Tsuneo Baba

Polychlorinated biphenyl(s) as a promotor in experimental hepatocarcinogenesis in rats

The effects of dietary polychlorinated biphenyls (PCBs) on hepatocarcinogenesis in female rats of Donryu strain receiving 3′-methyl-4-dimethyl-aminoazobenzene (3′-Me-DAB) were investigated. Oral administration of PCBs after administration of 3′-Me-DAB resulted in a high incidence (64%) of hepatocarcinoma. In contrast, administration of a similar amount of PCBs before, or together with 3′-Me-DAB did not induce hepatic tumors. Administration of a slightly larger amount of PCBs alone did not induce liver tumors, while administration of a slightly larger amount of 3′-Me-DAB alone caused only a low incidence (13%) of hepatocarcinoma. These results strongly suggest that PCBs exert a potent promoting action in experimental azo dye hepatocarcinogenesis.

Inactivation of cis-diamminedichloroplatinum (II) in blood and protection of its toxicity by sodium thiosulfate in rabbits.

SummaryThe mode of inactivation of cis-diamminedichloroplatinum(II) (DDP) in the bloodstream and protection from its toxicity by sodium thiosulfate (STS) were investigated in rabbits.Plasma ultrafiltrate in rabbits given 5 mg/kg DDP IV and various excess molar ratios of STS IV were assayed for the active platinum levels with a new microbiological assay system using an E. coli strain. The active platinum species in the plasma were inactivated completely by coadministration of a 400-fold excess of STS IV. The rabbits were almost completely protected against both BUN increase and body weight loss normally caused by DDP when 400-fold doses of STS were given. Diuretic effects were also observed.Our data provide evidence for the basis of optimum use of STS to protect against DDP toxicity. [6, 9]. This TRC with DDP and STS is now in clinical trial [7, 8], but the precise mode of protective action of STS against DDP toxicity has not been determined.We now present evidence that this protective effect is due to inactivation of biologically active DDP in the bloodstream.

Protection of antiproliferative effect of cis-diamminedichloroplatinum (II) by sodium thiosulfate.

SummaryUtilizing the phytohemagglutinin (PHA) stimulation assay of human peripheral blood mononuclear cells (PBM), the protective effect of sodium thiosulfate (STS) on the antiproliferative action of cis-diamminedichloroplatinum (II) (DDP) against human cells was investigated. DDP alone significantly inhibited the proliferation of PBM over the concentration range of 10-7 to 5x10-5M. The antiproliferative effect of DDP was significantly blocked when STS was added to the stimulation culture at the time of exposure to DDP at molar STS/DDP ratios of more than 500. However, STS at molar ratios of less than 100 induced minimal protection. Then, STS was added at various times after DDP exposure with a molar STS/DDP ratio of 1000. The protection was effective within 10 min after exposure to DDP at a concentration of 5x10-5M, whereas it was not effective beyond 30 min after the exposure. The results indicate that effective protection against DDP cytotoxicity in human cells can be achieved by the concurrent presence of STS with molar STS/DDP ratios of more than 500, but not when a molar STS/DDP ratio of less than 100 is used.

‘Two-Route Chemotherapy’ Using Cisplatin and Its Neutralizing Agent, Sodium Thiosulfate, for Intraperitoneal Cancer

The pharmacokinetics of intraperitoneal cisplatin (DDP) administered with simultaneous intravenous sodium thiosulfate (STS) were investigated by a bioassay system using the phytohemagglutinin (PHA) stimulation assay of human peripheral blood mononuclear cells (PBM). Active DDP in the plasma, assessed by the bioassay system, was almost completely inactivated, when the level of STS in the plasma was more than 500 times higher at molar STS/DDP ratios than that of DDP. However, the peak level of active DDP in the peritoneal cavity was not significantly decreased. Fourteen patients with intraperitoneal carcinoma were treated with intracavitary DDP chemotherapy in combination with STS in this setting. Of 8 patients with malignant ascites who were evaluable for response, 4 patients experienced complete disappearance of ascites and the remaining 4 patients responded with apparent decrease in the volume of their ascites. No serious drug-associated toxicity was encountered.

Newly identified type of β actin reduces invasiveness of mouse B16-melanoma

Low metastatic parent B16 melanoma and isolated B16‐F1 cell lines have a third actin designated as βm(Ax:previously). ßm actin is scantily or not at all detected in highly metastatic cell lines, such as B16‐F10 and BL6. To directly assess the physiological role of ßm in phenotypic changes of B16 melanoma, we transfected expression plasmids of βm into B16‐F10 cells. The actin expressed in the transfectants is located largely in cytoskeletal fractios. The transfectants exhibited a larger number of stress fibers and a lower invasiveness than did the recipient cells. Thus, βm actin plays an important role in the organization of actin stress fibers, the result being a decrease in invasiveness of B16 melanoma.

Augmented excretion of procathepsin L of a fos-transferred highly metastatic rat cell line

We previously reported that v-fos transfer to a src-transformed rat 3Y1 cell line (SR-3Y1-2) enhanced lung metastasis accompanied with an increase in invasiveness. When analyzing factors relating to the high invasiveness, with special reference to typical lysosomal proteases (cathepsins), involving degradation of stroma, we found that the excretion of procathepsin L was significantly larger in the fos-transferred highly metastatic cell line (fos-SR-3Y1-202) than that in the recipient cell lines. The cathepsin D-induced enzyme activity of the excreted procathepsin L in fos-SR-3Y1-202 was about 4 and 13 fold that of SR-3Y1-2 and 3Y1, respectively. The increase in the excretion of procathepsin L from fos-SR-3Y1-202 may play a role in the high invasiveness induced by transfer with the v-fos oncogene.

Altered expression of a third actin accompanying malignant progression in mouse B16 melanoma cells

The expression of actin was examined and compared in several mouse B16 melanoma cell lines with different metastatic ability, by the use of two‐dimensional gel electrophoresis or horizontal isoelectric focusing. In the mouse B16 melanoma cell lines, the expression of newly found Ax actin (Mr = 43,000, pl = 5.2) decreased with the increase in in vitro and in vivo selection cycles (F number) for high‐metastatic cells. On the contrary, the metastatic ability of each mouse cell line, assessed by lung colony‐forming ability following iv administration, increased with increase in the F number. The half life of Ax actin was much the same as that of β‐and γ‐actin and the different expressions of Ax actin between the low‐ (F=l) and high‐metastatic (F=10) cell lines were attributed to differences in the rate of synthesis but not in the decay rate of Ax actin. The Ax actin was incorporated into the cytoskeletal fraction with the same efficiency as β‐and γ‐actin. The invasiveness of the cells, assessed in vitro using matrigel, was increased with the decrease in Ax expression. The actin stress fibers, observed staining with rhodamine‐conjugated phalloidin, were organized better in a low‐metastatic cell line (F=l) than in a high‐metastatic one (F = 10). These results suggest to us that depression of Ax actin is involved in disorganization of the cytoskeletal system, the cellular flexibility and motility are enhanced and there is a consequent increase in the invasiveness and metastatic potential.

Differential expression of smooth muscle α-like actin between benign and malignant human pigment tissues

When examining proteins in human pigment tissues, we found that a third actin-like protein, in addition to beta- and gamma-actin was more frequent and in a larger amount in benign tissues such as blue nevus and nevus pigmentosus, than in malignant melanoma. This third actin-like protein was immunologically stained with monoclonal antibodies reacting with several actin species and specific for smooth muscle alpha-actin. We propose that this third actin-like protein is probably smooth muscle alpha-actin and that different expressions of this third actin may possibly serve as a sensitive biochemical marker for the diagnosis of human malignant melanoma.

Malignant progression of a transformed rat cell line by transfer of the v-fos oncogene.

Transfer of the v-fos oncogene into a rat cell line transformed by Rous sarcoma virus increased both the spontaneous and experimental lung-metastasis. Metastatic ability of each v-fos transferred cell line was dependent on both the manner of integration and transcriptional amount of the v-fos oncogene, but did not correlate with the growth rate in vivo. Expression of the src, myc or ras genes were not altered by transfer of the v-fos gene, except that the myc expression was enhanced in the cell line, which acquired augmentation of growth rate in vivo but not metastatic potential to the lung. Cells of the metastatic lung nodules of each cell line also possessed exogenous fos DNA and the transcripts. These results suggest that v-fos oncogene functions in the transfected cells and causes malignant progression.

Inactivation of cis-Diamminedichloroplatinum (II) in Blood by Sodium Thiosulfate

The mode of inactivation of cis-diamminedichloroplatinum (II) (DDP) in the bloodstream by sodium thiosulfate (STS) was investigated experimentally and clinically by a bioassay system using the phytohemagglutinin stimulation assay of human peripheral blood mononuclear cells. Active DDP in the plasma of dogs after 3 mg/kg of DDP injection, assessed by the bioassay system, was almost completely inactivated, when the level of STS in the plasma was more than 500 times higher at molar STS/DDP ratios than that of DDP. In 6 patients with hepatic malignancies who were treated with hepatic artery infusion of 3 mg/kg DDP and systemic STS, active DDP in the plasma was not detectable in the concurrent presence of STS at molar ratios of more than 500. Severe DDP toxicity in these patients was completely protected. The results indicate that an inactivation of DDP in the bloodstream after DDP injection and, further, an effective protection against DDP toxicity can be achieved by the concurrent presence of STS at molar ratios of more than 500 in the plasma of these patients.