Histological and cytochemical studies on the distribution of schizophyllan glucan (SPG) in cancer-inoculated animals. I. Differences in distribution and antitumor activity of 3H-SPG in sarcoma-180 inoculated females between ICR and DBA mice.

Abstract

Purified schizophyllan (SPG), which was not labeled with radioactive isotopes, was administered intraperitoneally or intramuscularly to female mice of the ICR and DBA strains every third day from the 13th day after sarcoma-180 inoculation to the 28th day. Four days after the last SPG administration, 400 μCi/head of 3H-SPG was injected intravenously. The liver, spleen, bone marrow, lymph nodes, thymus, and tumor were studied with whole-body, microscope, and electron microscope (EM) autoradiography (ARG). Anesthetized animals were used for whole-body ARG after tissue pieces were removed and fixed for micro-ARG and EM-ARG.In whole-body ARG, 3H-SPG was mainly accumulated in the liver, spleen, lymph nodes, thymus, bone marrow, and a capsular belt area of the tumor. In the tumor capsular belt area, a very strong accumulation was observed in ICR mice, but the accumulation was very weak in DBA mice.In micro-ARG, 3H-SPG was incorporated in the reticuloendothelial cells; Kupffer's cells in the liver, and reticulum cells and macrophages in the spleen, bone marrow, lymph nodes, and thymus. A large number of macrophages in the tumor capsular belt area were observed migrating between the tumor cells and 3H-SPG was strongly incorporated in their cytoplasm in ICR mice. But only a few macrophages were observed there in DBA mice.In EM-ARG, 3H-SPG was accumulated in special lysosomal granules in the reticuloendothelial cells, including Kupffer's cells and macrophages. The special granules were enveloped with a limiting membrane, and were composed of a compact fine filamentous substance and an electron opaque lysosomal cap structure (filamentous ball, Fb). The nature of these fine Fbs was exactly the same as that of SPG macromolecules observed in the negatively stained samples.There were no great differences on the observations by ARG and histology between the SPG-treated ICR and DBA mice, except in the tumor region. A large number of macrophages with many intracytoplasmic Fbs were migrating into the sarcoma nest in the capsular area, and many sarcoma cells were rapidly degenerating or had disappeared in the SPG-treated ICR mice. In DBA mice, however, there were no significant changes in the cancer nests; the cancer cells were growing and increasing rapidly, and the animals died within a month. These autoradiographic data suggest that the SPG granules (Fbs) containing activated macrophages in the ICR tumor nests play an important role in destroying the growing sarcoma cells, but there was no evidence of active macrophages in the DBA sarcoma nests. The Fbs in the macrophages in ICR mice probably produce a large amount of various lysosomal enzymes and act as activators of the destruction of sarcoma cells, but did not act in DBA mice. The reason for such a big difference between the two mouse strains was not clear, but some immunogenomic factors could be concerned.