Effect of several antibodies on the surface charge of Yoshida sarcoma cells in the absence of complements was examined by the method of cell electrophoresis. Cytotoxic effect of all antibodies used here was not observed.
The electrophoretic mobility of Yoshida sarcoma cells incubated with rabbit antisera against Yoshida sarcoma cells decreased and this was correlated with the agglutination titer. A similar reduction in mobility was observed by incubation with homologous antisera from tumor-rejecting rats. The electrophoretic mobility of Yoshida sarcoma cells inoculated into C3H mice began to decrease on the 6th day after tumor inoculation and humoral antibodies began to appear at that period. No detectable difference was noted in the effect of 7S- and 19S-antibodies on the mobility of the cells. Treatment of Yoshida sarcoma cells with neuraminidase did not affect the ability of the cell to absorb rabbit antibody. By incubation with antibodies against the cells pretreated with neuraminidase, there was no reduction in mobility in spite of adsorption of immune γ-globulin on the cell surface.
These results suggest that the decrease in mobility of the cells incubated with antibodies does not depend on degeneration of the cells due to cytotoxic effect of antibodies or electric charge of coated γ-globulin itself, and that adsorbed γ-globulin does not coat directly charged groups such as sialic acid on the cell surface, and also antigenicity of Yoshida sarcoma cells might be changed through the removal of sialic acid on the cell surface with neuraminidase. Difference of areas in which receptors are located may cause no effect or reduction in electrophoretic mobility and, by other possibility, reaction with antibodies at the cell surface might produce some structural rearrangement such as allosteric distortion of the cell surface.

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Quantitative studies were made on growth characteristics of spontaneous mammary tumors in C3H/He mice, especially related to host resistance. Spontaneous mammary tumors and the established ascites cell line, MM2 carcinoma cells, converted from a spontaneous mammary tumor, were used. Mice with heightened and lowered resistance were obtained by the proposed immunizing pretreatment, and by the whole-body X-ray irradiation, respectively.
Autografts and isografts of mouse mammary tumors, and the solid tumors of MM2 appeared to follow a cube-root growth pattern. This also seemed to be the case in the heightened and lowered resistance mice, which suggests the necessity of taking into consideration a number of mechanisms which might be related to departure from exponential growth, including host resistance against the growth of tumor cells that may be proportional to the surface.
The growth characteristics of ascites MM2 varied from cube-root growth to exponential growth, mainly depending on doses of the inoculum. The growth of ascites MM2 was significantly inhibited when the cells were inoculated into the peritoneum of the primary host bearing spontaneous mammary tumor and of syngeneic hosts bearing established MM2 solid tumor. These results suggest that the tumor-bearing hosts still have a capability of immune response against their own tumor.

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The surface structures of the plasma membranes isolated from rat liver and ascites hepatoma (AH-130 strain) were studied comparatively with an electron microscope.
1) The plasma membranes of both types of cells, negatively stained with potassium phosphotungstate, showed a fine granular structure on the surface, not showing any special difference between them.
2) When the plasma membranes were pretreated at 37° for 1hr or negatively stained at 37°, there was sometimes observed a hexagonal pattern in the liver plasma membranes but scarcely in the hepatoma membranes.
3) Trypsin treatment of the liver plasma membranes solubilized about 30% of the membrane-protein but had no effect on the emergence of the temperaturedependent hexagonal pattern.
4) Acetone treatment of the liver plasma membranes extracted about 70% of lipid inorganic phosphorus, and the temperature-dependent hexagonal pattern was no longer observed in the membranes.
5) Some discussions were made on the nature of the temperature-dependent hexagonal pattern.

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Biological characteristics of four lines, DBLA-1, -6, -9, and -10, of transplantable rat leukemia induced by N-nitrosobutylurea were investigated in order to find a suitable experimental model for chemotherapy of leukemia. Cytological studies on cell size, mitotic index, and chromosome constitution demonstrated that each cell line had its own characteristic, different from the others.
Transplantation experiments in Donryu rats by intraperitoneal or intravenous inoculation of the cells suggested that DBLA-1, -6, and 10 would be useful as the screening model.

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RNA biosynthesis and metabolism in mouse myeloma cells (X5563), producing γ-globulin continuously, was studied in vitro. The characterization of RNA, which was extracted by hot phenol-sodium dodecyl sulfate method with nonionic detergent (Brij 35), was analyzed by means of sucrose density gradient centrifugation and base composition analysis. RNA can be synthesized at constant rate for over 5hr in the cells, under our in vitro suspension culture condition. As the synthesis of 60-80S and 45S RNA is found in the nucleus and inhibited by low concentration of Actinomycin-D, this may be a DNA-dependent RNA synthesis.
Most of 45S RNA in myeloma cells is the precursor of ribosomal RNA. The transition of 45S into 32S proceeds normally in the nucleus, in the presence of Actinomycin-D or cycloheximide, but 18S and 28S RNA are not detected in the cytoplasm. The transfer of RNA from nucleus into cytoplasm may be closely, related to protein synthesis.

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The inhibitory action of various anticancer agents on DNA polymerase extracted from rat regenerating liver, bone marrow, and AH-130 ascites hepatoma was investigated in in vitro system and the following results were obtained.
1) Actinomycin-D markedly suppressed the activity of DNA polymerase extracted from bone marrow in a concentration of 1×10^-5M, but higher concentration was necessary to inhibit the enzyme extracted from the regenerating liver.
2) A similar result was obtained in the case of Chromomycin-A₃.
3) Mitomycin-C and 5-fluorouracil did not show any suppressive effect on DNA polymerase from the regenerating liver, bone marrow, or hepatoma.
4) Bleomycin apparently stimulated the enzyme activity when native DNA was used as a primer; however, it suppressed the enzyme activity when denatured DNA was used as a primer.

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The tumor regressive effect of lentinan is reduced to an appreciable extent by immunosup-pressive agents (X-irradiation or injection of 6-benzylthioguanosine), suggesting that the antitumor effect of lentinan is based on the immunological reaction of the host.

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All of the 30 adult C3Hf/Bi mice given weekly subcutaneous injections of N, N'-dimethyl-nitrosourea developed malignant lymphomas which originated in the thymus. All the tumors were composed of lymphocytic or lymphoblastic cells in which a considerable number of starry-sky cells were mingled.

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Mouse leukemia cells were labeled with ³H-uridine and these cells were used as the target cells for in vitro immune reactions. Radioactivity released from the cells after cytotoxic reaction by an antibody or by immune lymphocytes was proportional to the damaged cells. Application of the method for evaluation of cell damage was discussed.

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2, 2'-O-Cyclocytidine was active against L-1210 leukemia. Cures were observed at the optimal dose of the compound, though no cures were obtained at any dose of any of the known antitumor agents. The compound was less toxic than 1-β-D-arabinofuranosyl-cytosine and resistant to cytidine deaminase.

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