and
ammonium oxalate-insoluble (Fraction 4) fractions resulted in inhibition of
tumor growth, with Fraction 3 showing the most tumoricidal activity, producing regression of the right
tumor and inhibition of growth of the left, non-injected
tumor. The maximum effect was obtained using 0.5 mg of Fraction 3 and this amount was used in subsequent experiments. The antitumor effect of intratumorally administered Fraction 3 was enhanced by oral ad lib administration of feed containing 0.083% of Fraction 3. When immunized spleen cells from mice that had been cured by intratumoral administration of 0.5 mg of Fraction 3 were directly injected (2 x 10(7) cells/mouse) into the Meth-A
tumor,
tumor growth was inhibited. The
tumor cells on day 7 from the Fraction 3-treated right
tumor and from the left
tumor were cultured for 24 h and their culture supernatants were assayed for neutrophil or macrophage chemotactic activity. Significant
macrophage chemotactic factor activity was detected in the
culture media from the left
tumor tissue. Serum levels of
immunosuppressive acidic protein (IAP), produced by activated macrophages and neutrophils, increased transiently soon after
intradermal injection of 0.5 mg of Fraction 3. These results suggest that regression of the left non-injected
tumor was due to an immune reaction, involving induction of cytotoxic cells in the spleen, and the release of
chemotactic factors in the distant
tumor.